Properties S-CONPRI
like O
macro- O
and O
microstructure S-CONPRI
, O
mechanical B-CONPRI
properties E-CONPRI
like O
hardness S-PRO
and O
its O
course O
in O
the O
layers O
, O
high-cycle O
fatigue S-PRO
resistance O
in O
bending S-MANP
and O
fatigue B-PRO
damage E-PRO
mechanisms O
were O
investigated O
with O
the O
emphasis O
on O
fatigue S-PRO
crack O
initiation O
process S-CONPRI
evaluated O
using O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
. O


The O
results O
indicated O
that O
surface S-CONPRI
additive S-MATE
laser O
welded S-MANP
layers O
of O
a O
high O
quality S-CONPRI
can O
be S-MATE
reached O
. O


On O
the O
other O
hand O
, O
some O
drop O
of O
fatigue S-PRO
resistance O
and O
endurance B-PRO
limit E-PRO
was O
observed O
, O
affected O
by O
surface B-CONPRI
defects E-CONPRI
– O
small O
welding S-MANP
imperfections S-CONPRI
Ti-6Al-4V O
and O
AlSi5 S-MATE
wires O
were O
used O
for O
wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
using O
the O
direct O
current O
cold B-MANP
metal I-MANP
transfer E-MANP
welding O
. O


Ti B-MATE
alloy E-MATE
was O
deposited O
first O
, O
and O
then O
Al B-MATE
alloy E-MATE
was O
deposited O
on O
the O
Ti S-MATE
layer S-PARA
. O


A O
small O
amount O
of O
Ti B-MATE
alloy E-MATE
was O
melted S-CONPRI
when O
the O
first O
layer S-PARA
of O
Al B-MATE
alloy E-MATE
was O
deposited O
due O
to O
the O
low O
heat S-CONPRI
input O
. O


A O
component S-MACEQ
composed O
of O
Ti/Al O
dissimilar B-MATE
alloys E-MATE
can O
be S-MATE
produced O
. O


The O
interface S-CONPRI
layer O
between O
the O
Ti S-MATE
and O
Al B-MATE
alloys E-MATE
included O
a O
continuous O
layer S-PARA
and O
a O
discontinuous O
layer S-PARA
. O


The O
continuous O
layer S-PARA
was O
composed O
of O
Ti7Al5Si12 S-MATE
, O
and O
the O
discontinuous O
layer S-PARA
consisted O
of O
Ti S-MATE
( O
Al1-xSix O
) O
3 O
. O


Element S-MATE
Si O
was O
rich O
in O
the O
continuous O
layer S-PARA
. O


The O
hardness S-PRO
and O
modulus O
of O
the O
interface S-CONPRI
layer O
were O
between O
those O
of O
Al S-MATE
and O
Ti B-MATE
alloys E-MATE
. O


The O
average S-CONPRI
tensile O
strength S-PRO
of O
the O
component S-MACEQ
was O
79 O
MPa S-CONPRI
. O


The O
fracture S-CONPRI
located O
at O
the O
interface S-CONPRI
layer O
. O


A O
finite B-CONPRI
element I-CONPRI
model E-CONPRI
is O
developed O
to O
calculate O
the O
heat B-CONPRI
propagation E-CONPRI
of O
a O
circular O
thin-walled B-APPL
component E-APPL
fabricated S-CONPRI
in O
gas B-MANP
metal I-MANP
arc I-MANP
welding E-MANP
based O
additive B-MANP
manufacturing E-MANP
. O


The O
heat B-CONPRI
evolution E-CONPRI
, O
thermal B-PARA
cycle E-PARA
feature S-FEAT
, O
and O
temperature B-PARA
gradient E-PARA
in O
molten B-CONPRI
pool E-CONPRI
and O
deposited B-CHAR
layers E-CHAR
are O
revealed O
. O


The O
temperature S-PARA
simulations S-ENAT
at O
some O
locations O
are O
in O
agreement O
with O
measured O
values O
from O
thermocouples S-MACEQ
. O


As S-MATE
the O
deposition B-MANP
process E-MANP
proceeds O
, O
the O
high-temperature O
regions O
of O
the O
substrate S-MATE
and O
molten B-CONPRI
pool E-CONPRI
increase O
. O


The O
temperature B-PARA
gradient E-PARA
in O
the O
molten B-CONPRI
pool E-CONPRI
decreases O
with O
the O
increasing O
deposition S-CONPRI
height O
. O


The O
heat B-CONPRI
dissipation E-CONPRI
condition O
in O
the O
molten B-CONPRI
pool E-CONPRI
of O
current O
layer S-PARA
tightly O
depends O
on O
the O
deposition B-PARA
direction E-PARA
of O
fore O
layer S-PARA
. O


At O
the O
deposition S-CONPRI
ending O
moment O
, O
the O
heat B-CONPRI
conduction E-CONPRI
in O
the O
axial O
direction O
is O
the O
predominant O
heat B-CONPRI
dissipation E-CONPRI
orientation O
, O
whereas O
the O
circumferential O
orientation S-CONPRI
becomes O
the O
main O
heat B-CONPRI
dissipation E-CONPRI
direction O
in O
the O
top O
layers O
. O


An O
automated O
arc-welding-based B-MANP
additive I-MANP
manufacturing E-MANP
system O
was O
reported O
. O


Integrated O
additive S-MATE
and O
subtractive B-MANP
manufacturing E-MANP
methodology S-CONPRI
was O
developed O
. O


Deposition B-PARA
paths E-PARA
and O
welding S-MANP
parameters S-CONPRI
were O
automatically O
generated O
. O


User O
interface S-CONPRI
using O
only O
CAD B-ENAT
models E-ENAT
as S-MATE
inputs O
was O
developed O
. O


Arc B-MANP
welding E-MANP
has O
been O
widely O
explored O
for O
additive B-MANP
manufacturing E-MANP
of O
large O
metal S-MATE
components S-MACEQ
over O
the O
last O
three O
decades O
due O
to O
its O
lower O
capital B-CONPRI
cost E-CONPRI
, O
an O
unlimited O
build B-PARA
envelope E-PARA
, O
and O
higher O
deposition B-PARA
rates E-PARA
. O


Although O
significant O
improvements O
have O
been O
made O
, O
an O
arc B-MANP
welding E-MANP
process O
has O
yet O
to O
be S-MATE
incorporated O
in O
a O
commercially O
available O
additive B-MACEQ
manufacturing I-MACEQ
system E-MACEQ
. O


The O
next O
step S-CONPRI
in O
exploiting O
“ O
true O
” O
arc-welding-based B-MANP
additive I-MANP
manufacturing E-MANP
is O
to O
develop O
the O
automation S-CONPRI
software O
required O
to O
produce O
CAD-to-part S-CONPRI
capability O
. O


This O
study O
focuses O
on O
developing O
a O
fully O
automated O
system O
using O
robotic O
gas B-MANP
metal I-MANP
arc I-MANP
welding E-MANP
to O
additively B-MANP
manufacture E-MANP
metal O
components S-MACEQ
. O


The O
system O
contains O
several O
modules O
, O
including O
bead B-CONPRI
modelling E-CONPRI
, O
slicing S-CONPRI
, O
deposition B-CONPRI
path I-CONPRI
planning E-CONPRI
, O
weld S-FEAT
setting O
, O
and O
post-process B-MANP
machining E-MANP
. O


Among O
these O
modules O
, O
bead B-CONPRI
modelling E-CONPRI
provides O
the O
essential O
database S-ENAT
for O
process B-CONPRI
control E-CONPRI
, O
and O
an O
innovative O
path B-ENAT
planning E-ENAT
strategy O
fulfils O
the O
requirements O
of O
the O
automated O
system O
. O


Finally O
, O
a O
thin-walled B-MACEQ
aluminium I-MACEQ
structure E-MACEQ
has O
been O
fabricated S-CONPRI
automatically O
using O
only O
a O
CAD B-ENAT
model E-ENAT
as S-MATE
the O
informational O
input O
to O
the O
system O
. O


This O
exercise O
demonstrates O
that O
the O
developed O
system O
is O
a O
significant O
contribution O
towards O
the O
ultimate O
goal O
of O
producing O
a O
practical O
and O
highly O
automated O
arc-welding-based B-MANP
additive I-MANP
manufacturing E-MANP
system O
for O
industrial S-APPL
application O
. O


Laser B-MANP
additive I-MANP
manufacturing E-MANP
titanium O
alloy S-MATE
40 O
mm S-MANP
thick O
plate O
can O
obtain O
full O
penetration B-CONPRI
joint E-CONPRI
by O
EBW S-MANP
. O


In O
fusion B-CONPRI
zone E-CONPRI
, O
due O
to O
acicular O
α′ O
formation O
, O
the O
microhardness S-CONPRI
is O
higher O
than O
base B-MATE
metal E-MATE
and O
heat B-CONPRI
affected I-CONPRI
zone E-CONPRI
. O


All O
tensile S-PRO
samples S-CONPRI
fail O
in O
base B-MATE
metal E-MATE
. O


The O
L-joint S-FEAT
shows O
higher O
strength S-PRO
but O
lower O
ductility S-PRO
than O
T-joint S-FEAT
. O


Individually O
fabrication S-MANP
parts O
by O
laser B-MANP
additive I-MANP
manufacturing E-MANP
( O
LAM S-MANP
) O
and O
then O
jointing O
them O
together O
through O
electron B-MANP
beam I-MANP
welding E-MANP
( O
EBW S-MANP
) O
is O
a O
viable O
way O
for O
manufacturing S-MANP
large O
components S-MACEQ
with O
reduction S-CONPRI
of O
internal B-PRO
stress E-PRO
. O


For O
investigating O
the O
microstructure S-CONPRI
and O
mechanical B-CONPRI
property E-CONPRI
of O
EBW S-MANP
joint O
along O
longitudinal O
and O
transverse O
direction O
in O
LAMed O
component S-MACEQ
, O
two O
LAMed O
Ti–6.5Al–3.5Mo–1.5Zr–0.3Si S-MATE
plates O
were O
successfully O
welded S-MANP
without O
defects S-CONPRI
. O


Results O
show O
that O
the O
microstructure S-CONPRI
of O
base B-MATE
metal E-MATE
( O
BM S-MATE
) O
is O
a O
typical O
basket-weave B-CONPRI
morphology E-CONPRI
that O
exhibits O
lamellar S-CONPRI
α O
within O
β O
matrix O
. O


In O
heat B-CONPRI
affected I-CONPRI
zone E-CONPRI
( O
HAZ S-CONPRI
) O
, O
the O
part O
of O
primary O
α O
transforms O
to O
β O
with O
the O
some O
very O
fine O
lamellar S-CONPRI
αs O
precipitates S-MATE
out O
. O


Due O
to O
the O
fast O
solidification B-PARA
rate E-PARA
, O
a O
large O
number O
of O
acicular O
α′ O
forms O
in O
fusion B-CONPRI
zone E-CONPRI
( O
FZ S-CONPRI
) O
, O
leading O
to O
the O
highest O
microhardness S-CONPRI
. O


All O
tensile S-PRO
samples S-CONPRI
fail O
in O
BM S-MATE
region O
with O
the O
fracture S-CONPRI
type O
of O
intergranular O
dimpled O
fracture S-CONPRI
. O


Compared O
with O
the O
T-joint S-FEAT
, O
the O
L-joint S-FEAT
shows O
higher O
ultimate B-PRO
tensile I-PRO
strength E-PRO
and O
yield B-PRO
strength E-PRO
, O
but O
lower O
elongation S-PRO
and O
reduction B-CHAR
of I-CHAR
area E-CHAR
due O
to O
the O
morphology S-CONPRI
of O
columnar B-PRO
grains E-PRO
and O
the O
strong O
texture S-FEAT
of O
β O
< O
010 O
> O
parallel O
to O
the O
deposition B-PARA
direction E-PARA
. O


In O
Laser-based B-MANP
Manufacturing E-MANP
, O
the O
configuration S-CONPRI
of O
process B-CONPRI
parameters E-CONPRI
aims O
to O
maintain O
quality S-CONPRI
measures O
within O
specific O
boundaries S-FEAT
and O
it O
is O
obtained O
through O
experimentation O
. O


The O
idea O
developed O
and O
presented O
in O
this O
paper O
concerns O
the O
prediction S-CONPRI
of O
the O
performance S-CONPRI
of O
adaptive B-CONPRI
control E-CONPRI
policies O
, O
based O
on O
process B-CONPRI
modeling E-CONPRI
. O


Two O
examples O
of O
Laser-based B-MANP
Manufacturing E-MANP
are O
deployed O
in O
order O
to O
verify O
the O
response O
of O
adaptive B-CONPRI
control E-CONPRI
algorithms O
through O
empirical S-CONPRI
design S-FEAT
, O
Laser B-MANP
welding E-MANP
and O
Laser-based B-MANP
Additive I-MANP
Manufacturing E-MANP
processes O
. O


The O
penetration B-PARA
depth E-PARA
has O
been O
utilized O
as S-MATE
the O
quality S-CONPRI
criterion O
of O
the O
adaptive B-CONPRI
control E-CONPRI
loop O
for O
both O
processes S-CONPRI
. O


The O
solidification B-CONPRI
phase E-CONPRI
has O
also O
been O
examined O
. O


Dissolved O
oxygen S-MATE
in O
weld B-CONPRI
zone E-CONPRI
leads O
to O
distinct O
microstructures S-MATE
from O
base B-MATE
metal E-MATE
after O
annealing S-MANP
. O


The O
repaired O
specimens O
have O
lower O
plasticity S-PRO
and O
slightly O
higher O
strength S-PRO
than O
base B-MATE
metal E-MATE
. O


Columnar B-CONPRI
grain I-CONPRI
boundary E-CONPRI
α O
phases O
in O
weld B-CONPRI
zone E-CONPRI
are O
the O
earliest O
microcracks S-CONPRI
nucleation O
sites O
. O


Gas B-MANP
tungsten I-MANP
arc I-MANP
welding E-MANP
was O
used O
to O
repair O
the O
laser S-ENAT
additive B-MANP
manufactured E-MANP
Ti-5Al-5Mo-5V-1Cr-1Fe O
( O
Ti-55511 O
) O
alloy S-MATE
with O
a O
subsequent O
triplex O
annealing B-MANP
treatment E-MANP
. O


The O
tensile B-PRO
properties E-PRO
of O
heat S-CONPRI
treated O
specimens O
containing O
of O
different O
proportions O
of O
weld B-CONPRI
zone E-CONPRI
were O
designed S-FEAT
to O
evaluate O
the O
influence O
of O
weld B-CONPRI
zone E-CONPRI
on O
tensile B-PRO
properties E-PRO
of O
the O
alloy S-MATE
. O


Microstructures S-MATE
, O
microhardness S-CONPRI
and O
tensile B-CHAR
tests E-CHAR
were O
performed O
to O
study O
the O
mechanical B-CONPRI
properties E-CONPRI
and O
fracture S-CONPRI
behaviors O
of O
the O
specimens O
. O


Results O
show O
that O
dissolved O
oxygen S-MATE
in O
the O
weld B-CONPRI
zone E-CONPRI
has O
a O
strong O
influence O
on O
increasing O
the O
number O
of O
α O
phase B-CONPRI
nucleation I-CONPRI
sites E-CONPRI
that O
can O
lead S-MATE
to O
different O
αp O
morphologies S-CONPRI
in O
the O
base B-MATE
metal E-MATE
and O
weld B-CONPRI
zone E-CONPRI
. O


These O
different O
αp O
can O
lead S-MATE
to O
distinct O
microstructures S-MATE
after O
triplex O
annealing B-MANP
treatment E-MANP
but O
with O
similar O
α O
volume B-PARA
fractions E-PARA
. O


Besides O
, O
plasticity S-PRO
deterioration O
of O
the O
repaired O
tensile B-MACEQ
specimens E-MACEQ
is O
mainly O
attributed O
to O
the O
formation O
of O
columnar B-CONPRI
grain I-CONPRI
boundary E-CONPRI
α O
phases O
in O
the O
weld B-CONPRI
zone E-CONPRI
which O
are O
considered O
to O
be S-MATE
the O
earliest O
nucleation S-CONPRI
sites O
of O
microcracks S-CONPRI
and O
confirmed O
by O
in B-CONPRI
situ E-CONPRI
tensile O
test O
. O


With O
the O
increase O
of O
WZ S-CONPRI
proportions O
in O
the O
cross B-CONPRI
section E-CONPRI
of O
tensile B-MACEQ
specimens E-MACEQ
, O
the O
plasticity S-PRO
of O
the O
alloy S-MATE
gradually O
decreases O
. O


Ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
( O
UAM S-MANP
) O
is O
a O
solid-state S-CONPRI
additive B-MANP
manufacturing E-MANP
technique O
employing O
principles O
of O
ultrasonic B-MANP
welding E-MANP
coupled O
with O
mechanized O
tape O
layering O
to O
fabricate S-MANP
fully O
functional O
parts O
. O


However O
, O
parts O
fabricated S-CONPRI
using O
UAM S-MANP
often O
exhibit O
a O
reduction S-CONPRI
in O
strength S-PRO
levels O
when O
loaded O
normal O
to O
the O
welding B-FEAT
interfaces E-FEAT
( O
Z-direction S-FEAT
) O
. O


In O
this O
work O
, O
the O
effect O
of O
post-weld B-MANP
heat I-MANP
treatments E-MANP
( O
PWHT S-CONPRI
) O
on O
Al-6061 S-MATE
builds O
fabricated S-CONPRI
using O
the O
UAM S-MANP
process S-CONPRI
was O
explored O
aiming O
to O
improve O
the O
mechanical B-PRO
strength E-PRO
of O
the O
UAM S-MANP
builds S-CHAR
. O


Tensile B-CHAR
testing E-CHAR
with O
digital B-CONPRI
image I-CONPRI
correlation E-CONPRI
( O
DIC S-CONPRI
) O
coupled O
with O
metallography S-CONPRI
along O
with O
multi-scale B-CHAR
structure I-CHAR
characterization E-CHAR
( O
SEM-EBSD S-ENAT
) O
was O
used O
to O
investigate O
and O
rationalize O
the O
mechanical S-APPL
performance O
of O
the O
UAM S-MANP
builds S-CHAR
. O


It O
was O
established O
that O
PWHTs S-MANP
may O
improve O
the O
Z-strength S-PRO
level O
by O
the O
factor O
of O
~3÷3.5 O
( O
from O
~46 O
to O
177 O
MPa S-CONPRI
) O
. O


The O
improvements O
in O
the O
strength S-PRO
level O
were O
primarily O
aided O
by O
material B-CONPRI
aging E-CONPRI
and O
grain B-CONPRI
growth E-CONPRI
across O
the O
bond B-CONPRI
interface E-CONPRI
. O


Ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
( O
UAM S-MANP
) O
is O
a O
solid-state S-CONPRI
additive B-MANP
manufacturing I-MANP
process E-MANP
that O
uses O
fundamental O
principles O
of O
ultrasonic B-MANP
welding E-MANP
and O
sequential O
layering O
of O
tapes O
to O
fabricate S-MANP
complex O
three-dimensional S-CONPRI
( O
3-D S-CONPRI
) O
components S-MACEQ
. O


One O
of O
the O
factors O
limiting O
the O
use O
of O
this O
technology S-CONPRI
is O
the O
poor O
tensile B-PRO
strength E-PRO
along O
the O
z-axis S-CONPRI
. O


Recent O
work O
has O
demonstrated O
the O
improvement O
of O
the O
z-axis B-CONPRI
properties E-CONPRI
after O
post-processing B-MANP
treatments E-MANP
. O


The O
abnormally O
high O
stability S-PRO
of O
the O
grains S-CONPRI
at O
the O
interface S-CONPRI
during O
post-weld B-MANP
heat I-MANP
treatments E-MANP
is O
, O
however O
, O
not O
yet O
well O
understood O
. O


In O
this O
work O
we O
use O
multiscale O
characterization O
to O
understand O
the O
stability S-PRO
of O
the O
grains S-CONPRI
during O
post-weld B-MANP
heat I-MANP
treatments E-MANP
. O


Aluminum B-MATE
alloy E-MATE
( O
6061 O
) O
builds S-CHAR
, O
fabricated S-CONPRI
using O
ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
, O
were O
post-weld B-MANP
heat I-MANP
treated E-MANP
at O
180 O
, O
330 O
and O
580 O
°C O
. O


The O
grains S-CONPRI
close O
to O
the O
tape O
interfaces O
are O
stable O
during O
post-weld B-MANP
heat I-MANP
treatments E-MANP
at O
high O
temperatures S-PARA
( O
i.e. O
, O
580 O
°C O
) O
. O


This O
is O
in O
contrast O
to O
rapid B-CONPRI
grain I-CONPRI
growth E-CONPRI
that O
takes O
place O
in O
the O
bulk O
. O


Transmission B-CHAR
electron I-CHAR
microscopy E-CHAR
and O
atom-probe B-CHAR
tomography E-CHAR
display O
a O
significant O
enrichment O
of O
oxygen S-MATE
and O
magnesium S-MATE
near O
the O
stable O
interfaces O
. O


Based O
on O
the O
detailed O
characterization O
, O
two O
mechanisms O
are O
proposed O
and O
evaluated O
: O
nonequilibrium O
nano-dispersed B-MATE
oxides E-MATE
impeding O
the O
grain B-CONPRI
growth E-CONPRI
due O
to O
grain B-CONPRI
boundary E-CONPRI
pinning O
, O
or O
grain B-CONPRI
boundary E-CONPRI
segregation O
of O
magnesium S-MATE
and O
oxygen S-MATE
reducing O
the O
grain B-CONPRI
boundary I-CONPRI
energy E-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
will O
be S-MATE
an O
option O
to O
develop O
prototypes S-CONPRI
or O
mechanical B-MACEQ
parts E-MACEQ
that O
will O
be S-MATE
made O
faster O
and O
cheaper O
than O
other O
techniques O
such O
as S-MATE
laser O
cladding S-MANP
or O
electron B-CONPRI
beam E-CONPRI
. O


The O
main O
objective O
of O
this O
research S-CONPRI
was O
to O
study O
the O
optimal O
initial O
conditions O
of O
the O
proposed O
additive B-MACEQ
manufacturing I-MACEQ
system E-MACEQ
in O
order O
to O
obtain O
metal S-MATE
prototypes O
. O


This O
optimal O
conditions O
have O
been O
presented O
taking O
into O
account O
the O
measurements O
of O
geometrical O
conditions O
and O
surface B-MANP
finishing E-MANP
. O


The O
proposed O
additive B-MACEQ
manufacturing I-MACEQ
system E-MACEQ
consist O
on O
an O
integration O
of O
a O
Fronius B-MACEQ
TPS I-MACEQ
4000 I-MACEQ
CMT I-MACEQ
R E-MACEQ
welding O
machine S-MACEQ
with O
a O
BF30 O
Vario O
Optimun O
CNC B-MANP
milling E-MANP
machine O
. O


Once O
the O
material S-MATE
was O
selected O
, O
the O
optimal O
conditions O
to O
make O
the O
first O
layer S-PARA
have O
been O
obtained O
. O


Previous O
simple S-MANP
geometries S-CONPRI
, O
such O
as S-MATE
prismatic O
and O
cylindrical S-CONPRI
parts O
have O
been O
manufactured S-CONPRI
. O


Efficient O
way O
of O
depositing O
thin-walled O
overhang B-FEAT
features E-FEAT
, O
without O
supports S-APPL
, O
based O
on O
inclined O
slicing S-CONPRI
and O
weld-deposition S-CONPRI
. O


Uses O
higher O
order O
kinematics S-CONPRI
to O
the O
work B-MACEQ
piece E-MACEQ
for O
fabricating S-MANP
complex O
thin-walled O
fully B-PARA
dense E-PARA
functional O
metallic B-MACEQ
parts E-MACEQ
. O


Geometrical O
modelling S-ENAT
of O
the O
weld-bead S-FEAT
to O
predict O
the O
layer B-PARA
thickness E-PARA
of O
a O
given O
layer S-PARA
for O
bead-on-bead B-CONPRI
deposition E-CONPRI
. O


In-house O
MATLAB B-CONPRI
code E-CONPRI
to O
slice S-CONPRI
the O
CAD B-ENAT
model E-ENAT
and O
generate O
the O
tool B-CONPRI
path E-CONPRI
for O
inclined O
deposition S-CONPRI
of O
a O
given O
layer S-PARA
. O


Fabrication S-MANP
of O
complex O
thin-walled B-FEAT
parts E-FEAT
using O
GMAW S-MANP
based O
weld-deposition S-CONPRI
for O
illustration O
of O
above O
mentioned O
concepts O
. O


Gas B-MANP
Metal I-MANP
Arc I-MANP
Welding E-MANP
( O
GMAW S-MANP
) O
based O
weld-deposition B-CONPRI
process E-CONPRI
is O
one O
of O
the O
deposition-based O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
with O
the O
ability O
to O
produce O
fully B-PARA
dense E-PARA
complex O
functional O
metallic S-MATE
objects O
. O


Due O
to O
its O
high B-PARA
deposition I-PARA
rates E-PARA
, O
high O
material S-MATE
and O
power B-PARA
efficiency E-PARA
, O
lower O
investment O
costs O
, O
simpler O
setup O
and O
work O
environment O
requirements O
it O
is O
slowly O
becoming O
a O
viable O
metallic B-MANP
AM E-MANP
method O
. O


Amongst O
various O
geometrical B-FEAT
features E-FEAT
that O
can O
be S-MATE
realized O
in O
weld-deposition B-MANP
based I-MANP
AM E-MANP
, O
the O
thin-walled O
features O
( O
i.e. O
, O
features O
with O
one O
single O
deposition S-CONPRI
pass O
) O
are O
the O
toughest O
as S-MATE
the O
process S-CONPRI
has O
to O
overcome O
the O
bead-over-bead S-CONPRI
complexity O
. O


Based O
on O
geometric B-CONPRI
modelling E-CONPRI
and O
experimentation O
, O
this O
paper O
presents O
an O
efficient O
technique O
for O
producing O
the O
thin-walled O
metallic B-MACEQ
structures E-MACEQ
, O
including O
objects O
with O
undercut S-FEAT
features O
. O


This O
is O
possible O
by O
adding O
extra O
degrees B-CONPRI
of I-CONPRI
freedom E-CONPRI
or O
by O
using O
higher O
order O
kinematics S-CONPRI
to O
the O
work B-MACEQ
piece E-MACEQ
and/or O
to O
the O
deposition S-CONPRI
head O
by O
suitably O
aligning O
the O
overhanging B-FEAT
feature E-FEAT
in-line O
to O
the O
deposition B-PARA
direction E-PARA
. O


An O
in-house O
MATLAB B-CONPRI
code E-CONPRI
was O
developed O
to O
slice S-CONPRI
the O
CAD B-ENAT
model E-ENAT
and O
generate O
the O
tool B-CONPRI
path E-CONPRI
for O
inclined O
deposition S-CONPRI
of O
a O
given O
layer S-PARA
of O
a O
thin-walled B-MACEQ
model E-MACEQ
. O


A O
geometrical B-CONPRI
model E-CONPRI
proposed O
to O
predict O
the O
layer B-PARA
thickness E-PARA
of O
a O
given O
layer S-PARA
during O
such O
bead-on-bead B-CONPRI
deposition E-CONPRI
showed O
good O
correlation O
with O
experimental B-CONPRI
data E-CONPRI
. O


Some O
illustrative O
complex O
thin-walled B-APPL
components E-APPL
successfully O
fabricated S-CONPRI
using O
this O
model S-CONPRI
have O
also O
been O
presented O
. O


Additive B-MANP
layer I-MANP
manufacturing E-MANP
( O
ALM S-MANP
) O
, O
using O
gas B-MANP
tungsten I-MANP
arc I-MANP
welding E-MANP
( O
GTAW S-MANP
) O
as S-MATE
heat O
source S-APPL
, O
is O
a O
promising O
technology S-CONPRI
in O
producing O
Inconel B-MATE
625 E-MATE
components S-MACEQ
due O
to O
significant O
cost O
savings O
, O
high B-PARA
deposition I-PARA
rate E-PARA
and O
convenience O
of O
processing O
. O


With O
the O
purpose O
of O
revealing O
how O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
are O
affected O
by O
the O
location O
within O
the O
manufactured S-CONPRI
wall O
component S-MACEQ
, O
the O
present O
study O
has O
been O
carried O
out O
. O


The O
manufactured S-CONPRI
Inconel B-MATE
625 E-MATE
consists O
of O
cellular B-CONPRI
grains E-CONPRI
without O
secondary B-MATE
dendrites E-MATE
in O
the O
near-substrate O
region O
, O
columnar B-MATE
dendrites E-MATE
structure O
oriented O
upwards O
in O
the O
layer S-PARA
bands O
, O
followed O
by O
the O
transition S-CONPRI
from O
directional B-MATE
dendrites E-MATE
to O
equiaxed B-CONPRI
grain E-CONPRI
in O
the O
top O
region O
. O


With O
the O
increase O
in O
deposited O
height O
, O
segregation S-CONPRI
behavior O
of O
alloying B-MATE
elements E-MATE
Nb O
and O
Mo S-MATE
constantly O
strengthens O
with O
maximal O
evolution S-CONPRI
in O
the O
top O
region O
. O


The O
primary O
dendrite S-BIOP
arm O
spacing O
has O
a O
well O
coherence O
with O
the O
content O
of O
Laves B-CONPRI
phase E-CONPRI
. O


The O
microhardness S-CONPRI
and O
tensile B-PRO
strength E-PRO
show O
obvious O
variation S-CONPRI
in O
different O
regions O
. O


The O
microhardness S-CONPRI
and O
tensile B-PRO
strength E-PRO
of O
near-substrate O
region O
are O
superior O
to O
that O
of O
layer S-PARA
bands O
and O
top O
region O
. O


The O
results O
are O
further O
explained O
in O
detail O
through O
the O
weld B-CONPRI
pool E-CONPRI
behavior O
and O
temperature S-PARA
field O
measurement S-CHAR
. O


This O
paper O
describes O
results O
of O
seam B-MANP
welding E-MANP
of O
relatively O
high O
temperature S-PARA
melting B-CONPRI
materials E-CONPRI
, O
AISI B-MATE
304 E-MATE
, O
C-Mn B-MATE
steels E-MATE
, O
Ni-based B-MATE
alloys E-MATE
, O
CP O
Cu S-MATE
, O
CP O
Ni S-MATE
, O
Ti6Al4V S-MATE
and O
relatively O
low O
temperature S-PARA
melting B-CONPRI
material E-CONPRI
, O
AA6061 S-MATE
. O


It O
describes O
the O
seam B-MANP
welding E-MANP
of O
multi-layered O
similar O
and O
dissimilar O
metallic B-MATE
sheets E-MATE
. O


The O
method O
described O
and O
involved O
advancing O
a O
rotating O
non-consumable O
rod S-MACEQ
( O
CP O
Mo S-MATE
or O
AISI B-MATE
304 E-MATE
) O
toward O
the O
upper O
sheet S-MATE
of O
a O
metallic B-MATE
stack E-MATE
clamped O
under O
pressure S-CONPRI
. O


As S-MATE
soon O
as S-MATE
the O
distal O
end O
of O
the O
rod S-MACEQ
touched O
the O
top O
portion O
of O
the O
upper O
metallic B-MATE
sheet E-MATE
, O
an O
axial B-CONPRI
force E-CONPRI
was O
applied O
. O


After O
an O
initial O
dwell B-PARA
time E-PARA
, O
the O
metallic B-MATE
stack E-MATE
moved O
horizontally O
relative O
to O
the O
stationery O
non-consumable O
rod S-MACEQ
by O
a O
desired O
length O
, O
thereby O
forming S-MANP
a O
metallurgical B-CONPRI
bond E-CONPRI
between O
the O
metallic B-MATE
sheets E-MATE
. O


Multi-track O
and O
multi-metal O
seam B-FEAT
welds E-FEAT
of O
high O
temperature S-PARA
metallic B-MATE
sheets E-MATE
, O
AISI B-MATE
304 E-MATE
, O
C-Mn B-MATE
steel E-MATE
, O
Nickel-based B-MATE
alloys E-MATE
, O
Cp O
Cu S-MATE
, O
Ti6Al4V S-MATE
and O
low O
temperature S-PARA
metallic B-MATE
sheets E-MATE
, O
AA6061 S-MATE
were O
obtained O
. O


Optical S-CHAR
and O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
examination O
and O
180 O
degree O
U-bend B-CHAR
test E-CHAR
indicated O
that O
defect S-CONPRI
free O
seam B-FEAT
welds E-FEAT
could O
be S-MATE
obtained O
with O
this O
method O
. O


Tensile- B-CHAR
shear I-CHAR
testing E-CHAR
showed O
that O
the O
seam B-FEAT
welds E-FEAT
of O
AISI B-MATE
304 E-MATE
, O
C-Mn B-MATE
steel E-MATE
, O
Nickel-based B-MATE
alloy E-MATE
were O
stronger O
than O
the O
starting O
base B-MATE
metal E-MATE
counterparts O
while O
AA6061 S-MATE
was O
weaker O
due O
to O
softening O
. O


The O
metallurgical B-CONPRI
bonding E-CONPRI
at O
the O
interface S-CONPRI
between O
the O
metallic B-MATE
sheets E-MATE
was O
attributed O
to O
localized O
stick O
and O
slip O
at O
the O
interface S-CONPRI
, O
dynamic S-CONPRI
recrystallization O
and O
diffusion S-CONPRI
. O


The O
method O
developed O
can O
be S-MATE
used O
as S-MATE
a O
means O
of O
welding S-MANP
, O
cladding S-MANP
and O
additive B-MANP
manufacturing E-MANP
. O


In O
this O
paper O
the O
joinability O
of O
titanium S-MATE
Additive B-MANP
Manufactured E-MANP
( O
AM S-MANP
) O
parts O
is O
explored O
. O


Keyhole B-MANP
welding E-MANP
, O
using O
a O
pulsed B-ENAT
laser I-ENAT
beam E-ENAT
, O
of O
conventionally O
produced O
parts O
is O
compared O
to O
AM B-MACEQ
parts E-MACEQ
. O


Metal B-MANP
AM E-MANP
parts O
are O
notorious O
for O
having O
remaining O
porosities S-PRO
and O
other O
non-isotropic S-CONPRI
properties O
due O
to O
the O
layered O
manufacturing B-MANP
process E-MANP
. O


This O
study O
shows O
that O
due O
to O
these O
deficiencies O
more O
energy O
per O
unit O
weld B-PARA
length E-PARA
is O
required O
to O
obtain O
a O
similar O
keyhole O
geometry S-CONPRI
for O
titanium S-MATE
AM B-MACEQ
parts E-MACEQ
. O


It O
is O
also O
demonstrated O
that O
, O
with O
adjusted O
laser S-ENAT
process O
parameters S-CONPRI
, O
good O
quality B-CONPRI
welds E-CONPRI
for O
aerospace S-APPL
applications O
in O
terms O
of O
pressure B-PRO
resistance E-PRO
and O
leak O
tightness O
are O
achievable O
. O


Part O
size O
in O
additive B-MANP
manufacturing E-MANP
is O
limited O
by O
the O
size O
of O
building O
area S-PARA
of O
AM S-MANP
equipment O
. O


Occasionally O
, O
larger O
constructions O
that O
AM B-MACEQ
machines E-MACEQ
are O
able O
to O
produce O
, O
are O
needed O
, O
and O
this O
creates O
demand O
for O
welding S-MANP
AM B-MACEQ
parts E-MACEQ
together O
. O


However O
there O
is O
very O
little O
information O
on O
welding S-MANP
of O
additive B-MANP
manufactured E-MANP
stainless O
steels S-MATE
. O


The O
aim O
of O
this O
study O
was O
to O
investigate O
the O
weldability S-PRO
aspects O
of O
AM B-MATE
material E-MATE
. O


In O
this O
study O
, O
comparison O
of O
the O
bead S-CHAR
on O
plate O
welds S-FEAT
between O
AM B-MACEQ
parts E-MACEQ
and O
sheet B-MATE
metal E-MATE
parts O
is O
done.Used O
material S-MATE
was O
316L B-MATE
stainless I-MATE
steel E-MATE
, O
AM S-MANP
and O
sheet B-MATE
metal E-MATE
, O
and O
parts O
were O
welded S-MANP
with O
laser B-MANP
welding E-MANP
. O


Weld B-PARA
quality E-PARA
was O
evaluated O
visually O
from O
macroscopic B-CONPRI
images E-CONPRI
. O


Results O
show O
that O
there O
are O
certain O
differences O
in O
the O
welds S-FEAT
in O
AM B-MACEQ
parts E-MACEQ
compared O
to O
the O
welds S-FEAT
in O
sheet B-MATE
metal E-MATE
parts O
. O


Differences O
were O
found O
in O
penetration B-PARA
depths E-PARA
and O
in O
type O
of O
welding B-CONPRI
defects E-CONPRI
. O


Nevertheless O
, O
this O
study O
presents O
that O
laser B-MANP
welding E-MANP
is O
suitable O
process S-CONPRI
for O
welding S-MANP
AM B-MACEQ
parts E-MACEQ
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
of O
high O
γ′ O
strengthened O
Nickel-base B-MATE
superalloys E-MATE
, O
such O
as S-MATE
IN738LC O
, O
is O
of O
high O
interest O
for O
applications O
in O
hot O
section O
components S-MACEQ
for O
gas B-MACEQ
turbines E-MACEQ
. O


The O
creep S-PRO
property O
acts O
as S-MATE
the O
critical O
indicator O
of O
component S-MACEQ
performance O
under O
load O
at O
elevated O
temperature S-PARA
. O


In O
order O
to O
evaluate O
the O
short-term O
creep B-PRO
behavior E-PRO
, O
slow B-CONPRI
strain I-CONPRI
rate I-CONPRI
tensile E-CONPRI
( O
SSRT S-CONPRI
) O
tests O
were O
performed O
. O


IN738LC S-MATE
bars O
were O
built O
by O
laser B-MANP
powder-bed-fusion E-MANP
( O
L-PBF S-MANP
) O
and O
then O
subjected O
to O
hot B-MANP
isostatic I-MANP
pressing E-MANP
( O
HIP S-MANP
) O
followed O
by O
the O
standard S-CONPRI
two-step O
heat B-MANP
treatment E-MANP
. O


The O
samples S-CONPRI
were O
subjected O
to O
SSRT S-CONPRI
testing O
at O
850 O
°C O
under O
strain B-CONPRI
rates E-CONPRI
of O
1 O
× O
10−5/s O
, O
1 O
× O
10−6/s O
, O
and O
1 O
× O
10−7/s O
. O


In O
this O
research S-CONPRI
, O
the O
underlying O
creep B-CONPRI
deformation I-CONPRI
mechanism E-CONPRI
of O
AM S-MANP
processed O
IN738LC S-MATE
is O
investigated O
using O
the O
serial B-ENAT
sectioning E-ENAT
technique O
, O
electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
( O
EBSD S-CHAR
) O
, O
transmission B-CHAR
electron I-CHAR
microscopy E-CHAR
( O
TEM S-CHAR
) O
. O


On O
the O
creep S-PRO
mechanism O
of O
AM B-MATE
polycrystalline I-MATE
IN738LC E-MATE
, O
grain B-CONPRI
boundary I-CONPRI
sliding E-CONPRI
is O
predominant O
. O


However O
, O
due O
to O
the O
interlock O
feature S-FEAT
of O
grain B-CONPRI
boundaries E-CONPRI
in O
AM S-MANP
processed O
IN738LC S-MATE
, O
the O
grain B-CONPRI
structure E-CONPRI
retains O
its O
integrity S-CONPRI
after O
deformation S-CONPRI
. O


The O
dislocation B-CONPRI
motion E-CONPRI
acts O
as S-MATE
the O
major O
accommodation O
process S-CONPRI
of O
grain B-CONPRI
boundary I-CONPRI
sliding E-CONPRI
. O


Dislocations S-CONPRI
bypass O
the O
γ′ O
precipitates S-MATE
by O
Orowan B-CONPRI
looping E-CONPRI
and O
wavy O
slip O
. O


The O
rearrangement O
of O
screw B-CONPRI
dislocations E-CONPRI
is O
responsible O
for O
the O
formation O
of O
subgrains S-CONPRI
within O
the O
grain S-CONPRI
interior O
. O


This O
research S-CONPRI
elucidates O
the O
short-creep S-CONPRI
behavior O
of O
AM S-MANP
processed O
IN738LC S-MATE
. O


It O
also O
shed O
new O
light O
on O
the O
creep B-CONPRI
deformation I-CONPRI
mechanism E-CONPRI
of O
additive B-MANP
manufactured E-MANP
γ′ O
strengthened O
polycrystalline O
Nickel-base B-MATE
superalloys E-MATE
. O


Due O
to O
the O
cost O
advantage O
, O
weld-based B-MANP
Additive I-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
is O
suitable O
for O
directly O
fabricating S-MANP
large O
metallic B-MACEQ
parts E-MACEQ
. O


One O
of O
challenges O
for O
weld-based O
Additive S-MATE
M O
anufacturing O
is O
to O
build S-PARA
overhanging O
structure S-CONPRI
or O
tilt B-FEAT
structure E-FEAT
at O
a O
large O
slant B-PARA
angle E-PARA
, O
because O
liquid B-MATE
metal E-MATE
on O
the O
boundary S-FEAT
would O
flow O
down O
by O
gravity O
due O
to O
lack O
of O
sufficient O
support S-APPL
. O


In O
the O
present O
work O
, O
electromagnetically S-CONPRI
confined O
weld-based B-MANP
Additive I-MANP
Manufacturing E-MANP
is O
develop O
ed S-CHAR
to O
solve O
this O
problem O
. O


In O
the O
process S-CONPRI
, O
liquid B-MATE
metal E-MATE
is O
confined O
and O
semi-levitated O
by O
the O
Lorentz B-CONPRI
force E-CONPRI
exerted O
by O
magnetic B-CONPRI
field E-CONPRI
and O
thus O
the O
flow O
of O
liquid B-MATE
metal E-MATE
is O
restricted O
. O


Experiments O
and O
numerical B-ENAT
simulations E-ENAT
are O
performed O
to O
investigate O
the O
effect O
mechanism S-CONPRI
of O
electromagnetic B-CONPRI
confinement E-CONPRI
. O


Experimental S-CONPRI
results O
verify O
that O
the O
flow-down O
or O
collapse O
of O
liquid B-MATE
metal E-MATE
is O
impeded O
by O
electromagnetic B-CONPRI
confinement E-CONPRI
. O


With O
specific O
welding S-MANP
parameters S-CONPRI
, O
the O
maximum O
tilt B-FEAT
angle E-FEAT
of O
successful O
building O
increases O
from O
50° O
to O
60° O
when O
imposing O
electromagnetic B-CONPRI
confinement E-CONPRI
. O


New O
technologies S-CONPRI
can O
be S-MATE
justified O
with O
the O
advent O
of O
the O
additive B-MANP
manufacturing E-MANP
, O
excels O
by O
its O
flexibility B-CONPRI
in I-CONPRI
manufacturing E-CONPRI
parts O
of O
various O
geometries S-CONPRI
, O
good O
accuracy S-CHAR
and O
material S-MATE
waste O
reduction S-CONPRI
savings O
. O


This O
circumstance O
requires O
the O
application O
of O
techniques O
to O
determine O
the O
reliability S-CHAR
of O
the O
results O
in O
the O
deposition S-CONPRI
of O
layers O
in O
order O
to O
have O
a O
good O
accuracy S-CHAR
. O


This O
work O
aims O
to O
present O
a O
new O
technology S-CONPRI
applied O
to O
additive B-MANP
manufacturing E-MANP
, O
focusing O
on O
accuracy S-CHAR
in O
the O
deposition S-CONPRI
of O
layers O
, O
lower O
cost O
and O
user O
friendliness O
man-machine O
. O


New O
method O
was O
proposed O
in O
order O
to O
obtain O
advantages O
regarding O
the O
use O
of O
Plasma B-MANP
welding E-MANP
process O
. O


An O
apparatus O
for O
generating O
plasma S-CONPRI
was O
used O
to O
obtain O
the O
arc S-CONPRI
. O


Correlated S-CONPRI
magnitudes O
helped O
in O
determining O
Efficient O
Model S-CONPRI
of O
Deposition S-CONPRI
for O
use O
in O
offsetting O
the O
geometric O
and O
thermal O
errors S-CONPRI
. O


Computer B-CONPRI
simulations E-CONPRI
were O
applied O
to O
the O
new O
concept O
of O
deposition S-CONPRI
and O
the O
efficiency O
of O
the O
presented O
system O
was O
performed O
, O
but O
no O
experimental S-CONPRI
results O
are O
provided O
herein O
. O


Ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
( O
UAM S-MANP
) O
is O
a O
solid-state S-CONPRI
hybrid B-CONPRI
manufacturing E-CONPRI
technique O
. O


In O
this O
work O
characterization O
using O
electron B-ENAT
back I-ENAT
scatter I-ENAT
diffraction E-ENAT
was O
performed O
on O
aluminum–titanium O
dissimilar O
metal S-MATE
welds O
made O
using O
a O
9 O
kW O
ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
system O
. O


The O
results O
showed O
that O
the O
aluminum S-MATE
texture O
at O
the O
interface S-CONPRI
after O
ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
is O
similar O
to O
aluminum S-MATE
texture O
observed O
during O
accumulative O
roll B-MANP
bonding E-MANP
of O
aluminum B-MATE
alloys E-MATE
. O


It O
is O
finally O
concluded O
that O
the O
underlying O
mechanism S-CONPRI
of O
bond O
formation O
in O
ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
primarily O
relies O
on O
severe O
shear O
deformation S-CONPRI
at O
the O
interface S-CONPRI
. O


The O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
2Cr13 O
thin-wall O
part O
was O
deposited O
using O
robotic O
cold B-MANP
metal I-MANP
transfer E-MANP
( O
CMT S-MANP
) O
technology S-CONPRI
, O
and O
the O
location-related O
thermal O
history O
, O
densification S-MANP
, O
phase S-CONPRI
identification O
, O
microstructure S-CONPRI
, O
and O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
part O
were O
explored O
. O


The O
results O
show O
that O
pre-heating O
effect O
from O
previously O
built O
layers O
can O
be S-MATE
effectively O
used O
to O
reduce O
residual B-PRO
stresses E-PRO
; O
cooling B-PARA
rate E-PARA
firstly O
decreased O
rapidly O
and O
then O
kept O
stable O
in O
the O
15th–25th O
layers O
. O


The O
peaks O
of O
the O
α-Fe O
phase S-CONPRI
of O
the O
AM B-MACEQ
part E-MACEQ
drifted O
slightly O
toward O
a O
relatively O
smaller O
Bragg O
's O
angle O
as S-MATE
a O
result O
of O
solute B-MATE
atoms E-MATE
incorporation O
when O
compared O
with O
that O
of O
the O
base B-MATE
metal E-MATE
. O


As-deposited O
microstructure S-CONPRI
consisted O
of O
martensite S-MATE
and O
ferrite S-MATE
, O
along O
with O
( O
Fe S-MATE
, O
Cr S-MATE
) O
23C6 O
phase S-CONPRI
precipitated O
at O
α-Fe O
grain B-CONPRI
boundaries E-CONPRI
. O


Martensite S-MATE
content O
increased O
gradually O
from O
the O
5th O
layer S-PARA
to O
the O
25th O
layers O
, O
indicating O
that O
metastable S-PRO
martensite S-MATE
partly O
decomposed O
into O
stable O
ferrite S-MATE
due O
to O
the O
carbon B-MATE
atoms E-MATE
diffusion O
. O


The O
hardness S-PRO
and O
UTS S-PRO
changed O
slightly O
in O
the O
05th–15th O
layers O
and O
then O
increased O
quickly O
from O
the O
20th O
layer S-PARA
to O
the O
25th O
layers O
at O
the O
expense O
of O
ductility S-PRO
; O
the O
fracture S-CONPRI
process O
transformed O
from O
ductile S-PRO
( O
01st–10th O
layers O
) O
to O
mixed-mode O
( O
15th–20th O
layers O
) O
, O
and O
finally O
to O
brittle B-CONPRI
fracture E-CONPRI
( O
25th O
layer S-PARA
) O
. O


The O
findings O
above O
suggest O
that O
, O
despite O
the O
emergency O
of O
few O
pores S-PRO
and O
slightly O
inadequate O
ductility S-PRO
, O
this O
robotic O
CMT S-MANP
technology O
is O
a O
feasible O
method O
to O
obtain O
desired O
microstructures S-MATE
and O
enhanced O
mechanical B-CONPRI
properties E-CONPRI
for O
the O
WAAM S-MANP
2Cr13 O
part O
in O
comparison O
with O
its O
as-solutioned O
counterpart O
. O


An O
innovative O
and O
low O
cost O
additive B-MANP
layer I-MANP
manufacturing E-MANP
( O
ALM S-MANP
) O
process S-CONPRI
is O
used O
to O
produce O
γ-TiAl O
based O
alloy S-MATE
wall O
components S-MACEQ
. O


Gas B-MANP
tungsten I-MANP
arc I-MANP
welding E-MANP
( O
GTAW S-MANP
) O
provides O
the O
heat B-CONPRI
source E-CONPRI
for O
this O
new O
approach O
, O
combined O
with O
in-situ S-CONPRI
alloying S-FEAT
through O
separate O
feeding O
of O
commercially O
pure O
Ti S-MATE
and O
Al S-MATE
wires O
into O
the O
weld B-CONPRI
pool E-CONPRI
. O


This O
paper O
investigates S-CONPRI
the O
morphology S-CONPRI
, O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
additively B-MANP
manufactured E-MANP
TiAl O
material S-MATE
, O
and O
how O
these O
are O
affected O
by O
the O
location O
within O
the O
manufactured S-CONPRI
component S-MACEQ
. O


The O
typical O
additively O
layer S-PARA
manufactured O
morphology S-CONPRI
exhibits O
epitaxial S-PRO
growth O
of O
columnar B-PRO
grains E-PRO
and O
several O
layer S-PARA
bands O
. O


The O
fabricated S-CONPRI
γ-TiAl O
based O
alloy S-MATE
consists O
of O
comparatively O
large O
α2 O
grains S-CONPRI
in O
the O
near-substrate O
region O
, O
fully O
lamellar S-CONPRI
colonies O
with O
various O
sizes O
and O
interdendritic O
γ O
structure S-CONPRI
in O
the O
intermediate O
layer S-PARA
bands O
, O
followed O
by O
fine O
dendrites S-BIOP
and O
interdendritic O
γ O
phases O
in O
the O
top O
region O
. O


Microhardness S-CONPRI
measurements O
and O
tensile B-CHAR
testing E-CHAR
results O
indicated O
relatively O
homogeneous S-CONPRI
mechanical O
characteristics O
throughout O
the O
deposited O
material S-MATE
. O


The O
exception O
to O
this O
homogeneity O
occurs O
in O
the O
near-substrate O
region O
immediately O
adjacent O
to O
the O
pure O
Ti B-MATE
substrate E-MATE
used O
in O
these O
experiments O
, O
where O
the O
alloying S-FEAT
process O
is O
not O
as S-MATE
well O
controlled O
as S-MATE
in O
the O
higher O
regions O
. O


The O
tensile B-PRO
properties E-PRO
are O
also O
different O
for O
the O
vertical S-CONPRI
( O
build S-PARA
) O
direction O
and O
horizontal O
( O
travel O
) O
direction O
because O
of O
the O
differing O
microstructure S-CONPRI
in O
each O
direction O
. O


The O
microstructure S-CONPRI
variation O
and O
strengthening B-CONPRI
mechanisms E-CONPRI
resulting O
from O
the O
new O
manufacturing B-MANP
approach E-MANP
are O
analysed O
in O
detail O
. O


The O
results O
demonstrate O
the O
potential O
to O
produce O
full O
density S-PRO
titanium O
aluminide O
components S-MACEQ
directly O
using O
the O
new O
additive B-MANP
layer I-MANP
manufacturing E-MANP
method O
. O


Amorphous O
polymer B-MATE
melt E-MATE
is O
extruded S-MANP
and O
deposited O
filament-by-filament O
. O


Non-isothermal O
inter-diffusion O
from O
an O
anisotropic S-PRO
configuration O
is O
modelled O
. O


Weld B-PARA
thickness E-PARA
( O
∼Rg O
) O
is O
sufficient O
to O
achieve O
bulk O
mechanical B-PRO
strength E-PRO
at O
weld S-FEAT
. O


Reduced O
weld B-PRO
strength E-PRO
is O
attributed O
to O
a O
partially O
entangled O
structure S-CONPRI
. O


Although O
3D B-MANP
printing E-MANP
has O
the O
potential O
to O
transform O
manufacturing B-MANP
processes E-MANP
, O
the O
strength S-PRO
of O
printed O
parts O
often O
does O
not O
rival O
that O
of O
traditionally-manufactured O
parts O
. O


The O
fused-filament B-MANP
fabrication E-MANP
method O
involves O
melting S-MANP
a O
thermoplastic S-MATE
, O
followed O
by O
layer-by-layer S-CONPRI
extrusion S-MANP
of O
the O
molten O
viscoelastic S-PRO
material S-MATE
to O
fabricate S-MANP
a O
three-dimensional S-CONPRI
object O
. O


The O
strength S-PRO
of O
the O
welds S-FEAT
between O
layers O
is O
controlled O
by O
interdiffusion O
and O
entanglement O
of O
the O
melt S-CONPRI
across O
the O
interface S-CONPRI
. O


However O
, O
diffusion S-CONPRI
slows O
down O
as S-MATE
the O
printed O
layer S-PARA
cools O
towards O
the O
glass B-CONPRI
transition I-CONPRI
temperature E-CONPRI
. O


Diffusion S-CONPRI
is O
also O
affected O
by O
high O
shear O
rates O
in O
the O
nozzle S-MACEQ
, O
which O
significantly O
deform O
and O
disentangle O
the O
polymer S-MATE
microstructure S-CONPRI
prior O
to O
welding S-MANP
. O


In O
this O
paper O
, O
we O
model S-CONPRI
non-isothermal O
polymer S-MATE
relaxation O
, O
entanglement O
recovery O
, O
and O
diffusion S-CONPRI
processes O
that O
occur O
post-extrusion O
to O
investigate O
the O
effects O
that O
typical O
printing O
conditions O
and O
amorphous O
( O
non-crystalline O
) O
polymer S-MATE
rheology O
have O
on O
the O
ultimate O
weld S-FEAT
structure S-CONPRI
. O


Although O
we O
find O
the O
weld B-PARA
thickness E-PARA
to O
be S-MATE
of O
the O
order O
of O
the O
polymer S-MATE
size O
, O
the O
structure S-CONPRI
of O
the O
weld S-FEAT
is O
anisotropic S-PRO
and O
relatively O
disentangled O
; O
reduced O
mechanical B-PRO
strength E-PRO
at O
the O
weld S-FEAT
is O
attributed O
to O
this O
lower O
degree O
of O
entanglement O
. O


The O
microstructures S-MATE
of O
Al B-MATE
alloy E-MATE
6061 O
subjected O
to O
very-high-power O
ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
were O
systematically O
examined O
to O
understand O
the O
underlying O
ultrasonic B-MANP
welding E-MANP
mechanism S-CONPRI
. O


The O
microstructure S-CONPRI
of O
the O
weld S-FEAT
interface S-CONPRI
between O
the O
metal S-MATE
tapes O
consisted O
of O
fine O
, O
equiaxed B-CONPRI
grains E-CONPRI
resulting O
from O
recrystallization S-CONPRI
, O
which O
is O
driven O
by O
simple S-MANP
shear O
deformation S-CONPRI
along O
the O
ultrasonically O
vibrating O
direction O
of O
the O
tape O
surface S-CONPRI
. O


Void S-CONPRI
formation O
at O
the O
weld S-FEAT
interface S-CONPRI
is O
attributed O
to O
surface B-CONPRI
asperities E-CONPRI
resulting O
from O
pressure S-CONPRI
induced O
by O
the O
sonotrode S-MACEQ
at O
the O
initial O
tape O
deposition S-CONPRI
. O


Transmission B-CHAR
electron I-CHAR
microscopy E-CHAR
revealed O
that O
Al–Al O
metallic B-CONPRI
bonding E-CONPRI
without O
surface S-CONPRI
oxide S-MATE
layers O
was O
mainly O
achieved O
, O
although O
some O
oxide S-MATE
clusters O
were O
locally O
observed O
at O
the O
original O
interface S-CONPRI
. O


The O
results O
suggest O
that O
the O
oxide S-MATE
layers O
were O
broken O
up O
and O
then O
locally O
clustered O
on O
the O
interface S-CONPRI
by O
ultrasonic B-PARA
vibration E-PARA
. O


A O
theoretical S-CONPRI
analysis O
of O
the O
metal S-MATE
transfer O
behaviour O
and O
bead S-CHAR
shape O
formation O
using O
positional O
GMAW S-MANP
are O
provided O
. O


The O
effects O
of O
various O
process B-CONPRI
parameters E-CONPRI
on O
the O
stability S-PRO
of O
positional O
deposition S-CONPRI
are O
investigated O
. O


The O
effectiveness S-CONPRI
of O
the O
proposed O
strategy O
is O
verified O
by O
three O
complex O
samples S-CONPRI
using O
a O
positional O
GMAW-WAAM O
process S-CONPRI
. O


Robotic O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
technology S-CONPRI
has O
been O
widely O
employed O
to O
fabricate S-MANP
medium O
to O
large O
scale O
metallic S-MATE
components S-MACEQ
. O


It O
has O
the O
advantages O
of O
high B-PARA
deposition I-PARA
rates E-PARA
and O
low O
cost O
. O


Ideally O
, O
the O
deposition B-MANP
process E-MANP
is O
carried O
out O
in O
a O
flat O
position O
. O


The O
build B-PARA
direction E-PARA
is O
vertically O
upward O
and O
perpendicular O
to O
a O
horizontal O
worktable O
. O


However O
, O
it O
would O
be S-MATE
difficult O
to O
directly O
deposit O
complex O
parts O
with O
near O
horizontal O
‘ O
overhangs S-PARA
’ O
, O
and O
temporary O
supports S-APPL
may O
be S-MATE
required O
. O


Thus O
, O
it O
is O
necessary O
to O
find O
an O
alternative O
approach O
for O
the O
deposition S-CONPRI
of O
‘ O
overhangs S-PARA
’ O
without O
extra O
support S-APPL
in O
order O
to O
simplify O
the O
deposition S-CONPRI
set-up O
. O


This O
paper O
proposed O
a O
fabrication S-MANP
method O
of O
producing O
metallic B-MACEQ
parts E-MACEQ
with O
overhanging B-CONPRI
structures E-CONPRI
using O
the O
multi-directional O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
. O


Firstly O
, O
based O
on O
the O
metal S-MATE
droplet S-CONPRI
kinetics O
and O
weld B-PARA
bead I-PARA
geometry E-PARA
, O
two O
different O
Gas B-MANP
Metal I-MANP
Arc I-MANP
Welding E-MANP
( O
GMAW S-MANP
) O
metal S-MATE
transfer O
modes O
, O
namely O
short O
circuit O
transfer O
and O
free O
flight O
transfer O
, O
were O
evaluated O
for O
the O
multi-directional O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
. O


Subsequently O
, O
the O
effects O
of O
process B-CONPRI
parameters E-CONPRI
, O
including O
wire O
feed S-PARA
speed O
( O
WFS O
) O
, O
torch O
travel O
speed O
( O
TS O
) O
, O
nozzle S-MACEQ
to O
work O
distance O
( O
NTWD O
) O
and O
torch O
angle O
, O
on O
the O
stability S-PRO
of O
positional O
deposition S-CONPRI
were O
investigated O
. O


Finally O
, O
the O
effectiveness S-CONPRI
of O
the O
proposed O
strategy O
was O
verified O
by O
fabricating S-MANP
three O
complex O
samples S-CONPRI
with O
overhangs S-PARA
. O


Wire B-MANP
Arc I-MANP
Additive I-MANP
Manufacturing E-MANP
underwent O
remarkable O
development O
in O
the O
past O
decade O
. O


In O
the O
present O
work O
effect O
of O
welding S-MANP
parameters S-CONPRI
on O
additively O
deposited B-CHAR
layer E-CHAR
width O
is O
investigated O
. O


MIG B-MANP
welding E-MANP
is O
chosen O
for O
the O
present O
study O
and O
Inconel S-MATE
825 O
having O
high O
industrial S-APPL
application O
is O
selected O
as S-MATE
wire O
spool S-MACEQ
. O


This O
paper O
is O
concentrating O
on O
the O
effect O
of O
weld S-FEAT
parameters S-CONPRI
on O
additively O
deposited B-CHAR
layer E-CHAR
width O
using O
the O
Taguchi B-CONPRI
method E-CONPRI
. O


Waviness S-FEAT
, O
weld S-FEAT
cracks O
, O
porosity S-PRO
, O
and O
discontinuity O
of O
weld B-CONPRI
bead E-CONPRI
of O
a O
surface S-CONPRI
can O
be S-MATE
reduced O
by O
selection O
and O
optimising O
the O
parameters S-CONPRI
; O
otherwise O
, O
irregular O
shapes O
will O
come O
during O
the O
manufacturing S-MANP
of O
thin O
or O
thick O
wall O
construction S-APPL
by O
Wire B-MANP
Arc I-MANP
Additive I-MANP
Manufacturing E-MANP
. O


L9 O
Orthogonal O
array O
is O
used O
in O
Taguchi O
for O
the O
experimentation O
to O
analyze O
input O
parameters S-CONPRI
, O
namely O
, O
Welding S-MANP
speed O
, O
Wire O
feed S-PARA
speed O
and O
Voltage O
. O


Best O
parameter S-CONPRI
combination O
and O
significant O
parameters S-CONPRI
are O
obtained O
from O
the O
main O
effect O
plot O
and O
analysis O
of O
variance O
respectively O
. O


A O
mathematical S-CONPRI
model O
on O
the O
response O
variable O
is O
generated O
using O
a O
linear O
regression B-CONPRI
model E-CONPRI
. O


At O
0.55 O
m/min O
welding S-MANP
velocity O
, O
4 O
m/min O
Wire O
feed S-PARA
speed O
and O
18 O
V S-MATE
Voltage O
is O
having O
least O
bead B-CHAR
Width E-CHAR
of O
3.07 O
mm S-MANP
length O
. O


0.25 O
m/min O
welding S-MANP
velocity O
, O
8 O
m/min O
Wire O
feed S-PARA
speed O
and O
28 O
V S-MATE
Voltage O
is O
having O
highest O
bead B-CHAR
Width E-CHAR
of O
15.83 O
mm S-MANP
length O
. O


Confirmation O
tests O
are O
carried O
out O
after O
obtaining O
optimized O
parameters S-CONPRI
and O
results O
are O
correlated S-CONPRI
with O
obtained O
results O
. O


Wire O
based O
Additive B-MANP
Manufacturing E-MANP
provides O
an O
attractive O
option O
to O
powder-based O
processes S-CONPRI
due O
to O
their O
high B-PARA
deposition I-PARA
rates E-PARA
. O


In O
the O
present O
work O
effect O
of O
welding S-MANP
parameters S-CONPRI
on O
pre-positioned O
wire O
Electron B-CONPRI
Beam E-CONPRI
additively O
deposited B-CHAR
layer E-CHAR
width O
is O
investigated O
. O


Electron B-MANP
Beam I-MANP
welding E-MANP
is O
chosen O
for O
the O
present O
study O
and O
Ti6Al4V S-MATE
having O
high O
aerospace S-APPL
application O
is O
selected O
as S-MATE
filler O
wire O
. O


This O
paper O
concentrates O
on O
the O
effect O
of O
weld S-FEAT
parameters S-CONPRI
on O
additively O
deposited B-CHAR
layer E-CHAR
width O
using O
the O
Taguchi B-CONPRI
method E-CONPRI
. O


Unacceptable O
weld S-FEAT
cracks O
, O
porosity S-PRO
, O
and O
discontinuity O
of O
weld B-CONPRI
bead E-CONPRI
of O
a O
surface S-CONPRI
can O
be S-MATE
reduced O
by O
selection O
and O
optimizing O
the O
parameters S-CONPRI
; O
otherwise O
, O
irregular O
shapes O
will O
come O
during O
the O
manufacturing S-MANP
of O
thin O
or O
thick O
wall O
construction S-APPL
by O
Wire O
Electron B-MANP
Beam I-MANP
Additive I-MANP
Manufacturing E-MANP
. O


L9 O
Orthogonal O
array O
is O
used O
in O
Taguchi O
for O
the O
experimentation O
to O
analyze O
input O
parameters S-CONPRI
, O
namely O
, O
Welding S-MANP
speed O
, O
Accelerating O
voltage O
and O
Beam S-MACEQ
current O
. O


Best O
parameter S-CONPRI
combination O
and O
significant O
parameters S-CONPRI
are O
obtained O
from O
the O
main O
effect O
plot O
and O
analysis O
of O
variance O
respectively O
. O


A O
mathematical S-CONPRI
model O
on O
the O
response O
variable O
is O
generated O
using O
a O
linear O
regression B-CONPRI
model E-CONPRI
. O


At O
700 O
mm/min O
welding S-MANP
speed O
, O
138 O
kV O
accelerating O
voltage O
and O
05 O
mA O
beam S-MACEQ
current O
is O
having O
least O
bead B-CHAR
Width E-CHAR
of O
2.30222 O
mm S-MANP
length O
. O


500 O
mm/min O
welding S-MANP
speed O
, O
142 O
kV O
accelerating O
voltage O
and O
09 O
mA O
beam S-MACEQ
current O
is O
having O
highest O
bead B-CHAR
Width E-CHAR
of O
4.09 O
mm S-MANP
length O
. O


Confirmation O
tests O
are O
carried O
out O
after O
obtaining O
optimized O
parameters S-CONPRI
and O
results O
are O
correlated S-CONPRI
with O
obtained O
results O
. O


Comparison O
between O
laser B-MANP
welding E-MANP
and O
laser-based B-MANP
additive I-MANP
manufacturing E-MANP
parameters O
is O
established O
. O


Major O
process B-CONPRI
parameters E-CONPRI
during O
laser-based B-MANP
additive I-MANP
manufacturing E-MANP
and O
their O
influence O
are O
discussed O
. O


Remedies O
for O
avoid O
several O
problems O
found O
during O
additive B-MANP
manufacturing E-MANP
are O
proposed O
. O


As S-MATE
metallic O
additive B-MANP
manufacturing E-MANP
grew O
in O
sophistication O
, O
users O
have O
requested O
greater O
control O
over O
the O
systems O
, O
namely O
the O
ability O
to O
fully O
change O
the O
process B-CONPRI
parameters E-CONPRI
. O


The O
goal O
of O
this O
manuscript S-CONPRI
is O
to O
review O
the O
effects O
of O
major O
process B-CONPRI
parameters E-CONPRI
on O
build S-PARA
quality O
( O
porosity S-PRO
, O
residual B-PRO
stress E-PRO
, O
and O
composition S-CONPRI
changes O
) O
and O
materials S-CONPRI
properties O
( O
microstructure S-CONPRI
and O
microsegregation S-CONPRI
) O
, O
and O
to O
serve O
as S-MATE
a O
guide O
on O
how O
these O
parameters S-CONPRI
may O
be S-MATE
modified O
to O
achieve O
specific O
design S-FEAT
goals O
for O
a O
given O
part O
. O


The O
focus O
of O
this O
paper O
is O
on O
laser B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
, O
but O
elements S-MATE
can O
be S-MATE
applied O
to O
electron B-CONPRI
beam E-CONPRI
powder O
bed B-MANP
fusion E-MANP
or O
direct B-MANP
energy I-MANP
deposition E-MANP
techniques O
. O


Stellite-6 O
FSW S-MANP
tools O
were O
developed O
on O
H13 B-MATE
steel E-MATE
by O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
. O


Tool S-MACEQ
performance S-CONPRI
was O
evaluated O
in O
friction S-CONPRI
stir O
welding/ O
processing O
of O
CuCrZr O
. O


No O
tool B-CONPRI
wear E-CONPRI
or O
plastic B-PRO
deformation E-PRO
was O
observed O
on O
Stellite-6 O
tool S-MACEQ
. O


This O
performed O
better O
than O
H13 S-MATE
as-received O
, O
heat S-CONPRI
treated O
and O
laser S-ENAT
remelted O
tools S-MACEQ
. O


Tool B-CONPRI
wear E-CONPRI
and O
failure B-PRO
mechanism E-PRO
investigated O
in O
conventional O
and O
AM S-MANP
tools O
. O


In O
the O
recent O
time O
friction B-MANP
stir I-MANP
welding E-MANP
( O
FSW S-MANP
) O
, O
a O
solid B-MANP
state I-MANP
welding E-MANP
process S-CONPRI
has O
rapidly O
gained O
attention O
for O
joining S-MANP
high O
melting B-PRO
point E-PRO
materials S-CONPRI
like O
Cu S-MATE
, O
Fe S-MATE
, O
Ti S-MATE
and O
their O
alloys S-MATE
apart O
from O
Al B-MATE
alloys E-MATE
due O
to O
its O
several O
advantages O
over O
fusion B-MANP
welding E-MANP
techniques O
. O


AISI O
H13 S-MATE
, O
a O
versatile O
chromium–molybdenum O
hot O
work O
hardened S-MANP
steel O
, O
has O
been O
the O
most O
commonly O
used O
as S-MATE
a O
tool S-MACEQ
material S-MATE
for O
aluminium B-MATE
alloys E-MATE
. O


However O
, O
low O
tool B-CONPRI
life E-CONPRI
due O
to O
plastic B-PRO
deformation E-PRO
and O
wear S-CONPRI
at O
elevated O
temperatures S-PARA
is O
limiting O
its O
application O
in O
welding S-MANP
of O
high O
melting B-PRO
point E-PRO
materials S-CONPRI
. O


In O
the O
present O
work O
the O
performances O
of O
as-received O
, O
heat S-CONPRI
treated O
, O
laser S-ENAT
remelted O
and O
Stellite S-MATE
6 O
hardfaced O
H13 B-MATE
steel E-MATE
tools O
in O
friction S-CONPRI
stir O
processing O
( O
FSP O
) O
of O
CuCrZr O
have O
been O
investigated O
. O


Stellite S-MATE
6 O
hardfaced O
FSW S-MANP
tools O
are O
developed O
by O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
process S-CONPRI
on O
H13 B-MATE
steel E-MATE
as S-MATE
a O
base O
material S-MATE
. O


In O
all O
these O
cases O
except O
the O
Stellite S-MATE
6 O
hardfaced O
tool S-MACEQ
, O
the O
shoulder O
and O
pin O
are O
found O
to O
deform O
plastically O
with O
significant O
wear S-CONPRI
of O
shoulder O
along O
with O
the O
diffusion S-CONPRI
of O
CuCrZr O
into O
tool S-MACEQ
from O
tool S-MACEQ
pin-shoulder O
interface S-CONPRI
. O


However O
, O
tools S-MACEQ
developed O
by O
AM B-MANP
process E-MANP
are O
found O
to O
remain O
intact O
without O
any O
significant O
deformation S-CONPRI
or O
wear S-CONPRI
. O


GMAW S-MANP
( O
Gas B-MANP
Metal I-MANP
Arc I-MANP
Welding E-MANP
) O
of O
titanium S-MATE
is O
not O
currently O
used O
in O
industry S-APPL
due O
to O
the O
high O
levels O
of O
spatter S-CHAR
generation O
, O
the O
wandering O
of O
the O
welding S-MANP
arc S-CONPRI
and O
the O
consequent O
waviness S-FEAT
of O
the O
weld B-CONPRI
bead E-CONPRI
. O


This O
paper O
reports O
on O
the O
use O
of O
laser B-MANP
welding E-MANP
in O
conduction O
mode O
to O
stabilize O
the O
CMT S-MANP
( O
Cold B-MANP
Metal I-MANP
Transfer E-MANP
) O
, O
a O
low O
heat S-CONPRI
input O
GMAW S-MANP
process O
. O


The O
stabilization S-CONPRI
and O
reshaping O
of O
Ti-6Al-4 B-MATE
V E-MATE
weld O
beads S-CHAR
was O
verified O
for O
laser S-ENAT
hybrid O
GMAW S-MANP
bead S-CHAR
on O
plate O
deposition S-CONPRI
. O


The O
laser B-CONPRI
beam E-CONPRI
was O
defocused O
, O
used O
in O
conduction O
mode O
, O
and O
was O
positioned O
concentric O
with O
the O
welding S-MANP
wire O
and O
the O
welding S-MANP
arc S-CONPRI
( O
CMT S-MANP
) O
.Finally O
, O
the O
results O
obtained O
for O
bead-on-plate O
welding S-MANP
were O
applied O
to O
an O
additively B-MANP
manufactured E-MANP
structure O
, O
in O
which O
a O
laser-hybrid O
stabilized O
sample S-CONPRI
was O
built O
and O
then O
evaluated O
against O
CMT-only O
sample S-CONPRI
. O


This O
work O
reveals O
that O
laser S-ENAT
can O
be S-MATE
used O
to O
stabilize O
the O
welding S-MANP
process S-CONPRI
, O
improve O
the O
weld-bead S-FEAT
shape O
of O
single O
and O
multiple O
layer S-PARA
depositions O
and O
increase O
the O
deposition B-PARA
rate E-PARA
of O
additive B-MANP
manufacture E-MANP
of O
Ti-6Al-4 B-MATE
V E-MATE
from1.7 O
kg/h O
to O
2.0 O
kg/h O
. O


Additive B-MANP
Manufacturing E-MANP
is O
an O
established O
process S-CONPRI
group O
that O
includes O
various O
technologies S-CONPRI
. O


In O
contrast O
to O
subtractive S-MANP
methods O
, O
complex O
components S-MACEQ
can O
be S-MATE
produced O
by O
applying O
layers O
of O
construction S-APPL
materials O
. O


In O
accordance O
with O
the O
standard S-CONPRI
VDI O
Guideline O
3405 O
, O
additive B-MANP
manufacturing E-MANP
technologies O
can O
be S-MATE
differentiated O
into O
wire- O
and O
powder-based O
technologies S-CONPRI
. O


The O
basis O
for O
these O
experimental S-CONPRI
investigations O
is O
a O
Wire B-MANP
Arc I-MANP
Additive I-MANP
Manufacturing E-MANP
( O
WAAM S-MANP
) O
process S-CONPRI
with O
a O
high O
build-up O
rate O
( O
Cold B-MANP
Metal I-MANP
Transfer E-MANP
- O
CMT S-MANP
) O
to O
produce O
a O
rectangular O
thin-walled B-APPL
component E-APPL
made O
of O
G4Si1 O
( O
1.5130 O
) O
. O


In O
order O
to O
analyze O
the O
influence O
of O
a O
subsequent O
forming B-MANP
process E-MANP
on O
the O
microstructural S-CONPRI
properties O
and O
the O
forming S-MANP
behavior O
of O
the O
components S-MACEQ
, O
compression B-CHAR
tests E-CHAR
were O
carried O
out O
. O


Therefore O
, O
cylindrical S-CONPRI
specimens O
were O
made O
out O
of O
the O
additively B-MANP
manufactured E-MANP
components O
by O
machining S-MANP
. O


To O
be S-MATE
able O
to O
take O
a O
possible O
anisotropy S-PRO
in O
the O
workpiece S-CONPRI
caused O
by O
the O
multi-layer O
welding S-MANP
into O
account O
, O
the O
samples S-CONPRI
were O
taken O
both O
along O
and O
across O
the O
welding S-MANP
direction O
. O


To O
evaluate O
the O
inhomogeneous O
component S-MACEQ
properties O
, O
cast S-MANP
specimens O
with O
a O
representative O
microstructure S-CONPRI
were O
produced O
by O
inductive O
melting S-MANP
of O
the O
filler O
material S-MATE
and O
subsequent O
a O
solidification S-CONPRI
with O
an O
appropriate O
cooling B-PARA
rate E-PARA
. O


In O
addition O
to O
the O
cold B-MANP
forming E-MANP
of O
the O
additively B-MANP
manufactured E-MANP
components O
, O
the O
investigation O
also O
includes O
hot B-MANP
forming E-MANP
and O
the O
influence O
of O
a O
corresponding O
heat B-MANP
treatment E-MANP
. O


The O
experimental S-CONPRI
examination O
was O
completed O
by O
the O
analysis O
of O
the O
microstructure S-CONPRI
of O
each O
material S-MATE
state.The O
aim O
of O
the O
research S-CONPRI
work O
was O
to O
prove O
the O
homogenization S-MANP
and O
optimization S-CONPRI
of O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
additive B-MANP
manufactured E-MANP
components O
due O
to O
a O
subsequent O
forming B-MANP
process E-MANP
. O


Highlight O
An O
experimental S-CONPRI
work O
to O
investigate O
the O
formation O
of O
the O
humping O
phenomena O
in O
the O
positional O
deposition S-CONPRI
using O
WAAM S-MANP
. O


Mechanism S-CONPRI
of O
humping O
formation O
is O
analysed O
to O
explain O
humping O
occurrence O
for O
positional O
deposition S-CONPRI
. O


The O
impacts O
of O
welding S-MANP
parameters S-CONPRI
and O
positions O
on O
humping O
formation O
are O
investigated O
through O
a O
series O
of O
tests O
. O


A O
series O
of O
guidelines O
are O
summarised O
to O
assist O
the O
path B-ENAT
planning E-ENAT
and O
process B-CONPRI
parameter E-CONPRI
selection O
processes S-CONPRI
in O
multi-directional O
WAAM S-MANP
. O


Wire B-MANP
Arc I-MANP
Additive I-MANP
Manufacturing E-MANP
( O
WAAM S-MANP
) O
is O
a O
promising O
technology S-CONPRI
for O
fabricating S-MANP
medium O
to O
large O
scale O
metallic B-MACEQ
parts E-MACEQ
with O
excellent O
productivity S-CONPRI
and O
flexibility S-PRO
. O


Due O
to O
the O
positional O
capability O
of O
some O
welding S-MANP
processes S-CONPRI
, O
WAAM S-MANP
is O
able O
to O
deposit O
parts O
with O
overhanging B-FEAT
features E-FEAT
in O
an O
arbitrary O
direction O
without O
additional O
support B-FEAT
structures E-FEAT
. O


There O
has O
been O
significant O
research S-CONPRI
on O
the O
humping O
phenomenon O
in O
the O
downhand O
welding S-MANP
, O
but O
it O
is O
doubtful O
whether O
the O
existing O
theories O
of O
humping O
formation O
can O
be S-MATE
applied O
in O
the O
positional O
deposition S-CONPRI
during O
WAAM S-MANP
process S-CONPRI
. O


This O
study O
has O
therefore O
provided O
an O
experimental S-CONPRI
work O
to O
investigate O
the O
formation O
of O
the O
humping O
phenomena O
in O
the O
positional O
deposition S-CONPRI
during O
additive B-MANP
manufacturing E-MANP
with O
the O
gas B-MANP
metal I-MANP
arc I-MANP
welding E-MANP
. O


Firstly O
, O
the O
mechanism S-CONPRI
of O
humping O
formation O
was O
analysed O
to O
explain O
humping O
occurrence O
for O
positional O
deposition S-CONPRI
. O


Then O
, O
the O
mechanism S-CONPRI
was O
validated O
through O
experiments O
with O
different O
welding S-MANP
parameters S-CONPRI
and O
positions O
. O


Finally O
, O
a O
series O
of O
guidelines O
are O
summarised O
to O
assist O
the O
path B-ENAT
planning E-ENAT
and O
process B-CONPRI
parameter E-CONPRI
selection O
processes S-CONPRI
in O
multi-directional O
WAAM S-MANP
. O


Automated O
weld S-FEAT
deposition S-CONPRI
coupled O
with O
the O
real-time O
robotic O
NDT S-CONPRI
is O
discussed O
. O


An O
intentionally O
embedded O
defect S-CONPRI
, O
a O
tungsten S-MATE
rod S-MACEQ
, O
is O
introduced O
for O
verification S-CONPRI
. O


A O
partially-filled O
groove O
sample S-CONPRI
is O
also O
manufactured S-CONPRI
and O
ultrasonically O
tested O
. O


For O
performance S-CONPRI
verification O
of O
the O
in-process O
inspection S-CHAR
system O
, O
an O
intentionally O
embedded O
defect S-CONPRI
, O
a O
tungsten S-MATE
rod S-MACEQ
, O
is O
introduced O
into O
the O
multi-pass O
weld S-FEAT
. O


A O
partially-filled O
groove O
( O
staircase O
) O
sample S-CONPRI
is O
also O
manufactured S-CONPRI
and O
ultrasonically O
tested O
to O
calibrate O
the O
real-time O
inspection S-CHAR
implemented O
on O
all O
seven O
layers O
of O
the O
weld S-FEAT
which O
are O
deposited O
progressively O
. O


The O
tungsten S-MATE
rod S-MACEQ
is O
successfully O
detected O
in O
the O
real-time O
NDE O
of O
the O
deposited O
position O
. O


Non-weldable O
Ni-based O
superalloy O
Alloy713ELC O
could O
be S-MATE
fabricated O
by O
electron B-MANP
beam I-MANP
melting E-MANP
. O


Process S-CONPRI
condition O
could O
be S-MATE
efficiently O
optimized O
by O
using O
support S-APPL
vector O
machine S-MACEQ
. O


Additive B-MANP
manufactured E-MANP
Alloy713ELC O
showed O
columnar B-PRO
grain E-PRO
along O
building B-PARA
direction E-PARA
. O


Additive B-MANP
manufactured E-MANP
Alloy713ELC O
showed O
good O
ductility S-PRO
along O
building B-PARA
direction E-PARA
. O


Additive B-MANP
manufactured E-MANP
Alloy713ELC O
showed O
good O
creep S-PRO
properties O
along O
building B-PARA
direction E-PARA
. O


An O
efficient O
optimization S-CONPRI
method O
based O
on O
a O
support S-APPL
vector O
machine S-MACEQ
( O
SVM O
) O
is O
used O
to O
optimize O
multiple O
process B-CONPRI
parameters E-CONPRI
of O
selective B-MANP
electron I-MANP
beam I-MANP
melting E-MANP
( O
SEBM S-MANP
) O
for O
a O
non-weldable O
nickel-base B-MATE
superalloy E-MATE
Alloy713ELC O
. O


The O
global O
optimum O
condition O
and O
the O
near O
optimum O
conditions O
are O
extracted S-CONPRI
to O
fabricate S-MANP
SEBM O
samples S-CONPRI
. O


All O
the O
SVM O
optimized O
conditions O
lead S-MATE
to O
near O
net O
shaped O
samples S-CONPRI
with O
even O
top O
surfaces S-CONPRI
. O


The O
sample S-CONPRI
fabricated S-CONPRI
under O
the O
global O
optimum O
condition O
for O
sample S-CONPRI
dimension S-FEAT
of O
10 O
mm S-MANP
exhibits O
pore-less O
cross-sections S-CONPRI
, O
columnar B-PRO
grains E-PRO
with O
fine O
γ′ O
precipitates S-MATE
and O
fine O
substructure O
, O
a O
small O
amount O
of O
grain B-PRO
boundary I-PRO
crack E-PRO
and O
excellent O
room O
temperature S-PARA
tensile O
properties S-CONPRI
. O


The O
samples B-CONPRI
fabricated E-CONPRI
under O
the O
global O
optimum O
condition O
and O
a O
near O
optimum O
condition O
with O
increased O
beam S-MACEQ
current O
for O
sample S-CONPRI
dimension S-FEAT
of O
15 O
mm S-MANP
exhibit O
excellent O
creep S-PRO
properties O
under O
980 O
°C O
. O


In O
both O
the O
two O
situations O
for O
sample S-CONPRI
dimensions S-FEAT
of O
10 O
mm S-MANP
and O
15 O
mm S-MANP
, O
SEBM S-MANP
samples S-CONPRI
with O
mechanical B-CONPRI
properties E-CONPRI
superior O
to O
conventional O
cast S-MANP
alloys S-MATE
can O
be S-MATE
achieved O
by O
testing S-CHAR
only O
1–3 O
SVM O
optimized O
conditions O
. O


We O
demonstrate O
the O
current O
method O
is O
effective O
for O
optimizing O
SEBM S-MANP
process S-CONPRI
, O
especially O
when O
multiple O
parameters S-CONPRI
need O
to O
be S-MATE
considered O
simultaneously O
. O


Besides O
, O
this O
method O
can O
rapidly O
provide O
not O
only O
a O
batch O
of O
conditions O
leading O
to O
samples S-CONPRI
with O
good O
top O
surfaces S-CONPRI
but O
also O
the O
optimum O
conditions O
leading O
to O
good O
building O
quality S-CONPRI
and O
superior O
mechanical B-CONPRI
properties E-CONPRI
. O


In O
gas B-MANP
tungsten I-MANP
arc I-MANP
welding E-MANP
( O
GTAW S-MANP
) O
based O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
, O
omni-directional O
deposition S-CONPRI
with O
side O
feeding O
is O
common O
when O
depositing O
complex O
parts O
, O
which O
is O
different O
from O
the O
gas B-MANP
metal I-MANP
arc I-MANP
welding E-MANP
( O
GMAW S-MANP
) O
. O


While O
side O
feeding O
may O
lead S-MATE
to O
unstable O
deposition B-MANP
process E-MANP
and O
deposition S-CONPRI
deviation O
. O


In O
this O
paper O
, O
a O
wire O
melting S-MANP
simulation O
model S-CONPRI
was O
established O
to O
analyse O
the O
behaviour O
of O
the O
wire O
in O
the O
arc S-CONPRI
column O
. O


An O
index O
of O
weld B-PARA
bead I-PARA
offset E-PARA
tolerance B-PARA
capacity E-PARA
is O
proposed O
to O
quantitatively S-CONPRI
analyse O
the O
sensitivity S-PARA
of O
the O
weld B-PARA
bead I-PARA
offset E-PARA
to O
the O
wire O
feed S-PARA
speed O
. O


Single-layer O
experiments O
were O
conducted O
to O
analyse O
the O
relationships O
between O
the O
deposition S-CONPRI
parameters O
and O
the O
weld S-FEAT
melting/bead O
offset S-CONPRI
. O


A O
multi-layer O
sample S-CONPRI
with O
an O
actual O
usable O
area S-PARA
ratio O
of O
95.11 O
% O
was O
deposited O
by O
using O
the O
proposed O
model S-CONPRI
and O
the O
optimized O
deposition S-CONPRI
parameters O
. O


The O
experimental S-CONPRI
results O
show O
that O
the O
control O
of O
the O
weld S-FEAT
melting S-MANP
offset O
is O
the O
key O
factor O
in O
realizing O
the O
stability S-PRO
and O
accuracy S-CHAR
of O
omni-directional O
GTAW-based O
AM S-MANP
. O


Advancement O
in O
manufacturing B-MANP
technology E-MANP
, O
prototyping S-CONPRI
, O
machining S-MANP
etc O
. O


are O
concerned O
with O
material S-MATE
optimization O
, O
process B-CONPRI
optimization E-CONPRI
, O
financial O
optimization S-CONPRI
and O
sustainable S-CONPRI
development O
. O


The O
current O
review O
on O
characterization O
, O
applications O
and O
process S-CONPRI
study O
of O
various O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
deals O
with O
the O
systematic O
use O
of O
resources O
in O
product B-CONPRI
development E-CONPRI
. O


The O
comprehensive O
description O
on O
additive B-MANP
manufacturing E-MANP
techniques O
, O
its O
applications O
and O
needs O
are O
illustrated O
. O


The O
attempt O
is O
to O
diagnose O
the O
research S-CONPRI
gap O
in O
the O
process S-CONPRI
study O
and O
to O
forecast O
the O
new O
methodology S-CONPRI
and O
applications O
in O
the O
all O
the O
field O
like O
automobile S-APPL
, O
aerospace S-APPL
, O
biomedical S-APPL
etc O
. O


through O
AM S-MANP
. O


The O
tool S-MACEQ
making O
for O
friction B-MANP
stir I-MANP
welding E-MANP
purpose O
, O
complex B-CONPRI
geometries E-CONPRI
, O
etc O
. O


were O
fabricated S-CONPRI
without O
increasing O
the O
overall O
cost O
through O
AM B-MANP
techniques E-MANP
. O


The O
applications O
of O
AM B-MANP
techniques E-MANP
in O
composite S-MATE
based O
materials S-CONPRI
are O
also O
characterized O
. O


The O
comparative O
analysis O
between O
subtractive S-MANP
and O
additive B-MANP
manufacturing E-MANP
are O
highlighted O
and O
future O
scope O
is O
tried O
to O
identify O
. O


Internal O
defects S-CONPRI
in O
additive B-MANP
manufactured E-MANP
Mo O
are O
analyzed O
. O


3D S-CONPRI
Computed O
Tomography O
is O
used O
to O
analyze O
the O
3D S-CONPRI
information O
. O


Volume S-CONPRI
and O
sphericity O
distribution S-CONPRI
of O
defects S-CONPRI
are O
studied O
. O


Formation O
mechanisms O
of O
different O
internal O
defects S-CONPRI
are O
proposed O
. O


Relationship O
between O
defects S-CONPRI
and O
process B-CONPRI
parameters E-CONPRI
is O
disclosed O
. O


Molybdenum S-MATE
( O
Mo S-MATE
) O
is O
an O
important O
high-temperature O
structural O
material S-MATE
but O
has O
poor O
processability O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
leads O
to O
a O
new O
possibility O
of O
fabricating S-MANP
Mo O
structural O
parts O
. O


However O
, O
a O
large O
number O
of O
internal O
defects S-CONPRI
appear O
during O
welding S-MANP
and O
AM B-MANP
processes E-MANP
in O
Mo S-MATE
and O
its O
alloys S-MATE
, O
which O
is O
far O
from O
well O
understood O
and O
has O
greatly O
limited O
their O
application O
. O


In O
this O
paper O
, O
the O
formation O
and O
evolution S-CONPRI
mechanisms O
of O
internal O
defects S-CONPRI
in O
Mo S-MATE
are O
systematically O
studied O
, O
based O
on O
the O
state-of-the-art S-CONPRI
high-resolution S-PARA
computed B-CHAR
tomography E-CHAR
. O


This O
study O
demonstrates O
three O
main O
types O
of O
defects S-CONPRI
in O
Mo S-MATE
: O
( O
1 O
) O
small O
spherical S-CONPRI
pores S-PRO
; O
( O
2 O
) O
inverted O
pear-shaped O
pores S-PRO
; O
and O
( O
3 O
) O
cavities O
. O


The O
first O
type O
is O
similar O
to O
the O
observation O
in O
welded S-MANP
Mo S-MATE
, O
while O
the O
last O
two O
types O
are O
not O
reported O
before O
, O
which O
are O
associated O
with O
the O
heat S-CONPRI
cycling O
process S-CONPRI
during O
AM S-MANP
. O


The O
formation O
mechanism S-CONPRI
of O
different O
types O
of O
internal O
defects S-CONPRI
is O
proposed O
based O
on O
the O
experimental S-CONPRI
observations O
. O


Material B-MANP
extrusion E-MANP
( O
MatEx O
) O
additive B-MANP
manufacturing E-MANP
ranges O
in O
size O
from O
the O
desktop O
scale O
fused B-MANP
filament I-MANP
fabrication E-MANP
( O
FFF S-MANP
) O
to O
the O
room O
scale O
big O
area S-PARA
additive B-MANP
manufacturing E-MANP
( O
BAAM O
) O
. O


The O
principles O
of O
how O
FFF S-MANP
and O
BAAM O
operate O
are O
similar O
– O
polymer B-MATE
feedstocks E-MATE
are O
heated O
until O
molten O
and O
then O
extruded S-MANP
to O
form O
three-dimensional S-CONPRI
parts O
through O
layer-by-layer S-CONPRI
additive B-MANP
manufacturing E-MANP
. O


This O
study O
compares O
heat B-CONPRI
transfer E-CONPRI
in O
FFF S-MANP
and O
BAAM O
using O
finite B-CONPRI
element E-CONPRI
thermal O
modeling S-ENAT
. O


Parameterization O
is O
performed O
across O
material B-CONPRI
properties E-CONPRI
, O
layer S-PARA
number O
, O
and O
print S-MANP
speed O
at O
the O
desktop O
and O
room O
scale O
for O
MatEx O
. O


BAAM O
stays O
hotter O
than O
FFF S-MANP
for O
a O
longer O
period O
of O
time O
, O
which O
facilitates O
interlayer O
diffusion S-CONPRI
and O
weld S-FEAT
formation O
, O
but O
can O
also O
lead S-MATE
to O
slumping O
or O
sagging O
. O


Changes O
in O
thermal B-CONPRI
diffusivity E-CONPRI
affect O
FFF S-MANP
more O
than O
BAAM O
, O
with O
FFF S-MANP
exhibiting O
a O
local O
maximum O
in O
weld S-FEAT
time O
at O
the O
thermal B-CONPRI
diffusivity E-CONPRI
of O
ABS S-MATE
. O


For O
BAAM O
, O
the O
temperature S-PARA
and O
thermal O
history O
of O
the O
center O
of O
an O
extruded S-MANP
bead S-CHAR
differs O
greatly O
from O
the O
surface S-CONPRI
of O
the O
bead S-CHAR
, O
which O
has O
important O
implications O
for O
process B-CONPRI
monitoring E-CONPRI
, O
property S-CONPRI
prediction S-CONPRI
, O
and O
part O
performance S-CONPRI
. O


Wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
, O
WAAM S-MANP
, O
is O
a O
popular O
wire-feed O
additive B-MANP
manufacturing E-MANP
technology O
that O
creates O
components S-MACEQ
through O
the O
deposition S-CONPRI
of O
material S-MATE
layer-by-layer S-CONPRI
. O


WAAM S-MANP
has O
become O
a O
promising O
alternative O
to O
conventional B-MANP
machining E-MANP
due O
to O
its O
high B-PARA
deposition I-PARA
rate E-PARA
, O
environmental O
friendliness O
and O
cost O
competitiveness O
. O


In O
this O
research S-CONPRI
work O
, O
a O
comparison O
is O
made O
between O
two O
different O
WAAM S-MANP
technologies S-CONPRI
, O
GMAW S-MANP
( O
gas B-MANP
metal I-MANP
arc I-MANP
welding E-MANP
) O
and O
PAW S-MANP
( O
plasma B-MANP
arc I-MANP
welding E-MANP
) O
. O


Comparative O
between O
processes S-CONPRI
is O
centered O
in O
the O
main O
variations S-CONPRI
while O
manufacturing S-MANP
Mn4Ni2CrMo O
steel S-MATE
walls O
concerning O
geometry S-CONPRI
and O
process B-CONPRI
parameters E-CONPRI
maintaining O
the O
same O
deposition S-CONPRI
ratio O
as S-MATE
well O
as S-MATE
the O
mechanical S-APPL
and O
metallographic O
properties S-CONPRI
obtained O
in O
the O
walls O
with O
both O
processes S-CONPRI
, O
in O
which O
the O
applied O
energy O
is O
significantly O
different O
. O


This O
study O
shows O
that O
acceptable O
mechanical S-APPL
characteristics O
are O
obtained O
in O
both O
processes S-CONPRI
compared O
to O
the O
corresponding O
forging S-MANP
standard O
for O
the O
tested O
material S-MATE
, O
values O
are O
23 O
% O
higher O
for O
UTS S-PRO
and O
56 O
% O
for O
elongation S-PRO
in O
vertical S-CONPRI
direction O
in O
the O
PAW S-MANP
process O
compared O
to O
GMAW S-MANP
( O
no O
differences O
in O
UTS S-PRO
and O
elongation S-PRO
results O
for O
horizontal O
direction O
and O
in O
Charpy O
for O
both O
directions O
) O
and O
without O
significant O
directional O
effects O
of O
the O
additive B-MANP
manufacturing E-MANP
technology O
used O
. O


Based O
on O
cold B-MANP
metal I-MANP
transfer E-MANP
welding O
, O
wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
is O
used O
to O
manufacture S-CONPRI
9Cr O
ferritic/martensitic O
nuclear O
grade O
steel S-MATE
component S-MACEQ
for O
the O
first O
time O
. O


The O
microstructure S-CONPRI
mainly O
consists O
of O
untempered O
martensite S-MATE
laths O
showing O
columnar O
laths O
and O
equiaxed O
laths O
. O


Positions O
at O
different O
heights O
along O
the O
deposition B-PARA
direction E-PARA
have O
no O
significant O
influence O
on O
micro O
hardness S-PRO
and O
tensile B-PRO
properties E-PRO
. O


Tensile B-PRO
properties E-PRO
in O
the O
horizontal O
and O
vertical S-CONPRI
directions O
show O
anisotropy S-PRO
. O


Fracture S-CONPRI
surfaces O
mainly O
exhibit O
typical O
mixed O
mode O
fracture S-CONPRI
. O


Wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
technology S-CONPRI
was O
successfully O
applied O
to O
manufacture S-CONPRI
the O
9Cr O
ferritic/martensitic O
nuclear O
grade O
steel S-MATE
for O
the O
first O
time O
. O


With O
the O
purpose O
of O
revealing O
how O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
are O
affected O
by O
the O
different O
locations O
within O
the O
manufactured S-CONPRI
wall O
, O
cold B-MANP
metal I-MANP
transfer E-MANP
( O
CMT S-MANP
) O
welding S-MANP
was O
used O
as S-MATE
heat O
source S-APPL
, O
the O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
additively B-MANP
manufactured E-MANP
9Cr O
ferritic/martensitic O
wall O
in O
the O
different O
locations O
have O
been O
investigated O
. O


The O
results O
show O
that O
the O
differences O
in O
the O
mechanical B-CONPRI
properties E-CONPRI
were O
related O
to O
the O
anisotropy S-PRO
in O
microstructure S-CONPRI
. O


The O
microstructure S-CONPRI
mainly O
consisted O
of O
untempered O
martensite S-MATE
laths O
showing O
columnar O
laths O
and O
equiaxed O
laths O
. O


As S-MATE
the O
height O
of O
the O
deposited O
wall O
increased O
, O
the O
microstructures S-MATE
exhibited O
differences O
. O


Positions O
at O
different O
heights O
had O
no O
significant O
influence O
on O
micro O
hardness S-PRO
and O
room-temperature O
tensile B-CHAR
testing E-CHAR
results O
. O


However O
, O
the O
tensile B-PRO
properties E-PRO
including O
the O
ultimate B-PRO
tensile I-PRO
strength E-PRO
, O
0.2 O
% O
offset S-CONPRI
yield O
strength S-PRO
and O
elongation S-PRO
exhibited O
anisotropy S-PRO
for O
the O
perpendicular O
to O
and O
parallel O
to O
the O
deposition B-PARA
direction E-PARA
. O


The O
defects S-CONPRI
and O
tensile S-PRO
fracture S-CONPRI
behavior O
were O
also O
analyzed O
carefully O
. O


The O
findings O
suggest O
that O
, O
despite O
the O
emergency O
of O
a O
few O
shortcomings O
, O
the O
WAAM S-MANP
technology S-CONPRI
is O
a O
feasible O
method O
to O
obtain O
9Cr O
ferritic/martensitic O
nuclear O
grade O
steel S-MATE
parts O
. O


Wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
is O
a O
metal B-MANP
additive I-MANP
manufacturing E-MANP
process O
based O
on O
gas B-MANP
metal I-MANP
arc I-MANP
welding E-MANP
and O
it O
is O
known O
to O
be S-MATE
economically O
convenient O
for O
large O
metal S-MATE
parts O
with O
low O
complexity S-CONPRI
. O


The O
main O
issue O
WAAM S-MANP
is O
the O
sensibility O
to O
heat B-PRO
accumulation E-PRO
, O
i.e. O
, O
a O
progressive O
increase O
in O
the O
internal O
energy O
of O
the O
workpiece S-CONPRI
due O
to O
the O
high O
heat S-CONPRI
input O
of O
the O
deposition B-MANP
process E-MANP
, O
that O
is O
responsible O
of O
excessive O
remelting O
of O
the O
lower O
layers O
and O
the O
related O
change O
in O
bead B-CHAR
geometry E-CHAR
. O


A O
promising O
technique O
to O
mitigate O
such O
issue O
is O
to O
use O
an O
air O
jet O
impinging O
on O
the O
deposited O
material S-MATE
to O
increase O
the O
rate O
of O
convective O
heat B-CONPRI
transfer E-CONPRI
. O


Different O
samples S-CONPRI
are O
manufactured S-CONPRI
using O
AWS O
ER70S-6 S-MATE
as S-MATE
filler O
material S-MATE
, O
using O
as S-MATE
cooling O
approaches O
free O
convection O
and O
air O
jet O
impingement O
, O
with O
different O
interlayer O
idle O
times O
. O


The O
measurement S-CHAR
of O
substrate S-MATE
temperatures O
has O
been O
used O
to O
validate O
the O
process B-ENAT
simulation E-ENAT
, O
used O
for O
obtaining O
the O
temperature S-PARA
field O
of O
the O
whole O
part O
. O


The O
results O
indicate O
that O
air O
jet O
impingement O
has O
a O
significant O
impact S-CONPRI
on O
the O
process S-CONPRI
, O
limiting O
the O
progressive O
increase O
in O
the O
interlayer O
temperature S-PARA
as S-MATE
compared O
to O
free O
convection O
cooling S-MANP
. O


From O
the O
results O
arise O
that O
the O
optimal O
idle O
time O
is O
30 O
s S-MATE
, O
as S-MATE
a O
compromise O
between O
productivity S-CONPRI
and O
reduction S-CONPRI
of O
heat B-PRO
accumulation E-PRO
, O
independently O
from O
the O
cooling S-MANP
strategy O
. O


Friction S-CONPRI
stir O
additive B-MANP
manufacturing E-MANP
( O
FSAM O
) O
was O
performed O
successfully O
using O
2 O
mm S-MANP
thick O
sheets S-MATE
of O
2195-T8 O
aluminum-lithium O
alloy S-MATE
. O


The O
influence O
of O
the O
tool S-MACEQ
pin O
shape O
and O
process B-CONPRI
parameters E-CONPRI
on O
the O
interfacial B-CONPRI
bonding E-CONPRI
features O
among O
the O
additive B-MANP
manufactured E-MANP
layers O
was O
discussed O
, O
and O
the O
effects O
of O
interfacial O
defects S-CONPRI
on O
the O
performances O
of O
the O
additive S-MATE
build O
were O
analyzed O
based O
on O
microstructures S-MATE
, O
hardness S-PRO
profiles O
, O
and O
mechanical B-CONPRI
property E-CONPRI
evaluations O
. O


It O
is O
shown O
that O
the O
shape O
of O
the O
tool S-MACEQ
pin O
is O
one O
of O
the O
key O
factors O
in O
influencing O
the O
bonding S-CONPRI
interface O
between O
two O
manufactured S-CONPRI
layers O
. O


The O
cylindrical S-CONPRI
pin O
and O
the O
conical O
pin O
with O
three O
flats O
are O
not O
suitable O
for O
the O
FSAM O
process S-CONPRI
since O
very O
poor O
material S-MATE
mixing O
features O
are O
produced O
along O
the O
bonding S-CONPRI
interface O
. O


Although O
the O
material S-MATE
mixing O
degree O
of O
bonding S-CONPRI
interface O
is O
obviously O
improved O
at O
the O
advancing O
side O
( O
AS S-MATE
) O
interface S-CONPRI
of O
the O
nugget O
zone O
( O
NZ O
) O
by O
using O
the O
convex O
featured O
pin O
or O
the O
pin O
with O
three O
concave O
arc S-CONPRI
grooves O
, O
the O
material S-MATE
mixing O
degree O
at O
the O
retreating O
side O
( O
RS O
) O
interface S-CONPRI
of O
the O
NZ O
is O
always O
insufficient O
. O


Meanwhile O
, O
the O
weak-bonding O
defects S-CONPRI
along O
the O
bonding S-CONPRI
interfaces O
could O
be S-MATE
formed O
, O
which O
are O
originated O
from O
the O
hooking O
defects S-CONPRI
on O
the O
RS O
. O


The O
weak-bonding O
defects S-CONPRI
are O
related O
to O
the O
oxides S-MATE
and O
impurities S-PRO
existing O
at O
the O
original O
bonding S-CONPRI
interfaces O
as S-MATE
well O
as S-MATE
the O
insufficient O
stirring O
action O
of O
the O
tool S-MACEQ
pin O
. O


The O
welding S-MANP
rotation O
speeds O
of O
800 O
, O
900 O
and O
1000 O
rpm O
for O
giving O
welding S-MANP
speed O
of O
100 O
mm/min O
were O
used O
in O
the O
additive B-MANP
manufacturing I-MANP
processes E-MANP
of O
2195-T8 O
aluminum-lithium O
alloy S-MATE
, O
in O
which O
the O
optimum O
microstructure S-CONPRI
is O
obtained O
with O
the O
rotation O
speed O
of O
800 O
rpm O
. O


The O
soften O
degree O
for O
the O
multilayered O
build S-PARA
is O
obvious O
, O
and O
the O
hardness S-PRO
profiles O
across O
the O
different O
bonding S-CONPRI
interfaces O
are O
always O
uneven O
. O


Meanwhile O
, O
compared O
with O
the O
AS S-MATE
interface O
, O
the O
fluctuation O
of O
the O
hardness S-PRO
value O
at O
the O
RS O
interface S-CONPRI
is O
greater O
. O


The O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
multilayered O
build S-PARA
are O
inhomogeneous O
, O
and O
the O
maximum O
tensile B-PRO
strength E-PRO
of O
the O
multilayered O
build S-PARA
is O
only O
reached O
the O
56.6 O
% O
of O
the O
base B-MATE
metal E-MATE
. O


The O
mechanical B-CONPRI
properties E-CONPRI
are O
closely O
associated O
with O
the O
soften O
tendency O
of O
the O
material S-MATE
and O
the O
degree O
of O
the O
amelioration O
of O
weak-bonding O
defect S-CONPRI
along O
the O
bonding S-CONPRI
interface O
. O


The O
influence O
of O
the O
addition O
of O
filler O
powder S-MATE
on O
the O
microstructure S-CONPRI
and O
properties S-CONPRI
of O
laser-welded O
Ti2AlNb O
joints O
was O
comparatively O
investigated O
using O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
, O
transmission B-CHAR
electron I-CHAR
microscopy E-CHAR
, O
electron O
back O
scattered O
diffraction S-CHAR
, O
and O
tensile B-CHAR
tests E-CHAR
. O


The O
heat B-CONPRI
affected I-CONPRI
zone E-CONPRI
( O
HAZ S-CONPRI
) O
of O
laser-additive-welded O
joints O
was O
divided O
into O
B2 O
, O
B2 O
+ O
α2 O
, O
and O
B2 O
+ O
α2 O
+ O
O S-MATE
— O
three O
regions O
with O
increasing O
distance O
from O
the O
fusion S-CONPRI
line O
. O


The O
HAZ S-CONPRI
of O
laser-welded O
joints O
could O
only O
be S-MATE
divided O
into O
two O
regions O
, O
viz. O
, O
B2 O
+ O
α2 O
and O
B2 O
+ O
α2 O
+ O
O S-MATE
. O


The O
microstructure S-CONPRI
of O
the O
fusion B-CONPRI
zone E-CONPRI
was O
composed O
of O
a O
single O
B2 O
phase S-CONPRI
for O
both O
laser B-MANP
welding E-MANP
and O
laser-additive O
welding S-MANP
. O


Columnar B-PRO
grains E-PRO
were O
observed O
in O
the O
fusion B-CONPRI
zone E-CONPRI
of O
laser-welded O
joints O
, O
while O
the O
B2 O
grains S-CONPRI
in O
the O
fusion B-CONPRI
zone E-CONPRI
of O
laser-additive-welded O
joints O
were O
basically O
equiaxed O
. O


A O
misorientation O
angle O
distribution S-CONPRI
analysis O
showed O
that O
the O
fraction S-CONPRI
of O
high-angle O
grain B-CONPRI
boundaries E-CONPRI
of O
laser-additive-welded O
joints O
was O
higher O
than O
that O
of O
laser-welded O
joints O
. O


The O
addition O
of O
filler O
powder S-MATE
promoted O
heterogeneous B-CONPRI
nucleation E-CONPRI
during O
solidification S-CONPRI
in O
laser-additive O
welding S-MANP
. O


Following O
tensile B-CHAR
tests E-CHAR
at O
room O
temperature S-PARA
, O
failure S-CONPRI
tended O
to O
occur O
in O
the O
fusion B-CONPRI
zone E-CONPRI
of O
the O
laser-welded O
joints O
and O
in O
the O
HAZ S-CONPRI
of O
the O
laser-additive-welded O
joints O
. O


The O
laser-additive-welded O
joints O
exhibited O
better O
tensile B-PRO
properties E-PRO
because O
of O
the O
higher O
Mo S-MATE
content O
as S-MATE
well O
as S-MATE
the O
equiaxed O
microstructure S-CONPRI
of O
the O
fusion B-CONPRI
zone E-CONPRI
. O


A O
flat O
specimen O
and O
a O
curved O
specimen O
with O
a O
thickness O
of O
50 O
mm S-MANP
were O
excavated O
from O
a O
large O
circular O
wire+arc B-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
mockup O
. O


The O
biaxial O
internal B-PRO
residual I-PRO
stress E-PRO
distributions S-CONPRI
in O
the O
specimens O
were O
measured O
using O
the O
two-cut O
contour S-FEAT
method O
. O


The O
stress B-PRO
distributions E-PRO
in O
the O
large O
circular O
WAAM S-MANP
mockup O
were O
deduced O
, O
and O
the O
effects O
of O
specimen O
shape O
and O
dimension S-FEAT
on O
the O
remnant O
stress B-PRO
distributions E-PRO
in O
the O
specimens O
were O
discussed O
. O


The O
investigated O
results O
show O
that O
the O
stress S-PRO
in O
the O
circular O
WAAM S-MANP
mockup O
has O
a O
similar O
distribution S-CONPRI
as S-MATE
that O
in O
thick O
multipass O
joints O
at O
the O
weld S-FEAT
centerline O
, O
the O
stress S-PRO
in O
the O
curved O
specimen O
extracted S-CONPRI
from O
a O
large O
circular O
WAAM S-MANP
mockup O
can O
reflect O
the O
stress B-PRO
distribution E-PRO
trend O
in O
the O
mockup O
. O


For O
specimens O
excavated O
from O
a O
large O
circular O
mockup O
, O
the O
specimen O
shape O
has O
no O
significant O
effect O
on O
the O
through-thickness O
axial O
stress B-PRO
distribution E-PRO
, O
while O
it O
has O
a O
significant O
effect O
on O
the O
hoop O
stress B-PRO
distribution E-PRO
. O


Carbon B-MATE
fiber E-MATE
reinforced O
plastic S-MATE
( O
CFRP O
) O
is O
an O
extremely O
beneficial O
composite B-MATE
material E-MATE
in O
the O
aerospace S-APPL
and O
automobile S-APPL
industries O
owing O
to O
its O
high-strength-to-weight O
ratio O
, O
high O
stiffness S-PRO
, O
lightweight S-CONPRI
, O
and O
corrosion B-CONPRI
resistance E-CONPRI
. O


A O
thin O
layer S-PARA
material O
such O
as S-MATE
Titanium O
( O
Ti S-MATE
) O
is O
often O
used O
along O
with O
CFRP O
laminates S-CONPRI
to O
address O
these O
issues O
. O


These O
techniques O
have O
several O
limitations O
including O
weight S-PARA
addition O
, O
stress B-CONPRI
cracking E-CONPRI
, O
delamination S-CONPRI
, O
and O
limited O
operating O
temperatures S-PARA
. O


These O
limitations O
can O
be S-MATE
readily O
addressed O
by O
the O
use O
of O
solid-state B-MANP
welding E-MANP
techniques O
based O
on O
ultrasonic O
energy O
. O


One O
such O
technique O
is O
the O
Ultrasonic B-MANP
Additive I-MANP
Manufacturing E-MANP
( O
UAM S-MANP
) O
process S-CONPRI
, O
which O
is O
capable O
of O
fabricating S-MANP
3D B-CONPRI
structures E-CONPRI
of O
CFRP/Ti O
laminar O
composites S-MATE
. O


Preliminary O
experimental S-CONPRI
studies O
proved O
the O
feasibility S-CONPRI
of O
using O
the O
UAM S-MANP
process S-CONPRI
to O
join O
CFRP/Ti O
stacks O
. O


Further O
development O
of O
this O
process S-CONPRI
needs O
a O
detailed O
investigation O
of O
the O
process B-CONPRI
parameters E-CONPRI
. O


This O
study O
aims O
to O
study O
the O
effect O
of O
critical O
process B-CONPRI
parameters E-CONPRI
including O
the O
ultrasonic O
energy O
and O
pre-surface O
roughness S-PRO
on O
the O
shear B-PRO
strength E-PRO
of O
the O
fabricated S-CONPRI
CFRP/Ti O
stacks O
using O
the O
UAM S-MANP
process S-CONPRI
. O


The O
study O
found O
that O
both O
ultrasonic O
energy O
and O
surface B-PRO
roughness E-PRO
have O
a O
positive O
impact S-CONPRI
on O
the O
resulting O
shear B-PRO
strengths E-PRO
of O
the O
UAM S-MANP
fabricated S-CONPRI
structures O
. O


Magnetic O
Arc S-CONPRI
Oscillation O
was O
applied O
during O
the O
construction S-APPL
of O
single-pass O
multi-layer O
walls O
of O
low B-MATE
carbon I-MATE
steel E-MATE
and O
Ti6Al4V S-MATE
by O
the O
Gas S-CONPRI
Tungsten O
Arc S-CONPRI
Welding-based O
Wire B-MANP
and I-MANP
Arc I-MANP
Additive I-MANP
Manufacturing E-MANP
process S-CONPRI
, O
and O
the O
influence O
on O
the O
geometry S-CONPRI
and O
the O
process S-CONPRI
stability O
was O
evaluated O
. O


The O
geometric O
features O
were O
assessed O
using O
transverse O
section O
macrographs O
and O
the O
effects O
of O
different O
patterns O
and O
frequencies O
of O
oscillation O
on O
the O
arc S-CONPRI
characteristics O
, O
metal S-MATE
transfer O
and O
weld B-CONPRI
pool E-CONPRI
behavior O
during O
the O
layer S-PARA
deposition S-CONPRI
were O
investigated O
using O
high O
speed O
and O
welding S-MANP
cameras O
. O


Furthermore O
, O
the O
distribution S-CONPRI
of O
material S-MATE
along O
the O
wall O
length O
becomes O
more O
homogeneous S-CONPRI
. O


An O
explanation O
of O
the O
effects O
of O
Magnetic O
Arc S-CONPRI
Oscillation O
on O
the O
wall O
geometry S-CONPRI
based O
on O
forces S-CONPRI
that O
act O
on O
the O
molten B-MATE
metal E-MATE
during O
layer S-PARA
deposition S-CONPRI
was O
made O
. O


Because O
of O
the O
swinging O
movement O
of O
the O
welding S-MANP
arc S-CONPRI
, O
the O
heat S-CONPRI
is O
distributed O
over O
a O
larger O
area S-PARA
, O
and O
the O
power S-PARA
density S-PRO
decreases O
. O


Thus O
, O
fewer O
previous O
layers O
are O
remelted O
, O
and O
the O
volume S-CONPRI
and O
the O
weight S-PARA
of O
the O
weld B-CONPRI
pool E-CONPRI
reduce O
. O


The O
weld B-CONPRI
pool E-CONPRI
temperature S-PARA
drops O
, O
and O
the O
surface B-PRO
tension E-PRO
force S-CONPRI
and O
the O
viscous O
friction S-CONPRI
increase O
. O


The O
distribution S-CONPRI
of O
arc B-PARA
pressure E-PARA
also O
becomes O
less O
concentrated O
, O
and O
the O
arc S-CONPRI
force O
on O
the O
molten B-MATE
metal E-MATE
decreases O
. O


Additionally O
, O
a O
magnetic O
force S-CONPRI
appears O
on O
the O
molten B-MATE
metal E-MATE
, O
which O
contributes O
to O
a O
change O
in O
the O
direction O
of O
the O
resultant B-PARA
force E-PARA
on O
the O
weld B-CONPRI
pool E-CONPRI
. O


The O
article O
presents O
new O
findings O
on O
arc S-CONPRI
stability O
in O
twin-wire O
robotic O
arc B-MANP
welding E-MANP
corresponding O
to O
the O
torch O
orientation S-CONPRI
and O
electrodes S-MACEQ
' O
position O
. O


The O
two O
mutually O
influencing O
co-existing O
arcs O
affect O
the O
stability S-PRO
of O
counterpart O
arc S-CONPRI
, O
and O
thereby O
alter O
the O
weld B-CONPRI
bead E-CONPRI
properties S-CONPRI
. O


The O
investigation O
divulges O
that O
electrode S-MACEQ
positions O
and O
torch O
orientation S-CONPRI
significantly O
impact B-CONPRI
arc E-CONPRI
stability O
which O
in O
turn O
impacts O
the O
heat S-CONPRI
input O
and O
weld B-PARA
bead I-PARA
geometry E-PARA
. O


The O
arc S-CONPRI
penetration O
in O
tandem O
orientation S-CONPRI
is O
augmented O
by O
the O
secondary O
arc S-CONPRI
that O
operates O
in O
the O
same O
weld B-CONPRI
pool E-CONPRI
. O


While O
the O
transverse O
orientation S-CONPRI
improves O
the O
arc S-CONPRI
stability O
and O
facilitates O
a O
wider O
weld B-CONPRI
bead E-CONPRI
with O
reasonable O
weld S-FEAT
penetration S-CONPRI
suitable O
for O
applications O
such O
as S-MATE
wire O
additive B-MANP
manufacturing E-MANP
and O
cladding S-MANP
. O


An O
approach O
for O
predicting O
arc S-CONPRI
stability O
as S-MATE
a O
function O
of O
process B-CONPRI
parameters E-CONPRI
is O
a O
significant O
contribution O
from O
this O
investigation O
. O


The O
insight O
into O
the O
arching O
phenomenon O
in O
twin-wire O
gas B-MANP
metal I-MANP
arc I-MANP
welding E-MANP
due O
to O
the O
investigation O
is O
expected O
to O
help O
the O
machine S-MACEQ
builders O
to O
design S-FEAT
an O
appropriate O
controller S-MACEQ
that O
minimizes O
arc S-CONPRI
interference O
. O


This O
study O
presents O
investigations O
on O
the O
additive B-MANP
manufacturing E-MANP
of O
hot B-MATE
work I-MATE
steel E-MATE
with O
the O
energy-reduced O
gas B-MANP
metal I-MANP
arc I-MANP
welding E-MANP
( O
GMAW S-MANP
) O
process S-CONPRI
, O
which O
is O
a O
cold B-MANP
metal I-MANP
transfer E-MANP
( O
CMT S-MANP
) O
process S-CONPRI
. O


The O
paper O
analyses O
the O
influence O
of O
arc S-CONPRI
energy O
and O
the O
thermal O
field O
on O
the O
resulting O
mechanical B-CONPRI
properties E-CONPRI
and O
microstructure S-CONPRI
of O
the O
material S-MATE
. O


The O
investigations O
were O
carried O
out O
with O
hot O
work O
tool S-MACEQ
steel S-MATE
X37CrMoV O
5-1 O
, O
which O
is O
used O
for O
the O
manufacturing S-MANP
of O
plastic S-MATE
moulds S-MACEQ
, O
hot B-MANP
extrusion E-MANP
dies S-MACEQ
, O
and O
forging S-MANP
dies S-MACEQ
. O


The O
results O
show O
that O
this O
steel S-MATE
can O
be S-MATE
used O
to O
generate O
3D S-CONPRI
metal O
components S-MACEQ
or O
structures O
with O
high O
reproducibility S-CONPRI
, O
near-net-shaped O
geometry S-CONPRI
, O
absence O
of O
cracks O
, O
and O
a O
deposition B-PARA
rate E-PARA
of O
up O
to O
3.6 O
kg/h O
. O


The O
variation S-CONPRI
of O
the O
wire O
feed S-PARA
speed O
and O
the O
welding S-MANP
speed O
enables O
the O
production S-MANP
of O
weld B-CONPRI
beads E-CONPRI
of O
width O
up O
to O
9.4 O
mm S-MANP
. O


The O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
generated O
structures O
can O
be S-MATE
adapted O
by O
the O
dominant O
thermal O
field O
, O
which O
in O
turn O
is O
influenced O
by O
the O
bypass O
temperature S-PARA
and O
the O
electric B-PARA
arc E-PARA
energy O
. O


If O
the O
bypass O
temperature S-PARA
is O
above O
the O
martensite S-MATE
start O
temperature S-PARA
( O
Ms O
) O
, O
there O
is O
a O
homogeneous S-CONPRI
hardness S-PRO
level O
along O
the O
height O
of O
the O
additively B-MANP
manufactured E-MANP
structure O
height O
as S-MATE
long O
as S-MATE
the O
energy O
produced O
by O
the O
welding S-MANP
arc S-CONPRI
is O
enough O
to O
keep O
the O
temperature S-PARA
of O
all O
layers O
above O
Ms. O
Wire-arc B-MANP
additive I-MANP
manufacturing E-MANP
has O
become O
an O
alternative O
way O
to O
produce O
industrial S-APPL
parts O
. O


In O
this O
work O
15 O
kg O
walls O
are O
built O
with O
an O
effective O
building O
rate O
of O
4.85 O
kg/h O
using O
an O
ER100 O
wire O
providing O
good O
tensile B-PRO
properties E-PRO
and O
toughness S-PRO
under O
welding S-MANP
conditions O
. O


The O
thermal O
evolution S-CONPRI
of O
the O
walls O
during O
manufacturing S-MANP
is O
measured O
by O
thermocouples S-MACEQ
and O
an O
IR S-CHAR
camera S-MACEQ
: O
it O
depends O
on O
process B-CONPRI
parameters E-CONPRI
, O
deposit O
strategy O
and O
the O
size O
of O
the O
part O
. O


The O
walls O
are O
then O
characterised O
as S-MATE
deposit O
and O
after O
heat B-MANP
treatment E-MANP
through O
hardness S-PRO
, O
tensile S-PRO
and O
Charpy-V O
notch S-FEAT
tests O
. O


The O
results O
show O
a O
fine O
microstructure S-CONPRI
with O
unexpected O
retained B-MATE
austenite E-MATE
and O
coarse O
allotriomorphic O
ferrite S-MATE
in O
the O
as S-MATE
deposited O
walls O
. O


The O
final O
hardness S-PRO
values O
vary O
from O
about O
220 O
to O
280 O
HV2 O
; O
the O
yield B-PRO
stress E-PRO
and O
tensile B-PRO
strength E-PRO
are O
520 O
and O
790 O
MPa S-CONPRI
, O
respectively O
, O
and O
a O
toughness S-PRO
of O
about O
50 O
J O
is O
obtained O
at O
room O
temperature S-PARA
. O


The O
heat B-MANP
treatment E-MANP
transforms O
the O
retained B-MATE
austenite E-MATE
, O
leading O
to O
an O
improvement O
of O
the O
yield B-PRO
stress E-PRO
to O
600 O
MPa S-CONPRI
. O


Ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
is O
a O
promising O
approach O
for O
making O
net-shaped O
multi-material B-CONPRI
laminates E-CONPRI
from O
material S-MATE
combinations O
difficult O
to O
process S-CONPRI
with O
fusion-based O
additive B-MANP
manufacturing E-MANP
techniques O
. O


The O
properties S-CONPRI
of O
these O
multi-material B-CONPRI
laminates E-CONPRI
depend O
sensitively O
on O
the O
interface S-CONPRI
between O
the O
constituents O
, O
which O
can O
be S-MATE
decorated O
with O
pores S-PRO
as S-MATE
well O
as S-MATE
thin O
intermetallic S-MATE
layers O
. O


Here O
, O
we O
develop O
process B-CONPRI
models E-CONPRI
for O
junction S-APPL
growth O
and O
interdiffusion O
during O
ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
of O
dissimilar O
metals S-MATE
. O


These O
process B-CONPRI
models E-CONPRI
are O
validated O
against O
published O
experimental B-CONPRI
data E-CONPRI
, O
then O
used O
to O
generate O
process S-CONPRI
diagrams O
which O
reveal O
that O
high O
normal O
loads O
and O
high O
sonotrode S-MACEQ
velocities O
can O
reduce O
intermetallic S-MATE
growth O
while O
maintaining O
strong O
interlayer O
bonding S-CONPRI
. O


Ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
( O
UAM S-MANP
) O
is O
a O
solid-state S-CONPRI
manufacturing B-MANP
technology E-MANP
for O
producing O
near-net O
shape O
metallic B-MACEQ
parts E-MACEQ
combining O
additive S-MATE
ultrasonic O
metal S-MATE
welding O
and O
subtractive B-MANP
machining E-MANP
. O


Even O
though O
UAM S-MANP
has O
been O
demonstrated O
to O
produce O
robust O
metal S-MATE
builds S-CHAR
in O
Al–Al O
, O
Al–Ti O
, O
Al-steel O
, O
Cu–Cu O
, O
Al–Cu O
, O
and O
other O
material S-MATE
systems O
, O
UAM S-MANP
welding O
of O
high O
strength S-PRO
steels S-MATE
has O
proven O
challenging O
. O


This O
study O
investigates S-CONPRI
process O
and O
post-processing S-CONPRI
methods O
to O
improve O
UAM S-MANP
steel S-MATE
weld O
quality S-CONPRI
and O
demonstrates O
the O
UAM B-MANP
fabrication E-MANP
of O
stainless B-MATE
steel E-MATE
410 O
( O
SS S-MATE
410 O
) O
builds S-CHAR
which O
possess O
, O
after O
post-processing S-CONPRI
, O
mechanical B-CONPRI
properties E-CONPRI
comparable O
with O
bulk O
material S-MATE
. O


Unlike O
UAM B-MANP
fabrication E-MANP
of O
softer O
metals S-MATE
, O
this O
study O
shows O
that O
increasing O
the O
baseplate O
temperature S-PARA
from O
38∘C O
( O
100∘F O
) O
to O
204∘C O
( O
400∘F O
) O
improves O
interfacial O
strength S-PRO
and O
structural O
homogeneity O
of O
the O
UAM S-MANP
steel S-MATE
samples S-CONPRI
. O


Further O
improvement O
in O
strength S-PRO
is O
achieved O
through O
post-processing S-CONPRI
. O


The O
hot B-MANP
isostatic I-MANP
pressing E-MANP
( O
HIP S-MANP
) O
post O
treatment O
improves O
the O
shear B-PRO
strength E-PRO
of O
UAM S-MANP
samples S-CONPRI
to O
344 O
MPa S-CONPRI
from O
154 O
MPa S-CONPRI
for O
as-welded O
samples S-CONPRI
. O


Microstructural B-CHAR
analyses E-CHAR
with O
SEM S-CHAR
and O
EBSD S-CHAR
show O
no O
evidence O
of O
body B-CONPRI
centered I-CONPRI
cubic E-CONPRI
( O
BCC S-CONPRI
) O
ferrite S-MATE
to O
face B-CONPRI
centered I-CONPRI
cubic E-CONPRI
( O
FCC S-CONPRI
) O
austenite S-MATE
transformation O
taking O
place O
during O
UAM S-MANP
welding O
of O
SS S-MATE
410 O
. O


The O
weld B-PARA
quality E-PARA
improvement O
of O
UAM S-MANP
steel S-MATE
at O
higher O
baseplate O
temperatures S-PARA
is O
believed O
to O
be S-MATE
caused O
by O
the O
reduction S-CONPRI
of O
the O
yield B-PRO
strength E-PRO
of O
SS S-MATE
410 O
at O
elevated O
temperature S-PARA
. O


HIP S-MANP
treatment O
is O
shown O
to O
increase O
the O
overall O
hardness S-PRO
of O
UAM S-MANP
SS S-MATE
410 O
from O
204 O
± O
7 O
HV O
to O
240 O
± O
16 O
HV O
due O
to O
the O
formation O
of O
local O
pockets O
of O
martensite S-MATE
. O


Nanohardness O
tests O
show O
that O
the O
top O
of O
layer S-PARA
n O
is O
harder O
than O
the O
bottom O
of O
layer S-PARA
n+1 O
due O
to O
grain B-CONPRI
boundary E-CONPRI
strengthening O
. O


The O
locked O
in O
residual B-PRO
stresses E-PRO
in O
a O
monopile O
structure S-CONPRI
have O
a O
great O
impact S-CONPRI
on O
its O
fatigue B-PRO
life E-PRO
. O


The O
new O
emerged O
technology S-CONPRI
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
, O
which O
is O
widely O
used O
in O
other O
industries S-APPL
such O
as S-MATE
aerospace S-APPL
and O
automotive S-APPL
, O
has O
the O
potential O
to O
significantly O
improve O
a O
lifespan O
of O
the O
structure S-CONPRI
by O
managing O
the O
residual B-PRO
stress E-PRO
fields O
and O
microstructure S-CONPRI
in O
the O
future O
monopiles O
, O
and O
moreover O
reduce O
the O
manufacturing B-CONPRI
cost E-CONPRI
. O


In O
order O
to O
achieve O
this O
goal O
, O
new O
materials S-CONPRI
that O
are O
used O
for O
additive B-MANP
manufacturing E-MANP
parts O
fabrication S-MANP
and O
their O
behaviour O
in O
the O
harsh O
marine O
environment O
and O
under O
operational O
loading O
conditions O
need O
to O
be S-MATE
understood O
. O


Also O
purely O
welding B-MANP
fabrication E-MANP
technique O
employed O
during O
AM B-MANP
process E-MANP
is O
likely O
to O
significantly O
affect O
crack B-CONPRI
growth E-CONPRI
behaviour O
in O
air O
as S-MATE
well O
as S-MATE
in O
seawater O
. O


This O
paper O
presents O
a O
review O
of O
additive B-MANP
manufacturing E-MANP
technology O
and O
suitable O
techniques O
for O
offshore O
structures O
. O


Existing O
literature O
that O
reports O
current O
data S-CONPRI
on O
fracture S-CONPRI
toughness O
and O
fatigue B-CONPRI
crack I-CONPRI
growth E-CONPRI
tests O
conducted O
on O
AM B-MACEQ
parts E-MACEQ
is O
summarised O
and O
analysed O
, O
highlighting O
different O
steel S-MATE
grades O
and O
applications O
, O
with O
the O
view O
to O
illustrating O
the O
requirements O
for O
the O
new O
optimised O
functionally B-FEAT
graded I-FEAT
structures E-FEAT
in O
offshore O
wind O
structures O
by O
means O
of O
AM B-MANP
technique E-MANP
. O


In O
this O
paper O
, O
the O
results O
of O
two O
different O
wire O
based O
additive-layer-manufacturing O
systems O
are O
compared O
: O
in O
one O
system O
Ti-6Al4V O
is O
deposited O
by O
a O
Nd B-MATE
: I-MATE
YAG E-MATE
laser B-CONPRI
beam E-CONPRI
, O
in O
the O
other O
by O
an O
arc S-CONPRI
beam O
( O
tungsten B-MANP
inert I-MANP
gas E-MANP
process S-CONPRI
) O
. O


Mechanical B-CONPRI
properties E-CONPRI
of O
the O
deposits O
and O
of O
plate O
material S-MATE
are O
presented O
and O
evaluated O
with O
respect O
to O
aerospace S-APPL
material O
specifications S-PARA
. O


The O
mechanical B-CHAR
tests E-CHAR
including O
static O
tension O
and O
high O
cycle O
fatigue S-PRO
were O
performed O
in O
as-built O
, O
stress-relieved O
and O
annealed O
conditions.Generally O
, O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
components S-MACEQ
are O
competitive O
to O
cast S-MANP
and O
even O
wrought B-MATE
material E-MATE
properties S-CONPRI
and O
can O
attain O
properties S-CONPRI
suitable O
for O
space O
or O
aerospace S-APPL
applications O
. O


Realizing O
improved O
strength S-PRO
in O
composite S-MATE
metallic O
materials S-CONPRI
remains O
a O
challenge O
using O
conventional B-MANP
welding E-MANP
and O
joining S-MANP
systems O
due O
to O
the O
generation O
and O
development O
of O
brittle S-PRO
intermetallic O
compounds O
caused O
by O
complex O
thermal B-CONPRI
profiles E-CONPRI
during O
solidification S-CONPRI
. O


Here O
, O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
process S-CONPRI
was O
used O
to O
fabricate S-MANP
a O
steel-nickel O
structural B-CONPRI
component E-CONPRI
, O
whose O
average S-CONPRI
tensile O
strength S-PRO
of O
634 O
MPa S-CONPRI
significantly O
exceeded O
that O
of O
feedstock B-MATE
materials E-MATE
( O
steel S-MATE
, O
537 O
MPa S-CONPRI
and O
nickel S-MATE
, O
455 O
MPa S-CONPRI
) O
, O
which O
has O
not O
been O
reported O
previously O
. O


The O
as-fabricated O
sample S-CONPRI
exhibited O
hierarchically O
structural O
heterogeneity S-CONPRI
due O
to O
the O
interweaving O
deposition S-CONPRI
strategy O
. O


The O
improved O
mechanical B-CONPRI
response E-CONPRI
during O
tensile B-CHAR
testing E-CHAR
was O
due O
to O
the O
inter-locking O
microstructure S-CONPRI
forming S-MANP
a O
strong O
bond O
at O
the O
interface S-CONPRI
and O
solid B-MATE
solutions E-MATE
strengthening O
from O
the O
intermixing O
of O
the O
Fe S-MATE
and O
Ni S-MATE
increased O
the O
interface S-CONPRI
strength O
, O
beyond O
the O
sum O
of O
parts O
. O


The O
research S-CONPRI
offers O
a O
new O
route O
for O
producing O
high-quality O
steel-nickel O
dissimilar O
structures O
and O
widens O
the O
design S-FEAT
opportunities O
of O
monolithic S-PRO
components S-MACEQ
, O
with O
site-specific O
properties S-CONPRI
, O
for O
specific O
structural O
or O
functional O
applications O
. O


Wire B-MANP
Arc I-MANP
Additive I-MANP
Manufacturing E-MANP
( O
WAAM S-MANP
) O
is O
a O
fusion- O
and O
wire-based B-MANP
additive I-MANP
manufacturing E-MANP
technology S-CONPRI
which O
has O
gained O
industrial S-APPL
interest O
for O
the O
production S-MANP
of O
medium-to-large O
components S-MACEQ
with O
high O
material S-MATE
deposition B-PARA
rates E-PARA
. O


However O
, O
in-depth O
studies O
on O
performance S-CONPRI
indicators O
that O
incorporate O
economic O
and O
environmental O
sustainability S-CONPRI
still O
have O
to O
be S-MATE
carried O
out O
. O


The O
first O
aim O
of O
the O
paper O
has O
been O
to O
quantify O
the O
performance S-CONPRI
metrics O
of O
WAAM-based O
manufacturing B-MANP
approaches E-MANP
, O
while O
varying O
the O
size O
and O
the O
deposited O
material S-MATE
of O
the O
component S-MACEQ
. O


Wire-arc B-MANP
additive I-MANP
manufacturing E-MANP
is O
an O
additive B-MANP
manufacturing E-MANP
technology O
which O
allows O
for O
high B-PARA
deposition I-PARA
rates E-PARA
and O
is O
well O
suited O
for O
manufacturing S-MANP
larger O
parts O
in O
a O
short O
time O
compared O
to O
other O
additive B-MANP
manufacturing E-MANP
technologies O
. O


The O
technology S-CONPRI
has O
already O
received O
considerable O
industrial S-APPL
take-up O
for O
various B-MATE
materials E-MATE
and O
applications O
. O


The O
aim O
of O
this O
work O
is O
to O
investigate O
the O
alloy S-MATE
EN O
AW O
6016 O
as S-MATE
wire O
stock O
for O
WAAM S-MANP
. O


To O
establish O
this O
, O
aluminum S-MATE
wire O
was O
produced O
by O
wire B-MANP
drawing E-MANP
. O


Using O
this O
wire O
, O
specimens O
were O
produced O
on O
base O
plate O
material S-MATE
using O
a O
variety O
of O
process B-CONPRI
parameters E-CONPRI
. O


These O
parts O
were O
then O
used O
to O
evaluate O
the O
mechanical B-CONPRI
properties E-CONPRI
. O


Further O
properties S-CONPRI
such O
as S-MATE
porosity O
and O
hardness S-PRO
were O
investigated O
using O
light O
optical B-CHAR
microscopy E-CHAR
. O


Based O
on O
the O
results O
, O
the O
potential O
of O
the O
alloy S-MATE
for O
WAAM S-MANP
of O
lightweight S-CONPRI
parts O
is O
discussed O
. O


Cu-Al O
alloy S-MATE
was O
in-situ B-CONPRI
fabricated E-CONPRI
by O
twin O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
. O


Addition O
of O
about O
2 O
% O
silicon S-MATE
to O
the O
copper-aluminum O
alloy S-MATE
helps O
to O
increase O
the O
hardness S-PRO
by O
0.5–1 O
times O
. O


With O
the O
aluminum S-MATE
content O
increases O
, O
the O
yield B-PRO
strength E-PRO
increases O
150 O
MPa S-CONPRI
. O


CuAl2 O
with O
the O
different O
crystal B-PRO
structures E-PRO
were O
synthetized O
. O


Present O
work O
investigated O
the O
use O
of O
Cold B-MANP
Metal I-MANP
Transfer E-MANP
( O
CMT S-MANP
) O
welding S-MANP
for O
additive B-MANP
manufacturing E-MANP
of O
copper‑aluminum O
alloys S-MATE
with O
addition O
of O
silicon S-MATE
in O
small O
amount O
. O


The O
additive B-MANP
manufacturing E-MANP
was O
successfully O
demonstrated O
through O
two O
samples S-CONPRI
with O
the O
4.34 O
% O
( O
sample-1 O
) O
and O
6.58 O
% O
( O
sample-2 O
) O
aluminum S-MATE
content O
, O
which O
is O
not O
much O
different O
with O
the O
content O
of O
the O
design S-FEAT
. O


The O
analyses O
of O
performance S-CONPRI
of O
samples S-CONPRI
reveal O
that O
both O
samples S-CONPRI
have O
good O
strength S-PRO
and O
ductility S-PRO
. O


It O
is O
also O
found O
addition O
of O
silicon S-MATE
in O
small O
amount O
( O
2.1 O
% O
–2.4 O
% O
) O
effectively O
improves O
hardness S-PRO
, O
tensile B-PRO
strength E-PRO
and O
0.2 O
% O
offset S-CONPRI
Yield O
Strength S-PRO
in O
comparison O
to O
pure O
copper‑aluminum O
alloy S-MATE
. O


The O
results O
of O
X-ray B-CHAR
diffraction E-CHAR
( O
XRD S-CHAR
) O
, O
showed O
that O
sample-2 O
possessed O
CuAl2 O
with O
different O
crystal B-PRO
structure E-PRO
whereas O
sample-1 O
did O
not O
. O


It O
is O
found O
that O
an O
increase O
in O
aluminum S-MATE
caused O
both O
tensile B-PRO
strength E-PRO
and O
0.2 O
% O
offset S-CONPRI
Yield O
Strength S-PRO
to O
increase O
, O
however O
, O
increase O
in O
yield B-PRO
strength E-PRO
was O
very O
significant O
( O
155 O
MPa S-CONPRI
i.e O
. O


In O
this O
study O
, O
the O
0.2Pct O
offset S-CONPRI
Yield O
Strength S-PRO
of O
sample-1 O
is O
150 O
MPa S-CONPRI
more O
than O
that O
of O
sample-2 O
. O


Embedding O
with O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
a O
process S-CONPRI
of O
incorporating O
functional B-CONPRI
components E-CONPRI
, O
such O
as S-MATE
sensors O
and O
actuators S-MACEQ
, O
in O
the O
printed O
structure S-CONPRI
by O
inserting O
them O
into O
a O
specially O
designed S-FEAT
cavity O
. O


The O
print S-MANP
process O
has O
to O
be S-MATE
interrupted O
after O
the O
cavity O
is O
printed O
to O
insert S-MACEQ
the O
component S-MACEQ
. O


This O
allows O
for O
multifunctional O
structures O
to O
be S-MATE
created O
directly O
from O
the O
build B-MACEQ
plate E-MACEQ
. O


However O
, O
previous O
research S-CONPRI
has O
shown O
that O
this O
process S-CONPRI
interruption O
causes O
failure S-CONPRI
at O
the O
paused O
layer S-PARA
due O
to O
the O
cooling S-MANP
between O
the O
layers O
. O


The O
presence O
of O
the O
designed S-FEAT
cavity O
further O
impacts O
the O
strength S-PRO
of O
the O
part O
due O
to O
a O
reduction S-CONPRI
in O
the O
effective O
cross-section O
in O
contact S-APPL
between O
the O
paused O
and O
the O
resumed O
layers O
. O


This O
research S-CONPRI
presents O
a O
methodology S-CONPRI
to O
predict O
the O
weld B-PRO
strength E-PRO
between O
the O
layers O
of O
an O
embedded O
material B-MANP
extrusion E-MANP
structure O
by O
obtaining O
the O
thermal O
history O
at O
the O
layer S-PARA
interface S-CONPRI
as S-MATE
a O
result O
of O
process S-CONPRI
interruption O
. O


An O
infrared S-CONPRI
camera S-MACEQ
and O
an O
embedded O
thermocouple S-MACEQ
are O
used O
to O
obtain O
the O
thermal O
history O
of O
the O
depositing O
fresh O
layer S-PARA
and O
of O
the O
layer S-PARA
interface S-CONPRI
, O
respectively O
. O


The O
impact S-CONPRI
of O
toolpath S-PARA
design S-FEAT
on O
the O
thermal O
history O
of O
the O
layer S-PARA
interface S-CONPRI
is O
considered O
by O
dividing O
the O
cross-section O
area S-PARA
into O
zones O
with O
similar O
thermal O
history O
. O


Polymer S-MATE
weld O
theory O
is O
utilized O
to O
predict O
the O
strength S-PRO
at O
these O
different O
zones O
, O
where O
material B-CONPRI
properties E-CONPRI
are O
obtained O
through O
rheology S-PRO
measurements O
. O


These O
strength S-PRO
values O
for O
the O
zones O
are O
then O
used O
to O
predict O
the O
load O
at O
failure S-CONPRI
for O
different O
specimens O
by O
treating O
them O
as S-MATE
composites O
. O


Findings O
confirm O
that O
this O
approach O
can O
be S-MATE
used O
to O
more O
accurately S-CHAR
predict O
tensile B-CHAR
loads E-CHAR
at O
failure S-CONPRI
for O
embedded O
structures O
, O
with O
errors S-CONPRI
ranging O
from O
1 O
% O
to O
20 O
% O
depending O
on O
the O
toolpath S-PARA
geometry S-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
the O
umbrella O
term O
that O
covers O
a O
variety O
of O
techniques O
that O
build S-PARA
up O
structures O
layer-by-layer S-CONPRI
as S-MATE
opposed O
to O
machining S-MANP
and O
other O
subtracting O
methods O
. O


It O
keeps O
evolving O
as S-MATE
an O
important O
technology S-CONPRI
in O
prototyping S-CONPRI
and O
the O
development O
of O
new O
devices O
. O


However O
, O
using O
AM S-MANP
on O
a O
larger O
scale O
is O
still O
challenging O
, O
as S-MATE
traditional O
methods O
require O
the O
AM B-MACEQ
machines E-MACEQ
to O
be S-MATE
larger O
than O
the O
manufactured S-CONPRI
structure O
. O


The O
focus O
in O
this O
paper O
is O
the O
feasibility S-CONPRI
of O
large-scale O
AM S-MANP
of O
metallic B-MATE
materials E-MATE
by O
arc B-MANP
welding E-MANP
. O


A O
series O
of O
experiments O
with O
robotic O
arc B-MANP
welding E-MANP
using O
an O
ABB O
IRB2400/10 O
robot S-MACEQ
are O
presented O
and O
discussed O
. O


These O
experiment S-CONPRI
will O
help O
map O
some O
of O
the O
challenges O
that O
need O
to O
be S-MATE
addressed O
in O
future O
work O
. O


Hydrodynamic O
flow O
is O
used O
for O
surface B-MANP
finishing E-MANP
of O
additive B-MANP
manufactured E-MANP
channels O
. O


The O
surface B-FEAT
finish E-FEAT
quality S-CONPRI
( O
Ra O
and O
Rz O
) O
of O
additive B-MANP
manufactured E-MANP
channels O
improves O
by O
> O
90 O
% O
. O


The O
surface B-FEAT
integrity E-FEAT
of O
the O
channels O
also O
improves O
after O
surface B-MANP
finishing E-MANP
. O


A O
surface B-PRO
roughness E-PRO
ratio O
of O
≈1.0 O
is O
achieved O
in O
the O
additive B-MANP
manufactured E-MANP
channel O
. O


The O
surface B-MANP
finishing E-MANP
of O
internal O
channels O
for O
components S-MACEQ
built O
using O
additive B-MANP
manufacturing E-MANP
is O
a O
challenge O
. O


The O
resulting O
surface B-FEAT
finish E-FEAT
uniformity O
of O
additive B-MANP
manufactured E-MANP
internal O
channels O
( O
such O
as S-MATE
fuel O
transfer B-CONPRI
lines E-CONPRI
and O
cooling S-MANP
passages O
) O
is O
an O
issue O
. O


Therefore O
, O
we O
propose O
a O
novel O
surface B-MANP
finishing E-MANP
technique O
using O
controlled O
hydrodynamic O
multiphase O
flow O
with O
abrasion O
phenomenon O
to O
overcome O
the O
challenges O
in O
the O
surface B-MANP
finishing E-MANP
of O
additive B-MANP
manufactured E-MANP
internal O
channels O
. O


In O
this O
study O
, O
we O
performed O
the O
internal O
surface B-MANP
finishing E-MANP
on O
AlSi10Mg S-MATE
components O
manufactured S-CONPRI
by O
direct B-MANP
metal I-MANP
laser I-MANP
sintering E-MANP
. O


We O
investigated O
the O
surface B-FEAT
finish E-FEAT
potential O
of O
the O
proposed O
hydrodynamic O
cavitation S-CONPRI
abrasive S-MATE
finishing O
( O
HCAF O
) O
by O
varying O
the O
process B-CONPRI
parameters E-CONPRI
, O
namely O
, O
the O
hydrodynamic O
upstream O
and O
downstream O
fluid S-MATE
pressures O
, O
fluid S-MATE
temperature O
, O
abrasive S-MATE
concentration O
, O
and O
processing O
time O
. O


The O
HCAF O
process S-CONPRI
resulted O
in O
greater O
than O
90 O
% O
( O
Ra O
and O
Rz O
) O
surface B-FEAT
finish E-FEAT
improvements O
with O
an O
acceptable O
thickness O
loss O
from O
the O
internal O
channels O
. O


We O
precisely O
mapped O
the O
surface B-CHAR
morphology E-CHAR
transformation O
at O
the O
demarcated O
zones O
over O
the O
processing O
time O
and O
explained O
the O
material S-MATE
removal O
mechanism S-CONPRI
. O


In O
addition O
, O
we O
analyzed O
and O
discussed O
the O
surface B-FEAT
integrity E-FEAT
of O
the O
channels O
in O
terms O
of O
the O
microstructure S-CONPRI
, O
surface S-CONPRI
hardness S-PRO
, O
and O
residual B-PRO
stress E-PRO
. O


Furthermore O
, O
we O
performed O
large-area O
surface B-CONPRI
topography E-CONPRI
measurements O
. O


Then O
, O
we O
analyzed O
the O
resulting O
areal O
surface B-FEAT
texture E-FEAT
parameters S-CONPRI
to O
determine O
the O
uniformity O
and O
flatness S-PRO
of O
the O
surface S-CONPRI
after O
internal O
surface B-MANP
finishing E-MANP
. O


Finally O
, O
we O
discussed O
the O
significance O
of O
using O
the O
proposed O
HCAF O
process S-CONPRI
for O
complex O
additive B-MANP
manufactured E-MANP
internal O
channels O
. O


Additive B-MANP
manufacturing E-MANP
can O
produce O
very O
complex O
and O
highly O
integrated O
parts O
that O
can O
not O
be S-MATE
manufactured O
by O
traditional O
methods O
. O


The O
aim O
of O
this O
study O
was O
to O
find O
out O
the O
laser S-ENAT
weldability O
of O
the O
printed O
AlSi10Mg S-MATE
material O
without O
filler O
material S-MATE
. O


The O
laser S-ENAT
used O
in O
these O
welding S-MANP
experiments O
was O
Yb S-MATE
: O
YAG S-MATE
disk O
laser S-ENAT
. O


The O
laser S-ENAT
wavelength O
was O
1030 O
nm O
and O
the O
maximum O
output O
power S-PARA
on O
the O
workpiece S-CONPRI
surface S-CONPRI
was O
4 O
kW O
. O


AlSi10Mg S-MATE
is O
a O
widely O
used O
material S-MATE
in O
parts O
that O
are O
produced O
utilizing O
the O
SLM S-MANP
technique O
. O


The O
material S-MATE
has O
very O
good O
corrosion B-CONPRI
resistance E-CONPRI
properties O
, O
good O
electrical B-PRO
conductivity E-PRO
and O
excellent O
thermal B-PRO
conductivity E-PRO
. O


AlSi10Mg S-MATE
has O
proven O
to O
be S-MATE
much O
easier O
to O
print S-MANP
than O
steel B-MATE
materials E-MATE
, O
so O
it O
is O
a O
popular O
material S-MATE
also O
in O
prototype S-CONPRI
production S-MANP
. O


Based O
on O
welding S-MANP
tests O
, O
laser B-MANP
welding E-MANP
without O
filler O
material S-MATE
is O
suitable O
for O
AlSi10Mg S-MATE
material O
and O
the O
static O
strength S-PRO
of O
the O
weld S-FEAT
is O
reasonably O
good O
compared O
to O
the O
base O
material S-MATE
. O


However O
, O
AlSi10Mg S-MATE
can O
be S-MATE
found O
to O
be S-MATE
challenging O
due O
to O
its O
composition S-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
has O
experienced O
a O
remarkably O
growth O
over O
the O
last O
few O
years O
, O
making O
possible O
not O
only O
to O
make O
prototypes S-CONPRI
, O
but O
also O
to O
produce O
final O
products O
, O
so O
nowadays O
most O
of O
recent O
works O
are O
focused O
in O
metal B-MANP
additive I-MANP
manufacturing E-MANP
. O


The O
main O
objective O
of O
this O
work O
is O
to O
show O
the O
first O
experiences O
in O
the O
development O
of O
a O
cost O
effective O
metal B-MANP
additive I-MANP
manufacturing E-MANP
system O
on O
the O
basis O
of O
gas B-MANP
metal I-MANP
arc I-MANP
welding E-MANP
( O
GMAW S-MANP
) O
. O


The O
proposed O
system O
, O
wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
, O
integrates O
a O
cold B-MANP
metal I-MANP
transfer E-MANP
( O
CMT S-MANP
) O
welding S-MANP
equipment S-MACEQ
patented O
by O
Fronius® O
, O
and O
a O
CNC B-MANP
milling E-MANP
machine O
Optimus O
with O
three O
axis O
and O
it O
presents O
the O
advantages O
to O
reduce O
the O
heat B-PRO
accumulation E-PRO
originated O
using O
a O
conventional O
GMAW S-MANP
equipment S-MACEQ
and O
the O
possibility O
to O
implement O
surface B-FEAT
finish E-FEAT
operations O
by O
milling S-MANP
. O


Additive S-MATE
processes O
show O
a O
smaller O
amount O
of O
wasted O
material S-MATE
. O


For O
material S-MATE
removal O
ratios O
over O
55 O
% O
additive S-MATE
processes O
show O
less O
demand O
of O
energy O
. O


For O
material S-MATE
removal O
ratios O
over O
75 O
% O
additive S-MATE
processes O
show O
less O
processing O
time O
. O


This O
paper O
aims O
to O
analyze O
and O
compare O
the O
electrical S-APPL
energy O
and O
material S-MATE
efficiency O
of O
machining S-MANP
, O
additive S-MATE
and O
hybrid B-CONPRI
manufacturing E-CONPRI
. O


The O
analysis O
of O
the O
manufacturing B-MANP
processes E-MANP
is O
based O
on O
machine B-MACEQ
tool E-MACEQ
data S-CONPRI
from O
a O
sample S-CONPRI
process S-CONPRI
. O


To O
get O
a O
generalized O
statement O
about O
the O
energy O
consumption O
of O
the O
investigated O
processes S-CONPRI
the O
electrical S-APPL
energy O
demand O
was O
extrapolated O
as S-MATE
a O
function O
of O
the O
material S-MATE
removal O
ratio O
. O


The O
results O
indicate O
that O
hybrid B-CONPRI
manufacturing E-CONPRI
becomes O
beneficial O
from O
an O
environmental O
point O
of O
view O
compared O
to O
milling S-MANP
, O
when O
the O
material S-MATE
removal O
ratio O
exceeds O
55 O
% O
. O


The O
electrical S-APPL
break-even O
point O
for O
selective B-MANP
laser I-MANP
melting E-MANP
is O
approximated O
to O
82 O
% O
material S-MATE
removal O
ratio O
from O
data S-CONPRI
extrapolation O
. O


Subsequently O
, O
opportunities O
for O
electrical S-APPL
energy O
and O
material S-MATE
efficiency O
improvements O
are O
presented O
for O
these O
technologies S-CONPRI
to O
gain S-PARA
an O
understanding O
of O
how O
each O
can O
contribute O
to O
a O
more O
sustainable B-CONPRI
manufacturing E-CONPRI
landscape O
. O


The O
chemical B-CONPRI
composition E-CONPRI
of O
the O
deposited O
metal S-MATE
could O
be S-MATE
estimated O
. O


The O
chemical B-CONPRI
composition E-CONPRI
could O
be S-MATE
changed O
gradually O
using O
proposed O
process S-CONPRI
. O


Wire O
and O
arc-based O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
is O
an O
additive B-MANP
manufacturing E-MANP
technique O
applying O
arc B-MANP
welding E-MANP
technology O
, O
where O
the O
metal S-MATE
melted S-CONPRI
by O
the O
arc S-CONPRI
discharge O
is O
accumulated O
and O
deposited O
. O


High-performance O
products O
with O
an O
excellent O
mechanical S-APPL
or O
chemical O
properties S-CONPRI
can O
be S-MATE
obtained O
using O
more O
than O
two O
materials S-CONPRI
through O
wire O
and O
arc-based O
AM S-MANP
. O


However O
, O
thermal B-PRO
stress E-PRO
and O
residual B-PRO
stress E-PRO
can O
form O
around O
the O
interface S-CONPRI
between O
two O
materials S-CONPRI
. O


Therefore O
, O
the O
objective O
of O
this O
study O
is O
to O
control O
the O
chemical B-CONPRI
composition E-CONPRI
of O
the O
deposited O
metal S-MATE
so O
that O
it O
changes O
gradually O
near O
the O
interface S-CONPRI
. O


Intermediate O
layers O
, O
with O
controlled O
chemical B-CONPRI
compositions E-CONPRI
, O
were O
inserted O
between O
the O
materials B-CONPRI
boundary E-CONPRI
. O


To O
regulate O
the O
chemical B-CONPRI
composition E-CONPRI
of O
the O
deposited O
metal S-MATE
, O
a O
filler O
wire O
was O
added O
into O
the O
molten B-CONPRI
pool E-CONPRI
during O
the O
deposition B-MANP
process E-MANP
. O


Results O
revealed O
that O
the O
chemical B-CONPRI
composition E-CONPRI
changed O
gradually O
near O
the O
interface S-CONPRI
using O
the O
proposed O
method O
. O


Selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
is O
gaining O
increasing O
relevance O
in O
industry S-APPL
. O


Residual B-CONPRI
deformations E-CONPRI
and O
internal B-PRO
stresses E-PRO
caused O
by O
the O
repeated O
layerwise O
melting S-MANP
of O
the O
metal B-MATE
powder E-MATE
and O
transient S-CONPRI
cooling S-MANP
of O
the O
solidified O
layers O
still O
presents O
a O
significant O
challenge O
to O
the O
profitability O
and O
quality S-CONPRI
of O
the O
process S-CONPRI
. O


Excessive O
distortions O
or O
cracking S-CONPRI
may O
lead S-MATE
to O
expensive O
rejects O
. O


In O
practice O
, O
critical O
additively B-MANP
manufactured E-MANP
parts O
are O
either O
iteratively O
pre-compensated O
or O
redesigned O
based O
on O
production S-MANP
experience O
. O


To O
satisfy O
the O
need O
for O
improved O
understanding O
of O
this O
complex O
manufacturing B-MANP
process E-MANP
, O
CAE S-ENAT
software O
providers O
have O
recently O
developed O
solutions O
to O
simulate O
the O
SLM S-MANP
process S-CONPRI
. O


ANSYS S-APPL
Additive S-MATE
Print O
and O
ANSYS S-APPL
Additive S-MATE
Suite.ANSYS O
Additive S-MATE
Print O
( O
AAP O
) O
, O
a O
user-oriented O
software S-CONPRI
, O
and O
ANSYS S-APPL
Additive S-MATE
Suite O
( O
AAS O
) O
, O
a O
software S-CONPRI
requiring O
advanced O
experience O
with O
Finite B-CONPRI
Element I-CONPRI
Methods E-CONPRI
( O
FEM S-CONPRI
) O
, O
are O
investigated O
and O
validated O
with O
regard O
to O
residual B-CONPRI
deformations E-CONPRI
. O


For O
the O
evaluation O
of O
the O
two O
programs O
, O
calibration S-CONPRI
and O
validation B-CONPRI
geometries E-CONPRI
were O
printed O
by O
SLM S-MANP
in O
Ti–6Al–4V O
and O
residual B-CONPRI
deformations E-CONPRI
have O
been O
measured O
by O
3D B-CHAR
scanning E-CHAR
. O


The O
results O
have O
been O
used O
for O
the O
calibration S-CONPRI
of O
isotropic S-PRO
and O
anisotropic S-PRO
strain O
scaling O
factors O
in O
AAP O
, O
and O
for O
sensitivity B-CONPRI
analyses E-CONPRI
on O
the O
effect O
of O
basic O
model S-CONPRI
parameters O
in O
AAS O
. O


The O
actual O
validation S-CONPRI
of O
the O
programs O
is O
performed O
on O
the O
basis O
of O
different O
sample S-CONPRI
geometries S-CONPRI
with O
varying O
wall B-FEAT
thickness E-FEAT
and O
deformation S-CONPRI
characteristic.While O
both O
simulation S-ENAT
approaches O
, O
AAP O
and O
AAS O
, O
are O
capable O
of O
predicting O
the O
qualitative S-CONPRI
characteristics O
of O
the O
residual B-CONPRI
deformations E-CONPRI
sufficiently O
well O
, O
accurate S-CHAR
quantitative O
results O
are O
difficult O
to O
obtain O
. O


AAP O
is O
more O
accessible O
and O
yields O
accurate S-CHAR
results O
within O
the O
calibrated S-CONPRI
regime O
. O


Extrapolation O
to O
other O
geometries S-CONPRI
introduces O
uncertainties O
, O
however O
. O


Numerical O
efforts O
and O
modelling S-ENAT
uncertainties O
as S-MATE
well O
as S-MATE
requirements O
for O
an O
extensive O
set S-APPL
of O
material S-MATE
parameters O
reduce O
its O
practicality O
, O
however O
. O


More O
appropriate O
calibration S-CONPRI
geometries O
, O
continuing O
extension O
of O
a O
more O
reliable O
material S-MATE
database S-ENAT
, O
improved O
user O
guidelines O
and O
increased O
numerical O
efficiency O
are O
key O
in O
the O
future O
establishment O
of O
the O
process B-ENAT
simulation E-ENAT
approaches O
in O
the O
industrial S-APPL
practice O
. O


The O
loss O
of O
elemental O
Mg S-MATE
was O
non-negligible O
during O
WAAM S-MANP
. O


With O
the O
loss O
rate O
of O
elemental O
Mg S-MATE
increasing O
, O
the O
tensile B-PRO
strength E-PRO
and O
hardness S-PRO
of O
WAAM S-MANP
component S-MACEQ
decreased O
. O


In O
WAAM S-MANP
component S-MACEQ
of O
Al-Mg B-MATE
alloy E-MATE
, O
the O
lattice S-CONPRI
parameters O
decreased O
with O
the O
Mg S-MATE
loss O
rate O
increasing O
. O


Elemental O
Mg S-MATE
is O
easily O
evaporated S-MANP
or O
burnt O
during O
welding S-MANP
or O
wire B-MANP
+ I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
, O
and O
results O
in O
a O
fluctuation O
of O
the O
composition S-CONPRI
and O
mechanical S-APPL
performances O
. O


Elemental O
Mg S-MATE
loss O
during O
the O
WAAM S-MANP
of O
Al–Mg O
alloy S-MATE
was O
investigated O
and O
the O
effect O
of O
Mg S-MATE
loss O
on O
the O
mechanical B-CONPRI
properties E-CONPRI
was O
discussed O
based O
on O
results O
from O
the O
chemical B-CONPRI
composition E-CONPRI
measurement O
and O
mechanical B-CONPRI
properties E-CONPRI
test O
. O


The O
elemental O
Mg S-MATE
distribution S-CONPRI
in O
the O
WAAM S-MANP
component S-MACEQ
was O
uniform O
, O
but O
obvious O
element S-MATE
enrichment O
occurred O
near O
the O
fusion B-CONPRI
zone E-CONPRI
of O
the O
substrate S-MATE
. O


With O
an O
increase O
in O
the O
loss O
rate O
of O
elemental O
Mg S-MATE
, O
the O
tensile B-PRO
strength E-PRO
and O
average S-CONPRI
hardness O
of O
the O
WAAM S-MANP
component S-MACEQ
decreased O
, O
whereas O
the O
elongation S-PRO
increased O
. O


During O
the O
WAAM S-MANP
of O
the O
Al–Mg O
alloy S-MATE
, O
with O
an O
increase O
in O
the O
Mg S-MATE
loss O
rate O
, O
the O
lattice S-CONPRI
parameters O
decreased O
because O
the O
solid O
solubility S-PRO
decreased O
in O
the O
Al S-MATE
matrix O
during O
the O
WAAM S-MANP
. O


Ring B-MANP
rolling E-MANP
is O
a O
flexible O
forming B-MANP
process E-MANP
used O
to O
produce O
seamless O
rings O
with O
various O
dimensions S-FEAT
and O
cross B-CONPRI
sections E-CONPRI
. O


For O
smaller O
rings O
of O
up O
to O
500 O
mm S-MANP
diameter S-CONPRI
, O
mechanical S-APPL
ring O
rolling S-MANP
machines S-MACEQ
can O
be S-MATE
used O
. O


A O
special O
design S-FEAT
is O
a O
4-mandrel-table O
rolling B-MACEQ
mill E-MACEQ
, O
which O
achieves O
high O
productivity S-CONPRI
due O
to O
the O
fact O
that O
the O
precursor S-MATE
rings O
are O
continuously O
conveyed O
through O
the O
roll O
gap O
by O
rotation O
of O
the O
table O
. O


The O
mechanical S-APPL
machines S-MACEQ
are O
usually O
integrated O
into O
a O
process B-ENAT
chain E-ENAT
that O
involves O
shearing S-MANP
of O
blocks O
, O
forging S-MANP
of O
blanks O
and O
ring B-MANP
rolling E-MANP
as S-MATE
the O
final O
process S-CONPRI
step O
. O


Especially O
profiled O
cross B-CONPRI
sections E-CONPRI
may O
require O
multiple O
forming S-MANP
steps O
to O
reach O
the O
final O
ring O
geometry S-CONPRI
. O


To O
increase O
the O
flexibility S-PRO
of O
the O
process S-CONPRI
, O
it O
seems O
viable O
to O
use O
highly O
productive O
additive B-MANP
manufacturing I-MANP
processes E-MANP
such O
as S-MATE
wire-arc O
additive B-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
to O
produce O
pre-forms O
for O
the O
ring B-MANP
rolling E-MANP
process S-CONPRI
. O


WAAM S-MANP
is O
based O
on O
arc B-MANP
welding E-MANP
and O
allows O
for O
processing O
various B-MATE
materials E-MATE
with O
high B-PARA
deposition I-PARA
rates E-PARA
. O


In O
this O
case O
, O
a O
more O
complex O
cross B-CONPRI
section E-CONPRI
can O
be S-MATE
manufactured O
, O
so O
that O
a O
single O
ring B-MANP
rolling E-MANP
stage O
may O
be S-MATE
sufficient O
. O


However O
, O
no O
previous O
research S-CONPRI
on O
ring B-MANP
rolling E-MANP
of O
additively B-MANP
manufactured E-MANP
pre-form O
is O
known O
. O


The O
present O
contribution O
aims O
at O
analyzing O
the O
hot B-MANP
forming E-MANP
behavior O
of O
pre-forms O
made O
by O
WAAM S-MANP
during O
ring B-MANP
rolling E-MANP
. O


The O
microstructure B-CONPRI
evolution E-CONPRI
and O
the O
achieved O
mechanical B-CONPRI
properties E-CONPRI
will O
be S-MATE
evaluated O
. O


The O
goal O
of O
this O
project O
is O
to O
determine O
the O
efficiency O
of O
3D B-MANP
printed E-MANP
welding O
jigs S-MACEQ
in O
pre-series O
body O
shops O
. O


The O
design S-FEAT
of O
these O
jigs S-MACEQ
and O
how O
they O
function O
compared O
to O
conventional O
jig S-MACEQ
systems O
is O
analyzed O
. O


Additive B-APPL
manufactured I-APPL
parts E-APPL
possess O
the O
advantage O
of O
easier O
production S-MANP
of O
complex O
parts O
which O
would O
serve O
the O
purpose O
of O
designing O
custom O
jigs S-MACEQ
for O
different O
intricate O
detailed O
parts O
with O
odd O
orientations S-CONPRI
. O


While O
machining S-MANP
custom O
jigs S-MACEQ
can O
be S-MATE
costly O
, O
3D B-MANP
printing E-MANP
these O
jigs S-MACEQ
provides O
precision S-CHAR
as S-MATE
well O
as S-MATE
reduces O
costs O
and O
setup O
time O
since O
they O
are O
designed S-FEAT
for O
their O
specific O
application O
. O


Large O
components S-MACEQ
can O
be S-MATE
made O
by O
laser B-MANP
welding E-MANP
EBM-built O
plates O
to O
wrought S-CONPRI
counterparts O
. O


Influence O
of O
the O
welding S-MANP
angles O
between O
EBM S-MANP
build B-PARA
direction E-PARA
and O
weld B-CONPRI
bead E-CONPRI
was O
studied O
. O


Microhardness S-CONPRI
of O
each O
zone O
is O
determined O
by O
the O
local O
microstructure S-CONPRI
. O


Tensile B-PRO
properties E-PRO
depend O
on O
the O
EBM S-MANP
base B-MATE
metal E-MATE
due O
to O
the O
internal O
defects S-CONPRI
. O


The O
mechanism S-CONPRI
of O
stress S-PRO
during O
uniaxial O
tension O
is O
discussed O
based O
on O
columnar B-PRO
grains E-PRO
and O
the O
internal O
defects S-CONPRI
. O


Electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
is O
an O
established O
powder-bed O
additive B-MANP
manufacturing I-MANP
process E-MANP
for O
small-to-medium-sized O
components S-MACEQ
of O
Ti-6Al-4V S-MATE
. O


For O
further O
employing O
EBM S-MANP
on O
fabricating S-MANP
large-scale O
components S-MACEQ
, O
an O
effort O
has O
been O
made O
by O
joining S-MANP
EBM-built O
Ti-6Al-4V S-MATE
plates O
to O
wrought S-CONPRI
counterparts O
using O
laser B-MANP
welding E-MANP
, O
and O
the O
welding S-MANP
angles O
between O
EBM S-MANP
build B-PARA
direction E-PARA
and O
weld B-CONPRI
bead E-CONPRI
have O
been O
chosen O
as S-MATE
0° O
, O
30° O
and O
45° O
. O


The O
influence O
of O
the O
welding S-MANP
angles O
on O
the O
microstructure S-CONPRI
, O
microhardness S-CONPRI
of O
base B-MATE
metals E-MATE
, O
fusion B-CONPRI
zone E-CONPRI
, O
and O
heat-affected O
zones O
, O
as S-MATE
well O
as S-MATE
the O
macro S-FEAT
tensile O
test O
have O
been O
characterized O
. O


The O
microhardness S-CONPRI
of O
each O
zone O
is O
determined O
by O
the O
local O
microstructure S-CONPRI
, O
and O
the O
macro S-FEAT
tensile O
properties S-CONPRI
largely O
depend O
on O
the O
EBM S-MANP
base B-MATE
metal E-MATE
due O
to O
the O
internal O
defects S-CONPRI
generated O
during O
the O
EBM S-MANP
process O
. O


The O
effect O
of O
welding S-MANP
angles O
on O
tensile B-PRO
strengths E-PRO
is O
not O
significant O
, O
while O
the O
elongation S-PRO
drops O
from O
9.4 O
% O
to O
5.8 O
% O
as S-MATE
the O
welding S-MANP
angle O
increases O
from O
0° O
to O
45° O
. O


The O
mechanism S-CONPRI
of O
stress S-PRO
during O
uniaxial O
tension O
on O
EBM S-MANP
base B-MATE
metal E-MATE
is O
discussed O
based O
on O
the O
stress S-PRO
state O
of O
columnar B-PRO
grains E-PRO
and O
the O
internal O
defects S-CONPRI
. O


Wire-arc B-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
has O
received O
substantial O
attention O
in O
recent O
years O
due O
to O
the O
very O
high O
build B-CHAR
rates E-CHAR
. O


When O
bulky O
structures O
are O
generated O
using O
standard S-CONPRI
layer-by-layer S-CONPRI
tool O
paths O
, O
the O
build B-CHAR
rate E-CHAR
in O
the O
outer O
contour S-FEAT
of O
the O
part O
may O
lag O
behind O
the O
build B-CHAR
rate E-CHAR
in O
the O
interior O
. O


In O
WAAM S-MANP
, O
the O
profile S-FEAT
of O
a O
single O
weld B-CONPRI
bead E-CONPRI
resembles O
a O
parabola O
. O


In O
order O
to O
keep O
the O
build B-CHAR
rate E-CHAR
constant O
at O
each O
point O
of O
the O
layer S-PARA
, O
optimal O
overlapping O
distances O
can O
be S-MATE
determined O
. O


This O
paper O
presents O
novel O
multi-bead O
overlapping O
models O
for O
tool B-CONPRI
path E-CONPRI
generation O
. O


Mathematical S-CONPRI
models O
are O
established O
to O
minimize O
valleys O
between O
adjacent O
weld B-CONPRI
beads E-CONPRI
by O
accounting O
for O
the O
overlapping O
volume S-CONPRI
. O


The O
proposed O
models O
are O
validated O
by O
manufacturing S-MANP
solid O
blocks O
from O
mild B-MATE
steel E-MATE
with O
the O
recommended O
overlapping O
distances O
. O


Macrographs O
are O
recorded O
to O
analyze O
the O
boundary S-FEAT
profiles O
. O


High-integrity O
ceramic-metal S-MATE
composites O
combine O
electrical S-APPL
, O
thermal O
, O
and O
corrosion B-CONPRI
resistance E-CONPRI
with O
excellent O
mechanical S-APPL
robustness O
. O


Ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
( O
UAM S-MANP
) O
is O
a O
low O
temperature S-PARA
process S-CONPRI
that O
enables O
dissimilar O
material S-MATE
welds O
without O
inducing O
brittle S-PRO
phases O
. O


In O
this O
study O
, O
multiple O
layers O
of O
Yttria-stabilized O
zirconia S-MATE
( O
YSZ S-MATE
) O
films O
are O
jointed O
between O
layers O
of O
Al S-MATE
6061-H18 O
matrix O
using O
a O
9 O
kW O
UAM S-MANP
system O
. O


UAM S-MANP
is O
advantageous O
over O
existing O
metal-ceramic O
composite S-MATE
fabrication O
techniques O
by O
continuously O
joining S-MANP
ceramics S-MATE
to O
metals S-MATE
at O
a O
speed O
of O
2 O
m/min O
while O
requiring O
a O
moderate O
temperature S-PARA
that O
is O
55 O
% O
of O
the O
melting B-PRO
point E-PRO
of O
aluminum S-MATE
. O


The O
welding B-FEAT
interface E-FEAT
, O
which O
is O
found O
to O
include O
a O
10 O
nm O
thick O
diffusion S-CONPRI
zone O
, O
is O
investigated O
using O
optical B-CHAR
microscopy E-CHAR
and O
energy-dispersive O
X-ray S-CHAR
( O
EDX S-CHAR
) O
spectroscopy S-CONPRI
. O


The O
shear B-PRO
strengths E-PRO
of O
the O
as-welded O
and O
heat-treated S-MANP
composites S-MATE
are O
72 O
MPa S-CONPRI
and O
103 O
MPa S-CONPRI
, O
respectively O
. O


The O
shear O
deformation S-CONPRI
and O
failure B-PRO
mechanism E-PRO
of O
the O
YSZ-Al O
composites S-MATE
are O
investigated O
via O
finite B-CONPRI
element E-CONPRI
modeling O
. O


Additive B-MANP
manufacturing E-MANP
based O
method O
was O
used O
to O
join O
Polypropylene S-MATE
to O
Al-Mg B-MATE
alloy E-MATE
. O


Obtained O
joint S-CONPRI
was O
a O
combination O
of O
welding S-MANP
and O
mechanical S-APPL
lock O
among O
constituents O
. O


Additive S-MATE
filling O
pattern S-CONPRI
and O
printing O
temperature S-PARA
affected O
mechanical S-APPL
behavior O
. O


Introduced O
method O
was O
a O
fast O
and O
versatile O
technique O
for O
joining S-MANP
metal O
to O
polymer S-MATE
. O


Fused B-MANP
Deposition I-MANP
Modeling E-MANP
with O
Polypropylene B-MATE
filament E-MATE
was O
employed O
to O
make O
a O
lap S-CONPRI
joint S-CONPRI
between O
Polypropylene S-MATE
and O
pre-punched O
Al-Mg B-MATE
alloy E-MATE
sheets O
, O
in O
the O
form O
of O
bonds O
between O
the O
polymeric O
substrate S-MATE
and O
the O
additive S-MATE
part O
and O
mechanical S-APPL
lock O
between O
the O
additive S-MATE
part O
and O
aluminum S-MATE
base O
sheet S-MATE
. O


Effects O
of O
the O
joint B-CONPRI
interface E-CONPRI
area S-PARA
( O
hole O
diameter S-CONPRI
of O
5–13 O
mm S-MANP
) O
and O
preheating S-MANP
of O
the O
substrates O
( O
room O
temperature S-PARA
, O
50 O
and O
90℃ O
) O
were O
investigated O
on O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
joints O
. O


Peak O
load O
in O
the O
tensile-shear O
and O
cross-tension O
tests O
increased O
with O
enhancement O
of O
the O
joint B-CONPRI
interface E-CONPRI
area S-PARA
( O
up O
to O
˜280 O
N S-MATE
and O
˜160 O
N S-MATE
, O
respectively O
) O
. O


Preheating S-MANP
of O
the O
substrates O
increased O
the O
joint S-CONPRI
strength O
via O
improvement O
in O
the O
bonds O
between O
the O
polymer S-MATE
sheet O
and O
the O
additive S-MATE
part O
and O
increase O
in O
the O
adhesion S-PRO
force O
between O
the O
printed O
layers O
. O


Tungsten S-MATE
is O
receiving O
increasing O
interest O
as S-MATE
a O
plasma S-CONPRI
facing S-MANP
material O
in O
the O
ITER O
fusion S-CONPRI
reactor O
, O
collimators O
, O
and O
other O
structural O
, O
high O
temperature S-PARA
applications O
. O


Concurrently O
, O
there O
is O
a O
demand O
for O
manufacturing S-MANP
techniques O
capable O
of O
processing O
tungsten S-MATE
into O
the O
desired O
geometries S-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
is O
a O
promising O
technique O
able O
to O
produce O
complex O
parts O
, O
but O
the O
structural B-PRO
integrity E-PRO
is O
compromised O
by O
microcracking O
. O


This O
work O
combines O
thermomechanical S-CONPRI
simulations S-ENAT
with O
in B-CONPRI
situ E-CONPRI
high-speed O
video O
of O
microcracking O
in O
single O
laser-melted O
tracks O
, O
visualizing O
the O
ductile-to-brittle O
transition S-CONPRI
. O


Microcracking O
is O
shown O
to O
occur O
in O
a O
narrow O
temperature S-PARA
interval O
between O
450 O
K S-MATE
– O
650 O
K S-MATE
, O
and O
to O
be S-MATE
strain O
rate O
dependent O
. O


The O
size O
of O
the O
crack-affected O
area S-PARA
around O
the O
scan O
track O
is O
determined O
by O
the O
maximum O
Von O
Mises O
residual B-PRO
stress E-PRO
, O
whereas O
crack O
network O
morphology S-CONPRI
depends O
on O
the O
local B-CONPRI
orientation E-CONPRI
of O
the O
principal B-PRO
stress E-PRO
. O


The O
fundamental O
understanding O
provided O
by O
this O
work O
contributes O
to O
future O
efforts O
in O
crack O
free O
, O
additively B-MANP
manufactured E-MANP
tungsten O
. O


Due O
to O
rapid O
, O
localized O
heating S-MANP
and O
cooling S-MANP
, O
distortions O
accumulate O
in O
additive B-MANP
manufactured E-MANP
laser O
metal B-CONPRI
deposition E-CONPRI
( O
LMD S-MANP
) O
components S-MACEQ
, O
leading O
to O
a O
loss O
of O
dimensional B-CHAR
accuracy E-CHAR
or O
even O
cracking S-CONPRI
. O


Numerical O
welding S-MANP
simulations S-ENAT
allow O
the O
prediction S-CONPRI
of O
these O
deviations O
and O
their O
optimization S-CONPRI
before O
conducting O
experiments O
. O


To O
assess O
the O
viability O
of O
the O
simulation S-ENAT
tool O
for O
the O
use O
in O
a O
predictive O
manner O
, O
comprehensive O
validations O
with O
experimental S-CONPRI
results O
on O
the O
newly-built O
part O
need O
to O
be S-MATE
conducted.In O
this O
contribution O
, O
a O
predictive O
, O
mechanical S-APPL
simulation O
of O
a O
thin-walled O
, O
curved O
LMD S-MANP
geometry S-CONPRI
is O
shown O
for O
a O
30-layer O
sample S-CONPRI
of O
1.4404 O
stainless B-MATE
steel E-MATE
. O


The O
part O
distortions O
are O
determined O
experimentally O
via O
an O
in-situ S-CONPRI
digital B-CONPRI
image I-CONPRI
correlation E-CONPRI
measurement O
using O
the O
GOM O
Aramis O
system O
and O
compared O
with O
the O
simulation S-ENAT
results O
. O


With O
this O
benchmark S-MANS
, O
the O
performance S-CONPRI
of O
a O
numerical O
welding S-MANP
simulation S-ENAT
in O
additive B-MANP
manufacturing E-MANP
is O
discussed O
in O
terms O
of O
result O
accuracy S-CHAR
and O
usability O
. O


Welding S-MANP
of O
dissimilar O
metals S-MATE
is O
challenging O
, O
particularly O
between O
crystalline O
metals S-MATE
and O
metallic B-MATE
glasses E-MATE
( O
MGs O
) O
. O


In O
this O
study O
, O
Zr65.7Cu15.6Ni11.7Al3.7Ti3.3 O
( O
wt O
% O
) O
MG S-MATE
structures O
were O
built O
on O
304 O
stainless B-MATE
steel E-MATE
( O
SS S-MATE
) O
substrates O
by O
laser-foil-printing O
( O
LFP S-MATE
) O
additive B-MANP
manufacturing E-MANP
technology O
in O
which O
MG S-MATE
foils O
were O
laser S-ENAT
welded O
layer-by-layer S-CONPRI
onto O
the O
SS S-MATE
substrate O
with O
a O
transition S-CONPRI
route O
, O
i.e. O
, O
SS S-MATE
→ O
V S-MATE
→ O
Ti S-MATE
→ O
Zr S-MATE
→ O
MG S-MATE
. O


The O
direct O
welding S-MANP
of O
MG S-MATE
on O
SS S-MATE
would O
lead S-MATE
to O
the O
formation O
of O
various O
brittle S-PRO
intermetallics O
and O
the O
consequent O
peeling O
off O
of O
the O
welded S-MANP
MG S-MATE
foils O
from O
the O
SS S-MATE
substrate O
, O
which O
could O
be S-MATE
resolved O
via O
the O
use O
of O
V/Ti/Zr O
intermediate O
layers O
. O


The O
chemical B-CONPRI
composition E-CONPRI
, O
formed O
phases O
, O
and O
micro-hardness O
were O
characterized O
in O
the O
dissimilar O
joints O
by O
energy B-CHAR
dispersive I-CHAR
spectroscopy E-CHAR
, O
X-ray B-CHAR
diffraction E-CHAR
, O
and O
micro-indentation O
. O


Since O
the O
intermediate O
materials S-CONPRI
were O
highly O
compatible O
with O
the O
base B-MATE
metals E-MATE
or O
the O
adjacent O
intermediate O
metals S-MATE
, O
undesirable O
intermetallics S-MATE
were O
not O
detected O
in O
the O
dissimilar O
joint S-CONPRI
. O


The O
bonding S-CONPRI
tensile O
strength S-PRO
between O
the O
SS S-MATE
substrate O
and O
the O
MG S-MATE
part O
with O
intermediate O
layers O
was O
measured O
about O
477 O
MPa S-CONPRI
. O


The O
manufacturing S-MANP
of O
components S-MACEQ
from O
the O
titanium B-MATE
alloy I-MATE
Ti-6Al-4 I-MATE
V E-MATE
is O
of O
great O
significance O
for O
many O
industrial B-CONPRI
sectors E-CONPRI
. O


The O
production S-MANP
of O
high-performance O
Ti-6Al-4 B-MATE
V E-MATE
components S-MACEQ
typically O
requires O
multiple O
hot O
forging S-MANP
steps O
and O
leads O
to O
parts O
with O
tolerances S-PARA
that O
need O
extensive O
machining S-MANP
to O
create O
the O
final O
shape O
. O


For O
many O
applications O
, O
net-shape O
technologies S-CONPRI
such O
as S-MATE
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
could O
enable O
a O
higher O
material S-MATE
yield O
. O


Thus O
, O
the O
advantages O
of O
AM S-MANP
and O
forging S-MANP
operations O
could O
be S-MATE
exploited O
by O
combining O
both O
processes S-CONPRI
to O
new O
hybrid O
process B-ENAT
chains E-ENAT
. O


The O
present O
study O
investigates S-CONPRI
the O
use O
of O
Wire-Arc B-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
for O
hybrid B-CONPRI
manufacturing E-CONPRI
of O
Ti-6Al-4 B-MATE
V E-MATE
aerospace B-MACEQ
components E-MACEQ
. O


Two O
process S-CONPRI
routes O
are O
investigated O
that O
combine O
forming S-MANP
and O
AM B-MANP
processes E-MANP
. O


In O
the O
first O
process S-CONPRI
route O
, O
a O
WAAM S-MANP
process S-CONPRI
is O
used O
to O
generate O
a O
pre-shaped O
semi-finished O
part O
. O


The O
semi-finished O
part O
will O
then O
be S-MATE
forged O
using O
a O
single O
forming S-MANP
tool O
to O
obtain O
the O
final O
part O
contour S-FEAT
. O


The O
second O
process S-CONPRI
route O
utilizes O
a O
conventionally O
forged O
pre-form O
, O
onto O
which O
features O
of O
the O
final O
workpiece S-CONPRI
are O
added O
using O
WAAM S-MANP
. O


The O
results O
confirm O
that O
hybrid B-ENAT
technologies E-ENAT
combining O
WAAM S-MANP
and O
forging S-MANP
are O
very O
promising O
for O
Ti-6Al-4 B-MATE
V E-MATE
part O
production S-MANP
. O


A O
jet O
engine O
blade O
produced O
by O
WAAM S-MANP
and O
subsequent O
forging S-MANP
shows O
microstructures S-MATE
typically O
produced O
in O
conventional O
processing O
of O
Ti-6Al-4 B-MATE
V I-MATE
alloy E-MATE
and O
exhibits O
tensile B-PRO
properties E-PRO
, O
which O
exceed O
the O
specification S-PARA
level O
of O
cast S-MANP
and O
forged O
Ti-6Al-4 B-MATE
V E-MATE
material S-MATE
. O


Features O
created O
by O
WAAM S-MANP
on O
forged O
pre-forms O
are O
shown O
to O
reach O
the O
mechanical B-CONPRI
properties E-CONPRI
required O
to O
combine O
both O
technologies S-CONPRI
. O


The O
combination O
of O
WAAM S-MANP
and O
forging S-MANP
may O
hence O
be S-MATE
used O
to O
develop O
new O
manufacturing B-CONPRI
chains E-CONPRI
that O
allow O
for O
higher O
material S-MATE
yield O
and O
flexibility S-PRO
than O
conventional O
forging S-MANP
. O


This O
paper O
explores O
the O
application O
of O
the O
‘ O
mortise-and-tenon O
’ O
concept O
for O
joining S-MANP
hollow O
section O
aluminium S-MATE
profiles O
to O
composite S-MATE
strips O
or O
sheets S-MATE
. O


Wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
is O
combined O
with O
joining S-MANP
by O
forming S-MANP
to O
fabricate S-MANP
the O
tenons O
and O
to O
obtain O
the O
mechanical S-APPL
interlocking O
with O
the O
mortises O
available O
in O
the O
strips O
( O
or O
sheets S-MATE
) O
. O


The O
workability O
limits S-CONPRI
are O
established O
by O
means O
of O
an O
analytical O
model S-CONPRI
that O
combines O
plastic B-PRO
deformation E-PRO
, O
instability O
and O
fracture S-CONPRI
. O


Experimental S-CONPRI
and O
finite B-CHAR
element I-CHAR
modelling E-CHAR
are O
utilized O
to O
develop O
the O
overall O
joining S-MANP
process O
and O
to O
validate O
the O
round O
‘ O
mortise-and-tenon O
’ O
design S-FEAT
resulting O
from O
the O
analytical O
model S-CONPRI
. O


The O
proposed O
joining S-MANP
process O
also O
circumvents O
the O
need O
to O
design S-FEAT
extra O
fixing O
and O
interlocking O
features O
in O
low O
cost O
hollow O
section O
aluminium S-MATE
profiles O
for O
easy O
assembling O
. O


There O
exist O
several O
variants O
of O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
applicable O
for O
metals S-MATE
and O
alloys S-MATE
. O


The O
two O
main O
groups O
are O
Directed B-MANP
Energy I-MANP
Deposition E-MANP
( O
DED S-MANP
) O
and O
Powder B-MANP
Bed I-MANP
Fusion E-MANP
( O
PBF S-MANP
) O
. O


AM S-MANP
has O
advantages O
and O
disadvantages O
when O
compared O
to O
more O
traditional B-MANP
manufacturing E-MANP
methods O
. O


The O
best O
candidate O
products O
are O
those O
with O
complex B-PRO
shape E-PRO
and O
small O
series O
and O
particularly O
individualized O
product O
. O


Repair O
welding S-MANP
is O
often O
individualized O
as S-MATE
defects O
may O
occur O
at O
various O
instances O
in O
a O
component S-MACEQ
. O


This O
method O
was O
used O
before O
it O
became O
categorized O
as S-MATE
AM S-MANP
and O
in O
most O
cases O
, O
it O
is O
a O
DED S-MANP
process O
. O


PBF S-MANP
processes O
are O
more O
useful O
for O
smaller O
items O
and O
can O
give O
a O
finer O
surface S-CONPRI
. O


Both O
DED S-MANP
and O
PBF S-MANP
products O
require O
subsequent O
surface B-MANP
finishing E-MANP
for O
high O
performance S-CONPRI
components S-MACEQ
and O
sometimes O
there O
is O
also O
a O
need O
for O
post O
heat B-MANP
treatment E-MANP
. O


Modelling S-ENAT
of O
AM S-MANP
as O
well O
as S-MATE
eventual O
post-processes O
can O
be S-MATE
of O
use O
in O
order O
to O
improve O
product B-CONPRI
quality E-CONPRI
, O
reducing O
costs O
and O
material S-MATE
waste O
. O


The O
paper O
describes O
the O
use O
of O
the O
finite B-CONPRI
element I-CONPRI
method E-CONPRI
to O
simulate O
these O
processes S-CONPRI
with O
focus O
on O
superalloys S-MATE
. O


Additive B-MANP
Manufacturing E-MANP
has O
recently O
emerged O
as S-MATE
an O
important O
industrial S-APPL
process O
that O
is O
capable O
of O
manufacturing S-MANP
parts O
with O
complex B-CONPRI
geometry E-CONPRI
. O


One O
of O
the O
drawbacks O
of O
metal B-MANP
additive I-MANP
manufacturing E-MANP
processes O
is O
the O
thermo-mechanical B-CONPRI
distortion E-CONPRI
of O
the O
parts O
during O
and O
after O
build S-PARA
due O
to O
heat S-CONPRI
effects O
. O


Inherent O
strain S-PRO
is O
widely O
adopted O
by O
researchers O
as S-MATE
the O
basis O
to O
predict O
part O
distortions O
during O
Metal B-MANP
Powder I-MANP
Bed I-MANP
Fusion I-MANP
Additive I-MANP
Manufacturing E-MANP
( O
PBFAM O
) O
process S-CONPRI
and O
is O
highly O
dependent O
on O
the O
laser S-ENAT
hatch O
pattern S-CONPRI
sintering O
on O
each O
layer S-PARA
during O
the O
printing B-MANP
process E-MANP
. O


There O
is O
a O
clear O
need O
to O
predict O
inherent O
strains O
for O
a O
given O
arbitrary O
hatch O
pattern S-CONPRI
for O
a O
part O
model S-CONPRI
so O
that O
hatch O
patterns O
can O
be S-MATE
optimized O
for O
achieving O
part O
quality S-CONPRI
. O


In O
this O
paper O
, O
we O
propose O
a O
neural B-CONPRI
network E-CONPRI
based O
method O
to O
predict O
inherent O
strain S-PRO
for O
any O
given O
hatch O
pattern S-CONPRI
that O
is O
adopted O
during O
the O
part O
build S-PARA
. O


The O
authors O
assumed O
that O
the O
temperature S-PARA
profile S-FEAT
inside O
the O
heat B-CONPRI
affected I-CONPRI
zone E-CONPRI
within O
each O
layer S-PARA
is O
the O
same O
if O
the O
part O
model S-CONPRI
is O
reasonably O
large O
. O


To O
start O
with O
, O
inherent O
strains O
of O
two O
hatch O
pattern S-CONPRI
pools O
with O
different O
hatch O
angles O
were O
obtained O
by O
thermo-mechanical S-CONPRI
simulation S-ENAT
with O
temperature S-PARA
profiles S-FEAT
obtained O
through O
translation O
and O
rotation O
of O
a O
single O
layer S-PARA
of O
simulation S-ENAT
. O


A O
feedforward O
backpropagation O
neural B-CONPRI
network E-CONPRI
was O
created O
and O
trained O
with O
data S-CONPRI
obtained O
from O
an O
initial O
hatch O
pattern S-CONPRI
pool O
for O
predicting O
inherent O
strains O
. O


The O
data S-CONPRI
from O
a O
second O
hatch O
pattern S-CONPRI
pool O
was O
then O
utilized O
to O
validate O
the O
network O
and O
test O
the O
efficacy O
of O
the O
prediction S-CONPRI
of O
the O
trained O
neural B-CONPRI
network E-CONPRI
. O


The O
results O
show O
that O
the O
trained O
neural B-CONPRI
network E-CONPRI
is O
capable O
of O
predicting O
the O
inherent O
strain S-PRO
of O
any O
arbitrary O
hatch O
pattern S-CONPRI
within O
an O
acceptable O
error S-CONPRI
. O


Since O
the O
trained O
neural B-CONPRI
network E-CONPRI
can O
predict O
inherent O
strain S-PRO
quickly O
for O
any O
given O
hatch O
pattern S-CONPRI
, O
this O
could O
provide O
the O
basis O
for O
hatch O
pattern B-CONPRI
optimization E-CONPRI
of O
any O
part O
model S-CONPRI
to O
increase O
part O
build S-PARA
accuracy S-CHAR
and O
achieve O
part O
GD S-MATE
& O
T O
callouts O
. O


An O
innovative O
manufacturing B-MANP
process E-MANP
among O
the O
metal S-MATE
3D B-MANP
printing E-MANP
techniques O
for O
stainless B-MATE
steel E-MATE
material S-MATE
is O
first O
introduced O
in O
Structural B-CONPRI
Engineering E-CONPRI
field O
. O


For O
structural B-FEAT
design E-FEAT
purposes O
, O
the O
main O
issues O
in O
the O
realization O
of O
Wire-and-Arc O
Additive B-MANP
Manufactured E-MANP
stainless O
steel S-MATE
concern O
inherent O
geometrical O
imperfections S-CONPRI
to O
be S-MATE
properly O
characterized O
and O
the O
main O
material B-CONPRI
properties E-CONPRI
, O
influenced O
by O
the O
orientation S-CONPRI
of O
the O
elements S-MATE
. O


The O
first O
results O
of O
a O
wide O
experimental S-CONPRI
campaign O
devoted O
to O
assess O
the O
geometrical O
and O
mechanical S-APPL
characterization O
of O
Wire-and-Arc O
Additive B-MANP
Manufactured E-MANP
stainless O
steel B-MATE
elements E-MATE
evidence O
the O
need O
of O
proper O
evaluation O
of O
an O
effective O
geometry S-CONPRI
to O
derive O
the O
main O
mechanical S-APPL
parameters O
, O
which O
differ O
from O
the O
traditionally O
manufactured S-CONPRI
stainless O
steel B-MATE
material E-MATE
. O


Additive B-MANP
Manufacturing E-MANP
has O
recently O
gained O
great O
importance O
to O
produce O
metallic S-MATE
structural O
elements S-MATE
for O
civil O
engineering S-APPL
applications O
. O


While O
a O
lot O
of O
research S-CONPRI
effort O
has O
been O
focused O
on O
different O
technologies S-CONPRI
( O
such O
as S-MATE
Powder O
Bed B-MANP
Fusion E-MANP
) O
, O
there O
is O
still O
quite O
limited O
knowledge O
concerning O
the O
structural O
response O
of O
Wire-and-Arc O
Additive B-MANP
Manufactured E-MANP
( O
WAAM S-MANP
) O
metallic B-MATE
elements E-MATE
, O
as S-MATE
very O
few O
experimental S-CONPRI
campaigns O
aimed O
at O
assessing O
their O
geometrical O
and O
mechanical B-CONPRI
properties E-CONPRI
have O
been O
carried O
out O
. O


The O
paper O
presents O
selected O
results O
of O
a O
wide O
experimental S-CONPRI
campaign O
focused O
on O
the O
assessment O
of O
the O
main O
geometrical O
and O
mechanical B-CONPRI
properties E-CONPRI
of O
Wire-and-Arc O
Additive B-MANP
Manufactured E-MANP
( O
WAAM S-MANP
) O
stainless B-MATE
steel E-MATE
material S-MATE
, O
carried O
out O
at O
the O
Topography S-CHAR
and O
Structural B-CONPRI
Engineering E-CONPRI
Labs O
of O
University O
of O
Bologna O
. O


In O
detail O
, O
the O
focus O
is O
on O
the O
characterization O
of O
the O
surface S-CONPRI
irregularities O
by O
means O
of O
various O
measuring O
techniques O
and O
on O
the O
evaluation O
of O
the O
main O
material S-MATE
mechanical O
properties S-CONPRI
, O
including O
tensile S-PRO
and O
compressive B-PRO
strengths E-PRO
, O
Young O
's O
modulus O
and O
post O
elastic S-PRO
behavior O
. O


Tests O
results O
have O
been O
interpreted O
through O
statistical O
tools S-MACEQ
in O
order O
to O
derive O
mean O
values O
and O
gather O
information O
about O
the O
variability S-CONPRI
of O
both O
geometrical O
and O
mechanical S-APPL
parameters O
. O


In O
this O
work O
, O
rapid B-ENAT
prototyping E-ENAT
and O
physical O
modelling S-ENAT
are O
used O
to O
evaluate O
four O
different O
extruder S-MACEQ
and O
deposition S-CONPRI
concepts O
for O
the O
Hybrid O
Metal S-MATE
Extrusion S-MANP
& O
Bonding S-CONPRI
( O
HYB O
) O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
process S-CONPRI
for O
aluminium B-MATE
alloys E-MATE
. O


The O
HYB-AM O
process S-CONPRI
is O
a O
branch O
of O
the O
HYB O
joining S-MANP
technology O
and O
is O
currently O
utilizing O
an O
extruder S-MACEQ
design S-FEAT
that O
was O
initially O
developed O
for O
welding S-MANP
purposes O
. O


However O
, O
due O
to O
the O
different O
operating O
conditions O
of O
an O
AM B-MANP
process E-MANP
compared O
to O
a O
welding S-MANP
process S-CONPRI
, O
it O
is O
of O
interest O
to O
compare O
the O
current O
extruder S-MACEQ
to O
that O
of O
other O
alternatives O
to O
identify O
the O
optimal O
design S-FEAT
. O


Plastic S-MATE
models O
of O
the O
different O
extruders O
have O
been O
produced O
by O
rapid B-ENAT
prototyping E-ENAT
and O
attached O
to O
a O
CNC-machine O
. O


To O
test O
the O
performance S-CONPRI
of O
each O
design S-FEAT
, O
plasticine O
has O
been O
processed S-CONPRI
through O
the O
extruders O
and O
deposited O
on O
the O
machine S-MACEQ
bed S-MACEQ
. O


Key O
learnings O
from O
each O
cycle O
of O
designing O
, O
building O
and O
testing S-CHAR
have O
been O
used O
as S-MATE
inputs O
for O
the O
next O
iteration O
, O
to O
finally O
end O
up O
with O
a O
design S-FEAT
and O
the O
associated O
requirements O
upon O
which O
the O
further O
development O
process S-CONPRI
will O
be S-MATE
based O
. O


Qualitative S-CONPRI
study O
of O
the O
mechanism S-CONPRI
of O
surface B-PRO
tension E-PRO
driven O
flow O
. O


Analysis O
of O
driving O
forces S-CONPRI
and O
driving O
mechanism S-CONPRI
. O


Quantitative S-CONPRI
investigation O
of O
surface B-PRO
tension E-PRO
and O
surface S-CONPRI
shear B-PRO
stress E-PRO
distribution S-CONPRI
. O


3D S-CONPRI
distribution O
of O
solidification B-CONPRI
parameters E-CONPRI
. O


Semi-qualitatively O
prediction S-CONPRI
of O
solidified B-PRO
microstructure E-PRO
. O


A O
transient B-CONPRI
three-dimensional E-CONPRI
thermal-fluid-metallurgy O
model S-CONPRI
was O
proposed O
to O
study O
the O
surface B-PRO
tension E-PRO
driven O
flow O
and O
welding S-MANP
metallurgical S-APPL
behavior O
during O
laser S-ENAT
linear O
welding S-MANP
of O
304 O
stainless B-MATE
steel E-MATE
. O


Numerical B-ENAT
simulation E-ENAT
and O
experimental S-CONPRI
method O
were O
both O
used O
to O
investigate O
the O
thermal O
behavior O
, O
surface B-PRO
tension E-PRO
driven O
flow O
, O
driving O
mechanism S-CONPRI
and O
solidification S-CONPRI
characteristics O
. O


The O
temperature S-PARA
related O
driving O
force S-CONPRI
was O
qualitatively O
analyzed O
, O
and O
surface B-PRO
tension E-PRO
and O
surface S-CONPRI
shear B-PRO
stress E-PRO
were O
quantitatively S-CONPRI
studied O
. O


Numerical O
method O
and O
dimensional B-CHAR
analysis E-CHAR
were O
also O
carried O
out O
to O
understand O
the O
importance O
of O
different O
driving O
forces S-CONPRI
, O
respectively O
. O


The O
metallurgical S-APPL
model O
was O
sequentially O
coupled O
to O
the O
thermal-fluid O
model S-CONPRI
to O
calculate O
four O
solidification B-CONPRI
parameters E-CONPRI
. O


Temperature B-PARA
gradient E-PARA
was O
observed O
to O
be S-MATE
much O
larger O
at O
the O
front O
of O
the O
melt B-MATE
pool E-MATE
due O
to O
the O
effect O
of O
thermal B-PRO
conductivity E-PRO
, O
and O
decreased O
from O
center O
to O
the O
periphery O
. O


Both O
the O
surface B-PRO
tension E-PRO
and O
surface B-PRO
tension E-PRO
driven O
flow O
were O
found O
smaller O
in O
the O
central O
area S-PARA
. O


The O
maximum O
shear B-PRO
stress E-PRO
may O
reach O
2500 O
N/m2 O
and O
pushed O
an O
intense O
outward O
convection O
. O


The O
solidification B-CONPRI
parameters E-CONPRI
were O
used O
to O
predict O
the O
solidified O
morphology S-CONPRI
, O
and O
the O
prediction S-CONPRI
was O
well O
validated O
by O
experimental S-CONPRI
results O
. O


The O
obtained O
basic O
conclusions O
in O
this O
work O
demonstrated O
that O
this O
study O
of O
thermal-fluid-metallurgical O
behavior O
could O
provide O
an O
improved O
understanding O
of O
the O
surface B-PRO
tension E-PRO
driven O
flow O
and O
solidification S-CONPRI
behavior O
inside O
the O
melt B-MATE
pool E-MATE
of O
welding S-MANP
and O
additive B-MANP
manufacturing I-MANP
process E-MANP
. O


The O
microstructure B-CONPRI
evolution E-CONPRI
and O
tensile B-PRO
properties E-PRO
of O
laser-additive O
welded S-MANP
Ti2AlNb O
joints O
under O
different O
heat B-MANP
treatments E-MANP
were O
investigated O
in O
this O
paper O
. O


The O
heat B-MANP
treatment E-MANP
was O
conducted O
in O
the O
B2 O
+ O
O S-MATE
( O
HT1 O
) O
and O
B2 O
+ O
α2 O
+ O
O S-MATE
( O
HT2 O
) O
phase S-CONPRI
field O
to O
obtain O
different O
microstructural S-CONPRI
characteristics O
. O


For O
HT1 O
, O
due O
to O
the O
B2 O
→ O
O S-MATE
transformation O
, O
the O
microstructure S-CONPRI
of O
heat B-CONPRI
affected I-CONPRI
zone E-CONPRI
was O
B2 O
+ O
α2 O
+ O
O S-MATE
, O
B2 O
+ O
residual S-CONPRI
α2 O
+ O
O S-MATE
, O
and O
B2 O
+ O
O S-MATE
as S-MATE
the O
distance O
from O
the O
base B-MATE
metal E-MATE
increased O
. O


As S-MATE
for O
HT2 O
, O
the O
microstructure S-CONPRI
of O
heat B-CONPRI
affected I-CONPRI
zone E-CONPRI
was O
composed O
of O
B2 O
+ O
α2 O
+ O
rim-O O
+ O
primary O
O S-MATE
+ O
acicular O
O S-MATE
in O
the O
region O
close O
to O
the O
base B-MATE
metal E-MATE
, O
B2 O
+ O
intergranular O
α2 O
+ O
transformed O
O S-MATE
+ O
primary O
O S-MATE
+ O
acicular O
O S-MATE
in O
the O
region O
close O
to O
the O
fusion B-CONPRI
zone E-CONPRI
. O


The O
fusion B-CONPRI
zone E-CONPRI
was O
composed O
of O
B2 O
+ O
O S-MATE
laths O
after O
HT1 O
, O
and O
B2 O
+ O
intergranular O
α2 O
+ O
transformed O
O S-MATE
+ O
primary O
O S-MATE
+ O
acicular O
O S-MATE
after O
HT2 O
. O


The O
joints O
composed O
of O
B2 O
+ O
O S-MATE
phase O
exhibited O
higher O
tensile B-PRO
strength E-PRO
compared O
with O
the O
as-welded O
joints O
due O
to O
the O
strengthening S-MANP
effects O
of O
O S-MATE
phase O
. O


The O
intergranular O
α2 O
phase S-CONPRI
formed O
during O
HT2 O
was O
detrimental O
for O
the O
tensile B-PRO
strength E-PRO
. O


The O
joints O
exhibited O
no O
plastic B-PRO
deformation E-PRO
at O
room O
temperature S-PARA
after O
both O
heat B-MANP
treatments E-MANP
on O
account O
of O
the O
lack O
of O
independent O
slip O
systems O
in O
the O
O S-MATE
phase O
. O


The O
ductility S-PRO
of O
the O
heat-treated S-MANP
joints O
at O
650 O
°C O
was O
better O
than O
that O
at O
room O
temperature S-PARA
because O
more O
slip O
systems O
were O
activated O
in O
the O
O S-MATE
phase O
. O


Compared O
with O
the O
joints O
heat-treated S-MANP
in O
HT1 O
, O
the O
joints O
after O
HT2 O
exhibited O
better O
ductility S-PRO
at O
650 O
°C O
resulting O
from O
the O
coarse O
primary O
O S-MATE
laths O
and O
lower O
volume B-PARA
fraction E-PARA
of O
O S-MATE
phase O
. O


Corrosion B-CONPRI
resistance E-CONPRI
of O
carbon B-MATE
steel E-MATE
cladding O
is O
better O
than O
high B-MATE
speed I-MATE
steel E-MATE
. O


Wear B-PRO
resistance E-PRO
of O
specific O
carbon B-MATE
steel E-MATE
cladding O
is O
close O
to O
high B-MATE
speed I-MATE
steel E-MATE
. O


Submerged B-MANP
arc I-MANP
welding E-MANP
is O
available O
technology S-CONPRI
to O
improve O
wear S-CONPRI
and O
corrosion B-CONPRI
resistance E-CONPRI
of O
carbon B-MATE
steel E-MATE
. O


High-speed O
steel S-MATE
( O
HSS S-MATE
) O
, O
traditionally O
used O
in O
the O
hot B-MANP
rolling E-MANP
industry O
, O
suffers O
from O
the O
problem O
of O
wear S-CONPRI
and O
corrosion S-CONPRI
. O


For O
modifying O
the O
surface S-CONPRI
property S-CONPRI
of O
metal B-MATE
materials E-MATE
, O
submerged B-MANP
arc I-MANP
welding E-MANP
, O
among O
the O
industrial S-APPL
additive B-MANP
manufacturing E-MANP
technologies O
, O
is O
employed O
. O


In O
this O
study O
, O
we O
aim O
at O
improving O
the O
resistance S-PRO
of O
carbon B-MATE
steel E-MATE
cladding O
against O
corrosion S-CONPRI
and O
wear S-CONPRI
. O


To O
reduce O
cost O
, O
the O
HSS S-MATE
matrix O
is O
replaced O
by O
carbon B-MATE
steel E-MATE
. O


Electrochemical B-CONPRI
corrosion E-CONPRI
and O
high-temperature O
dry O
sliding O
wear S-CONPRI
experiments O
are O
implemented O
to O
study O
the O
corrosion S-CONPRI
and O
tribological S-CONPRI
behavior O
of O
HSS S-MATE
and O
surface-modified O
claddings O
. O


The O
wear S-CONPRI
and O
corrosion B-PRO
behaviors E-PRO
are O
characterized O
by O
potentiodynamic B-CHAR
polarization E-CHAR
, O
electrochemical S-CONPRI
impedance O
spectroscopy S-CONPRI
, O
wear S-CONPRI
rate O
, O
coefficient B-PRO
of I-PRO
friction E-PRO
, O
and O
worn O
surface B-CHAR
morphology E-CHAR
. O


The O
experimental S-CONPRI
results O
indicate O
that O
the O
corrosion S-CONPRI
current O
density S-PRO
( O
Icorr O
) O
of O
carbon B-MATE
steel E-MATE
claddings O
, O
ranging O
from O
11.023 O
× O
10−3 O
to O
3.372 O
× O
10−3 O
mA∙cm−2 O
, O
is O
lower O
than O
that O
of O
the O
HSS S-MATE
alloy S-MATE
( O
19.247 O
× O
10−3 O
mA∙cm−2 O
) O
. O


The O
passive O
film O
resistance S-PRO
of O
prepared O
carbon B-MATE
steel E-MATE
cladding-3 O
( O
1870 O
Ω∙cm2 O
) O
is O
in O
fact O
larger O
than O
the O
resistance S-PRO
of O
HSS S-MATE
( O
1075 O
Ω∙cm2 O
) O
. O


The O
corrosion B-CONPRI
resistance E-CONPRI
of O
surface-modified O
carbon B-MATE
steel E-MATE
claddings O
is O
better O
than O
that O
of O
the O
HSS S-MATE
. O


The O
wear S-CONPRI
rates O
of O
carbon B-MATE
steel E-MATE
cladding-2 O
( O
1.99 O
× O
10−7 O
mm3·N−1·mm−1 O
) O
and O
carbon B-MATE
steel E-MATE
cladding-3 O
( O
2.49 O
× O
10−7 O
mm3·N−1·mm−1 O
) O
approximate O
the O
wear S-CONPRI
rate O
of O
HSS S-MATE
( O
1.59 O
× O
10−7 O
mm3·N−1·mm−1 O
) O
. O


Moreover O
, O
the O
wear S-CONPRI
width O
of O
prepared O
carbon B-MATE
steel E-MATE
cladding-3 O
( O
550 O
μm O
) O
is O
slightly O
larger O
than O
that O
of O
HSS S-MATE
( O
500 O
μm O
) O
. O


The O
wear B-PRO
resistance E-PRO
of O
carbon B-MATE
steel E-MATE
cladding-3 O
approximates O
that O
of O
HSS S-MATE
. O


With O
the O
increase O
in O
the O
deposition S-CONPRI
height O
, O
the O
heat B-CONPRI
dissipation E-CONPRI
changes O
from O
three-dimensional S-CONPRI
on O
the O
substrate S-MATE
to O
one-dimensional O
on O
the O
depositing O
layer S-PARA
. O


The O
residual B-CONPRI
distortion E-CONPRI
can O
be S-MATE
effectively O
reduced O
by O
changing O
the O
depositing O
direction O
. O


The O
distortion S-CONPRI
of O
the O
reverse O
directions O
can O
be S-MATE
reduced O
by O
25 O
% O
. O


The O
stress B-CHAR
concentration E-CHAR
at O
the O
end O
of O
the O
arc S-CONPRI
point O
and O
the O
stress S-PRO
produced O
by O
the O
reverse O
depositing O
model S-CONPRI
are O
more O
uniform O
than O
those O
produced O
by O
the O
same O
depositing O
model S-CONPRI
. O


The O
complex O
residual B-PRO
stress E-PRO
and O
distortion S-CONPRI
experienced O
in O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
can O
have O
a O
serious O
impact S-CONPRI
on O
production S-MANP
. O


In O
this O
paper O
, O
a O
series O
of O
ten-layer O
depositing O
walls O
were O
deposited O
by O
WAAM S-MANP
using O
the O
same O
depositing O
direction O
and O
reverse O
depositing O
direction O
to O
study O
the O
effect O
of O
different O
heat S-CONPRI
conditions O
on O
the O
residual B-PRO
stress E-PRO
and O
distortion S-CONPRI
of O
the O
deposition S-CONPRI
wall O
. O


The O
temperature S-PARA
field O
, O
distortion S-CONPRI
, O
and O
residual B-PRO
stress E-PRO
under O
different O
paths O
were O
obtained O
by O
performing O
experiments O
. O


Meanwhile O
, O
to O
calculate O
the O
variations S-CONPRI
in O
the O
temperature S-PARA
, O
stress S-PRO
, O
and O
distortion S-CONPRI
under O
different O
depositing O
paths O
, O
a O
model S-CONPRI
of O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
was O
established O
by O
using O
a O
numerical O
model S-CONPRI
. O


The O
stress B-PRO
distribution E-PRO
in O
the O
reverse O
directions O
is O
more O
uniform O
than O
that O
in O
the O
same O
directions O
. O


By O
comparison O
with O
the O
results O
from O
an O
experimental S-CONPRI
and O
numerical O
analysis O
, O
the O
same O
depositing O
directions O
have O
a O
large O
temperature B-PARA
gradient E-PARA
and O
produce O
greater O
plastic S-MATE
distortion S-CONPRI
during O
solidification S-CONPRI
. O


A O
concept O
of O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
constrained O
optimisation O
of O
multi-axis O
additive B-MANP
manufacturing E-MANP
trajectory O
for O
parts O
of O
revolution O
is O
presented O
. O


For O
a O
constrained O
device O
configuration S-CONPRI
, O
the O
use O
of O
non-optimised O
trajectories O
can O
lead S-MATE
to O
manufacturing S-MANP
failure S-CONPRI
due O
to O
an O
axis O
overtravel O
or O
singularity O
state O
; O
problem O
which O
can O
be S-MATE
avoided O
thanks O
to O
the O
proposed O
methodology S-CONPRI
. O


The O
methodology S-CONPRI
has O
been O
validated O
by O
manufacturing S-MANP
parts O
of O
revolution O
on O
a O
multi-axis O
additive B-MANP
manufacturing E-MANP
device O
using O
a O
coaxial O
PLA S-MATE
deposition S-CONPRI
system O
. O


Parts O
manufactured S-CONPRI
with O
an O
optimised O
trajectory O
provide O
better O
geometrical O
accuracy S-CHAR
and O
less O
results O
dispersion S-CONPRI
than O
parts O
manufactured S-CONPRI
without O
optimisation O
. O


This O
work O
focuses O
on O
additive B-MANP
manufacturing E-MANP
by O
Directed B-MANP
Energy I-MANP
Deposition E-MANP
( O
DED S-MANP
) O
using O
a O
6-axis O
robot S-MACEQ
. O


To O
achieve O
this O
goal O
, O
a O
new O
layer-by-layer S-CONPRI
method O
coupled O
with O
a O
trajectory O
constrained O
optimization S-CONPRI
is O
presented O
. O


The O
layer-by-layer S-CONPRI
generation O
of O
optimized O
trajectories O
is O
validated O
experimentally O
on O
a O
6-axis O
robot S-MACEQ
using O
a O
PLA S-MATE
extrusion S-MANP
system O
. O


Experimental S-CONPRI
results O
show O
that O
the O
layer-by-layer S-CONPRI
trajectory O
optimization S-CONPRI
strategy O
applied O
to O
parts O
of O
revolution O
provides O
better O
geometrical O
accuracy S-CHAR
while O
improving O
the O
efficiency O
of O
the O
manufacturing S-MANP
device O
compared O
to O
non-optimized O
solutions O
. O


In O
the O
cold B-MANP
metal I-MANP
transfer I-MANP
additive I-MANP
manufacturing E-MANP
process O
of O
Ti-6Al-4V S-MATE
thin O
wall O
structure S-CONPRI
, O
ultrasonic B-MANP
peening E-MANP
treatment O
( O
UPT O
) O
in O
three O
directions O
is O
proposed O
to O
refine O
the O
large O
columnar O
prior-β O
grains S-CONPRI
and O
secondary O
α O
grains S-CONPRI
, O
and O
to O
improve O
anisotropy S-PRO
in O
tensile B-PRO
properties E-PRO
. O


The O
experimental S-CONPRI
results O
showed O
that O
UPT O
in O
three O
directions O
applied O
to O
each O
weld S-FEAT
right O
after O
arc S-CONPRI
extinguishing O
has O
a O
minor O
influence O
on O
the O
surface S-CONPRI
appearance O
, O
which O
shows O
no O
apparent O
plastic B-PRO
deformation E-PRO
, O
but O
has O
a O
great O
improvement O
in O
grain B-CHAR
refinement E-CHAR
. O


The O
changes O
in O
microstructure S-CONPRI
and O
dislocations S-CONPRI
of O
thin O
wall O
structure S-CONPRI
treated O
by O
UPT O
in O
three O
directions O
were O
observed O
. O


By O
comparing O
with O
those O
without O
UPT O
, O
the O
main O
causes O
for O
refinement O
of O
columnar O
prior-β O
and O
secondary O
α O
grains S-CONPRI
was O
explored O
, O
namely O
mechanical S-APPL
effects O
of O
ultrasonic O
at O
the O
temperature B-PARA
range E-PARA
of O
α O
’ O
dissolution O
temperature S-PARA
Tdiss O
– O
liquidus S-CONPRI
temperature O
Tl S-MATE
. O


Specimens O
with O
UPT O
have O
better O
properties S-CONPRI
, O
higher O
loads O
with O
the O
same O
indentation S-CONPRI
displacement O
in O
nano-indentation O
tests O
, O
an O
increase O
in O
ultimate B-PRO
tensile I-PRO
strength E-PRO
and O
a O
reduction S-CONPRI
in O
anisotropic S-PRO
percentage O
in O
tensile B-CHAR
tests E-CHAR
. O


2Cr13 O
thin-wall O
part O
with O
defect-free O
was O
additively B-MANP
manufactured E-MANP
by O
robot-assisted O
CMT S-MANP
technology O
. O


Martensite S-MATE
coarsened O
gradually O
from O
FZ S-CONPRI
to O
CZ O
while O
only O
ultra-fine O
acicular O
martensite S-MATE
in O
the O
top O
layer S-PARA
. O


A O
random O
crystallographic O
orientation S-CONPRI
in O
the O
middle O
region O
while O
a O
slightly O
fiber S-MATE
texture O
in O
the O
top O
layer S-PARA
Mechanical O
properties S-CONPRI
were O
evolved O
periodically O
due O
to O
the O
periodic O
microstructural B-CONPRI
evolution E-CONPRI
. O


Based O
on O
cold B-MANP
metal I-MANP
transfer E-MANP
( O
CMT S-MANP
) O
welding S-MANP
, O
wire-arc B-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
technology S-CONPRI
was O
adopted O
to O
manufacture S-CONPRI
2Cr13 O
part O
. O


The O
spatial O
periodicity O
of O
the O
microstructural B-CONPRI
evolution E-CONPRI
and O
the O
anti-indentation O
properties S-CONPRI
was O
explored O
. O


The O
results O
show O
that O
the O
as-deposited O
part O
was O
featured O
by O
periodic O
martensite S-MATE
laths O
within O
the O
block-shaped O
ferrite S-MATE
matrix O
in O
the O
inner O
layers O
, O
followed O
by O
epitaxial S-PRO
ferrite O
grains S-CONPRI
containing O
ultra-fine O
acicular O
martensite S-MATE
in O
the O
top O
layer S-PARA
only O
. O


A O
slightly O
decreased O
Fe S-MATE
intensity O
was O
caused O
by O
local O
elemental O
segregation S-CONPRI
during O
the O
re-melting O
process S-CONPRI
; O
the O
homogeneity O
of O
Fe S-MATE
and O
Cr S-MATE
was O
attributed O
to O
similar O
cooling S-MANP
conditions O
in O
the O
top O
layer S-PARA
. O


Elongated O
ferrite S-MATE
grains O
exhibited O
a O
slight O
fiber S-MATE
texture O
in O
the O
top O
layer S-PARA
and O
a O
random O
crystallographic O
orientation S-CONPRI
in O
the O
middle O
region O
. O


The O
anti-indentation O
properties S-CONPRI
evolved O
periodically O
due O
to O
the O
periodic O
microstructural S-CONPRI
characteristics O
. O


The O
obtained O
experimental S-CONPRI
results O
confirmed O
higher O
anti-indentation O
properties S-CONPRI
of O
the O
as-deposited O
part O
following O
comparison O
with O
the O
as-annealed O
base B-MATE
metal E-MATE
, O
while O
the O
elastic B-PRO
moduli E-PRO
of O
samples S-CONPRI
were O
not O
significantly O
different O
. O


Titanium B-MATE
alloys E-MATE
have O
high O
strength S-PRO
to O
low O
weight S-PARA
ratio O
, O
good O
creep S-PRO
resistance O
and O
high O
temperature S-PARA
strength B-PRO
properties E-PRO
. O


Based O
on O
these O
properties S-CONPRI
, O
Ti B-MATE
alloys E-MATE
are O
used O
as S-MATE
a O
‘ O
workhorse O
’ O
material S-MATE
in O
the O
aerospace B-APPL
industry E-APPL
such O
as S-MATE
engine O
blades O
, O
landing O
gear S-MACEQ
assemblies O
, O
large O
structural O
parts O
, O
airframe O
and O
drums O
etc O
. O


Traditional O
fabrication S-MANP
methods O
of O
Ti B-MATE
alloy E-MATE
are O
expensive O
and O
inferior O
in O
their O
mechanical B-CONPRI
properties E-CONPRI
. O


Due O
to O
continuous O
development O
in O
science O
and O
technology S-CONPRI
, O
many O
researchers O
have O
been O
attracted O
towards O
Wire O
Feed S-PARA
Additive B-MANP
Manufacturing E-MANP
( O
WFAM O
) O
for O
the O
fabrication S-MANP
of O
titanium S-MATE
and O
its O
alloys S-MATE
. O


WFAM O
has O
set S-APPL
a O
new O
trend S-CONPRI
by O
accomplishing O
the O
production S-MANP
demand O
of O
components S-MACEQ
from O
medium O
to O
large O
scale O
with O
moderate O
complexity S-CONPRI
. O


This O
additive B-MANP
manufacturing E-MANP
technology O
generally O
employes O
for O
high O
material B-CHAR
utilization E-CHAR
and O
higher O
deposition S-CONPRI
. O


This O
state O
of O
art S-APPL
highlights O
the O
remarkable O
achievements O
of O
WFAM O
processes S-CONPRI
followed O
by O
their O
effect O
of O
process B-CONPRI
parameters E-CONPRI
, O
microstructural S-CONPRI
changes O
, O
residual B-PRO
stresses E-PRO
and O
mechanical B-CONPRI
properties E-CONPRI
of O
Ti-6Al-4V B-MATE
alloy E-MATE
. O


Accurate S-CHAR
on-line O
weld S-FEAT
defects S-CONPRI
detection O
is O
still O
challenging O
for O
robotic B-MANP
welding I-MANP
manufacturing E-MANP
due O
to O
the O
complexity S-CONPRI
of O
weld S-FEAT
defects S-CONPRI
. O


This O
paper O
studied O
deep O
learning–based O
on-line O
defects S-CONPRI
detection O
for O
aluminum B-MATE
alloy E-MATE
in O
robotic O
arc B-MANP
welding E-MANP
using O
Convolutional O
Neural B-CONPRI
Networks E-CONPRI
( O
CNN O
) O
and O
weld S-FEAT
images S-CONPRI
. O


Firstly O
, O
an O
image S-CONPRI
acquisition O
system O
was O
developed O
to O
simultaneously O
collect O
weld S-FEAT
images S-CONPRI
, O
which O
can O
provide O
more O
information O
of O
the O
real-time O
weld S-FEAT
images S-CONPRI
from O
different O
angles O
including O
top O
front O
, O
top O
back O
and O
back O
seam S-MANP
. O


Then O
, O
a O
new O
CNN O
classification S-CONPRI
model O
with O
11 O
layers O
based O
on O
weld S-FEAT
image S-CONPRI
was O
designed S-FEAT
to O
identify O
weld B-CONPRI
penetration I-CONPRI
defects E-CONPRI
. O


In O
order O
to O
improve O
the O
robustness S-PRO
and O
generalization O
ability O
of O
the O
CNN O
model S-CONPRI
, O
weld S-FEAT
images S-CONPRI
from O
different O
welding S-MANP
current O
and O
feeding O
speed O
were O
captured O
for O
the O
CNN O
model S-CONPRI
. O


Based O
on O
the O
actual O
industry S-APPL
challenges O
such O
as S-MATE
the O
instability O
of O
welding S-MANP
arc S-CONPRI
, O
the O
complexity S-CONPRI
of O
the O
welding S-MANP
environment O
and O
the O
random O
changing O
of O
plate O
gap O
condition O
, O
two O
kinds O
of O
data S-CONPRI
augmentation O
including O
noise O
adding O
and O
image S-CONPRI
rotation O
were O
used O
to O
boost O
the O
CNN O
dataset O
while O
parameters B-CONPRI
optimization E-CONPRI
was O
carried O
out O
. O


Instead O
of O
decreasing O
the O
interference O
from O
arc S-CONPRI
light O
as S-MATE
in O
traditional O
way O
, O
the O
CNN O
model S-CONPRI
has O
taken O
full O
use O
of O
those O
arc S-CONPRI
lights O
by O
combining O
them O
in O
a O
various O
way O
to O
form O
the O
complementary O
features O
. O


Test O
results O
shows O
that O
the O
CNN O
model S-CONPRI
has O
better O
performance S-CONPRI
than O
our O
previous O
work O
with O
the O
mean O
classification S-CONPRI
accuracy S-CHAR
of O
99.38 O
% O
. O


This O
paper O
can O
provide O
some O
guidance O
for O
on-line O
detection O
of O
manufacturing S-MANP
quality O
in O
metal B-MANP
additive I-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
and O
laser B-MANP
welding E-MANP
. O


A O
high O
temperature S-PARA
gas-to-gas O
manifold-microchannel O
heat B-MACEQ
exchanger E-MACEQ
was O
fabricated S-CONPRI
. O


The O
heat B-MACEQ
exchanger E-MACEQ
core S-MACEQ
was O
3D B-MANP
printed E-MANP
using O
Inconel B-MATE
718 E-MATE
through O
DMLS S-MANP
. O


The O
heat B-MACEQ
exchanger E-MACEQ
was O
tested O
at O
600 O
°C O
with O
inlet S-MACEQ
pressure O
of O
450 O
kPa O
. O


The O
experimental S-CONPRI
results O
validated O
the O
numerical O
model S-CONPRI
. O


25 O
% O
higher O
heat B-PARA
transfer I-PARA
density E-PARA
compared O
to O
conventional O
plate O
fin O
heat B-MACEQ
exchangers E-MACEQ
. O


This O
work O
presents O
an O
additively B-MANP
manufactured E-MANP
manifold-microchannel O
heat B-MACEQ
exchanger E-MACEQ
made O
of O
Inconel B-MATE
718 E-MATE
and O
experimentally O
tested O
for O
high O
temperature S-PARA
aerospace S-APPL
applications O
. O


The O
heat B-MACEQ
exchanger E-MACEQ
core S-MACEQ
with O
a O
size O
of O
66 O
mm S-MANP
× O
74 O
mm S-MANP
× O
27 O
mm S-MANP
was O
fabricated S-CONPRI
as S-MATE
a O
single O
piece O
through O
the O
direct B-MANP
metal I-MANP
laser I-MANP
sintering E-MANP
process O
. O


Successful O
welding S-MANP
of O
additively B-MANP
manufactured E-MANP
headers O
with O
the O
heat B-MACEQ
exchanger E-MACEQ
core S-MACEQ
and O
conventionally O
manufactured S-CONPRI
flanges O
was O
demonstrated O
through O
the O
fabrication S-MANP
of O
the O
unit O
. O


The O
heat B-MACEQ
exchanger E-MACEQ
was O
tested O
using O
nitrogen S-MATE
( O
N2 S-MATE
) O
on O
the O
hot-side O
and O
air O
on O
the O
cold-side O
as S-MATE
the O
working O
fluids S-MATE
. O


A O
maximum O
heat S-CONPRI
duty O
of O
2.78 O
kW O
and O
a O
maximum O
overall O
heat B-CONPRI
transfer E-CONPRI
coefficient O
of O
1000 O
W/m2K O
were O
achieved O
during O
the O
experiments O
. O


The O
decent O
agreement O
between O
the O
experimental S-CONPRI
and O
the O
numerical O
results O
demonstrates O
the O
validity O
of O
the O
numerical O
analysis O
model S-CONPRI
used O
for O
heat B-CONPRI
transfer E-CONPRI
and O
pressure S-CONPRI
drop O
prediction S-CONPRI
of O
the O
additively B-MANP
manufactured E-MANP
manifold-microchannel O
heat B-MACEQ
exchanger E-MACEQ
. O


Compared O
to O
conventional O
plate O
fin O
heat B-MACEQ
exchangers E-MACEQ
, O
nearly O
25 O
% O
improvement O
in O
heat B-CONPRI
transfer E-CONPRI
density— O
the O
ratio O
between O
heat S-CONPRI
duty O
and O
mass O
( O
Q/m O
) O
—was O
noted O
at O
a O
coefficient O
of O
performance S-CONPRI
( O
COP O
) O
of O
62 O
. O


A O
3D S-CONPRI
heat O
and O
fluid B-PRO
flow E-PRO
model O
is O
developed O
for O
the O
multilayer O
deposition S-CONPRI
of O
wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacture E-MANP
. O


Utilizing O
a O
modified O
double O
ellipsoidal O
heat B-CONPRI
source E-CONPRI
model O
which O
shows O
better O
adaptability O
to O
free B-CONPRI
surface E-CONPRI
deformation S-CONPRI
. O


Predicting O
the O
morphology S-CONPRI
of O
molten B-CONPRI
pool E-CONPRI
and O
deposited B-CHAR
bead E-CHAR
in O
WAAM S-MANP
process S-CONPRI
using O
CFD S-APPL
model O
for O
the O
first O
time O
. O


Conduction O
is O
the O
dominant O
method O
of O
heat B-CONPRI
dissipation E-CONPRI
compared O
to O
convection O
and O
radiation S-MANP
to O
the O
air O
during O
deposition S-CONPRI
. O


A O
three-dimensional S-CONPRI
numerical O
model S-CONPRI
has O
been O
developed O
to O
investigate O
the O
fluid B-PRO
flow E-PRO
and O
heat B-CONPRI
transfer E-CONPRI
behaviors O
in O
multilayer O
deposition S-CONPRI
of O
plasma B-MANP
arc I-MANP
welding E-MANP
( O
PAW S-MANP
) O
based O
wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacture E-MANP
( O
WAAM S-MANP
) O
. O


The O
volume B-CONPRI
of I-CONPRI
fluid E-CONPRI
( O
VOF S-CONPRI
) O
and O
porosity S-PRO
enthalpy O
methods O
are O
employed O
to O
track O
the O
molten B-CONPRI
pool I-CONPRI
free I-CONPRI
surface E-CONPRI
and O
solidification S-CONPRI
front O
, O
respectively O
. O


A O
modified O
double O
ellipsoidal O
heat B-CONPRI
source E-CONPRI
model O
is O
utilized O
to O
ensure O
constant O
arc S-CONPRI
heat O
input O
in O
calculation O
in O
the O
case O
that O
molten B-CONPRI
pool E-CONPRI
surface O
dynamically O
changes O
. O


Transient S-CONPRI
simulations S-ENAT
were O
conducted O
for O
the O
1st O
, O
2nd O
and O
21st O
layer S-PARA
depositions O
. O


The O
shape O
and O
size O
of O
deposited B-CHAR
bead E-CHAR
and O
weld B-CONPRI
pool E-CONPRI
were O
predicted S-CONPRI
and O
compared O
with O
experimental S-CONPRI
results O
. O


The O
results O
show O
that O
for O
each O
layer S-PARA
of O
deposition S-CONPRI
the O
Marangoni O
force S-CONPRI
plays O
the O
most O
important O
role O
in O
affecting O
fluid B-PRO
flow E-PRO
, O
conduction O
is O
the O
dominant O
method O
of O
heat B-CONPRI
dissipation E-CONPRI
compared O
to O
convection O
and O
radiation S-MANP
to O
the O
air O
. O


As S-MATE
the O
layer S-PARA
number O
increases O
, O
the O
length O
and O
width O
of O
molten B-CONPRI
pool E-CONPRI
and O
the O
width O
of O
deposited B-CHAR
bead E-CHAR
increase O
, O
whilst O
the O
layer B-PARA
height E-PARA
decreases O
. O


In O
high O
layer S-PARA
deposition S-CONPRI
, O
where O
side O
support S-APPL
is O
absent O
, O
the O
depth O
of O
the O
molten B-CONPRI
pool E-CONPRI
at O
the O
rear O
part O
is O
almost O
flat O
in O
the O
Y S-MATE
direction O
. O


The O
profile S-FEAT
of O
the O
deposited B-CHAR
bead E-CHAR
is O
mainly O
determined O
by O
static O
pressure S-CONPRI
caused O
by O
gravity O
and O
surface B-PRO
tension E-PRO
pressure S-CONPRI
, O
therefore O
the O
bead S-CHAR
profile O
is O
nearly O
circular O
. O


The O
simulated O
profiles S-FEAT
and O
size O
dimensions S-FEAT
of O
deposited B-CHAR
bead E-CHAR
and O
molten B-CONPRI
pool E-CONPRI
were O
validated O
with O
experimental S-CONPRI
weld O
appearance O
, O
cross-sectional O
images S-CONPRI
and O
process S-CONPRI
camera S-MACEQ
images O
. O


Wire-based O
directed B-MANP
energy I-MANP
deposition I-MANP
additive I-MANP
manufacturing E-MANP
techniques O
( O
AM S-MANP
) O
permit O
the O
rapid O
production S-MANP
of O
large-scale O
structural B-CONPRI
components E-CONPRI
which O
are O
not O
currently O
possible O
using O
the O
more O
common O
powder B-MANP
bed I-MANP
fusion E-MANP
( O
PBF S-MANP
) O
AM S-MANP
methods O
. O


However O
, O
due O
to O
larger O
melt B-MATE
pool E-MATE
widths O
and O
higher O
energy O
inputs O
than O
PBF S-MANP
methods O
, O
local O
thermal O
history O
effects O
produce O
significant O
location-dependent O
microstructure S-CONPRI
, O
porosity S-PRO
, O
and O
mechanical S-APPL
behavior O
that O
necessitates O
thorough O
quantification O
of O
this O
emergent O
technology S-CONPRI
. O


Wire B-MANP
+ I-MANP
Arc I-MANP
Additive I-MANP
Manufacturing E-MANP
( O
WAAM S-MANP
) O
was O
used O
to O
produce O
austenitic S-MATE
stainless-steel O
single O
bead S-CHAR
walls O
in O
order O
to O
statistically O
quantify O
the O
variation S-CONPRI
of O
critical O
material B-CONPRI
properties E-CONPRI
within O
the O
build S-PARA
. O


Individual O
grain S-CONPRI
geometric O
properties S-CONPRI
evaluated O
using O
electron B-ENAT
back I-ENAT
scatter I-ENAT
diffraction E-ENAT
at O
different O
points O
in O
the O
build S-PARA
were O
well O
fit S-CONPRI
by O
a O
three-parameter O
Weibull O
cumulative O
distribution S-CONPRI
function O
, O
yet O
sufficiently O
different O
from O
averaged O
values O
. O


X-ray B-CHAR
diffraction E-CHAR
for O
each O
location O
disclosed O
a O
strong O
wire O
texture S-FEAT
in O
the O
build B-PARA
direction E-PARA
, O
leading O
to O
anisotropic S-PRO
elastic O
moduli O
values O
that O
were O
well O
described O
by O
directionally-dependent O
modulus O
predictions S-CONPRI
obtained O
from O
diffraction S-CHAR
peak O
analysis O
. O


Location-dependent O
mechanical S-APPL
behavior O
was O
examined O
and O
accurately S-CHAR
captured O
by O
an O
elasto-viscoplastic O
model S-CONPRI
based O
on O
the O
Fast-Fourier O
Transforms O
( O
EvpFFT O
) O
using O
the O
local O
microstructure S-CONPRI
orientation O
data S-CONPRI
as S-MATE
input O
. O


Overall O
, O
a O
high-quality O
build S-PARA
was O
realized O
, O
with O
minimal O
porosity S-PRO
of O
less O
than O
0.32 O
% O
, O
and O
median O
yield O
and O
tensile B-PRO
strength E-PRO
values O
of O
approximately O
320.4 O
± O
8.0 O
MPa S-CONPRI
and O
531.6 O
± O
8.2 O
MPa S-CONPRI
, O
respectively O
. O


Additively B-MANP
manufactured E-MANP
components O
made O
of O
metallic B-MATE
material E-MATE
are O
subject O
to O
special O
consideration O
for O
many O
R O
& O
D O
departments O
, O
since O
the O
process B-CONPRI
control E-CONPRI
is O
not O
yet O
sufficiently O
reliable O
and O
therefore O
an O
extensive O
quality S-CONPRI
assurance O
is O
necessary O
. O


For O
this O
reason O
, O
few O
structural B-CONPRI
components E-CONPRI
for O
aviation O
have O
been O
established O
so O
far O
. O


In O
this O
paper O
, O
a O
feasibility S-CONPRI
study O
for O
the O
use O
of O
laser B-MANP
metal I-MANP
deposition E-MANP
( O
LMD S-MANP
) O
for O
the O
additive B-MANP
manufacturing E-MANP
of O
a O
fuselage S-MACEQ
made O
of O
aluminum S-MATE
is O
carried O
out O
. O


The O
redistribution O
of O
alloying B-MATE
elements E-MATE
and O
the O
crystallographic O
characterizations O
in O
wire O
and O
arc S-CONPRI
additive B-MANP
manufactured E-MANP
( O
WAAM S-MANP
) O
super O
duplex O
stainless B-MATE
steel E-MATE
( O
SDSS O
) O
was O
investigated O
from O
the O
wire O
to O
the O
final O
as-deposited O
structure S-CONPRI
. O


The O
results O
showed O
that O
elemental O
partitioning O
between O
austenite S-MATE
and O
ferrite S-MATE
was O
suppressed O
in O
the O
last O
layer S-PARA
and O
the O
solidified O
droplet S-CONPRI
. O


The O
high O
Ni S-MATE
content O
but O
low O
Cr S-MATE
and O
N S-MATE
contents O
in O
the O
initial O
state O
of O
the O
intragranular O
austenite S-MATE
( O
IGA O
) O
confirmed O
the O
predominance O
of O
the O
chromium S-MATE
nitrides O
acted O
as S-MATE
the O
nucleation S-CONPRI
sites O
. O


Gathering O
of O
nitrogen S-MATE
was O
found O
more O
distinct O
in O
the O
coarsening O
IGA O
, O
Widmanstätten O
austenite S-MATE
( O
WA S-MANP
) O
than O
the O
grain B-CONPRI
boundary E-CONPRI
austenite S-MATE
( O
GBA O
) O
. O


The O
columnar O
epitaxial S-PRO
ferrite O
presented O
a O
strong O
< O
001 O
> O
texture S-FEAT
in O
the O
deposition B-PARA
direction E-PARA
, O
while O
the O
< O
001 O
> O
and O
< O
101 O
> O
orientations S-CONPRI
was O
found O
in O
the O
austenite S-MATE
. O


Random O
orientations S-CONPRI
of O
the O
intragranular O
secondary O
austenite S-MATE
was O
revealed O
. O


The O
Rotated O
Cube S-CONPRI
texture O
of O
the O
austenite S-MATE
grains O
were O
consumed O
by O
the O
“ O
recrystallization S-CONPRI
” O
textures O
( O
Brass S-MATE
, O
Rotated O
Brass S-MATE
, O
Cu S-MATE
, O
R O
, O
E O
, O
and O
F S-MANP
) O
caused O
by O
the O
austenite S-MATE
reformation O
. O


The O
low-angle O
interphase S-CONPRI
boundaries S-FEAT
between O
austenite S-MATE
and O
ferrite S-MATE
were O
predominated O
in O
the O
as-deposited O
wall O
, O
and O
, O
at O
which O
, O
the O
K–S O
orientation S-CONPRI
took O
the O
crucial O
part O
. O


A O
Taylor O
factor O
analysis O
revealed O
that O
through O
fabrication S-MANP
via O
additive S-MATE
process O
, O
the O
austenite S-MATE
became O
oriented O
“ O
harder O
” O
and O
contributed O
most O
to O
good O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
textured O
microstructure S-CONPRI
contributed O
about O
a O
2.6 O
% O
higher O
engineering S-APPL
strain O
in O
the O
Z O
direction O
and O
a O
27.8 O
MPa S-CONPRI
higher O
yield B-PRO
strength E-PRO
in O
the O
X O
direction O
. O


As-deposited O
Wire B-MANP
+ I-MANP
Arc I-MANP
Additively I-MANP
Manufactured E-MANP
( O
WAAM S-MANP
) O
Inconel S-MATE
( O
IN O
) O
718 O
contains O
Laves B-CONPRI
phase E-CONPRI
in O
the O
microstructure S-CONPRI
. O


A O
modified O
post-deposition O
heat B-MANP
treatment E-MANP
successfully O
dissolved O
Laves B-CONPRI
phase E-CONPRI
without O
precipitating O
δ O
phase S-CONPRI
. O


Changes O
to O
the O
grain B-CONPRI
structure E-CONPRI
through O
heat B-MANP
treatments E-MANP
reduced O
anisotropy S-PRO
in O
elevated O
temperature S-PARA
tensile O
properties S-CONPRI
. O


Elevated O
temperature S-PARA
tensile O
properties S-CONPRI
of O
WAAM S-MANP
IN O
718 O
meet O
minimum O
specifications S-PARA
for O
cast S-MANP
but O
not O
for O
wrought B-MATE
material E-MATE
. O


Wire B-MANP
+ I-MANP
Arc I-MANP
Additive I-MANP
Manufacturing E-MANP
( O
WAAM S-MANP
) O
can O
be S-MATE
used O
to O
create O
large O
free-form O
components S-MACEQ
out O
of O
specialist O
materials S-CONPRI
such O
as S-MATE
nickel-base O
superalloys S-MATE
. O


Inconel S-MATE
( O
IN O
) O
718 O
is O
well O
suited O
for O
the O
WAAM S-MANP
process S-CONPRI
due O
to O
its O
excellent O
weldability S-PRO
. O


However O
, O
during O
deposition S-CONPRI
, O
WAAM S-MANP
IN718 S-MATE
is O
susceptible O
to O
micro-segregation S-CONPRI
, O
leading O
to O
undesirable O
Laves B-CONPRI
phase E-CONPRI
formation O
in O
the O
interdendritic O
regions O
. O


Further O
, O
the O
WAAM S-MANP
process S-CONPRI
encourages O
columnar B-PRO
grain E-PRO
growth O
and O
the O
development O
of O
a O
strong O
fibre S-MATE
texture O
, O
leading O
to O
anisotropy S-PRO
in O
grain B-CONPRI
structure E-CONPRI
. O


This O
unfavourable O
microstructure S-CONPRI
can O
be S-MATE
addressed O
through O
specialised O
post-deposition O
homogenisation O
heat B-MANP
treatments E-MANP
. O


A O
new O
modified O
heat B-MANP
treatment E-MANP
was O
found O
to O
be S-MATE
effective O
in O
dissolving O
Laves B-CONPRI
phase E-CONPRI
, O
whereas O
a O
standard S-CONPRI
treatment O
precipitated O
δ O
phase S-CONPRI
. O


Tensile B-CHAR
test E-CHAR
results O
revealed O
that O
Laves S-CONPRI
and O
δ O
phases O
lead S-MATE
to O
low O
ductility S-PRO
when O
present O
in O
a O
precipitation-hardened O
matrix O
. O


The O
modified O
heat B-MANP
treatment E-MANP
also O
reduced O
the O
anisotropy S-PRO
in O
grain B-CONPRI
structure E-CONPRI
, O
leading O
to O
almost O
isotropic S-PRO
elevated O
temperature S-PARA
tensile O
properties S-CONPRI
, O
which O
meet O
minimum O
specifications S-PARA
for O
conventional O
cast S-MANP
but O
not O
for O
wrought B-MATE
material E-MATE
. O


Specialised O
post-deposition O
heat B-MANP
treatments E-MANP
, O
which O
address O
the O
unique O
microstructure S-CONPRI
of O
WAAM S-MANP
IN718 S-MATE
, O
are O
crucial O
to O
achieving O
optimal O
mechanical B-CONPRI
properties E-CONPRI
. O


Powder B-MANP
bed I-MANP
fusion I-MANP
process E-MANP
is O
one O
of O
the O
basic O
technique O
associated O
with O
additive B-MANP
manufacturing E-MANP
. O


It O
follows O
the O
basic O
principle O
of O
manufacturing S-MANP
the O
product O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
and O
their O
fusion S-CONPRI
. O


A O
heat B-CONPRI
source E-CONPRI
focuses O
its O
heat S-CONPRI
over O
a O
powder S-MATE
base O
material S-MATE
and O
heats O
the O
selected O
cross B-CONPRI
section E-CONPRI
area S-PARA
. O


Sources O
like O
laser B-CONPRI
beam E-CONPRI
, O
electron B-CONPRI
beam E-CONPRI
and O
infrared S-CONPRI
beam S-MACEQ
are O
used O
as S-MATE
heating O
tool S-MACEQ
. O


The O
process S-CONPRI
of O
heating S-MANP
allows O
the O
powder S-MATE
to O
take O
the O
shape O
of O
the O
intended O
object O
. O


Powder B-MANP
bed I-MANP
fusion I-MANP
process E-MANP
is O
compatible O
to O
every O
engineering B-MATE
material E-MATE
such O
as S-MATE
metals O
, O
ceramics S-MATE
polymers O
, O
composites S-MATE
etc O
. O


this O
technique O
is O
widely O
used O
in O
many O
industrial B-CONPRI
sectors E-CONPRI
such O
as S-MATE
aerospace S-APPL
, O
energy O
sector O
, O
transportation O
etc O
. O


A O
comprehensive O
overview O
on O
powder B-MANP
bed I-MANP
fusion I-MANP
process E-MANP
is O
presented O
in O
this O
review O
paper O
. O


Other O
popular O
techniques O
like O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
, O
selective B-MANP
laser I-MANP
sintering E-MANP
( O
SLS S-MANP
) O
, O
and O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
are O
also O
reviewed O
. O


Wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
, O
using O
cold B-MANP
metal I-MANP
transfer E-MANP
( O
CMT S-MANP
) O
as S-MATE
heat O
source S-APPL
, O
exhibits O
a O
great O
potential O
for O
additive B-MANP
manufacturing E-MANP
of O
magnesium B-MATE
alloys E-MATE
due O
to O
low O
heat S-CONPRI
input O
. O


With O
the O
purpose O
of O
revealing O
the O
relationship O
between O
the O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
WAAMed O
AZ31 O
material S-MATE
, O
the O
present O
study O
has O
been O
carried O
out O
. O


The O
average S-CONPRI
primary O
dendrite S-BIOP
arm O
spacing O
increases O
from O
17 O
μm O
at O
the O
bottom O
to O
39 O
μm O
at O
the O
top O
of O
the O
deposit O
, O
and O
the O
volume B-PARA
fraction E-PARA
of O
the O
interdendritic O
eutectic S-CONPRI
decreases O
from O
52.1 O
% O
to O
39.3 O
% O
. O


The O
microstructure S-CONPRI
of O
each O
layer S-PARA
except O
the O
top O
layer S-PARA
consists O
of O
vertical S-CONPRI
columnar B-MATE
dendrites E-MATE
and O
direction-changed O
columnar B-MATE
dendrites E-MATE
in O
sequence O
. O


The O
top O
layer S-PARA
appears O
equiaxed O
dendrites S-BIOP
due O
to O
columnar O
to O
equiaxed O
transition S-CONPRI
( O
CET O
) O
. O


The O
tensile B-PRO
properties E-PRO
present O
obvious O
anisotropic S-PRO
characteristics O
because O
of O
the O
epitaxial S-PRO
columnar O
dendritic O
growth O
along O
the O
building B-PARA
direction E-PARA
. O


The O
tensile B-PRO
properties E-PRO
also O
show O
obvious O
variation S-CONPRI
from O
the O
bottom O
to O
the O
top O
of O
the O
deposit O
because O
of O
the O
differing O
microstructures S-MATE
in O
different O
regions O
. O


The O
results O
are O
further O
analyzed O
in O
detail O
through O
the O
microstructure B-CONPRI
evolution E-CONPRI
resulted O
from O
the O
new O
manufacturing S-MANP
method O
. O


Using O
Electrical B-MANP
Discharge I-MANP
Machining E-MANP
in O
combination O
with O
forming S-MANP
is O
an O
option O
to O
manufacture S-CONPRI
a O
U-shaped O
First O
Wall O
without O
welding S-MANP
. O


Additive B-MANP
Manufacturing E-MANP
( O
e.g O
. O


Selective B-MANP
Laser I-MANP
Melting E-MANP
and O
Metal B-MATE
Powder E-MATE
Application O
) O
provides O
promising O
options O
for O
nuclear O
fusion S-CONPRI
applications O
. O


Selective B-MANP
Laser I-MANP
Melting E-MANP
is O
suitable O
to O
manufacture S-CONPRI
high O
complex O
and O
thin O
walled O
segments O
with O
internal O
channel S-APPL
structures O
. O


Metal B-MATE
Powder E-MATE
Application O
provides O
cost O
effective O
options O
to O
build S-PARA
First O
Wall O
relevant O
components S-MACEQ
. O


Different O
manufacturing S-MANP
routes O
are O
investigated O
at O
the O
KIT O
INR O
for O
the O
realization O
of O
First O
Walls O
( O
FW O
) O
for O
nuclear O
fusion S-CONPRI
components S-MACEQ
, O
such O
as S-MATE
the O
ITER O
Test O
Blanket O
Module O
( O
TBM O
) O
and O
DEMO O
Breeding O
Blankets O
( O
BB O
) O
for O
the O
Helium S-MATE
Cooled O
Pebble O
Bed S-MACEQ
( O
HCPB O
) O
Breeding O
concept O
. O


One O
conventional B-MANP
manufacturing E-MANP
route O
mainly O
basing O
of O
Electrical B-MANP
Discharge I-MANP
Machining E-MANP
( O
EDM S-MANP
) O
and O
forming S-MANP
was O
demonstrated O
successfully O
. O


Therefore O
, O
options O
also O
to O
apply O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
as S-MATE
alternative O
were O
investigated O
. O


This O
paper O
compares O
the O
HCPB O
reference O
concept O
for O
FW O
fabrication S-MANP
to O
innovative O
concepts O
basing O
on O
AM S-MANP
. O


The O
solid-state S-CONPRI
friction B-MANP
stir I-MANP
welding E-MANP
( O
FSW S-MANP
) O
process S-CONPRI
was O
used O
to O
join O
Al–Si12 O
parts O
fabricated S-CONPRI
via O
the O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
technique O
. O


The O
effect O
of O
the O
welding S-MANP
process S-CONPRI
on O
microstructural B-CONPRI
evolution E-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
samples S-CONPRI
is O
investigated O
in O
present O
work O
. O


Microstructural S-CONPRI
studies O
demonstrate O
that O
FSW S-MANP
is O
capable O
of O
changing O
Si S-MATE
phase B-CONPRI
morphologies E-CONPRI
( O
i.e O
. O


shape O
and O
size O
) O
resulting O
in O
various O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
stir O
zone O
of O
the O
welded B-FEAT
joint E-FEAT
shows O
significantly O
lower O
micro-hardness O
in O
comparison O
to O
the O
as-built O
SLM S-MANP
samples S-CONPRI
. O


Correspondingly O
, O
the O
friction B-MANP
stir I-MANP
welding E-MANP
process O
results O
in O
significant O
reduction S-CONPRI
of O
tensile B-PRO
strength E-PRO
, O
while O
ductility S-PRO
is O
strongly O
improved O
. O


The O
fully-reversed O
strain-controlled O
low-cycle O
fatigue S-PRO
( O
LCF O
) O
tests O
imply O
that O
at O
low O
strain S-PRO
amplitudes O
the O
FSW S-MANP
and O
SLM S-MANP
samples S-CONPRI
show O
almost O
the O
same O
fatigue B-PRO
life E-PRO
, O
while O
at O
the O
high O
strain S-PRO
amplitudes O
the O
SLM S-MANP
samples S-CONPRI
show O
superior O
LCF O
performance S-CONPRI
. O


Fracture S-CONPRI
analysis O
of O
fatigued O
samples S-CONPRI
reveals O
that O
the O
near-surface O
pores S-PRO
lead S-MATE
to O
the O
crack O
initiation O
in O
both O
SLM S-MANP
and O
FSW S-MANP
cases O
. O


Various O
methods O
have O
been O
reported O
to O
join O
carbon B-MATE
fiber E-MATE
reinforced O
polymer S-MATE
( O
CFRP O
) O
composites S-MATE
with O
aluminum B-MATE
alloy E-MATE
( O
AA O
) O
, O
with O
strengths S-PRO
ranging O
from O
13 O
MPa S-CONPRI
to O
112 O
MPa S-CONPRI
. O


This O
paper O
presents O
a O
new O
method O
for O
joining S-MANP
carbon B-MATE
fiber E-MATE
reinforced O
composites S-MATE
and O
metals S-MATE
using O
ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
( O
UAM S-MANP
) O
. O


Although O
UAM S-MANP
is O
a O
metal S-MATE
3D B-MANP
printing E-MANP
process O
, O
it O
is O
applied O
here O
to O
produce O
continuous O
CF-AA O
transition S-CONPRI
joints O
that O
can O
have O
uniform O
thickness O
across O
the O
CF O
and O
AA O
constituents O
. O


Joint S-CONPRI
strength O
is O
achieved O
by O
mechanical S-APPL
interlocking O
of O
CF O
loops O
within O
the O
AA O
matrix O
; O
tensile B-CHAR
tests E-CHAR
demonstrate O
that O
UAM S-MANP
CFRP-AA O
joints O
reach O
strengths S-PRO
of O
129.5 O
MPa S-CONPRI
. O


The O
dry O
CF O
fabric O
extending O
from O
these O
joints O
can O
be S-MATE
laid O
up O
and O
cured S-MANP
into O
a O
CFRP O
part O
, O
whereas O
the O
AA O
can O
be S-MATE
welded O
to O
metal S-MATE
structures O
using O
traditional O
metal S-MATE
welding O
techniques O
– O
hence O
their O
designation O
as S-MATE
“ O
transition S-CONPRI
joints. O
” O
This O
approach O
enables O
the O
incorporation O
of O
CFRP O
parts O
into O
vehicle O
structures O
without O
requiring O
modifications O
to O
existing O
metal S-MATE
welding O
infrastructure O
. O


Two O
failure B-PRO
modes E-PRO
, O
CF O
tow O
failure S-CONPRI
and O
AA O
failure S-CONPRI
, O
have O
been O
identified O
. O


It O
is O
shown O
that O
the O
joint B-CONPRI
failure E-CONPRI
mode O
can O
be S-MATE
designed O
for O
maximum O
strength S-PRO
or O
maximum O
energy O
dissipation O
by O
adjusting O
the O
ratio O
of O
embedded O
CF O
to O
AA O
matrix O
. O


Welded B-FEAT
joints E-FEAT
of O
SLM S-MANP
and O
CR S-MATE
stainless O
steels S-MATE
were O
produced O
by O
laser B-MANP
welding E-MANP
. O


A O
comparison O
of O
keyhole O
and O
heat B-CONPRI
conduction E-CONPRI
laser O
welding S-MANP
was O
performed O
. O


The O
influence O
of O
pre-heat B-MANP
treatment E-MANP
on O
the O
strength S-PRO
and O
weldability S-PRO
was O
revealed O
. O


The O
hardness S-PRO
of O
welding S-MANP
seams O
produced O
by O
head O
conduction O
is O
500 O
HV O
, O
by O
keyhole O
– O
280 O
HV O
. O


The O
welded B-FEAT
joints E-FEAT
strength S-PRO
is O
comparable O
to O
the O
SLM S-MANP
metal S-MATE
strength O
( O
1450 O
MPa S-CONPRI
) O
. O


The O
details O
produced O
by O
additive B-MANP
manufacturing E-MANP
have O
limitations O
in O
sizes O
, O
if O
you O
produce O
large O
details O
then O
there O
are O
large O
residual B-PRO
stresses E-PRO
. O


It O
is O
also O
economically O
advantageous O
to O
produce O
complexly O
configured O
details O
by O
additive B-MANP
manufacturing E-MANP
and O
then O
weld S-FEAT
them O
to O
rolled O
or O
wrought S-CONPRI
cheaper O
details O
. O


The O
aim O
of O
this O
study O
is O
to O
investigate O
the O
influence O
of O
pre-heat B-MANP
treatment E-MANP
on O
laser B-CONPRI
beam E-CONPRI
weldability O
of O
Selective B-MANP
Laser E-MANP
Welding O
( O
SLM S-MANP
) O
stainless B-MATE
steel E-MATE
to O
Cold B-MANP
Rolled E-MANP
( O
CR S-MATE
) O
stainless B-MATE
steel E-MATE
. O


The O
results O
of O
metallographic O
studies O
and O
mechanical B-CHAR
tests E-CHAR
of O
produced O
welds S-FEAT
are O
presented O
. O


The O
results O
showed O
that O
the O
pre-heat B-MANP
treatment E-MANP
of O
SLM S-MANP
workpieces O
affects O
the O
welded B-FEAT
joint E-FEAT
strength S-PRO
. O


The O
laser B-MANP
welding E-MANP
mode O
, O
keyhole O
or O
conduction O
, O
affected O
the O
microstructure S-CONPRI
and O
microhardness S-CONPRI
of O
the O
welds S-FEAT
. O


With O
the O
recent O
rise O
in O
the O
demand O
for O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
, O
the O
need O
for O
reliable O
simulation S-ENAT
tools O
to O
support S-APPL
experimental S-CONPRI
efforts O
grows O
steadily O
. O


Computational O
welding S-MANP
mechanics O
approaches O
can O
simulate O
the O
AM B-MANP
processes E-MANP
but O
are O
generally O
not O
validated O
for O
AM-specific O
effects O
originating O
from O
multiple O
heating S-MANP
and O
cooling S-MANP
cycles O
. O


To O
increase O
confidence O
in O
the O
outcomes O
and O
to O
use O
numerical B-ENAT
simulation E-ENAT
reliably O
, O
the O
result O
quality S-CONPRI
needs O
to O
be S-MATE
validated O
against O
experiments O
for O
in-situ S-CONPRI
and O
post-process S-CONPRI
cases O
. O


In O
this O
article O
, O
a O
validation S-CONPRI
is O
demonstrated O
for O
a O
structural O
thermomechanical S-CONPRI
simulation S-ENAT
model S-CONPRI
on O
an O
arbitrarily O
curved O
Directed B-MANP
Energy I-MANP
Deposition E-MANP
( O
DED S-MANP
) O
part O
: O
at O
first O
, O
the O
validity O
of O
the O
heat S-CONPRI
input O
is O
ensured O
and O
subsequently O
, O
the O
model S-CONPRI
’ O
s S-MATE
predictive O
quality S-CONPRI
for O
in-situ B-CONPRI
deformation E-CONPRI
and O
the O
bulging O
behaviour O
is O
investigated O
. O


For O
the O
in-situ B-CONPRI
deformations E-CONPRI
, O
3D-Digital O
Image S-CONPRI
Correlation O
measurements O
are O
conducted O
that O
quantify O
periodic O
expansion O
and O
shrinkage S-CONPRI
as S-MATE
they O
occur O
. O


The O
results O
show O
a O
strong O
dependency O
of O
the O
local O
stiffness S-PRO
of O
the O
surrounding O
geometry S-CONPRI
. O


The O
numerical B-ENAT
simulation E-ENAT
model S-CONPRI
is O
set S-APPL
up O
in O
accordance O
with O
the O
experiment S-CONPRI
and O
can O
reproduce O
the O
measured O
3-dimensional O
in-situ S-CONPRI
displacements O
. O


Furthermore O
, O
the O
deformations S-CONPRI
due O
to O
removal O
from O
the O
substrate S-MATE
are O
quantified O
via O
3D-scanning O
, O
exhibiting O
considerable O
distortions O
due O
to O
stress B-CONPRI
relaxation E-CONPRI
. O


Finally O
, O
the O
prediction S-CONPRI
of O
the O
deformed B-PRO
shape E-PRO
is O
discussed O
in O
regards O
to O
bulging O
simulation S-ENAT
: O
to O
improve O
the O
accuracy S-CHAR
of O
the O
calculated O
final O
shape O
, O
a O
novel O
extension O
of O
the O
model S-CONPRI
relying O
on O
the O
modified O
stiffness S-PRO
of O
inactive O
upper O
layers O
is O
proposed O
and O
the O
experimentally O
observed O
bulging O
could O
be S-MATE
reproduced O
in O
the O
finite B-CONPRI
element I-CONPRI
model E-CONPRI
. O


High-performance O
components S-MACEQ
from O
titanium B-MATE
alloy E-MATE
Ti-6Al-4V S-MATE
are O
used O
in O
many O
industries S-APPL
, O
particularly O
in O
aerospace S-APPL
, O
but O
also O
in O
the O
automotive S-APPL
and O
medical S-APPL
market O
. O


Traditionally O
, O
such O
components S-MACEQ
are O
produced O
by O
hot O
forging S-MANP
and O
subsequent O
post B-CONPRI
processing E-CONPRI
. O


The O
multi-stage O
forging S-MANP
process O
requires O
several O
expensive O
dies S-MACEQ
and O
leads O
to O
components S-MACEQ
with O
a O
high O
material S-MATE
oversize O
. O


Therefore O
, O
costly O
machining S-MANP
operations O
with O
machining S-MANP
removal O
up O
to O
more O
than O
90 O
% O
are O
necessary O
to O
produce O
the O
final O
geometry S-CONPRI
. O


New O
technologies S-CONPRI
, O
such O
as S-MATE
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
, O
could O
support S-APPL
traditional O
process B-ENAT
chains E-ENAT
and O
could O
enable O
a O
more O
resource-efficient O
production S-MANP
. O


However O
, O
in O
additive B-MANP
manufacturing E-MANP
production O
cycles O
are O
still O
long O
and O
manufacturing B-CONPRI
costs E-CONPRI
are O
very O
high O
, O
especially O
for O
larger O
parts O
. O


Thus O
, O
the O
production S-MANP
by O
AM S-MANP
is O
often O
limited O
to O
low O
quantities O
and O
smaller O
components S-MACEQ
. O


To O
overcome O
the O
above-mentioned O
disadvantages O
the O
present O
study O
proposes O
a O
hybrid B-CONPRI
manufacturing E-CONPRI
route O
, O
combining O
the O
advantages O
of O
forging S-MANP
and O
AM S-MANP
. O


The O
new O
manufacturing S-MANP
route O
could O
reduce O
the O
number O
of O
processing O
steps O
and O
forging S-MANP
dies S-MACEQ
, O
and O
additionally O
could O
provide O
efficient O
near-net-shape S-MANP
production O
. O


These O
features O
, O
such O
as S-MATE
ribs O
or O
other O
structural O
or O
functional O
geometries S-CONPRI
, O
will O
be S-MATE
added O
by O
additive B-MANP
manufacturing E-MANP
. O


The O
present O
study O
investigates S-CONPRI
the O
use O
of O
powder S-MATE
laser B-MANP
metal I-MANP
deposition E-MANP
( O
p-LMD O
) O
and O
wire-arc B-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
for O
hybrid B-CONPRI
manufacturing E-CONPRI
of O
Ti-6Al-4V S-MATE
aerospace S-APPL
forgings O
. O


BackgroundAdditive O
manufacturing S-MANP
( O
AM S-MANP
) O
is O
a O
rapidly O
expanding O
new O
technology S-CONPRI
involving O
challenges O
to O
occupational O
health O
. O


Here O
, O
metal S-MATE
exposure S-CONPRI
in O
an O
AM S-MANP
facility O
with O
large-scale O
metallic S-MATE
component S-MACEQ
production O
was O
investigated O
during O
two O
consecutive O
years O
with O
preventive O
actions O
in O
between.MethodsGravimetric O
analyzes O
measured O
airborne O
particle S-CONPRI
concentrations O
, O
and O
filters S-APPL
were O
analyzed O
for O
metal S-MATE
content O
. O


Particles S-CONPRI
from O
recycled S-CONPRI
powder S-MATE
were O
characterized O
. O


Airborne O
particle S-CONPRI
concentrations O
( O
< O
300 O
nm O
) O
showed O
transient S-CONPRI
peaks O
in O
the O
AM S-MANP
facility O
but O
were O
lower O
than O
those O
of O
the O
welding S-MANP
facility O
. O


Particle S-CONPRI
characterization O
of O
recycled S-CONPRI
powder S-MATE
showed O
fragmentation O
and O
condensates O
enriched O
in O
volatile O
metals S-MATE
. O


Biomonitoring O
showed O
a O
nonsignificant O
increase O
in O
the O
level O
of O
metals S-MATE
in O
urine O
in O
AM S-MANP
operators O
. O


Dermal O
cobalt S-MATE
and O
a O
trend S-CONPRI
for O
increasing O
urine O
metals S-MATE
during O
Workweek O
Year O
1 O
, O
but O
not O
in O
Year O
2 O
, O
indicated O
reduced O
exposure S-CONPRI
after O
preventive O
actions.ConclusionGravimetric O
analyses O
showed O
low O
total O
and O
inhalable O
dust O
exposure S-CONPRI
in O
AM S-MANP
operators O
. O


However O
, O
transient S-CONPRI
emission S-CHAR
of O
smaller O
particles S-CONPRI
constitutes O
exposure S-CONPRI
risks O
. O


Preventive O
actions O
implemented O
by O
the O
company S-APPL
reduced O
the O
workers O
' O
metal S-MATE
exposure S-CONPRI
despite O
unchanged O
emissions O
of O
particles S-CONPRI
, O
indicating O
a O
need O
for O
careful O
design S-FEAT
and O
regulation O
of O
the O
AM S-MANP
environments O
. O


HDPE S-MATE
polymer O
HX O
is O
fabricated S-CONPRI
using O
layer-by-layer S-CONPRI
line O
welding S-MANP
of O
plastic S-MATE
sheets O
. O


The O
polymer S-MATE
HX O
shows O
superior O
air-side O
performance S-CONPRI
over O
plane O
plate O
fin O
surface S-CONPRI
. O


In O
addition O
to O
their O
low O
cost O
and O
weight S-PARA
, O
polymer S-MATE
heat B-MACEQ
exchangers E-MACEQ
offer O
good O
anticorrosion O
and O
antifouling O
properties S-CONPRI
. O


In O
this O
work O
, O
a O
cost O
effective O
air-water O
polymer S-MATE
heat B-MACEQ
exchanger E-MACEQ
made O
of O
thin O
polymer S-MATE
sheets O
using O
layer-by-layer S-CONPRI
line O
welding S-MANP
with O
a O
laser S-ENAT
through O
an O
additive B-MANP
manufacturing I-MANP
process E-MANP
was O
fabricated S-CONPRI
and O
experimentally O
tested O
. O


The O
flow O
channels O
were O
made O
of O
150 O
μm-thick O
high B-MATE
density I-MATE
polyethylene E-MATE
sheets O
, O
which O
were O
15.5 O
cm O
wide O
and O
29 O
cm O
long O
. O


The O
experimental S-CONPRI
results O
show O
that O
the O
overall O
heat B-CONPRI
transfer E-CONPRI
coefficient O
of O
35–120 O
W/m2 O
K S-MATE
is O
achievable O
for O
an O
air-water O
fluid S-MATE
combination O
for O
air-side O
flow B-PARA
rate E-PARA
of O
3–24 O
L/s O
and O
water-side O
flow B-PARA
rate E-PARA
of O
12.5 O
mL/s O
. O


In O
addition O
, O
by O
fabricating S-MANP
a O
very O
thin O
wall O
heat B-MACEQ
exchanger E-MACEQ
( O
150 O
μm O
) O
, O
the O
wall O
thermal O
resistance S-PRO
, O
which O
usually O
becomes O
the O
limiting O
factor O
on O
polymer S-MATE
heat B-MACEQ
exchangers E-MACEQ
, O
was O
calculated O
to O
account O
for O
only O
3 O
% O
of O
the O
total O
thermal O
resistance S-PRO
. O


A O
comparison O
of O
the O
air-side O
heat B-CONPRI
transfer E-CONPRI
coefficient O
of O
the O
present O
polymer S-MATE
heat B-MACEQ
exchanger E-MACEQ
with O
some O
of O
the O
commercially O
available O
plain O
plate O
fin O
heat B-MACEQ
exchanger E-MACEQ
surfaces O
suggests O
that O
its O
performance S-CONPRI
in O
general O
is O
superior O
to O
that O
of O
common O
plain O
plate O
fin O
surfaces S-CONPRI
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
offers O
the O
possibility O
of O
locally O
reinforcing O
sheet B-MATE
metal E-MATE
or O
sheet B-MATE
metal E-MATE
products O
by O
adding O
patches O
that O
are O
metallurgically O
bonded O
to O
the O
substrate S-MATE
. O


Due O
to O
the O
high O
design B-CONPRI
freedom E-CONPRI
of O
AM S-MANP
, O
patches O
can O
be S-MATE
easily O
adapted O
to O
loads O
in O
geometry S-CONPRI
and O
thickness O
. O


However O
, O
the O
heat S-CONPRI
input O
and O
the O
high O
cooling B-PARA
rates E-PARA
during O
AM B-MANP
processes E-MANP
have O
a O
strong O
influence O
on O
the O
microstructure S-CONPRI
in O
the O
patch O
as S-MATE
well O
as S-MATE
in O
the O
substrate S-MATE
, O
which O
will O
affect O
forming S-MANP
properties O
. O


The O
aim O
of O
this O
work O
is O
to O
investigate O
the O
influence O
of O
patches O
produced O
by O
laser S-ENAT
material O
deposition S-CONPRI
( O
LMD S-MANP
) O
on O
formability S-PRO
of O
micro-alloyed O
sheet B-MATE
metals E-MATE
. O


After O
determining O
a O
suitable O
process S-CONPRI
window O
for O
metallurgically O
bonded O
patches O
without O
cracks O
and O
pores S-PRO
, O
investigations O
were O
carried O
out O
on O
the O
microstructure S-CONPRI
and O
mechanical B-CONPRI
properties E-CONPRI
of O
reinforced S-CONPRI
samples O
. O


This O
work O
includes O
metallographic O
examinations O
using O
optical B-CHAR
microscopy E-CHAR
, O
hardness S-PRO
measurements O
and O
tensile B-CHAR
tests E-CHAR
. O


The O
formability S-PRO
of O
sheets S-MATE
with O
local O
reinforcement S-PARA
was O
investigated O
by O
stretching O
and O
Nakajima O
tests O
. O


The O
heat S-CONPRI
input O
creates O
a O
heat B-CONPRI
affected I-CONPRI
zone E-CONPRI
( O
HAZ S-CONPRI
) O
directly O
next O
to O
the O
patches O
with O
a O
reduced O
strength S-PRO
, O
caused O
by O
recrystallization S-CONPRI
that O
may O
lead S-MATE
to O
failure S-CONPRI
in O
the O
forming B-MANP
process E-MANP
and O
thus O
limits S-CONPRI
the O
forming S-MANP
capacity S-CONPRI
of O
locally O
reinforced S-CONPRI
sheet O
metals S-MATE
. O


A O
subsequent O
laser B-PARA
heat E-PARA
treatment O
can O
homogenize O
the O
properties S-CONPRI
in O
the O
HAZ S-CONPRI
. O


Ti-6Al-4V S-MATE
samples S-CONPRI
produced O
by O
electron B-MANP
beam I-MANP
melting E-MANP
( O
EBM S-MANP
) O
are O
welded S-MANP
using O
solid-state S-CONPRI
friction B-MANP
welding E-MANP
( O
FW O
) O
process S-CONPRI
. O


The O
microstructure S-CONPRI
of O
the O
weld S-FEAT
sample S-CONPRI
shows O
the O
presence O
of O
fine O
equiaxed O
α O
grains S-CONPRI
with O
irregular O
β O
phase S-CONPRI
. O


Microstructural S-CONPRI
investigations O
reveal O
a O
pronounced O
change O
in O
the O
shape O
and O
size O
of O
the O
α O
phase S-CONPRI
in O
the O
weld B-MATE
metal E-MATE
as-compared O
to O
the O
base O
material S-MATE
along O
with O
the O
disappearance O
of O
columnar O
prior O
β O
grains S-CONPRI
. O


Such O
variations S-CONPRI
in O
the O
microstructure S-CONPRI
significantly O
change O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
FW O
material S-MATE
. O


The O
hardness S-PRO
in O
the O
weld B-CONPRI
zone E-CONPRI
increases O
and O
a O
decrease O
of O
hardness S-PRO
is O
observed O
along O
the O
heat B-CONPRI
affected I-CONPRI
zone E-CONPRI
( O
HAZ S-CONPRI
) O
with O
respect O
to O
the O
base B-MATE
metal E-MATE
as S-MATE
expected O
. O


Similarly O
, O
the O
room O
temperature S-PARA
tensile O
tests O
show O
an O
improvement O
of O
ductility S-PRO
in O
the O
welded B-MANP
EBM E-MANP
samples S-CONPRI
. O


However O
, O
the O
yield O
and O
the O
ultimate B-PRO
strength E-PRO
show O
a O
marginal O
drop O
in O
the O
welded S-MANP
samples S-CONPRI
compared O
to O
the O
as-prepared O
EBM S-MANP
specimens O
. O


The O
present O
work O
demonstrates O
that O
solid-state S-CONPRI
FW O
process S-CONPRI
not O
only O
permits O
successful O
joining S-MANP
of O
additively B-MANP
manufactured E-MANP
materials O
, O
but O
also O
helps O
in O
improving O
their O
ductility S-PRO
. O


Laser S-ENAT
zone O
with O
refined O
grains S-CONPRI
and O
more O
uniform O
element S-MATE
distribution S-CONPRI
forms O
by O
laser-arc O
hybrid O
additive B-MANP
manufacturing E-MANP
. O


Outstanding O
micro-hardness O
and O
tensile B-PRO
strength E-PRO
can O
be S-MATE
obtained O
by O
laser-arc O
hybrid O
additive B-MANP
manufacturing E-MANP
. O


Finer O
grains S-CONPRI
and O
significant O
decreasing O
of O
element S-MATE
segregation O
in O
laser S-ENAT
zone O
can O
help O
to O
strengthen O
mechanical B-CONPRI
properties E-CONPRI
. O


4043 O
AlSi O
alloy S-MATE
samples O
are O
fabricated S-CONPRI
by O
laser-arc O
hybrid O
additive B-MANP
manufacturing E-MANP
and O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
. O


To O
investigate O
the O
influence O
of O
laser B-CONPRI
energy E-CONPRI
on O
the O
fabricated S-CONPRI
sample O
, O
the O
microstructure S-CONPRI
evaluation O
and O
mechanical B-CONPRI
properties E-CONPRI
are O
studied O
. O


After O
the O
input O
of O
laser B-CONPRI
energy E-CONPRI
, O
there O
are O
laser S-ENAT
zones O
with O
finer O
grains S-CONPRI
and O
reduced O
Si S-MATE
segregation S-CONPRI
. O


As S-MATE
a O
result O
, O
the O
Si S-MATE
phases O
at O
grain B-CONPRI
boundaries E-CONPRI
in O
laser S-ENAT
zone O
are O
smaller O
than O
that O
in O
other O
zones O
. O


And O
it O
is O
found O
that O
semi-coherent O
interface S-CONPRI
between O
Al S-MATE
and O
Si S-MATE
phases O
with O
crystal B-PRO
orientation E-PRO
relations O
, O
[ O
110 O
] O
Al∥ O
[ O
110 O
] O
Si S-MATE
and O
( O
111 O
) O
Al∥ O
( O
220 O
) O
Si S-MATE
, O
indicating O
the O
Si S-MATE
phase S-CONPRI
tends O
to O
grow O
along O
( O
111 O
) O
Al S-MATE
plane O
. O


The O
results O
of O
mechanical B-CONPRI
properties E-CONPRI
show O
that O
the O
micro-hardness O
in O
laser S-ENAT
zone O
is O
54.3 O
HV0.05 O
, O
with O
the O
increment O
of O
19.08 O
% O
compared O
to O
that O
in O
heat-affected O
zone O
. O


And O
the O
tensile B-PRO
strength E-PRO
, O
yield B-PRO
strength E-PRO
and O
elongation S-PRO
after O
the O
input O
of O
laser B-CONPRI
energy E-CONPRI
are O
163.39 O
± O
1.68 O
MPa S-CONPRI
, O
75.60 O
± O
4.91 O
MPa S-CONPRI
and O
17.38 O
± O
5.44 O
% O
, O
which O
are O
7.56 O
% O
, O
8.45 O
% O
and O
3.45 O
% O
higher O
than O
that O
without O
laser S-ENAT
. O


The O
improved O
mechanical B-CONPRI
properties E-CONPRI
are O
due O
to O
the O
finer O
gains O
, O
reduced O
Si S-MATE
segregation S-CONPRI
and O
the O
crack O
deflection O
in O
LAHAM O
samples S-CONPRI
. O


The O
structure S-CONPRI
and O
properties S-CONPRI
of O
welded S-MANP
and O
additively B-MANP
manufactured E-MANP
alloys O
are O
affected O
by O
the O
microstructural B-CONPRI
evolution E-CONPRI
in O
the O
fusion B-CONPRI
zone E-CONPRI
( O
FZ S-CONPRI
) O
and O
heat B-CONPRI
affected I-CONPRI
zone E-CONPRI
( O
HAZ S-CONPRI
) O
. O


The O
motion O
of O
the O
liquid O
pool O
and O
the O
interdependence O
of O
grain B-CONPRI
growth E-CONPRI
in O
both O
the O
solid O
and O
liquid O
regions O
are O
important O
in O
the O
evolution S-CONPRI
of O
the O
final O
grain B-CONPRI
structure E-CONPRI
. O


Previous O
investigations O
of O
microstructure B-CONPRI
evolution E-CONPRI
have O
been O
limited O
to O
either O
the O
HAZ S-CONPRI
or O
the O
FZ S-CONPRI
and O
in O
many O
cases O
in O
idealized O
isothermal S-CONPRI
systems O
. O


Here O
we O
report O
the O
evolution S-CONPRI
of O
grain B-CONPRI
structure E-CONPRI
and O
topology S-CONPRI
in O
three O
dimensions S-FEAT
in O
both O
the O
FZ S-CONPRI
and O
the O
HAZ S-CONPRI
considering O
the O
motion O
of O
the O
liquid O
pool O
. O


Temporal O
and O
spatial B-CHAR
distributions E-CHAR
of O
temperature S-PARA
obtained O
from O
a O
well-tested O
heat B-CONPRI
transfer E-CONPRI
and O
liquid B-MATE
metal E-MATE
flow O
calculation O
are O
combined O
with O
Monte O
Carlo O
and O
topology S-CONPRI
calculations O
in O
a O
computationally O
efficient O
manner O
. O


The O
computed O
results O
are O
tested O
against O
independent O
experimental B-CONPRI
data E-CONPRI
for O
arc B-MANP
welding E-MANP
of O
an O
aluminum B-MATE
alloy E-MATE
. O


The O
average S-CONPRI
size O
of O
the O
columnar B-PRO
grains E-PRO
in O
the O
FZ S-CONPRI
and O
the O
equiaxed B-CONPRI
grains E-CONPRI
in O
the O
HAZ S-CONPRI
are O
shown O
to O
decrease O
with O
increasing O
scanning B-PARA
speed E-PARA
. O


For O
a O
given O
weld S-FEAT
, O
the O
size O
and O
aspect B-FEAT
ratio E-FEAT
of O
the O
columnar B-PRO
grains E-PRO
in O
the O
longitudinal O
and O
horizontal O
planes O
are O
shown O
to O
decrease O
with O
distance O
from O
the O
weld S-FEAT
interface S-CONPRI
. O


It O
is O
further O
shown O
that O
the O
grain B-PRO
size E-PRO
distributions S-CONPRI
and O
topological O
class O
distributions S-CONPRI
in O
the O
HAZ S-CONPRI
are O
largely O
unaffected O
by O
the O
temporal O
and O
spatial B-FEAT
variations E-FEAT
of O
the O
temperature S-PARA
created O
by O
different O
welding S-MANP
parameters S-CONPRI
. O


In O
laser B-MANP
welding E-MANP
and O
other O
processes S-CONPRI
, O
such O
as S-MATE
cladding O
and O
additive B-MANP
manufacturing E-MANP
, O
the O
weld B-PARA
bead I-PARA
geometry E-PARA
( O
depth O
of O
penetration S-CONPRI
and O
weld S-FEAT
width O
) O
can O
be S-MATE
controlled O
with O
different O
parameters S-CONPRI
. O


A O
common O
practice O
is O
to O
develop O
process B-CONPRI
parameters E-CONPRI
for O
a O
particular O
application O
based O
on O
an O
engineering S-APPL
approach O
using O
the O
system O
parameters S-CONPRI
i.e O
. O


laser B-PARA
power E-PARA
and O
travel O
speed O
. O


This O
study O
is O
focused O
on O
understanding O
of O
the O
phenomena O
controlling O
the O
weld S-FEAT
profile S-FEAT
in O
conduction O
welding S-MANP
for O
a O
wide O
range S-PARA
of O
beam B-PARA
diameters E-PARA
from O
0.07 O
mm S-MANP
to O
5.50 O
mm S-MANP
. O


It O
has O
been O
shown O
that O
the O
weld B-PARA
bead I-PARA
geometry E-PARA
can O
be S-MATE
controlled O
by O
the O
spatial O
and O
temporal O
distribution S-CONPRI
of O
laser B-CONPRI
energy E-CONPRI
on O
the O
surface S-CONPRI
of O
workpiece S-CONPRI
, O
such O
as S-MATE
power O
density S-PRO
, O
interaction O
time O
and O
energy B-PARA
density E-PARA
. O


This O
means O
that O
similar O
depths O
of O
penetration S-CONPRI
can O
be S-MATE
achieved O
with O
various O
optical S-CHAR
set-ups O
. O


It O
has O
been O
also O
found O
that O
it O
is O
more O
difficult O
to O
achieve O
pure O
conduction O
welds S-FEAT
with O
small O
beam B-PARA
diameters E-PARA
, O
which O
are O
typically O
used O
in O
powder B-MANP
bed I-MANP
additive I-MANP
manufacturing E-MANP
, O
due O
to O
high O
conduction O
losses O
and O
low O
vaporisation O
threshold O
. O


Ultrasonic B-MANP
Additive I-MANP
Manufacturing E-MANP
( O
UAM S-MANP
) O
is O
a O
hybrid B-CONPRI
manufacturing E-CONPRI
process O
that O
involves O
the O
layer-by-layer S-CONPRI
ultrasonic O
welding S-MANP
of O
metal S-MATE
foils O
in O
the O
solid B-CONPRI
state E-CONPRI
with O
periodic O
CNC B-MANP
machining E-MANP
to O
achieve O
the O
desired O
3D S-CONPRI
shape O
. O


UAM S-MANP
enables O
the O
fabrication S-MANP
of O
metal S-MATE
smart O
structures O
, O
because O
it O
allows O
the O
embedding O
of O
various O
components S-MACEQ
into O
the O
metal B-CONPRI
matrix E-CONPRI
, O
due O
to O
the O
high O
degree O
of O
plastic B-MATE
metal E-MATE
flow O
and O
the O
relatively O
low O
temperatures S-PARA
encountered O
during O
the O
layer S-PARA
bonding S-CONPRI
process O
. O


To O
further O
the O
embedding O
capabilities O
of O
UAM S-MANP
, O
in O
this O
paper O
we O
examine O
the O
ultrasonic B-MANP
welding E-MANP
of O
aluminium S-MATE
foils O
with O
features O
machined S-MANP
prior O
to O
bonding S-CONPRI
. O


These O
pre-machined O
features O
can O
be S-MATE
stacked O
layer-by-layer S-CONPRI
to O
create O
pockets O
for O
the O
accommodation O
of O
fragile S-CONPRI
components S-MACEQ
, O
such O
as S-MATE
electronic O
circuitry O
, O
prior O
to O
encapsulation S-CONPRI
. O


This O
manufacturing B-MANP
approach E-MANP
transforms O
UAM S-MANP
into O
a O
“ O
form-then-bond O
” O
process S-CONPRI
. O


By O
studying O
the O
deformation S-CONPRI
of O
aluminium S-MATE
foils O
during O
UAM S-MANP
, O
a O
statistical O
model S-CONPRI
was O
developed O
that O
allowed O
the O
prediction S-CONPRI
of O
the O
final O
location O
, O
dimensions S-FEAT
and O
tolerances S-PARA
of O
pre-machined O
features O
for O
a O
set S-APPL
of O
UAM S-MANP
process B-CONPRI
parameters E-CONPRI
. O


The O
predictive O
power S-PARA
of O
the O
model S-CONPRI
was O
demonstrated O
by O
designing O
a O
cavity O
to O
accommodate O
an O
electronic O
component S-MACEQ
( O
i.e O
. O


a O
surface B-ENAT
mount E-ENAT
resistor S-MACEQ
) O
prior O
to O
its O
encapsulation S-CONPRI
within O
the O
metal B-CONPRI
matrix E-CONPRI
. O


We O
also O
further O
emphasised O
the O
importance O
of O
the O
tensioning O
force S-CONPRI
in O
the O
UAM S-MANP
process S-CONPRI
. O


The O
current O
work O
paves O
the O
way O
for O
the O
creation O
of O
a O
novel O
system O
for O
the O
fabrication S-MANP
of O
three-dimensional S-CONPRI
electronic O
circuits O
embedded O
into O
an O
additively B-MANP
manufactured E-MANP
complex O
metal B-MATE
composite E-MATE
. O


Additive B-MANP
manufacturing E-MANP
of O
metals S-MATE
is O
an O
innovative O
near-net-shaped O
manufacturing B-MANP
technology E-MANP
used O
for O
producing O
final O
solid O
objects O
by O
depositing O
successive O
layers O
of O
material S-MATE
melted O
in O
powder S-MATE
or O
wire O
form O
using O
a O
focused O
heat B-CONPRI
source E-CONPRI
directed O
from O
an O
electron B-CONPRI
beam E-CONPRI
, O
laser B-CONPRI
beam E-CONPRI
, O
or O
plasma S-CONPRI
or O
electric B-PARA
arc E-PARA
. O


Wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
techniques O
, O
although O
have O
lesser O
precision S-CHAR
as S-MATE
compared O
to O
laser S-ENAT
or O
electron B-CONPRI
beam E-CONPRI
techniques O
but O
have O
the O
advantage O
of O
lower O
cost O
and O
lesser O
time O
required O
. O


In O
this O
research S-CONPRI
, O
gas B-MANP
metal I-MANP
arc I-MANP
welding E-MANP
( O
GMAW S-MANP
) O
process S-CONPRI
has O
been O
used O
using O
AWS O
ER70S-6 S-MATE
electrode S-MACEQ
wire O
to O
create O
a O
multi-layer O
single O
pass O
structure S-CONPRI
after O
controlling O
the O
parameters S-CONPRI
including O
current O
, O
voltage O
and O
travel O
speed O
so O
that O
uniform O
height O
is O
attained O
throughout O
the O
weld B-CONPRI
bead E-CONPRI
. O


The O
resulting O
material S-MATE
may O
have O
different O
directional O
mechanical B-CONPRI
properties E-CONPRI
because O
of O
factors O
including O
different O
penetration S-CONPRI
properties O
and O
bonding B-PRO
strength E-PRO
and O
also O
preheating S-MANP
and O
post-heating O
effects O
of O
successive O
layers O
. O


This O
study O
focuses O
on O
the O
impact S-CONPRI
toughness O
of O
the O
resulting O
material S-MATE
. O


Charpy O
impact B-CHAR
test E-CHAR
is O
carried O
out O
on O
the O
samples S-CONPRI
taken O
in O
both O
along O
the O
direction O
of O
deposition S-CONPRI
and O
in O
the O
direction O
perpendicular O
to O
it O
to O
analyze O
the O
impact S-CONPRI
toughness O
in O
different O
directions O
. O


To O
further O
investigate O
the O
behavior O
of O
the O
structure S-CONPRI
, O
Brinell B-PRO
hardness E-PRO
, O
metallography S-CONPRI
and O
fractography S-CHAR
have O
been O
performed O
. O


The O
results O
show O
that O
material S-MATE
has O
high O
impact S-CONPRI
toughness O
with O
very O
ductile S-PRO
behavior O
. O


High-efficiency O
elastocaloric O
refrigeration O
requires O
high-performance O
elastocaloric O
materials S-CONPRI
with O
both O
large O
surface B-PARA
areas E-PARA
to O
promote O
heat S-CONPRI
exchange O
rate O
and O
large O
elastocaloric O
effects O
to O
increase O
the O
amount O
of O
heat B-CONPRI
transfer E-CONPRI
. O


Ni-Ti O
shape B-MATE
memory I-MATE
alloys E-MATE
( O
SMAs S-MATE
) O
are O
the O
most O
promising O
elastocaloric O
materials S-CONPRI
but O
they O
are O
difficult O
to O
process S-CONPRI
by O
conventional O
methods O
due O
to O
their O
poor O
manufacturability S-CONPRI
. O


Here O
, O
we O
successfully O
developed O
Ni-Ti O
SMAs S-MATE
with O
large O
elastocaloric O
effects O
by O
additive B-MANP
manufacturing E-MANP
which O
has O
the O
capability O
to O
fabricate S-MANP
complex B-CONPRI
geometries E-CONPRI
with O
large O
surface B-PARA
areas E-PARA
. O


The O
phase S-CONPRI
transformation O
temperatures S-PARA
of O
these O
additively B-MANP
manufactured E-MANP
Ni-Ti O
SMAs S-MATE
, O
fabricated S-CONPRI
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
, O
can O
be S-MATE
tuned O
by O
varying O
the O
SLM S-MANP
processing O
parameters S-CONPRI
and/or O
post O
heat B-MANP
treatments E-MANP
and O
thus O
tunable O
large O
elastocaloric O
effects O
were O
achieved O
at O
different O
temperatures S-PARA
, O
which O
can O
be S-MATE
used O
for O
different O
applications O
. O


Owing O
to O
its O
large O
transformation O
entropy O
change O
and O
high O
yield B-PRO
strength E-PRO
as S-MATE
a O
result O
of O
precipitation B-MANP
hardening E-MANP
, O
the O
aged O
SLM S-MANP
fabricated S-CONPRI
alloy S-MATE
exhibits O
a O
remarkably O
large O
elastocaloric O
effect O
with O
an O
adiabatic O
temperature S-PARA
change O
as S-MATE
high O
as S-MATE
23.2 O
K S-MATE
, O
which O
is O
among O
the O
highest O
values O
reported O
for O
all O
Ni-Ti O
SMAs S-MATE
fabricated S-CONPRI
by O
both O
conventional O
methods O
and O
additive B-MANP
manufacturing E-MANP
. O


Furthermore O
, O
by O
virtue O
of O
the O
high O
yield B-PRO
strength E-PRO
and O
low O
stress B-PRO
hysteresis E-PRO
of O
the O
aged O
alloy S-MATE
, O
this O
large O
elastocaloric O
effect O
shows O
good O
stability S-PRO
during O
cycling O
. O


The O
achievement O
of O
such O
large O
elastocaloric O
effects O
in O
alloys S-MATE
fabricated O
by O
near-net-shape S-MANP
additive B-MANP
manufacturing E-MANP
may O
accelerate O
the O
implementation O
of O
high-efficiency O
elastocaloric O
refrigeration O
. O


This O
study O
is O
instructive O
for O
the O
development O
of O
advanced O
high-performance O
solid-state S-CONPRI
refrigeration O
materials S-CONPRI
by O
additive B-MANP
manufacturing E-MANP
. O


Due O
to O
the O
practicability O
of O
economically O
generating O
large-scale O
metal S-MATE
components S-MACEQ
with O
relatively O
high B-PARA
deposition I-PARA
rates E-PARA
, O
consequential O
progress O
has O
been O
made O
in O
the O
perspective O
of O
the O
Wire B-MANP
Arc I-MANP
Additive I-MANP
Manufacturing E-MANP
( O
WAAM S-MANP
) O
process S-CONPRI
. O


This O
article O
reviews O
the O
looming O
research S-CONPRI
on O
WAAM S-MANP
techniques O
and O
the O
commonly O
used O
metallic S-MATE
feedstock B-MATE
materials E-MATE
. O


The O
frequent O
defects S-CONPRI
that O
are O
produced O
in O
components S-MACEQ
during O
the O
WAAM S-MANP
process S-CONPRI
using O
different O
alloys S-MATE
are O
characterized O
including O
deformity O
, O
porosity S-PRO
, O
and O
cracking S-CONPRI
. O


Methods O
for O
enhancing O
the O
fabrication S-MANP
quality O
of O
the O
additively B-MANP
manufactured E-MANP
components O
are O
also O
discussed O
, O
with O
the O
consideration O
of O
the O
requirements O
of O
the O
distinct O
alloys S-MATE
. O


The O
implementation O
of O
the O
standardized O
Conventional O
Heat B-MANP
Treatment E-MANP
procedure O
to O
mitigate O
the O
defects S-CONPRI
in O
the O
WAAM S-MANP
process S-CONPRI
and O
in O
capturing O
the O
future O
possibilities O
that O
are O
efficient O
has O
been O
discussed O
. O


The O
unification O
of O
materials S-CONPRI
and O
manufacturing B-MANP
process E-MANP
to O
produce O
defect-free O
and O
structurally-sound O
deposited O
parts O
remains O
a O
crucial O
effort O
in O
the O
future O
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
, O
through O
directed B-MANP
energy I-MANP
deposition E-MANP
, O
supports S-APPL
planned O
composition S-CONPRI
changes O
between O
locations O
within O
a O
single O
component S-MACEQ
, O
allowing O
for O
functionally B-MATE
graded I-MATE
materials E-MATE
( O
FGMs O
) O
to O
be S-MATE
developed O
and O
fabricated S-CONPRI
. O


The O
formation O
of O
deleterious O
phases O
along O
a O
particular O
composition S-CONPRI
path O
can O
cause O
significant O
cracking S-CONPRI
during O
the O
AM S-MANP
build O
process S-CONPRI
that O
makes O
the O
composition S-CONPRI
path O
unviable O
to O
produce O
these O
FGMs O
, O
but O
it O
is O
challenging O
to O
predict O
which O
phases O
will O
be S-MATE
present O
in O
as-built O
additively B-MANP
manufactured E-MANP
parts O
by O
analyzing O
only O
equilibrium S-CONPRI
phase O
relations O
. O


Solute O
segregation S-CONPRI
during O
solidification S-CONPRI
can O
lead S-MATE
to O
the O
formation O
of O
non-equilibrium O
phases O
that O
are O
stable O
at O
compositions O
far O
from O
the O
nominal O
composition S-CONPRI
of O
the O
melt S-CONPRI
, O
leading O
to O
crack O
formation O
. O


We O
used O
this O
tool S-MACEQ
to O
compare O
the O
non-equilibrium O
phases O
predicted S-CONPRI
to O
form O
during O
the O
AM S-MANP
build O
process S-CONPRI
using O
the O
Scheil-Gulliver B-CONPRI
model E-CONPRI
with O
experimentally O
measured O
phases O
at O
several O
locations O
with O
different O
composition S-CONPRI
in O
a O
Ti-6Al-4V S-MATE
to O
Invar-36 O
FGM S-MANP
and O
a O
commercially O
pure O
Ti S-MATE
to O
Invar-36 O
FGM S-MANP
. O


We O
showed O
that O
the O
phases O
predicted S-CONPRI
to O
form O
by O
the O
Scheil-Gulliver B-CONPRI
model E-CONPRI
agree O
better O
with O
the O
experimental S-CONPRI
results O
than O
the O
predictions S-CONPRI
made O
by O
assuming O
equilibrium S-CONPRI
solidification O
, O
proving O
that O
the O
Scheil-Gulliver B-CONPRI
model E-CONPRI
can O
be S-MATE
applied O
to O
FGMs O
. O


Further O
, O
we O
demonstrated O
the O
use O
of O
our O
Scheil-Gulliver O
simulation S-ENAT
tool O
as S-MATE
a O
method O
of O
designing O
FGMs O
through O
screening O
potential O
FGM S-MANP
pathways O
by O
calculating O
the O
solidification B-CONPRI
phase E-CONPRI
fractions O
along O
the O
experimental S-CONPRI
gradient O
path O
in O
composition S-CONPRI
space O
. O


Ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
( O
UAM S-MANP
) O
is O
a O
solid-state S-CONPRI
manufacturing S-MANP
technique O
employing O
principles O
of O
ultrasonic B-MANP
welding E-MANP
coupled O
with O
mechanized O
tape O
layering O
to O
fabricate S-MANP
fully O
functional O
parts O
. O


However O
, O
UAM-fabricated O
parts O
often O
exhibit O
a O
reduction S-CONPRI
in O
strength S-PRO
when O
loaded O
normal O
to O
the O
welding B-FEAT
interfaces E-FEAT
( O
Z-direction S-FEAT
) O
. O


Here O
, O
the O
effect O
of O
hot B-MANP
isostatic I-MANP
pressing E-MANP
( O
HIP S-MANP
) O
on O
UAM S-MANP
builds S-CHAR
of O
aluminum B-MATE
alloy E-MATE
was O
explored O
. O


Tensile B-CHAR
testing E-CHAR
and O
microstructure S-CONPRI
characterization O
were O
conducted O
; O
it O
was O
established O
that O
HIP S-MANP
eliminated O
the O
brittle S-PRO
Z-direction O
fracture S-CONPRI
and O
improved O
the O
strength S-PRO
and O
ductility S-PRO
of O
the O
Z-direction S-FEAT
specimens O
. O


HIP S-MANP
eliminated O
voids S-CONPRI
and O
produced O
recrystallized S-MANP
structure O
; O
however O
, O
welding B-FEAT
interfaces E-FEAT
survived O
the O
HIP S-MANP
treatment O
. O


A O
virtual B-MACEQ
binocular E-MACEQ
vision O
system O
is O
designed S-FEAT
to O
monitor S-CONPRI
molten B-CONPRI
pool E-CONPRI
appearance O
. O


Effects O
of O
different O
stereo O
matching O
algorithms S-CONPRI
on O
reconstruction S-CONPRI
accuracy S-CHAR
are O
conducted O
. O


Molten B-CONPRI
pool E-CONPRI
appearance O
in O
wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
is O
reconstructed O
. O


Robust O
measurement S-CHAR
of O
layer S-PARA
geometry S-CONPRI
can O
help O
better O
understand O
the O
complex O
deposition B-MANP
process E-MANP
and O
provide O
feedback S-PARA
control O
to O
increase O
process S-CONPRI
stability O
of O
wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
. O


In O
this O
study O
, O
a O
virtual B-ENAT
binocular I-ENAT
vision I-ENAT
sensing E-ENAT
system O
is O
designed S-FEAT
to O
measure O
the O
layer S-PARA
width O
and O
torch O
height O
from O
top O
layer S-PARA
simultaneously O
. O


Considering O
that O
stereo O
matching O
is O
the O
most O
crucial O
step S-CONPRI
for O
3-D S-CONPRI
reconstruction O
in O
stereovision O
sensing S-APPL
, O
various O
matching O
algorithms S-CONPRI
, O
i.e O
. O


The O
matching O
algorithms S-CONPRI
are O
tested O
based O
on O
the O
standard S-CONPRI
datasets O
, O
indicating O
that O
the O
highest O
matching O
accuracy S-CHAR
comes O
from O
the O
GCI O
matching O
algorithm S-CONPRI
. O


Then O
, O
a O
standard S-CONPRI
cylinder O
is O
taken O
as S-MATE
an O
example O
to O
verify O
the O
effectiveness S-CONPRI
of O
the O
sensing B-CHAR
system E-CHAR
and O
algorithms S-CONPRI
. O


Finally O
, O
layer S-PARA
geometries S-CONPRI
in O
WAAM S-MANP
with O
various O
process B-CONPRI
parameters E-CONPRI
are O
determined O
. O


The O
width O
and O
height O
errors S-CONPRI
of O
layer S-PARA
geometry S-CONPRI
with O
the O
GCI O
matching O
algorithm S-CONPRI
are O
less O
than O
3.2 O
% O
. O


This O
study O
will O
lay S-CONPRI
a O
solid O
foundation O
for O
subsequent O
feedback S-PARA
control O
for O
layer S-PARA
geometry S-CONPRI
in O
WAAM S-MANP
. O


High-strain-rate O
deformation S-CONPRI
in O
ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
was O
analyzed O
by O
performing O
microstructural B-CHAR
characterization E-CHAR
via O
electron B-CHAR
microscopy E-CHAR
. O


The O
micro-asperities O
on O
the O
top O
tape O
surface S-CONPRI
, O
which O
were O
formed O
by O
contact S-APPL
with O
the O
sonotrode S-MACEQ
surface O
, O
underwent O
cyclic O
deformation S-CONPRI
in O
the O
shear B-PRO
direction E-PRO
at O
high O
strain B-CONPRI
rates E-CONPRI
during O
welding S-MANP
with O
an O
additional O
tape O
. O


This O
caused O
plastic S-MATE
flow O
and O
crushing S-CONPRI
of O
the O
micro-asperities O
, O
and O
a O
flattened O
interface S-CONPRI
was O
formed O
between O
the O
upper O
and O
lower O
tapes O
. O


Further O
, O
surface S-CONPRI
oxide S-MATE
films O
were O
fractured O
and O
dispersed O
by O
ultrasonic B-PARA
vibration E-PARA
, O
and O
metallurgical S-APPL
welding O
was O
achieved O
. O


304L O
stainless B-MATE
steel E-MATE
manufactured S-CONPRI
via O
LENS S-MANP
was O
characterized O
in O
its O
as-deposited O
state O
in O
3D S-CONPRI
using O
TriBeam O
tomography O
. O


Orientation S-CONPRI
gradients O
are O
linked O
to O
chemical O
segregation S-CONPRI
occurring O
during O
solidification S-CONPRI
. O


A O
sample S-CONPRI
of O
304L O
stainless B-MATE
steel E-MATE
manufactured S-CONPRI
by O
Laser B-MANP
Engineered I-MANP
Net I-MANP
Shaping E-MANP
( O
LENS S-MANP
) O
was O
characterized O
in O
3D S-CONPRI
using O
TriBeam O
tomography O
. O


The O
crystallographic O
, O
structural O
, O
and O
chemical O
properties S-CONPRI
of O
the O
as-deposited O
microstructure S-CONPRI
have O
been O
studied O
in O
detail O
. O


3D S-CONPRI
characterization O
reveals O
complex O
grain S-CONPRI
morphologies O
and O
large O
orientation S-CONPRI
gradients O
, O
in O
excess O
of O
10∘ O
, O
that O
are O
not O
easily O
interpreted O
from O
2D S-CONPRI
cross-sections O
alone O
. O


Misorientations O
were O
calculated O
via O
a O
methodology S-CONPRI
that O
locates O
the O
initial O
location O
and O
orientation S-CONPRI
of O
grains S-CONPRI
that O
grow O
during O
the O
build S-PARA
process O
. O


For O
larger O
grains S-CONPRI
, O
misorientation O
increased O
along O
the O
direction O
of O
solidification S-CONPRI
. O


For O
grains S-CONPRI
with O
complex B-CONPRI
morphologies E-CONPRI
, O
K-means O
clustering O
in O
orientation S-CONPRI
space O
is O
demonstrated O
as S-MATE
a O
useful O
approach O
for O
determining O
the O
initial O
growth O
orientation S-CONPRI
. O


The O
accumulation O
of O
misorientation O
is O
linked O
to O
the O
solutal O
and O
thermal O
solidification S-CONPRI
path O
, O
offering O
potential O
design S-FEAT
pathways O
for O
novel O
alloys S-MATE
more O
suited O
for O
additive B-MANP
manufacturing E-MANP
. O


In O
this O
study O
, O
Wire B-MANP
Arc I-MANP
Additive I-MANP
Manufacturing E-MANP
( O
WAAM S-MANP
) O
based O
Directed B-MANP
Energy I-MANP
Deposition E-MANP
( O
DED S-MANP
) O
process S-CONPRI
is O
used O
to O
build S-PARA
two O
parts O
, O
tube O
and O
wall O
from O
2209 O
Duplex O
Stainless B-MATE
Steel E-MATE
. O


Duplex O
stainless B-MATE
steel E-MATE
is O
extremely O
effective O
against O
stress B-CONPRI
corrosion I-CONPRI
cracking E-CONPRI
due O
to O
existence O
of O
an O
equal O
portion O
of O
austenite S-MATE
and O
ferrite S-MATE
phases O
. O


The O
challenge O
is O
monitoring O
of O
the O
process B-CONPRI
parameters E-CONPRI
and O
cooling B-PARA
rate E-PARA
to O
promote O
ferrite S-MATE
phase O
formation O
. O


To O
this O
end O
, O
three-dimensional S-CONPRI
transient O
thermal O
models O
of O
the O
additive B-MANP
manufactured E-MANP
( O
AM S-MANP
) O
parts O
are O
presented O
and O
the O
simulated O
thermal B-PARA
cycles E-PARA
are O
verified O
with O
the O
experimental S-CONPRI
results O
. O


The O
correlation O
between O
the O
calculated O
cooling B-PARA
rates E-PARA
and O
the O
phases O
formation O
in O
the O
WAAM S-MANP
parts O
is O
studied O
and O
revealed O
. O


The O
results O
highlight O
that O
slow O
cooling B-PARA
rate E-PARA
of O
the O
built O
layers O
at O
elevated O
temperatures S-PARA
promote O
austenite S-MATE
formation O
significantly O
in O
a O
ferrite S-MATE
matrix O
. O


Furthermore O
, O
the O
experimental S-CONPRI
mechanical O
examinations O
will O
illustrate O
the O
quality S-CONPRI
of O
the O
WAAM-made O
parts O
and O
compare O
their O
mechanical B-CONPRI
properties E-CONPRI
with O
their O
wrought S-CONPRI
counter-parts O
. O


Beam-based O
processes S-CONPRI
are O
popularly O
used O
for O
metal B-MANP
additive I-MANP
manufacturing E-MANP
, O
but O
there O
are O
significant O
gaps O
between O
their O
capabilities O
and O
the O
demand O
from O
industry S-APPL
and O
society O
. O


Examples O
include O
solidification S-CONPRI
issues O
, O
anisotropic S-PRO
mechanical O
properties S-CONPRI
, O
and O
restrictions O
on O
powder S-MATE
attributes O
. O


Non-beam-based O
additive S-MATE
processes O
are O
promising O
to O
bridge S-APPL
these O
gaps O
. O


In O
this O
viewpoint O
article O
, O
we O
introduce O
and O
discuss O
additive S-MATE
friction O
stir O
deposition S-CONPRI
, O
which O
is O
a O
fast O
, O
scalable O
, O
solid-state B-CONPRI
process E-CONPRI
that O
results O
in O
refined O
microstructures S-MATE
and O
has O
flexible O
options O
for O
feed S-PARA
materials O
. O


With O
comparisons O
to O
other O
additive S-MATE
processes O
, O
we O
discuss O
its O
benefits O
and O
limitations O
along O
with O
the O
pathways O
to O
widespread O
implementation O
of O
metal B-MANP
additive I-MANP
manufacturing E-MANP
. O


Metal B-MANP
additive I-MANP
manufacturing E-MANP
is O
nowadays O
a O
well-established O
technology S-CONPRI
for O
cutting S-MANP
edge O
applications O
in O
the O
automotive S-APPL
, O
aerospace S-APPL
, O
defense O
and O
medical S-APPL
sectors O
. O


Since O
additive S-MATE
metal O
deposition S-CONPRI
is O
basically O
a O
welding S-MANP
method O
, O
which O
creates O
parts O
by O
successively O
adding O
layers O
of O
material S-MATE
, O
there O
is O
a O
chance O
for O
defects S-CONPRI
like O
pores S-PRO
, O
cracks O
, O
inclusions S-MATE
and O
lack O
of O
fusion S-CONPRI
to O
develop O
. O


As S-MATE
a O
matter O
of O
fact O
, O
interlayer O
and O
intralayer O
defects S-CONPRI
are O
often O
observed O
in O
additive B-MANP
manufactured E-MANP
components O
. O


However O
, O
if O
one O
considers O
the O
typical O
end O
applications O
along O
with O
the O
high O
costs O
involved O
in O
metal S-MATE
additive B-MANP
manufactured E-MANP
components O
, O
a O
“ O
zero O
defect S-CONPRI
” O
target O
is O
close O
to O
mandatory O
for O
this O
technology S-CONPRI
. O


Planning S-MANP
an O
inclusion S-MATE
of O
the O
integrity S-CONPRI
assessment O
right O
into O
the O
additive B-MANP
manufacturing I-MANP
process E-MANP
would O
allow O
for O
quick O
corrective O
actions O
to O
be S-MATE
performed O
before O
the O
component S-MACEQ
is O
completed O
. O


Some O
effort O
has O
been O
spent O
in O
the O
quest O
of O
an O
efficient O
in-process O
flaw S-CONPRI
inspection O
, O
however O
, O
no O
conventional O
nondestructive B-CHAR
testing E-CHAR
( O
NDT S-CONPRI
) O
approach O
has O
been O
fully O
satisfying O
yet O
. O


This O
work O
suggests O
an O
experimental S-CONPRI
evaluation O
of O
the O
effectiveness S-CONPRI
of O
flying O
laser S-ENAT
scanning O
thermography O
, O
when O
detecting O
flaws S-CONPRI
on O
an O
Additively B-MANP
Manufactured E-MANP
acetabular O
cup O
prosthesis O
made O
in O
titanium B-MATE
alloy E-MATE
, O
where O
some O
defects S-CONPRI
have O
been O
artificially O
created O
. O


The O
rough O
surface S-CONPRI
scanned O
is O
what O
’ O
s S-MATE
typically O
left O
by O
the O
additive B-MANP
manufacturing I-MANP
process E-MANP
, O
and O
has O
been O
left O
so O
in O
order O
to O
prove O
the O
efficacy O
of O
the O
NDT S-CONPRI
inspection S-CHAR
in O
real O
conditions O
. O


Robot S-MACEQ
assisted O
additive B-MANP
manufacturing E-MANP
is O
an O
emerging O
disruptive O
technology S-CONPRI
. O


Multiple O
robots S-MACEQ
can O
be S-MATE
used O
to O
produce O
multi-material S-CONPRI
large O
objects O
. O


Robotic-systems O
can O
be S-MATE
used O
to O
develop O
hybrid B-ENAT
systems E-ENAT
where O
additive S-MATE
and O
subtractive B-MANP
process E-MANP
are O
combined O
. O


The O
additive B-MANP
manufacturing E-MANP
and O
the O
robotic O
applications O
are O
tremendously O
increasing O
in O
the O
manufacturing S-MANP
field O
. O


This O
review O
paper O
discusses O
the O
concept O
of O
robotic-assisted O
additive B-MANP
manufacturing E-MANP
. O


The O
leading O
additive B-MANP
manufacturing E-MANP
methods O
that O
can O
be S-MATE
used O
with O
a O
robotic O
system O
are O
presented O
and O
discussed O
in O
detail O
. O


The O
information O
flow O
required O
to O
produce O
an O
object O
from O
a O
CAD B-ENAT
model E-ENAT
through O
a O
robotic-assisted O
system O
, O
different O
from O
the O
traditional O
information O
flow O
in O
a O
conventional O
additive B-MANP
manufacturing E-MANP
approach O
is O
also O
detailed O
. O


Examples O
of O
the O
use O
of O
robotic-assisted O
additive B-MACEQ
manufacturing I-MACEQ
systems E-MACEQ
are O
presented O
. O


130 O
mm S-MANP
thick O
welds S-FEAT
were O
manufactured S-CONPRI
in O
a O
nuclear O
steel S-MATE
using O
gas-tungsten O
arc S-CONPRI
, O
submerged-arc O
and O
electron B-MANP
beam I-MANP
welding E-MANP
. O


Residual B-PRO
stresses E-PRO
were O
measured O
using O
the O
contour S-FEAT
method O
and O
incremental O
deep-hole O
drilling S-MANP
, O
before O
and O
after O
PWHT S-CONPRI
. O


Results O
show O
that O
the O
effectiveness S-CONPRI
of O
PWHT S-CONPRI
is O
best O
assessed O
on O
large O
weld S-FEAT
mock-ups O
. O


In O
this O
study O
we O
aim O
to O
determine O
how O
the O
choice O
of O
welding S-MANP
process S-CONPRI
might O
impact S-CONPRI
on O
the O
through-life O
performance S-CONPRI
of O
critical O
nuclear O
components S-MACEQ
such O
as S-MATE
the O
reactor O
pressure S-CONPRI
vessel O
, O
steam O
generators O
and O
pressuriser O
in O
a O
pressurised O
water O
reactor O
. O


Attention O
is O
devoted O
to O
technologies S-CONPRI
that O
are O
currently O
employed O
in O
the O
fabrication S-MANP
of O
such O
components S-MACEQ
, O
i.e O
. O


narrow-gap O
variants O
of O
gas-tungsten O
arc B-MANP
welding E-MANP
( O
GTAW S-MANP
) O
and O
submerged B-MANP
arc I-MANP
welding E-MANP
( O
SAW S-MANP
) O
, O
as S-MATE
well O
as S-MATE
a O
technology S-CONPRI
that O
might O
be S-MATE
applied O
in O
the O
future O
( O
electron B-MANP
beam I-MANP
welding E-MANP
) O
. O


The O
residual B-PRO
stresses E-PRO
that O
are O
introduced O
by O
welding S-MANP
operations O
will O
have O
an O
influence O
on O
the O
integrity S-CONPRI
of O
critical O
components S-MACEQ
over O
a O
design S-FEAT
lifetime O
that O
exceeds O
60 O
years O
. O


With O
a O
view O
to O
making O
an O
assessment O
based O
on O
residual B-PRO
stress E-PRO
as S-MATE
pertinent O
as S-MATE
possible O
, O
weld S-FEAT
test O
pieces O
were O
manufactured S-CONPRI
with O
each O
process S-CONPRI
at O
a O
thickness O
that O
is O
representative O
for O
such O
components S-MACEQ
, O
i.e O
. O


130 O
mm S-MANP
. O


Stability S-PRO
in O
robotic O
GTA O
additive B-MANP
manufacturing E-MANP
is O
detected O
by O
optical B-CHAR
measurements E-CHAR
. O


Deposition S-CONPRI
height O
is O
controlled O
with O
a O
feedback S-PARA
controller S-MACEQ
. O


Comparison O
between O
open O
and O
closed-loop B-MACEQ
control E-MACEQ
is O
conducted O
. O


Additive B-MANP
manufacturing E-MANP
employing O
Gas S-CONPRI
Tungsten O
Arc S-CONPRI
( O
GTA O
) O
as S-MATE
the O
heat B-CONPRI
source E-CONPRI
is O
capable O
of O
fabricating S-MANP
fully O
dense O
metal S-MATE
components S-MACEQ
layer O
upon O
layer S-PARA
. O


In O
this O
work O
, O
a O
visual O
sensor S-MACEQ
, O
comprising O
a O
camera S-MACEQ
and O
composite S-MATE
filters O
, O
is O
developed O
for O
automatically O
real-time O
sensing S-APPL
of O
the O
fabrication S-MANP
process O
. O


The O
aim O
is O
to O
keep O
stable O
manufacture S-CONPRI
, O
and O
the O
deviations O
of O
the O
deposited O
height O
are O
compensated O
by O
designing O
an O
integral O
separation O
PID O
controller S-MACEQ
to O
adjust O
the O
wire O
feed S-PARA
speed O
in O
the O
next O
layer S-PARA
. O


The O
optical B-CHAR
measurement E-CHAR
technique O
and O
the O
controller S-MACEQ
are O
estimated O
via O
building O
multi-layer O
single-pass O
walls O
. O


The O
results O
show O
that O
the O
process S-CONPRI
stability O
in O
GTA-based O
additive B-MANP
manufacturing E-MANP
is O
well O
controlled O
when O
the O
designed S-FEAT
visual O
sensor S-MACEQ
and O
the O
proposed O
closed-loop B-MACEQ
controller E-MACEQ
are O
applied O
. O


Titanium S-MATE
is O
one O
of O
the O
best O
suitable O
materials S-CONPRI
for O
manufacturing S-MANP
bio O
implants S-APPL
and O
its O
application O
areas S-PARA
are O
orthopedics O
, O
dentistry S-APPL
etc O
. O


There O
are O
many O
features O
possess O
by O
titanium S-MATE
which O
make O
it O
appropriate O
are O
its O
biocompatibility S-PRO
, O
resistance S-PRO
to O
corrosion S-CONPRI
, O
wearing O
, O
osteoporosis O
etc O
. O


The O
Cp- O
Titanium S-MATE
and O
titanium-based O
alloys S-MATE
are O
categorized O
in O
three O
ways O
depending O
upon O
its O
microstructure S-CONPRI
such O
as S-MATE
( O
α O
+ O
β O
) O
, O
α- O
type O
, O
β-type O
and O
comparative O
analysis O
are O
done O
its O
behavior O
, O
stability S-PRO
through O
SEM S-CHAR
. O


This O
review O
paper O
discussed O
the O
conventional O
and O
modern O
methods O
of O
fabricating S-MANP
the O
bio-implants O
and O
also O
summarizes O
the O
various O
additive B-MANP
manufacturing E-MANP
techniques O
. O


Two O
NiCu O
alloys S-MATE
with O
various O
contents O
of O
Mn S-MATE
, O
Ti S-MATE
, O
Al S-MATE
and O
C S-MATE
were O
deposited O
in O
a O
shape O
of O
single-bead O
multi O
layered O
walls O
using O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
technology S-CONPRI
. O


To O
modify O
solute B-MATE
atom E-MATE
concentrations O
and O
particle S-CONPRI
number O
density S-PRO
values O
, O
the O
as-welded O
alloys S-MATE
were O
subjected O
to O
annealing S-MANP
at O
1100 O
°C O
and O
age-hardening O
heat B-MANP
treatment E-MANP
in O
the O
610-480 O
°C O
temperature B-PARA
range E-PARA
. O


Microstructure S-CONPRI
characterisation O
was O
carried O
out O
using O
optical S-CHAR
, O
scanning S-CONPRI
, O
conventional O
transmission S-CHAR
and O
atomic O
resolution S-PARA
transmission O
electron B-CHAR
microscopy E-CHAR
. O


Work B-MANP
hardening E-MANP
behaviour O
was O
studied O
using O
tensile B-CHAR
testing E-CHAR
. O


For O
similar O
deposition S-CONPRI
and O
heat B-MANP
treatment E-MANP
conditions O
, O
an O
alloy S-MATE
with O
higher O
C S-MATE
and O
Al S-MATE
, O
and O
lower O
Mn S-MATE
contents O
exhibited O
a O
higher O
number O
density S-PRO
of O
> O
20 O
nm O
TiC O
particles S-CONPRI
, O
higher O
number O
density S-PRO
of O
< O
20 O
nm O
γ′-Ni3 O
( O
Al S-MATE
, O
Ti S-MATE
) O
particles S-CONPRI
, O
and O
, O
associated O
with O
these O
, O
superior O
hardness S-PRO
, O
tensile B-PRO
strength E-PRO
, O
strain B-MANP
hardening E-MANP
rate O
and O
toughness S-PRO
. O


The O
comparative O
effect O
of O
solid B-MATE
solution E-MATE
and O
precipitation S-CONPRI
strengthening O
on O
work B-MANP
hardening E-MANP
behaviour O
and O
fracture S-CONPRI
mode O
is O
discussed O
. O


PCA-RF O
was O
proposed O
for O
on-line O
defect S-CONPRI
detection O
in O
arc B-MANP
welding E-MANP
. O


The O
classification S-CONPRI
accuracy S-CHAR
was O
improved O
from O
79.3 O
% O
to O
91.8 O
% O
. O


Feature S-FEAT
importance O
was O
qualitatively O
evaluated O
and O
selection O
pattern S-CONPRI
was O
given O
. O


Higher O
gradient O
of O
Fe S-MATE
might O
cause O
the O
greater O
change O
of O
Fe S-MATE
I O
( O
407.84 O
nm O
) O
Accurate S-CHAR
on-line O
weld S-FEAT
defect S-CONPRI
detection O
in O
robotic O
arc B-MANP
welding E-MANP
manufacturing O
is O
still O
challenging O
, O
due O
to O
the O
complexity S-CONPRI
and O
diversity O
of O
weld S-FEAT
defects S-CONPRI
. O


In O
this O
study O
, O
a O
new O
real-time O
defect S-CONPRI
identification O
method O
is O
proposed O
for O
Al B-MATE
alloys E-MATE
in O
robotic O
arc B-MANP
welding E-MANP
, O
using O
arc S-CONPRI
optical O
spectroscopy S-CONPRI
and O
an O
integrated O
learning O
method O
. O


Spectrum O
feature S-FEAT
was O
extracted S-CONPRI
, O
based O
on O
the O
absolute O
coefficients O
of O
the O
principal O
components S-MACEQ
. O


Feature S-FEAT
importance O
was O
quantitatively S-CONPRI
evaluated O
using O
the O
mean O
decrease O
accuracy S-CHAR
of O
Principal O
Component S-MACEQ
Analysis-Random O
Forest O
( O
PCA-RF O
) O
. O


The O
proposed O
PCA-RF O
proved O
to O
effectively O
identify O
five O
classes O
of O
weld S-FEAT
defects S-CONPRI
with O
better O
performance S-CONPRI
than O
support S-APPL
vector O
machine S-MACEQ
and O
back O
propagation O
neural B-CONPRI
network E-CONPRI
. O


Finally O
, O
the O
selection O
pattern S-CONPRI
of O
spectrum O
feature S-FEAT
subset O
was O
investigated O
, O
before O
revealing O
the O
correlation O
mechanism S-CONPRI
of O
the O
selected O
lines O
spectrum O
and O
weld S-FEAT
process S-CONPRI
. O


Barriers O
for O
the O
integration O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technologies S-CONPRI
in O
the O
commercial O
vehicle O
industry S-APPL
are O
identified O
. O


A O
cost B-CONPRI
model E-CONPRI
for O
estimating O
the O
manufacturing B-CONPRI
cost E-CONPRI
of O
a O
build S-PARA
task O
using O
selective B-MANP
laser I-MANP
melting E-MANP
is O
proposed O
in O
a O
cost B-CONPRI
estimation E-CONPRI
. O


A O
general O
procedure O
and O
framework S-CONPRI
to O
develop O
a O
hybrid O
additive-subtractive O
process B-ENAT
chain E-ENAT
has O
been O
proposed O
. O


A O
closed-loop O
quality B-CONPRI
control E-CONPRI
model S-CONPRI
to O
realize O
a O
long-term O
product O
and O
process S-CONPRI
quality O
control O
with O
AM S-MANP
is O
developed O
. O


Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
is O
the O
umbrella O
term O
for O
manufacturing B-MANP
processes E-MANP
that O
add O
materials S-CONPRI
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
to O
create O
parts O
. O


AM B-MANP
technologies E-MANP
show O
numerous O
potentials O
in O
terms O
of O
rapid B-ENAT
prototyping E-ENAT
, O
tooling S-CONPRI
and O
direct B-CONPRI
manufacturing E-CONPRI
of O
functional O
parts O
and O
imply O
revolutionary O
benefits O
for O
the O
manufacturing S-MANP
industry S-APPL
. O


Currently O
, O
many O
industrial S-APPL
areas S-PARA
are O
marching O
to O
a O
more O
comprehensive O
application O
of O
AM S-MANP
. O


Hence O
, O
the O
development O
of O
new O
tools S-MACEQ
, O
methods O
, O
and O
concepts O
for O
guiding O
companies S-APPL
to O
implement O
AM B-MANP
technologies E-MANP
requires O
more O
research S-CONPRI
attention O
. O


This O
paper O
introduces O
the O
results O
of O
a O
research S-CONPRI
project O
carried O
out O
by O
academic O
and O
industrial S-APPL
partners O
from O
the O
German O
commercial O
vehicle O
industry S-APPL
. O


The O
research S-CONPRI
project O
addressed O
four O
issues O
for O
a O
long-term O
application O
of O
AM B-MANP
technologies E-MANP
: O
identification O
of O
barriers O
for O
AM S-MANP
applications O
, O
cost B-CONPRI
estimation E-CONPRI
for O
AM S-MANP
application O
, O
design S-FEAT
of O
hybrid O
additive-subtractive O
process B-ENAT
chains E-ENAT
, O
and O
quality S-CONPRI
management O
with O
AM S-MANP
. O


Wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
is O
a O
competitive O
technology S-CONPRI
for O
fabricating S-MANP
metallic O
parts O
with O
complex B-CONPRI
structure E-CONPRI
and O
geometry S-CONPRI
. O


The O
basis O
of O
planning S-MANP
the O
deposition B-PARA
paths E-PARA
is O
the O
beads S-CHAR
overlapping O
model S-CONPRI
( O
BOM O
) O
. O


The O
existing O
overlapping O
models O
consider O
only O
the O
geometric O
area S-PARA
of O
adjacent O
beads S-CHAR
, O
but O
ignore O
the O
spreading O
of O
the O
melted S-CONPRI
weld O
beads S-CHAR
. O


The O
objective O
of O
the O
research S-CONPRI
was O
to O
develop O
an O
enhanced O
BOM O
( O
E.BOM O
) O
for O
WAAM S-MANP
, O
which O
takes O
the O
spreading O
of O
the O
weld B-CONPRI
beads E-CONPRI
into O
consideration O
. O


A O
deposited B-CHAR
bead E-CHAR
spreads O
to O
the O
already O
deposited O
neighboring O
bead S-CHAR
and O
as S-MATE
a O
consequence O
, O
its O
center O
point O
deviates O
from O
the O
center O
point O
of O
the O
fed O
( O
to O
be S-MATE
melted O
) O
wire O
. O


Experiments O
were O
designed S-FEAT
to O
explore O
the O
relationships O
between O
the O
geometries S-CONPRI
of O
the O
beads S-CHAR
, O
and O
the O
offset S-CONPRI
distance O
between O
the O
center O
of O
a O
weld B-CONPRI
bead E-CONPRI
and O
the O
center O
of O
the O
fed O
wire O
. O


An O
artificial B-ENAT
neural I-ENAT
network E-ENAT
was O
used O
to O
predict O
the O
offset S-CONPRI
distance O
of O
a O
certain O
weld B-CONPRI
bead E-CONPRI
based O
on O
the O
results O
of O
the O
experiments O
. O


In O
addition O
, O
a O
reasoning O
algorithm S-CONPRI
was O
implemented O
to O
calculate O
the O
optimal O
distance O
between O
the O
centers O
of O
adjacent O
deposition B-PARA
paths E-PARA
in O
order O
to O
achieve O
a O
planned O
center O
distance O
between O
adjacent O
beads S-CHAR
. O


The O
E.BOM O
has O
been O
tested O
by O
validation S-CONPRI
experiments O
. O


On O
the O
one O
hand O
, O
it O
improves O
the O
surface S-CONPRI
flatness S-PRO
of O
layers O
of O
MLMB O
parts O
produced O
by O
WAAM S-MANP
. O


Wire B-MANP
+ I-MANP
Arc I-MANP
Additive I-MANP
Manufacture E-MANP
is O
a O
suitable O
technique O
to O
manufacture S-CONPRI
large-scale O
unalloyed O
tungsten S-MATE
components S-MACEQ
The O
orientation S-CONPRI
of O
the O
wire B-PARA
feeding E-PARA
influences O
the O
occurrence O
of O
defects S-CONPRI
as S-MATE
lack O
of O
fusion S-CONPRI
, O
pores S-PRO
and O
micro-cracks S-CONPRI
The O
orientation S-CONPRI
of O
the O
wire B-PARA
feeding E-PARA
influences O
the O
microstructure S-CONPRI
of O
the O
tungsten S-MATE
deposits O
Front O
wire B-PARA
feeding E-PARA
allowed O
to O
produce O
fully-dense O
crack-free O
unalloyed O
tungsten S-MATE
deposits O
The O
manufacturing S-MANP
of O
refractory-metals O
components S-MACEQ
presents O
some O
limitations O
induced O
by O
the O
materials S-CONPRI
' O
characteristic O
low-temperature O
brittleness O
and O
high O
susceptibility S-PRO
to O
oxidation S-MANP
. O


Powder B-MANP
metallurgy E-MANP
is O
typically O
the O
manufacturing B-MANP
process E-MANP
of O
choice O
. O


Recently O
, O
Wire B-MANP
+ I-MANP
Arc I-MANP
Additive I-MANP
Manufacture E-MANP
has O
proven O
capable O
to O
produce O
fully-dense O
large-scale O
metal S-MATE
parts O
at O
relatively O
low O
cost O
, O
by O
using O
high-quality O
wire O
as S-MATE
feedstock O
. O


In O
this O
study O
, O
this O
technique O
has O
been O
used O
for O
the O
production S-MANP
of O
large-scale O
tungsten S-MATE
linear O
structures O
. O


The O
orientation S-CONPRI
of O
the O
wire B-PARA
feeding E-PARA
has O
been O
studied O
and O
optimised O
to O
obtain O
defect-free O
tungsten S-MATE
deposits O
. O


In O
particular O
, O
front O
wire B-PARA
feeding E-PARA
eliminated O
the O
occurrence O
of O
pores S-PRO
and O
micro-cracks S-CONPRI
, O
when O
compared O
to O
side O
wire B-PARA
feeding E-PARA
. O


The O
microstructure S-CONPRI
, O
the O
occurrence O
of O
defects S-CONPRI
and O
their O
relationship O
with O
the O
deposition B-MANP
process E-MANP
have O
also O
been O
discussed O
. O


Despite O
the O
repetitive O
thermal B-PARA
cycles E-PARA
and O
the O
inherent O
brittleness O
of O
the O
material S-MATE
, O
the O
as-deposited O
structures O
were O
free O
from O
internal O
cracks O
and O
the O
layer S-PARA
dimensions S-FEAT
were O
stable O
during O
the O
entire O
deposition B-MANP
process E-MANP
. O


This O
enabled O
the O
production S-MANP
of O
a O
relatively O
large-scale O
component S-MACEQ
, O
with O
the O
dimension S-FEAT
of O
210 O
× O
75 O
× O
12 O
mm S-MANP
. O


This O
study O
has O
demonstrated O
that O
Wire B-MANP
+ I-MANP
Arc I-MANP
Additive I-MANP
Manufacture E-MANP
can O
be S-MATE
used O
to O
produce O
large-scale O
parts O
in O
unalloyed O
tungsten S-MATE
by O
complete O
fusion S-CONPRI
, O
presenting O
a O
potential O
alternative O
to O
the O
powder B-MANP
metallurgy E-MANP
manufacturing S-MANP
route O
. O


An O
innovative O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
system O
using O
low O
power S-PARA
pulsed O
laser B-MANP
assisted I-MANP
MIG I-MANP
arc I-MANP
welding E-MANP
( O
L-M O
) O
was O
proposed O
to O
manufacture S-CONPRI
metal O
products O
. O


With O
the O
purpose O
of O
revealing O
how O
width O
and O
height O
dimension S-FEAT
of O
the O
manufactured S-CONPRI
thin-wall O
component S-MACEQ
are O
affected O
by O
the O
laser B-PARA
power E-PARA
, O
the O
present O
study O
has O
been O
carried O
out O
. O


The O
width O
decreased O
with O
the O
increasing O
of O
the O
laser B-PARA
power E-PARA
within O
a O
certain O
range S-PARA
of O
laser B-PARA
power E-PARA
, O
and O
the O
height O
increased O
proportionally O
under O
the O
equal O
deposition B-PARA
rate E-PARA
. O


The O
width O
and O
height O
fluctuation O
reduced O
while O
adding O
the O
low O
power S-PARA
laser S-ENAT
, O
both O
the O
standard B-CHAR
deviation E-CHAR
decreased O
by O
more O
than O
50％ O
when O
the O
laser B-PARA
power E-PARA
was O
400 O
W. O
The O
coefficient O
of O
materials S-CONPRI
utilization O
was O
up O
to O
91.12 O
% O
, O
and O
increased O
by O
more O
than O
15 O
% O
while O
using O
L-M O
based O
AM S-MANP
to O
fabricate S-MANP
thin-wall O
parts O
with O
a O
proper O
laser B-PARA
power E-PARA
. O


In O
comparison O
with O
the O
common O
GMAW-based O
AM S-MANP
method O
, O
the O
L-M O
based O
AM S-MANP
method O
shows O
feasibility S-CONPRI
to O
manufacture S-CONPRI
a O
narrower O
thin-wall O
component S-MACEQ
with O
better O
surface B-PARA
quality E-PARA
and O
higher O
stability S-PRO
, O
and O
also O
with O
higher O
deposition S-CONPRI
efficiency O
. O


Wire B-MANP
and I-MANP
Arc I-MANP
Additive I-MANP
Manufacturing E-MANP
( O
WAAM S-MANP
) O
is O
a O
metal S-MATE
3D B-MANP
printing E-MANP
technique O
based O
on O
robotic B-MANP
welding E-MANP
. O


This O
technique O
yields O
potential O
in O
decreasing O
material S-MATE
consumption O
due O
to O
its O
high O
material S-MATE
efficiency O
and O
freedom O
of O
shape O
. O


Empirical S-CONPRI
measurements O
of O
WAAM S-MANP
, O
using O
a O
deposition B-PARA
rate E-PARA
of O
1 O
kg/h O
, O
were O
performed O
on O
site O
of O
MX3D O
. O


The O
measured O
power S-PARA
consumption O
per O
kg O
stainless B-MATE
steel E-MATE
is O
2.72 O
kW O
, O
of O
which O
1.74 O
is O
consumed O
by O
the O
welder O
, O
0.44 O
by O
the O
robotic B-MACEQ
arm E-MACEQ
, O
and O
0.54 O
by O
the O
ventilation O
. O


The O
material S-MATE
loss O
was O
1.1 O
% O
. O


A O
98 O
% O
argon S-MATE
2 O
% O
CO2 S-MATE
welding O
gas S-CONPRI
was O
used O
with O
a O
flow O
of O
12 O
l/min.A O
cradle-to-gate O
Life B-CONPRI
Cycle E-CONPRI
Assessment O
( O
LCA O
) O
was O
performed O
. O


To O
give O
this O
assessment O
context O
, O
green O
sand B-MANP
casting E-MANP
and O
CNC B-MANP
milling E-MANP
were O
additionally O
assessed O
, O
through O
literature O
and O
databases S-ENAT
. O


The O
purpose O
of O
this O
study O
is O
to O
develop O
insight O
into O
the O
environmental O
impact S-CONPRI
of O
WAAM S-MANP
. O


Results O
indicate O
that O
, O
in O
terms O
of O
total O
ReCiPe O
endpoints O
, O
the O
environmental O
impact S-CONPRI
of O
producing O
a O
kg O
of O
stainless B-MATE
steel E-MATE
308 O
l O
product O
using O
WAAM S-MANP
is O
comparable O
to O
green O
sand B-MANP
casting E-MANP
. O


It O
equals O
CNC B-MANP
milling E-MANP
with O
a O
material B-PARA
utilization I-PARA
fraction E-PARA
of O
0.75 O
. O


Stainless B-MATE
steel E-MATE
is O
the O
main O
cause O
of O
environmental O
damage S-PRO
in O
all O
three O
techniques O
, O
emphasizing O
the O
importance O
of O
WAAM S-MANP
's O
mass O
reduction S-CONPRI
potential O
. O


When O
environmentally O
comparing O
the O
three O
techniques O
for O
fulfilling O
a O
certain O
function O
, O
optimized O
designs S-FEAT
should O
be S-MATE
introduced O
for O
each O
manufacturing S-MANP
technique O
. O


Results O
can O
vary O
significantly O
based O
on O
product O
shape O
, O
function O
, O
materials S-CONPRI
, O
and O
process B-PARA
settings E-PARA
. O


Method O
of O
tensile S-PRO
triangles O
was O
applied O
to O
weld S-FEAT
shape O
design S-FEAT
. O


Method O
of O
tensile S-PRO
triangles O
and O
low O
transformation O
temperature S-PARA
weld O
metal S-MATE
were O
combined O
for O
weld B-FEAT
joint E-FEAT
design S-FEAT
. O


Effect O
of O
interpass B-PARA
temperature E-PARA
on O
residual B-PRO
stress E-PRO
in O
welded B-FEAT
joint E-FEAT
was O
investigated O
. O


Stress B-CHAR
concentration E-CHAR
and O
residual B-PRO
stress E-PRO
have O
a O
significant O
influence O
on O
fatigue B-PRO
life E-PRO
of O
welded B-FEAT
joints E-FEAT
. O


In O
order O
to O
reduce O
the O
stress B-CHAR
concentration E-CHAR
of O
welded B-FEAT
joints E-FEAT
, O
a O
mathematical S-CONPRI
design S-FEAT
method O
of O
tensile S-PRO
triangles O
( O
MTT O
) O
based O
on O
bionics O
was O
applied O
to O
weld S-FEAT
shape O
design S-FEAT
. O


Accordingly O
, O
the O
stress B-CHAR
concentration E-CHAR
of O
various O
weld B-CONPRI
beads E-CONPRI
in O
the O
corner O
boxing O
welded B-FEAT
joint E-FEAT
and O
the O
fillet S-FEAT
welded O
T-joint S-FEAT
was O
dissected O
using O
our O
in-house O
FEM S-CONPRI
software O
JWRIAN O
. O


It O
was O
found O
that O
there O
existed O
a O
large O
stress B-CHAR
concentration E-CHAR
in O
the O
conventional O
welded B-FEAT
joints E-FEAT
, O
whereas O
those O
welded B-FEAT
joints E-FEAT
with O
elongated O
weld B-CONPRI
bead E-CONPRI
were O
accompanied O
by O
a O
lower O
stress B-CHAR
concentration E-CHAR
, O
especially O
for O
elongated O
weld B-CONPRI
bead E-CONPRI
with O
MTT O
design S-FEAT
. O


Furthermore O
, O
among O
the O
weld S-FEAT
shapes O
of O
the O
corner O
boxing O
fillet S-FEAT
welded O
joint S-CONPRI
, O
the O
rectangle O
shape O
of O
weld B-CONPRI
bead E-CONPRI
had O
the O
minimum O
stress B-CHAR
concentration E-CHAR
factor O
( O
1.05 O
) O
. O


For O
the O
fillet S-FEAT
welded O
T-joint S-FEAT
with O
MTT O
design S-FEAT
, O
the O
stress B-CHAR
concentration E-CHAR
of O
weld S-FEAT
toe O
decreased O
dramatically O
with O
the O
increase O
of O
the O
index O
of O
designed S-FEAT
shape O
, O
but O
there O
was O
a O
minor O
difference O
of O
stress B-CHAR
concentration E-CHAR
at O
weld S-FEAT
root O
between O
the O
weld B-CONPRI
beads E-CONPRI
with O
MTT O
design S-FEAT
. O


In O
addition O
, O
application O
of O
low O
transformation O
temperature S-PARA
( O
LTT O
) O
weld B-MATE
metal E-MATE
utilizing O
martensitic O
transformation O
to O
the O
fillet S-FEAT
welded O
T-joints O
can O
produce O
compressive O
residual B-PRO
stress E-PRO
at O
weld S-FEAT
toe O
. O


Additive-manufactured O
AlSi10Mg S-MATE
boxes O
were O
studied O
under O
lateral O
crushing S-CONPRI
. O


Experimental S-CONPRI
tests O
and O
numerical B-ENAT
simulations E-ENAT
were O
conducted O
. O


The O
constitutive O
model S-CONPRI
was O
calibrated S-CONPRI
using O
tensile B-CHAR
tests E-CHAR
in O
three O
directions O
. O


The O
influence O
of O
the O
yield O
surface S-CONPRI
, O
the O
adopted O
thickness O
and O
the O
element S-MATE
type O
were O
studied O
. O


An O
experimental S-CONPRI
and O
numerical O
study O
on O
the O
quasi-static S-CONPRI
loading O
of O
AlSi10Mg S-MATE
square O
boxes O
produced O
by O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
was O
carried O
out O
. O


The O
goal O
was O
to O
evaluate O
the O
applicability O
of O
common O
finite B-CHAR
element I-CHAR
modelling E-CHAR
techniques O
to O
3D-printed B-APPL
parts E-APPL
at O
material S-MATE
and O
component S-MACEQ
scales O
, O
under O
large O
deformations S-CONPRI
and O
fracture S-CONPRI
. O


Uniaxial O
tensile B-MACEQ
specimens E-MACEQ
were O
extracted S-CONPRI
and O
tested O
at O
different O
orientations S-CONPRI
, O
and O
a O
hypo-elastic–plastic O
model S-CONPRI
with O
Voce O
hardening S-MANP
and O
Cockcroft–Latham O
’ O
s S-MATE
fracture S-CONPRI
criterion O
was O
calibrated S-CONPRI
against O
the O
experimental S-CONPRI
results O
. O


The O
boxes O
were O
crushed O
laterally O
until O
failure S-CONPRI
using O
a O
spherical S-CONPRI
actuator S-MACEQ
. O


The O
considered O
material S-MATE
and O
finite B-CONPRI
element I-CONPRI
models E-CONPRI
were O
proved O
well O
suited O
for O
the O
prediction S-CONPRI
of O
the O
structural O
response O
of O
the O
additively B-MANP
manufactured E-MANP
components O
in O
the O
studied O
scenario O
. O


Wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
is O
an O
efficient O
technique O
for O
fabricating S-MANP
large O
and O
complex O
components S-MACEQ
that O
are O
applied O
in O
the O
manufacturing S-MANP
industry S-APPL
. O


In O
this O
study O
, O
anisotropic S-PRO
mechanical O
properties S-CONPRI
of O
a O
low-carbon O
high-strength O
steel S-MATE
component S-MACEQ
fabricated O
by O
WAAM S-MANP
were O
investigated O
via O
mechanical B-CHAR
testing E-CHAR
, O
and O
the O
transversal O
and O
longitudinal O
deformation S-CONPRI
behavior O
of O
the O
component S-MACEQ
were O
studied O
using O
the O
digital B-CONPRI
image I-CONPRI
correlation E-CONPRI
( O
DIC S-CONPRI
) O
method O
. O


Additionally O
, O
the O
features O
of O
microstructure S-CONPRI
, O
texture S-FEAT
, O
and O
fracture S-CONPRI
mode O
of O
the O
inter-layer O
area S-PARA
and O
deposited O
area S-PARA
were O
also O
investigated O
to O
reveal O
the O
mechanism S-CONPRI
of O
anisotropy S-PRO
. O


The O
results O
showed O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
longitudinal O
specimens O
were O
inferior O
to O
that O
of O
the O
transversal O
specimens O
. O


Several O
strain S-PRO
concentration O
zones O
in O
the O
longitudinal O
specimen O
were O
relevant O
to O
the O
inter-layer O
characteristics O
observed O
from O
the O
fracture S-CONPRI
surface O
and O
macrostructure O
, O
which O
was O
confirmed O
by O
the O
strain S-PRO
evolution S-CONPRI
recorded O
by O
DIC S-CONPRI
. O


The O
inter-layer O
areas S-PARA
were O
proved O
to O
be S-MATE
the O
weak O
link O
in O
the O
deposited O
component S-MACEQ
by O
scanning B-MACEQ
electron I-MACEQ
microscope E-MACEQ
( O
SEM S-CHAR
) O
and O
electron B-CHAR
backscatter I-CHAR
diffraction E-CHAR
( O
EBSD S-CHAR
) O
analysis O
results O
, O
including O
various O
phase B-CONPRI
composition E-CONPRI
, O
phase B-CONPRI
morphology E-CONPRI
, O
misorientation O
angle O
, O
grain B-PRO
size E-PRO
, O
Schmid O
factor O
, O
and O
texture S-FEAT
. O


Finally O
, O
based O
on O
the O
fractography S-CHAR
analysis O
, O
anisotropy S-PRO
resulted O
from O
inter-layer O
zones O
is O
also O
confirmed O
via O
the O
comparison O
of O
transversal O
and O
longitudinal O
fracture S-CONPRI
morphology O
. O


In O
the O
present O
work O
, O
a O
novel O
direct B-MANP
energy I-MANP
deposition E-MANP
method O
for O
metal B-MANP
additive I-MANP
manufacturing E-MANP
is O
developed O
employing O
laminar O
plasma S-CONPRI
as S-MATE
the O
heat B-CONPRI
source E-CONPRI
. O


With O
a O
combination O
of O
modified O
process B-CONPRI
parameters E-CONPRI
, O
a O
high-performance O
308L O
stainless B-MATE
steel E-MATE
component S-MACEQ
with O
four O
hollow O
straight O
walls O
is O
prepared O
. O


The O
behavior O
of O
phase S-CONPRI
formation O
, O
microstructure S-CONPRI
, O
density S-PRO
and O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
samples S-CONPRI
with O
different O
heights O
were O
investigated O
. O


Transformation O
from O
columnar O
to O
equiaxed O
dendrites S-BIOP
can O
be S-MATE
observed O
as S-MATE
the O
height O
of O
wall O
increases O
from O
the O
substrate S-MATE
to O
about O
30 O
mm S-MANP
. O


The O
average S-CONPRI
density O
of O
the O
sample S-CONPRI
reaches O
98.3 O
% O
. O


Anisotropic S-PRO
property O
is O
observed O
in O
the O
bottom O
and O
middle O
regions O
, O
while O
the O
top O
region O
is O
isotropic S-PRO
. O


Laser S-ENAT
welding–brazing O
of O
Ti/Al O
butt O
joints O
was O
performed O
with O
coaxial O
Al–10Si–Mg O
powders S-MATE
feeding O
. O


The O
experimental S-CONPRI
results O
indicated O
that O
a O
sound O
Ti/Al O
butt O
joint S-CONPRI
could O
be S-MATE
obtained O
by O
an O
additive S-MATE
layer O
approach O
. O


The O
influence O
of O
the O
laser S-ENAT
melting O
deposition B-PARA
layers E-PARA
on O
the O
weld S-FEAT
appearance O
, O
interfacial O
microstructure S-CONPRI
and O
tensile B-PRO
properties E-PRO
were O
investigated O
. O


The O
morphology S-CONPRI
and O
thickness O
distributions S-CONPRI
of O
the O
interfacial O
intermetallic B-MATE
compounds E-MATE
( O
IMC O
) O
at O
the O
brazing S-APPL
interface O
along O
the O
thickness O
direction O
of O
the O
joint S-CONPRI
varied O
with O
the O
number O
of O
deposition B-PARA
layers E-PARA
. O


Continuous O
serrated O
IMC O
was O
obtained O
in O
joints O
produced O
by O
seven O
deposition B-PARA
layers E-PARA
, O
and O
the O
IMC O
layer S-PARA
was O
distributed O
homogenously O
along O
the O
thickness O
direction O
. O


The O
microstructure S-CONPRI
of O
the O
IMC O
layer S-PARA
was O
composed O
of O
a O
nanosized O
granular O
Ti7Al5Si12 S-MATE
phase S-CONPRI
and O
serrated O
Ti S-MATE
( O
Al S-MATE
, O
Si S-MATE
) O
3 O
phase S-CONPRI
. O


The O
maximum O
tensile S-PRO
joint S-CONPRI
strength O
reached O
240 O
MPa S-CONPRI
, O
80 O
% O
of O
that O
of O
the O
aluminum S-MATE
base O
metal S-MATE
, O
and O
the O
lower O
tensile B-PRO
strength E-PRO
of O
the O
other O
joints O
was O
caused O
by O
insufficient O
IMC O
layer S-PARA
or O
a O
porosity S-PRO
defect S-CONPRI
. O


The O
bypass-coupled O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
process S-CONPRI
was O
studied O
, O
and O
the O
arc S-CONPRI
characteristics O
and O
droplet S-CONPRI
transfer O
behavior O
during O
the O
deposition B-MANP
process E-MANP
were O
examined O
. O


The O
effects O
of O
the O
bypass O
current O
, O
wire B-PARA
feeding E-PARA
speed O
, O
wire B-PARA
feeding E-PARA
height O
, O
and O
wire B-PARA
feeding E-PARA
angle O
on O
the O
droplet S-CONPRI
transfer O
mode O
were O
investigated O
via O
a O
single O
variable O
experiment S-CONPRI
. O


There O
are O
two O
primary O
modes O
of O
droplet S-CONPRI
transfer O
during O
the O
deposition B-MANP
process E-MANP
: O
free O
droplet S-CONPRI
transfer O
and O
bridging S-CONPRI
transfer O
. O


When O
the O
transfer O
process S-CONPRI
is O
in O
the O
bridging S-CONPRI
transfer O
mode O
, O
a O
smooth O
deposition S-CONPRI
wall O
is O
obtained O
. O


As S-MATE
the O
wire B-PARA
feeding E-PARA
speed O
increases O
, O
the O
transfer O
mode O
of O
the O
droplet S-CONPRI
gradually O
changes O
from O
the O
free O
transfer O
mode O
to O
the O
bridging S-CONPRI
transfer O
mode O
. O


The O
larger O
the O
distance O
between O
the O
wire O
tip O
and O
the O
surface S-CONPRI
of O
the O
base B-MATE
metal E-MATE
, O
the O
higher O
the O
wire O
feed S-PARA
speed O
required O
to O
achieve O
bridging S-CONPRI
transfer O
. O


There O
is O
a O
linear O
relationship O
between O
the O
droplet S-CONPRI
diameter S-CONPRI
and O
the O
cubic O
root O
of O
the O
wire B-PARA
feeding E-PARA
speed O
. O


Finally O
, O
the O
droplet S-CONPRI
transfer O
behavior O
is O
discussed O
using O
droplet S-CONPRI
force O
analysis O
. O


This O
article O
describes O
the O
results O
of O
the O
study O
of O
optimal O
conditions O
for O
welding S-MANP
alloy S-MATE
products O
- O
Inconel B-MATE
718 E-MATE
, O
made O
with O
the O
method O
of O
layered O
laser S-ENAT
growing O
( O
SLM S-MANP
) O
. O


The O
results O
of O
the O
study O
of O
the O
influence O
of O
linear O
energy O
, O
rigid O
fixation O
of O
parts O
during O
welding S-MANP
and O
heat B-MANP
treatment E-MANP
on O
microhardness S-CONPRI
, O
welding S-MANP
deformation S-CONPRI
and O
the O
microstructure S-CONPRI
of O
the O
welded B-FEAT
joint E-FEAT
are O
presented O
. O


An O
adaptive O
quadrature O
technique O
for O
calculating O
linear O
heat B-CONPRI
conduction E-CONPRI
in O
metal B-MANP
additive I-MANP
manufacturing E-MANP
was O
derived O
. O


A O
melt B-MATE
pool E-MATE
tracking O
algorithm S-CONPRI
is O
also O
described O
for O
improved O
calculation O
efficiency O
. O


The O
adaptive O
algorithm S-CONPRI
was O
verified O
against O
an O
analytical B-CONPRI
solution E-CONPRI
and O
Riemann O
sum O
integration O
approach O
. O


The O
adaptive O
integration O
technique O
is O
demonstrated O
for O
a O
highly O
transient S-CONPRI
scan B-PARA
pattern E-PARA
at O
long O
length O
and O
time B-FEAT
scales E-FEAT
. O


Solidification S-CONPRI
dynamics O
are O
important O
for O
determining O
final O
microstructure S-CONPRI
in O
additively B-MANP
manufactured E-MANP
parts O
. O


Recently O
, O
researchers O
have O
adopted O
semi-analytical B-CONPRI
approaches E-CONPRI
for O
predicting O
heat B-CONPRI
conduction E-CONPRI
effects O
at O
length O
and O
time B-FEAT
scales E-FEAT
not O
accessible O
to O
complex O
multi-physics O
numerical O
models O
. O


The O
present O
work O
focuses O
on O
improving O
a O
semi-analytical O
heat B-CONPRI
conduction E-CONPRI
model O
for O
additive B-MANP
manufacturing E-MANP
by O
designing O
an O
adaptive O
integration O
technique O
. O


The O
proposed O
scheme O
considers O
material B-CONPRI
properties E-CONPRI
, O
process S-CONPRI
conditions O
, O
and O
the O
inherent O
physical O
behavior O
of O
the O
transient B-CONPRI
heat I-CONPRI
conduction E-CONPRI
around O
both O
stationary O
and O
moving O
heat B-CONPRI
sources E-CONPRI
. O


The O
full O
algorithm S-CONPRI
is O
then O
implemented O
and O
compared O
against O
a O
simple S-MANP
Riemann O
sum O
integration O
scheme O
for O
a O
variety O
of O
cases O
that O
highlight O
process S-CONPRI
and O
material S-MATE
variations O
relevant O
to O
additive B-MANP
manufacturing E-MANP
. O


The O
new O
scheme O
is O
shown O
to O
have O
significant O
improvements O
in O
computational B-CONPRI
efficiency E-CONPRI
, O
solution S-CONPRI
accuracy S-CHAR
, O
and O
usability O
. O


WAAM S-MANP
was O
carried O
out O
to O
build S-PARA
a O
flange O
using O
robotic O
GMAW S-MANP
with O
AA5183 O
wire O
on O
an O
AA6082 O
support S-APPL
plate O
. O


Some O
intergranular O
hot B-CONPRI
cracking E-CONPRI
was O
found O
in O
the O
reheated O
areas S-PARA
close O
to O
the O
fusion B-CONPRI
boundary E-CONPRI
. O


The O
hardness S-PRO
level O
was O
around O
75 O
kg/mm2 O
and O
70–75 O
kg/mm2 O
in O
the O
hoorisontal O
and O
vertical S-CONPRI
plane O
, O
respectively O
. O


Reasonable O
isotropic S-PRO
yield O
and O
tensile B-PRO
strength E-PRO
of O
145 O
and O
293MPa O
were O
achieved O
, O
respectively O
. O


The O
present O
study O
addresses O
wire B-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
of O
AA5183 O
aluminium B-MATE
alloy E-MATE
using O
conventional O
gas B-MANP
metal I-MANP
arc I-MANP
welding E-MANP
deposition S-CONPRI
on O
20 O
mm S-MANP
thick O
AA6082-T6 O
plate O
as S-MATE
support O
material S-MATE
. O


Microscopic O
examination O
demonstrates O
that O
the O
process S-CONPRI
is O
feasible O
, O
but O
can O
be S-MATE
further O
optimized O
to O
reduce O
gas S-CONPRI
porosity O
and O
hot B-CONPRI
cracking E-CONPRI
. O


Hardness S-PRO
measurements O
confirmed O
relative O
high O
hardness S-PRO
, O
i.e. O
, O
around O
75 O
kg/mm2 O
in O
the O
horizontal O
plane O
, O
and O
between O
70 O
and O
75 O
kg/mm2 O
in O
the O
vertical S-CONPRI
plane O
down O
to O
the O
AA6082 O
support S-APPL
plate O
with O
100 O
kg/mm2 O
. O


Mechanical B-CHAR
testing E-CHAR
resulted O
in O
yield O
and O
tensile B-PRO
strength E-PRO
of O
145 O
and O
293 O
MPa S-CONPRI
, O
respectively O
, O
with O
lowest O
value O
in O
the O
through O
thickness O
( O
Z O
) O
direction O
. O


The O
ductility S-PRO
was O
high O
for O
orientations S-CONPRI
parallel O
( O
X O
) O
with O
and O
perpendicular O
( O
Y S-MATE
) O
to O
the O
layer S-PARA
deposition B-PARA
direction E-PARA
. O


The O
thickness O
of O
intermetallic B-MATE
compounds E-MATE
( O
IMCs O
) O
is O
one O
of O
the O
main O
factors O
affecting O
the O
weld B-PARA
quality E-PARA
. O


In O
addition O
, O
the O
IMC O
thickness O
will O
affect O
the O
product B-CHAR
functionality E-CHAR
, O
e.g. O
, O
the O
thermal O
or O
electrical B-PRO
conductivity E-PRO
of O
the O
IMC O
layer S-PARA
can O
be S-MATE
the O
limiting O
factor O
in O
the O
related O
applications O
. O


Modeling S-ENAT
and O
prediction S-CONPRI
of O
the O
IMC O
thickness O
in O
the O
friction B-MANP
stir I-MANP
welding E-MANP
( O
FSW S-MANP
) O
process S-CONPRI
is O
an O
important O
role O
that O
has O
not O
been O
elaborated O
in O
the O
literature O
. O


That O
model S-CONPRI
is O
suitable O
for O
the O
pure O
( O
intrinsic O
) O
diffusion S-CONPRI
process O
and O
does O
not O
consider O
the O
main O
unique O
characteristic O
of O
FSW S-MANP
, O
i.e. O
, O
the O
stirring O
and O
subsequent O
linear O
velocity O
of O
particles S-CONPRI
( O
that O
has O
an O
impact S-CONPRI
on O
the O
diffusion S-CONPRI
process O
) O
. O


To O
address O
this O
research S-CONPRI
gap O
, O
first O
, O
we O
develop O
a O
new O
model S-CONPRI
for O
the O
IMC O
thickness O
that O
takes O
the O
velocity O
of O
particles S-CONPRI
into O
account O
. O


Second O
, O
we O
provide O
an O
analysis O
on O
the O
velocity O
of O
particles S-CONPRI
in O
FSW S-MANP
based O
on O
vortex O
dynamics O
. O


Third O
, O
we O
analyze O
the O
proposed O
IMC O
thickness O
model S-CONPRI
with O
experimental B-CONPRI
data E-CONPRI
from O
the O
literature O
, O
discuss O
the O
added O
values O
of O
our O
model S-CONPRI
, O
and O
finally O
examine O
a O
case B-CONPRI
study E-CONPRI
. O


Understanding O
various O
manufacturing B-MANP
processes E-MANP
can O
further O
lead S-MATE
to O
the O
improvement O
of O
the O
existing O
processes S-CONPRI
and O
the O
development O
of O
novel O
processes S-CONPRI
. O


Inconel B-MATE
718 E-MATE
thin O
wall O
was O
fabricated S-CONPRI
by O
PPAAM O
. O


Both O
CET O
and O
DCT O
can O
be S-MATE
found O
in O
the O
as-built O
sample S-CONPRI
. O


Temperature B-PARA
gradient E-PARA
and O
SDA O
remelting O
contribute O
to O
grain B-CONPRI
structure E-CONPRI
transformation O
. O


The O
morphology S-CONPRI
of O
Nb-rich O
phases O
is O
sensitive O
to O
the O
grain B-CONPRI
structure E-CONPRI
and O
cooling B-PARA
rate E-PARA
. O


Abundant O
γ′/γ″ O
phases O
precipitate S-MATE
during O
HT O
and O
enhance O
mechanical B-CONPRI
properties E-CONPRI
. O


Inconel B-MATE
718 E-MATE
thin O
wall O
has O
been O
fabricated S-CONPRI
by O
pulsed B-MANP
plasma I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
PPAAM O
) O
technology S-CONPRI
, O
which O
is O
more O
convenient O
and O
cost-saving O
in O
comparison O
with O
other O
high O
energy O
beam S-MACEQ
additive B-MANP
manufacturing E-MANP
technologies O
. O


During O
PPAAM O
, O
heat S-CONPRI
input O
was O
reduced O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
to O
decrease O
the O
heat B-PRO
accumulation E-PRO
. O


The O
as-fabricated O
sample S-CONPRI
exhibited O
diverse O
grain S-CONPRI
morphologies O
at O
different O
locations O
. O


Columnar B-MATE
dendrites E-MATE
, O
cellular O
dendrites S-BIOP
, O
cells S-APPL
and O
equiaxial O
dendrites S-BIOP
accompanying O
many O
Laves B-CONPRI
phases E-CONPRI
, O
MC S-MATE
particles O
in O
the O
interdendritic O
regions O
can O
be S-MATE
observed O
. O


The O
largest O
primary O
dendritic B-BIOP
arm I-BIOP
spacing E-BIOP
( O
∼41.7 O
μm O
) O
and O
Nb-rich O
phases O
area S-PARA
fraction O
( O
3.68 O
% O
) O
were O
found O
in O
the O
middle O
region O
of O
the O
as-fabricated O
sample S-CONPRI
. O


After O
standard S-CONPRI
heat B-MANP
treatment E-MANP
, O
Laves B-CONPRI
phases E-CONPRI
dissolved O
into O
the O
matrix O
so O
that O
a O
number O
of O
γ′ O
and O
γ″ O
phases O
were O
formed O
. O


Besides O
, O
some O
rod-like O
δ O
phases O
could O
also O
be S-MATE
found O
near O
grain B-CONPRI
boundaries E-CONPRI
. O


The O
mechanisms O
of O
microstructural B-CONPRI
evolution E-CONPRI
and O
phases O
precipitation S-CONPRI
were O
analyzed O
in O
detail O
. O


The O
test O
values O
of O
the O
as-fabricated O
sample S-CONPRI
demonstrated O
a O
slightly O
higher O
tensile B-PRO
strength E-PRO
and O
dramatically O
outstanding O
ductility S-PRO
compared O
with O
cast S-MANP
Inconel O
718 O
alloy S-MATE
. O


Applying O
standard S-CONPRI
heat B-MANP
treatment E-MANP
could O
remarkably O
enhance O
the O
tensile B-PRO
strength E-PRO
but O
decrease O
the O
ductility S-PRO
and O
make O
them O
comparable O
with O
wrought B-MATE
Inconel I-MATE
718 I-MATE
alloy E-MATE
due O
to O
the O
precipitation S-CONPRI
of O
strengthening B-CONPRI
phases E-CONPRI
. O


Maraging B-MATE
steel E-MATE
microlattice O
was O
printed O
by O
SLM S-MANP
, O
crushed O
, O
and O
simulated O
using O
FEM S-CONPRI
. O


SEM S-CHAR
and O
micro-CT S-CHAR
was O
performed O
on O
as-built O
samples S-CONPRI
to O
verify O
structural B-PRO
integrity E-PRO
. O


Two O
modeling S-ENAT
techniques O
are O
presented O
based O
on O
as-built O
and O
as-designed O
geometries S-CONPRI
. O


FESEM S-CHAR
was O
performed O
on O
the O
crushed O
lattice S-CONPRI
for O
failure S-CONPRI
analysis O
. O


Good O
agreement O
is O
found O
between O
the O
experiment S-CONPRI
and O
the O
simulations S-ENAT
. O


Additive S-MATE
metal O
manufacturing S-MANP
techniques O
, O
in O
particular O
laser-based O
powder B-MANP
bed I-MANP
fusion E-MANP
methods O
, O
are O
revolutionary O
in O
their O
capabilities O
to O
fabricating S-MANP
new O
classes O
of O
lightweight S-CONPRI
and O
complex O
materials S-CONPRI
called O
metallic S-MATE
microlattices O
. O


In O
this O
paper O
, O
a O
microlattice O
structure S-CONPRI
was O
designed S-FEAT
for O
energy B-CHAR
absorption E-CHAR
purposes O
and O
further O
additively B-MANP
manufactured E-MANP
using O
maraging B-MATE
steel E-MATE
( O
Maraging300 O
) O
powder S-MATE
through O
Laser-powder O
bed B-MANP
fusion E-MANP
( O
L-PBF S-MANP
) O
technique O
. O


In O
addition O
, O
several O
cylindrical S-CONPRI
bars O
and O
cubes O
in O
horizontal O
and O
vertical S-CONPRI
directions O
were O
manufactured S-CONPRI
to O
perform O
uniaxial O
tensile S-PRO
and O
compression B-CHAR
tests E-CHAR
on O
bulk O
L-PBF S-MANP
Maraging300 O
. O


The O
manufactured S-CONPRI
microlattices O
were O
characterized O
using O
different O
electron B-CHAR
microscopy E-CHAR
techniques O
including O
scanning B-CHAR
electron I-CHAR
microscopy E-CHAR
and O
micro-CT B-CHAR
analysis E-CHAR
to O
ensure O
that O
the O
desired O
structural B-PRO
integrity E-PRO
was O
achieved O
. O


In O
addition O
, O
the O
microlattice O
was O
then O
crushed O
using O
a O
universal O
mechanical B-CHAR
testing E-CHAR
machine S-MACEQ
to O
evaluate O
its O
performance S-CONPRI
experimentally O
under O
quasi-static S-CONPRI
uniaxial O
compressive B-PRO
loading E-PRO
conditions O
. O


Along O
with O
the O
crush O
, O
a O
nonlinear O
finite B-CONPRI
element I-CONPRI
model E-CONPRI
with O
predictive O
capabilities O
was O
then O
developed O
using O
commercial O
package O
( O
LS-DYNA O
) O
for O
axial O
crush O
of O
the O
microlattice O
to O
compare O
its O
expected O
performance S-CONPRI
. O


Two O
finite B-CONPRI
element I-CONPRI
models E-CONPRI
are O
developed O
using O
the O
as-built O
geometry S-CONPRI
from O
the O
printed O
lattice S-CONPRI
, O
and O
the O
as-designed O
geometry S-CONPRI
. O


The O
effect O
of O
model S-CONPRI
parameters O
is O
discussed O
and O
very O
good O
agreement O
between O
the O
experimental S-CONPRI
results O
and O
the O
finite B-CONPRI
element E-CONPRI
prediction O
was O
observed O
. O


Finally O
statistical O
analysis O
of O
the O
model S-CONPRI
and O
failure S-CONPRI
analysis O
of O
the O
crushed O
lattice S-CONPRI
is O
presented O
. O


Hybrid O
Metal S-MATE
Extrusion S-MANP
and O
Bonding S-CONPRI
Additive B-MANP
Manufacturing E-MANP
( O
HYB-AM O
) O
is O
a O
new O
solid-state B-CONPRI
process E-CONPRI
for O
the O
production S-MANP
of O
3D B-FEAT
metal I-FEAT
structures E-FEAT
. O


In O
HYB-AM O
, O
the O
wire O
feedstock S-MATE
is O
continuously O
processed S-CONPRI
through O
an O
extruder S-MACEQ
and O
deposited O
in O
a O
stringer-by-stringer O
manner O
to O
form O
layers O
and O
eventually O
a O
near O
net-shape O
component S-MACEQ
. O


In O
this O
work O
, O
the O
layer S-PARA
bonding S-CONPRI
of O
AA6082 O
samples S-CONPRI
produced O
by O
this O
process S-CONPRI
has O
been O
investigated O
by O
means O
of O
tensile B-CHAR
testing E-CHAR
, O
hardness S-PRO
measurements O
and O
microscope S-MACEQ
analyses O
. O


Furthermore O
, O
a O
novel O
method O
for O
the O
fabrication S-MANP
of O
miniature O
tensile B-MACEQ
specimens E-MACEQ
for O
assessing O
the O
bond B-CONPRI
strength E-CONPRI
across O
the O
layers O
is O
presented O
and O
applied O
. O


The O
test O
results O
reveal O
that O
the O
ultimate B-PRO
tensile I-PRO
strength E-PRO
is O
approaching O
that O
of O
the O
substrate B-MATE
material E-MATE
of O
the O
same O
alloy S-MATE
, O
yet O
with O
a O
somewhat O
lower O
elongation S-PRO
prior O
to O
fracture S-CONPRI
. O


Microscope S-MACEQ
analyses O
show O
that O
the O
bonded O
interfaces O
are O
fully B-PARA
dense E-PARA
; O
however O
, O
the O
fracture S-CONPRI
surfaces O
reveal O
regions O
of O
kissing-bonds O
and O
lack O
of O
bonding S-CONPRI
. O


Still O
, O
these O
preliminary O
investigations O
indicate O
that O
the O
HYB-AM O
process S-CONPRI
, O
upon O
further O
optimization S-CONPRI
, O
has O
the O
potential O
of O
processing O
high O
quality S-CONPRI
aluminum B-MATE
alloy E-MATE
components O
. O


Ferritic/martensitic O
( O
FM O
) O
steels S-MATE
are O
being O
targeted O
for O
use O
in O
a O
range S-PARA
of O
advanced O
reactor O
concepts O
as S-MATE
cladding O
and O
structural B-CONPRI
components E-CONPRI
. O


FM O
steels S-MATE
for O
nuclear O
reactor O
applications O
have O
historically O
been O
produced O
using O
traditional O
methods O
( O
e.g. O
, O
casting S-MANP
and O
forging S-MANP
) O
, O
but O
recently O
, O
additive B-MANP
manufacturing I-MANP
processes E-MANP
have O
become O
of O
interest O
for O
making O
FM-based O
components S-MACEQ
. O


Here O
, O
the O
laser-blown-powder O
additive B-MANP
manufacturing I-MANP
process E-MANP
was O
used O
to O
fabricate S-MANP
an O
FM O
steel S-MATE
, O
HT9 O
, O
followed O
by O
microstructural S-CONPRI
and O
mechanical S-APPL
performance O
evaluations O
to O
determine O
the O
viability O
of O
future O
use O
of O
additive B-MANP
manufacturing E-MANP
for O
FM-based O
component S-MACEQ
fabrication O
. O


Results O
showed O
that O
the O
as-built O
condition O
formed O
a O
layered B-CONPRI
structure E-CONPRI
with O
alternating O
layers O
of O
δ-ferrite O
and O
martensite S-MATE
, O
which O
resulted O
in O
anisotropic S-PRO
engineering O
and O
true-stress O
, O
true-strain O
mechanical S-APPL
performance O
. O


Post-build O
normalizing S-CONPRI
and O
tempering S-MANP
treatments O
alerted O
the O
prior O
austenite S-MATE
grain O
size O
and O
precipitate S-MATE
distributions S-CONPRI
, O
and O
drove O
the O
mechanical S-APPL
performance O
to O
near-isotropic O
properties S-CONPRI
that O
mimic S-MACEQ
wrought-processed O
properties S-CONPRI
. O


A O
new O
method O
to O
forming S-MANP
bulk O
metallic B-MATE
glass E-MATE
employed O
ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
is O
proposed O
. O


The O
bulk O
Ni-based O
metallic B-MATE
glass E-MATE
can O
be S-MATE
formed O
layer-by-layer S-CONPRI
with O
ultrasonic B-PARA
vibration E-PARA
energy O
. O


The O
internal O
hardness S-PRO
and O
modulus O
of O
the O
bulk O
metallic B-MATE
glass E-MATE
are O
higher O
with O
ultrasonic B-MANP
additive I-MANP
manufacturing E-MANP
. O


It O
is O
difficult O
to O
produce O
bulk O
blanks O
directly O
from O
metallic B-MATE
glass E-MATE
, O
which O
limits S-CONPRI
its O
application O
. O


Ni-based O
metallic-glass O
thin O
strips O
that O
can O
be S-MATE
manufactured O
easily O
were O
used O
to O
manufacture S-CONPRI
bulk O
metallic B-MATE
glass E-MATE
additively O
by O
ultrasonic B-MANP
bonding E-MANP
. O


The O
effects O
of O
ultrasonic B-PARA
vibration E-PARA
energy O
on O
the O
quality S-CONPRI
of O
the O
additive B-MANP
manufacturing E-MANP
of O
bulk O
Ni-based O
metallic B-MATE
glass E-MATE
were O
studied O
. O


The O
experimental S-CONPRI
results O
showed O
that O
a O
fully O
amorphous B-CONPRI
structure E-CONPRI
of O
bulk O
Ni-based O
metallic B-MATE
glass E-MATE
can O
be S-MATE
obtained O
with O
an O
appropriate O
ultrasonic B-PARA
vibration E-PARA
energy O
. O


The O
thermal B-CONPRI
properties E-CONPRI
were O
almost O
unchanged O
, O
and O
the O
hardness S-PRO
and O
elastic B-PRO
modulus E-PRO
of O
the O
Ni-based O
metallic B-MATE
glass E-MATE
were O
improved O
compared O
with O
the O
original O
material S-MATE
. O


Additive B-MANP
manufacturing E-MANP
of O
bulk O
metallic B-MATE
glass E-MATE
by O
ultrasonic B-MANP
bonding E-MANP
can O
broaden O
the O
application O
field O
of O
metallic B-MATE
glass E-MATE
. O


A O
key O
challenge O
for O
successful O
exploitation O
of O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
across O
a O
broad O
range S-PARA
of O
industries S-APPL
is O
the O
development O
of O
fundamental O
understanding O
of O
the O
relationships O
between O
process B-CONPRI
control E-CONPRI
and O
mechanical S-APPL
performance O
of O
manufactured S-CONPRI
components S-MACEQ
. O


In O
particular O
, O
laser B-CONPRI
beam E-CONPRI
powder O
bed B-MANP
fusion E-MANP
( O
PBF-LB O
) O
is O
identified O
as S-MATE
a O
key O
process S-CONPRI
for O
manufacture S-CONPRI
of O
metallic B-MANP
AM E-MANP
components S-MACEQ
. O


Ti-6Al-4V B-MATE
alloy E-MATE
is O
an O
important O
metal B-MATE
alloy E-MATE
for O
numerous O
high-performance O
applications O
, O
including O
the O
biomedical S-APPL
and O
aerospace B-APPL
industries E-APPL
. O


This O
paper O
presents O
initial O
developments O
on O
a O
model S-CONPRI
for O
microstructure S-CONPRI
prediction O
in O
PBF-LB O
manufacturing S-MANP
of O
Ti-6Al-4V S-MATE
, O
primarily O
focused O
on O
solid-state B-CONPRI
phase E-CONPRI
transformation O
and O
dislocation B-PRO
density E-PRO
evolution O
. O


The O
motivation O
is O
to O
quantify O
microstructure S-CONPRI
variables O
which O
control O
mechanical S-APPL
behavior O
, O
including O
tensile B-PRO
strength E-PRO
and O
ductility S-PRO
. O


A O
finite B-CONPRI
element E-CONPRI
( O
FE S-MATE
) O
based O
model S-CONPRI
of O
the O
process S-CONPRI
is O
adopted O
for O
thermal O
history O
prediction S-CONPRI
. O


Phase S-CONPRI
transformation O
kinetics O
for O
transient S-CONPRI
non-isothermal O
conditions O
are O
adopted O
and O
implemented O
within O
a O
stand-alone O
code O
, O
based O
on O
the O
FE-predicted O
thermal O
histories O
of O
sample S-CONPRI
material S-MATE
points O
. O


The O
evolution S-CONPRI
and O
spatial B-FEAT
variations E-FEAT
of O
phase B-CONPRI
fractions E-CONPRI
, O
α O
lath O
width O
and O
dislocation B-PRO
density E-PRO
are O
presented O
, O
to O
provide O
an O
assessment O
of O
the O
resulting O
microstructure-sensitivity O
of O
mechanical B-CONPRI
properties E-CONPRI
. O


Friction S-CONPRI
stir O
processing O
( O
FSP O
) O
is O
combined O
with O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
with O
selective B-MANP
laser I-MANP
melting E-MANP
to O
locally O
enhance O
the O
material B-CONPRI
properties E-CONPRI
of O
a O
metallic B-MACEQ
part E-MACEQ
. O


A O
groove O
inside O
aluminium S-MATE
1060 O
alloy S-MATE
sheet O
is O
filled O
with O
an O
aluminium S-MATE
7075 O
alloy S-MATE
powder O
by O
AM S-MANP
. O


While O
the O
overall O
hardness S-PRO
of O
the O
stir O
zone O
( O
SZ O
) O
increases O
significantly O
, O
the O
heterogeneous S-CONPRI
microstructure O
results O
in O
a O
unique O
uneven O
hardness S-PRO
distribution S-CONPRI
in O
the O
SZ O
. O


Tensile B-CHAR
tests E-CHAR
confirm O
the O
effectiveness S-CONPRI
of O
the O
suggested O
technique O
. O


In O
laser-foil-printing O
additive B-MANP
manufacturing E-MANP
, O
3D S-CONPRI
metallic O
glass S-MATE
structures O
can O
be S-MATE
built O
by O
laser B-MANP
welding E-MANP
of O
amorphous O
foils O
, O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
, O
upon O
a O
crystalline O
metal S-MATE
substrate O
. O


In O
this O
paper O
, O
weldability S-PRO
studies O
for O
laser B-MANP
welding E-MANP
of O
Zr52.5Ti5Al10Ni14.6Cu17.9 O
amorphous O
foils O
onto O
a O
Ti-6Al-4V S-MATE
( O
Ti S-MATE
6-4 O
) O
or O
Zr S-MATE
702 O
substrate S-MATE
are O
conducted O
. O


After O
laser B-MANP
welding E-MANP
, O
the O
weldments O
are O
analyzed O
using O
X-ray S-CHAR
diffractometer O
, O
optical S-CHAR
microscope S-MACEQ
, O
scanning B-MACEQ
electron I-MACEQ
microscope E-MACEQ
equipped O
with O
energy B-CHAR
dispersive I-CHAR
spectroscopy E-CHAR
and O
micro-hardness O
tester O
. O


The O
results O
show O
that O
Zr S-MATE
702 O
is O
a O
suitable O
substrate S-MATE
for O
Zr-based O
metallic B-MATE
glass E-MATE
structure O
since O
crack-free B-CONPRI
weld E-CONPRI
joints O
can O
be S-MATE
obtained O
owing O
to O
the O
formation O
of O
ductile S-PRO
α-Zr O
, O
while O
Ti S-MATE
6-4 O
is O
not O
an O
appropriate O
substrate S-MATE
since O
it O
has O
high O
cracking S-CONPRI
susceptibility O
due O
to O
the O
formation O
of O
a O
large O
amount O
of O
hard O
and O
brittle S-PRO
intermetallics O
near O
the O
foil-substrate O
interface S-CONPRI
. O


It O
was O
found O
that O
the O
mixing S-CONPRI
between O
melted S-CONPRI
substrate O
and O
foil S-MATE
is O
not O
uniform O
but O
exhibits O
a O
distinct O
“ O
swirl O
” O
pattern S-CONPRI
. O


The O
swirl O
structure S-CONPRI
is O
more O
pronounced O
in O
Ti S-MATE
6-4 O
than O
in O
Zr S-MATE
702 O
substrate S-MATE
which O
may O
contribute O
to O
its O
high O
cracking S-CONPRI
susceptibility O
. O


The O
aforementioned O
mixing S-CONPRI
leads O
to O
partial O
crystallization S-CONPRI
of O
the O
first O
amorphous O
layer S-PARA
; O
however O
, O
fully O
amorphous O
is O
achieved O
in O
the O
additional O
welding S-MANP
layers O
. O


The O
deposition B-MANP
process E-MANP
of O
wire B-MANP
and I-MANP
arc I-MANP
additive I-MANP
manufacturing E-MANP
( O
WAAM S-MANP
) O
is O
usually O
planned O
based O
on O
a O
bead B-CHAR
geometry E-CHAR
model O
( O
BGM O
) O
, O
which O
represents O
the O
relationship O
between O
bead B-CHAR
geometries E-CHAR
( O
e.g O
. O


width O
, O
height O
) O
and O
required O
deposition S-CONPRI
parameters O
. O


However O
, O
the O
actual O
deposition S-CONPRI
situation O
may O
deviate O
from O
the O
one O
in O
which O
the O
BGM O
is O
built O
, O
such O
as S-MATE
varied O
heat B-CONPRI
dissipation E-CONPRI
conditions O
, O
resulting O
in O
morphological O
changes O
of O
deposited B-CHAR
beads E-CHAR
and O
geometrical O
errors S-CONPRI
in O
the O
formed O
parts O
. O


In O
this O
paper O
, O
a O
novel O
control O
mechanism S-CONPRI
for O
enhancing O
the O
fabrication S-MANP
accuracy S-CHAR
of O
WAAM S-MANP
based O
on O
fuzzy-logic O
inference S-CONPRI
is O
proposed O
. O


It O
considers O
the O
geometrical O
errors S-CONPRI
measured O
on O
already O
deposited B-CHAR
layers E-CHAR
and O
deposition S-CONPRI
context O
to O
adjust O
deposition S-CONPRI
parameters O
of O
beads S-CHAR
in O
the O
subsequent O
layer S-PARA
, O
forming S-MANP
an O
interlayer O
closed-loop B-MACEQ
control E-MACEQ
( O
ICLC O
) O
mechanism S-CONPRI
. O


This O
paper O
not O
only O
presents O
the O
theoretical S-CONPRI
fundamentals O
of O
the O
ICLC O
mechanism S-CONPRI
but O
also O
reports O
the O
technical O
details O
about O
utilizing O
this O
mechanism S-CONPRI
to O
control O
the O
forming S-MANP
height O
of O
multi-layer O
multi-bead O
( O
MLMB O
) O
components S-MACEQ
. O


A O
fuzzy-logic O
inference S-CONPRI
machine O
was O
applied O
as S-MATE
the O
core B-MACEQ
component E-MACEQ
for O
calculating O
speed O
change O
of O
bead S-CHAR
deposition O
based O
on O
height O
error S-CONPRI
and O
previously O
applied O
change O
. O


In O
terms O
of O
validation S-CONPRI
, O
the O
effectiveness S-CONPRI
of O
the O
proposed O
control O
mechanism S-CONPRI
and O
the O
implemented O
controller S-MACEQ
was O
investigated O
through O
both O
simulative O
studies O
and O
real-life O
experiments O
. O


The O
fabricated S-CONPRI
cuboid O
blocks O
showed O
good O
accuracy S-CHAR
in O
height O
with O
a O
maximum O
error S-CONPRI
of O
0.20 O
mm S-MANP
. O


The O
experimental S-CONPRI
results O
implied O
that O
the O
proposed O
ICLC O
approach O
facilitates O
deposition S-CONPRI
continuity O
of O
WAAM S-MANP
, O
and O
thus O
enables O
process B-CONPRI
automation E-CONPRI
for O
robotic O
manufacturing S-MANP
. O


A O
hybrid O
additive B-MANP
manufacturing E-MANP
technology O
for O
fabricating S-MANP
functionally O
graded O
materials S-CONPRI
( O
FGMs O
) O
is O
proposed O
in O
this O
paper O
. O


The O
new O
process S-CONPRI
represents O
a O
combination O
of O
two O
existing O
additive B-MANP
manufacturing I-MANP
processes E-MANP
, O
selective B-MANP
laser I-MANP
melting E-MANP
( O
SLM S-MANP
) O
and O
cold O
spraying O
( O
CS O
) O
. O


The O
targeted O
experiment S-CONPRI
of O
Al S-MATE
and O
Al S-MATE
+ O
Al2O3 S-MATE
deposited O
onto O
SLM S-MANP
Ti6Al4V O
via O
CS O
reveals O
that O
the O
hybrid O
additive B-MANP
manufacturing I-MANP
process E-MANP
can O
produce O
thick O
, O
dense O
and O
machinable O
FGMs O
composed O
of O
non-weldable O
metals S-MATE
without O
intermetallic S-MATE
phase O
formation O
at O
the O
multi-materials O
interface S-CONPRI
. O


The O
SLM S-MANP
Ti6Al4V O
part O
exhibited O
fully O
acicular O
martensitic O
microstructure S-CONPRI
in O
contrast O
with O
α O
+ O
β O
microstructure S-CONPRI
in O
the O
Ti6Al4V B-MATE
feedstock E-MATE
, O
while O
the O
grain B-CONPRI
structure E-CONPRI
of O
the O
CS O
Al S-MATE
part O
had O
no O
significant O
change O
as S-MATE
compared O
with O
the O
Al S-MATE
feedstock O
. O


Due O
to O
the O
phase S-CONPRI
transformation O
of O
the O
SLM S-MANP
part O
and O
work B-MANP
hardening E-MANP
of O
the O
CS O
part O
, O
the O
overall O
hardness S-PRO
of O
the O
FMGs O
was O
higher O
than O
that O
of O
the O
feedstock S-MATE
. O


The O
emerging O
trend S-CONPRI
of O
manufacturing S-MANP
is O
keenly O
focused O
on O
increasing O
the O
productivity S-CONPRI
. O


Many O
alternatives O
to O
enhance O
the O
productivity S-CONPRI
of O
a O
manufacturing S-MANP
industry S-APPL
involves O
reformation O
of O
production S-MANP
cycle O
, O
increasing O
the O
life O
of O
cutting B-APPL
tool E-APPL
, O
reducing O
the O
design S-FEAT
complexity S-CONPRI
, O
etc O
. O


However O
, O
the O
increasing O
nature O
of O
size O
reduction S-CONPRI
and O
complexion O
in O
design S-FEAT
seeks O
alternate O
method O
of O
manufacturing S-MANP
. O


The O
additive B-MANP
manufacturing E-MANP
is O
an O
emerging O
methodology S-CONPRI
used O
for O
meeting O
the O
needs O
of O
growing O
demand O
. O


It O
is O
a O
process S-CONPRI
of O
manufacturing S-MANP
parts O
by O
depositing O
materials S-CONPRI
which O
is O
contrary O
to O
that O
of O
conventional O
. O


This O
work O
presents O
a O
complete O
investigational O
survey O
on O
various O
additive B-MANP
manufacturing E-MANP
techniques O
, O
integration O
of O
digital O
pre-processing O
procedures O
, O
and O
product-based O
process S-CONPRI
designing O
. O


The O
process S-CONPRI
of O
creating O
models O
with O
reduced O
development O
and O
manufacturing S-MANP
time O
is O
discussed O
in O
an O
absolute O
manner O
. O


Several O
application-based O
materials S-CONPRI
are O
described O
in O
details O
along O
with O
few O
properties S-CONPRI
at O
the O
end O
of O
rapid B-MANP
manufacturing E-MANP
. O


Additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
processes S-CONPRI
such O
as S-MATE
Wire-Arc O
Additive B-MANP
Manufacturing E-MANP
( O
WAAM S-MANP
) O
are O
highly O
flexible O
and O
particularly O
suited O
for O
manufacturing S-MANP
complex B-CONPRI
geometries E-CONPRI
in O
small O
batch-sizes O
. O


In O
the O
case O
of O
large O
batch-sizes O
, O
the O
low O
production S-MANP
rate O
of O
WAAM S-MANP
is O
a O
bottleneck S-CONPRI
, O
and O
therefore O
forming B-MANP
processes E-MANP
with O
higher O
production S-MANP
rates O
are O
more O
suitable O
. O


However O
, O
forming B-MANP
processes E-MANP
such O
as S-MATE
closed O
die S-MACEQ
forging O
require O
dedicated O
tooling S-CONPRI
and O
hence O
lack O
the O
flexibility S-PRO
needed O
to O
produce O
product O
variants O
. O


The O
current O
study O
proposes O
to O
combine O
additive B-MANP
manufacturing E-MANP
with O
forging S-MANP
to O
form O
hybrid O
components S-MACEQ
with O
high O
complexity S-CONPRI
and O
acceptable O
production S-MANP
rates O
. O


However O
, O
the O
main O
challenge O
in O
achieving O
a O
combination O
of O
these O
manufacturing B-MANP
technologies E-MANP
is O
the O
design S-FEAT
of O
the O
process B-ENAT
chain E-ENAT
, O
ensuring O
that O
the O
final O
properties S-CONPRI
meet O
the O
specifications S-PARA
of O
the O
part O
. O


In O
this O
regard O
, O
the O
process S-CONPRI
sequence O
of O
forming S-MANP
followed O
by O
WAAM S-MANP
is O
investigated O
. O


The O
base O
material S-MATE
EN O
AW-6082 O
was O
formed O
to O
a O
preform O
by O
forging S-MANP
, O
followed O
by O
the O
deposition S-CONPRI
of O
different O
aluminum B-MATE
alloys E-MATE
by O
WAAM S-MANP
. O


The O
evolution S-CONPRI
of O
mechanical B-CONPRI
properties E-CONPRI
such O
as S-MATE
hardness O
and O
microstructure S-CONPRI
was O
analyzed O
. O


Based O
on O
the O
experimental S-CONPRI
observations O
, O
strategies O
to O
improve O
the O
performance S-CONPRI
of O
the O
hybrid O
components S-MACEQ
are O
presented O
. O


In O
order O
to O
achieve O
a O
polytropic O
expansion O
through O
a O
reciprocating O
machine S-MACEQ
, O
an O
extremely O
compact S-MANP
heat O
exchanger O
is O
designed S-FEAT
. O


It O
is O
a O
Mini O
Channel S-APPL
Heat O
Exchanger O
( O
MCHE O
) O
, O
cross-flow O
configuration S-CONPRI
, O
aluminium S-MATE
made O
. O


So O
, O
the O
additive B-MANP
manufacturing E-MANP
DMLS O
technique O
was O
used O
to O
make O
the O
exchanger O
. O


Then O
a O
simplified O
design S-FEAT
calculation O
is O
used O
to O
roughly O
predict O
its O
performance S-CONPRI
. O


Finally O
, O
the O
experimental S-CONPRI
test O
rig O
and O
the O
experimental B-CONPRI
data E-CONPRI
are O
shown O
. O


The O
rapid B-ENAT
prototyping E-ENAT
has O
been O
developed O
from O
the O
1980s O
to O
produce O
models O
and O
prototypes S-CONPRI
until O
the O
technologies B-CONPRI
evolution E-CONPRI
today O
. O


Nowadays O
, O
these O
technologies S-CONPRI
have O
other O
names O
such O
as S-MATE
3D B-MANP
printing E-MANP
or O
additive B-MANP
manufacturing E-MANP
, O
and O
so O
forth O
, O
but O
they O
all O
have O
the O
same O
origins O
from O
rapid B-ENAT
prototyping E-ENAT
. O


The O
design S-FEAT
and O
manufacturing B-MANP
process E-MANP
stood O
the O
same O
until O
new O
requirements O
such O
as S-MATE
a O
better O
integration O
on O
production B-MANP
line E-MANP
, O
a O
largest O
series O
of O
manufacturing S-MANP
or O
the O
reduce O
weight S-PARA
of O
products O
due O
to O
heavy O
costs O
of O
machines S-MACEQ
and O
materials S-CONPRI
. O


The O
ability O
to O
produce O
complex B-CONPRI
geometries E-CONPRI
allows O
proposing O
of O
design S-FEAT
and O
manufacturing S-MANP
solutions O
in O
the O
industrial S-APPL
field O
in O
order O
to O
be S-MATE
ever O
more O
effective O
. O


The O
additive B-MANP
manufacturing E-MANP
( O
AM S-MANP
) O
technology S-CONPRI
develops O
rapidly O
with O
news O
solutions O
and O
markets O
which O
sometimes O
need O
to O
demonstrate O
their O
reliability S-CHAR
. O


The O
community O
needs O
to O
survey O
some O
evolutions S-CONPRI
such O
as S-MATE
the O
new O
exchange B-CONPRI
format E-CONPRI
, O
the O
faster O
3D B-MANP
printing E-MANP
systems O
, O
the O
advanced O
numerical B-ENAT
simulation E-ENAT
or O
the O
emergence O
of O
new O
use O
. O


We O
propose O
to O
review O
the O
different O
AM B-MANP
technologies E-MANP
and O
the O
new O
trends S-CONPRI
to O
get O
a O
global O
overview O
through O
the O
engineering S-APPL
and O
manufacturing B-MANP
process E-MANP
. O


This O
article O
describes O
the O
engineering S-APPL
and O
manufacturing B-CONPRI
cycle E-CONPRI
with O
the O
3D B-APPL
model E-APPL
management O
and O
the O
most O
recent O
technologies S-CONPRI
from O
the O
evolution S-CONPRI
of O
additive B-MANP
manufacturing E-MANP
. O


Finally O
, O
the O
use O
of O
AM S-MANP
resulted O
in O
new O
trends S-CONPRI
that O
are O
exposed O
below O
with O
the O
description O
of O
some O
new O
economic B-CONPRI
activities E-CONPRI
. O


The O
first O
method O
to O
create O
a O
three-dimensional S-CONPRI
object O
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
using O
computer-aided B-ENAT
design E-ENAT
( O
CAD S-ENAT
) O
was O
rapid B-ENAT
prototyping E-ENAT
, O
developed O
in O
the O
1980s O
to O
produce O
models O
and O
prototype S-CONPRI
parts O
. O


The O
main O
advantage O
of O
the O
Additive B-MANP
Manufacturing E-MANP
( O
AM S-MANP
) O
is O
its O
ability O
to O
create O
almost O
any O
possible O
shape O
and O
this O
capacity S-CONPRI
is O
run O
by O
the O
layer-by-layer S-CONPRI
manufacturing O
. O


AM B-MANP
technology E-MANP
is O
most O
commonly O
used O
for O
modelling S-ENAT
, O
prototyping S-CONPRI
, O
tooling S-CONPRI
through O
an O
exclusive O
machine S-MACEQ
or O
3D B-MACEQ
printer E-MACEQ
. O


AM S-MANP
is O
largely O
used O
for O
manufacturing S-MANP
short-term O
prototypes S-CONPRI
but O
it O
is O
also O
used O
for O
small-scale O
series O
production S-MANP
and O
tooling S-CONPRI
applications O
( O
Rapid B-MANP
Tooling E-MANP
) O
. O


This O
technology S-CONPRI
was O
created O
to O
help O
and O
support S-APPL
the O
engineers O
in O
their O
conceptualisation S-CONPRI
. O


Among O
the O
major O
advances O
that O
this O
process S-CONPRI
presented O
to O
product B-CONPRI
development E-CONPRI
are O
the O
time O
and O
cost B-CONPRI
reduction E-CONPRI
, O
human B-CONPRI
interaction E-CONPRI
, O
and O
consequently O
the O
product B-CONPRI
cycle E-CONPRI
development O
. O


Those O
shapes O
could O
indeed O
be S-MATE
very O
difficult O
to O
manufacture S-CONPRI
with O
other O
processes S-CONPRI
( O
e.g O
. O


milling S-MANP
, O
moulding S-CONPRI
) O
. O


The O
complex B-CONPRI
geometries E-CONPRI
or O
the O
curved B-CONPRI
surfaces E-CONPRI
needed O
have O
to O
be S-MATE
maintained O
with O
a O
support B-MATE
material E-MATE
. O


The O
feedback S-PARA
has O
a O
great O
influence O
on O
the O
quality S-CONPRI
or O
effectiveness S-CONPRI
of O
the O
manufactured S-CONPRI
model O
. O


From O
one O
technology S-CONPRI
to O
another O
, O
the O
manufacture B-CONPRI
direction E-CONPRI
, O
the O
model B-CONPRI
orientation E-CONPRI
and O
the O
material S-MATE
behaviour O
are O
important O
to O
get O
an O
accurate S-CHAR
model O
and O
an O
efficient O
production S-MANP
. O


Nowadays O
, O
these O
technologies S-CONPRI
have O
other O
names O
such O
as S-MATE
3D B-MANP
printing E-MANP
, O
and O
so O
forth O
, O
but O
they O
all O
have O
the O
same O
origins O
from O
rapid B-ENAT
prototyping E-ENAT
. O


The O
demand O
of O
AM B-MACEQ
machines E-MACEQ
is O
increasingly O
growing O
since O
the O
1990s O
. O


Due O
to O
the O
evolution S-CONPRI
of O
rapid B-ENAT
prototyping E-ENAT
technologies O
, O
it O
has O
become O
possible O
to O
obtain O
parts O
representative O
of O
a O
mass B-CONPRI
production E-CONPRI
within O
a O
very O
short O
time O
. O


AM S-MANP
perfectly O
fits S-CONPRI
into O
the O
numerical B-CONPRI
design E-CONPRI
and O
manufacturing B-CONPRI
chain E-CONPRI
. O


AM S-MANP
is O
very O
complementary O
with O
the O
reverse B-CONPRI
engineering E-CONPRI
to O
reproduce O
or O
repair O
a O
model S-CONPRI
. O


Many O
rapid B-ENAT
prototyping E-ENAT
technologies O
have O
appeared O
on O
the O
market O
based O
on O
the O
same O
layers B-MANP
manufacturing E-MANP
approach O
. O


AM S-MANP
or O
3D B-MANP
printing E-MANP
have O
strongly O
been O
developed O
and O
currently O
propose O
several O
solutions O
. O


Use O
of O
AM S-MANP
leads O
to O
new O
practices O
in O
different O
domains O
which O
push O
the O
manufacturer S-CONPRI
to O
adapt O
. O


The O
evolution S-CONPRI
of O
AM B-MANP
technologies E-MANP
also O
leads O
to O
news O
solutions O
driven O
by O
very O
strong O
demand O
. O


Use O
and O
evolution S-CONPRI
change O
gradually O
the O
product B-CONPRI
life I-CONPRI
cycle E-CONPRI
in O
order O
to O
reducing O
the O
manufacturing B-CONPRI
cost E-CONPRI
and O
time O
while O
increasing O
reliability S-CHAR
. O


We O
propose O
to O
realise O
a O
technologic S-CONPRI
review O
of O
manufacturing B-MANP
processes E-MANP
followed O
by O
their O
illustrative O
scheme O
. O


We O
have O
chosen O
to O
classify O
the O
AM S-MANP
by O
manufacturing B-MANP
technologies E-MANP
to O
explain O
them O
. O


First O
of O
all O
, O
we O
will O
describe O
the O
design B-CONPRI
process E-CONPRI
before O
the O
technologies S-CONPRI
description O
while O
involving O
some O
industrial S-APPL
and O
academic O
trends S-CONPRI
. O


The O
stages O
involved O
to O
the O
product B-FEAT
design E-FEAT
and O
the O
rapid B-ENAT
prototyping E-ENAT
show O
that O
the O
cycle B-CONPRI
development E-CONPRI
is O
specific O
. O


These O
rapid B-ENAT
prototyping E-ENAT
processes S-CONPRI
generally O
consist O
of O
a O
substance S-CONPRI
, O
such O
as S-MATE
fluids O
, O
waxes S-MATE
, O
powders S-MATE
or O
laminates S-CONPRI
, O
which O
serve O
as S-MATE
basis O
for O
model B-MANP
construction E-MANP
as S-MATE
well O
as S-MATE
sophisticated O
computer-automated B-MACEQ
equipment E-MACEQ
to O
control O
the O
processing B-CONPRI
techniques E-CONPRI
such O
as S-MATE
deposition O
, O
sintering S-MANP
, O
lasing S-ENAT
, O
etc O
. O


There O
exist O
two O
possibilities O
to O
start O
an O
AM S-MANP
cycle O
, O
begin O
with O
a O
virtual B-ENAT
model E-ENAT
or O
a O
physical B-CONPRI
model E-CONPRI
. O


The O
virtual B-ENAT
model E-ENAT
created O
by O
a O
CAD S-ENAT
software O
can O
be S-MATE
either O
a O
surface S-CONPRI
or O
a O
solid B-CONPRI
model E-CONPRI
. O


On O
the O
other O
hand O
, O
3D B-CONPRI
data E-CONPRI
from O
the O
physical B-CONPRI
model E-CONPRI
is O
not O
at O
all O
straightforward O
and O
it O
requires O
data B-CHAR
acquisition E-CHAR
through O
a O
method O
known O
as S-MATE
a O
reverse B-CONPRI
engineering E-CONPRI
. O


The O
process S-CONPRI
begins O
with O
a O
3D B-APPL
model E-APPL
in O
CAD S-ENAT
software O
before O
converting O
it O
in O
STL B-MANS
format E-MANS
file S-MANS
. O


This O
format O
is O
treated O
by O
specific O
software S-CONPRI
, O
own O
to O
the O
AM B-MANP
technology E-MANP
, O
which O
cuts O
the O
piece O
in O
slices S-CONPRI
to O
get O
a O
new O
file S-MANS
containing O
the O
information O
for O
each O
layer S-PARA
. O


The O
specific O
software S-CONPRI
generates O
the O
hold O
to O
maintain O
the O
complex B-CONPRI
geometries E-CONPRI
automatically O
with O
sometimes O
the O
possibility O
to O
choose O
some O
parameters S-CONPRI
. O


We O
can O
decompose O
the O
engineering S-APPL
and O
manufacturing B-CONPRI
cycle E-CONPRI
by O
Part O
design S-FEAT
in O
CAD S-ENAT
or O
reverse B-CONPRI
engineering E-CONPRI
by O
3D B-CHAR
scanning E-CHAR
. O


Skills O
optimisation O
in O
CAE S-ENAT
to O
adapt O
the O
part O
to O
the O
manufacturing B-MANP
technology E-MANP
chosen O
. O


Conversion O
of O
part O
geometry S-CONPRI
in O
exchange B-CONPRI
format E-CONPRI
( O
STL S-MANS
) O
. O


Exchange O
file S-MANS
implementation O
into O
the O
specific O
software S-CONPRI
of O
the O
AM B-MACEQ
machine E-MACEQ
. O


Configuration S-CONPRI
and O
orientation S-CONPRI
of O
the O
set S-APPL
( O
parts O
and O
supports S-APPL
) O
. O


Slicing S-CONPRI
of O
the O
part O
by O
the O
specific O
software S-CONPRI
. O


Computation S-CONPRI
and O
layers B-MANP
manufacturing E-MANP
. O


Post-processing S-CONPRI
. O


This O
new O
file S-MANS
is O
often O
proprietary O
of O
the O
machine S-MACEQ
manufacturer O
. O


Rapid B-MANP
manufacturing E-MANP
machine S-MACEQ
implement O
the O
last O
file S-MANS
to O
realise O
the O
layer-by-layer S-CONPRI
manufacturing O
. O


The O
operator O
has O
to O
prepare O
the O
machine S-MACEQ
with O
its O
raw B-MATE
material E-MATE
( O
powder S-MATE
, O
resin S-MATE
cartridge S-MACEQ
( O
s S-MATE
) O
, O
polymer S-MATE
spool O
( O
s S-MATE
) O
, O
etc O
) O
and O
the O
manufacturing S-MANP
source O
( O
laser S-ENAT
, O
printing B-MACEQ
head E-MACEQ
( O
s S-MATE
) O
, O
binder S-MATE
cartridge O
( O
s S-MATE
) O
, O
etc O
) O
. O


For O
the O
manufacturing S-MANP
, O
the O
support B-MATE
material E-MATE
maintains O
the O
external O
and O
internal O
surfaces S-CONPRI
to O
keep O
a O
steady O
geometry S-CONPRI
with O
a O
structure S-CONPRI
using O
scaffolding S-ENAT
. O


In O
most O
cases O
, O
the O
support B-MATE
material E-MATE
is O
cleaned O
during O
the O
finishing S-MANP
( O
ex O
. O


MJM S-MANP
Technology O
) O
or O
recycled S-CONPRI
during O
the O
post-processing S-CONPRI
( O
e.g O
. O


SLS S-MANP
, O
SLM S-MANP
, O
CJD/3DP S-MANP
Technologies O
) O
. O


This O
step S-CONPRI
depends O
on O
the O
complex B-CONPRI
geometry E-CONPRI
fabricated O
and O
if O
there O
is O
need O
an O
additional O
hold O
resulting O
in O
a O
loss O
of O
material S-MATE
. O


Some O
technologies S-CONPRI
allow O
extracting S-CONPRI
of O
the O
main O
material S-MATE
, O
thanks O
to O
holes O
inside O
closed O
geometry S-CONPRI
. O


The O
post-processing S-CONPRI
step O
sometimes O
includes O
a O
hardening S-MANP
or O
infiltration S-CONPRI
of O
the O
main O
material S-MATE
to O
obtain O
the O
final O
piece O
. O


Several O
manufacturing B-CONPRI
constraints E-CONPRI
require O
a O
feedback S-PARA
while O
involving O
rules O
to O
get O
a O
precisely O
and O
compliant O
model S-CONPRI
. O


Rapid B-ENAT
prototyping E-ENAT
techniques O
are O
classified O
in O
two O
categories O
: O
subtractive S-MANP
, O
and O
additive S-MATE
. O


Subtractive S-MANP
technologies O
work O
by O
removing O
raw B-MATE
material E-MATE
out O
of O
a O
workpiece S-CONPRI
until O
the O
desired O
shape O
is O
obtained O
. O


They O
include O
cutting S-MANP
( O
laser-cutting S-MANP
or O
water-jet B-MANP
cutting E-MANP
) O
and O
machining S-MANP
( O
lathing S-MANP
and O
milling S-MANP
) O
. O


Conversely O
, O
the O
additive B-ENAT
technologies E-ENAT
work O
by O
adding O
of O
the O
raw B-MATE
material E-MATE
. O


Modelling S-ENAT
is O
a O
very O
important O
step S-CONPRI
in O
AM S-MANP
because O
it O
shapes O
the O
product O
but O
it O
also O
must O
take O
in O
account O
some O
knowledge O
since O
the O
experiments O
and O
equipment S-MACEQ
are O
costly O
. O


Various O
potential O
empirical S-CONPRI
modelling O
techniques O
coexist O
so O
that O
the O
choice O
of O
an O
appropriate O
modelling S-ENAT
technique O
for O
a O
given O
AM B-MANP
process E-MANP
can O
be S-MATE
made O
. O


To O
develop O
models O
based O
on O
only O
given O
data S-CONPRI
, O
several O
well-known O
statistical B-CONPRI
methods E-CONPRI
such O
as S-MATE
regression O
analysis O
or O
response B-CONPRI
surface I-CONPRI
methodology E-CONPRI
can O
be S-MATE
applied O
. O


The O
formulation O
of O
the O
physics-based B-CONPRI
models E-CONPRI
requires O
in-depth O
understanding O
of O
the O
process S-CONPRI
and O
is O
not O
an O
easy O
task O
in O
presence O
of O
partial B-CONPRI
information E-CONPRI
about O
the O
process S-CONPRI
. O


Few O
research S-CONPRI
studies O
have O
been O
conducted O
to O
improve O
the O
prediction S-CONPRI
ability O
of O
the O
GP S-CONPRI
( O
Genetic B-ENAT
Programming E-ENAT
) O
and O
the O
MGGP S-ENAT
( O
Multi-Gene B-ENAT
Genetic I-ENAT
Programming E-ENAT
) O
models O
by O
hybridising S-CONPRI
them O
with O
the O
other O
potential O
computational B-CONPRI
intelligence E-CONPRI
methods O
such O
as S-MATE
artificial B-ENAT
neural I-ENAT
network E-ENAT
( O
ANN S-ENAT
) O
, O
fuzzy B-CONPRI
logic E-CONPRI
, O
M5 O
’ O
regression S-CONPRI
trees O
and O
support B-CONPRI
vector I-CONPRI
regression E-CONPRI
. O


MGGP S-ENAT
is O
the O
most O
popular O
variant O
of O
GP S-CONPRI
used O
recently O
. O


Those O
approaches O
provide O
a O
model S-CONPRI
in O
the O
form O
of O
a O
mathematical B-CONPRI
equation E-CONPRI
reflecting O
the O
relationship O
between O
the O
mechanical B-CONPRI
behaviours E-CONPRI
and O
the O
given O
input O
parameters S-CONPRI
. O


The O
performance S-CONPRI
of O
ANN S-ENAT
is O
found O
to O
be S-MATE
better O
than O
those O
of O
GP S-CONPRI
and O
regression S-CONPRI
, O
showing O
the O
effectiveness S-CONPRI
of O
ANN S-ENAT
in O
predicting O
the O
performance S-CONPRI
characteristics O
of O
prototype S-CONPRI
. O


The O
STL S-MANS
( O
STereoLithography S-MANP
or O
Standard B-MANS
Tessellation I-MANS
Language E-MANS
) O
file S-MANS
format O
was O
created O
by O
3D B-APPL
Systems E-APPL
in O
1987 O
and O
became O
a O
standard S-CONPRI
for O
the O
additive B-MANP
manufacturing E-MANP
. O


The O
STL S-MANS
file S-MANS
creation O
process S-CONPRI
mainly O
converts O
the O
continuous O
geometry S-CONPRI
in O
the O
CAD B-MANS
file E-MANS
into O
a O
header S-CONPRI
, O
small O
triangles O
or O
coordinates B-CONPRI
triplet E-CONPRI
list O
of O
x O
, O
y S-MATE
and O
z O
coordinates S-PARA
and O
the O
normal B-CONPRI
vector E-CONPRI
to O
the O
triangles O
. O


Each O
facet S-CONPRI
is O
uniquely O
identified O
by O
a O
normal B-CONPRI
vector E-CONPRI
and O
three O
vertices S-PARA
. O


The O
facets S-CONPRI
define O
the O
surfaces S-CONPRI
of O
a O
3D B-APPL
object E-APPL
. O


Each O
facet S-CONPRI
is O
part O
of O
the O
boundary S-FEAT
between O
the O
interior O
and O
the O
exterior O
of O
the O
object O
and O
each O
triangle O
facet S-CONPRI
must O
share O
two O
vertices S-PARA
with O
each O
of O
its O
adjacent B-CONPRI
triangles E-CONPRI
. O


The O
surface S-CONPRI
creation O
can O
generate O
errors S-CONPRI
because O
of O
holes O
or O
intersecting O
triangles O
and O
it O
is O
sometimes O
necessary O
to O
repair O
the O
STL S-MANS
model S-CONPRI
. O


The O
slicing B-CONPRI
process E-CONPRI
also O
introduces O
inaccuracy O
to O
the O
file S-MANS
because O
here O
the O
algorithm S-CONPRI
replaces O
the O
continuous O
contour S-FEAT
with O
discrete B-CONPRI
stair I-CONPRI
steps E-CONPRI
. O


Edges O
are O
added O
after O
the O
slicing B-CONPRI
process E-CONPRI
. O


Today O
, O
the O
computation S-CONPRI
data O
and O
the O
mesh B-CONPRI
generation E-CONPRI
is O
no O
longer O
an O
obstacle O
to O
process B-CONPRI
models E-CONPRI
. O


The O
computer S-ENAT
power O
used O
is O
sufficient O
to O
get O
a O
refined O
STL S-MANS
file S-MANS
with O
many O
triangles O
. O


More O
the O
3D B-APPL
model E-APPL
refined O
is O
high O
, O
the O
clearer O
the O
details O
are O
and O
the O
bigger O
the O
file B-PARA
size E-PARA
is O
. O


According O
to O
the O
2014 O
Wohlers O
Report O
, O
consumers O
of O
3D B-MACEQ
printers E-MACEQ
are O
classified O
as S-MATE
those O
that O
cost O
less O
than O
$ O
5000 O
. O


The O
Cornell O
University O
and O
the O
University O
of O
Bath O
have O
designed S-FEAT
the O
first O
open-source S-CONPRI
3D B-MACEQ
printers E-MACEQ
which O
are O
widely O
recognised O
in O
the O
area S-PARA
: O
Fab O
@ O
home O
and O
RepRap S-APPL
. O


The O
entered O
range S-PARA
3D B-MACEQ
printers E-MACEQ
are O
predominantly O
based O
on O
Fused B-MANP
Deposition I-MANP
Modeling E-MANP
( O
FDM S-MANP
) O
technology S-CONPRI
, O
but O
more O
recently O
machines S-MACEQ
derived O
from O
stereolithography S-MANP
have O
entered O
the O
market O
due O
to O
expiring O
patents S-CONPRI
. O


It O
is O
typically O
to O
demonstrate O
that O
low-cost O
machines S-MACEQ
have O
a O
low O
performance S-CONPRI
. O


For O
example O
, O
the O
FDM S-MANP
consumer O
technology S-CONPRI
suffers O
from O
anisotropic S-PRO
mechanical O
properties S-CONPRI
as S-MATE
well O
as S-MATE
a O
limited O
selection O
of O
thermoplastic B-MATE
materials E-MATE
. O


A O
FDM S-MANP
professional O
printer S-MACEQ
costs O
between O
$ O
10,000 O
and O
$ O
300,000 O
. O


Typical O
laser S-ENAT
and O
electron B-ENAT
beam-based E-ENAT
systems O
can O
cost O
anywhere O
between O
$ O
500,000 O
and O
$ O
1 O
M. O
While O
these O
machines S-MACEQ
are O
typically O
high O
in O
performance S-CONPRI
, O
they O
come O
at O
a O
high O
cost O
. O


The O
commercial O
3D B-MACEQ
printers E-MACEQ
that O
use O
more O
advanced O
techniques O
to O
print S-MANP
objects O
are O
usually O
equipped O
with O
proprietary O
software S-CONPRI
which O
slice S-CONPRI
the O
3D B-APPL
model E-APPL
and O
command O
the O
machine S-MACEQ
. O


Companies S-APPL
that O
sell O
professional O
3D B-MACEQ
printers E-MACEQ
include O
3D B-APPL
Systems E-APPL
, O
Stratasys S-APPL
, O
Solido B-APPL
LTD E-APPL
, O
Voxeljet O
and O
ExOne O
. O


Both O
Hewlett B-APPL
Packard E-APPL
and O
Xerox S-APPL
‘ O
are O
investing O
in O
3D B-MANP
printing E-MANP
research O
and O
technology S-CONPRI
development O
. O


Each O
AM B-MANP
technologies E-MANP
have O
manufacturing B-CONPRI
constraints E-CONPRI
linked O
by O
printing B-ENAT
technology E-ENAT
, O
used O
material S-MATE
and O
expected O
functions O
( O
aesthetic S-CONPRI
, O
mechanical S-APPL
, O
use O
, O
etc O
) O
. O


Areas B-CONPRI
of I-CONPRI
interest E-CONPRI
which O
have O
used O
3D B-MANP
printing E-MANP
to O
create O
objects O
include O
aeronautics S-APPL
, O
architecture S-APPL
, O
automotive B-APPL
industries E-APPL
, O
art S-APPL
, O
dentistry S-APPL
, O
fashion S-CONPRI
, O
food O
, O
jewellery S-CONPRI
, O
medicine S-CONPRI
, O
pharmaceuticals S-APPL
, O
robotics S-APPL
and O
toys S-MACEQ
. O


Automotive S-APPL
manufacturers O
exploited O
the O
technology S-CONPRI
because O
of O
the O
ability O
to O
help O
new O
products O
get O
quickly O
to O
the O
market O
and O
in O
a O
predictable S-CONPRI
manner O
. O


Aerospace S-APPL
companies O
are O
interested O
in O
these O
technologies S-CONPRI
because O
of O
the O
ability O
to O
realise O
highly O
complex O
and O
high-performance O
products O
. O


Integrating O
mechanical B-CONPRI
functionality E-CONPRI
, O
eliminating O
assembly S-MANP
features O
and O
making O
it O
possible O
to O
create O
internal O
functionality O
( O
like O
cooling B-MACEQ
channels E-MACEQ
) O
, O
internal O
honeycomb S-CONPRI
style O
structures O
, O
new O
topological B-FEAT
optimisation E-FEAT
structure S-CONPRI
etc O
. O


combine O
to O
create O
lightweight B-MACEQ
structures E-MACEQ
. O


Medical B-APPL
industries E-APPL
are O
particularly O
interested O
in O
AM B-MANP
technology E-MANP
because O
of O
the O
ease O
in O
which O
3D B-ENAT
medical I-ENAT
imaging E-ENAT
data O
can O
be S-MATE
converted O
into O
solid O
objects O
. O


Thus O
, O
each O
AM B-MANP
technology E-MANP
have O
advantages O
and O
disadvantages O
for O
own O
applications O
and O
we O
propose O
to O
review O
them O
. O


Authors O
have O
chosen O
to O
classify O
the O
technologies S-CONPRI
according O
to O
hardening B-MACEQ
system E-MACEQ
or O
melting B-MACEQ
system E-MACEQ
which O
are O
characterised O
by O
a O
laser S-ENAT
, O
a O
flashing B-CONPRI
source E-CONPRI
, O
an O
extrusion S-MANP
or O
a O
jetting S-MANP
. O


SLA S-MACEQ
– O
Stereolithography S-MANP
is O
the O
first O
of O
the O
technologies S-CONPRI
developed O
originally O
and O
simultaneously O
in O
France O
and O
in O
the O
USA O
to O
tackle O
rapid B-ENAT
prototyping E-ENAT
bottlenecks S-CONPRI
, O
as S-MATE
well O
as S-MATE
faster O
and O
better O
design S-FEAT
needs O
( O
CAD S-ENAT
induced O
) O
. O


In O
1986 O
, O
3D B-APPL
Systems E-APPL
was O
founded O
by O
Chuck S-MACEQ
Hull O
to O
commercialise O
this O
process S-CONPRI
. O


Photolithographic B-MANP
systems E-MANP
build S-PARA
shapes O
using O
light O
to O
selectively O
solidify S-CONPRI
photosensitive B-MATE
resins E-MATE
. O


The O
laser B-MANP
lithography E-MANP
approach O
is O
currently O
one O
of O
the O
most O
used O
AM B-MANP
technologies E-MANP
. O


Models O
are O
defined O
by O
scanning S-CONPRI
a O
laser B-CONPRI
beam E-CONPRI
over O
a O
photopolymer S-MATE
surface O
. O


For O
a O
few O
years O
, O
researchers O
have O
developed O
techniques O
to O
apply O
SLA S-MACEQ
to O
directly O
make O
ceramics S-MATE
. O


Ceramic B-MATE
powder E-MATE
( O
silica S-MATE
and O
alumina S-MATE
) O
is O
dispersed O
in O
a O
fluid B-MATE
UV I-MATE
curable I-MATE
monomer E-MATE
to O
prepare O
a O
ceramic–UV O
curable O
monomer S-MATE
suspension O
. O


The O
building B-CHAR
process E-CHAR
is O
the O
same O
as S-MATE
conventional O
SLA S-MACEQ
and O
the O
monomer B-MATE
solution E-MATE
is O
cured S-MANP
forming O
a O
ceramic–polymer O
composite S-MATE
layer O
. O


The O
prototypes S-CONPRI
have O
higher O
stiffness S-PRO
than O
a O
standard S-CONPRI
workpiece O
and O
their O
temperature B-PRO
resistance E-PRO
over O
200 O
°C O
. O


A O
higher B-PARA
resolution E-PARA
machine O
has O
been O
developed O
and O
called O
microstereolithography S-MANP
and O
it O
can O
print S-MANP
a O
layer S-PARA
with O
thickness O
of O
less O
than O
10 O
μm O
. O


The O
microstereolithography S-MANP
shares O
the O
same O
principle O
with O
its O
macro B-CONPRI
scale E-CONPRI
counterpart O
, O
but O
in O
different O
dimensions S-FEAT
. O


In O
microstereolithography S-MANP
, O
an O
UV B-CONPRI
laser I-CONPRI
beam E-CONPRI
is O
focused O
to O
1–2 O
μm O
to O
solidify S-CONPRI
a O
thin O
layer S-PARA
of O
1–10 O
μm O
in O
thickness O
. O


Submicron B-PARA
resolution E-PARA
of O
the O
x–y–z O
translation O
stages O
and O
the O
fine O
UV B-CONPRI
beam E-CONPRI
spot O
enable O
precise B-MANP
fabrication E-MANP
of O
real O
3D S-CONPRI
complex O
microstructures S-MATE
. O


SLM S-MANP
– O
Selective B-MANP
Laser I-MANP
Melting E-MANP
– O
the O
system O
starts O
by O
applying O
a O
thin O
layer S-PARA
of O
the O
powder B-MATE
material E-MATE
spread O
by O
a O
roller S-MACEQ
on O
the O
building B-MACEQ
platform E-MACEQ
. O


A O
powerful O
laser B-CONPRI
beam E-CONPRI
then O
fuses S-MANP
the O
powder S-MATE
at O
exactly O
the O
points O
defined O
by O
the O
computer-generated S-CONPRI
component S-MACEQ
design O
data S-CONPRI
. O


The O
platform S-MACEQ
is O
then O
lowered O
and O
another O
layer S-PARA
of O
powder S-MATE
is O
applied O
. O


Once O
again O
the O
material S-MATE
is O
fused S-CONPRI
so O
as S-MATE
to O
bond O
with O
the O
layer S-PARA
below O
at O
the O
predefined B-CONPRI
points E-CONPRI
. O


During O
the O
process S-CONPRI
, O
successive O
layers O
of O
metal B-MATE
powder E-MATE
are O
fully O
melted S-CONPRI
and O
consolidated O
on O
top O
of O
each O
other O
. O


Today O
, O
the O
3D B-MACEQ
printer E-MACEQ
manufacturers O
propose O
machines S-MACEQ
with O
powerful O
double O
or O
multi B-CONPRI
laser I-CONPRI
technology E-CONPRI
with O
layers O
from O
75 O
to O
150 O
μm O
in O
thickness O
. O


The O
material S-MATE
types O
that O
can O
be S-MATE
processed O
include O
steel S-MATE
, O
stainless B-MATE
steel E-MATE
, O
cobalt B-MATE
chrome E-MATE
, O
titanium S-MATE
and O
aluminium S-MATE
. O


Electron B-MANP
Beam I-MANP
Melting E-MANP
is O
a O
powder B-MANP
process E-MANP
which O
distinguishes O
by O
its O
superior O
accuracy S-CHAR
and O
high-power O
electron B-CONPRI
beam E-CONPRI
( O
up O
to O
3000 O
W O
while O
maintaining O
a O
scan B-PARA
speed E-PARA
) O
that O
generates O
the O
energy O
needed O
for O
high O
melting B-CONPRI
capacity E-CONPRI
and O
high O
productivity S-CONPRI
. O


Selective B-MANP
Laser I-MANP
Sintering E-MANP
( O
SLS S-MANP
) O
– O
use O
a O
high-power B-CONPRI
laser E-CONPRI
to O
fuse S-MANP
small O
particles S-CONPRI
( O
polyamide S-MATE
, O
steel S-MATE
, O
titanium S-MATE
, O
alloys S-MATE
, O
ceramic B-MATE
powders E-MATE
, O
etc O
) O
. O


As S-MATE
the O
SLM S-MANP
, O
the O
powder B-MACEQ
bed E-MACEQ
is O
lowered O
by O
one O
layer B-PARA
thickness E-PARA
, O
a O
new O
layer S-PARA
of O
powder S-MATE
is O
applied O
on O
top O
, O
and O
the O
process S-CONPRI
is O
repeated O
until O
the O
model S-CONPRI
is O
completed O
. O


But O
what O
sets O
sintering S-MANP
apart O
from O
melting S-MANP
is O
that O
the O
sintering S-MANP
processes S-CONPRI
do O
not O
fully O
melt S-CONPRI
the O
powder S-MATE
, O
but O
heat S-CONPRI
it O
to O
the O
point O
that O
the O
powder S-MATE
can O
fuse S-MANP
together O
on O
a O
molecular O
level O
. O


The O
latest O
SLS S-MANP
machines S-MACEQ
offer O
laser B-PARA
powers E-PARA
from O
30 O
W O
to O
200 O
W O
in O
a O
CO² O
chamber B-MACEQ
controlled E-MACEQ
( O
in O
range S-PARA
ProX O
and O
sPro O
) O
. O


The O
porosity S-PRO
of O
the O
material S-MATE
can O
be S-MATE
controlled O
. O


This O
porosity S-PRO
requests O
a O
post-treatment S-MANP
by O
infiltration S-CONPRI
to O
harden S-CONPRI
the O
final O
model S-CONPRI
like O
the O
bronze S-MATE
use O
to O
the O
steel S-MATE
. O


The O
SLS B-CONPRI
prototypes E-CONPRI
have O
a O
greater O
dimensional B-CHAR
accuracy E-CHAR
than O
the O
PolyJet S-CONPRI
and O
3DP S-MANP
models O
. O


Direct B-MANP
Metal I-MANP
Laser I-MANP
Sintering E-MANP
( O
DMLS S-MANP
) O
– O
is O
similar O
to O
SLS S-MANP
with O
some O
differences O
. O


The O
technology S-CONPRI
is O
a O
powder B-MANP
bed I-MANP
fusion I-MANP
process E-MANP
by O
melting S-MANP
the O
metal B-MATE
powder E-MATE
locally O
using O
the O
focused B-CONPRI
laser I-CONPRI
beam E-CONPRI
. O


A O
product O
is O
manufactured S-CONPRI
layer B-CONPRI
by I-CONPRI
layer E-CONPRI
along O
the O
Z O
axis O
and O
the O
powder S-MATE
is O
deposited O
via O
a O
scraper S-MACEQ
moving O
in O
the O
XY O
plane O
. O


The O
DMLS S-MANP
process O
from O
EOS© O
is O
well O
established O
for O
the O
net B-MANP
shape E-MANP
fabrication S-MANP
of O
prototype S-CONPRI
and O
short B-CONPRI
series I-CONPRI
tooling E-CONPRI
for O
plastic B-MANP
injection I-MANP
moulding E-MANP
. O


The O
first O
generation O
of O
EOS S-APPL
machine O
includes O
a O
200-W O
laser B-MACEQ
source E-MACEQ
when O
the O
second O
generation O
( O
EOSINT O
M280 O
) O
was O
launched O
with O
a O
400-W O
fibre B-CONPRI
laser E-CONPRI
. O


The O
trend S-CONPRI
shows O
an O
increase O
in O
laser B-PARA
power E-PARA
and O
also O
an O
increase O
in O
work O
chamber O
. O


DMLS S-MANP
often O
refers O
to O
the O
process S-CONPRI
that O
is O
applied O
to O
metal B-MATE
alloys E-MATE
for O
the O
manufacturing S-MANP
direct O
parts O
in O
the O
industry S-APPL
including O
aerospace S-APPL
, O
dental S-APPL
, O
medical S-APPL
and O
other O
industry S-APPL
that O
have O
small O
to O
medium O
size O
, O
highly O
complex O
parts O
and O
the O
tooling B-APPL
industry E-APPL
to O
make O
direct O
tooling B-MACEQ
inserts E-MACEQ
. O


Today O
, O
recent O
developments O
in O
the O
powders S-MATE
coupled O
with O
the O
durability S-PRO
of O
the O
materials S-CONPRI
are O
extending O
its O
reach O
to O
the O
direct B-CONPRI
manufacturing E-CONPRI
of O
functional B-CONPRI
prototypes E-CONPRI
for O
powder B-MANP
metallurgical E-MANP
and O
cast S-MANP
components O
. O


Support B-FEAT
structures E-FEAT
are O
required O
for O
most O
geometry S-CONPRI
because O
the O
powder S-MATE
alone O
is O
not O
sufficient O
to O
hold O
in O
place O
the O
liquid B-PRO
phase E-PRO
created O
when O
the O
laser S-ENAT
is O
scanning S-CONPRI
the O
powder S-MATE
. O


The O
rapid B-MANP
manufacturing E-MANP
of O
parts O
by O
the O
DMLS S-MANP
process O
requires O
the O
use O
of O
a O
powder S-MATE
, O
which O
is O
composed O
of O
two O
types O
of O
particles S-CONPRI
. O


One O
type O
has O
a O
low O
melting B-PRO
point E-PRO
, O
and O
the O
other O
a O
high O
melting B-PRO
point E-PRO
. O


The O
high-melting B-PRO
point E-PRO
particles O
generate O
a O
solid B-CONPRI
matrix E-CONPRI
, O
while O
the O
particles S-CONPRI
with O
the O
low O
melting B-PRO
point E-PRO
bind S-MANP
the O
matrix O
after O
being O
melted S-CONPRI
by O
the O
laser B-CONPRI
energy E-CONPRI
input O
. O


In O
order O
to O
reduce O
lead B-PARA
time E-PARA
and O
increase O
in O
build B-PARA
speed E-PARA
, O
a O
new O
technology S-CONPRI
has O
emerged O
derivative O
from O
SLA S-MACEQ
. O


On O
the O
same O
principle O
proposed O
by O
Pomerantz O
a O
photomask S-MATE
system O
( O
masking S-CONPRI
technology O
) O
to O
produce O
3D B-APPL
models E-APPL
, O
the O
DLP S-MANP
– O
Digital B-MANP
Light I-MANP
Processing E-MANP
, O
also O
known O
as S-MATE
FTI O
– O
Film B-MANP
Transfer I-MANP
Imaging E-MANP
, O
use O
the O
UV S-CONPRI
photopolymerised B-MATE
materials E-MATE
. O


A O
film O
is O
coated S-APPL
in O
resin S-MATE
which O
is O
then O
cured S-MANP
by O
a O
UV B-CONPRI
flash E-CONPRI
of O
light O
from O
a O
projector S-MACEQ
for O
each O
slice S-CONPRI
of O
product O
. O


Unlike O
the O
3D B-MACEQ
laser I-MACEQ
printer E-MACEQ
, O
the O
DLP S-MANP
projector O
projects O
the O
entire O
layer S-PARA
, O
and O
not O
only O
of O
lines O
or O
points O
. O


This O
method O
allows O
building O
much O
quicker O
than O
other O
methods O
of O
rapid B-ENAT
prototyping E-ENAT
by O
substituting O
scanning B-PARA
time E-PARA
of O
a O
laser S-ENAT
. O


With O
SLA S-MACEQ
, O
the O
part O
descends O
downward O
into O
the O
resin S-MATE
, O
whereas O
it O
is O
pulled O
upward O
out O
of O
the O
resin S-MATE
in O
a O
DLP B-MACEQ
printer E-MACEQ
. O


SLA S-MACEQ
process S-CONPRI
is O
gentler O
on O
the O
forming B-MACEQ
implant E-MACEQ
than O
the O
DLP S-MANP
process O
because O
, O
in O
DLP S-MANP
, O
the O
part O
must O
attach O
much O
more O
firmly O
to O
the O
build B-MACEQ
platform E-MACEQ
to O
prevent O
damage S-PRO
when O
newly O
formed O
layers O
are O
peeled O
from O
the O
basement B-MACEQ
plate E-MACEQ
after O
each O
exposure S-CONPRI
. O


The O
building B-MACEQ
platform E-MACEQ
can O
be S-MATE
angled O
upward O
and O
the O
light B-MACEQ
source E-MACEQ
down O
in O
some O
masking B-MACEQ
machines E-MACEQ
( O
e.g O
. O


Phidias O
technologies S-CONPRI
with O
Prodways O
3D B-MACEQ
printer E-MACEQ
) O
. O


The O
DLP S-MANP
technology O
is O
known O
for O
its O
high B-PARA
resolution E-PARA
, O
typically O
able O
to O
reach O
a O
layer B-PARA
thickness E-PARA
of O
down O
to O
30 O
μm O
. O


A O
new O
innovation O
in O
mask-image-projection S-CONPRI
based O
on O
the O
stereolithography S-MANP
process S-CONPRI
has O
been O
developed O
to O
produce O
objects O
with O
digital B-CONPRI
materials E-CONPRI
. O


The O
proposed O
approach O
is O
based O
on O
projecting O
mask B-CONPRI
images E-CONPRI
with O
a O
new O
two-channel S-CONPRI
system O
design S-FEAT
which O
reduces O
the O
separation B-CONPRI
force E-CONPRI
between O
a O
cured B-CONPRI
layer E-CONPRI
and O
the O
resin B-MACEQ
vat E-MACEQ
. O


The O
fabrication S-MANP
results O
demonstrate O
that O
the O
developed O
dual-material S-CONPRI
process O
can O
successfully O
produce O
3D B-APPL
objects E-APPL
with O
spatial B-CONPRI
control E-CONPRI
over O
placement O
of O
both O
material S-MATE
and O
structure S-CONPRI
. O


Close O
to O
DLP S-MANP
principle O
, O
the O
Continuous B-MANP
Liquid I-MANP
Interface I-MANP
Production E-MANP
( O
CLIP S-MANP
) O
production S-MANP
is O
a O
new O
type O
of O
AM S-MANP
that O
uses O
photopolymerisation S-CONPRI
working O
in O
continuous O
, O
thanks O
to O
a O
projector S-MACEQ
and O
the O
ability O
to O
control O
oxygen S-MATE
levels O
throughout O
an O
oxygen-permeable B-MATE
membrane E-MATE
. O


This O
latter O
process S-CONPRI
is O
30 O
times O
faster O
than O
the O
SLS S-MANP
or O
the O
MJM S-MANP
. O


Extrusion S-MANP
technologies- O
Fused B-MANP
Deposition I-MANP
Modeling E-MANP
( O
FDM S-MANP
) O
is O
a O
layer S-PARA
AM B-MANP
process E-MANP
that O
uses O
a O
thermoplastic B-MATE
filament E-MATE
by O
fused B-MANP
depositing E-MANP
. O


FDM S-MANP
is O
trademarked O
by O
Stratasys S-APPL
Inc O
in O
the O
late O
1980s O
and O
the O
equivalent O
term O
is O
Fused B-MANP
Filament I-MANP
Fabrication E-MANP
( O
FFF S-MANP
) O
. O


The O
filament S-MATE
is O
extruded S-MANP
through O
a O
nozzle S-MACEQ
to O
print S-MANP
one O
cross B-CONPRI
section E-CONPRI
of O
an O
object O
, O
then O
moving O
up O
vertically O
to O
repeat O
the O
process S-CONPRI
for O
a O
new O
layer S-PARA
. O


The O
most O
used O
materials S-CONPRI
in O
FDM S-MANP
are O
ABS S-MATE
, O
PLA S-MATE
and O
PC S-MATE
( O
Polycarbonate S-MATE
) O
but O
you O
can O
find O
out O
new O
blends S-MATE
containing O
wood S-MATE
and O
stone S-MATE
as S-MATE
well O
as S-MATE
filaments O
with O
rubbery B-CONPRI
characteristics E-CONPRI
. O


Compared O
to O
ABS S-MATE
, O
PLA S-MATE
responds O
differently O
to O
moisture O
, O
to O
ageing B-ENAT
UV E-ENAT
with O
a O
discoloration S-CONPRI
and O
to O
withdrawal O
of O
material S-MATE
. O


To O
predict O
the O
mechanical B-CONPRI
behaviour E-CONPRI
of O
FDM S-MANP
parts O
, O
it O
is O
critical O
to O
understand O
the O
material B-CONPRI
properties E-CONPRI
of O
the O
raw O
FDM S-MANP
process O
material S-MATE
, O
and O
the O
effect O
that O
FDM S-MANP
build B-PARA
parameters E-PARA
have O
on O
anisotropic B-PRO
material I-PRO
properties E-PRO
. O


The O
support B-MATE
material E-MATE
is O
often O
made O
of O
another O
material S-MATE
and O
is O
detachable S-CONPRI
or O
soluble S-CONPRI
from O
the O
actual O
part O
at O
the O
end O
of O
the O
manufacturing B-MANP
process E-MANP
( O
except O
for O
the O
low-cost O
solutions O
, O
which O
use O
the O
same O
raw B-MATE
material E-MATE
) O
. O


The O
disadvantages O
are O
that O
the O
resolution S-PARA
on O
the O
z O
axis O
is O
low O
compared O
to O
other O
AM B-MANP
process E-MANP
( O
0.25 O
mm S-MANP
) O
, O
so O
if O
a O
smooth B-CONPRI
surface E-CONPRI
is O
needed O
a O
finishing B-MANP
process E-MANP
is O
required O
and O
it O
is O
a O
slow O
process S-CONPRI
sometimes O
taking O
days O
to O
build S-PARA
large O
complex O
parts O
. O


FDM S-MANP
technology O
is O
the O
most O
popular O
of O
desktop B-MACEQ
3D I-MACEQ
printers E-MACEQ
and O
the O
less O
expensive O
professional O
printers S-MACEQ
. O


Directed B-MANP
Energy I-MANP
Deposition E-MANP
( O
DED S-MANP
) O
– O
covers O
a O
range S-PARA
of O
terminology O
: O
Laser B-MANP
Engineered I-MANP
Net I-MANP
Shaping E-MANP
( O
LENS S-MANP
) O
, O
directed B-MANP
light I-MANP
fabrication E-MANP
( O
IFF S-MANP
– O
Ion B-MANP
Fusion I-MANP
Formation E-MANP
) O
, O
Direct B-MANP
Metal I-MANP
Deposition E-MANP
( O
DMD S-MANP
) O
, O
3D B-MANP
laser I-MANP
cladding E-MANP
. O


It O
is O
a O
more O
complex O
printing B-MANP
process E-MANP
commonly O
used O
to O
repair O
or O
add O
additional O
material S-MATE
to O
existing O
components S-MACEQ
. O


LENS S-MANP
is O
used O
to O
melt S-CONPRI
the O
surface S-CONPRI
of O
the O
target O
point O
while O
a O
stream O
of O
powdered B-MATE
metal E-MATE
is O
delivered O
onto O
the O
small O
targeted O
point O
. O


IFF S-MANP
melts O
a O
metal B-MATE
wire E-MATE
or O
powder S-MATE
with O
a O
plasma B-MACEQ
welding I-MACEQ
torch E-MACEQ
to O
form O
an O
object O
. O


This O
is O
a O
near-net-shape B-MANP
manufacturing E-MANP
process O
that O
uses O
a O
very O
hot O
ionised B-CONPRI
gas E-CONPRI
to O
deposit O
a O
metal S-MATE
in O
small O
amounts O
. O


DMD S-MANP
melts O
metal B-MATE
wire E-MATE
by O
electron B-CONPRI
beam E-CONPRI
as S-MATE
feedstock O
used O
to O
form O
an O
object O
within O
a O
vacuum B-MACEQ
chamber E-MACEQ
. O


The O
objects O
created O
in O
DED S-MANP
can O
be S-MATE
larger O
, O
even O
up O
to O
several O
feet O
long O
. O


Dough B-CONPRI
Deposition I-CONPRI
Modeling E-CONPRI
( O
DDM S-CONPRI
) O
– O
groups O
the O
marginal O
processes S-CONPRI
which O
file S-MANS
different O
doughs S-MATE
( O
Figure O
6 O
) O
. O


Some O
technologies S-CONPRI
based O
on O
FDM B-MACEQ
printers E-MACEQ
use O
a O
syringe S-MACEQ
to O
deposit O
a O
dough B-MATE
material E-MATE
like O
silicone S-MATE
, O
food B-MATE
dough E-MATE
, O
chocolate S-MATE
, O
etc O
. O


A O
syringe-based B-MACEQ
extrusion I-MACEQ
tool E-MACEQ
which O
uses O
a O
linear B-MACEQ
stepper I-MACEQ
motor E-MACEQ
to O
control O
the O
syringe B-PARA
plunger I-PARA
position E-PARA
. O


The O
medical S-APPL
research O
uses O
the O
deposition S-CONPRI
of O
biomaterial S-MATE
and O
cells S-APPL
to O
realise O
a O
tissue B-CONPRI
structure E-CONPRI
. O


It O
presents O
a O
novel O
method O
for O
the O
deposition S-CONPRI
of O
biopolymers S-MATE
in O
high-resolution S-PARA
structures O
, O
using O
a O
pressure-activated B-MACEQ
microsyringe E-MACEQ
. O


Other O
works O
show O
applications O
to O
extrude S-MANP
a O
bio-based B-MATE
material E-MATE
to O
reconstitute O
a O
model S-CONPRI
and O
preserve O
the O
ecological B-CONPRI
environment E-CONPRI
. O


Experimentation O
uses O
a O
piston S-APPL
and O
3D B-MACEQ
printer I-MACEQ
head E-MACEQ
adapted O
on O
a O
CNC B-MACEQ
machine E-MACEQ
to O
deposit O
a O
pulpwood S-MATE
based O
on O
wood B-MATE
flour E-MATE
to O
create O
a O
reconstituted B-CONPRI
wood I-CONPRI
product E-CONPRI
. O


Jet B-MANP
technologies E-MANP
- O
MJM S-MANP
– O
Multi B-MANP
Jet I-MANP
Modeling E-MANP
– O
deposits O
droplets S-CONPRI
of O
photopolymer B-MATE
materials E-MATE
with O
multi B-MACEQ
jets E-MACEQ
on O
a O
building B-MACEQ
platform E-MACEQ
in O
ultra-thin B-CONPRI
layers E-CONPRI
until O
the O
part O
is O
completed O
. O


Two O
different O
photopolymer B-MATE
materials E-MATE
are O
used O
for O
building O
, O
one O
for O
the O
actual O
model S-CONPRI
and O
another O
gel S-MATE
like O
material S-MATE
for O
supporting O
. O


The O
photopolymer B-MATE
layers E-MATE
are O
cured S-MANP
by O
UV B-MACEQ
lamps E-MACEQ
and O
a O
gel-like B-MATE
polymer E-MATE
supports O
the O
complexity S-CONPRI
of O
geometry S-CONPRI
in O
wrapping S-CONPRI
it O
. O


The O
soluble S-CONPRI
gel-like S-MATE
( O
support B-MATE
material E-MATE
) O
is O
then O
removed O
by O
a O
water B-MANP
jet E-MANP
. O


The O
PolyJet B-MANP
technique E-MANP
reproduced O
details O
more O
accurately S-CHAR
with O
a O
very O
good O
surface B-FEAT
finish E-FEAT
and O
smoothness S-CONPRI
. O


The O
accuracy S-CHAR
of O
a O
PolyJet B-MACEQ
machine E-MACEQ
can O
reach O
thickness O
from O
50 O
to O
25 O
μm O
, O
besides O
the O
parts O
have O
a O
higher B-PARA
resolution E-PARA
. O


Also O
known O
as S-MATE
Thermojet O
, O
some O
systems O
can O
produce O
wax S-MATE
models O
in O
jetting S-MANP
tiny O
droplets S-CONPRI
of O
melted B-MATE
liquid I-MATE
material E-MATE
which O
cool O
and O
harden S-CONPRI
on O
impact S-CONPRI
to O
form O
the O
solid O
object O
. O


3DP S-MANP
– O
three-dimensional B-MANP
printing E-MANP
, O
also O
known O
as S-MATE
CJP O
– O
Colour B-MANP
Jet I-MANP
Printing E-MANP
, O
combines O
powders S-MATE
and O
binders S-MATE
. O


3DP S-MANP
has O
been O
developed O
by O
the O
MIT O
. O


Each O
layer S-PARA
is O
created O
by O
spreading O
a O
thin O
powder S-MATE
layer S-PARA
with O
a O
roller S-MACEQ
and O
the O
powder S-MATE
is O
selectively O
linked O
by O
inkjet B-MANP
printing E-MANP
of O
a O
binder S-MATE
. O


The O
build B-MACEQ
tray E-MACEQ
goes O
down O
to O
create O
the O
next O
layer S-PARA
. O


This O
process S-CONPRI
has O
been O
used O
to O
fabricate S-MANP
numerous O
metal S-MATE
, O
ceramic S-MATE
, O
silica S-MATE
and O
polymeric B-MATE
components E-MATE
of O
any O
geometry S-CONPRI
for O
a O
wide O
array O
of O
applications O
. O


Other O
powders S-MATE
have O
been O
tested O
to O
realise O
green B-PRO
products E-PRO
in O
wood S-MATE
. O


3DP S-MANP
can O
print S-MANP
in O
multicolour O
directly O
into O
the O
part O
during O
the O
build S-PARA
process O
from O
a O
colour O
cartridge S-MACEQ
. O


The O
final O
model S-CONPRI
is O
extracted S-CONPRI
from O
the O
powder B-MACEQ
bed E-MACEQ
to O
realise O
infiltration S-CONPRI
with O
liquid B-MATE
glue E-MATE
. O


The O
infiltrate O
improves O
the O
colour O
definition O
and O
the O
mechanical B-CONPRI
behaviours E-CONPRI
. O


3DP S-MANP
can O
provide O
architects O
a O
useful O
tool S-MACEQ
to O
quickly O
create O
a O
realistic O
model S-CONPRI
. O


Prometal S-MANP
is O
a O
3D B-MANP
printing E-MANP
process O
to O
build S-PARA
rapid O
tools S-MACEQ
and O
dies S-MACEQ
. O


This O
is O
a O
powder-based O
process S-CONPRI
in O
which O
stainless B-MATE
steel E-MATE
is O
used O
. O


The O
printing B-MANP
process E-MANP
occurs O
when O
a O
liquid B-MATE
binder E-MATE
is O
spurt O
out O
in O
jets O
to O
steel B-MATE
powder E-MATE
. O


A O
final O
treatment O
is O
required O
to O
solidify S-CONPRI
the O
part O
like O
sintering S-MANP
, O
infiltration S-CONPRI
and O
finishing B-MANP
processes E-MANP
. O


Liquid B-MANP
Metal I-MANP
Jetting E-MANP
( O
LMJ S-MANP
) O
involves O
the O
jetting S-MANP
of O
molten B-MATE
metal E-MATE
in O
a O
process S-CONPRI
similar O
to O
inkjet B-MANP
printing E-MANP
, O
whereby O
individual O
molten O
droplets S-CONPRI
are O
ejected O
and O
connected O
to O
each O
other O
. O


This O
process S-CONPRI
is O
not O
commercially O
available O
yet O
. O


LOM S-MANP
– O
Laminated O
Objet O
Manufacturing S-MANP
– O
is O
a O
rapid B-ENAT
prototyping E-ENAT
process S-CONPRI
where O
a O
part O
is O
sequentially O
built O
from O
layers O
of O
paper O
. O


The O
process S-CONPRI
consists O
of O
the O
thermal O
adhesive B-CONPRI
bonding E-CONPRI
and O
laser B-CONPRI
patterning E-CONPRI
of O
uniformly-thick O
paper O
layers O
. O


The O
system O
includes O
an O
x-y O
plotter B-MACEQ
device E-MACEQ
positioned O
above O
a O
work B-MACEQ
table E-MACEQ
vertically O
movable O
. O


The O
x-y O
plotter B-MACEQ
device E-MACEQ
includes O
a O
forming S-MANP
tool O
to O
create O
a O
layer S-PARA
from O
a O
sheet S-MATE
of O
material S-MATE
positioned O
on O
the O
work B-MACEQ
table E-MACEQ
. O


The O
layers O
are O
bonded O
to O
each O
other O
with O
heat-sensitive B-MATE
adhesives E-MATE
provided O
on O
one O
side O
thereof O
. O


A O
bonding S-CONPRI
tool O
or O
fuser S-MACEQ
is O
mounted O
to O
translate O
across O
the O
work B-MACEQ
table E-MACEQ
and O
apply O
a O
lamination B-PARA
force E-PARA
and O
heat S-CONPRI
to O
each O
of O
the O
layers O
. O


The O
layers O
are O
superimposed O
to O
give O
the O
final O
object O
and O
the O
layer B-PARA
resolution E-PARA
is O
defined O
by O
the O
thickness O
of O
the O
paper B-MATE
sheet E-MATE
. O


3D B-MACEQ
printers E-MACEQ
can O
print S-MANP
in O
full O
colours O
( O
Mcor O
Technologies S-CONPRI
) O
. O


Stratoconception S-CONPRI
is O
a O
rapid B-ENAT
prototyping E-ENAT
process S-CONPRI
with O
layers O
of O
sheets S-MATE
. O


It O
consists O
in O
the O
decomposition S-PRO
of O
a O
model S-CONPRI
by O
calculating O
a O
set S-APPL
of O
elementary O
layers O
called O
‘ O
strata S-CONPRI
’ O
and O
by O
placing O
reinforcing B-MACEQ
pieces E-MACEQ
and O
inserts S-MACEQ
in O
strata S-CONPRI
. O


The O
elementary O
layer S-PARA
are O
displayed O
and O
manufactured S-CONPRI
by O
rapid O
milling S-MANP
or O
laser-cutting S-MANP
. O


The O
strata S-CONPRI
are O
assembled O
with O
inserts S-MACEQ
to O
rebuild O
the O
final O
object O
. O


This O
process S-CONPRI
is O
useful O
thanks O
to O
milling S-MANP
of O
a O
low-cost O
sheet S-MATE
in O
raw B-MATE
material E-MATE
( O
wood S-MATE
, O
MDF S-MATE
, O
PVC S-MATE
, O
aluminium S-MATE
, O
etc O
) O
. O


When O
you O
find O
out O
the O
AM B-MANP
technologies E-MANP
and O
you O
can O
use O
some O
of O
them O
, O
experts O
know O
that O
several O
manufacturing B-CONPRI
constraints E-CONPRI
and O
mechanical B-CONPRI
behaviours E-CONPRI
bring O
complications O
. O


For O
example O
, O
the O
powder B-ENAT
technology E-ENAT
leads O
to O
extract O
the O
final O
product O
outside O
of O
a O
power S-PARA
bed S-MACEQ
before O
cleaning S-MANP
it O
and O
often O
to O
applying O
a O
post-treatment S-MANP
. O


Moreover O
, O
the O
manufacturing S-MANP
orientation O
of O
the O
model S-CONPRI
influences O
the O
quality S-CONPRI
of O
geometry S-CONPRI
because O
of O
material B-CONPRI
gradient E-CONPRI
and O
the O
manufacturing S-MANP
direction O
. O


The O
part O
orientation S-CONPRI
can O
deeply O
modify O
the O
planarity S-CONPRI
, O
the O
circularity S-CONPRI
and O
the O
surface B-CHAR
accuracy E-CHAR
. O


You O
have O
the O
same O
constraints O
with O
other O
technologies S-CONPRI
as S-MATE
the O
3DP S-MANP
or O
DED S-MANP
. O


The O
internal B-PRO
structure E-PRO
of O
product O
due O
to O
the O
material B-CONPRI
orientation E-CONPRI
, O
the O
manufacturing B-MANP
technology E-MANP
and O
its O
manufacturing S-MANP
by O
layers O
generates O
use O
constraints O
which O
need O
to O
be S-MATE
integrated O
. O


We O
can O
quote O
in O
a O
non-exhaustive O
list O
the O
anisotropy S-PRO
for O
the O
part O
made O
by O
FDM S-MANP
, O
the O
crack B-CONPRI
propagation E-CONPRI
for O
powdered O
parts O
and O
the O
ageing B-ENAT
UV E-ENAT
for O
the O
models O
in O
photopolymers S-MATE
. O


You O
can O
find O
out O
the O
accuracy S-CHAR
of O
some O
AM B-MACEQ
machines E-MACEQ
from O
manufacturer S-CONPRI
sources O
on O
the O
Table O
1 O
. O


From O
a O
3D B-MACEQ
printer E-MACEQ
to O
another O
, O
designer O
does O
not O
answer O
to O
the O
same O
need O
and O
accuracy S-CHAR
is O
often O
decisive O
to O
get O
a O
reliable O
product O
or O
a O
functional B-CONPRI
mechanism E-CONPRI
. O


Furthermore O
, O
the O
post-treatment S-MANP
, O
post-machining S-MANP
or O
post-finishing S-MANP
are O
often O
required O
to O
get O
a O
finished O
product O
. O


The O
recycling S-CONPRI
and O
the O
raw B-MATE
material E-MATE
cost O
have O
to O
be S-MATE
taken O
into O
account O
too O
. O


To O
sum O
up O
, O
a O
set S-APPL
of O
stages O
are O
to O
define O
in O
upstream O
to O
assess O
the O
AM B-MANP
technology E-MANP
implications O
. O


The O
incrementation O
of O
experience O
greatly O
improves O
the O
engineering S-APPL
and O
manufacturing B-MANP
process E-MANP
. O


The O
expiring O
patents S-CONPRI
open O
the O
market O
for O
others O
manufacturers O
proposing O
of O
new O
machines S-MACEQ
. O


Since O
February O
2014 O
, O
a O
major O
patent S-CONPRI
related O
to O
SLS S-MANP
expired O
( O
Apparatus O
for O
producing O
parts O
by O
selective B-MANP
sintering E-MANP
n.d. O
) O
. O


New O
technologies S-CONPRI
resulting O
from O
expiring O
patents S-CONPRI
appear O
with O
the O
solutions O
proposed O
by O
the O
companies S-APPL
DWS O
Systems O
( O
Italy O
) O
or O
Formlabs O
( O
USA O
) O
. O


3D B-MANP
printing E-MANP
applied O
to O
medical S-APPL
has O
appeared O
for O
some O
years O
through O
different O
applications O
. O


The O
organ B-CONPRI
transplantation E-CONPRI
sector O
has O
difficulties O
and O
the O
organ B-MANP
printing E-MANP
by O
jet O
based O
on O
3d B-APPL
tissue I-APPL
engineering E-APPL
offers O
a O
possible O
solution S-CONPRI
. O


Some O
research S-CONPRI
define O
organ B-MANP
printing E-MANP
as S-MATE
a O
rapid B-ENAT
prototyping E-ENAT
computer-aided O
3D B-ENAT
printing I-ENAT
technology E-ENAT
based O
on O
using O
layer-by-layer B-CONPRI
deposition E-CONPRI
of O
cell S-APPL
and/or O
cell S-APPL
aggregates S-MATE
into O
a O
3D B-MATE
gel E-MATE
with O
sequential O
maturation O
of O
the O
printed B-CONPRI
construct E-CONPRI
into O
perfused O
and O
vascularised O
living O
tissue O
or O
organ O
. O


The O
success O
of O
an O
implantation S-MANP
depends O
on O
compatible O
materials S-CONPRI
. O


We O
can O
find O
a O
variety O
of O
biomaterials S-MATE
such O
as S-MATE
curable O
synthetic O
polymers S-MATE
, O
synthetic B-MATE
gels E-MATE
and O
naturally B-MATE
derived I-MATE
hydrogels E-MATE
. O


Prosthetic S-APPL
is O
the O
first O
biomedical S-APPL
area S-PARA
which O
has O
used O
the O
3D B-MANP
printing E-MANP
and O
it O
presents O
several O
successes O
. O


We O
can O
quote O
a O
patient O
’ O
s S-MATE
skull O
anatomy O
reproduced O
via O
3D B-MANP
printing E-MANP
for O
pre-surgical O
use O
in O
manual O
implant S-APPL
design S-FEAT
and O
production S-MANP
and O
the O
enhancement O
of O
the O
fixation O
stability S-PRO
of O
the O
custom O
made O
total O
hip B-MACEQ
prostheses E-MACEQ
and O
restore O
the O
original O
biomechanical S-APPL
characteristics O
of O
the O
joint S-CONPRI
. O


Several O
applications O
combine O
some O
degradable O
or O
allogeneic B-BIOP
scaffolding E-BIOP
with O
cellular B-APPL
bioprinting E-APPL
to O
create O
customised O
biologic O
prosthetics S-APPL
that O
have O
the O
great O
potential O
to O
serve O
as S-MATE
transplantable O
replacement O
tissue O
. O


New O
articles O
showed O
that O
the O
medical S-APPL
3D B-MANP
Printing E-MANP
market O
might O
reach O
983.2 O
million O
$ O
by O
the O
year O
2020 O
. O


Projects O
for O
home O
construction S-APPL
through O
3D B-MANP
printing E-MANP
are O
emerging O
such O
as S-MATE
the O
Shanghai O
WinSun O
Decoration O
Engineering S-APPL
Company S-APPL
. O


This O
company S-APPL
can O
print S-MANP
the O
basic O
components S-MACEQ
separately O
before O
assembling O
them O
on O
site O
. O


These O
concrete S-MATE
houses O
are O
built O
in O
one O
day O
by O
3D B-MANP
printing E-MANP
and O
their O
construction S-APPL
costs O
about O
3800 O
$ O
. O


The O
3D B-MACEQ
printer E-MACEQ
developed O
by O
the O
Chinese O
group O
is O
much O
larger O
than O
a O
conventional B-CONPRI
system E-CONPRI
and O
uses O
the O
same O
DDM B-ENAT
technology E-ENAT
. O


The O
building B-APPL
industry E-APPL
introduced O
a O
vocabulary O
such O
as S-MATE
rapid O
construction S-APPL
or O
rapid O
building O
. O


The O
use O
of O
the O
STL B-MANS
format E-MANS
limits S-CONPRI
the O
exchange O
of O
trades O
data S-CONPRI
. O


If O
the O
STL B-MANS
format E-MANS
allows O
exporting O
from O
a O
surfacing O
model S-CONPRI
towards O
the O
specific O
software S-CONPRI
, O
the O
designer O
needs O
to O
insert S-MACEQ
rules O
in O
upstream O
work O
in O
CAD S-ENAT
. O


The O
emergence O
of O
more O
enriched O
new O
exchange B-CONPRI
format E-CONPRI
appears O
such O
as S-MATE
the O
Additive B-MANS
Manufacturing I-MANS
file I-MANS
Format E-MANS
( O
AMF S-CONPRI
) O
with O
important O
parameters S-CONPRI
( O
< O
material S-MATE
> O
, O
< O
composite S-MATE
> O
, O
< O
metadata S-ENAT
> O
, O
etc O
. O


) O
or O
the O
STL S-MANS
2.0 O
. O


Alternative O
file S-MANS
format O
exports O
are O
also O
required O
to O
support S-APPL
depiction O
of O
complex O
organic O
geometry S-CONPRI
, O
whilst O
allowing O
multiple-material S-CONPRI
and O
mono/multicolour S-CONPRI
capabilities O
; O
the O
development O
of O
STL S-MANS
2.0 O
or O
Additive B-MANS
Manufacturing I-MANS
file I-MANS
Format E-MANS
( O
AMF S-CONPRI
) O
is O
promising O
, O
particularly O
for O
the O
composition S-CONPRI
of O
complex B-CONPRI
geometries E-CONPRI
and O
multiple-material S-CONPRI
. O


The O
article O
shows O
that O
we O
need O
to O
transfer O
more O
trades O
data S-CONPRI
to O
the O
additive B-MACEQ
manufacturing I-MACEQ
machine E-MACEQ
through O
an O
enriched O
exchange B-CONPRI
format E-CONPRI
. O


The O
standard S-CONPRI
ISO/ASTM S-MANS
52915:2013 O
Standard S-CONPRI
specification S-PARA
for O
additive B-MANS
manufacturing I-MANS
file I-MANS
format E-MANS
( O
AMF S-CONPRI
) O
Version O
1.15 O
describes O
a O
framework S-CONPRI
for O
an O
interchange O
format O
to O
address O
the O
current O
and O
future O
needs O
of O
additive B-MANP
manufacturing E-MANP
technology O
. O


The O
manufacturing S-MANP
units O
and O
the O
small O
size O
of O
AM B-MACEQ
build I-MACEQ
tray E-MACEQ
complicate O
the O
production B-MANP
line E-MANP
. O


Industrials O
seek O
to O
reduce O
the O
lead B-PARA
time E-PARA
and O
increase O
in O
build B-PARA
speed E-PARA
but O
a O
lot O
of O
additive B-MANP
manufacturing E-MANP
technologies O
are O
not O
adapted O
. O


The O
interoperability S-CONPRI
is O
little O
studied O
by O
3D B-MACEQ
printer E-MACEQ
manufacturers O
. O


Reflecting O
the O
strategy O
of O
some O
companies S-APPL
like O
ExOne O
or O
Voxeljet O
, O
the O
professional O
3D B-MACEQ
printers E-MACEQ
can O
be S-MATE
combined O
to O
the O
production B-MANP
line E-MANP
and O
offer O
the O
largest O
printers S-MACEQ
on O
the O
world O
market O
for O
3D B-MANP
printing E-MANP
of O
sand S-MATE
and O
metal B-MATE
materials E-MATE
. O


Announced O
as S-MATE
a O
new O
industrial B-CONPRI
revolution E-CONPRI
, O
the O
additive B-MANP
manufacturing E-MANP
technologies O
will O
make O
the O
difference O
when O
it O
will O
be S-MATE
interoperable O
with O
the O
set S-APPL
of O
manufacturing B-MANP
process E-MANP
. O


Development O
orientations S-CONPRI
show O
that O
the O
new O
3D B-MACEQ
printers E-MACEQ
will O
be S-MATE
more O
integrated O
inside O
the O
production B-MANP
line E-MANP
with O
the O
automation S-CONPRI
and O
the O
connectivity O
with O
the O
digital B-ENAT
chain E-ENAT
. O


A O
recent O
example O
is O
the O
emergence O
of O
hybrid B-ENAT
system E-ENAT
combining O
the O
3D B-MANP
printing E-MANP
by O
laser B-MANP
deposition I-MANP
of I-MANP
metals E-MANP
( O
DMD S-MANP
) O
and O
the O
CNC B-MANP
machining E-MANP
through O
the O
LASERTEC O
AdditiveManufacturing6 O
solution S-CONPRI
proposed O
by O
DMG O
MORI© O
which O
accelerates O
the O
realisation O
of O
the O
finished O
product O
. O


In O
order O
to O
reduce O
the O
time O
and O
cost O
of O
moulds B-MANP
fabrication E-MANP
, O
additive B-MANP
manufacturing E-MANP
is O
used O
to O
develop O
and O
manufacture S-CONPRI
systems O
of O
rapid B-MANP
tooling E-MANP
. O


Powder-based B-MANP
sintering E-MANP
processes O
are O
now O
able O
to O
produce O
metal S-MATE
moulds O
that O
can O
withstand O
a O
few O
thousand O
cycles O
of O
injection B-MANP
moulding E-MANP
. O


AM B-MANP
technologies E-MANP
propose O
to O
manufacture S-CONPRI
of O
sand B-MACEQ
moulds E-MACEQ
for O
the O
casting S-MANP
. O


A O
method O
to O
produce O
a O
lost B-MACEQ
mould E-MACEQ
for O
casting S-MANP
is O
used O
with O
the O
thermojet B-ENAT
technology E-ENAT
by O
wax S-MATE
. O


We O
saw S-MANP
that O
some O
powder B-ENAT
technologies E-ENAT
could O
realise O
sand B-MACEQ
moulds E-MACEQ
for O
casting S-MANP
( O
Voxeljet O
, O
ExOne O
) O
. O


Other O
approaches O
ally O
the O
additive B-MANP
manufacturing E-MANP
technology O
and O
the O
topological B-FEAT
optimisation E-FEAT
to O
realise O
a O
rapid B-MANP
tooling E-MANP
and O
to O
use O
less O
material S-MATE
while O
keeping O
its O
properties S-CONPRI
. O


The O
layers B-MANP
manufacturing E-MANP
is O
able O
to O
improve O
a O
product O
or O
a O
tooling S-CONPRI
by O
inserting O
new O
methods O
as S-MATE
cooling O
channels O
or O
sensors S-MACEQ
. O


For O
example O
, O
an O
injection B-MACEQ
mould E-MACEQ
manufactured O
by O
a O
Stratoconception S-CONPRI
and O
after O
assembly S-MANP
of O
strata S-CONPRI
, O
cooling B-MACEQ
channels E-MACEQ
are O
provided O
in O
the O
various O
inter-stratum O
planes O
for O
allowing O
a O
fluid S-MATE
to O
pass O
through O
the O
part O
. O


You O
must O
perceive O
that O
this O
type O
of O
method O
can O
improve O
the O
behaviour O
of O
a O
moulded S-MACEQ
part O
by O
adjusting O
the O
location O
of O
the O
cooling B-MACEQ
channels E-MACEQ
to O
a O
specific O
geometry S-CONPRI
. O


Another O
challenge O
is O
to O
reduce O
weight S-PARA
and O
decrease O
the O
material S-MATE
used O
while O
keeping O
the O
product O
functions O
( O
mechanical S-APPL
, O
use… O
) O
. O


Moreover O
, O
the O
main O
and O
support B-MATE
material E-MATE
can O
be S-MATE
expensive O
in O
the O
AM B-MANP
technology E-MANP
. O


Topology B-FEAT
optimisation E-FEAT
is O
a O
mathematical S-CONPRI
approach O
that O
optimises O
material S-MATE
layout S-CONPRI
within O
a O
given O
design B-CONPRI
space E-CONPRI
, O
for O
a O
given O
set S-APPL
of O
loads O
and O
boundary B-CONPRI
conditions E-CONPRI
so O
that O
the O
resulting O
layout S-CONPRI
meets O
a O
prescribed O
set S-APPL
of O
performance S-CONPRI
targets O
. O


Using O
topology B-FEAT
optimization E-FEAT
, O
engineers O
can O
find O
the O
best O
concept B-CONPRI
design E-CONPRI
that O
meets O
the O
design S-FEAT
requirements O
. O


Any O
complex B-CONPRI
geometry E-CONPRI
is O
feasible O
in O
additive B-MANP
manufacturing E-MANP
, O
the O
topological B-FEAT
optimisation E-FEAT
implementation O
of O
a O
model S-CONPRI
leads O
to O
a O
new O
internal B-PRO
structure E-PRO
while O
maintaining O
conditions O
( O
mechanical S-APPL
, O
design S-FEAT
shape O
, O
functions O
, O
etc O
) O
. O


Topologically S-CONPRI
, O
optimised O
parts O
have O
been O
created O
with O
internal B-FEAT
geometry E-FEAT
, O
using O
a O
narrow-waited O
structure S-CONPRI
that O
avoids O
the O
need O
for O
building O
supports S-APPL
. O


Additive B-MANP
manufacturing E-MANP
technology O
standards S-CONPRI
are O
intended O
to O
endorse O
the O
knowledge O
of O
the O
industry S-APPL
, O
help O
stimulate O
research S-CONPRI
and O
encourage O
the O
implementation O
of O
technology S-CONPRI
. O


The O
standards S-CONPRI
define O
terminology O
, O
measure O
the O
performance S-CONPRI
of O
different O
production S-MANP
processes S-CONPRI
, O
ensure O
the O
quality S-CONPRI
of O
the O
end O
products O
, O
and O
specify O
procedures O
for O
the O
calibration S-CONPRI
of O
additive B-MACEQ
manufacturing I-MACEQ
machines E-MACEQ
. O


Several O
major O
standards S-CONPRI
were O
created O
very O
recently O
by O
the O
International B-MANS
Organisation I-MANS
for I-MANS
Standardisation E-MANS
( O
ISO S-MANS
) O
; O
we O
can O
mention O
the O
main O
ones O
: O
ISO B-MANS
17296-2:2015 E-MANS
: O
Overview O
of O
process S-CONPRI
categories O
and O
feedstock S-MATE
. O


It O
describes O
the O
process S-CONPRI
fundamentals O
of O
AM S-MANP
with O
the O
existing O
processes S-CONPRI
and O
the O
different O
types O
of O
materials S-CONPRI
used O
. O


ISO B-MANS
17296-3:2014 E-MANS
: O
Main O
characteristics O
and O
corresponding O
test O
methods O
: O
It O
covers O
the O
principal O
requirements O
applied O
to O
testing S-CHAR
with O
the O
main O
quality S-CONPRI
characteristics O
of O
parts O
, O
the O
appropriate O
test O
procedures O
, O
and O
the O
recommendations O
. O


ISO/ASTM S-MANS
DIS O
2019 O
: O
Standard S-CONPRI
Practice O
– O
Guide O
for O
Design S-FEAT
for O
AM S-MANP
: O
It O
is O
being O
developed O
since O
2015 O
and O
will O
bring O
together O
good O
practices O
in O
design S-FEAT
for O
getting O
a O
reliable O
product O
. O


You O
can O
also O
find O
other O
standards S-CONPRI
specifying O
the O
terminology O
in O
AM S-MANP
or O
the O
requirements O
for O
purchased O
AM B-MACEQ
parts E-MACEQ
. O


In O
recent O
decades O
additive B-MANP
manufacturing E-MANP
has O
evolved O
from O
a O
prototyping S-CONPRI
to O
a O
production S-MANP
technology O
. O


It O
is O
used O
to O
produce O
end-use-parts O
for O
medical S-APPL
, O
aerospace S-APPL
, O
automotive S-APPL
and O
other O
industrial S-APPL
applications O
from O
small O
series O
up O
to O
100,000 O
of O
commercially O
successful O
products O
. O


Metal B-MANP
additive I-MANP
manufacturing E-MANP
processes O
are O
relatively O
slow O
, O
require O
complex O
preparation O
and O
post-processing B-MANP
treatment E-MANP
while O
using O
expensive O
machinery O
, O
resulting O
in O
high O
production B-CONPRI
costs E-CONPRI
per O
product O
. O


Design B-FEAT
for I-FEAT
Additive I-FEAT
Manufacturing E-FEAT
aims O
at O
optimizing O
the O
product B-FEAT
design E-FEAT
to O
deal O
with O
the O
complexity S-CONPRI
of O
the O
production S-MANP
processes S-CONPRI
, O
while O
also O
defining O
decisive O
benefits O
of O
the O
AM S-MANP
based O
product O
in O
the O
usage O
stages O
of O
its O
life B-CONPRI
cycle E-CONPRI
. O


Recent O
investigations O
have O
shown O
that O
the O
lack O
of O
knowledge O
on O
DfAM O
tools S-MACEQ
and O
techniques O
are O
seen O
as S-MATE
one O
of O
the O
barriers O
for O
the O
further O
implementation O
of O
AM S-MANP
. O


This O
paper O
presents O
a O
framework S-CONPRI
for O
DfAM O
methods O
and O
tools S-MACEQ
, O
subdivided O
into O
three O
distinct O
stages O
of O
product B-CONPRI
development E-CONPRI
: O
AM B-MANP
process E-MANP
selection O
, O
product O
redesign O
for O
functionality O
enhancement O
, O
and O
product B-CONPRI
optimization E-CONPRI
for O
the O
AM B-MANP
process E-MANP
chosen O
. O


It O
will O
illustrate O
the O
applicability O
of O
the O
design S-FEAT
framework O
using O
examples O
from O
both O
research S-CONPRI
and O
industry S-APPL
. O


Additive B-MANP
manufacturing E-MANP
was O
first O
developed O
in O
the O
late O
1980 O
with O
increasing O
quality S-CONPRI
and O
market O
penetration S-CONPRI
ever O
since O
. O


Starting O
as S-MATE
prototyping O
technology S-CONPRI
it O
has O
developed O
into O
a O
technology S-CONPRI
that O
allows O
for O
mass B-CONPRI
production E-CONPRI
of O
end O
use O
parts O
. O


In O
2018 O
BMW O
has O
reported O
on O
3D B-MANP
printing E-MANP
of O
its O
one O
millionth O
component S-MACEQ
in O
series O
production S-MANP
. O


Major O
AM S-MANP
markets O
that O
include O
aerospace S-APPL
, O
automotive S-APPL
, O
consumer B-APPL
products E-APPL
, O
medical S-APPL
, O
and O
general O
industries S-APPL
report O
simular O
success O
stories O
. O


According O
to O
a O
study O
by O
Deloitte B-ENAT
AM E-ENAT
is O
implemented O
within O
industry S-APPL
to O
increase O
the O
perceived O
value O
in O
any O
of O
three O
area S-PARA
's O
: O
profit O
, O
risk O
and O
time O
. O


Next O
to O
that O
the O
tactical O
path O
along O
which O
these O
industries S-APPL
have O
incorporated O
AM S-MANP
implementation O
can O
be S-MATE
characterized O
by O
product O
and/or O
supply B-CONPRI
chain E-CONPRI
change O
. O


Four O
different O
paths O
have O
been O
identified O
: O
Path O
1 O
describes O
companies S-APPL
that O
do O
not O
seek O
radical O
modification O
of O
their O
products O
and O
supply B-CONPRI
chain E-CONPRI
, O
but O
look O
at O
AM S-MANP
to O
improve O
their O
value O
proposition O
to O
the O
customer O
. O


Typical O
examples O
of O
the O
use O
of O
AM S-MANP
for O
path O
1 O
are O
printed O
prototypes S-CONPRI
and O
tools S-MACEQ
and O
fixtures O
. O


Path O
2 O
looks O
at O
AM S-MANP
as O
a O
means O
to O
define O
new O
business B-APPL
cases E-APPL
in O
which O
the O
production S-MANP
of O
end O
user O
products O
can O
be S-MATE
realized O
beneficially O
. O


Examples O
include O
for O
example O
the O
production S-MANP
of O
spare O
parts O
and O
production S-MANP
on O
problematic O
production S-MANP
locations O
like O
space O
, O
war O
zones O
and O
the O
oil S-MATE
& O
gas S-CONPRI
industry O
. O


Path O
3 O
describes O
strategies O
being O
enabled O
by O
AM S-MANP
based O
new O
product O
performance S-CONPRI
. O


Examples O
are O
the O
fuel B-MACEQ
nozzle E-MACEQ
by O
GE S-MATE
, O
embedded B-ENAT
electronics E-ENAT
and O
lightweight B-MACEQ
structures E-MACEQ
. O


Path O
4 O
describes O
companies S-APPL
that O
base O
their O
new O
business B-APPL
models E-APPL
on O
changes O
in O
both O
the O
supply B-CONPRI
chains E-CONPRI
and O
the O
products O
. O


An O
example O
for O
this O
path O
is O
the O
3D B-CHAR
scanning E-CHAR
and O
printing O
of O
custom O
shoes O
in O
retail O
stores O
. O


All O
tactical O
development O
paths O
described O
above O
deal O
with O
product B-FEAT
design E-FEAT
within O
an O
AM-based O
supply B-CONPRI
chain E-CONPRI
. O


It O
is O
required O
both O
for O
the O
realization O
of O
AM-based O
enhanced O
product O
performance S-CONPRI
as S-MATE
well O
as S-MATE
when O
printing O
more O
standard S-CONPRI
product B-FEAT
designs E-FEAT
; O
these O
designs S-FEAT
also O
have O
to O
be S-MATE
optimized O
for O
specific O
AM B-MANP
process E-MANP
opportunities O
and O
constraints O
so O
they O
are O
produced O
reliably O
, O
on O
time O
and O
cost O
efficiently O
. O


Design B-FEAT
for I-FEAT
Additive I-FEAT
Manufacturing E-FEAT
describes O
methodologies O
used O
to O
optimize O
the O
product B-FEAT
design E-FEAT
with O
the O
goal O
of O
improving O
performance S-CONPRI
in O
all O
lifecycle O
stages O
. O


The O
lack O
of O
knowledge O
on O
DfAM O
has O
been O
identified O
as S-MATE
one O
of O
the O
barriers O
that O
holds O
back O
further O
adoption O
of O
AM S-MANP
in O
industry S-APPL
. O


This O
can O
be S-MATE
attributed O
to O
the O
attention O
given O
to O
AM S-MANP
as O
a O
production S-MANP
technology O
, O
which O
only O
blossomed O
over O
the O
last O
decade O
. O


Attention O
to O
design S-FEAT
for O
AM S-MANP
trailed O
behind O
and O
only O
grew O
in O
importance O
when O
interest O
in O
commercial O
production S-MANP
of O
end O
user O
goods O
increased O
. O


The O
CIRP O
community O
has O
published O
papers O
related O
to O
AM B-MANP
processes E-MANP
, O
AM B-MATE
materials E-MATE
, O
specific O
AM S-MANP
application O
areas S-PARA
and O
AM S-MANP
geometrical O
aspects O
. O


The O
CIRP O
keynote O
paper O
by O
Thompson O
focused O
on O
DfAM O
and O
disclosed O
the O
width O
and O
complexity S-CONPRI
of O
the O
DfAM O
theme O
, O
and O
addressed O
many O
of O
the O
themes O
that O
should O
be S-MATE
considered O
as S-MATE
part O
of O
product B-CONPRI
development E-CONPRI
for O
AM S-MANP
. O


These O
topics O
ranged O
from O
design S-FEAT
strategies O
and O
artefact O
design S-FEAT
up O
to O
economic O
and O
strategic O
considerations O
on O
the O
implementation O
of O
AM S-MANP
within O
industrial S-APPL
product O
development O
processes S-CONPRI
. O


The O
paper O
focussed O
on O
design B-CONPRI
considerations E-CONPRI
that O
should O
be S-MATE
addressed O
when O
deciding O
on O
the O
transition S-CONPRI
from O
classical O
production S-MANP
processes S-CONPRI
to O
additive B-MANP
manufacturing E-MANP
. O


This O
keynote O
paper O
focuses O
on O
the O
state O
of O
the O
art S-APPL
on O
methods O
and O
tools S-MACEQ
related O
to O
the O
design S-FEAT
of O
geometry S-CONPRI
or O
functional O
AM S-MANP
artefacts O
within O
an O
industrial S-APPL
setting O
. O


A O
general O
introduction O
to O
AM B-MANP
processes E-MANP
and O
process S-CONPRI
steps O
will O
be S-MATE
presented O
2 O
. O


Section O
3 O
will O
present O
a O
framework S-CONPRI
for O
the O
selection O
and O
application O
of O
DfAM O
methods O
and O
tools S-MACEQ
. O


In O
Sections O
4the O
DfAM O
framework S-CONPRI
will O
be S-MATE
discussed O
in O
more O
detail O
; O
lightweighting S-PRO
, O
internal B-CONPRI
topology E-CONPRI
, O
surface S-CONPRI
topolgy O
, O
material S-MATE
complexity S-CONPRI
and O
part O
integration O
. O


When O
required O
, O
methods O
and O
examples O
of O
application O
will O
focus O
on O
AM S-MANP
based O
production S-MANP
of O
metal S-MATE
parts O
in O
an O
industrial S-APPL
setting O
. O


The O
applicability O
of O
the O
design S-FEAT
framework O
is O
however O
not O
limited O
to O
the O
examples O
given O
but O
can O
, O
at O
a O
generic O
level O
, O
be S-MATE
apllied O
to O
the O
majority O
of O
the O
known O
AM B-MANP
processes E-MANP
. O


2 O
Additive B-MANP
manufacturing E-MANP
AM O
is O
defined O
by O
the O
ISO/ASTM S-MANS
joint O
standard S-CONPRI
52900:2018 O
as S-MATE
the O
process S-CONPRI
of O
joining S-MANP
materials O
to O
make O
parts O
from O
3D B-APPL
model E-APPL
data O
, O
usually O
layer S-PARA
upon O
layer S-PARA
, O
as S-MATE
opposed O
to O
subtractive B-MANP
manufacturing E-MANP
and O
formative O
manufacturing S-MANP
methodologies O
. O


Note O
that O
this O
definition O
is O
very O
general O
and O
can O
be S-MATE
applied O
to O
a O
wide O
range S-PARA
of O
technologies S-CONPRI
. O


Hybrid B-ENAT
technologies E-ENAT
that O
for O
example O
use O
additive S-MATE
plus O
subtractive B-MANP
processes E-MANP
within O
a O
single O
machine S-MACEQ
may O
therefore O
not O
be S-MATE
considered O
as S-MATE
AM B-MACEQ
machines E-MACEQ
in O
the O
strict O
definition O
of O
the O
term O
. O


For O
the O
near O
future O
it O
is O
foreseen O
that O
fully O
automated O
manufacturing S-MANP
lines O
, O
combining O
AM S-MANP
in O
tight O
and O
repetitive O
sequences O
alongside O
other O
fully O
automated O
production S-MANP
and O
handling O
processes S-CONPRI
, O
will O
become O
the O
standard S-CONPRI
for O
the O
modern O
factory O
. O


2.1 O
AM B-MANP
processes E-MANP
According O
to O
ISO/ASTM S-MANS
there O
are O
currently O
seven O
AM B-MANP
process E-MANP
categories O
that O
result O
in O
a O
3D S-CONPRI
CAD O
model S-CONPRI
being O
formed O
into O
a O
solid O
, O
integrated O
part O
: O
Binder B-MANP
jetting E-MANP
: O
droplet S-CONPRI
printing O
of O
a O
liquid O
used O
to O
bind S-MANP
powder O
particles S-CONPRI
together O
; O
Directed B-MANP
energy I-MANP
deposition E-MANP
: O
material S-MATE
is O
simultaneously O
fed O
into O
a O
moving O
focused O
energy O
region O
; O
Material B-MANP
extrusion E-MANP
: O
material S-MATE
is O
fed O
through O
a O
nozzle S-MACEQ
in O
a O
liquid B-CONPRI
state E-CONPRI
after O
which O
solidifies O
; O
Material B-MANP
jetting E-MANP
: O
material S-MATE
is O
jetted O
in O
liquid B-CONPRI
droplet I-CONPRI
form E-CONPRI
after O
which O
it O
solidifies O
; O
Powder B-MANP
bed I-MANP
fusion E-MANP
: O
powder B-MATE
material E-MATE
is O
selectively O
heated O
so O
that O
the O
particles S-CONPRI
partially O
or O
fully O
melt S-CONPRI
to O
form O
a O
solid B-CONPRI
matrix E-CONPRI
; O
Sheet B-MANP
lamination E-MANP
: O
sheets S-MATE
of O
material S-MATE
are O
bonded O
together O
either O
before O
or O
after O
the O
part O
outline O
is O
separated O
from O
the O
sheets S-MATE
; O
Vat B-MANP
photopolymerisation E-MANP
: O
a O
platform S-MACEQ
is O
dropped O
through O
or O
raised O
above O
a O
vat S-MACEQ
of O
liquid O
resin S-MATE
where O
light O
is O
used O
to O
selectively O
solidify S-CONPRI
it O
. O


Most O
of O
these O
categories O
have O
so O
far O
resulted O
mainly O
in O
machines S-MACEQ
that O
are O
designed S-FEAT
for O
one-off O
prototypes S-CONPRI
or O
for O
production S-MANP
that O
heavily O
employs O
manual O
work O
. O


Whilst O
the O
AM B-MANP
technology E-MANP
itself O
is O
largely O
automated O
, O
the O
design B-CONPRI
process E-CONPRI
, O
machine B-MACEQ
setup E-MACEQ
and O
finishing S-MANP
stages O
may O
require O
a O
significant O
amount O
of O
knowledge O
and O
skills O
to O
perform O
. O


All O
the O
above O
processes S-CONPRI
were O
initially O
developed O
to O
create O
parts O
from O
different O
polymeric B-MATE
materials E-MATE
, O
with O
the O
exception O
of O
sheet B-MANP
lamination E-MANP
. O


Some O
of O
these O
technologies S-CONPRI
have O
now O
been O
developed O
to O
a O
level O
where O
they O
have O
been O
incorporated O
into O
large O
batch B-CONPRI
production E-CONPRI
. O


Some O
of O
these O
batches O
can O
be S-MATE
considered O
to O
be S-MATE
part O
of O
a O
continuous B-MANP
production I-MANP
line E-MANP
. O


The O
most O
well-known O
of O
these O
would O
be S-MATE
AM B-MACEQ
machines E-MACEQ
used O
in O
production S-MANP
of O
teeth O
aligners O
and O
hearing B-APPL
aids E-APPL
. O


These O
examples O
show O
that O
when O
the O
additional O
complexity S-CONPRI
of O
form O
and/or O
the O
individual O
part O
cost O
allows O
it O
, O
AM S-MANP
can O
be S-MATE
used O
for O
final O
part O
production S-MANP
of O
parts O
. O


The O
impact S-CONPRI
of O
AM S-MANP
on O
process B-ENAT
chain E-ENAT
towards O
final O
production S-MANP
is O
however O
most O
heavily O
felt O
when O
producing O
metal S-MATE
parts O
. O


All O
of O
the O
above O
process S-CONPRI
categories O
have O
a O
means O
in O
which O
to O
arrive O
at O
a O
metal S-MATE
part O
. O


The O
first O
approach O
is O
by O
mixing S-CONPRI
metal S-MATE
particles O
with O
the O
material B-FEAT
joining E-FEAT
mechanism O
. O


For O
example O
, O
metal S-MATE
particles O
can O
be S-MATE
added O
to O
photopolymers S-MATE
in O
vat B-MANP
photopolymerisation E-MANP
or O
mixed O
with O
polymer S-MATE
powder O
in O
powder B-MANP
bed I-MANP
fusion E-MANP
or O
with O
filament S-MATE
in O
material B-MANP
extrusion E-MANP
. O


In O
general O
this O
will O
end O
in O
a O
blended O
part O
that O
exhibits O
some O
of O
the O
properties S-CONPRI
of O
the O
metal S-MATE
like O
improved O
surface S-CONPRI
hardness S-PRO
or O
heat B-CONPRI
deflection E-CONPRI
. O


The O
second O
approach O
is O
where O
the O
parts O
above O
are O
used O
in O
a O
secondary O
furnace S-MACEQ
cycle O
to O
burn O
off O
the O
polymer S-MATE
and O
cause O
the O
metal S-MATE
particles O
to O
sinter S-MANP
together O
. O


This O
process S-CONPRI
therefore O
requires O
an O
additional O
programmable O
furnace S-MACEQ
to O
achieve O
this O
effect O
. O


In O
addition O
to O
the O
process S-CONPRI
categories O
mentioned O
in O
the O
previous O
paragraph O
, O
binder B-MANP
jetting E-MANP
is O
also O
widely O
used O
in O
this O
manner O
. O


It O
should O
be S-MATE
noted O
in O
particular O
that O
part O
shrinkage S-CONPRI
will O
occur O
using O
this O
approach O
. O


This O
shrinkage S-CONPRI
can O
be S-MATE
minimised O
if O
an O
infiltrant O
is O
used O
to O
fill O
in O
voids S-CONPRI
prior O
to O
densification S-MANP
. O


For O
example O
420 B-MATE
stainless I-MATE
steel E-MATE
parts O
can O
be S-MATE
infiltrated O
with O
bronze S-MATE
at O
1100 O
. O


Many O
technologies S-CONPRI
have O
been O
refined O
to O
a O
level O
where O
geometric B-FEAT
tolerances E-FEAT
are O
highly O
predictable S-CONPRI
and O
achieving O
up O
to O
97 O
% O
final O
density S-PRO
values O
. O


Conventional O
polymer S-MATE
AM B-MATE
materials E-MATE
can O
often O
be S-MATE
used O
in O
casting S-MANP
processes O
to O
achieve O
metal S-MATE
parts O
. O


Some O
of O
the O
original O
processes S-CONPRI
were O
developed O
around O
waxes S-MATE
as S-MATE
a O
means O
to O
integrate O
with O
conventional B-MANP
investment I-MANP
casting E-MANP
. O


It O
was O
found O
later O
that O
other O
, O
stronger O
polymers S-MATE
could O
be S-MATE
used O
in O
this O
way O
provided O
the O
casting B-MACEQ
shells E-MACEQ
were O
strengthened O
and O
the O
burnout B-CHAR
conditions E-CHAR
were O
modified O
. O


Four O
of O
the O
above O
process S-CONPRI
categories O
can O
directly O
produce O
metal S-MATE
parts O
; O
powder B-MANP
bed I-MANP
fusion E-MANP
, O
directed B-MANP
energy I-MANP
deposition E-MANP
, O
material B-MANP
jetting E-MANP
, O
and O
sheet B-MANP
lamination E-MANP
. O


It O
is O
interesting O
to O
note O
that O
sheet B-MANP
lamination E-MANP
is O
largely O
a O
hybrid O
process S-CONPRI
. O


In O
sheet B-MANP
lamination E-MANP
there O
can O
be S-MATE
a O
large O
amount O
of O
material S-MATE
, O
often O
much O
more O
than O
is O
used O
for O
the O
part O
itself O
, O
that O
is O
separated O
from O
the O
part O
in O
a O
subtractive S-MANP
manner O
during O
the O
AM B-MANP
process E-MANP
. O


These O
sheets S-MATE
can O
be S-MATE
metal O
and O
bonded O
together O
using O
ultrasonic B-MANP
bonding E-MANP
. O


This O
is O
a O
low O
temperature S-PARA
welding O
process S-CONPRI
for O
joining S-MANP
dissimular O
metals S-MATE
and O
can O
for O
example O
allow O
embedding O
of O
electronics S-CONPRI
in O
the O
structure S-CONPRI
without O
damaging O
it O
. O


It O
is O
a O
niche O
AM S-MANP
route O
towards O
metal S-MATE
parts O
. O


By O
far O
the O
most O
widely O
used O
AM S-MANP
approach O
for O
metal S-MATE
parts O
is O
powder B-MANP
bed I-MANP
fusion E-MANP
. O


This O
is O
largely O
because O
of O
the O
basic O
simplicity O
of O
the O
process S-CONPRI
combined O
with O
the O
fact O
that O
a O
range S-PARA
metals S-MATE
is O
readily O
available O
and O
suitable O
for O
mainstream O
applications O
. O


A O
beam S-MACEQ
of O
energy O
is O
used O
to O
selectively O
melt S-CONPRI
the O
powders S-MATE
to O
form O
the O
solid O
part O
. O


Electron B-MANP
beam I-MANP
melting E-MANP
is O
available O
but O
most O
systems O
use O
laser B-CONPRI
energy E-CONPRI
, O
normally O
in O
a O
sealed O
chamber O
, O
in O
an O
inert B-CONPRI
gas E-CONPRI
environment O
or O
a O
vacuum O
. O


This O
sealed O
chamber O
may O
be S-MATE
at O
an O
elevated O
temperature S-PARA
but O
still O
considerably O
below O
the O
melting B-PRO
point E-PRO
of O
the O
metal S-MATE
. O


Since O
this O
means O
very O
large O
thermal B-PARA
gradients E-PARA
, O
it O
is O
normal O
to O
connect O
the O
parts O
to O
a O
solid B-MACEQ
substrate E-MACEQ
in O
a O
similar O
way O
to O
processes S-CONPRI
that O
require O
support B-FEAT
structures E-FEAT
. O


These O
supports S-APPL
have O
a O
different O
purpose O
in O
that O
they O
anchor O
the O
part O
to O
prevent O
internal B-PRO
stress E-PRO
warpage O
during O
build S-PARA
. O


Directed B-MANP
energy I-MANP
deposition E-MANP
is O
a O
process S-CONPRI
that O
almost O
entirely O
focuses O
on O
metal S-MATE
parts O
. O


A O
high O
energy O
source S-APPL
is O
used O
to O
melt S-CONPRI
metals O
that O
are O
delivered O
in O
either O
powder S-MATE
or O
wire O
form O
. O


The O
energy B-FEAT
focal I-FEAT
point E-FEAT
is O
also O
where O
the O
material S-MATE
is O
delivered O
and O
so O
there O
is O
a O
periodic O
melting S-MANP
followed O
by O
rapid B-MANP
solidification E-MANP
. O


Similar O
issues O
to O
powder B-MANP
bed I-MANP
fusion E-MANP
exist O
regarding O
residual B-PRO
stresses E-PRO
with O
the O
additional O
complexity S-CONPRI
of O
a O
significantly O
varying O
thermal O
environment O
. O


Since O
there O
is O
no O
surrounding O
powder S-MATE
to O
help O
stabilise O
the O
heat B-CONPRI
transfer E-CONPRI
, O
the O
directed B-MANP
energy I-MANP
deposition I-MANP
process E-MANP
will O
have O
differing O
cooling S-MANP
profiles O
dependent O
on O
the O
mass O
of O
surrounding O
material S-MATE
at O
the O
energy O
delivery O
point O
. O


Material B-MANP
jetting E-MANP
for O
the O
production S-MANP
of O
metal S-MATE
parts O
is O
hampered O
by O
the O
high O
temperatures S-PARA
needed O
to O
get O
the O
metals S-MATE
in O
the O
proper O
liquid B-CONPRI
state E-CONPRI
. O


As S-MATE
a O
result O
this O
technology S-CONPRI
, O
when O
used O
to O
directly O
fabricate S-MANP
metal O
parts O
, O
is O
still O
in O
the O
development O
stage O
. O


2.2 O
AM B-MANP
process E-MANP
steps O
The O
process S-CONPRI
of O
creating O
an O
additively B-MANP
manufactured I-MANP
product E-MANP
can O
be S-MATE
subdevided O
into O
seven O
steps O
. O


1 O
Model S-CONPRI
design S-FEAT
. O


3D S-CONPRI
CAD O
software S-CONPRI
can O
be S-MATE
used O
to O
create O
a O
solid O
or O
surface B-ENAT
model E-ENAT
or O
scan O
data S-CONPRI
is O
used O
to O
create O
the O
3D B-FEAT
geometry E-FEAT
; O
2 O
STL S-MANS
file S-MANS
creation O
. O


The O
3D B-APPL
model E-APPL
is O
converted O
into O
a O
file S-MANS
format O
that O
is O
understood O
by O
AM B-MACEQ
machines E-MACEQ
. O


The O
STL S-MANS
file S-MANS
format O
is O
widely O
used O
and O
approximates O
the O
3D B-APPL
model E-APPL
by O
a O
surface S-CONPRI
that O
is O
constructed O
using O
triangles O
. O


Other O
file S-MANS
formats O
exist O
that O
are O
better O
suited O
to O
advanced O
AM S-MANP
features O
like O
multi O
material S-MATE
parts O
; O
3 O
Build S-PARA
preperation O
. O


The O
STL S-MANS
file S-MANS
is O
transferred O
to O
the O
build B-PARA
preparation E-PARA
software O
, O
where O
the O
location O
and O
orientation S-CONPRI
of O
the O
part O
in O
the O
build B-PARA
envelope E-PARA
are O
defined O
. O


The O
software B-CONPRI
slices E-CONPRI
the O
geometry S-CONPRI
into O
individual O
layers O
. O


For O
each O
layer S-PARA
the O
geometric O
data S-CONPRI
of O
that O
layer S-PARA
, O
in O
combination O
with O
the O
machine B-PARA
parameters E-PARA
, O
like O
laser B-PARA
power E-PARA
, O
layer B-PARA
thickness E-PARA
and O
scan B-PARA
patterns E-PARA
, O
is O
translated O
into O
build S-PARA
instructions O
for O
the O
AM B-MACEQ
machine E-MACEQ
; O
4 O
The O
build S-PARA
process O
. O


After O
the O
build S-PARA
process O
the O
part O
is O
removed O
from O
the O
build B-PARA
plate/envelope E-PARA
and O
excess O
material S-MATE
is O
removed O
. O


Additional O
post-processing S-CONPRI
steps O
might O
be S-MATE
needed O
to O
improve O
the O
functional O
characteristics O
of O
the O
part O
. O


6 O
Quality S-CONPRI
and O
inspection S-CHAR
. O


Often O
quality S-CONPRI
and O
inspection S-CHAR
methods O
are O
applied O
that O
are O
based O
on O
other O
production S-MANP
technologies O
like O
casting S-MANP
and O
forging S-MANP
. O


But O
the O
complexity S-CONPRI
of O
the O
geometry S-CONPRI
can O
induce O
unique O
inspection S-CHAR
problems O
like O
inaccesable O
surfaces S-CONPRI
or O
the O
absence O
of O
measuring O
datum B-CHAR
planes E-CHAR
; O
7 O
Application O
. O


For O
most O
industrial S-APPL
parts O
produced O
by O
additive B-MANP
manufacturing E-MANP
the O
expected O
benefits O
in O
the O
use O
phase S-CONPRI
are O
the O
reason O
for O
designing O
parts O
to O
be S-MATE
created O
by O
additive B-MANP
manufacturing E-MANP
. O


2.3 O
AM S-MANP
design O
stages O
As S-MATE
mentioned O
in O
Thompson O
, O
the O
AM S-MANP
design O
process S-CONPRI
has O
to O
take O
into O
account O
a O
lot O
of O
aspects O
related O
to O
several O
key O
performance S-CONPRI
indicators O
. O


Globally O
, O
as S-MATE
defined O
in O
the O
standard S-CONPRI
ISO/ASTM S-MANS
52910:2018 O
the O
AM S-MANP
design O
steps O
can O
be S-MATE
structured O
into O
three O
global O
stages O
. O


The O
first O
stage O
relates O
to O
go/no-go O
evaluations O
concerning O
the O
part O
, O
tool S-MACEQ
or O
product O
to O
be S-MATE
considered O
. O


Manufacturability S-CONPRI
issues O
will O
have O
to O
be S-MATE
checked O
at O
this O
stage O
even O
before O
defining O
any O
geometry S-CONPRI
. O


Before O
that O
, O
however O
, O
crucial O
decisions O
must O
be S-MATE
made O
with O
respect O
to O
functional O
decomposition S-PRO
and O
functional O
integration O
. O


One O
later O
decision O
will O
be S-MATE
to O
define O
the O
complete O
manufacturing S-MANP
for O
each O
feature S-FEAT
as S-MATE
well O
as S-MATE
the O
scheduling O
of O
the O
individual O
manufacturing S-MANP
operations O
, O
with O
possible O
use O
of O
different O
manufacturing B-MANP
technologies E-MANP
. O


The O
material S-MATE
and O
its O
characteristics O
will O
also O
have O
to O
be S-MATE
defined O
for O
each O
voxel S-CONPRI
of O
the O
part O
. O


The O
definition O
of O
the O
material S-MATE
characteristics O
must O
be S-MATE
fixed O
as S-MATE
well O
as S-MATE
the O
definition O
of O
transitions O
between O
different O
materials S-CONPRI
in O
different O
regions O
of O
the O
objects O
. O


These O
possibilities O
are O
limited O
to O
AM B-MANP
technologies E-MANP
that O
allow O
assembly S-MANP
of O
different O
materials S-CONPRI
or O
grading O
material S-MATE
characteristics O
in O
a O
given O
part O
. O


The O
third O
stage O
corresponds O
to O
the O
final O
check O
and O
optimization S-CONPRI
of O
process S-CONPRI
characteristics O
with O
respect O
to O
the O
best O
possible O
properties S-CONPRI
of O
the O
manufactured S-CONPRI
objects O
. O


For O
example O
, O
the O
number O
of O
parts O
produced O
is O
dependent O
on O
the O
choice O
of O
orientation S-CONPRI
of O
the O
part O
and O
consequently O
on O
the O
support B-FEAT
structures E-FEAT
that O
are O
minimized O
with O
respect O
to O
an O
optimum O
part O
geometry S-CONPRI
. O


These O
three O
global O
design S-FEAT
stages O
serve O
to O
minimize O
the O
technical O
and O
economic O
risks O
before O
going O
to O
manufacturing S-MANP
. O


Design S-FEAT
does O
not O
therefore O
just O
rely O
on O
a O
simple S-MANP
set S-APPL
of O
design S-FEAT
guidelines O
. O


A O
global O
and O
systemic O
vision O
of O
the O
complete O
value O
chain O
has O
to O
be S-MATE
considered O
with O
respect O
to O
global O
indicators O
like O
in O
particular O
lead B-PARA
time E-PARA
, O
cost O
and O
quality S-CONPRI
, O
in O
order O
to O
evaluate O
feasibility S-CONPRI
, O
suitability O
and O
stability S-PRO
of O
AM-based O
value O
chain O
performances O
. O


3 O
A O
DfAM O
framework S-CONPRI
Design S-FEAT
for O
manufacturing S-MANP
and O
assembly S-MANP
has O
been O
around O
for O
many O
years O
and O
deals O
with O
the O
design S-FEAT
of O
products O
while O
focussing O
on O
both O
the O
manufacturing S-MANP
and O
assembly S-MANP
process O
. O


The O
goal O
of O
DfMA O
is O
to O
include O
manufacturing S-MANP
and O
assembly S-MANP
knowledge O
early O
in O
the O
design S-FEAT
proces O
to O
increase O
chances O
of O
success O
and O
shorten O
the O
development O
cycle O
. O


Many O
variants O
exist O
, O
focussed O
for O
example O
on O
specific O
production S-MANP
technologies O
like O
injection B-MANP
molding E-MANP
or O
casting S-MANP
. O


DfAM O
focusses O
on O
AM B-MANP
processes E-MANP
but O
differs O
from O
other O
DfX O
processes S-CONPRI
. O


It O
deals O
with O
many O
different O
AM B-MANP
process E-MANP
variants O
and O
needs O
to O
take O
the O
whole O
process B-ENAT
chain E-ENAT
into O
account O
to O
be S-MATE
successful O
while O
research S-CONPRI
has O
shown O
that O
the O
number O
of O
interacting O
aspects O
that O
define O
successful O
production S-MANP
is O
large O
. O


Finally O
, O
AM S-MANP
is O
a O
new O
group O
of O
processes S-CONPRI
that O
provides O
other O
opportunities O
and O
constraints O
to O
traditional O
forming S-MANP
and O
subtractive B-MANP
processes E-MANP
which O
implies O
non-traditional O
approaches O
to O
product B-FEAT
design E-FEAT
are O
required O
. O


Many O
papers O
exist O
on O
individual O
aspects O
of O
the O
design B-CONPRI
process E-CONPRI
while O
for O
a O
succesful O
design B-CONPRI
process E-CONPRI
all O
relevant O
aspects O
should O
be S-MATE
taken O
into O
account O
. O


The O
framework S-CONPRI
defines O
a O
structured O
method O
to O
link O
design S-FEAT
challenges O
to O
specific O
design S-FEAT
goals O
and O
focusses O
on O
the O
3 O
stages O
presented O
2.3 O
. O


Examples O
used O
will O
focus O
on O
AM-based O
manufacturing S-MANP
of O
metal S-MATE
products O
although O
the O
framework S-CONPRI
is O
generic O
in O
nature O
and O
can O
also O
be S-MATE
applied O
for O
other O
material/process O
combinations O
. O


3.1 O
AM S-MANP
suitability O
Additive B-MANP
manufacturing E-MANP
is O
a O
relatively O
new O
group O
of O
production S-MANP
processes S-CONPRI
, O
of O
which O
integration O
in O
industry S-APPL
is O
just O
starting O
to O
gain S-PARA
momentum O
. O


This O
momentum O
might O
be S-MATE
attributed O
to O
the O
claims O
of O
a O
future O
where O
AM S-MANP
will O
realize O
low O
cost O
efficient O
production S-MANP
of O
any O
shape O
in O
any O
material S-MATE
. O


Current O
industrial S-APPL
additive B-MANP
manufacturing E-MANP
practice O
shows O
that O
this O
bright O
future O
is O
yet O
to O
be S-MATE
. O


Timely O
identification O
of O
the O
match O
between O
design S-FEAT
task O
, O
product O
requirements O
and O
AM S-MANP
capabilities O
is O
needed O
. O


proposes O
to O
base O
this O
evaluation O
on O
the O
following O
criteria O
: O
Do O
available O
AM B-MATE
materials E-MATE
match O
the O
product O
application O
? O
Does O
the O
product B-FEAT
design E-FEAT
fit S-CONPRI
the O
build B-PARA
envelope E-PARA
of O
AM S-MANP
hardware O
? O
Can O
the O
product B-CHAR
functionality E-CHAR
improve O
when O
applying O
the O
following O
product B-FEAT
design E-FEAT
modifications O
or O
product O
opportunities O
? O
- O
Part O
customization O
- O
Lightweighting S-PRO
- O
Use O
of O
internal O
channels O
or O
structures O
- O
Functional O
integration O
- O
The O
use O
of O
designed S-FEAT
surface O
structures O
- O
The O
use O
of O
multi-material S-CONPRI
or O
gradient O
material S-MATE
parts O
. O


This O
is O
to O
evaluate O
the O
balance O
between O
the O
expected O
economic O
benefits O
of O
product B-FEAT
design E-FEAT
opportunities O
against O
, O
in O
most O
cases O
, O
the O
increased O
manufacturing B-CONPRI
costs E-CONPRI
. O


The O
dominant O
objectives O
established O
in O
that O
last O
paper O
are O
improved O
part O
performance S-CONPRI
, O
manufacturing S-MANP
and O
reduction S-CONPRI
of O
lead B-PARA
time E-PARA
. O


3.2 O
AM B-MATE
material E-MATE
, O
process S-CONPRI
and O
machine B-PARA
selection E-PARA
If O
AM S-MANP
potential O
has O
been O
established O
then O
AM S-MANP
resources O
should O
be S-MATE
identified O
, O
as S-MATE
these O
affect O
downstream O
design S-FEAT
choices O
. O


This O
includes O
the O
decision O
between O
direct O
AM-based O
production S-MANP
, O
indirect O
AM-based O
production S-MANP
or O
hybrid O
approaches O
. O


Also O
post-processing S-CONPRI
steps O
, O
needed O
to O
reach O
the O
required O
product O
characteristics O
, O
could O
be S-MATE
identified O
in O
this O
stage O
. O


For O
reasons O
of O
process B-CONPRI
chain I-CONPRI
selection E-CONPRI
, O
hybrid O
production S-MANP
processes S-CONPRI
can O
be S-MATE
subdivided O
based O
on O
the O
method O
used O
to O
generate O
the O
bulk O
of O
the O
geometry S-CONPRI
. O


From O
an O
industrial S-APPL
perspective O
some O
hybrid B-ENAT
technologies E-ENAT
use O
conventional O
technologies S-CONPRI
to O
create O
the O
bulk O
of O
the O
part O
and O
use O
AM S-MANP
as O
a O
subsequent O
production S-MANP
method O
to O
add O
detailing O
features O
. O


This O
sequencing O
of O
processes S-CONPRI
can O
have O
economic O
benefits O
or O
can O
result O
in O
parts O
that O
exceed O
the O
standard S-CONPRI
build B-PARA
chamber E-PARA
dimensions O
. O


An O
AM B-MANP
process E-MANP
that O
produces O
the O
bulk O
of O
the O
part O
using O
AM B-MANP
technologies E-MANP
and O
integrates O
subtractive S-MANP
technologies O
during O
the O
build S-PARA
process O
can O
be S-MATE
seen O
as S-MATE
the O
second O
group O
of O
hybrid O
processes S-CONPRI
. O


For O
metal S-MATE
parts O
this O
sub-group O
typically O
consists O
of O
DED-based B-ENAT
metal I-ENAT
additive I-ENAT
manufacturing I-ENAT
technologies E-ENAT
and O
with O
milling S-MANP
to O
post-process S-CONPRI
functional O
, O
internal O
or O
hard O
to O
reach O
surfaces S-CONPRI
. O


Based O
on O
interdependencies O
and O
sequencing O
of O
process S-CONPRI
steps O
, O
alternative O
processing O
chains O
can O
be S-MATE
generated O
and O
evaluated O
. O


Based O
on O
the O
design S-FEAT
requirements O
and O
selections O
already O
made O
, O
Bikas O
proposes O
to O
use O
screening O
and O
selection O
for O
AM B-MANP
processes E-MANP
based O
on O
criteria O
related O
to O
machine S-MACEQ
, O
material S-MATE
, O
process S-CONPRI
and O
part O
constraints O
. O


The O
Senvol B-ENAT
database E-ENAT
links O
AM B-MANP
processes E-MANP
to O
available O
materials S-CONPRI
and O
build S-PARA
envelops O
of O
industrial S-APPL
AM B-MACEQ
machines E-MACEQ
. O


Also O
the O
screening O
and O
ranking O
method O
proposed O
by O
Ashby O
can O
be S-MATE
applied O
for O
AM B-MATE
material E-MATE
and O
process B-CONPRI
selection E-CONPRI
. O


3.3 O
Initial O
cost B-CONPRI
estimation E-CONPRI
The O
decision O
to O
apply O
additive B-MANP
manufacturing E-MANP
for O
functional O
parts O
involves O
balancing O
the O
cost O
of O
additive B-MANP
manufacturing E-MANP
against O
the O
expected O
benefits O
during O
the O
design S-FEAT
, O
production S-MANP
and O
use O
phase S-CONPRI
. O


Although O
the O
cost/benefits B-CHAR
analysis E-CHAR
during O
the O
early O
design S-FEAT
stage O
is O
important O
, O
information O
required O
for O
detailed O
cost B-CONPRI
estimation E-CONPRI
is O
often O
missing O
. O


Knowledge O
on O
the O
expected O
product O
volume S-CONPRI
, O
production S-MANP
technology O
and O
required O
post-processing S-CONPRI
steps O
can O
give O
insight O
into O
the O
expected O
costs O
. O


For O
the O
early O
cost B-CONPRI
estimation E-CONPRI
of O
the O
production S-MANP
of O
the O
part O
, O
the O
costs O
are O
often O
expressed O
as S-MATE
cost O
per O
cm3 O
of O
the O
printed O
part O
. O


Most O
cost B-CONPRI
estimations E-CONPRI
found O
in O
literature O
only O
take O
the O
process S-CONPRI
related O
post-processing S-CONPRI
steps O
into O
consideration O
and O
additional O
costs O
must O
be S-MATE
taken O
into O
account O
when O
the O
functionality O
of O
the O
printed O
part O
has O
to O
be S-MATE
improved O
also O
. O


Most O
cost B-CONPRI
estimation E-CONPRI
calculations O
are O
based O
on O
the O
assumption O
of O
in-house O
production S-MANP
and O
an O
idealized O
representation O
of O
the O
AM B-MANP
process E-MANP
investigated O
. O


It O
is O
assumed O
that O
one O
AM B-MACEQ
machine E-MACEQ
is O
used O
for O
one O
product O
the O
whole O
life O
time O
of O
the O
machine S-MACEQ
, O
resulting O
in O
a O
high O
machine S-MACEQ
load O
. O


For O
example O
, O
Baumers O
presents O
a O
cost O
breakdown O
for O
metal B-MATE
powder E-MATE
bed S-MACEQ
based O
production S-MANP
of O
a O
stainless B-MATE
steel I-MATE
304L E-MATE
product O
with O
wire B-CONPRI
erosion E-CONPRI
support S-APPL
removal O
and O
de-powdering S-PRO
as S-MATE
post O
processing O
steps O
. O


Based O
on O
that O
analysis O
four O
major O
cost O
aspects O
were O
identified O
: O
Indirect O
cost O
, O
material S-MATE
costs O
, O
labor B-CONPRI
costs E-CONPRI
, O
and O
risk O
associated O
costs O
. O


Risk O
related O
costs O
include O
build B-CHAR
failures E-CHAR
and O
accounts O
for O
26 O
% O
of O
the O
AM S-MANP
unit O
cost O
. O


In O
the O
production S-MANP
of O
laser S-ENAT
based O
powder B-MANP
bed I-MANP
fusion E-MANP
system O
was O
compared O
to O
an O
electron B-CHAR
beam I-CHAR
variant E-CHAR
. O


The O
AM S-MANP
deposition O
rates O
are O
relatively O
slow O
and O
are O
identified O
as S-MATE
the O
major O
driver O
for O
the O
manufacturing B-CONPRI
costs E-CONPRI
. O


An O
alternative O
cost B-CONPRI
estimation E-CONPRI
study O
was O
presented O
by O
Baldinger O
and O
focusses O
on O
buy O
scenarios O
for O
AM B-MACEQ
parts E-MACEQ
. O


The O
cost B-CONPRI
estimations E-CONPRI
are O
based O
on O
reviews O
of O
the O
cost O
price O
for O
obtaining O
an O
AM B-MACEQ
part E-MACEQ
through O
commercial O
service O
providers O
and O
focused O
on O
both O
plastic B-MATE
and I-MATE
metallic I-MATE
parts E-MATE
. O


This O
research S-CONPRI
compared O
twenty-one O
AM S-MANP
service O
providers O
worldwide O
and O
found O
that O
the O
main O
cost O
drivers O
for O
this O
scenario O
are O
total O
volume S-CONPRI
of O
the O
order O
, O
packing O
density S-PRO
in O
the O
build B-PARA
envelope E-PARA
and O
the O
number O
of O
parts O
ordered O
. O


It O
seems O
that O
two O
strategies O
are O
applied O
by O
the O
companies S-APPL
; O
group O
A O
and O
B S-MATE
. O


Companies S-APPL
in O
group O
A O
use O
cost B-CONPRI
estimation E-CONPRI
strategies O
where O
part O
cost O
is O
almost O
independent O
of O
the O
number O
of O
parts O
ordered O
. O


These O
companies S-APPL
focus O
on O
optimizing O
the O
utilization O
of O
the O
build B-PARA
volume E-PARA
and O
have O
a O
slightly O
longer O
lead B-PARA
time E-PARA
. O


Companies S-APPL
in O
group O
B S-MATE
estimate O
cost O
for O
each O
order O
separately O
, O
have O
a O
large O
difference O
in O
cost O
per O
cm3 O
for O
order O
sizes O
one O
and O
one-hundred O
, O
but O
have O
a O
slightly O
shorter O
lead B-PARA
time E-PARA
. O


2 O
Post-processing S-CONPRI
can O
add O
considerably O
to O
the O
cost O
of O
AM B-MACEQ
parts E-MACEQ
. O


In O
many O
cost B-CONPRI
models E-CONPRI
only O
the O
costs O
of O
the O
post-processing S-CONPRI
steps O
directly O
related O
to O
the O
AM B-MANP
process E-MANP
are O
considered O
. O


For O
example O
, O
Lindeman O
calculated O
the O
post-processing S-CONPRI
costs O
for O
metal S-MATE
parts O
produced O
by O
L-PBF S-MANP
to O
be S-MATE
between O
4 O
and O
14 O
% O
. O


Simpson O
gives O
a O
more O
generic O
overview O
of O
post-processing S-CONPRI
cost O
for O
metal B-MANP
AM E-MANP
. O


3.4 O
Build S-PARA
job O
considerations O
Build S-PARA
jobs O
are O
usually O
considered O
during O
the O
phase S-CONPRI
of O
process B-CONPRI
planning E-CONPRI
. O


Process B-CONPRI
planning E-CONPRI
is O
one O
of O
the O
most O
important O
activities O
in O
manufacturing S-MANP
planning O
and O
is O
a O
pivotal O
link O
between O
design S-FEAT
and O
manufacturing S-MANP
. O


Compared O
to O
traditional O
processing O
, O
the O
context O
changes O
for O
Additive B-MANP
Manufacturing E-MANP
, O
but O
it O
is O
still O
within O
the O
manufacturing S-MANP
scope O
. O


Although O
AM B-MACEQ
machines E-MACEQ
are O
highly O
integrated O
and O
automatic O
, O
before O
enabling O
the O
building B-CHAR
process E-CHAR
for O
a O
machine S-MACEQ
, O
there O
are O
also O
some O
preparation O
tasks O
that O
should O
be S-MATE
done O
after O
receiving O
a O
design S-FEAT
model O
and O
its O
related O
production S-MANP
requirements O
. O


In O
this O
chain O
, O
optimization S-CONPRI
of O
the O
number O
of O
parts O
and O
their O
relative O
positioning O
in O
2D S-CONPRI
or O
in O
3D S-CONPRI
, O
is O
required O
when O
building O
multiple O
parts O
. O


Support B-FEAT
generation E-FEAT
could O
be S-MATE
achieved O
before O
or O
after O
the O
nesting S-CONPRI
stage O
. O


Layer S-PARA
building O
can O
then O
be S-MATE
normally O
achieved O
by O
slicing S-CONPRI
the O
3D S-CONPRI
set O
of O
nested O
or O
packed O
parts O
with O
their O
support B-FEAT
structures E-FEAT
. O


In O
some O
cases O
this O
stage O
is O
very O
different O
because O
the O
orientation S-CONPRI
of O
the O
part O
during O
the O
process S-CONPRI
changes O
. O


In O
such O
cases O
, O
the O
generation O
of O
the O
material S-MATE
deposition S-CONPRI
trajectory O
has O
to O
be S-MATE
achieved O
by O
taking O
into O
account O
non-planar O
layers O
. O


Alternative O
operations O
of O
adding O
and O
subtracting O
material S-MATE
and O
functions O
are O
sometimes O
considered O
to O
improve O
manufacturing S-MANP
efficiency O
, O
as S-MATE
an O
alternative O
solution S-CONPRI
to O
conventional O
methods O
like O
welding S-MANP
and O
machining S-MANP
. O


This O
approach O
, O
usually O
named O
hybrid B-CONPRI
manufacturing E-CONPRI
, O
needs O
specific O
AM B-MANP
process E-MANP
planning O
solutions O
in O
order O
to O
process S-CONPRI
from O
feature B-FEAT
decomposition E-FEAT
to O
a O
complete O
part O
recomposition O
, O
taking O
into O
account O
sequencing O
aspects O
and O
material S-MATE
excess O
regions O
for O
machining S-MANP
depending O
on O
expected O
dimensional O
and O
surface B-PARA
qualities E-PARA
. O


However O
, O
orientation S-CONPRI
and O
placement O
have O
to O
be S-MATE
validated O
with O
respect O
to O
global O
thermal O
conditions O
of O
manufacturing S-MANP
. O


As S-MATE
material O
and O
geometry S-CONPRI
are O
obtained O
at O
the O
same O
time O
, O
it O
is O
mandatory O
to O
validate O
the O
material S-MATE
quality O
induced O
by O
the O
input O
of O
energy O
during O
the O
material S-MATE
transformation O
and O
the O
consequences O
on O
the O
metallurgical S-APPL
properties O
of O
the O
part O
. O


Consequently O
, O
potential O
deformations S-CONPRI
are O
also O
calculated O
and O
some O
modifications O
of O
strategy O
are O
also O
possible O
in O
order O
to O
compromise O
between O
production S-MANP
performance B-CONPRI
parameters E-CONPRI
and O
part O
material B-CONPRI
properties E-CONPRI
. O


Some O
simulation S-ENAT
tools O
exist O
starting O
from O
the O
nested O
or O
packed O
global O
model S-CONPRI
integrating O
support B-FEAT
structures E-FEAT
. O


For O
some O
specific O
applications O
, O
process B-CONPRI
planning E-CONPRI
for O
AM S-MANP
may O
also O
generate O
assembly S-MANP
instructions O
. O


This O
occurs O
when O
a O
part O
's O
size O
exceeds O
the O
build B-PARA
volume E-PARA
of O
a O
machine S-MACEQ
and O
it O
can O
be S-MATE
decomposed O
into O
several O
small O
sections O
to O
be S-MATE
made O
separately O
. O


3.5 O
AM B-MANP
process E-MANP
constraints O
Like O
with O
all O
technologies S-CONPRI
, O
there O
are O
many O
constraints O
to O
AM S-MANP
. O


This O
section O
will O
focus O
on O
four O
primary O
constraints O
that O
are O
common O
to O
all O
AM B-MANP
process E-MANP
categories O
and O
particularly O
relevant O
to O
the O
AM S-MANP
of O
metals S-MATE
: O
Speed O
of O
build S-PARA
, O
materials S-CONPRI
, O
build B-PARA
envelope E-PARA
, O
and O
accuracy S-CHAR
. O


Although O
AM S-MANP
used O
to O
be S-MATE
called O
Rapid B-ENAT
Prototyping E-ENAT
, O
one O
is O
now O
quite O
accustomed O
to O
having O
prototypes S-CONPRI
built O
quickly O
, O
but O
this O
is O
difficult O
to O
scale O
up O
. O


Furthermore O
, O
there O
is O
increasing O
demand O
for O
AM S-MANP
to O
be S-MATE
used O
in O
mainstream O
production S-MANP
, O
which O
requires O
much O
faster O
throughput S-CHAR
. O


AM S-MANP
has O
the O
benefits O
of O
geometric B-CONPRI
freedom E-CONPRI
, O
no O
minimum O
batch O
constraint O
and O
rapid O
change O
between O
batches O
, O
which O
meets O
many O
of O
the O
demands O
of O
modern O
manufacturing S-MANP
industry S-APPL
. O


The O
hunt O
is O
therefore O
on O
for O
faster O
AM B-MANP
technology E-MANP
. O


Many O
metal B-MANP
AM E-MANP
systems O
use O
lasers O
due O
to O
the O
demand O
for O
large O
amounts O
of O
focussed O
energy O
. O


The O
ideal O
situation O
would O
be S-MATE
to O
provide O
the O
required O
energy O
over O
an O
entire O
layer S-PARA
simultaneously O
but O
so O
far O
this O
has O
not O
been O
demonstrated O
to O
be S-MATE
possible O
. O


A O
compromise O
is O
the O
supply O
of O
multiple O
laser B-CONPRI
beams E-CONPRI
controlled O
simultaneously O
. O


Different O
lasers O
can O
be S-MATE
used O
to O
process S-CONPRI
different O
regions O
with O
finer B-CHAR
spots E-CHAR
being O
used O
for O
more O
detailed O
parts O
and O
wider O
beams O
to O
process S-CONPRI
bulk B-FEAT
regions E-FEAT
. O


Careful O
attention O
must O
be S-MATE
given O
to O
beam B-PARA
control E-PARA
so O
that O
they O
do O
n't O
affect O
each O
other O
, O
including O
the O
vapour O
trails O
from O
the O
molten B-MATE
metal E-MATE
regions O
. O


A O
contrasting O
approach O
to O
increasing O
throughput S-CHAR
for O
batch B-CONPRI
production E-CONPRI
of O
metal S-MATE
parts O
is O
the O
use O
of O
binder B-MANP
jetting I-MANP
methods E-MANP
or O
material B-MANP
extrusion E-MANP
with O
metal-filled O
binder S-MATE
materials O
. O


Such O
methods O
can O
achieve O
faster O
AM S-MANP
throughput O
and O
can O
be S-MATE
more O
easily O
scaled O
to O
create O
larger O
parts O
. O


The O
downsides O
relate O
to O
increases O
in O
post-processing S-CONPRI
times O
during O
heat B-MANP
treatment E-MANP
and O
during O
machine S-MACEQ
finishing S-MANP
, O
if O
required O
. O


These O
requirements O
are O
also O
driving O
the O
development O
of O
open-architecture O
, O
robot-based O
metal B-MANP
AM E-MANP
systems O
, O
like O
Wire O
Arc S-CONPRI
AM S-MANP
and O
Laser B-MANP
Metal I-MANP
Deposition E-MANP
. O


There O
is O
a O
huge O
and O
increasing O
number O
of O
metals S-MATE
and O
other O
materials S-CONPRI
used O
to O
make O
products O
. O


Most O
of O
these O
metals S-MATE
are O
carefully O
chosen O
to O
suit O
product O
requirements O
in O
strength S-PRO
, O
chemical B-PRO
resistance E-PRO
, O
thermal B-CONPRI
properties E-CONPRI
, O
processability O
, O
cost O
, O
etc O
. O


In O
comparison O
, O
there O
are O
a O
very O
few O
materials S-CONPRI
available O
in O
AM S-MANP
. O


All O
AM B-MANP
processes E-MANP
are O
suited O
to O
a O
subset O
of O
materials S-CONPRI
, O
the O
requirements O
for O
which O
can O
be S-MATE
very O
specific O
, O
like O
the O
need O
for O
photo-curable B-MATE
resins E-MATE
. O


Many O
materials S-CONPRI
can O
be S-MATE
formed O
by O
AM S-MANP
using O
thermal B-CONPRI
energy E-CONPRI
, O
but O
the O
amounts O
of O
energy O
vary O
considerably O
. O


It O
is O
not O
easy O
to O
melt S-CONPRI
metals O
in O
an O
AM B-MANP
process E-MANP
chamber O
specifically O
built O
for O
polymers S-MATE
for O
example O
. O


In O
addition O
, O
raw B-MATE
materials E-MATE
often O
need O
to O
be S-MATE
presented O
with O
well-defined O
morphology S-CONPRI
, O
like O
in O
filament S-MATE
or O
carefully-graded O
powder S-MATE
distributions S-CONPRI
. O


However O
, O
even O
within O
a O
smaller O
range S-PARA
of O
materials S-CONPRI
the O
processing O
requirements O
can O
still O
be S-MATE
difficult O
to O
specify O
. O


Metals S-MATE
within O
L-PBF B-MACEQ
systems E-MACEQ
for O
example O
will O
absorb O
laser B-CONPRI
energy E-CONPRI
in O
different O
proportions O
. O


The O
physics S-CONPRI
around O
phase S-CONPRI
change O
behaviour O
and O
effects O
in O
the O
molten O
state O
can O
all O
be S-MATE
quite O
different O
, O
significantly O
affecting O
the O
final O
material S-MATE
microstructure O
. O


Furthermore O
, O
much O
of O
this O
is O
significantly O
different O
from O
other O
manufacturing B-MANP
processes E-MANP
like O
casting S-MANP
and O
forging S-MANP
. O


All O
these O
need O
to O
be S-MATE
carefully O
studied O
before O
AM B-MATE
materials E-MATE
can O
be S-MATE
released O
to O
the O
market O
. O


As S-MATE
, O
AM S-MANP
becomes O
more O
widespread O
, O
one O
can O
expect O
more O
materials S-CONPRI
to O
become O
available O
but O
it O
is O
widely O
accepted O
that O
range S-PARA
of O
materials S-CONPRI
needs O
to O
be S-MATE
increased O
. O


Having O
said O
that O
, O
current O
AM B-MATE
materials E-MATE
like O
Ti-6Al-4V S-MATE
, O
316 O
stainless B-MATE
steel E-MATE
and O
CoCr B-MATE
alloys E-MATE
, O
etc O
. O


Many O
products O
are O
made O
from O
metals S-MATE
because O
of O
the O
needs O
for O
strength S-PRO
and O
accuracy S-CHAR
. O


In O
AM S-MANP
, O
part O
strength S-PRO
is O
often O
acceptable O
but O
part O
accuracy S-CHAR
is O
very O
often O
not O
. O


Metal S-MATE
parts O
are O
often O
mated O
with O
others O
and O
so O
the O
joining S-MANP
surfaces O
must O
align O
with O
each O
other O
. O


Most O
metal B-MANP
AM E-MANP
processes O
create O
parts O
with O
poor O
surface B-FEAT
finish E-FEAT
, O
usually O
no O
better O
than O
15 O
Rz O
and O
very O
often O
considerably O
worse O
. O


Machine S-MACEQ
finishing S-MANP
is O
therefore O
a O
common O
requirement O
as S-MATE
a O
post-process S-CONPRI
. O


Thermally O
induced O
distortion S-CONPRI
due O
to O
large O
temperature B-PARA
gradients E-PARA
during O
builds S-CHAR
and O
corresponding O
residual B-PRO
stresses E-PRO
is O
also O
a O
common O
phenomenon O
for O
metal B-MANP
AM E-MANP
. O


Features O
may O
therefore O
be S-MATE
imprecisely O
located O
and O
it O
may O
be S-MATE
better O
to O
provide O
a O
machining B-PARA
allowance E-PARA
in O
the O
initial O
AM B-MACEQ
part E-MACEQ
design O
. O


The O
introduction O
of O
hybrid O
machines S-MACEQ
that O
combine O
AM S-MANP
with O
subtractive S-MANP
and O
other O
manufacturing B-MANP
processes E-MANP
that O
operate O
in O
a O
sequential O
manner O
aim O
to O
overcome O
issues O
around O
part O
accuracy S-CHAR
. O


This O
is O
particularly O
useful O
where O
the O
requirement O
is O
internal O
to O
the O
part O
geometry S-CONPRI
and O
difficult O
to O
achieve O
as S-MATE
a O
post-process S-CONPRI
. O


3.6 O
AM S-MANP
post-processing O
constraints O
For O
much O
of O
the O
time O
that O
AM B-MANP
technology E-MANP
has O
been O
under O
development O
, O
post-processing S-CONPRI
has O
been O
something O
that O
you O
would O
rather O
not O
do O
and O
eliminate O
if O
possible O
. O


AM S-MANP
is O
now O
considered O
as S-MATE
something O
that O
can O
shorten O
process B-ENAT
chains E-ENAT
, O
not O
eliminate O
them O
entirely O
. O


Sometimes O
it O
may O
be S-MATE
appropriate O
to O
include O
a O
design S-FEAT
feature O
in O
the O
post-process S-CONPRI
rather O
than O
in O
the O
AM S-MANP
build O
itself O
. O


Post-processing S-CONPRI
tasks O
can O
be S-MATE
broadly O
divided O
in O
terms O
of O
those O
that O
can O
require O
significant O
manual O
intervention O
and O
those O
that O
can O
be S-MATE
carried O
out O
in O
a O
largely O
automated O
fashion S-CONPRI
. O


Of O
course O
this O
depends O
on O
the O
available O
technology S-CONPRI
to O
achieve O
these O
tasks O
as S-MATE
well O
as S-MATE
the O
level O
of O
investment O
, O
quality S-CONPRI
issues O
, O
volume S-CONPRI
of O
production S-MANP
, O
etc O
. O


Post-processing S-CONPRI
can O
also O
be S-MATE
considered O
in O
terms O
of O
those O
that O
need O
to O
be S-MATE
carried O
out O
due O
to O
the O
characteristics O
of O
the O
AM B-MANP
process E-MANP
used O
and O
those O
that O
are O
more O
aimed O
at O
enhancement O
of O
the O
AM B-MACEQ
parts E-MACEQ
. O


Like O
with O
the O
previous O
classification S-CONPRI
, O
there O
are O
overlaps O
or O
grey O
areas S-PARA
, O
around O
where O
exactly O
surface B-FEAT
finish E-FEAT
fits S-CONPRI
for O
example O
. O


This O
can O
also O
form O
part O
of O
the O
decision O
making O
in O
the O
process S-CONPRI
design S-FEAT
The O
AM B-MANP
technology E-MANP
specific O
processes S-CONPRI
mainly O
refer O
to O
the O
chosen O
build S-PARA
process O
and O
are O
aimed O
at O
providing O
a O
consistent O
quality S-CONPRI
of O
output O
suited O
to O
the O
general O
application O
. O


Many O
processes S-CONPRI
use O
support B-FEAT
structures E-FEAT
which O
have O
to O
be S-MATE
removed O
somehow O
, O
often O
requiring O
further O
finishing S-MANP
of O
regions O
where O
the O
supports S-APPL
connected O
with O
the O
part O
. O


Build B-CONPRI
strategies E-CONPRI
often O
revolve O
around O
minimising O
the O
amount O
of O
supports S-APPL
or O
avoiding O
key O
surfaces S-CONPRI
for O
aesthetic S-CONPRI
or O
accuracy S-CHAR
reasons O
. O


For O
many O
machines S-MACEQ
, O
flat O
and O
curved B-CONPRI
surfaces E-CONPRI
can O
appear O
different O
due O
to O
the O
stair-stepping O
phenomena O
. O


Abrasive S-MATE
or O
chemical O
finishing S-MANP
can O
be S-MATE
used O
to O
make O
these O
surfaces S-CONPRI
appear O
more O
uniform O
. O


A O
further O
post-processing S-CONPRI
task O
can O
revolve O
around O
excess O
material S-MATE
that O
may O
be S-MATE
adhering O
to O
the O
part O
surfaces S-CONPRI
. O


This O
may O
be S-MATE
a O
surrounding O
material S-MATE
that O
protects O
these O
surfaces S-CONPRI
or O
they O
may O
be S-MATE
residual O
material S-MATE
due O
to O
inconsistencies O
in O
the O
process S-CONPRI
, O
similar O
to O
flash S-MATE
in O
moulding S-CONPRI
operations O
. O


Although O
specific O
to O
powder-based O
AM B-MANP
technology E-MANP
, O
pore-filling O
and O
densification S-MANP
can O
also O
be S-MATE
application O
specific O
in O
terms O
of O
the O
material S-MATE
chosen O
to O
create O
a O
fully B-PARA
dense E-PARA
part O
. O


Densification S-MANP
can O
also O
be S-MATE
in O
the O
form O
of O
a O
furnace S-MACEQ
cycle O
, O
perhaps O
using O
hot B-MANP
isostatic I-MANP
pressing E-MANP
. O


Since O
some O
processes S-CONPRI
can O
be S-MATE
slightly O
heterogeneous S-CONPRI
in O
nature O
, O
accounting O
for O
shrinkage S-CONPRI
may O
require O
careful O
preparation O
and O
difficult O
to O
precisely O
control O
. O


Metal B-MANP
AM E-MANP
parts O
in O
particular O
are O
commonly O
used O
as S-MATE
fully O
functional O
parts O
. O


Choice O
of O
metal S-MATE
as S-MATE
a O
part O
material S-MATE
often O
relates O
to O
part O
strength S-PRO
and O
while O
precision S-CHAR
can O
represent O
a O
problem O
. O


Finish B-MANP
machining E-MANP
of O
key O
surfaces S-CONPRI
is O
often O
required O
, O
much O
in O
the O
same O
way O
as S-MATE
we O
would O
treat O
a O
casting S-MANP
. O


In O
these O
specific O
regions O
it O
may O
be S-MATE
appropriate O
to O
grow O
some O
of O
these O
surfaces S-CONPRI
in O
the O
design S-FEAT
phase O
to O
provide O
sufficient O
machining B-PARA
allowance E-PARA
to O
ensure O
high O
quality S-CONPRI
, O
accurate S-CHAR
results O
. O


It O
can O
be S-MATE
argued O
that O
there O
will O
be S-MATE
fewer O
of O
these O
surfaces S-CONPRI
to O
finish O
since O
it O
is O
common O
thinking O
that O
AM S-MANP
allows O
for O
part B-CONPRI
consolidation E-CONPRI
due O
to O
the O
ability O
to O
create O
internalised O
features O
. O


Although O
it O
is O
quite O
possible O
to O
print S-MANP
features O
like O
holes O
and O
screw-threads O
using O
AM S-MANP
, O
the O
precision S-CHAR
demands O
on O
such O
features O
can O
be S-MATE
very O
stringent O
and O
beyond O
the O
capacity S-CONPRI
of O
the O
AM B-MANP
technology E-MANP
used O
. O


It O
may O
be S-MATE
possible O
to O
save O
material S-MATE
by O
printing O
a O
hole O
but O
the O
time O
taken O
to O
finish O
a O
partially-made O
hole O
may O
be S-MATE
the O
same O
, O
or O
even O
longer O
, O
than O
to O
drill S-MACEQ
a O
complete O
hole O
in O
a O
blank S-MATE
space O
. O


This O
may O
be S-MATE
even O
more O
relevant O
if O
the O
hole O
contained O
a O
screw B-FEAT
thread E-FEAT
. O


Again O
, O
it O
can O
be S-MATE
argued O
that O
this O
adds O
complexity S-CONPRI
to O
the O
process S-CONPRI
decision-making O
, O
but O
it O
is O
pertinent O
when O
relating O
to O
heavily O
industrial S-APPL
applications O
. O


Coatings S-APPL
can O
go S-MATE
from O
simple S-MANP
paint O
jobs O
to O
improve O
aesthetics O
and O
seal O
against O
corrosive S-PRO
atmospheres O
through O
to O
providing O
significant O
functional O
properties S-CONPRI
, O
including O
bioactive B-CONPRI
features E-CONPRI
. O


These O
tasks O
may O
require O
significantly O
specialised O
facilities O
to O
those O
used O
in O
other O
production S-MANP
steps O
and O
as S-MATE
such O
may O
be S-MATE
outsourced O
. O


This O
could O
also O
be S-MATE
the O
case O
with O
other O
forms O
of O
chemical O
and O
heat B-MANP
treatment E-MANP
. O


Many O
AM B-MACEQ
parts E-MACEQ
can O
include O
complex O
internal O
or O
difficult O
to O
reach O
features O
. O


Should O
these O
features O
require O
finishing S-MANP
, O
it O
may O
be S-MATE
somewhat O
difficult O
to O
achieve O
a O
stable O
quality S-CONPRI
, O
even O
when O
using O
automated O
techniques O
. O


Some O
methods O
are O
under O
development O
to O
address O
these O
issues O
but O
more O
effort O
could O
be S-MATE
made O
and O
in O
fact O
most O
methods O
for O
surface B-MANP
finishing E-MANP
are O
highly O
manual O
in O
nature O
. O


3.7 O
AM S-MANP
quality O
, O
inspection S-CHAR
and O
certification O
Many O
AM S-MANP
applications O
can O
be S-MATE
found O
in O
highly O
regulated O
industries S-APPL
, O
like O
aerospace S-APPL
and O
medicine S-CONPRI
. O


This O
is O
even O
the O
case O
within O
the O
medical B-APPL
industry E-APPL
where O
one O
might O
expect O
such O
parts O
to O
be S-MATE
customised O
to O
suit O
a O
patient O
's O
needs O
and O
anatomy O
. O


Quality B-CONPRI
control E-CONPRI
, O
inspection S-CHAR
and O
certification O
would O
therefore O
be S-MATE
conducted O
in O
a O
similar O
fashion S-CONPRI
to O
conventionally O
manufactured S-CONPRI
parts O
. O


Validation S-CONPRI
in O
these O
cases O
is O
as S-MATE
much O
about O
ensuring O
consistency S-CONPRI
in O
the O
manufacturing B-MANP
process E-MANP
and O
traceability O
of O
the O
supply B-CONPRI
chain E-CONPRI
as S-MATE
it O
is O
about O
the O
functionality O
of O
the O
part O
. O


The O
US O
Federal O
Food O
and O
Drug O
Administration O
is O
widely O
regarded O
as S-MATE
a O
key O
standards S-CONPRI
organisation O
around O
the O
world O
and O
many O
other O
countries O
base O
their O
own O
medical S-APPL
standards O
on O
the O
FDA S-MANS
. O


In O
2017 O
the O
FDA S-MANS
published O
guidelines O
related O
to O
technical O
use O
of O
AM S-MANP
in O
medical B-APPL
devices E-APPL
. O


These O
guidelines O
cover O
aspects O
related O
to O
AM-based O
design S-FEAT
of O
medical B-APPL
devices E-APPL
as S-MATE
well O
as S-MATE
how O
they O
are O
manufactured S-CONPRI
and O
validated O
. O


Certification O
of O
medical B-APPL
devices E-APPL
is O
required O
if O
there O
is O
a O
medium O
to O
high O
risk O
potential O
to O
the O
user O
. O


All O
implantable B-MACEQ
devices E-MACEQ
would O
be S-MATE
Class O
II O
or O
Class O
III O
, O
whilst O
AM S-MANP
produced O
foot B-MACEQ
orthotics E-MACEQ
are O
class O
I O
, O
requiring O
no O
premarket O
notification O
to O
prove O
they O
have O
been O
clinically O
tested O
certification O
) O
. O


The O
medical B-APPL
device E-APPL
manufacturer S-CONPRI
Stryker O
released O
their O
Spine O
Tritanium O
PL B-MATE
Cage E-MATE
around O
2016 O
. O


AM S-MANP
is O
used O
to O
create O
a O
complex O
porous S-PRO
geometry S-CONPRI
of O
titanium S-MATE
that O
aims O
to O
promote O
bone B-CONPRI
ingrowth E-CONPRI
in O
a O
lumbar B-CONPRI
spine I-CONPRI
fusion I-CONPRI
process E-CONPRI
. O


It O
is O
possible O
that O
introduction O
of O
this O
device O
may O
have O
been O
premature O
as S-MATE
it O
is O
believed O
that O
more O
experimental S-CONPRI
work O
is O
needed O
to O
establish O
the O
boundaries S-FEAT
for O
fatigue S-PRO
in O
AM S-MANP
lattice O
structures O
. O


It O
should O
be S-MATE
noted O
that O
similar O
porous S-PRO
and O
irregular O
lattice B-FEAT
structures E-FEAT
have O
been O
used O
in O
100,000s O
of O
successful O
acetabular O
hip B-APPL
implant E-APPL
cases O
. O


This O
issue O
of O
possible O
failure S-CONPRI
will O
be S-MATE
even O
more O
important O
should O
the O
device O
have O
a O
customisable O
geometry S-CONPRI
. O


The O
FDA S-MANS
refers O
to O
these O
as S-MATE
Customised O
or O
Humanitarian-use O
devices O
. O


These O
must O
also O
be S-MATE
limited O
in O
number O
and O
subject O
to O
significant O
medical S-APPL
board O
scrutiny O
. O


Medical S-APPL
authorities O
are O
currently O
at O
a O
significant O
cross-road O
as S-MATE
to O
how O
to O
provide O
custom B-APPL
implants E-APPL
for O
more O
widespread O
use O
. O


Aerospace S-APPL
certification O
, O
through O
the O
Federal O
Aviation O
Authority O
, O
also O
appears O
to O
be S-MATE
at O
a O
similar O
cross-road O
. O


However O
, O
it O
is O
noted O
that O
many O
parts O
already O
in O
use O
could O
be S-MATE
repaired O
when O
damaged O
using O
AM B-MANP
techniques E-MANP
, O
most O
specifically O
using O
Directed B-MANP
Energy I-MANP
Deposition E-MANP
. O


Many O
safety S-CONPRI
critical O
parts O
, O
like O
turbine B-APPL
blades E-APPL
, O
could O
be S-MATE
repaired O
in O
this O
way O
. O


Emphasis O
must O
therefore O
be S-MATE
on O
the O
AM B-MANP
process E-MANP
to O
ensure O
that O
functionality O
is O
maintained O
to O
a O
suitable O
standard S-CONPRI
. O


For O
example O
Air O
New O
Zealand O
are O
saving O
significant O
repair B-PARA
costs E-PARA
by O
making O
their O
own O
replacement O
seat O
tray-tables O
using O
materials S-CONPRI
like O
the O
flame-retardant O
ULTEM O
9085 O
polymer B-MATE
material E-MATE
from O
Stratasys S-APPL
. O


This O
is O
just O
part O
of O
a O
much O
wider O
push O
to O
demonstrate O
a O
sustainable S-CONPRI
industry S-APPL
for O
AM S-MANP
in O
aerospace S-APPL
. O


Many O
of O
the O
above O
issues O
for O
medical S-APPL
and O
aerospace S-APPL
are O
reflected O
in O
a O
more O
general O
form O
within O
the O
standards S-CONPRI
under O
development O
by O
ISO S-MANS
Technical O
Committee O
261 O
in O
conjunction O
with O
the O
ASTM O
F42 O
Group O
. O


Numerous O
techniques O
, O
like O
the O
printing O
of O
test O
coupons O
alongside O
critical O
components S-MACEQ
, O
machine B-PARA
calibration E-PARA
and O
material S-MATE
storage O
, O
etc O
. O


This O
has O
led S-APPL
to O
significant O
improvements O
in O
process B-CONPRI
monitoring E-CONPRI
within O
industrial S-APPL
scale O
AM B-MACEQ
machines E-MACEQ
. O


Many O
polymer-based O
systems O
have O
camera S-MACEQ
monitoring O
that O
allow O
determining O
the O
build B-PARA
status E-PARA
and O
remote O
intervention O
if O
problems O
can O
be S-MATE
seen O
. O


Many O
metal S-MATE
L-PBF B-MACEQ
systems E-MACEQ
also O
have O
optional O
laser B-PARA
power E-PARA
and O
melt-pool O
sensing S-APPL
to O
determine O
the O
state O
of O
part O
with O
the O
possibility O
of O
detecting O
a O
failure S-CONPRI
before O
it O
damages O
the O
machine S-MACEQ
. O


4 O
Tools S-MACEQ
and O
methods O
for O
designing O
lightweight S-CONPRI
parts O
Lightweight S-CONPRI
design S-FEAT
always O
has O
been O
a O
hot O
topic O
in O
structural B-CONPRI
engineering E-CONPRI
. O


AM B-MANP
processes E-MANP
can O
produce O
highly O
complex B-CONPRI
structures E-CONPRI
, O
constructed O
using O
both O
internally O
and O
externally O
very O
complex O
surfaces S-CONPRI
. O


More O
importantly O
, O
there O
is O
no O
clear O
relationship O
between O
the O
complexity S-CONPRI
of O
the O
part O
and O
the O
associated O
production B-CONPRI
cost E-CONPRI
, O
providing O
more O
freedom O
to O
explore O
the O
design B-CONPRI
space E-CONPRI
to O
its O
full O
extent O
. O


As S-MATE
a O
result O
, O
not O
only O
conventional O
lightweighting S-PRO
design S-FEAT
tools O
are O
used O
for O
AM S-MANP
, O
but O
also O
some O
new O
methods O
have O
emerged O
to O
fully O
grasp O
the O
benefits O
of O
AM S-MANP
. O


In O
relation O
to O
lightweight S-CONPRI
design S-FEAT
for O
AM S-MANP
, O
four O
groups O
of O
methods O
and O
tools S-MACEQ
can O
be S-MATE
identified O
: O
topology B-FEAT
optimization E-FEAT
, O
generative B-ENAT
design E-ENAT
, O
lattice B-FEAT
structure E-FEAT
filling O
, O
and O
bio-inspired B-FEAT
design E-FEAT
. O


4.1 O
Topology B-FEAT
optimization E-FEAT
Topology S-CONPRI
optimization S-CONPRI
was O
originally O
used O
for O
mechanical S-APPL
design S-FEAT
problems O
to O
answer O
a O
layout S-CONPRI
optimization O
question O
: O
how O
to O
put O
the O
right O
material S-MATE
in O
the O
right O
place O
of O
a O
pre-defined O
design B-CONPRI
space E-CONPRI
? O
The O
objective O
was O
to O
obtain O
the O
expected O
mechanical B-CONPRI
properties E-CONPRI
at O
minimum O
material S-MATE
use O
. O


The O
method O
uses O
numerical O
analysis O
and O
design S-FEAT
solution O
update O
steps O
in O
an O
iterative O
way O
, O
mostly O
guided O
by O
gradient O
computation S-CONPRI
or O
non-gradient B-CONPRI
discrete I-CONPRI
approaches E-CONPRI
. O


Traditionally O
, O
TO O
is O
driven O
by O
an O
objective O
function O
, O
minimizing O
or O
maximizing O
while O
being O
subjected O
to O
a O
set S-APPL
of O
predefined O
constraints O
, O
such O
as S-MATE
mass O
, O
deformation S-CONPRI
, O
vibration B-PARA
frequency E-PARA
, O
etc O
. O


Usually O
, O
continuous B-CONPRI
design I-CONPRI
variables E-CONPRI
are O
used O
to O
solve O
the O
TO O
problem O
in O
a O
discretized O
way O
. O


During O
this O
optimization S-CONPRI
iteration O
process S-CONPRI
, O
segments O
of O
the O
predefined O
initial O
design B-CONPRI
space E-CONPRI
are O
step S-CONPRI
by O
step S-CONPRI
removed O
so O
as S-MATE
to O
arrive O
at O
the O
minimal O
part O
volume/mass O
. O


Initial O
methods O
developed O
remove O
materials S-CONPRI
bit O
by O
bit O
using O
a O
strain S-PRO
energy O
distribution S-CONPRI
and O
a O
preset O
threshold O
value O
. O


More O
advanced O
methods O
use O
genetic B-CONPRI
algorithms E-CONPRI
that O
both O
add O
and O
remove O
materials S-CONPRI
. O


porous S-PRO
structures O
and O
lattice B-FEAT
structures E-FEAT
, O
but O
with O
relaxed O
mathematical S-CONPRI
constraints O
. O


As S-MATE
stated O
in O
, O
even O
current O
pure O
TO O
studies O
still O
face S-CONPRI
problems O
, O
such O
as S-MATE
efficiency O
, O
general O
applicability O
, O
ease O
of O
use O
, O
etc O
. O


Many O
of O
them O
only O
use O
relatively O
simple S-MANP
boundary B-CONPRI
conditions E-CONPRI
with O
limited O
constraints O
, O
e.g O
. O


When O
introducing O
extra O
AM S-MANP
related O
constraints O
such O
as S-MATE
support O
structures/overhangs O
, O
minimum O
printable O
features O
, O
anisotropic B-PRO
material I-PRO
properties E-PRO
, O
heat-transfer O
, O
thermal O
strain/stress O
into O
TO O
, O
this O
would O
result O
in O
more O
complex O
constraints O
or O
boundary B-CONPRI
conditions E-CONPRI
. O


This O
again O
would O
result O
in O
more O
difficulties O
for O
the O
TO O
process S-CONPRI
to O
find O
the O
solutionwith O
an O
effective O
and O
fast O
converging O
simulation S-ENAT
process S-CONPRI
. O


Attracted O
by O
the O
great O
potential O
of O
AM S-MANP
, O
researchers O
investigated O
TO O
with O
AM S-MANP
constraints O
, O
focussing O
on O
generating O
an O
optimal O
topologically B-CONPRI
lightweight E-CONPRI
material S-MATE
layout S-CONPRI
, O
to O
be S-MATE
printed O
without O
any O
manufacturing S-MANP
problems O
. O


Therefore O
, O
recent O
researches O
on O
TO O
for O
DfAM O
are O
geared O
towards O
print-ready O
designs S-FEAT
bridging S-CONPRI
challenges O
in O
design S-FEAT
and O
printing O
. O


One O
is O
to O
represent O
AM S-MANP
constraints O
with O
mathematical S-CONPRI
models O
and O
embed O
them O
into O
the O
TO O
iteration O
process S-CONPRI
. O


The O
other O
is O
to O
use O
TO O
to O
generate O
one O
or O
a O
set S-APPL
of O
finite O
reference O
design S-FEAT
solutions O
and O
apply O
design B-CONPRI
rules E-CONPRI
or O
experience O
to O
adapt O
these O
solutions O
manually O
or O
automatically O
to O
the O
AM S-MANP
constraints O
. O


This O
last O
category O
thus O
applies O
AM S-MANP
constraints O
in O
the O
post-processing S-CONPRI
stage O
of O
a O
given O
TO O
result O
. O


For O
ease O
of O
practice O
, O
most O
of O
the O
earliest O
works O
directly O
tried O
to O
use O
existing O
traditional O
TO O
, O
or O
other O
similar O
structure B-CONPRI
optimization E-CONPRI
methods O
, O
for O
lightweight S-CONPRI
design S-FEAT
in O
DfAM O
, O
without O
considering O
any O
AM S-MANP
constraints O
. O


The O
main O
reason O
for O
this O
was O
the O
assumption O
that O
AM S-MANP
can O
overcome O
manufacturing S-MANP
problems O
of O
TO O
generated O
structure S-CONPRI
as S-MATE
these O
structures O
would O
encounter O
in O
conventional B-MANP
manufacturing E-MANP
processes O
. O


Although O
the O
2D S-CONPRI
or O
3D S-CONPRI
TO O
produced O
structures O
could O
be S-MATE
printed O
by O
polymer S-MATE
AM B-MANP
processes E-MANP
, O
the O
direct O
application O
of O
the O
existing O
non-tailored O
TO O
may O
have O
difficulty O
using O
metallic B-MANP
AM E-MANP
. O


This O
is O
more O
complicated O
due O
to O
the O
multi-physical O
phenomena O
which O
can O
not O
be S-MATE
handled O
by O
relatively O
simple S-MANP
macro S-FEAT
mechanic O
and O
geometric O
based O
calculations O
. O


A O
large O
number O
of O
researchers O
began O
to O
associate O
specific O
AM S-MANP
constraints O
with O
their O
TO O
process S-CONPRI
, O
either O
as S-MATE
a O
TO O
process S-CONPRI
driver O
or O
a O
TO O
post-processor O
. O


However O
, O
their O
efforts O
are O
mainly O
focusing O
at O
2D S-CONPRI
problems O
with O
consideration O
of O
only O
one O
simple S-MANP
or O
limited O
subset O
of O
AM S-MANP
constraints O
, O
e.g O
. O


support S-APPL
volume O
or O
overhang B-PARA
area E-PARA
. O


For O
example O
Leary O
, O
describes O
a O
variant O
where O
traditional O
TO O
is O
conducted O
and O
a O
boundary B-CONPRI
decomposition I-CONPRI
algorithm E-CONPRI
is O
applied O
to O
detect O
and O
decompose O
the O
internal O
or O
external O
boundary S-FEAT
areas S-PARA
needing O
support B-FEAT
structures E-FEAT
. O


Then O
, O
the O
detected O
and O
decomposed O
relatively O
large O
cavities O
are O
filled O
with O
a O
set S-APPL
of O
smaller O
generated O
boundaries S-FEAT
so O
as S-MATE
to O
avoid O
the O
appearance O
of O
overhang S-PARA
as S-MATE
shown O
in O
7 O
. O


In O
that O
example O
even O
though O
a O
sophisticated O
decomposition S-PRO
algorithm S-CONPRI
was O
designed S-FEAT
and O
the O
use O
of O
support B-FEAT
structure E-FEAT
in O
printing O
was O
mostly O
avoided O
, O
the O
result O
is O
still O
far O
from O
optimal O
. O


2D S-CONPRI
results O
sometimes O
are O
quite O
useless O
in O
practice O
since O
the O
broadened O
design B-CONPRI
freedom E-CONPRI
exists O
in O
3D S-CONPRI
, O
not O
2D S-CONPRI
. O


Taking O
the O
TO O
example O
in O
7 O
, O
we O
can O
easily O
rotate O
the O
2D S-CONPRI
result O
around O
the O
X-axis O
in O
the O
3D S-CONPRI
and O
then O
we O
will O
find O
that O
there O
is O
no O
need O
of O
support B-FEAT
structures E-FEAT
. O


This O
means O
all O
the O
optimization S-CONPRI
steps O
are O
useless O
if O
we O
simply O
change O
the O
build B-PARA
orientation E-PARA
. O


The O
dilemma O
may O
be S-MATE
caused O
by O
two O
factors O
: O
the O
TO O
researcher O
has O
a O
lack O
of O
knowledge O
on O
the O
AM B-MANP
processes E-MANP
or O
the O
direct O
embedding O
of O
AM S-MANP
constraints O
with O
mathematical S-CONPRI
models O
in O
the O
2D S-CONPRI
or O
3D S-CONPRI
TO O
processes S-CONPRI
is O
quite O
tough O
. O


Readers O
may O
find O
more O
representative O
research S-CONPRI
on O
2D S-CONPRI
TO O
for O
AM S-MANP
lightweight O
design S-FEAT
in O
. O


To O
extend O
beyond O
2D S-CONPRI
, O
researchers O
adopted O
the O
decomposition S-PRO
method O
as S-MATE
proposed O
in O
and O
tried O
to O
extend O
it O
to O
3D S-CONPRI
TO O
for O
AM S-MANP
. O


However O
, O
like O
the O
2D S-CONPRI
cases O
presented O
above O
, O
reducing O
support B-FEAT
structures E-FEAT
is O
based O
on O
the O
compromise O
of O
adding O
more O
volume S-CONPRI
in O
the O
structure S-CONPRI
itself O
, O
which O
will O
decrease O
the O
global O
optimality O
. O


In O
addition O
, O
it O
is O
still O
not O
a O
real O
3D S-CONPRI
TO O
for O
AM S-MANP
design O
since O
the O
decomposition S-PRO
and O
overhang B-PARA
angle E-PARA
control O
with O
volume S-CONPRI
filling O
still O
uses O
2D B-PARA
operations E-PARA
. O


`For O
these O
investigations O
discussed O
above O
, O
the O
2D S-CONPRI
TO O
process S-CONPRI
is O
relatively O
easy O
to O
realize O
when O
only O
considering O
overhang S-PARA
or O
support B-FEAT
structure E-FEAT
AM S-MANP
constraint O
. O


However O
, O
complexity S-CONPRI
in O
AM S-MANP
is O
generally O
manifested O
in O
3D S-CONPRI
. O


Hence O
, O
a O
lot O
of O
recent O
research S-CONPRI
is O
directed O
towards O
the O
development O
of O
tailored O
3D S-CONPRI
TO O
methods O
for O
AM S-MANP
design O
. O


As S-MATE
is O
the O
case O
with O
the O
2D S-CONPRI
variants O
, O
these O
3D S-CONPRI
TO O
practices O
mainly O
focus O
on O
how O
to O
minimize O
overhang B-PARA
area E-PARA
or O
support S-APPL
volumes O
, O
as S-MATE
these O
constraints O
are O
relatively O
easy O
to O
integrate O
in O
the O
TO O
process S-CONPRI
. O


In O
, O
intensive O
discussions O
and O
experimental S-CONPRI
computations O
were O
conducted O
for O
the O
support S-APPL
volume O
constrained O
3D S-CONPRI
TO O
for O
AM S-MANP
design O
. O


Level O
set S-APPL
based O
Pareto S-CONPRI
is O
adopted O
to O
control O
and O
alter O
the O
shape O
boundary S-FEAT
where O
support B-FEAT
structure E-FEAT
may O
be S-MATE
required O
. O


It O
is O
hard O
to O
find O
a O
unique O
optimal O
solution S-CONPRI
, O
as S-MATE
each O
solution S-CONPRI
is O
a O
compromise O
between O
the O
constraints O
added O
. O


A O
set S-APPL
of O
Pareto S-CONPRI
solutions O
are O
provided O
, O
as S-MATE
seen O
in O
9 O
. O


As S-MATE
stated O
in O
, O
the O
elimination O
of O
support S-APPL
volume O
may O
be S-MATE
possible O
but O
will O
hardly O
work O
for O
real O
3D S-CONPRI
TO O
problems O
in O
AM S-MANP
design O
. O


Even O
though O
it O
is O
hard O
to O
totally O
avoid O
the O
use O
of O
support B-FEAT
structures E-FEAT
, O
researchers O
in O
still O
tried O
to O
obtain O
optimal O
3D S-CONPRI
TO O
structures O
without O
supports S-APPL
for O
several O
relative O
simple S-MANP
demonstration O
cases O
. O


To O
avoid O
the O
use O
of O
supports S-APPL
this O
study O
includes O
a O
simplified O
AM S-MANP
fabrication O
model S-CONPRI
, O
implemented O
as S-MATE
a O
layerwise O
filtering O
procedure O
into O
a O
topology B-FEAT
optimization E-FEAT
formulation O
. O


In O
this O
way O
, O
unprintable O
geometries S-CONPRI
are O
excluded O
from O
the O
design B-CONPRI
space E-CONPRI
, O
resulting O
in O
fully O
self-supporting S-FEAT
optimized O
designs S-FEAT
. O


Similar O
ideas O
can O
be S-MATE
found O
in O
where O
support S-APPL
constraint O
is O
applied O
. O


However O
, O
this O
as S-MATE
a O
compromise O
between O
the O
structural B-CHAR
performance E-CHAR
and O
global O
volume S-CONPRI
. O


The O
author O
of O
also O
understands O
that O
it O
would O
be S-MATE
hard O
to O
avoid O
the O
use O
of O
support B-FEAT
structure E-FEAT
, O
and O
proposed O
to O
optimize O
the O
3D B-CONPRI
structure E-CONPRI
with O
necessary O
support B-FEAT
structure E-FEAT
in O
parallel O
so O
as S-MATE
to O
obtain O
a O
better O
compromise O
. O


In O
this O
study O
, O
two O
separate O
density B-PRO
fields E-PRO
were O
proposed O
to O
describe O
the O
component S-MACEQ
and O
support B-FEAT
structure E-FEAT
layouts O
respectively O
. O


A O
simple S-MANP
critical O
overhang B-PARA
angle E-PARA
was O
imposed O
into O
the O
TO O
process S-CONPRI
as S-MATE
a O
constraint O
. O


The O
examples O
presented O
in O
10 O
and O
11 O
show O
that O
more O
volume S-CONPRI
used O
for O
supports S-APPL
, O
which O
can O
be S-MATE
seen O
as S-MATE
waste O
material S-MATE
, O
results O
in O
more O
material S-MATE
saved O
for O
the O
main O
structure S-CONPRI
. O


Actually O
, O
optimizing O
the O
functionality O
of O
supports S-APPL
for O
3D B-CONPRI
structures E-CONPRI
to O
be S-MATE
printed O
by O
metallic B-MANP
AM E-MANP
processes O
would O
be S-MATE
a O
more O
important O
goal O
than O
optimizing O
material S-MATE
savings O
, O
since O
the O
support B-FEAT
structures E-FEAT
in O
metallic B-MANP
AM E-MANP
processes O
have O
a O
profound O
impact S-CONPRI
on O
the O
final O
printing O
quality S-CONPRI
. O


For O
example O
, O
the O
build B-PARA
orientation E-PARA
has O
a O
direct O
impact S-CONPRI
on O
the O
TO O
process S-CONPRI
since O
it O
determines O
the O
TO O
solution S-CONPRI
space O
. O


In O
, O
the O
combined O
optimization S-CONPRI
of O
part O
topology S-CONPRI
, O
support B-FEAT
structure E-FEAT
and O
build B-PARA
orientation E-PARA
is O
investigated O
. O


The O
research S-CONPRI
into O
these O
complex O
interrelationships O
are O
limited O
to O
2D S-CONPRI
simple O
cases O
, O
where O
the O
impact S-CONPRI
of O
build B-PARA
orientation E-PARA
to O
TO O
and O
support S-APPL
optimization S-CONPRI
is O
clear O
. O


This O
implies O
that O
more O
work O
should O
be S-MATE
done O
in O
this O
direction O
for O
real O
3D S-CONPRI
industrial O
cases O
. O


If O
we O
take O
the O
slicing S-CONPRI
and O
toolpath B-PARA
planning E-PARA
as S-MATE
additional O
considerations O
into O
the O
3D S-CONPRI
TO O
process S-CONPRI
, O
the O
complexity S-CONPRI
would O
be S-MATE
increased O
even O
further O
. O


Finally O
, O
there O
are O
researchers O
working O
on O
level O
set S-APPL
TO O
methods O
to O
include O
AM B-MATE
material E-MATE
deposition O
path/toolpath O
as S-MATE
constraints O
to O
control O
sharp B-FEAT
angles E-FEAT
, O
deposition B-CHAR
gaps E-CHAR
, O
minimum O
inner O
hole B-FEAT
size E-FEAT
and O
minimum O
strut B-PARA
size E-PARA
in O
the O
topology S-CONPRI
formation O
process S-CONPRI
. O


If O
the O
manufacturability S-CONPRI
of O
an O
AM S-MANP
TO O
solution S-CONPRI
could O
not O
be S-MATE
guaranteed O
, O
any O
kind O
of O
optimal O
design S-FEAT
may O
bring O
no O
application O
value O
. O


In O
, O
manufacturability S-CONPRI
of O
the O
AM S-MANP
components O
and O
the O
cooling B-PARA
rate E-PARA
are O
considered O
as S-MATE
constraints O
and O
a O
shape O
based O
TO O
method O
is O
proposed O
. O


The O
manufacturability S-CONPRI
is O
checked O
for O
each O
layer S-PARA
. O


More O
recently O
, O
a O
new O
constraint O
function O
of O
the O
domain S-CONPRI
which O
controls O
the O
negative O
impact S-CONPRI
of O
porosity S-PRO
on O
elastic B-PRO
structures E-PRO
in O
the O
framework S-CONPRI
of O
shape O
and O
topology B-FEAT
optimization E-FEAT
is O
defined O
as S-MATE
a O
special O
shape O
derivative O
and O
proposed O
to O
embed O
into O
a O
level O
set S-APPL
TO O
process S-CONPRI
for O
AM S-MANP
lightweight O
design S-FEAT
. O


Even O
these O
methods O
can O
obtain O
a O
manufacturable S-CONPRI
TO O
layout S-CONPRI
, O
the O
boundaryproblems O
brought O
by O
a O
density S-PRO
based O
TO O
method O
still O
pose O
challenges O
for O
AM B-MANP
processes E-MANP
. O


Therefore O
, O
level O
set S-APPL
based O
methods O
or O
boundary B-CONPRI
decomposition E-CONPRI
with O
spline B-ENAT
interpolation E-ENAT
are O
usually O
used O
to O
do O
post-processing S-CONPRI
of O
the O
TO O
results O
. O


From O
the O
discussion O
of O
existing O
research S-CONPRI
presented O
above O
, O
there O
are O
still O
a O
lot O
of O
difficulties O
for O
the O
development O
of O
tailored O
TO O
methods O
and O
tools S-MACEQ
for O
AM S-MANP
lightweight O
design S-FEAT
. O


The O
work O
discussed O
is O
all O
based O
on O
a O
single O
material S-MATE
showing O
isotropic S-PRO
properties O
. O


However O
, O
with O
digital O
controlled O
deposition S-CONPRI
, O
theoretically O
AM S-MANP
can O
print S-MANP
different O
materials S-CONPRI
with O
different O
gradients O
for O
multi-functional B-CONPRI
structures E-CONPRI
. O


For O
example O
, O
jetting-based O
AM B-MANP
processes E-MANP
can O
print S-MANP
smart O
structures O
with O
multiple O
polymers S-MATE
. O


Hence O
, O
TO O
methods O
and O
tools S-MACEQ
to O
help O
designers O
to O
allocate O
different O
material S-MATE
to O
different O
regions O
with O
optimal O
quantities O
for O
an O
expected O
multi-functional B-CONPRI
structure E-CONPRI
become O
critical O
. O


In O
, O
a O
multivariate B-CONPRI
SIMP I-CONPRI
method E-CONPRI
is O
proposed O
to O
optimize O
an O
application O
dependent O
multi-material B-CONPRI
layout E-CONPRI
. O


The O
inclusion S-MATE
of O
multiple O
materials S-CONPRI
in O
the O
topology B-FEAT
optimization I-FEAT
process E-FEAT
has O
the O
potential O
to O
eliminate O
the O
narrow O
, O
weak O
, O
hinge-like O
sections O
that O
are O
often O
present O
in O
single-material O
compliant B-CONPRI
mechanisms E-CONPRI
. O


The O
demonstration O
example O
is O
the O
realization O
of O
a O
3-phase O
, O
multi-material B-CONPRI
2D I-CONPRI
compliant I-CONPRI
mechanism E-CONPRI
. O


One O
can O
foresee O
that O
if O
some O
work O
in O
the O
future O
can O
help O
realize O
multi-material S-CONPRI
topology O
optimization S-CONPRI
for O
3D B-FEAT
metal I-FEAT
structures E-FEAT
, O
then O
the O
complexity S-CONPRI
capability O
of O
AM S-MANP
can O
be S-MATE
further O
explored O
not O
only O
for O
lightweight S-CONPRI
design S-FEAT
but O
also O
for O
a O
combined O
multi-function B-FEAT
design E-FEAT
. O


Currently O
, O
metallic S-MATE
FDM S-MANP
process O
with O
metallurgical S-APPL
solidification O
as S-MATE
a O
post-process S-CONPRI
can O
theoretically O
realize O
the O
joining S-MANP
of O
multiple O
metals S-MATE
. O


There O
has O
been O
extensive O
exploration O
of O
TO O
for O
AM S-MANP
in O
diverse O
application O
examples O
either O
via O
standard S-CONPRI
TO O
tools S-MACEQ
or O
AM S-MANP
oriented O
tools S-MACEQ
. O


Reports O
have O
presented O
industrial S-APPL
design S-FEAT
cases O
to O
show O
the O
great O
potential O
of O
TO O
tools S-MACEQ
for O
AM S-MANP
lightweight O
design S-FEAT
. O


EADS O
presented O
a O
component S-MACEQ
for O
Airbus S-APPL
. O


However O
, O
there O
are O
no O
details O
about O
how O
to O
embed O
the O
AM S-MANP
constraints O
in O
the O
design B-CONPRI
process E-CONPRI
of O
the O
example O
. O


In O
the O
second O
example O
, O
a O
minimum O
AM S-MANP
feature O
size O
is O
embedded O
into O
the O
density S-PRO
based O
TO O
process S-CONPRI
and O
allows O
to O
define O
arbitrary O
objective O
functions O
for O
multi-physic O
fields O
, O
which O
is O
crucial O
for O
gradient-based O
, O
and O
thus O
all O
topology B-FEAT
optimization E-FEAT
. O


An O
example O
on O
the O
comparison O
study O
of O
designing O
a O
heat B-MACEQ
sink E-MACEQ
between O
traditional O
parametric B-CONPRI
optimization E-CONPRI
and O
AM S-MANP
oriented O
TO O
is O
presented O
in O
15 O
. O


Apart O
from O
density-based O
methods O
or O
level O
set S-APPL
methods O
, O
evolutionary O
TO O
methods O
were O
also O
investigated O
for O
AM S-MANP
design O
. O


In O
, O
a O
recently O
developed O
topology B-FEAT
optimization E-FEAT
method O
called O
Iso-XFEM S-CHAR
is O
used O
. O


This O
method O
is O
capable O
of O
generating O
high B-PARA
resolution E-PARA
topology O
optimized O
solutions O
using O
isolines/isosurfaces O
of O
a O
structural B-CHAR
performance E-CHAR
criterion O
. O


XFEM O
is O
similar O
to O
the O
BESO B-CONPRI
method E-CONPRI
, O
but O
removes O
or O
adds O
materials S-CONPRI
within O
elements S-MATE
. O


However O
, O
there O
is O
no O
description O
how O
the O
TO O
process S-CONPRI
is O
tailored O
for O
AM S-MANP
. O


It O
is O
not O
difficult O
to O
image S-CONPRI
that O
embedding O
AM S-MANP
constraints O
into O
an O
evolutionary O
TO O
process S-CONPRI
would O
be S-MATE
more O
difficult O
than O
that O
of O
density S-PRO
or O
level O
set S-APPL
based O
methods O
since O
the O
process S-CONPRI
uses O
discrete B-ENAT
optimization E-ENAT
. O


In O
addition O
, O
evolutionary O
based O
methods O
still O
have O
more O
difficulties O
in O
selection O
of O
stopping O
criteria O
or O
convergence B-CONPRI
analysis E-CONPRI
. O


As S-MATE
shown O
and O
discussed O
above O
, O
though O
some O
commercial O
tools S-MACEQ
are O
ready O
for O
use O
, O
very O
little O
AM S-MANP
constraints O
are O
considered O
. O


The O
current O
TO O
methods O
and O
commercialized O
tools S-MACEQ
still O
stay O
very O
close O
to O
the O
traditional O
TO O
tools S-MACEQ
. O


In O
addition O
, O
including O
both O
academic O
and O
industrial S-APPL
examples O
, O
those O
studies O
commonly O
lack O
experimental S-CONPRI
verification O
and O
there O
is O
no O
explicit O
agreement O
by O
the O
scientific O
community O
on O
their O
aspect B-FEAT
ratio E-FEAT
, O
which O
sets O
barriers O
for O
comparison O
and O
TO O
performance S-CONPRI
benchmarking O
. O


Therefore O
, O
there O
is O
still O
slot O
of O
work O
to O
be S-MATE
done O
for O
developing O
standard S-CONPRI
testing O
and O
experimental S-CONPRI
benchmarking O
examples O
. O


4.2 O
Generative B-ENAT
design E-ENAT
For O
the O
TO O
methods O
discussed O
above O
, O
people O
are O
trying O
to O
develop O
a O
fully O
automatic O
way O
to O
define O
a O
unique O
optimal O
lightweight B-MACEQ
structure E-MACEQ
design S-FEAT
. O


However O
, O
it O
is O
difficult O
to O
converge O
to O
the O
optimal O
solution S-CONPRI
, O
especially O
when O
multiple O
objectives O
are O
set S-APPL
. O


Hence O
, O
a O
compromise O
should O
be S-MATE
made O
to O
sample S-CONPRI
the O
solution S-CONPRI
space O
when O
the O
theoretical S-CONPRI
global O
optimal O
could O
not O
be S-MATE
located O
. O


This O
introduces O
another O
design S-FEAT
method O
for O
AM S-MANP
, O
generative B-ENAT
design E-ENAT
. O


GD S-MATE
is O
a O
set S-APPL
of O
methods O
that O
apply O
a O
generative O
system O
, O
rule-based O
or O
algorithm-based O
, O
to O
explore O
the O
design B-CONPRI
space E-CONPRI
and O
generate O
candidate O
solutions O
for O
designers O
. O


It O
is O
usually O
practiced O
for O
architectural O
design S-FEAT
. O


In O
structure B-FEAT
design E-FEAT
, O
we O
usually O
use O
the O
second O
method O
, O
applying O
evolutionary O
algorithms S-CONPRI
to O
sample S-CONPRI
and O
generate O
design S-FEAT
solutions O
that O
are O
close O
to O
predefined O
objectives O
and O
criteria O
. O


in O
, O
it O
is O
easy O
to O
adapt O
to O
evolutionary O
generative B-ENAT
design E-ENAT
for O
AM S-MANP
. O


Based O
on O
traditional O
TO O
methods O
, O
discretized O
version O
of O
the O
density S-PRO
based O
SIMP O
method O
, O
commercial O
software S-CONPRI
providers O
announced O
new O
functions O
of O
generative B-ENAT
design E-ENAT
for O
AM S-MANP
in O
their O
structure B-FEAT
design E-FEAT
tools O
and O
presented O
a O
couple O
of O
industrial S-APPL
design S-FEAT
cases O
with O
numerical O
results O
. O


For O
example O
, O
16 O
gives O
one O
design S-FEAT
example O
with O
a O
set S-APPL
of O
filtered O
candidate O
solutions O
. O


Similarly O
, O
as S-MATE
TO O
, O
GD S-MATE
is O
not O
new O
, O
but O
introducing O
AM S-MANP
constraints O
in O
traditional O
GD S-MATE
is O
still O
difficult O
. O


To O
solve O
this O
problem O
, O
recently O
, O
researchers O
developed O
a O
new O
evolutionary O
generative B-ENAT
design E-ENAT
method O
for O
AM S-MANP
lightweight O
design S-FEAT
to O
mimic S-MACEQ
termite O
behavior O
for O
volume S-CONPRI
construction S-APPL
. O


The O
proposed O
methodology S-CONPRI
uses O
multi-agent O
algorithms S-CONPRI
that O
simultaneously O
design S-FEAT
, O
structurally O
optimize O
and O
appraise O
the O
manufacturability S-CONPRI
of O
parts O
produced O
by O
additive B-MANP
manufacturing E-MANP
. O


Voxels S-CONPRI
are O
used O
to O
carry O
the O
design B-CONPRI
rules E-CONPRI
and O
manufacturing B-CONPRI
constraints E-CONPRI
for O
reasoning O
and O
combination O
during O
the O
geometry B-CONPRI
evolution E-CONPRI
process O
. O


However O
, O
this O
method O
considers O
support B-FEAT
structures E-FEAT
as S-MATE
the O
only O
AM S-MANP
constraint O
and O
has O
difficulty O
to O
include O
more O
. O


For O
generative B-ENAT
design E-ENAT
for O
AM S-MANP
, O
there O
is O
still O
a O
lot O
of O
work O
to O
do O
to O
include O
more O
AM S-MANP
constraints O
and O
develop O
more O
efficient O
decision O
making O
tools S-MACEQ
to O
help O
designers O
define O
optimization S-CONPRI
criteria O
and O
candidate O
solution S-CONPRI
ranking O
schemes O
. O


Some O
commercial O
tools S-MACEQ
are O
now O
available O
however O
. O


On O
the O
other O
hand O
, O
when O
doing O
structure B-FEAT
design E-FEAT
via O
generative B-ENAT
design E-ENAT
methods O
, O
the O
global O
optimum O
and O
computational O
cost O
should O
be S-MATE
given O
attention O
. O


Recently O
, O
researchers O
began O
to O
combine O
TO O
with O
generative B-ENAT
models E-ENAT
, O
e.g. O
, O
generative B-ENAT
adversarial I-ENAT
networks E-ENAT
, O
and O
proposed O
a O
new O
concept O
, O
deep B-FEAT
generative I-FEAT
design E-FEAT
, O
which O
owns O
the O
learning O
capability O
from O
the O
iteration O
process S-CONPRI
and O
existing O
design S-FEAT
data S-CONPRI
. O


These O
concepts O
hold O
the O
potential O
to O
better O
integrate O
existing O
AM S-MANP
processing O
knowledge O
into O
the O
generative B-ENAT
design E-ENAT
procedure O
to O
populate O
and O
explore O
more O
qualified O
AM S-MANP
design O
solutions O
. O


Certainly O
, O
generative B-ENAT
design E-ENAT
is O
not O
only O
used O
for O
topology B-FEAT
optimization E-FEAT
but O
also O
can O
be S-MATE
applied O
to O
form O
synthesis O
, O
lattice S-CONPRI
and O
surface B-FEAT
structure E-FEAT
optimization S-CONPRI
and O
trabecular B-FEAT
structures E-FEAT
as S-MATE
a O
way O
to O
explore O
more O
design B-CONPRI
freedom E-CONPRI
using O
AM S-MANP
. O


4.3 O
Lattice B-FEAT
structure E-FEAT
filling O
Directly O
removing O
or O
adding O
material S-MATE
in O
the O
design B-CONPRI
space E-CONPRI
to O
search O
for O
the O
global O
optimal O
material S-MATE
topology O
solution S-CONPRI
is O
common O
to O
TO O
and O
generative B-ENAT
design E-ENAT
methods O
and O
, O
as S-MATE
stated O
above O
, O
there O
are O
many O
difficulties O
. O


As S-MATE
a O
compromise O
, O
generative B-ENAT
design E-ENAT
can O
include O
human O
knowledge O
to O
interactively O
select O
the O
candidate O
solutions O
so O
as S-MATE
to O
reduce O
the O
problem O
complexity S-CONPRI
. O


Therefore O
, O
this O
is O
an O
indirect O
lightweight S-CONPRI
design S-FEAT
method O
for O
AM S-MANP
, O
which O
is O
also O
called O
lattice B-CONPRI
configuration E-CONPRI
, O
18 O
. O


To O
obtain O
lattice B-FEAT
structures E-FEAT
, O
generally O
we O
have O
two O
approaches O
: O
1 O
. O


Homogenization S-MANP
and O
2 O
. O


Density S-PRO
based O
mapping O
. O


The O
former O
homogenizes O
the O
lattice B-FEAT
structure E-FEAT
as S-MATE
representative O
volume S-CONPRI
elements S-MATE
, O
like O
solid O
material S-MATE
. O


The O
lattice B-FEAT
structures E-FEAT
are O
similar O
to O
the O
micro O
porous S-PRO
for O
the O
traditional O
solid O
structure S-CONPRI
in O
homogenized B-PRO
volumes E-PRO
. O


In O
this O
way O
, O
special O
properties S-CONPRI
should O
be S-MATE
assigned O
to O
the O
representative O
volumes O
and O
then O
we O
can O
apply O
traditional O
TO O
or O
other O
structure B-CONPRI
optimization E-CONPRI
methods O
to O
operate O
the O
special O
volumes O
. O


Representative O
researches O
that O
apply O
this O
method O
can O
be S-MATE
found O
in O
and O
19 O
illustrates O
the O
general O
workflow S-CONPRI
. O


The O
second O
approach O
maps O
the O
density S-PRO
values O
obtained O
from O
non-penalized O
TO O
results O
onto O
the O
explicit O
predefined O
lattice B-FEAT
structures E-FEAT
with O
optional O
adaptation O
to O
improve O
the O
approximation O
accuracy S-CHAR
of O
mechanical B-CONPRI
response E-CONPRI
. O


Based O
on O
this O
approach O
, O
uniform O
or O
graded O
lattice B-FEAT
structures E-FEAT
can O
be S-MATE
obtained O
. O


Example O
studies O
can O
be S-MATE
found O
in O
. O


20 O
shows O
an O
example O
where O
different O
predefined O
lattice B-FEAT
structures E-FEAT
are O
used O
to O
map O
the O
solid O
volume S-CONPRI
TO O
contours S-FEAT
. O


Although O
the O
two O
appraoches O
are O
not O
hard O
to O
understand O
, O
the O
operation O
and O
optimization S-CONPRI
of O
lattice B-FEAT
structures E-FEAT
is O
quite O
complicated O
, O
especially O
for O
large O
size O
structure B-FEAT
design E-FEAT
. O


The O
first O
problem O
is O
the O
representation/digitalization O
of O
lattice B-FEAT
structures E-FEAT
. O


Usually O
, O
solid O
representation O
or O
surface S-CONPRI
representation O
can O
be S-MATE
used O
for O
individual O
lattice B-FEAT
units E-FEAT
. O


But O
when O
filled O
into O
solid B-MACEQ
hulls E-MACEQ
, O
the O
number O
of O
lattice B-FEAT
units E-FEAT
is O
very O
big O
, O
which O
makes O
the O
CAD B-MANS
file E-MANS
difficult O
to O
operate O
, O
including O
sweeping O
, O
meshing/mapping O
and O
tessellation S-FEAT
. O


Secondly O
, O
when O
doing O
numerical B-ENAT
simulation E-ENAT
, O
the O
computation S-CONPRI
cost O
is O
much O
higher O
since O
many O
more O
finite B-CONPRI
element E-CONPRI
units O
are O
required O
. O


Thirdly O
, O
when O
filling O
lattice B-FEAT
structures E-FEAT
into O
solid B-MACEQ
hulls E-MACEQ
, O
one O
needs O
to O
use O
uniform O
lattice S-CONPRI
in O
trimming S-MANP
or O
non-uniform O
lattice S-CONPRI
with O
conformal O
interface S-CONPRI
, O
which O
depends O
on O
specific O
design S-FEAT
cases O
. O


Some O
researchers O
stated O
that O
conformal B-FEAT
lattice I-FEAT
structures E-FEAT
have O
better O
structural B-CHAR
performance E-CHAR
than O
that O
of O
uniformed O
. O


However O
, O
the O
operation O
of O
conformal B-FEAT
lattice E-FEAT
is O
more O
complicated O
and O
more O
difficult O
to O
control O
the O
manufacturability S-CONPRI
since O
they O
are O
not O
, O
like O
uniform O
lattices S-CONPRI
usually O
are O
, O
derived O
from O
benchmarking O
results O
. O


After O
that O
, O
the O
computation S-CONPRI
cost O
is O
a O
big O
issue O
, O
not O
only O
for O
the O
representation O
, O
but O
also O
for O
simulation S-ENAT
and O
manufacturing S-MANP
. O


That O
is O
why O
some O
researchers O
proposed O
to O
use O
kernel O
or O
symbolic O
representations O
for O
lattice B-FEAT
units E-FEAT
. O


Finally O
, O
the O
most O
important O
challenge O
is O
how O
to O
obtain O
the O
global O
optimum O
when O
using O
lattice B-FEAT
structures E-FEAT
. O


The O
approximation O
process S-CONPRI
further O
reduces O
the O
original O
design B-CONPRI
space E-CONPRI
and O
introduces O
more O
errors S-CONPRI
. O


Predefined O
and O
benchmarked O
limited O
lattice B-FEAT
structures E-FEAT
with O
fixed O
parameters S-CONPRI
are O
just O
a O
subset O
of O
the O
design S-FEAT
variants O
. O


Actually O
, O
even O
for O
predefined O
lattice B-FEAT
units E-FEAT
, O
there O
are O
more O
parameters S-CONPRI
that O
can O
be S-MATE
modified O
and O
adjusted O
to O
specific O
design S-FEAT
cases O
. O


Currently O
, O
many O
optimization S-CONPRI
studies O
for O
lattice B-FEAT
structures E-FEAT
are O
only O
limited O
to O
density S-PRO
, O
represented O
by O
strut B-PARA
diameter E-PARA
, O
and O
very O
little O
work O
focuses O
on O
parameter S-CONPRI
optimization S-CONPRI
and O
computation S-CONPRI
benchmarking O
for O
large O
lattice B-FEAT
structure I-FEAT
design E-FEAT
cases O
. O


Therefore O
, O
to O
be S-MATE
practical O
, O
current O
methods O
and O
tools S-MACEQ
from O
academic O
codes O
or O
commercial O
software S-CONPRI
tools O
all O
adopt O
knowledge O
based O
methods O
with O
TO O
methods O
for O
lattice B-FEAT
filling E-FEAT
. O


Usually O
, O
a O
lattice S-CONPRI
library O
is O
built O
to O
store O
predefined O
lattice B-FEAT
units E-FEAT
, O
benchmarked O
with O
numerical B-ENAT
simulation E-ENAT
or O
manufacturability S-CONPRI
analysis O
, O
and O
then O
a O
limited O
set S-APPL
of O
control O
options O
, O
concerning O
the O
lattice B-FEAT
unit I-FEAT
size E-FEAT
, O
strut B-PARA
diameter E-PARA
, O
layout S-CONPRI
orientation O
, O
etc. O
, O
are O
available O
for O
the O
filling O
operation O
. O


This O
is O
the O
main O
workflow S-CONPRI
of O
current O
tools S-MACEQ
. O


As S-MATE
said O
before O
, O
although O
relatively O
small O
or O
medium O
sized O
lattice B-FEAT
structures E-FEAT
can O
be S-MATE
obtained O
, O
one O
not O
only O
sacrifices O
the O
stiffness S-PRO
but O
also O
it O
may O
be S-MATE
more O
difficult O
to O
search O
for O
the O
original O
global O
optimal O
lightweight S-CONPRI
design S-FEAT
solution O
. O


If O
one O
only O
considers O
the O
lightweight S-CONPRI
effect O
in O
the O
design S-FEAT
, O
lattice B-FEAT
filling E-FEAT
may O
not O
be S-MATE
the O
optimal O
choice O
. O


However O
, O
lattice B-FEAT
structures E-FEAT
can O
bring O
other O
benefits O
, O
e.g O
. O


energy B-CHAR
absorption E-CHAR
and O
heat B-CONPRI
conduction E-CONPRI
that O
solid O
structures O
may O
not O
have O
. O


This O
would O
be S-MATE
an O
important O
factor O
to O
encourage O
research S-CONPRI
and O
practice O
in O
the O
lattice B-CONPRI
domain E-CONPRI
. O


5 O
Tools S-MACEQ
and O
methods O
for O
optimizing O
surface B-FEAT
structure E-FEAT
As S-MATE
discussed O
above O
, O
the O
global O
optimal O
for O
structure B-FEAT
design E-FEAT
is O
usually O
hard O
to O
obtain O
. O


Similar O
to O
lattice B-FEAT
structures E-FEAT
, O
which O
are O
made O
artificially O
, O
natural O
porous S-PRO
structures O
become O
a O
set S-APPL
of O
special O
elements S-MATE
to O
deal O
with O
specific O
design S-FEAT
requirements O
. O


Examples O
include O
among O
others O
lightweight S-CONPRI
infill S-PARA
, O
porous B-FEAT
scaffolds E-FEAT
, O
energy O
absorbers O
, O
micro-reactors S-MACEQ
, O
heat B-MACEQ
conductors E-MACEQ
, O
or O
self-adaptating O
structures O
. O


These O
structures/functionalities O
have O
been O
known O
for O
some O
time O
, O
but O
due O
to O
the O
ability O
of O
AM S-MANP
to O
produce O
these O
complex B-CONPRI
structures E-CONPRI
, O
they O
now O
become O
part O
of O
the O
solution S-CONPRI
principles O
that O
can O
be S-MATE
applied O
by O
the O
product O
designer O
. O


Hence O
, O
the O
mimicking O
and O
post-processing S-CONPRI
of O
natural O
inspired O
or O
randomly O
generated O
complex O
topologies S-CONPRI
become O
a O
new O
design S-FEAT
practice O
, O
which O
is O
called O
bio-inspired S-CONPRI
or O
biomimetic B-FEAT
design E-FEAT
. O


Its O
goal O
is O
to O
generate O
either O
lightweight B-MACEQ
structures E-MACEQ
with O
unexpected O
mechanical B-CONPRI
properties E-CONPRI
, O
similar O
to O
the O
lightweight S-CONPRI
design S-FEAT
methods O
mentioned O
in O
the O
last O
section O
, O
or O
multi-functional O
surface B-FEAT
structures E-FEAT
as S-MATE
addressed O
here O
. O


This O
type O
of O
design S-FEAT
is O
more O
difficult O
than O
that O
of O
relatively O
regular O
or O
conformal O
periodic O
lattice B-FEAT
structures E-FEAT
. O


Hence O
, O
the O
design S-FEAT
and O
simulation S-ENAT
focuses O
more O
on O
the O
form O
and O
shape O
of O
the O
surfaces S-CONPRI
while O
the O
mechanical B-CONPRI
properties E-CONPRI
and O
AM S-MANP
constraints O
are O
hard O
to O
consider O
due O
to O
their O
extreme O
complexity S-CONPRI
. O


Generally O
, O
two O
design S-FEAT
approaches O
, O
direct/indirect O
reproduction O
of O
natural O
topologies S-CONPRI
via O
reverse B-CONPRI
engineering E-CONPRI
and O
generic O
bio-inspiration S-CONPRI
using O
design B-CONPRI
rules E-CONPRI
or O
guidelines O
, O
are O
conducted O
in O
this O
domain S-CONPRI
. O


Driven O
by O
the O
wide O
application O
in O
the O
medical S-APPL
domain S-CONPRI
, O
scaffolds S-FEAT
and O
implants S-APPL
usually O
require O
similar O
internal O
surface B-FEAT
topologies E-FEAT
to O
the O
natural O
structures O
they O
are O
mimicing O
. O


cell S-APPL
spreading O
, O
strength S-PRO
distribution S-CONPRI
. O


The O
main O
methods O
to O
generate O
irregular O
porous S-PRO
structures O
with O
complex O
internal O
surface B-FEAT
topologies E-FEAT
are O
either O
filling O
or O
hollowing O
materials S-CONPRI
from O
an O
initial O
design S-FEAT
via O
specific O
algorithms S-CONPRI
. O


A O
representative O
filling O
method O
is O
Triply B-CONPRI
Periodic I-CONPRI
Minimal I-CONPRI
Surface E-CONPRI
, O
which O
is O
an O
implicit B-FEAT
surface E-FEAT
with O
intricate O
structures O
. O


Researchers O
add O
different O
operation B-ENAT
algorithms E-ENAT
to O
do O
the O
filling O
with O
these O
surface S-CONPRI
units O
so O
as S-MATE
to O
approximate O
the O
original O
CAD B-ENAT
model E-ENAT
's O
skin O
. O


For O
the O
hollowing O
process S-CONPRI
, O
sub-volumes O
are O
generated O
via O
a O
set S-APPL
of O
specific O
algorithms S-CONPRI
within O
the O
original O
3D S-CONPRI
CAD O
model S-CONPRI
and O
used O
to O
do O
Boolean B-ENAT
operations E-ENAT
. O


A O
shape O
function O
is O
applied O
in O
to O
design S-FEAT
a O
pore S-PRO
model S-CONPRI
and O
then O
a O
subtractive S-MANP
Boolean B-ENAT
operation E-ENAT
is O
conducted O
between O
the O
pore S-PRO
and O
the O
original O
solid O
CAD B-ENAT
models E-ENAT
to O
obtain O
the O
final O
scaffold B-CONPRI
model E-CONPRI
. O


The O
process S-CONPRI
is O
illustrated O
in O
23 O
. O


Similarly O
, O
a O
Voronoi B-FEAT
tessellation E-FEAT
method O
is O
adopted O
in O
to O
do O
the O
material B-CONPRI
hollowing E-CONPRI
. O


Apart O
from O
the O
internal O
surface B-FEAT
structure E-FEAT
generation O
, O
external O
surface B-FEAT
structure E-FEAT
design S-FEAT
also O
attracts O
attention O
since O
using O
AM S-MANP
to O
print S-MANP
complex B-PRO
shapes E-PRO
for O
art S-APPL
or O
customized O
shapes O
has O
become O
popular O
. O


In O
artistic O
design S-FEAT
, O
T-splines S-FEAT
and O
Voronoi B-FEAT
tessellation E-FEAT
or O
predefined O
pattern S-CONPRI
bases O
are O
commonly O
used O
for O
defining O
complex O
surface B-FEAT
topologies E-FEAT
. O


In O
, O
a O
generative B-ENAT
design E-ENAT
method O
is O
applied O
to O
populate O
complex O
surface B-FEAT
topologies E-FEAT
via O
the O
use O
of O
predefined O
patterns O
. O


A O
recursive O
grammar O
is O
set S-APPL
for O
the O
generation O
of O
solid O
boundary S-FEAT
surface O
models O
, O
suitable O
for O
a O
variety O
of O
design S-FEAT
domains O
. O


Freeform B-CONPRI
3D E-CONPRI
surface O
topologies S-CONPRI
can O
be S-MATE
formed O
by O
a O
set S-APPL
of O
2-manifold O
polygonal O
sub O
meshes O
as S-MATE
shown O
in O
24 O
. O


However O
, O
the O
optimization S-CONPRI
for O
artistic O
design S-FEAT
is O
not O
so O
obvious O
. O


To O
develop O
special O
surface B-FEAT
structures E-FEAT
for O
personalized O
casts/braces O
, O
a O
new O
topology B-FEAT
optimization E-FEAT
method O
is O
proposed O
in O
. O


The O
novel O
TO O
method O
is O
based O
on O
thin O
plate O
elements S-MATE
on O
the O
two-dimensional S-CONPRI
manifold B-FEAT
surfaces E-FEAT
instead O
of O
3D B-FEAT
solid I-FEAT
elements E-FEAT
so O
as S-MATE
to O
reduce O
the O
computation S-CONPRI
cost O
for O
shape O
optimization S-CONPRI
. O


To O
decrease O
the O
threshold O
of O
customization O
of O
surface B-FEAT
structure E-FEAT
for O
the O
public O
when O
using O
AM S-MANP
, O
in O
, O
an O
interactive O
CAD S-ENAT
design O
tool S-MACEQ
is O
proposed O
. O


This O
tool S-MACEQ
uses O
predefined O
reference O
unit O
models O
with O
the O
inputs O
of O
user O
's O
stylings O
to O
automatically O
generate O
customized O
hollowed O
surface B-FEAT
topologies E-FEAT
for O
fashion S-CONPRI
. O


Similar O
to O
other O
existing O
3D S-CONPRI
porous O
structure B-FEAT
design E-FEAT
methods O
, O
this O
tool S-MACEQ
is O
mainly O
based O
on O
Voronoi B-FEAT
tessellation E-FEAT
and O
curve O
fitting O
methods O
. O


26 O
shows O
the O
surface B-FEAT
topology E-FEAT
generation O
process S-CONPRI
. O


The O
main O
advantage O
of O
this O
tool S-MACEQ
is O
that O
its O
predefined O
reference O
models O
can O
be S-MATE
benchmarked O
and O
tested O
to O
ensure O
manufacturability S-CONPRI
, O
which O
will O
avoid O
problems O
during O
AM S-MANP
. O


Similar O
to O
structure S-CONPRI
topology O
optimization S-CONPRI
, O
surface B-FEAT
structure E-FEAT
design S-FEAT
and O
optimization B-CONPRI
face E-CONPRI
more O
difficulties O
in O
the O
modelling S-ENAT
, O
simulation S-ENAT
and O
embracing O
of O
AM S-MANP
constraints O
. O


This O
requires O
more O
work O
on O
the O
data S-CONPRI
structure O
, O
simulation S-ENAT
driven O
analysis O
and O
optimization S-CONPRI
. O


A O
lightweight S-CONPRI
and O
convenient O
analysis O
platform S-MACEQ
should O
be S-MATE
developed O
to O
efficiently O
acquire O
the O
calculation O
results O
for O
valid O
surface B-FEAT
structure E-FEAT
design S-FEAT
and O
optimization S-CONPRI
. O


Currently O
, O
there O
is O
very O
little O
research S-CONPRI
invesigating O
the O
design S-FEAT
guidelines O
of O
surface B-FEAT
structure E-FEAT
in O
AM S-MANP
. O


Most O
of O
the O
design S-FEAT
pratices O
are O
limited O
at O
non-metallic O
AM B-MANP
processes E-MANP
. O


However O
, O
there O
is O
an O
ugent O
need O
in O
the O
medical B-APPL
application E-APPL
domain S-CONPRI
where O
special O
functional O
surface B-FEAT
structures E-FEAT
are O
critical O
. O


27 O
presents O
a O
dental S-APPL
component S-MACEQ
where O
a O
bio-insipred B-FEAT
surface I-FEAT
structure E-FEAT
with O
a O
special O
treatment O
function O
is O
printed O
using O
L-PBF S-MANP
. O


Reverse B-CONPRI
engineering E-CONPRI
is O
used O
to O
generate O
the O
surface B-FEAT
structure E-FEAT
. O


However O
, O
the O
modelling S-ENAT
and O
function O
validation S-CONPRI
of O
such O
surface B-FEAT
structure E-FEAT
has O
not O
yet O
been O
studied O
. O


Hence O
, O
design S-FEAT
methods O
and O
modelling S-ENAT
tools O
should O
be S-MATE
developed O
to O
support S-APPL
the O
medical S-APPL
fabrication S-MANP
application O
for O
metal B-MANP
AM E-MANP
processes O
. O


6 O
Manual O
optimization S-CONPRI
of O
internal B-FEAT
part I-FEAT
topology E-FEAT
One O
of O
the O
enablers O
within O
AM S-MANP
is O
the O
ability O
to O
optimize O
the O
internal B-FEAT
part I-FEAT
topology E-FEAT
. O


In O
the O
previous O
sections O
automated O
topology B-FEAT
optimization E-FEAT
procedures O
for O
internal O
and O
surface S-CONPRI
part O
geometry S-CONPRI
were O
discussed O
. O


In O
many O
cases O
these O
automated O
methods O
are O
not O
required O
or O
applicable O
and O
other O
ways O
of O
defining O
the O
internal B-FEAT
part I-FEAT
topology E-FEAT
are O
used O
. O


With O
subtractive S-MANP
methods O
, O
structuring O
the O
product O
internal O
surfaces S-CONPRI
is O
hard O
or O
limited O
to O
very O
basic O
geometric O
features O
and O
production S-MANP
steps O
. O


Many O
of O
the O
commercially O
successful O
AM S-MANP
applications O
relate O
to O
internal O
transport S-CHAR
of O
media O
through O
the O
AM S-MANP
product O
. O


In O
relation O
to O
the O
additive B-MANP
manufacturing E-MANP
challenges O
, O
three O
subsets O
of O
AM S-MANP
features O
for O
internal O
transport S-CHAR
of O
media O
can O
be S-MATE
identified O
; O
macro B-FEAT
channel I-FEAT
geometry E-FEAT
, O
mini/micro B-CONPRI
channels E-CONPRI
and O
printed O
permeability S-PRO
. O


For O
macro B-FEAT
channel I-FEAT
geometry E-FEAT
, O
down-facing O
surfaces S-CONPRI
of O
the O
channel S-APPL
may O
experience O
stability S-PRO
problems O
during O
printing O
. O


For O
mini/micro B-CONPRI
channels E-CONPRI
, O
the O
feature B-PARA
size E-PARA
may O
be S-MATE
close O
to O
the O
limitations O
of O
the O
printing O
device O
which O
may O
result O
in O
walls O
failing O
to O
print S-MANP
, O
channels O
being O
blocked O
and O
cumbersome O
removal O
of O
excess O
print S-MANP
material S-MATE
. O


Finally O
, O
AM B-FEAT
permeable I-FEAT
structures E-FEAT
are O
created O
by O
ensuring O
process-induced O
porosity S-PRO
. O


Here O
the O
main O
challenge O
is O
finding O
stable O
process B-PARA
settings E-PARA
that O
allow O
for O
both O
the O
production S-MANP
of O
permeable B-FEAT
and I-FEAT
solid I-FEAT
structures E-FEAT
. O


6.1 O
Internal B-FEAT
geometry E-FEAT
at O
macro B-FEAT
level E-FEAT
In O
classical B-MANP
part I-MANP
production E-MANP
, O
channels O
for O
the O
transportation O
of O
viscous O
media O
are O
manufactured S-CONPRI
using O
conventional B-MANP
subtractive I-MANP
production I-MANP
methods E-MANP
like O
drilling S-MANP
, O
thus O
resulting O
in O
straight B-FEAT
channels E-FEAT
with O
round B-FEAT
cross I-FEAT
section E-FEAT
and O
sharp O
corners O
. O


With O
the O
use O
of O
AM S-MANP
the O
location O
and O
shape O
of O
these O
channels O
can O
be S-MATE
optimized O
. O


In O
L-PBF S-MANP
and O
at O
macro B-FEAT
level E-FEAT
, O
the O
top O
surfaces S-CONPRI
of O
the O
round O
holes O
have O
the O
tendency O
to O
sag O
or O
collapse O
, O
and O
the O
cross B-CONPRI
section E-CONPRI
of O
the O
channel S-APPL
has O
to O
be S-MATE
optimized O
. O


Thomas O
investigated O
the O
quality S-CONPRI
of O
produced O
channels O
and O
found O
that O
round O
holes O
up O
to O
a O
diameter S-CONPRI
of O
7mm O
could O
be S-MATE
printed O
with O
minimal O
problems O
. O


Above O
that O
, O
sagging O
of O
the O
overhanging O
surface S-CONPRI
is O
noticed O
, O
as S-MATE
well O
as S-MATE
possible O
curl O
, O
leading O
to O
recoater O
collisions O
. O


Other O
channel S-APPL
designs O
have O
been O
proposed O
. O


With O
the O
use O
of O
AM S-MANP
, O
cooling B-MACEQ
channels E-MACEQ
in O
injection B-MANP
molding E-MANP
inserts O
can O
be S-MATE
made O
conformal O
to O
the O
mold S-MACEQ
's O
product O
surface S-CONPRI
and O
located O
in O
areas S-PARA
critical O
to O
the O
quality S-CONPRI
of O
the O
die S-MACEQ
's O
function O
. O


Conformal B-MACEQ
cooling I-MACEQ
channels E-MACEQ
have O
been O
used O
to O
reduce O
cycle O
time O
and O
product B-CHAR
warpage E-CHAR
. O


Kitayama O
compared O
the O
effect O
of O
conformal B-MACEQ
cooling I-MACEQ
channels E-MACEQ
and O
conventional B-MACEQ
cooling I-MACEQ
channels E-MACEQ
for O
injection B-MANP
molding E-MANP
. O


Results O
showed O
an O
improvement O
of O
the O
cycle O
time O
of O
53 O
% O
and O
a O
reduction S-CONPRI
of O
product B-CHAR
warpage E-CHAR
by O
46 O
% O
compared O
to O
conventional B-MACEQ
cooling I-MACEQ
channels E-MACEQ
. O


Although O
conformal B-CONPRI
cooling E-CONPRI
for O
IM O
is O
widely O
researched O
and O
benefits O
have O
been O
proven O
, O
actual O
application O
in O
industry S-APPL
lags O
behind O
. O


It O
is O
considered O
beneficial O
only O
for O
complex O
plastic S-MATE
geometries S-CONPRI
, O
that O
are O
difficult O
to O
cool O
quickly O
and O
uniformly O
and O
for O
very O
high O
production S-MANP
volumes O
. O


H O
researched O
using O
conformal B-MACEQ
cooling I-MACEQ
channels E-MACEQ
in O
hot B-MANP
metal I-MANP
extrusion E-MANP
and O
also O
found O
significant O
production S-MANP
efficiency O
improvements O
. O


Current O
research S-CONPRI
into O
manifold O
design S-FEAT
has O
two O
main O
themes O
; O
mass O
reduction S-CONPRI
and O
flow O
optimization S-CONPRI
. O


Conventional O
methods O
create O
straight O
cooling B-MACEQ
channels E-MACEQ
, O
where O
connections O
result O
in O
pressure S-CONPRI
loss O
, O
increase O
the O
temperature S-PARA
and O
noise O
, O
which O
influences O
the O
reliability S-CHAR
and O
lifetime O
of O
the O
system O
. O


Ma O
investigated O
multiple O
geometry S-CONPRI
adjustments O
which O
can O
be S-MATE
made O
when O
using O
AM S-MANP
. O


AM S-MANP
enables O
the O
design S-FEAT
of O
fluent B-FEAT
corners E-FEAT
, O
smooth O
transitions O
between O
cooling B-MACEQ
channel E-MACEQ
diameters O
and O
the O
removal O
of O
unwanted O
drilling S-MANP
cavities O
, O
resulting O
in O
decrease O
in O
pressure S-CONPRI
loss O
by O
up O
to O
a O
factor O
of O
3 O
. O


6.2 O
Mini O
and O
Micro O
internal B-FEAT
geometry E-FEAT
in O
AM S-MANP
For O
mini O
and O
micro B-CONPRI
levels E-CONPRI
of O
geometry S-CONPRI
, O
used O
for O
transport S-CHAR
of O
fluidic O
media O
, O
the O
minimal O
feature B-PARA
size E-PARA
of O
the O
AM B-MANP
technology E-MANP
chosen O
is O
often O
the O
limiting O
factor O
. O


Thomas O
investigated O
some O
of O
these O
limits S-CONPRI
, O
for O
example O
as S-MATE
shown O
in O
31 O
. O


Printing O
of O
free O
standing O
walls O
and O
pilars O
is O
also O
a O
limiting O
factor O
as S-MATE
both O
the O
achievable O
minimal O
cross O
sectional O
area S-PARA
and O
maximal O
aspect B-FEAT
ratio E-FEAT
are O
limited O
. O


In O
sectors O
like O
heating S-MANP
, O
ventilation O
, O
and O
air O
conditioning O
, O
automotive S-APPL
, O
aero O
and O
electro-cooling S-CHAR
, O
heat B-MACEQ
exchangers E-MACEQ
play O
a O
vital O
role O
in O
the O
energy O
efficiency O
. O


The O
heat B-CONPRI
transfer E-CONPRI
performance O
is O
dependent O
on O
the O
surface B-PARA
area E-PARA
to O
volume S-CONPRI
ratio O
. O


Using O
mini O
and O
micro O
channels O
, O
this O
ratio O
can O
be S-MATE
increased O
, O
thus O
increasing O
the O
performance/mass O
ratio O
of O
the O
heat B-MACEQ
exchanger E-MACEQ
. O


Arie O
investigated O
the O
performance S-CONPRI
of O
Ti64 S-MATE
air-water O
manifold-microchannel O
heat B-MACEQ
exchangers E-MACEQ
. O


Key O
to O
the O
intended O
efficiency O
increase O
was O
the O
production S-MANP
of O
thin O
fins O
with O
high B-FEAT
aspect I-FEAT
ratio E-FEAT
's O
. O


Non O
AM-based O
production S-MANP
alternatives O
were O
considered O
slow O
, O
costly O
, O
not O
able O
to O
meet O
the O
aspect B-FEAT
ratios E-FEAT
or O
not O
possible O
to O
produce O
in O
the O
desired O
material S-MATE
. O


Compared O
to O
classical O
designs S-FEAT
the O
manifold O
micro-channel O
show O
respectively O
30performance O
increase O
in O
gravimetric O
heat B-PARA
transfer I-PARA
density E-PARA
. O


It O
was O
argued O
that O
inaccuracy O
of O
the O
production S-MANP
process S-CONPRI
reduced O
the O
manifold O
performance S-CONPRI
as S-MATE
some O
of O
the O
channels O
were O
blocked O
and O
the O
ideal O
fin O
thickness O
of O
150 O
could O
not O
be S-MATE
realized O
. O


Mei O
put O
the O
use O
of O
AM S-MANP
to O
a O
case B-CONPRI
study E-CONPRI
where O
they O
produced O
a O
highly O
integrated O
catalytic B-MACEQ
burner E-MACEQ
for O
auxiliary B-MACEQ
power I-MACEQ
units E-MACEQ
based O
on O
PEM-fuel B-MACEQ
cells E-MACEQ
. O


This O
resulted O
in O
a O
volume B-CONPRI
reduction E-CONPRI
of O
70 O
% O
from O
41L O
to O
11L O
and O
a O
weight S-PARA
reduction S-CONPRI
of O
60 O
% O
from O
30 O
kg O
to O
12 O
kg O
. O


6.3 O
Printed O
permeability S-PRO
Calignano O
investigated O
the O
relation O
between O
material S-MATE
and O
process S-CONPRI
properties O
to O
fabricate S-MANP
both O
stochastic S-CONPRI
and O
non-stochastic B-FEAT
porous I-FEAT
structures E-FEAT
. O


Parts O
were O
created O
using O
three O
different O
scanning B-CONPRI
strategies E-CONPRI
scanning S-CONPRI
lines O
, O
and O
rotating O
scanning B-PARA
patterns E-PARA
for O
each O
new O
layer S-PARA
) O
and O
by O
modifying O
the O
hatch B-PARA
distance E-PARA
hd O
. O


It O
was O
found O
that O
hatch B-PARA
distances E-PARA
in O
excess O
of O
0.20 O
mm S-MANP
were O
needed O
to O
be S-MATE
able O
to O
create O
distinct O
walls O
. O


Below O
that O
, O
wall O
formation O
was O
hampered O
by O
agglomeration O
of O
powder B-MATE
particles E-MATE
. O


The O
rotating O
scanning B-CONPRI
strategy E-CONPRI
using O
hd O
of O
0.5 O
mm S-MANP
resulted O
in O
stochastic S-CONPRI
, O
foam-like B-CONPRI
structures E-CONPRI
, O
both O
with O
open O
and O
closed O
pores S-PRO
and O
porosity S-PRO
values O
of O
43Collins O
investigated O
the O
use O
and O
production S-MANP
of O
a O
permeable B-BIOP
membrane E-BIOP
heatsink O
produced O
by O
AM S-MANP
. O


In O
order O
to O
find O
the O
process B-PARA
settings E-PARA
that O
will O
result O
in O
permeable O
walls O
, O
test O
cubes O
were O
printed O
with O
fins O
on O
top O
with O
a O
height O
of O
1 O
mm S-MANP
and O
wall B-FEAT
thicknesses E-FEAT
varying O
from O
150 O
to O
500 O
The O
core S-MACEQ
of O
the O
cubes O
was O
used O
to O
determine O
bulk B-PRO
porosity E-PRO
. O


All O
fins O
below O
300 O
failed O
to O
print S-MANP
while O
300 O
fins O
were O
successfully O
printed O
only O
for O
process B-PARA
settings E-PARA
resulting O
in O
low O
bulk B-PRO
porosity E-PRO
. O


The O
400 O
and O
500 O
fins O
printed O
successfully O
for O
all O
process B-PARA
settings E-PARA
used O
. O


7 O
Functional B-CONPRI
material I-CONPRI
complexity E-CONPRI
The O
design B-CONPRI
process E-CONPRI
can O
also O
consider O
that O
to O
solve O
some O
technological O
problems O
or O
to O
optimise O
some O
local O
properties S-CONPRI
, O
some O
processes S-CONPRI
allow O
building O
up O
multi-material S-CONPRI
objects O
or O
objects O
with O
material B-CONPRI
gradients E-CONPRI
. O


In O
some O
cases O
there O
has O
been O
significant O
progress O
although O
it O
increases O
the O
complexity S-CONPRI
of O
simulation S-ENAT
and O
of O
process B-CONPRI
planning E-CONPRI
of O
AM-based O
value O
chains O
. O


In O
addition O
, O
there O
are O
no O
standard S-CONPRI
functionalities O
in O
the O
commercial O
software S-CONPRI
that O
could O
support S-APPL
such O
definitions O
, O
which O
must O
be S-MATE
managed O
manually O
or O
directly O
defined O
on O
the O
legacy O
software S-CONPRI
associated O
to O
specific O
processes S-CONPRI
. O


One O
basic O
functionality O
relates O
to O
material B-CONPRI
gradient E-CONPRI
of O
polymers S-MATE
and O
elastomer S-MATE
parts O
manufactured S-CONPRI
with O
voxel-based O
technologies S-CONPRI
. O


The O
design B-CONPRI
process E-CONPRI
criticaly O
addresses O
the O
local O
characteristics O
of O
the O
material S-MATE
for O
each O
voxel S-CONPRI
of O
the O
object O
. O


Another O
feature S-FEAT
that O
is O
mostly O
used O
for O
metallic B-MACEQ
parts E-MACEQ
is O
lattice B-FEAT
structure E-FEAT
that O
could O
help O
in O
designing O
internal B-PRO
structures E-PRO
used O
to O
support S-APPL
the O
parts O
but O
also O
to O
minimize O
weight S-PARA
with O
respect O
to O
given O
functionalities O
. O


In O
highly O
developed O
sectors O
for O
metal S-MATE
fabrication S-MANP
, O
in O
particular O
aeronautic O
and O
medical B-APPL
applications E-APPL
, O
AM B-MANP
processes E-MANP
use O
many O
metals S-MATE
like O
stainless B-MATE
steel E-MATE
, O
titanium S-MATE
, O
aluminum S-MATE
, O
cobalt B-MATE
chrome E-MATE
and O
nickel B-MATE
alloys E-MATE
. O


An O
important O
feature S-FEAT
of O
metal S-MATE
is O
its O
microstructure S-CONPRI
. O


For O
a O
given O
metal S-MATE
, O
there O
can O
be S-MATE
a O
variety O
of O
microstructural S-CONPRI
features O
that O
affect O
its O
mechanical B-CONPRI
properties E-CONPRI
. O


The O
size O
of O
grains S-CONPRI
, O
micro-segregation S-CONPRI
of O
alloying B-MATE
elements E-MATE
, O
phases O
within O
the O
metal S-MATE
and O
size O
of O
dendrites S-BIOP
relates O
to O
the O
tensile B-PRO
strength E-PRO
and O
ductility S-PRO
. O


During O
the O
AM B-MANP
process E-MANP
, O
the O
microstructure S-CONPRI
is O
formed O
in-situ S-CONPRI
and O
would O
depend O
obviously O
on O
the O
process B-CONPRI
parameters E-CONPRI
and O
material S-MATE
used O
. O


The O
microstructure S-CONPRI
of O
metals S-MATE
determines O
the O
mechanical B-CONPRI
properties E-CONPRI
of O
the O
part O
such O
as S-MATE
yield O
strength S-PRO
, O
ductility S-PRO
and O
hardness S-PRO
. O


Varying O
the O
process B-CONPRI
parameters E-CONPRI
like O
the O
energy O
sources O
and O
fill O
patterns O
can O
lead S-MATE
to O
differences O
in O
grain B-CONPRI
structure E-CONPRI
. O


Such O
issues O
are O
both O
a O
very O
important O
potential O
advantage O
but O
also O
an O
additional O
complexity S-CONPRI
when O
considering O
the O
AM S-MANP
design O
process S-CONPRI
. O


Functionally B-MATE
Graded I-MATE
Materials E-MATE
are O
defined O
as S-MATE
a O
class B-MATE
of I-MATE
advanced I-MATE
materials E-MATE
characterised O
by O
spatial B-FEAT
variation E-FEAT
in O
material S-MATE
composition S-CONPRI
across O
the O
volume S-CONPRI
, O
contributing O
to O
corresponding O
changes O
in O
material B-CONPRI
properties E-CONPRI
in O
line O
with O
the O
functional O
requirements O
. O


The O
multi-functional O
status O
of O
a O
component S-MACEQ
is O
tailored O
through O
the O
material S-MATE
allocation O
at O
microstructure S-CONPRI
to O
meet O
an O
intended O
performance S-CONPRI
requirement O
. O


Microstructural S-CONPRI
gradation O
contributes O
to O
a O
smooth O
transition S-CONPRI
between O
properties S-CONPRI
of O
the O
material S-MATE
. O


Another O
approach O
is O
based O
on O
Young O
's O
modulus O
variation S-CONPRI
for O
the O
determination O
of O
the O
mechanical S-APPL
propertiesgradients O
, O
and O
consequently O
material S-MATE
microstructure O
or O
composition S-CONPRI
variations O
. O


Another O
interesting O
proposition O
comes O
from O
who O
proposes O
an O
interpretation O
of O
the O
material S-MATE
with O
intermediary B-MACEQ
density E-MACEQ
as S-MATE
a O
lattice B-FEAT
cellular I-FEAT
structure E-FEAT
that O
could O
be S-MATE
composed O
by O
several O
materials S-CONPRI
. O


Homogeneous B-PRO
FGM I-PRO
composition E-PRO
creates O
porosity S-PRO
or O
density B-PRO
gradients E-PRO
by O
modulating O
the O
spatial B-FEAT
microstructure E-FEAT
or O
morphology S-CONPRI
of O
lattice B-FEAT
structures E-FEAT
across O
the O
volume S-CONPRI
of O
material S-MATE
through O
a O
voxel S-CONPRI
approach O
. O


This O
method O
can O
be S-MATE
called O
densification S-MANP
FGMThe O
directionality O
, O
magnitude S-PARA
and O
density B-ENAT
concentration E-ENAT
of O
the O
material S-MATE
substance O
in O
a O
monolithic S-PRO
anisotropic B-MATE
composite E-MATE
structure O
contributes O
to O
functional O
deviations O
such O
as S-MATE
stiffness O
and O
elasticity S-PRO
. O


The O
gradual O
transition S-CONPRI
from O
a O
solid O
exterior O
to O
a O
porous S-PRO
core S-MACEQ
leads O
to O
an O
excellent O
strength-to-weight O
ratio O
. O


Even O
if O
new O
standards S-CONPRI
are O
partly O
addressing O
such O
models O
, O
the O
development O
of O
mathematical S-CONPRI
representations O
useful O
for O
both O
design S-FEAT
and O
simulation S-ENAT
is O
still O
in O
progress O
. O


FGM S-MANP
can O
also O
address O
the O
aspect O
of O
multi-materiality O
through O
an O
approach O
of O
dynamically O
composed O
gradients O
or O
complex B-CONPRI
morphology E-CONPRI
. O


The O
geometric O
and O
material S-MATE
arrangement O
of O
the O
phases O
controls O
the O
overall O
functions O
and O
properties S-CONPRI
of O
the O
FGM S-MANP
component S-MACEQ
. O


Multi-material S-CONPRI
FGM S-MANP
seeks O
to O
improve O
the O
interfacial B-MATE
bond E-MATE
between O
dissimilar O
or O
incompatible O
materials S-CONPRI
. O


Distinct O
boundaries S-FEAT
can O
be S-MATE
removed O
through O
a O
heterogeneous S-CONPRI
compositional O
transition S-CONPRI
from O
a O
dispersed O
to O
an O
interconnected O
second O
phase S-CONPRI
structure O
, O
graded O
layers O
with O
discrete O
compositional O
parameters S-CONPRI
or O
smooth O
concentration O
gradients O
. O


Once O
again O
, O
material S-MATE
models O
are O
too O
complicated O
to O
be S-MATE
used O
for O
simulation S-ENAT
. O


Demonstration O
and O
validation S-CONPRI
during O
the O
design S-FEAT
phase O
of O
expected O
characteristics O
is O
still O
to O
be S-MATE
expected O
in O
a O
general O
manner O
. O


But O
this O
is O
an O
interesting O
issue O
to O
be S-MATE
expected O
because O
, O
by O
fusing S-CONPRI
one O
material S-MATE
to O
another O
three-dimensionally S-CONPRI
using O
a O
dynamic S-CONPRI
gradient O
, O
the O
printed O
component S-MACEQ
can O
have O
the O
optimum O
properties S-CONPRI
of O
both O
materials S-CONPRI
. O


It O
can O
be S-MATE
transitional O
in O
weight S-PARA
, O
yet O
retaining O
its O
toughness S-PRO
, O
wear B-PRO
resistance E-PRO
, O
impact S-CONPRI
resistance O
or O
its O
physical O
, O
chemical O
, O
biochemical O
or O
mechanical B-CONPRI
properties E-CONPRI
. O


Multi-material S-CONPRI
FGM S-MANP
can O
also O
provide O
location-specific O
properties S-CONPRI
tailored O
at O
small O
sections O
or O
strategic O
locations O
around O
pre-determined O
parts O
. O


Some O
AM B-MANP
technologies E-MANP
are O
providing O
such O
opportunities O
. O


Construction S-APPL
of O
such O
parts O
could O
be S-MATE
of O
interest O
to O
solve O
design S-FEAT
issues O
in O
order O
to O
avoid O
multi-part O
assemblies O
or O
complex O
joints O
for O
example O
. O


Simulation S-ENAT
models O
are O
still O
to O
be S-MATE
implemented O
and O
validated O
mostly O
because O
the O
design S-FEAT
of O
heterogeneous S-CONPRI
compositional O
gradients O
are O
very O
complex O
. O


They O
can O
be S-MATE
divided O
into O
four O
types O
: O
a O
transition S-CONPRI
between O
two O
materials S-CONPRI
, O
three O
materials S-CONPRI
or O
above O
, O
switched O
composition S-CONPRI
between O
different O
locations O
or O
a O
combination O
of O
density S-PRO
and O
compositional O
gradation O
. O


The O
key O
design S-FEAT
parameters O
of O
FGM S-MANP
include O
the O
dimension S-FEAT
of O
the O
gradient O
vector O
, O
the O
geometric B-FEAT
shape E-FEAT
and O
the O
repartition O
of O
the O
equipotential B-CONPRI
surfaces E-CONPRI
. O


The O
features O
and O
functionality O
of O
the O
component S-MACEQ
are O
further O
determined O
by O
the O
direction O
of O
the O
gradient O
within O
the O
material S-MATE
composition S-CONPRI
. O


The O
design S-FEAT
and O
types O
of O
the O
volumetric O
gradient O
can O
be S-MATE
classified O
according O
to O
1D O
, O
2D S-CONPRI
and O
3D S-CONPRI
, O
and O
distribution S-CONPRI
of O
materials S-CONPRI
uniformly O
or O
through O
special O
patterns O
. O


Defining O
the O
optimum O
material S-MATE
distribution S-CONPRI
function O
requires O
extensive O
knowledge O
of O
material S-MATE
data S-CONPRI
that O
includes O
the O
chemical B-CONPRI
composition E-CONPRI
, O
its O
characteristics O
and O
the O
manufacturing B-CONPRI
constraints E-CONPRI
. O


At O
present O
, O
there O
are O
no O
design S-FEAT
guidelines O
on O
material S-MATE
compatibility O
, O
mixing S-CONPRI
range O
for O
materials S-CONPRI
with O
variable O
and O
non-uniform O
properties S-CONPRI
and O
a O
framework S-CONPRI
for O
optimal O
property S-CONPRI
distribution S-CONPRI
such O
as S-MATE
choice O
of O
spatial O
, O
gradient O
distribution S-CONPRI
and O
the O
arrangement O
of O
transition B-CONPRI
phases E-CONPRI
is O
also O
lacking O
. O


When O
generating O
graded O
components S-MACEQ
of O
high O
to O
low O
strength S-PRO
, O
the O
changing O
material B-CONPRI
properties E-CONPRI
brought O
about O
by O
modifications O
to O
the O
microstructure S-CONPRI
have O
to O
be S-MATE
carefully O
measured O
and O
quantified O
. O


Tamas-Williams O
suggested O
two O
useful O
approaches O
to O
model S-CONPRI
the O
response O
of O
functionally B-FEAT
graded I-FEAT
components E-FEAT
using O
the O
exponential O
law O
idealisation O
and O
material B-MATE
elements E-MATE
Finite B-CONPRI
Element I-CONPRI
Method I-CONPRI
analysis E-CONPRI
can O
also O
be S-MATE
used O
to O
show O
and O
suggest O
an O
optimised O
set S-APPL
of O
elements S-MATE
under O
pre-determined O
circumstances O
to O
provide O
a O
better O
understanding O
of O
how O
the O
material B-CONPRI
properties E-CONPRI
will O
behave O
. O


In O
order O
to O
generalise O
the O
use O
of O
FGM S-MANP
, O
it O
is O
crucial O
to O
understand O
the O
resulting O
differences O
between O
the O
predicted S-CONPRI
and O
real O
components S-MACEQ
. O


By O
knowing O
the O
required O
mix O
of O
properties S-CONPRI
, O
the O
required O
arrangement O
of O
phases O
, O
and O
compatibility O
of O
materials S-CONPRI
design B-CONPRI
rules E-CONPRI
and O
methods O
have O
to O
be S-MATE
established O
to O
avoid O
undesirable O
results O
. O


Knowledge O
of O
the O
relationship O
can O
be S-MATE
gained O
through O
shared O
databases S-ENAT
as S-MATE
a O
catalogue O
of O
material S-MATE
performance O
information O
. O


Richards O
first O
proposed O
a O
computational O
approach O
of O
using O
CPPN O
encodings O
and O
a O
scalable O
algorithm S-CONPRI
using O
NEAT O
to O
embed O
functional O
morphologies S-CONPRI
and O
macro-properties S-PRO
of O
physical O
features O
using O
multi-material S-CONPRI
FGM S-MANP
through O
voxel-based O
descriptions O
by O
a O
function O
of O
its O
Cartesian O
coordinates S-PARA
. O


Some O
progresses O
are O
still O
expected O
but O
FGM S-MANP
or O
multi-material S-CONPRI
parts O
in O
general O
are O
being O
seriously O
considered O
as S-MATE
solutions O
for O
design S-FEAT
evolution O
of O
products O
in O
the O
future O
. O


This O
is O
already O
used O
for O
polymers S-MATE
and O
elastomers S-MATE
and O
this O
is O
in O
progress O
for O
metallic S-MATE
products O
. O


8 O
Assembly S-MANP
and O
part O
integration O
considerations O
It O
is O
well O
recognized O
that O
it O
is O
possible O
to O
exploit O
the O
potential O
of O
additive B-MANP
manufacturing E-MANP
at O
product O
level O
. O


As S-MATE
one O
may O
infer O
by O
the O
existing O
standards S-CONPRI
, O
AM B-MANP
technologies E-MANP
already O
play O
a O
significant O
role O
not O
only O
for O
single O
parts O
but O
also O
at O
product O
level O
. O


Therefore O
, O
the O
classical O
Design B-FEAT
for I-FEAT
Assembly E-FEAT
approaches O
have O
to O
be S-MATE
reconsidered O
in O
order O
to O
take O
advantage O
of O
these O
AM S-MANP
opportunities O
. O


An O
n-part O
product O
may O
be S-MATE
classified O
as S-MATE
static O
, O
movable O
, O
or O
compliant O
assembly S-MANP
and O
it O
may O
have O
components S-MACEQ
of O
the O
same O
or O
different O
materials S-CONPRI
. O


AM B-MANP
technologies E-MANP
enable O
the O
possibility O
to O
produce O
not O
only O
a O
single O
part O
of O
an O
assembly S-MANP
, O
but O
directly O
the O
assembled O
product O
. O


This O
review O
shows O
many O
possible O
joints O
directly O
fabricated S-CONPRI
either O
using O
polymers S-MATE
or O
metals S-MATE
. O


Furthermore O
a O
deep O
discussion O
of O
polymer-based O
non-assembly O
mechanisms O
may O
be S-MATE
found O
in O
, O
proving O
that O
the O
polymer-based O
AM B-MANP
technologies E-MANP
are O
close O
to O
maturity O
for O
this O
kind O
of O
application O
. O


35 O
shows O
a O
metallic B-FEAT
compliant I-FEAT
joint E-FEAT
for O
a O
snake-like O
surgical O
robot S-MACEQ
, O
produced O
by O
PBF S-MANP
. O


In O
36 O
, O
the O
detail O
design S-FEAT
of O
a O
rotational O
joint S-CONPRI
and O
a O
snap-fit B-FEAT
feature E-FEAT
are O
shown O
for O
a O
nanosatellite O
metallic S-MATE
cubic B-FEAT
structure E-FEAT
fabricated O
by O
L-PBF S-MANP
. O


But O
what O
about O
the O
design B-CONPRI
rules E-CONPRI
to O
fully O
exploit O
the O
AM B-MANP
technologies E-MANP
in O
assembly S-MANP
manufacturing O
? O
In O
the O
following O
, O
a O
brief O
analysis O
of O
the O
design B-CONPRI
rules E-CONPRI
and O
in O
particular O
of O
the O
part B-CONPRI
consolidation E-CONPRI
steps O
in O
designing O
a O
product O
will O
be S-MATE
considered O
. O


8.1 O
Assembly S-MANP
design O
rules O
As S-MATE
deeply O
discussed O
in O
, O
when O
dealing O
with O
assemblies O
and O
AM B-MANP
technologies E-MANP
, O
one O
main O
issue O
still O
to O
be S-MATE
adequately O
addressed O
is O
the O
geometrical O
product O
specification S-PARA
. O


In O
fact O
, O
no O
specific O
ISO-GPS O
or O
ASME-GD O
& O
T O
standard S-CONPRI
dedicated O
to O
AM B-MANP
processes E-MANP
exists O
, O
leaving O
design S-FEAT
as S-MATE
a O
cumbersome O
process S-CONPRI
of O
defining O
geometrical O
requirements O
of O
assembly S-MANP
features O
or O
of O
single O
parts O
using O
a O
language O
dedicated O
to O
conventionally O
manufactured B-CONPRI
products E-CONPRI
. O


Referring O
to O
an O
assembly S-MANP
with O
fixed O
connection O
type O
, O
general O
rules O
to O
design S-FEAT
fasteners/connectors O
, O
in O
particular O
snap-fit B-FEAT
features E-FEAT
, O
are O
presented O
with O
respect O
to O
polymer-based O
AM B-MANP
processes E-MANP
in O
, O
and O
to O
metal-based O
ones O
in O
. O


These O
general O
rules O
address O
issues O
on O
fastener/connector O
shape O
, O
wall B-FEAT
thickness E-FEAT
, O
gap O
width O
, O
staircase O
effect O
on O
sloped O
surfaces S-CONPRI
, O
and O
on O
the O
influence O
of O
anisotropy S-PRO
on O
the O
assembly S-MANP
product O
mechanical S-APPL
behavior O
. O


Dealing O
with O
non-assembly O
mechanisms O
, O
design B-CONPRI
rules E-CONPRI
are O
discussed O
mainly O
referring O
to O
polymer-based O
AM B-MANP
processes E-MANP
like O
extrusion-based O
, O
material B-MANP
jetting E-MANP
, O
and O
vat B-MANP
photopolymerization E-MANP
processes S-CONPRI
. O


The O
design B-CONPRI
rules E-CONPRI
refer O
to O
the O
minimization O
and O
the O
removal O
of O
the O
supports S-APPL
used O
during O
the O
non-assembly O
product O
fabrication S-MANP
, O
the O
effect O
of O
build B-PARA
orientation E-PARA
on O
the O
smoothness S-CONPRI
of O
the O
mechanism S-CONPRI
, O
and O
the O
selection O
of O
the O
clearance S-CONPRI
between O
assembled O
parts O
. O


Considering O
the O
latter O
issue O
, O
in O
a O
benchmark S-MANS
is O
proposed O
to O
assess O
the O
lowest O
clearance B-PRO
limits E-PRO
for O
non-assembly O
mechanisms O
. O


8.2 O
Part B-CONPRI
consolidation E-CONPRI
Part O
consolidation S-CONPRI
is O
the O
first O
and O
most O
relevant O
step S-CONPRI
in O
design B-FEAT
for I-FEAT
assembly E-FEAT
. O


But O
this O
is O
not O
the O
case O
when O
exploiting O
AM B-MANP
processes E-MANP
since O
they O
enable O
non-assembly O
mechanisms O
, O
multi-material B-MANP
printing E-MANP
, O
and O
easier O
functional O
integration O
. O


A O
significant O
example O
of O
AM B-MACEQ
part E-MACEQ
consolidation O
is O
the O
one O
reported O
in O
. O


The O
original O
portable O
hydraulic O
manifold O
was O
used O
for O
in-situ S-CONPRI
testing O
of O
aircraft B-APPL
components E-APPL
, O
a O
17-part O
assembly S-MANP
, O
and O
was O
completely O
redesigned O
as S-MATE
a O
single-part O
product O
, O
with O
60 O
% O
less O
weight S-PARA
, O
the O
same O
footprint O
, O
a O
53 O
% O
shorter O
height O
, O
and O
with O
a O
more O
reliable O
and O
robust O
design S-FEAT
with O
respect O
to O
the O
original O
one O
, O
deeply O
exploiting O
a O
metal B-MANP
powder I-MANP
bed I-MANP
fusion E-MANP
technology O
. O