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Numerical modelling of the gas-powder flow during the laser
metal deposition for
additive manufacturing Quanren ZENGa, Yankang TIANa, Zhenhai
XUa, b, and Yi QINa, 1
a Centre for Precision Manufacturing, Department of Design,
Manufacture and Engineering Management, University of Strathclyde,
Glasgow, G1 1XJ, UK
b National Key Labfor Precision Hot Processing of Metals &
School of Materials Science and Engineering, Harbin Institute of
Technology, Harbin 150001, China
Abstract. As one of the most popular additive manufacturing (AM)
technologies in the aerospace industry, laser metal deposition
(LMD) employs moving laser to melt the coaxially ejected metal
powders near the laser focal point, forms a molten pool on the
substrate and consequently traps the powders and solidifies the
tracks to construct the components with complex geometry
layer-by-layer. The mechanical properties and functionality-related
performance of the deposited components by LMD depend on the
factors such as metal powder’s material/shape, supply status of
powders and gas, laser-related manufacturing parameters. According
to these influencing factors, there are 4 sub-processes to be
modelled in sequence to realize holistic LMD modelling: (1)CFD
simulation of the gas-powder flow; (2)laser-powders interaction;
(3)formation of molten pool due to laser irradiation with mass and
heat addition; (4)solidification of molten pool with deposited
metal powders and formed solid track. In this paper, gas-powder
flow within the internal passages of laser deposition head and then
ejecting from the nozzles’ tips were modelled and analyzed to give
a well-depicted image of the related key physics during the LMD
process. An in-depth study of the gas-powder flow in LMD via
numerical simulation could give a better understanding of
subsequent formation mechanism of molten pool and deposited tracks,
which will eventually offer more controllable and optimized
processing parameter sets to improve the functionality-related
performance of LMDed parts.
Keywords. additive manufacturing(AM), laser metal deposition
(LMD), gas-powder flow, molten pool formation, solidification,
deposited solid track
1. Introduction
Laser metal deposition (LMD) is a promising additive
manufacturing technology for the fabrication of the near net shape
parts with streams of metal powder for some high performance
applications in the aircraft & aerospace, high performance
automotive, medical device, nuclear industry[1]. Many physical
phenomena and influencing factors involve in the LMD additive
manufacturing process and all of them will have direct or indirect
effect on the microstructure and material properties of the final
deposited parts[2-4]. A full control of these influencing factors
and processing variables such as laser power, scanning speed,
powder density, powder feed rate, size distribution and other
processing variables, is required to achieve high-quality deposited
parts. However,
1 Corresponding Author, Prof Yi Qin, DMEM, University of
Strathclyde, UK; [email protected]
-
choosing ttime consfrom beindevelop avariable se
2. Descrip
In LMD, aand are acthe nozzleplane prioand formspowders klayer
and beam movsub-procemodellinginteractionpowder mand forme
This powder fldetails of
3. Numer
The gas-pnozzles’ tflow can turbulent i
the reasonablesuming and exng wider useda reliable numet for
producin
ption/breakd
as shown in Fccelerated andes’ tips; then tor to depositios a
molten pkeep depositinthe molten z
ves away. Accsses could be
g: (1) CFD sn[6]; (3) form
mass and heat;ed solid track.
F
research mailow in LMDgas-powder fl
rical Modellin
powder flows itips and the sube characteriinert gas and
e and robust pxpensive[5]. Td in practical
merical modelng crack free
own of LMD
ig.1, metal pod becomes a fthe powder jeon on the subpool
trapping ng and adding one finally socording to themodelled in
simulation of ation of molt(4) solidifica
Fig. 1 Schematic
inly focused; and a 3D Clow status of L
ng of gas-pow
in the nozzlesubstrate are nized as a twothe secondary
processing varThis to some e
l production.l which couldand reliable p
D process
owders firstly fully developeets interact witstrate, which the
incident
into the moltolidifies and fese physical phsequence and the
gas-pow
ten pool due ation of molte
diagram of holist
on the firstCFD model wLMD process
wder flow for
s’ ducts and wnot a simple oo-phase flow,y phase consis
riable set via extent hinders
A more expd serve to ideparts by using
flow within thed flow beforeth the laser beis melted duepowder
jets;
ten pool on theforms the trachenomena andthen coupled
wder flow[4]; (to laser irrad
en pool with d
tic LMD process
sub-process owhich could was establish
LMD
within the interone-phase turb, in which thsts of the meta
experiment iss the LMD Apecting alternaentify proper LMD.
he deposition e being ejecteeam near the le to the laser the
melted e surface of thcks/clads whend procedures, to realize
hol
(2) laser/metadiation with adeposited meta
[1]
of modelling accurately sim
hed and analyz
raction zone bbulent flow. Inhe primary phal powder par
s obviously AM process native is to
processing
head ducts ed out from laser focus irradiation or trapped he
growing en the laser
there are 4 listic LMD al powders addition of al powders
gas-metal mulate the zed.
between the n fact, this hase is the rticles. The
-
behavior othe particlcan be hasize districoupling tkind of
stainvolved turbulencedeveloped
.
(a) deposit
As shconical mcentral nointernal pdiagram ogas-powdreaches a the
deposinozzles’ tithen intermaximus domain arof overall
complicattaken for steady-stainlets; (2)coupled dradiation with an
av
For thinner gas the melt p(argon) vi
of particles sules and the flo
andled by the ibution. The ithe discrete anable balance[7in the
powdee phenomenod based on the
tion head
Fig.2 The prac
hown in Fig.2etal structure
ozzle for gas aassages and d
of how the laser mixture isfully developition head andips, 4
gas-pow
rsect with eacpowder mas
re discretized calculation sp
ted geometry modelling of
ate turbulent f)the powder discrete phaseis temporarily
verage diamethe deposition nozzle to pro
pool. The TiAia 4 nozzles w
uspended in aow. Turbulentconcept of ed
interaction of nd continuous7-9]. To realizeer feeding syson for
the ge nozzle setup
(b) geome
ctical laser deposi
2(a), the typicawith 4 copperand laser passducts are giveser
deposition s firstly injecped flow whild nozzles. Onwder mixed jech
other to fos concentratiby different lpeed and the(such as the nf
the gas-powflow with a cparticles volue modeling (y neglected; (er
of 100um. simulation, a
otect the laser Al powders wewhich are spac
a turbulent flot dispersion ofddy diffusion the particle a
s phase until te the simulatiostem of the Lgas-powder flshown in
Fig
etry of internal pa
ition head and its
al constructior powder nozzsing through en in Fig.2(b)head
deliver
cted into the le travelling thnce the gas-poets will firstly orm
a small cion of the galevel of meshrequired accunozzle tip andwder
flow: (1constant veloume fraction (DPM) is ado(4)the particle.
25L/min argooptics from t
ere delivered ced equally a
ow depends of both the partenergy in som
and gas couldthe solutions ion and analyzLMD depositiflow, a
nume.2(a).
assages
internal geometr
on of a real lazles facing to coaxially. its ). Fig.2(b)
alspowders withinlets of lase
hrough the paowder flow isflying withouircular focuseas-powder
flohes to both couracy at some d focus plane))gas-powder
ocity and presis less than
opted; (3)the e size is assum
on jet is supplthe reboundinto the melt pround the inn
n the propertiticles and the me range of td be solved byin both
phasese powder flowion head, esperical model
(c) meshes of C
ry with passages
aser depositiona focal point adetailed geom
so shows the h assistance oer deposition assages and du
sprayed out ut interactive aed spot whichow. Fig.2(c) nsider the
imlocal critical
) Some assummixture is tr
ssure distribut10% and theheat transfe
med to be sph
ied and ejecteg particles anool by using
ner gas nozzle
ies of both carrier gas
the particle y two-way s achieve a w behavior
pecially the has been
CFD domain
n head is a and 1 main metry with schematic
of gas.. The n head and ducts inside
from the 4 actions and h show the shows the
mprovement areas with
mptions are reated as a tion at the e one-way
er by laser herical and
ed from the nd to shield
carrier gas e. The total
-
flow rate around thcarrier gatip/outlet iThe initiaTable 1.
Tab
Inputs for
pressure oInner gas dInner gas fInner gas fpressure ocarrier
gascarrier gascarrier gas
4. Results
There areparticle mbeing ejecaffect the If powdermolten
povariable m
(a) velocity
The velocvelocity ooutlet of constantlyof the velacceleratebeing
ejecmaximumThe collisdue to the
of the carrierhe main inner as-powder jetis 1.17mm. E
al conditions f
ble 1 Material pro
r CFD
f inner gas at inledensity (Ar) flow velocity (Arflow rate (Ar)
f carrier gas at in
s density (Ar) s flow(Ar) s flow rate (Ar)
s and discussi
e many outpumass concentra
cted from thefurther sub-pr
rs have sufficiool on the subsmay need to pa
of gas-powder (t
Fig.3
city of gas-poof the gas-pownozzles. It is
y while the selocity for the ed in the passcted out from
m magnitude (asion of particl blown gas. A
gas for the 4gas nozzle a
ts be trappedach of the nozfor CFD simu
operties & proces
Value
et 300 MPa1.67 kg/m
r) 0.118 m/416.7 mm
nlet 300 MPa1.67 kg/m0.588 m/83.3 mm
ion of CFD si
ut variables fration, DPM nue nozzles, arerocesses of deiently
large vestrate, then theay attention to
wo phase) (b) ve
3 CFD simulation
owder flow iwder flow is
s because the ectional area n
dispersed posages and dum the nozzlesaround 40m/s)es means
the
As shown in Fi
4 nozzles is 5 and point to td to the meltzzles is titled
ulation of gas
ssing parameters u
Inputs f
a average m3 powder /s powder m3/s powder a dia of cem3 number
/s dia of po
m3/s Stand-o
imulation
from CFD simnumber of colle the main vaeposition and selocity
and cae rebounding
o.
elocity of powder
n result of the velo
is shown in t still within inlet pressur
near the nozzlowders is showucts of nozzles, their veloc) before
they possiblity thaig.3(c), the co
L/min. Thesethe melt poolt pool. The d65 degree fro-powder
flow
used for numerica
for CFD
diameter of powdensity (TiAl) flow rate (inlet)flow velocity
(inentral nozzle (outof powder nozzleowder nozzles(ou
ff distance
mulation, in wlision and trajariables of insolidification
annot been absvelocity of po
r(discrete phase) (
ocities of gas & p
the Fig.3(a). the nozzle dure and flow rle is at the miwn in the
Figes stage-by-stcities keep incollide with e
at powder willollision are mo
e 4 nozzles ar which coulddiameter of t
om the substraw are given an
al simulation of L
Value
ders 100um 3910kg/m2.55 (g/m
let) 0.118m/tlet) 6.4mm es 4 utlet) 1.17mm
9.5 mm
which particlejectory of pow
nterest that wof molten poosorbed or trapowders is anot
(c) DPM number
powder
We could seucts especiallyrate of gas arinimum. The g.3(b). The
paage. After th
ncreasing and each other neal collide with ost likely to be
re installed d make the the nozzle ate surface. nd listed in
LMD
/m3 min) /s
m
e velocity, wders after
will directly ol in LMD. pped by the ther output
r of collisions
ee the max ly near the re supplied magnitude
articles are he particles d reach the ar the focus.
each other e happened
-
within thechange. Bcollide unThis meancollision
(a) PM
(c) PM
F
Particle mspecified where thevariation ejecting otravelling
4(b)), the jets travelblurred. Wparticle mIf the focaheat
couldfocal poinextremelyconsequenshows a la(c). It is mand even
b
e internal ductBut after the pntil four jets ons that the
pountil they are
MC at different di
MC at the level y=
Fig. 4 Particle ma
mass concentrplane or in a
e particles areof particle m
out from the nto and concenparticle mass
ls to the levelWhen the 4 j
mass concentraal point of a d be employednt and the poy
important fntly generatioarger influencmainly becausbounce back
o
ts especially apowders are ejf the powders
owders ejectedintersected w
stances away from
=-6.5mm
ass concentration
ration is a vaspecified vol
e more likely mass concentra
nozzles, therentrating on a ps concentrationl of y=-6.5mmjets
travels toation of the 4 jlaser beam isd to melt the dsition of the
for full fusion of crack-fre
cing area of pase that it is neonce comes in
at the positionjected out fros from the 4 nd from the no
with each other
m nozzle tip (b
(d)
at different locat
ariable that delume. It couldto gather. Fig
ation along the is a clear trpoint of intersn of the 4 jetsm
(Fig. 4(b)),o the level ojets seem to c
s just at this lodensest cloud convergent h
on of the deee and high-qarticle mass cear the focal
nto contact wit
n where its secom the nozzlesnozzles concenozzles will flyr near
the foca
b) PMC at the lev
)PMC around lase
tions away from t
escribe the ded give the strag. 4(a) showshe stand-off drend
that the section. At ths are separate, the boundarf y=-9.5mm
converge at thocation, then of particles. M
highest particlepoisted substquality depoisoncentration tpoint
and somth the substrat
ctional area has, they are lesntrate on the f
y with less poal point.
vel y=-1mm
er focus level y=-
the outlet of nozz
ensity of partaightforward is the simulatedistance of LM
4 jets of pae level of y=- and discrete.y of 4 jets is (Fig.
4(c)), t
he middle of ththe highest la
Matching the e mass concetrate and parted tracks. Ththan that of
Fime particles wte.
as a abrupt ss likely to focus leve.
ossibility of
-9.5mm
zle
ticles on a impression
ed result of MD. After articles are -1mm (Fig. . When the s
becoming the highest he domain. aser power laser beam
entration is rticles and he Fig.4(d) ig.4(b) and will
collide
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5. Conclusions
LMD, based on blowing a powder stream into a moving
laser-induced melt pool, is widely employed in the field of
advanced manufacturing, such as rapid manufacturing, surface
enhancement, tooling and repair. In LMDS, metal powders firstly
travel in the laser deposition head, then eject out from the 4
nozzles, gradually converge into the focal point and get molten
near or within the molten pool, and finally deposited as a track
layer on the substrate. Modelling of LMD is difficult as it is
characterized by multiple phase changes, mass and heat flows. In
this research, the whole LMD process is analyzed and the gas-powder
flow including powder conveyance and dispersion are detailedly
investigate due to its direct influence on the subsequent track
formation and residual stress on the substrate. The proposed CFD
numerical model of gas-powder flow could be used to gain full
insight into the powder deposition process and to analyze the
influence of the geometrical & processing parameters such as
the standoff distance, volumetric gas flow rate, and powder mass
flow rate on the quality of the LMD. Also, the developed model
provides important parameters for the calculation of the heat
transfer boundary condition for the holistic LMD process once the
laser radiation is added into the model.
Acknowledgement
The authors would like to acknowledge the support from EU H2020
project MMTECH (GA 633776) for the research reported in this
paper.
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