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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
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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