Icomp 2016

On the Numerical Simulation of
AM Processes
M. Chiumenti1,2, M. Cervera1, N. Dialami1, C. Agelet de Saracibar1
1 International Center for Numerical Methods in Engineering (CIMNE)
UPC BarcelonaTech, Barcelona, Spain
W. Huang2, X. Lin2, L. Wei2, Y. Zheng2, L. Ma2
2 State Key Laboratory of Solidification Processing (SKLSP)
Northwestern Polytechnical University (NWPU), Xi’an, China
2nd International Conference on
Computational Methods in Manufacturing Processes
Liège, Belgium, 18-20 May 2016
ICOMP 2016

 Introduction, motivation and goals
 Problem statement
 Computational model
 Numerical simulations
 Concluding remarks
Outline
Outline
June 19, 2016 Carlos Agelet de Saracibar 2

 Introduction, motivation and goals
o Additive Manufacturing (AM)
o AM Technologies
o AM Applications
o Key Benefits of AM
o Challenges of AM
o Goals
Outline > Introduction, Motivation and Goals
Introduction, Motivation and Goals

 Additive Manufacturing (AM)
“Additive Manufacturing (AM) is a process of joining materials to make objects
from 3D model data, usually layer upon layer, as opposed to subtractive
manufacturing methodologies” (ASTM-F2792-12a)
Additive Manufacturing (AM)

 AM Technologies
AM Technologies
AM Powder Bed Fusion (PBF) Directed Energy Deposition (DED)
Raw material Powder Powder, Wire
Energy source Laser, EB Laser, EB, Arc welding
Deposition rate 0.1-0.2 [Kg/h] 0.5-5 [Kg/h]
Layer thickness 0.01-0.1 [mm] 0.25-3.0[mm]
Techniques Selective Laser Sintering
(SLS), Selective Laser
Melting (SLM), Electron
Beam Melting (EBM)
Laser Metal Deposition (LMD)/Laser
Engineered Net Shaping (LENS),
Shaped Metal Deposition (SMD),
Laser Metal Deposition-wire (LMD-w)
Features Complex Shapes, Low
Deposition Rates, High
Dimensional Accuracy,
Small Components
Higher Deposition Rates, Lower
Dimensional Accuracy, Larger
Components
Applications Tooling, Functional Parts,
Prototypes
Metal Part Repair, Add Features to
Parts, Tooling, Functional Parts

 DED AM Technologies
AM Technologies
DED AM Blown Powder Wire-feed
Raw material Powder Wire
Energy source Laser, EB Laser, EB, Arc welding
Deposition rate 0.5-2.3 [Kg/h] 2.5-5 [Kg/h]
Layer thickness 0.25-1.0 [mm] 1.0-3.0 [mm]
Techniques Laser Metal Deposition
(LMD)/Laser Engineered Net
Shaping (LENS)
Shaped Metal Deposition (SMD),
Hot-wire Gas Tungsten Arc Welding
(HW-GTAW), Laser Metal
Deposition-wire (LMD-w)
Features High Deposition Rates, Low
Dimensional Accuracy, Large
Parts
Higher Deposition Rates, Lower
Dimensional Accuracy,
Larger Parts
Application Metal Part Repair, Add
Features to Parts, Tooling,
Functional Parts
Metal Part Repair, Add Features to
Parts, Tooling, Functional Parts

 Powder Bed Fusion (PBF) AM Technology
AM Technologies
AM process in which thermal energy
(laser/EB) selectively fuses regions of a
powder bed
o Selective Laser Sintering (SLS)
o Selective Laser Melting (SLM)
o Electron Beam Melting (EBM)

 Directed Energy Deposition (DED) AM Technology: Blown Powder
AM Technologies
AM process in which focused thermal
energy (laser/EB) is used to fuse powder
materials by melting as they are being
deposited
o Laser Metal Deposition (LMD)/Laser
Engineered Net Shaping (LENS)

 Directed Energy Deposition (DED) AM Technology: Wire-feed
AM Technologies
AM process in which focused thermal
energy (laser/EB/arc welding) is used to fuse
wire-feed materials by melting, being then
deposited
o Shaped Metal Deposition (SMD)
o Laser Metal Deposition-wire (LMD-w)
Object

AM Applications

 AM Applications: Sectors and Consumer Uses
AM Applications
Source: Wohlers Report 2014 Source: Wohlers Report 2014

 Innovation
o Freedom of design, complex shapes, inner cavities or foam/lattice structures,
impossible to produce by machining
o Thin walls and shapes difficult to produce by casting
o Light weight parts with lattice/foam inner structures
Key Benefits of AM
 Process and cost optimization
o Flexibility in design changes, agility of manufacturing operations, customized
design
o Reduced time to market
o No need for expensive and time-consuming part tooling and prototypes
o Lower energy consumption and less waste
 Enhanced mechanical properties
o Rapid cooling of each deposited layer
o Finer grain size compared to casting or forming technologies

 Geometrical accuracy
Challenges of AM
 Distortions
o Assembling problems
o High contact pressures
 Residual stresses
 Porosity
 Cracking, delamination, and swelling
 Substrate adherence and warping
 Scan strategy
 Deposition strategy

 Computational modeling and high-fidelity numerical simulation of
Wire-feed (SMD), Blown Powder (LMD/LENS), and Powder Bed
Fusion (SLS, SLM) AM processes
Goals
 Validation of the computational model for the numerical simulation
of Wire-feed (SMD), Blown Powder (LMD/LENS), and Powder Bed
Fusion (SLS, SLM) AM processes
 Sensitivity to different boundary conditions (heat convection, heat
radiation, environment temperature, clamping temperature),
material parameters (latent heat of fusion), and process parameters
(power absorption, pre-heating, hatches-by-hatches activation
sequence, layer-by-layer activation sequence) in the numerical
simulation of Blown Powder (LMD/LENS) AM processes

 Introduction
o Coupled thermomechanical problem
o Thermal problem
o Mechanical problem
Outline > Problem Statement
Problem Statement

 Solution method: Isothermal operator split
Coupled Thermomecanical Problem
Thermal Problem
Obtain the thermal variables (temperature) at constant configuration,
keeping constant the mechanical variables (displacement/pressure)
Mechanical Problem
Obtain the mechanical variables (displacement/pressure), keeping
constant the thermal variables (temperature)
( )( ) ( ) [ ], div in 0,LH f Q Tθ θ θ= − + Ω×q
( )
( )
[ ]
,
in 0,1
0
p
T
e p
K
θ
θ
θ
∇ + ∇⋅ + = 

Ω×
∇⋅ − − = 

s u f 0
u

 Energy balance equation: Strong form
 Enthalpy rate: Heat capacity + latent heat terms
 Solid/Liquid volume fractions
 Heat flux: Fourier law
Thermal Problem
( )( ) ( ) [ ], div in 0,LH f Q Tθ θ θ= − + Ω×q
( )( )
( )( ) ( )( )
( )
( ) ( ) ( ) ( )
, ,
,
L L
L L
L
L S
H f H f
H f f
f
C L f C L f
θ θ θ θ
θ θ θ θ
θ
θ θ θ θ θ θ
∂ ∂
= +
∂ ∂
= + = −

  
( ) ( )gradkθ θ θ= −q
( ) ( ) 1S Lf fθ θ+ =

 Heat source: Wire-feed AM (SMD)
Power input:
Arc voltage:
Current intensity:
Power efficiency:
MD volume:
Wire-feed volume:
 Heat source: Blown Powder (LMD/LENS)/Powder Bed Fusion AM (SLS,
SLM)
Laser power input:
Power absorption:
Melting pool volume:
Thermal Problem
eff eff
MD feed
P V I
Q
V V
η η= =
effη
P
feedV
V
I
absη
P
poolV
abs
pool
P
Q
V
η=
MDV

 Energy balance equation: Variational form
 Boundary domain
The boundary domain is changing during the AM process
Thermal Problem
( ) ( )( ) ( ) ( )
( ) ( ) 0
, , ,
, ,
clamp env
S
cond conv rad
C L f k Q
q q q
δθ θ θ θ δθ θ δθ
δθ δθ δθ∂ Ω ∂ Ω
− + ∇ ∇ =
− − + ∀ ∈



 Normal heat flux by conduction (clamping system): Newton law
Considering contact between metallic materials, the value of the HTC by
conduction is usually very high, around 1000 W/m2 K. Hence, the prescribed heat
flux by conduction BC can be replaced by a prescribed temperature BC at the
corresponding contact surface (clamping system).
 Prescribed temperature (clamping system)
Thermal Problem
[ ]on 0,clamp clamp Tθ θ= ∂ Ω×
( )( ) [ ]on 0,cond cond clamp clampq h Tθ θ θ= − ∂ Ω×

 Normal heat flux by convection (environment): Newton law
 Normal heat flux by radiation (environment): Stefan-Boltzmann law
 Normal heat flux by convection+radiation (environment): Newton law
Thermal Problem
( )( ) [ ]on 0,conv conv env envq h Tθ θ θ= − ∂ Ω×
( ) [ ]4 4
on 0,rad rad rad env envq Tσ ε θ θ= − ∂ Ω×
( )( ) [ ]
( ) ( ) ( )( )2 2
on 0,loss loss env env
loss conv rad rad env env
q h T
h h
θ θ θ
θ θ σ ε θ θ θ θ
= − ∂ Ω×
= + + +
( )( ) [ ]
( ) ( )( )2 2
on 0,rad rad env env
rad rad rad env env
q h T
h
θ θ θ
θ σ ε θ θ θ θ
= − ∂ Ω×
= + +

 Linear momentum balance equation: Mixed u/p strong form
 Linear momentum balance equation: Mixed u/p variational form
Mechanical Problem
( )
( )
( )
[ ]
,
in 0,1
0
p
T
e p
K
θ
θ
θ
θ
∇ + ∇⋅ + = 

Ω×
∇⋅ − − = 

s u f 0
u
( ) ( )( ) ( ) ( )
( ) ( )( ) ( )
0, , , , ,
1
, , , 0
s
p
p e p p p p
K
σ
θ
δ θ δ δ δ δ
δ θ δ δ δ
θ
∂ Ω
∇⋅ + ∇= + ∀ ∈
 
∇⋅ − − = ∀ ∈  
 
u s u u f u t u u
u



 Thermoelastic constitutive equations
 Thermal volumetric strain: Thermal contraction + shrinkage due to
phase-change
Mechanical Problem: Solid Phase
( ) ( )( )
( ) ( ) ( )( ), 2 dev p
p K e
G
θ
θ θ
θ θ
= ∇⋅ −
= −
u
s u uε ε
( ) ( )cool pc
e e eθ
θ θ= +
logpc L
S
e
ρ
ρ
=
( ) ( )( ) ( )( )3 3cool
ref S S ref
e θ α θ θ θ α θ θ θ= − − −

 Thermoelastic constitutive equations
 Thermal volumetric strain: Thermal contraction + shrinkage due to
phase-change
( ) ( )( )
( ) ( ) ( )( ), 2 dev p
p K e
G
θ
θ θ
θ θ
= ∇⋅ −
= −
u
s u uε ε
( ) ( )cool pc
e e eθ
θ θ= +
pc
pc S L L S
S S L
V VV
e
V V
ρ ρ
ρ
−∆
=− = =
−
( ) ( )( ) ( )( )3 3cool
ref S S ref
e θ α θ θ θ α θ θ θ= − − −

 J2-plasticity model: Yield function
 Radius of the J2 yield surface
 Associative plastic flow rule
( , , , ): ( , )q R qθ θΦ = − −s q s q
( ) ( )( )0
, 2 3R q qθ σ θ= −
( )
( )
( , , , )
( , , , ) 2 3
( , , , )
p
q
q
q
q
γ θ γ
ξ γ θ γ
γ θ γ
= ∂ Φ = − −
= ∂ Φ =
= ∂ Φ =− − −





σ
q
s q s q s q
s q
s q s q s q



ε
ξ

 Elastic strain tensor: zero volumetric and deviatoric elastic strains
 Thermal volumetric strain: shrinkage due to phase-change
 Mass density
Mechanical Problem: Mushy Phase
( ) ( )
( ) ( )
log log
1
1
pc
S
S
L
L
L
e e
f
θ
θ θ
ρ ρθ θ
ρ
ρ
ρ
= ==
−
−
( ) ( ) ( )S S L L
f fρ θ θ ρ θ ρ= +
( )
( )( )dev
0
p
eθ
θ
−
∇⋅ − =
=u
u
0ε ε

 Thermal volumetric strain: shrinkage due to phase-change
 Mass density
( ) ( ) ( )S S L L
f fρ θ θ ρ θ ρ= +
( ) ( )
( )
( )
( )
( )
( )
( )
pc
pc L S
S
L
L L
L
V V V
e e f
V V
θ θ θ ρ ρ θ ρ ρ
θ θ θ
θ θ ρ ρ
∆
==− = = =
− − −
( )
( )( )dev
0
p
eθ
θ
−
∇⋅ − =
=u
u
0ε ε

 Rate-dependent J2-plasticity model: Yield function
 Non-Newtonian model
( )
( , , , ):
m
q
θ
θ ηγΦ ==s q s
( , , , )
( , , , ) 0
( , , , )
p
q
q
q
q
γ θ γ
ξ γ θ
γ θ
 = ∂ Φ =

= ∂ Φ =

= ∂ Φ =
σ
q
s q s s
s q
s q 0



ε
ξ
( )
( ) 1
3
2
2
dev
3
m
p p
p
θσ
η ε
ε
−
= =s  

ε ε

 Thermal volumetric strain: zero thermal strain
 Strain tensor: purely plastic deviatoric
Mechanical Problem: Liquid-like Phase
( )
( )( )dev
0
p
eθ
θ
−
∇⋅ − =
=u
u
0ε ε
( ) 0 0eθ
θ= ⇒ ∇⋅=u
( ) ( )
( ) ( )
dev dev
dev
tr 0, p p
p
= ∇⋅ = = =
= =
u u u
u u
ε ε ε ε
ε ε ε

 Rate-dependent J2-plasticity model: Yield function
 Norton-Hoff model
Mechanical Problem: Liquid-like Phase
( , , , ):q θ ηγΦ ==s q s
( , , , )
( , , , ) 0
( , , , )
p
q
q
q
q
γ θ γ
ξ γ θ
γ θ
 = ∂ Φ =

= ∂ Φ =

= ∂ Φ =
σ
q
s q s s
s q
s q 0



ε
ξ
2
3
p p
p
σ
η η
ε
= = =s   

ε ε ε

 Introduction
o FE Activation strategy
o Welding pool volume
o Scanning path: Common Layer Interface (CLI)
o Incompressibility constraint
Outline > Computational Model
Computational Model

 FE Activation strategy: Passive/active elements
• A FE mesh of the full domain is considered
• Elements are classified as: passive and active
o Passive elements are defined by setting their material properties to very low
fictitious values. They are computed and assembled
o Active elements are defined by setting their material properties to their physical
values. They are computed and assembled
o Passive elements are switched on to active elements on each time step, according
to the welding/melting path
FE Activation Strategy
Drawbacks
• High computational cost, as all elements have to be computed and assembled,
and the full system of equations has to be solved
• Too lower values for the fictitious material properties may lead to ill-
conditioning of the system of equations
• Strains and temperature gradients of passive elements are accumulated,
transforming into spurious stresses and heat fluxes when they are activated

 FE Activation strategy: Born/dead elements
• A FE mesh of the full domain is considered
• Elements are classified as: active, inactive, and activated
o Active elements are computed and assembled
o Inactive elements are not computed
o Activated elements are those elements that are switched on at each time step,
according to the welding/melting path. They are computed and assembled
Drawbacks
• Profile of solution matrix and number of equations is changing
• Activated elements share nodes with active elements and material is not free
to expand during the heating phase, leading to non-zero initial displacements
and spurious thermal stresses when they are activated. They have to be
removed as part of the activation procedure.

 Control volume and octree-based searching algorithm
• To set up the activation process, a control volume is defined by the cross
section of the layer and the welding speed.
• All the elements belonging to this domain are identified using an octree-based
searching algorithm and their status is changed from inactive to activated
elements.
 M. Chiumenti, M. Cervera, A. Salmi, C. Agelet de Saracibar, N. Dialami, K. Matsui (2010), Finite element modeling of
multi-pass welding and shaped metal deposition processes, Computer Methods in Applied Mechanics and Engineering
199 (37-40) 2343-2359

 Control volume: wire-feed (SMD) AM
processes
The MD volume must be equal to the volume
of wire-feed melted by the arc welding:
The cross section area of the MD is given by:
MD feedV V=
2
4
MD MD MD
feed wire feed
V S v t
V v t
π
φ
= ∆
= ∆
2
4
feed
MD wire
MD
v
S
v
π
φ=
 M. Chiumenti, M. Cervera, A. Salmi, C. Agelet de Saracibar, N. Dialami, K. Matsui (2010), Finite element modeling of
multi-pass welding and shaped metal deposition processes, Computer Methods in Applied Mechanics and Engineering
199 (37-40) 2343-2359

 Control volume: Blown Powder
(LMD/LENS)/Powder Bed Fusion
(SLS, SLM) AM processes
The cross section area of the MD is given
by:
where,
MD MD MDS h b=
MD MD MDV S v t= ∆
average thickness of MD layer
average width of MD layer
MD
MD
h
b
=
=

 Pool control volume: Blown Powder (LMD/LENS)/Powder Bed Fusion
(SLS, SLM) AM processes
The cross section area of the pool control volume is given by:
where is the laser spot size and is the welding pool penetration in the
substrate.
 Octree-based searching algorithm is used to look for elements
belonging to the pool control volume
 Welding pool volume for Blown Powder (LMD/LENS)/Powder Bed
Fusion (SLS, SLM) AM processes, where the heat source/power
density is applied
Welding Pool Volume
pool pool poolS r h=
pool pool MDV S v t= ∆
poolh
1
e
pool
n e
pool poole e V
V V= ∈
= ∑
poolr

 The Common Layer Interface (CLI) is a universal format for the input
of geometry data to model fabrication systems based on layer
manufacturing technologies (LMT), such as LMD/LENS, SLS, or SLM
 Definition of the scanning sequence using the CLI format
o Layer defines the layer entry level
o Polyline defines the section boundaries of the layer
o Hatches define the filling section of the layer
Scanning Path: Common Layer Interface (CLI)

 LMD/LENS scanning sequence: Polyline and hatches for a layer
Scanning Path: Common Layer Interface (CLI)

 Isochoric behaviour: Liquid-like phase
• Purely viscous Norton-Hoff behaviour
• Zero thermal strains
 Isochoric plastic behaviour: Solid phase
• J2 Thermo-elasto-plastic material model
• Isochoric plasticity
 FE technology for incompressibility constraints
 M. Cervera, M. Chiumenti, Q. Valverde, C. Agelet de Saracibar (2003), Mixed linear/linear simplicial elements for
incompressible elasticity and plasticity, Computer Methods in Applied Mechanics and Engineering 192 (49), 5249-5263
Incompressibility Constraint
• Hexahedral elements
o Q1P0 elements
o B-bar elements
o EAS elements
• Tetrahedral elements
o ASGS stabilized P1P1 elements
o OSS stabilized P1P1 elements
Incompressibility
Quasi-Incompressibility

 Introduction
o SMD Boss
o SMD 10 Layers Strip Band
o SMD Hanging Lug of a Jet Engine Turbine Blade
o LMD/LENS 10 Layers Strip Band
Outline > Numerical Simulations
Numerical Simulations

 Experimental setting at ITP: SMD of a Boss
SMD – Boss
TC1
TC2
Upper surface Lower surface
TC3
TC4
Clamping system
Experimental SMDExperimental SMDExperimental SMD
Before AM After AM After AM

 SMD welding path, gometry, and thermocouple locations
SMD – Boss
114mm
45mm
50mm
10mm
20mm
Th2
Th4
Th1
Th3 114mm
45mm
50mm
10mm
20mm
Th2
Th4
Th1
Th3
Th3 Th4
Th2Th1
45mm
15mm
Th3 Th4
Th2Th1
45mm
15mm
50mm

 SMD Process parameters
SMD – Boss
Gas Tungsten Arc Welding (GTAW)
Voltage 12 [V]
Current Intensity 180 [A]
Power Efficiency 0.75 (SMD)
0.90 (pre-heating)
SMD
Welding speed 22 [mm/min] (SMD)
20 [mm/min] (pre-heating)
Layer height 1.471 [mm]
Pre-heating passes 6
Layers 34

 Material properties: INCONEL 718 (wire feed + base material)
SMD – Boss
INCONEL 718
Solidus Temperature 1260 [ºC]
Liquidus Temperature 1335 [ºC]
Latent Heat 240 [kJ/kg]
Thermal Shrinkage 3 %
Mass Density Temperature dependent
Specific Heat Temperature dependent
Thermal Conductivity Temperature dependent
Yield Stress Temperature dependent

SMD – Boss
Mass density
Conductivity
Specific heat
Yield stress

 Thermal and Mechanical BC
SMD – Boss
Thermal BC: Convection and radiation
HTC convection 25 [W/m2 K]
Emissivity 0.6
Environment temperature 20 [ºC]
Mechanical BC
Isostatic clamping of the base
plate

 FE mesh
SMD – Boss
FE mesh: 6,114 Q1P0 hexahedral elements

 Temperature map evolution and temperature contour fill at the end
of the SMD process, just before the cooling phase
SMD – Boss
Temperature contour fill at the end of the
SMD process, just before the cooling phase

 Temperature evolution at the 4 thermocouple locations
SMD – Boss

 Experimental setting at ITP: SMD of a 10-layers strip band
SMD – 10 Layers Strip Band
Before AM After AM
Clamping system and TC locations on upper surface

 Geometry, clamping system and thermocouple locations

Voltage 12 [V]
Power Efficiency 0.75 (SMD)
0.90 (pre-heating)
SMD
Welding speed Variable
Layer height Variable
Layers 10

Pre-heating (1-2) and SMD (3-12) paths
Path Welding Speed
[mm/min]
Area
[mm2]
Width
[mm]
Height
[mm]
Area
[mm2]
1 100 12.000 1.000
2 100 12.000 1.000
3 200 13.570 10.400 1.212 13.570
4 200 13.570 8.500 1.436 13.570
5 300 9.050 7.860 1.106 9.050
6 350 7.760 7.260 1.026 7.760
7 375 7.240 6.660 1.040 7.240
8 400 6.790 6.040 1.069 6.790
9 425 6.390 5.390 1.118 6.390
10 450 6.030 4.690 1.197 6.030
11 475 5.710 3.920 1.327 5.710
12 500 5.430 3.010 1.567 5.430
SMD: 10 layers
Pre-heating: 2 passes

INCONEL 718

Mass density
Conductivity
Specific heat
Yield stress

Emissivity 0.6
Mechanical BC
Isostatic clamping of the base
plate

 FE mesh

 Vertical displacement contour fill after the cooling phase and
temperature map evolution
Vertical displacement contour fill after the
cooling phase
Temperature map evolution

 Temperature evolution at the 6 thermocouple locations
0
100
200
300
400
500
600
700
800
900
0 50 100 150 200 250 300 350 400 450 500
Time (sec)
Temp.
Point1 Exp.
Point1 Num.
Point4 Exp.
Point4 Num.
0
100
200
300
400
500
600
700
800
900
0 50 100 150 200 250 300 350 400 450 500
Time (sec)
Temp
Point3 Exp.
Point3 Num.
Point5 Exp.
Point5 Num.
0
100
200
300
400
500
600
700
0 50 100 150 200 250 300 350 400 450 500
Time (sec)
Temp.
Point2 Exp.
Point2 Num.
Point6 Exp.
Point6 Num.
Lower surface: TC1 and TC4
Upper surface: TC2 and TC6Upper surface: TC3 and TC5

 Deformation of transversal and longitudinal sections
Transversal sections
Longitudinal sections

 Residual stresses after cooling: J2 stress

 Experimental setting at ITP: SMD of a hanging lug of a jet
engine turbine blade
SMD – Hanging Lug of a Jet Engine Turbine Blade
Before AM After AM After AM
After AM

Voltage 12.5 [V]
Efficiency 0.75 (SMD)
0.90 (pre-heating)
SMD
Welding speed 110 [mm/min]
Deposition height 0.7 [mm]
Layers 10

INCONEL 718

Mass density
Conductivity
Specific heat
Yield stress

Emissivity 0.6
Mechanical BC
Isostatic clamping of the
flange
Fixed
Uz = 0

 Subcomponent geometry and FE mesh detail
800,455 OSS P1P1 tetrahedral elements (full component)
350,000 OSS P1P1 tetrahedral elements (blue+green domains) for SMD

 Temperature map evolution and temperature contour fill at different
time steps
Temperature map evolution
Temperature contour fill at different
time steps

 Residual stresses contour fill: J2 stress and maximum principal stress
J2 stress Maximum principal stress

 Blown Powder technology at SKLSP, Xi’an, China
LSF-III B Laser Solid Forming (LSF) machine at SKLSP, Xi’an, China
LMD/LENS – 10 Layers Strip Band

 Experimental setting at SKLSP: LMD/LENS of a 10 layers strip
band
Substrate and supporting system After the AM process
Before AM After AM

 Geometry, clamping area and location of thermocouples
Lower surface
Upper surface

 Process parameters for the LSF machine
LMD/LENS process parameters: LSF machine
Laser power 2 [kW]
Laser beam spot size 1.6 [mm]
Offset distance 0.8 [mm]
Up-lift height 0.3 [mm]
Scanning speed 10 [mm/s]
Back speed 50 [mm/s]
Powder feeding 8.5 [g/min]
Layers 10
Hatches for each layer 7

 Process parameters used in the LMD/LENS numerical simulation
LMD/LENS process parameters: Numerical simulation
Laser power 2 [kW]
Power absorption 16.5 %
Scanning speed 10 [mm/s]
Back speed 50 [mm/s]
Penetration 0.28 [mm]
Layer thickness 0.28 [mm]
Layer width 1.75 [mm]
Overlapping 50 %
Layers 10
Hatches for each layer 7

 Material properties: Ti-6Al-4V (powder + substrate material)
Ti-6Al-4V
Thermal Expansion Temperature dependent
Elastic Young Modulus Temperature dependent

 Material properties: Ti-6Al-4V (powder + substrate material)
Mass Density ConductivitySpecific heat
Yield stressLTE coefficient Young modulus

 Thermal BC: Heat convection and radiation (reference model 1)
 TD HTC loss by convection+radiation (model 2)
Thermal BC: Heat convection and radiation (environment)
Emissivity 0.7
Environment temperature Time dependent
Temperature [ºC] HTC loss [W/m2 K]
20 6
200 10
400 20
600 40
800 70
1000 110
1200 160

 Linear TD HTC loss by convection+radiation (simplified model 3)
 Linear TD HTC loss by convection+radiation (simplified model 4)
 Thermal BC: Heat conduction
20 6
1200 160
20 6
1200 90
Thermal BC: Heat conduction (clamping system)
HTC conduction 50 [W/m2 K]
Clamping temperature Time dependent

 Time-dependent environment and clamping temperature
Environment temperature: measured and
numerical data used in the simulation
Clamping temperature: measured and
numerical data used in the simulation
TC were placed too close to the process area, being affected by the heat
radiation during the AM process

 FE mesh
FE mesh detail
AM Strip band: 80 mm x 7 mm x 2.8 mm
Time step: automatic with Cu = 1

 Temperature map evolution
o Pre-heating phase
o AM phase: 10 layers, 7 hatches/layer
o Cooling phase

 Substrate oxidation and temperature contour fill at the end of the AM
process

 Temperature evolution at TC CH1-CH3: lower surface
Zoom boxNumerical
Experimental
Experimental
Numerical
Very good agreement between
numerical and experimental
temperature evolution at TC

 Temperature evolution at TC CH4-CH5: upper surface
Zoom box
Numerical
Experimental
Experimental
Numerical
Very good agreement between
numerical and experimental
temperature evolution at TC
TC on upper surface were shielded to
protect them from radiation, but still
suffer from heat radiation effects

 LMD/LENS vs SLS AM Technology: temperature at TC CH1 and CH2
SLS
LMD/LENS
LMD/LENS
SLS
LMD/LENS and SLS are quite different
AM technologies, but the numerical
results look very similar
LMD/LENS SLS

 Sensitivity to power absorption: temperature at TC CH1
Power absorption during AM process
set to 16.5%
Power absorption
set to 30%
Power absorption
set to 10%
Power absorption
set to 10%
Power absorption
set to 16.5%
Power absorption
set to 30%
Power absorption
set to 16.5%
Zoom box
High sensitivity to power absorption

 Sensitivity to pre-heating phase: temperature at TC CH2
Power absorption during AM phase
set to 16.5%, while during pre-
heating phase is set to 10%
Zoom box
Cooling
Without pre-heating
With pre-heating
AM
Pre-heating
Without pre-heating
With pre-heating
Pre-heating shows a lower power
absorption

 Sensitivity to latent heat: temperature at TC CH1-CH3
Latent heat contribution is negligible
Zoom box
set to 16.5%

 Sensitivity to heat radiation/convection: temperature at TC CH1-CH3
set to 16.5%
Only convection
Convection + radiation
Only convection
Only convection with
reduced power absorption
Heat radiation is the key heat
dissipation mechanism

 Sensitivity to heat radiation/convection: temperature at TC CH2
Only radiation
TD HTC loss (convection+radiation)
Linear convection with
max HTC = 160
Linear convection with
max HTC = 90
Heat loss due to radiation+convection
can be simulated using a Newton law
with a TD HTC
set to 16.5%

 Sensitivity to environment temperature: temperature at TC CH1-CH3
Environment temperature
set to 25 ºC
Measured environment
temperature at TC
Environment temperature used in
the reference simulation
Sensitivity to environment
temperature is negligible
Environment temperature:
measured and simplified used in
the reference numerical simulation
Numerical reference:
Time-dependent
environment temperature

 Sensitivity to HTC conduction: temperature at TC CH1
HTC conduction = 1000
Most suitable HTC was 50, far from the
typical value of 1000 when contact is
almost perfect (bolts torque was very
low because applied just manually)
Clamping temperature: measured
and simplified used in the
reference numerical simulation
HTC conduction = 50
Measured clamping
temperature at TC
Clamping temperature used in

 Sensitivity to clamping temperature: temperature at TC CH1
Clamping temperature
set to 25 ºC
Measured clamping
temperature at TC
Clamping temperature used in
Sensitivity to clamping temperature is
negligible during AM phase, but
better accuracy in cooling phase if
clamping temperature is known
Clamping temperature: measured
and simplified used in the
reference numerical simulation
Time-dependent clamping
temperature

 Sensitivity to AM activation sequence: temperature at TC CH1-CH3
By hatches
By layers
Zoom box
Zoom box

 Sensitivity to AM activation sequence: temperature map evolutions
By hatches By layers

 Computational cost
Strategy CPU time [s] Computational cost ratio [%]
Reference 1356 100
No phase-change 473 35
Hatch-by-hatch 61 4
Layer-by-layer 29 2

 Introduction
Outline > Concluding Remarks
Concluding Remarks

 Remarkable accuracy in the numerical simulation of DED AM
technologies (wire-feed SMD and blown powder LMD/LENS), has
been achieved
Concluding Remarks
 High sensitivity to power absorption. Power absorption for blown
powder (LMD/LENS) technology, is very low (around 15% of the
power input). Pre-heating phase shows a lower power absorption
(around 10% of the power input)
 Latent heat of fusion contribution due to liquid-solid phase-change
can be neglected, saving up to a 65% of the total CPU time
 Heat radiation is the key mechanism to dissipate heat through the
boundaries with the environment. It cannot be neglected, but Stefan-
Boltzmann law can be replaced by a Newton law using a TD HTC.
Total heat loss by convection + radiation can be conveniently
simulated using a single Newton law with a TD HTC

 Most suitable HTC by conduction at the clamping system was 50
W/m2 K, being far from the typical value of 1000 W/m2 K when
contact is almost perfect. This can be explained by the fact that the
bolts torque was very low because applied just manually
Concluding Remarks
 Time variation of the environment (closed chamber) temperature and
clamping system temperature can be neglected. Nevertheless, better
accuracy can be achieved in the cooling phase if the time-dependent
clamping temperature is available
 CPU time can be drastically reduced using a hatch-by-hatch or even a
layer-by-layer AM activation sequence. Average temperature
evolution can be well captured, but the accuracy on the local thermal
history is lost, and the mechanical response can be compromised

 Efficient Manufacturing for Aerospace Components Using Additive Manufacturing, Net
Shape HIP and Investment Casting (EMUSIC), H2020-MG-2015_SingleStage-A, Project
no. 690725, EC
 Computer Aided Technologies for Additive Manufacturing (CAxMan), H2020-FoF-
2015_CNECT, Project no. 680448, EC
 Computational Cloud Services and Workflows for Agile Engineering. HPC Workflow for
Simulation of Additive Manufacturing for Improving the Production of Gearboxes
(CLOUDFLOW), CloudFlow-2, Project no. 609100, EC
 Virtual Engineering for Robust Manufacturing with Design Integration (VERDI), FP6-
2003-AERO-1, AST4-CT-2005-516046, Project no. 516046, EC
 State Administration of Foreign Experts Affairs of China through the High-end Experts
Recruitment Program
 National Natural Science Foundation of China, Grants 51323008 and 51271213
 National Basic Research Program of China, Grant 2011CB610402
 National High Technology Research and Development Program of China, Grant
2013AA031103
 Specialized Research Fund for the Doctoral Program of Higher Education of China, Grant
20116102110016
 Yasmine Lebbar
Outline > Acknowledgments
Acknowledgments

Icomp 2016

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