Institut für Werkzeugmaschinenund BetriebswissenschaftenProf. Dr.-Ing. M. ZähProf. Dr.-Ing. G. Reinhart
DETERMINATION OF PROCESS PARAMETERS FOR ELECTRON BEAM SINTERING (EBS)
Hannover, November 6th 2008European Comsol Conference
Dipl.-Ing. Markus Kahnert
Presented at the COMSOL Conference 2008 Hannover
12.11.2008 Seite 2© iwb 2008
1. Introduction – Electron Beam Sintering (EBS)2. Objective of the present work3. Mathematical model
- Overview- Heat Source Model- Material Properties
4. Numerical Model5. Simulation Results and Discussion6. Conclusion
Outline
12.11.2008 Seite 3© iwb 2008
1. Introduction – Electron Beam Sintering (EBS)2. Objective of the present work3. Mathematical model
- Overview- Heat Source Model- Material Properties
4. Numerical Model5. Simulation Results and Discussion6. Conclusion
Outline
12.11.2008 Seite 4© iwb 2008
Electron beam sintering
Electron Beam Sintering
electron beam generator
electron beam
building volume
building plate
building volumewith metal-powder
sintered layer
building plate
part
preheatedarea
new layer ofmetal powder
divergence of the electron beam
focusedelectron beam
sinteredlayer
re-coating preheating scanningwith different
strategies
12.11.2008 Seite 5© iwb 2008
Electron Beam Sintering (EBS)
Potentials of the electron beam
High beam power and energy densityFast, massless beam deflection„Quasi-simultaneous“ beam exposureUniform insertion of energyOpen configurable beam figures
Vacuum chamber
Beam generator
Mechanical pumps
12.11.2008 Seite 6© iwb 2008
1. Introduction – Electron Beam Sintering (EBS)2. Objective of the present work3. Mathematical model
- Overview- Heat Source Model- Material Properties
4. Numerical Model5. Simulation Results and Discussion6. Conclusion
Outline
12.11.2008 Seite 7© iwb 2008
Objective of the present work
Process stability• Metal parts production• Two major deficiencies can be observed
- Balling- Delamination
Process cannot be examined due to accessibility and resolution of thermography unit
Understanding of the process needs to be enhanced
Analysis of the beam-material interaction by means of FEA
Balling
Delamination
12.11.2008 Seite 8© iwb 2008
1. Introduction – Electron Beam Sintering (EBS)2. Objective of the present work3. Mathematical model
- Overview- Heat Source Model- Material Properties
4. Numerical Model5. Simulation Results and Discussion6. Conclusion
Outline
12.11.2008 Seite 9© iwb 2008
Mathematical Model
Overview
MathematicalModel
FEM-Simulation
Resultanalysis
Knowledge to use in real process
Powderproperties
Temperatur [K]
Zeit [s]
Validation
time [s]
temperature [K]
0
20
40
60
80
273 773 1273 1773Temperatur [K]
heat conductivity [W/(mK)]
12.11.2008 Seite 10© iwb 2008
time=0.002 isosurface: heat source [W/m³]
Heat Source Model
• Horizontal intensity according to a Gaussian distribution
• Vertical intensity follows a 2nd degree polynom
• Power efficiency: 78%
• Superposition
• Penetration depth at given accelerating voltage and powder density: 62 µm
• Moving Heat Source at constant velocity
Mathematical Model
12.11.2008 Seite 11© iwb 2008
Temperature Dependence of Material Properties
0
20
40
60
80
273 773 1273 1773Temperatur [K]
heat conductivity [W/(mK)]
0,980,940,860,830,810,80,78ε
13961208755680569481333T [K]
emissity of metal powder
• Thermomechanical properties of metal powders are not common knowledge due to trade secrets and multitude of powders
• Experiments and analytical models available
• Heat capacity is similar to that of massive material
• Heat conductivity and emissivity modelled and validated
Mathematical Model
12.11.2008 Seite 12© iwb 2008
1. Introduction – Electron Beam Sintering (EBS)2. Objective of the present work3. Mathematical model
- Overview- Heat Source Model- Material Properties
4. Numerical Model5. Simulation Results and Discussion6. Conclusion
Outline
12.11.2008 Seite 13© iwb 2008
Numerical Model
Numerical Model
solidified material
powder material
model lengthtrace widthpowder layerthickness
electron beam(Ib, Ua, vs)
powder(tl, υp )
hatch distance h
x
yz
solid materialmelt line
Square to bemeleted
beam spotdiameter db
Part
Scanning pattern
Model
Meshed modelThermal analysis
12.11.2008 Seite 14© iwb 2008
1. Introduction – Electron Beam Sintering (EBS)2. Objective of the present work3. Mathematical model
- Overview- Heat Source Model- Material Properties
4. Numerical Model5. Simulation Results and Discussion6. Conclusion
Outline
12.11.2008 Seite 15© iwb 2008
Simulation Results and Discussion
Objective of the Simulation
0.1 mmhhatch distance
0.1 m/svsscan speed
1353 Kυppreheating temperature
100 µmtllayer thickness
200 µmdbbeam spot diameter
1 mAIbbeam current
100 kVUaaccelerating voltage
ValueVariableProcess parameter
1.0·10-04 mpowder layer thickness
2.0·10-03 mmodel length
2.0·10-04 mtrace width
6.2·10-05 mSEB penetration depth
ValueVariableModel parameter
Starting Conditions and Process Parameters
• Calculation of the size and shape of the melt pool
• Simulation of the heat distribution within one melt line
Powder: 3.4 g/cm³Massive: 7,9 g/cm³
Density
20-63 µmGrain Size
316L (1.4404)Material
ValueMaterial parameters
12.11.2008 Seite 16© iwb 2008
Simulation Results and Discussion
Heat distribution within one melt linetemperature [K] @ various depths
x=0 m; y=1*10-3 m; z=0 mx=0 m; y=1*10-3 m; z=-1*10-4 mx=0 m; y=1*10-3 m; z=-2*10-4 m
• Simulation of the transient temperature distribution in the center of a melt line at various depths
• Complete melting of a layer at point z=-1*10-4 m (= layer thickness)
• After the powder has reached melting temperature, the layer thickness decreases proportional to its density increase
TS= 1699 K
12.11.2008 Seite 17© iwb 2008
Simulation Results and Discussion
Calculation of the size and shape of the melt pool
L/W=3.8
mm
time=0.002 sisosurface: temperature [K]
solid
vBeam=const. electronbeam
liquid
system boundary
phase 1preheated powder
phase 2heat input
phase 3liquid
phase 4phase change
phase 5solid
solid
vBeam=const. electronbeam
liquid
system boundary
phase 1preheated powder
phase 2heat input
phase 3liquid
phase 4phase change
phase 5solid
• Calculation of the Size and shape of the melt pool according to real process parameters
• L/W-ratio is 3.8, no balling observed
• in comparison: 2.1 in laserbeam-based processes (SLM, DMLS, etc.)
• Possible reasons:- preheating temperature- vacuum in the process area- different beam-material interaction
• Research efforts to be done
12.11.2008 Seite 18© iwb 2008
1. Introduction – Electron Beam Sintering (EBS)2. Objective of the present work3. Mathematical model
- Overview- Heat Source Model- Material Properties
4. Numerical Model5. Simulation Results and Discussion6. Conclusion
Outline
12.11.2008 Seite 19© iwb 2008
Conclusion
Manufacturing of EBS parts only possible with considerable process knowledge
Simulation carried out in order to evaluate necessary beam power and other process parameters
FE-Modelling of the energy input based on a mathematical abstracted heat sourceand a discretized powder bed is an effective tool
Differences between Laser- and Electron Beam-based processes discovered
Model can be transferred to alternative additive layer manufacturing technologies
Institut für Werkzeugmaschinenund BetriebswissenschaftenProf. Dr.-Ing. M. ZähProf. Dr.-Ing. G. Reinhart
Dipl.-Ing. Markus Kahnert
Telefon +49 (0) 821 / 5 68 83 - 33 Telefax +49 (0) 821 / 5 68 83 - 50 E-Mail: [email protected]
Adresseiwb Anwenderzentrum AugsburgBeim Glaspalast 586153 Augsburg www.iwb-augsburg.de
Kontakt:
12.11.2008 Seite 21© iwb 2008
Requirements in production technology
innovative technologies for an economicmanufacturing of complex parts (powder based manufacturing methods – SLM, DMLS, EBS)
wide range of processable materials (high quality steel, titanium alloys, aluminum alloys)
efficient numerical methods for virtual design of manufacturing processes – Finite-Element-Analysis (FEA)
customized, complex products
powder based manufacturing processes
engine componentmold insert for injection dies
source: ConceptLaser
source: DaimlerChrysler
Mega-trends:Demand for individualization of products increases (“mass customisation”)Products become more complexLife cycles shorten
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