Simulations of Thermo-Mechanical Characteristics in Electron Beam Additive Manufacturing
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SIMULATIONS OF THERMO-MECHANICAL CHARACTERISTICS IN ELECTRON BEAM ADDITIVE MANUFACTURING (EBAM) Ninggang (George) Shen Dr. Kevin Chou 11/14/2012 The University of Alabama-Mechanical Engineering 1
Simulations of Thermo-Mechanical Characteristics in Electron Beam Additive Manufacturing
1. SIMULATIONS OF THERMO-MECHANICAL CHARACTERISTICS IN ELECTRON
BEAM ADDITIVE MANUFACTURING (EBAM) Ninggang (George) Shen Dr. Kevin
Chou 11/14/2012The University of Alabama-Mechanical Engineering
1
2. Outline of the contents1. Introduction2. Thermo-mechanical
modeling3. FE model application4. Thermo-mechanical analysis5.
Conclusions6. Future workThe University of Alabama-Mechanical
Engineering 2
3. 1. Introduction and research objectivesWhats Electron Beam
Additive Manufacturing (EBAM)? Metallic powders melt by electron
beam Rapid self-cool to solidify Produced in layer-building fashion
Why EBAM? Be able to build full-density functional metallic
products Eco-friendly High building rate (Ti-6Al-4V: 25-50 cm3/hour
[1])The University of Alabama-Mechanical Engineering 3
4. 1. Introduction and research objectivesPowder materials
Study of porosity effects on heat transfer Metallic powders are
preheated to slightly sintered before each deposition; Porosities
in powder bed affect thermal response very much Fig. 1 SEM picture
of Ti-6Al-4V powder Fig 2. SEM picture of sintered Ti-6Al-4V
powderThe University of Alabama-Mechanical Engineering 4
5. 1. Introduction and research objectivesPotential part
quality problem in EBAM: Delamination The induced residual stresses
are greater than the bonding ability between layers Fig. 3
Delamination [2]The University of Alabama-Mechanical Engineering
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6. 1. Introduction and research objectivesA 3D Finite Element
(FE) thermo-mechanical model was developed to: Investigate the
thermo-mechanical response in EBAM Behavior of thermal and residual
stress Deformation analysisThe University of Alabama-Mechanical
Engineering 6
7. 2. Thermo-mechanical modeling Assumptions: Conical
volumetric body heat flux Gaussian intensity distribution in
deposition plane Linear decay along penetrationFig. 4 Actual
keyhole example and idealization [3] Fig. 5 Horizontal intensity
distribution @ z = 0 The University of Alabama-Mechanical
Engineering 7
8. 2. Thermo-mechanical modelingFig. 4 Thermal & mechanical
bulk material materials [4,5] Fig. 5 Thermal conductivity of both
bulk and powder The University of Alabama-Mechanical Engineering
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9. 2. Thermo-mechanical modeling Tab. 1 Truth table of material
determination DTemp > 0 DTemp < 0 Temp < Tmelting 0 0 Temp
> Tmelting 0 1 0 powder, 1 solid Latent heat of fusion is
considered as well Fig. 6 Flow chart of the user subroutine coupled
UMATH and DFLUXThe University of Alabama-Mechanical Engineering
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10. 3. FE model application Tab. 2 Parameters in the melting
simulation Parameters Values Solidus temperature, TS ( C) 1605
Liquidus temperature, TL ( C) 1665 Latent heat of fusion, Lf
(kJ/Kg) 440 Electron beam diameter, (mm) 0.4 Absorption efficiency,
0.9 Scan speed, v (m/sec) 0.4 Acceleration voltage, U (kV) 60 Beam
current, Ib (mA) 2 Powder layer thickness, t-layer (mm) 0.1
Porosity, 30% Beam penetration depth, dP (mm) 0.1 Fig. 7 New FE
model configuration Preheat temperature, Tpreheat ( C) 750The
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11. 3. FE model applicationFig. 8 Schematic of the cross-raster
scan patternapplied in the multi-layer EBAM thermalanalysis. The
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12. 4. Thermo-mechanical analysis Fig. 10 the simulated
residual stress profile comparisonFig. 9 the simulated temperature
contour comparison Fig. 11 the simulated residual stress
distribution comparison The University of Alabama-Mechanical
Engineering 12
13. 4. Thermo-mechanical analysisFig. 12 Simulated temperature
fields and molten pool Fig. 13 Simulated temperature fields and
molten poolgeometry. geometry for raster scan: a) the temperature
fields of layer-1; b) the cross sectional view of the field in a).
The University of Alabama-Mechanical Engineering 13
14. 4. Thermo-mechanical analysisFig. 14 Simulated temperature
history and thermalstress histories close the beam center starting
point. Fig. 15 Simulated thermal stress fields of single straight
scan just before cooling: a) Longitudinal stress; b) Transverse
stress. The University of Alabama-Mechanical Engineering 14
15. 4. Thermo-mechanical analysis Fig. 16 Simulated residual
stress fields of single straight scan: a) Longitudinal stress; b)
Transverse stress.The University of Alabama-Mechanical Engineering
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16. 4. Thermo-mechanical analysisFig. 17 Simulated thermal
stress and its cross sectional view. Fig. 18 Simulated thermal
stress fields and their cross sectional views at the end of the 10
sec break between two sequential layers: a) Longitudinal stress; b)
Transverse stress. The University of Alabama-Mechanical
Engineering
17. 4. Thermo-mechanical analysisFig. 19 Simulated residual
stress fields and their crosssectional views: a) Longitudinal
stress; b) Transversestress. Fig. 20 Simulated deformations (mm)
for: a) Single straight scan; b) Multi-layer crossed raster scan.
The University of Alabama-Mechanical Engineering
18. 5. Conclusions The raster scan pattern affects the
temperatures and molten pool due to the residual heat from previous
adjacent scan Thermal stress histories on top (for both
longitudinal and transverse) Compressive just before beam coming;
Tensile - solidified Vertical thermal stress distribution (for both
longitudinal and transverse) Tensile in solidified and the
compressive just beneath the tensile Vertical residual stress
distribution (for both longitudinal and transverse) Max. tensile in
solidified and it decreases to the compressive for a certain
penetration. The largest deformation follows the track of beam
centerThe University of Alabama-Mechanical Engineering 18
19. 6. Future work Fig. 21 Hatch meltingThe University of
Alabama-Mechanical Engineering 19
20. AcknowledgementSponsor: NASA, No. NNX11AM11ACollaborator:
Marshall Space Flight Center (Huntsville, AL), Advanced
Manufacturing Team. The University of Alabama-Mechanical
Engineering 20
21. Q&A Thank you for your attention! Any Question?The
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22. Reference[1] Available from: http://www.arcam.com/.[2]
Zaeh, M. F., and Lutzmann, S., 2010, "Modelling and simulation of
electron beam melting," Production Engeering. Research and
Development, 4, pp. 15-23.[3] Lampa, C., Kaplan, A. F. H., Powell,
J., and Magnusson, C., 1997, "An analytical thermodynamic model of
laser welding," Journal of Physics D: Applied Physics, 30(9), p.
1293.[4] Yang, J., Sun, S., Brandt, M., and Yan, W., 2010,
"Experimental investigation and 3D finite element prediction of the
heat affected zone during laser assisted machining of Ti6Al4V
alloy," Journal of Materials Processing Technology, 210(15), pp.
2215-2222.[5] Liu, C., Wu, B., and Zhang, J., 2010, "Numerical
Investigation of Residual Stress in Thick Titanium Alloy Plate
Joined with Electron Beam Welding," Metallurgical and Materials
Transactions B, 41(5), pp. 1129-1138. The University of
Alabama-Mechanical Engineering 22