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 5

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 8

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 9

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 University of Alabama-Mechanical Engineering 10

11. 3. FE model applicationFig. 8 Schematic of the cross-raster scan patternapplied in the multi-layer EBAM thermalanalysis. The University of Alabama-Mechanical Engineering 11

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 15

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 University of Alabama-Mechanical Engineering 21

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