本研究是以ANSYS Fluent建立三維暫態模型，模擬選擇性雷射熔融法之多層及多重軌跡掃描，而模擬的材料為不鏽鋼316L。在驗證的部分是以東台的AM250機台來作實驗，並在熔池尺寸上有一定之準確度。
利用溫度場比較不同鋪粉時間、雷射功率及掃描速率對熔池尺寸、溫度梯度的影響，並根據能量利用性與製程效率定義製程效益參數，再以此參數作為雷射參數選用之判斷標準。最後以所選擇之雷射參數探討單向與雙向兩種掃描方式、基板預熱及粉末預熱對於溫度場之影響，其中包括溫度分布、溫度梯度分布、溫度梯度、冷卻速率及製程效益參數。
根據不同參數比較之模擬結果顯示，在多層及多軌掃描中，當雷射功率愈大、掃描速率愈慢時，可以使溫度梯降低及熔池尺寸增加，而透過製程效益參數分析後，雷射功率200W、掃描速率960mm/s為製程效益較佳之雷射參數，並以此雷射參數作後續探討。在掃描方式的探討中得出，單向掃描具有較均勻的溫度場。結合上述設定後探討基板預熱之影響性，發現基板預熱可以有效降低溫度梯度及冷卻速率，但其影響性會隨著層數的增加而減少；在粉末預熱方面，對溫度梯度、冷卻速率之影響不如基板預熱明顯，但其影響性會隨層數的增加而變大，因此兩種預熱方式皆有其所適合的情況。

In this study, a three-dimensional transient model is established by ANSYS Fluent to simulate multi-layer and multi-track scanning in Selective Laser Melting method. The simulated material is stainless steel 316L. In the verification part, the experiment was carried out with the AM250 machine from TONGTAI MACHINE & TOOL CO., LTD. The results show that there is a certain degree of accuracy in the size of the molten pool.
The temperature field is used to compare the effects of different laying times, laser powers and scanning speeds on the size and temperature gradient of the molten pool. According to the energy utilization and process efficiency, the process benefit parameters are defined, and these two parameters are used as the judgment criteria for the selection of the laser parameters. Finally, the selected laser parameter are used to investigate the effects of different scanning methods, substrate preheating and powder preheating on the temperature field, including temperature distribution, temperature gradient distribution, temperature gradient, cooling rate and process benefit parameters.
According to the simulation results of different parameters in multi-layer and multi-track scanning, when the laser power is larger and the scanning speed is slower, the temperature gradient will decrease and the size of the molten pool will increase. After the selection of process benefit parameters, the laser power of 200W and the scanning speed of 960mm/s are laser parameters with better process benefits. These laser parameters will be used for subsequent discussion. After the above settings are combined, the influence of substrate preheating is discussed. The results show that substrate preheating can effectively reduce the temperature gradient and cooling rate, but its influence will decrease as the number of layers increases. In the powder preheating method, the effect on temperature gradient and cooling rate is not as obvious as substrate preheating. However, its influence will increase as the number of layers increases, so both preheating methods have their suitability.

參考文獻
1. Y. Li, D. Gu, “Parametric analysis of thermal behavior during selective laser melting additive manufacturing of aluminum alloy powder,” Materials and Design, Vol. 63, pp. 856-867, 2014.
2. K. Kempen, L. Thijs, B. Vrancken, S. Buls, J. Van Humbeeck, and J.P. Kruth, “Lowering thermal gradients in Selective Laser melting by pre-heating the baseplate,” Solid Freeform Fabrication Symposium Proceedings, 2013.
3. I. Yadroitsev, “Selective laser melting:direct manufacturing of 3D-objects by selective laser melting of metal powders,” LAP Lambert Academic Publishing, 2009.
4. M. Mani, B. Lane, A. Donmez, S. Feng, S. Moylan, and R. Fesperman, “Measurement science needs for real-time control of additive manufacturing powder bed fusion processes,” National Institute of Standards and Technology, NISTIR-8036, 2015.
5. A.B. Spierings and G. Levy, “Comparison of density of stainless steel 316L parts produced with selective laser melting using different powder grades,” Solid Freeform Fabrication Symposium Proceedings, pp. 342-353, 2009.
6. J. Zhou, Y. Zhang, and J.K. Chen, “Numerical simulation of random packing of spherical particles for powder-based additive manufacturing,” Journal of Manufacturing Science and Engineering, Vol. 131, pp. 031004, 2009.
7. M. Rombouts, L. Froyen, A.V. Gusarov, E.H. Bentefour, and C. Glorieux, “Light extinction in metallic powder beds: correlation with powder structure,” Journal of Applied Physics, Vol. 98, pp. 013533, 2005.
8. F. Thummler and R. Oberacker, “An introduction to powder metallurgy,” Oxford Science Publications, 1993.
9. L.X. Yang, X.F. Peng, and B.X. Wang, “Numerical modeling and experimental investigation on the characteristics of molten pool during laser processing,” Internationa1 Journa1 of Heat and Mass Transfer, Vol. 44, Issue 23, pp. 4465-4473, 2001.
10. P.D. Lee, P.N. Quested, and M. Mclean, “Modelling of marangoni effects in electron beam melting,” Philosophical Transactions of the Royal Society A, Vol. 356, pp. 1027-1044, 1998
11. G. Tsotrid, H. Rother, and E.D. Hondros, “Marangoni flow and the shapes of laser-melted pools,” Naturwissenschaften Vol. 76, pp. 216-218, 1989.
12. L. Han, F.W. Liou, and S. Musti, “Thermal behavior and geometry model of melt pool in laser material process,” Journal of Heat Transfer, Vol. 127, pp.1005-1014, 2005.
13. J. Zhang, F. Liou, W. Seufzer, and K. Taminger, “A coupled finite element cellular automaton model to predict thermal history and grain morphology of Ti-6Al-4V during direct metal deposition (DMD),” Additive Manufacturing, Vol. 11, pp. 32-39, 2016.
14. Y. Huang, M.B. Khamesee, and E. Toyserkani, “A comprehensive analytical model for laser powder-fed additive manufacturing,” Additive Manufacturing, Vol. 12, pp. 90-99, 2016.
15. V. Fallah, M. Alimardani, S.F. Corbin, and A. Khajepour, “Temporal development of melt-pool morphology and clad geometry in laser powder deposition,” Computational Materials Science, Vol. 50, pp. 2124-2134, 2011.
16. E. Toyserkani, A. Khajepour, and S. Corbin,“3-D finite element modeling of laser cladding by powder injection: effects of laser pulse shaping on the process,” Optics and Lasers in Engineering, Vol. 41, Issue 6, pp. 848-867, 2004.
17. H. Zhao, G. Zhang, Z. Yin, and L. Wu, “A 3D dynamic analysis of thermal behavior during single-pass multi-layer weld-based rapid prototyping,” Journal of Materials Processing Technology, Vol. 211, pp. 488-495, 2011.
18. J. Xiong, Y. Lei, and R. Li, “Finite element analysis and experimental validation of thermal behavior for thin-walled parts in GMAW-based additive manufacturing with various substrate preheating temperatures,” Applied Thermal Engineering, Vol. 126, pp. 43-52, 2017.
19. E. Yasa, J. Deckers, and J.P. Kruth, “The investigation of the influence of laser re-melting on density, surface quality and microstructure of selective laser melting parts,” Rapid Prototyping Journal, Vol. 17, pp. 312-327, 2011.
20. K. Zeng, D. Pal, B. Stucker, “A review of thermal analysis methods in Laser Sintering and Selective Laser Melting,” Solid Free, pp. 796-814, 2012.
21. D. Wang, Y. Yang, X. Su, and Y. Chen, “Study on energy input and its influences on single-track, multi-track, and multi-layer in SLM,” The International Journal of Advanced Manufacturing Technology, Vol. 58, pp 1189-1199, 2012.
22. X. Dinga, L. Wanga, and S. Wanga, “Comparison study of numerical analysis for heat transfer and fluid flow under two different laser scan pattern during selective laser melting,” Optik, Vol. 127, pp. 10898-10907, 2016.
23. K. Antony, N. Arivazhagan∗, K. Senthilkumaran, “Numerical and experimental investigations on laser melting ofstainless steel 316L metal powders,” Journal of Manufacturing Processes, Vol. 16, pp. 345–355, 2014.
24. Y. Huang, L.J. Yang, X.Z. Du, and Y.P. Yang, “Finite element analysis of thermal behavior of metal powder during selective laser melting,” Internationa1 Journa1 of Thermal Science, Vol. 104, pp. 146-157, 2016.
25. A. Foroozmehr, M. Badrossamay, E. Foroozmehr, and S. Golabi, “Finite Element Simulation of Selective Laser Melting process considering optical penetration depth of laser in powder bed,” Materials and Design, Vol. 89, pp. 255-263, 2016.
26. I.A.Roberts, C.J.Wang, R.Esterlein, M.Stanford, D.J.Mynors, “A three-dimensional finite element analysis of the temperature field during laser melting of metal powders in additive layer manufacturing,” International Journal of Machine Tools & Manufacture, Vol. 49, pp 916-923, 2009.
27. I. Yadroitsev, Ph. Bertrand, I. Smurov, “Parametric analysis of the selective laser melting process,” Applied Surface Science, Vol. 253, pp. 8064–8069, 2007.
28. R. Klein, “Laser welding of plastics,” Wiley-VCH, 2011.
29. 楊隆昌, “雷射發展的趨勢與應用,” September, 2013.
30. 劉國基、張百齊, “Nd-YAG雷射的加工應用,” 遠東學報, Vol. 19, 2001.
31. “Gaussian beam optics,” marketplace.idexop.com, A157-A172, August, 1997.
32. S. Louhenkilpi and F. Imre, “A lézersugnyagtudományifolyamatszimuláció － Hőkezelésmodellezése,” 2011.
33. 許阿娟, 朱嘉雯, 林桂芬, 陳志隆,“光學系統設計進階篇-第九章 高斯光束,”fourth version, 2002版.
34. B.V. L’vov, “Thermal decomposition of solids and melts new thermochemical approcach to the mechanism, kinetics and methodology,” Springer, Vol. 7, pp.35-38, 2007.
35. ANSYS, “Ansys Fluent. 15.0 Theory Guide,” ANSYS Inc., 2013.
36. V.R. Voller and C. Prakash, “A fixed grid numerical modelling methodology for convection-diffusion mushy region phase-change problems,” International Journal of Heat and Mass Transfer, Vol. 30, pp.1709-1719, 1987.
37. Z. Zhang, “Modeling of Al evaporation and marangoni flow in electron beam button melting of Ti-6Al-4V.” Master’s Thesis, The University of British Columbia, Vancouver, 2013.
38. A. Klassen, T. Scharowsky and C. K¨orner, “Evaporation model for beam based additive manufacturing using free surface lattice Boltzmann methods,” J. Phys. D: Appl. Phys. 47, 2014.
39. J.P. Bellot, D. Ablitzer and E. Hess, "Aluminum volatilization and inclusion removal in the electron beam cold hearth melting of Ti alloys," Metallurgical and Materials Transactions B, Vol. 31, pp. 845-854, 2000.
40. A. Powell, U. Pal, J. Van Den Avyle, B. Damkroger and J. Szekely, "Analysis of Multicomponent Evaporation in Electron Beam Melting and Refining of Titanium Alloys," Metallurgical and Materials Transactions B, Vol. 28B, pp. 1227-1239, 1997.
41. M. Ritchie, P.D. Lee, A. Mitchell, S.L. Cockcroft and T. Wang, “X-ray-based measurement of composition during electron beam melting of AISI 316 stainless steel: Part II. Evaporative processes and simulation,” Metallurgical and Materials Transactions A, Vol. 34, pp. 863-877, 2003.
42. Y.P. Lei, H. Murakawa, Y. W. Shi, and X.Y. Li, “Numerical analysis of the competitive influence of marangoni flow and evaporation on heat surface temperature and molten pool shape in laser surface remelting,” Computational Materials Science, Vol. 21, pp.276-290, 2001.
43. T.C. Chawla, D.L. Graff, R.C. Borg, G.L. Bordner, D.P. Weber, and D. Miller, “Thermophysical properties of mixed oxide fuel and stainless steel type 316 for use in transition phase analysis,” Nuclear Engineering and Design, Vol. 67, pp. 57-74, 1981.
44. B.V. L’vov, “Thermal decomposition of solids and melts: new thermochemical; approach to the mechanism, kinetics and methodology,” Springer, Vol. 7, pp. 35-38, 2007.
45. S.A. Khairallah, A.T. Anderson, A. Rubenchik, W.E. King, “Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones,” Acta Materialia, Vol. 108, pp. 36-45, 2016.
46. J.C. Chen and Y.C. Huang, “Thermocapillary flows of surface melting due to a moving heat flux,” International Journal of Heat and Mass Transfer, Vol. 34, pp. 663-671, 1991.
47. A. RUBENCHIK, S. WU, S. MITCHELL, I. GOLOSKER, M. LEBLANC, AND N. PETERSON, “Direct measurements of temperature-dependent laser absorptivity of metal powders,” Applied Optics, Vol. 54, No. 24, pp. 7230-7233, 2015.
48. K.C. Mills, “Recommended values of thermophysical properties for selected commercial alloy,” Woodhead Publishing, 2002.
49. S. Patankar, “Numerical Heat Transfer and Fluid Flow,” Hemisphere Series on Computational Methods in Mechanics and Thermal Science, 1980.
50. T.C. Chawla, D.L. Graff, R.C. Borg, G.L. Bordner, D.P. Weber, and D. Miller, “Thermophysical properties of mixed oxide fuel and stainless steel type 316 for use in transition phase analysis,” Nuclear Engineering and Design, Vol. 67, pp. 57-74, 1981.
51. J. Yin, H. Zhu, L. Ke, W. Lei, C. Dai, and D. Zuo, “Simulation of temperature distribution in single metallic powder layer for laser micro-sintering,” Computational Materials Science, Vol. 53, pp. 333-339, 2012.
52. A. Hussein, H. Liang, C. Yan, and R. Everson, “Finite element simulation of the temperature and stress fields in single layers built without-support in selective laser melting,” Materials and Design, Vol. 52, pp. 638-647, 2013.
53. ANSYS, “ANSYS Fluent. 15.0 UDF Manual,” ANSYS Inc., 2013.