本文藉由Ansys Fluent R15.0建立二維軸對稱模型，模擬選擇性雷射熔融法定點加熱不鏽鋼316L金屬粉末，考慮熔池表面張力效應(馬蘭戈尼效應)，比較不同雷射能量、雷射半徑對金屬熔池發展的影響，並於最後與移動熱源做連結，討論在雷射高移動速度下，馬蘭戈尼效應影響的劇烈與否。
根據模擬結果顯示，在熔融不鏽鋼316L金屬粉末過程中，其熔池受到馬蘭戈尼效應的影響，其內部流動為逆時針方向之流動，產生一較深、較窄的熔池形狀。
固定雷射半徑，增加雷射能量會增加粉末融熔的效益，但在雷射能量大於30 W時其溫度會高於蒸發溫度，造成金屬粉末之損耗，亦會浪費能量，應盡量避免，故雷射能量應選用大於5 W及小於等於30 W之間；固定雷射能量，增加雷射半徑雖然會增加熔池寬，但是熔池深會隨著減少，且雷射半徑增加至 以上時，其熔池寬成長幅度會減緩，且有下降的趨勢，故雷射半經應選低於 。
在增加雷射移動速度下，即每單位點之照射時間越短，其馬蘭戈尼效應對熔池幾何、熔池體積影響較不顯著，但對表面溫度之影響較顯著，且增加雷射能量會使溫度差距更明顯，故即便在照射時間極短下，仍不宜忽略此效應。

In this study, a numerical model is developed to investigate the molten pool of stainless steel 316L metal powder by fixed- point heating in Selective Laser Melting (SLM). This model also considers the effects of buoyancy, Marangoni forces, radiation and convection heat losses. Furthermore, it relates to moving heat source to consider whether Marangoni effects highly affects molten pool or not in high laser scanning speed. The results show that Marangoni forces make the shape of molten pool much deeper and narrower. The benefits of powder melting will increase with increasing the laser power, but the temperature will be higher than the evaporation temperature if the laser energy greater than 30W. It will not only make metal powder mass loss but waste energy. So the laser energy should be chosen between 5 to 30 W. The increase of laser beam radius will decrease molten pool depth but increase molten pool width. When the beam radius increase to more than , the growth rate of molten pool width will slow down. So the beam radius should not be chosen greater than . Furthermore, the higher laser scanning speed means the shorter irradiation time per unit point, the effect of the Marangoni force is not significant on volume but on surface temperature of the molten pool. Based on the result, it is inappropriate to neglect the effect of Marangoni force during the SLM simulation even though the irradiation time is very short.

1. L.E. Loh, C.K. Chua, W.Y. Yeong, J. Song, M. Mapar, S.L. Sing, Z.H. Liu and D.Q. Zhang, “Numerical investigation and an effective modelling on the selective laser melting (SLM) process with aluminum alloy 6061,” Internal Journal of Heat and Mass Transfer, Vol. 80, pp.288-300, 2015.
2. 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.
3. K. Zeng, D. Pal and B. Stucker, “A review of thermal analysis methods in laser sintering and selective laser melting,” SFF Samposium, pp.796-814, 2012.
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. I. Yadroitsev, “Selective laser melting:direct manufacturing of 3D-objects by selective laser melting of metal powders,” LAP Lambert Academic Publishing, 2009.
6. A.B. Spierings and G. Levy, “Comparison of density of stainless steel 316L parts produced with selective laser melting using different powder grades,” Proceedings of the 20th solid freeform fabrication symposium, pp.342-353, 2009.
7. 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, 2009.
8. 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, 2005.
9. F. Thummler and R. Oberacker, “An introduction to powder metallurgy,” Oxford Science Publications, 1993.
10. Y. Li and 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.
11. F. Ali, B. Mohsen, 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.
12. S.A. Khairallah and A. Anderson, “Mesoscopic simulation model of selective laser melting of stainless steel powder,” Journal of Materials Processing Technology, Vol.214, pp.2627-2636, 2014.
13. A.V. Gusarov, I. Yadroitsev, P.h. Bertrand and I. Smurov, “Heat transfer modelling and stability analysis of selective laser melting,” Applied Surface Science, Vol.254, pp.975-979, 2007.
14. 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.
15. 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.
16. R. Klein, “Laser welding of plastics,” Wiley-VCH, 2011
17. 楊隆昌, 雷射發展的趨勢與應用, September, 2013.
18. 劉國基、張百齊, “Nd-YAG雷射的加工應用,” 遠東學報, Vol.19, 2001.
19. ”Gaussian beam optics,”, Available: http://www.cvimellesgriot.com/, pp.1919-1928, 1997.
20. S. Louhenkilpi and F. Imre, “Anyagtudományifolyamatszimuláció –Hőkezelésmodellezése,” 2011.
21. 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.
22. “Gaussian beam optics,” marketplace.idexop.com, A157-A172.
23. 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.
24. Ansys, “Ansys Fluent. 15.0 User’s Manual,” Ansys Inc., 2013.
25. 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.
26. G. Tsotridis, H. Rother and E.D. Hondros,”Marangoni flow and the shapes of laser-melted pools,” Naturwissenschaften76, pp.216-218, 1989.
27. 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.
28. 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.
29. ANSYS, “Ansys Fluent. 15.0 Theory Guide,” ANSYS Inc., 2013.
30. 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.
31. K.C. Mills, “Recommended values of thermophysical properties for selected commercial alloy,” Woodhead Publishing, 2002.
32. N.E. Hodge, R.M. Ferencz and J.M. Solberg, “Implementation of a thermomechanical model for the simulation of selectrive laser melting,” Computational Mech, Vol.54, pp.33-51, 2014.
33. 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.
34. A.M. Rubenchik, S. Wu, S. Mitchell, I. Golosker, M. Leblanc and N. Peterson, “Direct measure ments of temperature-dependent laser absorptivity of metal powders,” Applied Optics, Vol.54, pp.7230-7233, 2015.