| Summary: | 碩士 === 國立成功大學 === 機械工程學系 === 106 === In this study, a numerical model is established to investigate the molten pool of stainless steel 316L metal powder by multi-track scanning in Selective Laser Melting (SLM). The results show that the influence of Marangoni effect on the temperature field becomes greater with increasing laser power at scanning speed 640mm/s. When laser power maintains 150W, the decrease of scanning speed makes the shape of molten pool much deeper and narrower. Based on the results, it is inappropriate to neglect Marangoni effect during SLM simulation with these laser parameters. According to parameters analysis with energy utilization and manufacturing time, laser power 200W and scanning speed 800mm/s are more suitable parameters for melting effectiveness of powder. Through the analysis of hatch spacing which is found, if the overlapping rate exceeds 50%, it makes temperature gradient too large and is easy to cause thermal stress concentration, which is unfavorable for the manufacturing parts. Compared to the overlapping rate 30%, the temperature gradient is lower and molten pools show good bonding. We have also researched the implementation of two preheating methods to improve SLM process. Substrate preheating can help to have the lower temperature gradient and cooling rate. To avoid causing excessive the evaporation of material, it is better that the preheating temperature is controlled under 700K. Powder preheating shows no significant change in reducing the temperature gradient and the cooling rate. Therefore, it couldn’t improve the quality of the parts effectively.
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