Numerical Study on Melt Flow and Formation Mechanism of Spatter in Selective Laser Melting of Ti-6Al-4 V Alloy

Abstract

During the selective laser melting (SLM) process, the flow of the active molten pool presents various unstable states, which triggers various defects that affect the forming quality of the Ti-6Al-4 V alloy. Through an experimental comparison of Ti-6Al-4 V alloy samples under different laser energy densities in this study, it was found that as the laser energy density increased, the sample density showed a trend of first increasing (E_V = 0.125–0.200 J/mm) and then decreasing (E_V = 0.200–0.550 J/mm). The forming quality of the sample surface showed a continuous decreasing trend. Under the same laser energy density [E_V (P = 165 W, v = 300 mm/s) = E_V (P = 330 W, v = 600 mm/s) = 0.550 J/mm], the surface quality of the sample formed at a low power and speed was significantly improved. To explore the underlying reasons for these phenomena, a reliable three-dimensional model was constructed to simulate the melt flow inside the molten pool during the SLM process. The simulation results showed that as the laser energy density increased, the movement of the fluid inside the molten pool became intense. This led to periodic collapse inside the keyhole, resulting in the formation of bubble defects. A large amount of molten material accumulated behind the molten pool, affecting the surface forming quality of the sample. In addition, the eruption of a large amount of high-temperature metal vapor exacerbated the spatter phenomenon. This research provides a reference basis for further understanding the causes of defect formation during processing and improving the forming quality of later products.