Role of operating and environmental conditions in determining molten pool dynamics during electron beam melting and selective laser melting

Electron beam melting (EBM) and selective laser melting (SLM) are representative powder bed fusion additive manufacturing methods. Because EBM and SLM have different operating and environmental conditions, such as ambient pressure of the chamber, initial temperature, and heat source, they have different molten pool dynamics. In this study, single-bead melting experiments using EBM and SLM were performed in conjunction with computational thermal-fluid dynamics simulations in high-energy conditions to highlight the differences in the molten pool dynamics of EBM and SLM. The experimental results reveal that SLM is more likely to melt in the keyhole mode than EBM under nominally identical line energy. The simulations showed that the instantaneous maximum temperature of the SLM molten pool is much lower than that of the EBM molten pool. An increase in the preheating temperature is found to strengthen the vapor recoil pressure; however, the vapor recoil pressure under vacuum is maintained at a considerably low level in EBM. Compared to EBM, the high atmospheric pressure and multiple laser reflections during SLM significantly enhance the effect of the vapor recoil pressure on the melt surface. The findings of this study can be useful for the formulation of appropriate processing strategies for the two processes.