A numerical study on the generation and migration of bubbles in laser powder bed fusion IN 718 alloy

Abstract

An integrated multiphysics numerical simulation for the single track Laser-Powder Bed Fusion (L-PBF) process was developed utilizing both computational fluid dynamics (CFD) and discrete element method (DEM) models. This meso-scale simulation comprehensively accounted for diverse phenomena, including melting/solidification/evaporation, radiation and heat transfer, multi-phase flow, recoil pressure force, and the Marangoni effect, among others. By employing various laser energy densities in the numerical simulations, the study unveiled the mechanism governing bubble formation and the subsequent migration process. The complex dynamics of the melt pool were driven by the interaction and competition of multiple forces, leading to the development of a clockwise vortex. The simulation results demonstrated that enclosed bubbles primarily formed at the bottom of the keyhole due to the vortex effect. While some bubbles escaped from the molten pool's top surface along the vortex, others remained trapped inside, resulting in the formation of near-spherical pore defects in the solidified metal.