Laser powder-bed fusion additive manufacturing: physics of complex melt flow and formation mechanisms of pores, spatter and denudation zones

摘要

This study demonstrates the significant effect of the recoil pressure andMarangoni convection in laser powder bed fusion (L-PBF) of 316L stainlesssteel. A three-dimensional high fidelity powder-scale model reveals how thestrong dynamical melt flow generates pore defects, material spattering(sparking), and denudation zones. The melt track is divided into threesections: a topological depression, a transition and a tail region, each beingthe location of specific physical effects. The inclusion of laser ray-tracingenergy deposition in the powder-scale model improves over traditionalvolumetric energy deposition. It enables partial particle melting, whichimpacts pore defects in the denudation zone. Different pore formationmechanisms are observed at the edge of a scan track, at the melt pool bottom(during collapse of the pool depression), and at the end of the melt track(during laser power ramp down). Remedies to these undesirable pores arediscussed. The results are validated against the experiments and thesensitivity to laser absorptivity is discussed.