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

TL;DR

This paper models the complex physics of melt flow in laser powder-bed fusion, revealing how recoil pressure and Marangoni convection cause defects like pores and spatter, validated with experiments.

Contribution

It introduces a high-fidelity powder-scale model with laser ray-tracing, providing new insights into pore formation mechanisms in L-PBF.

Findings

Melt flow dynamics generate specific defect types.

Laser ray-tracing improves energy deposition accuracy.

Different pore formation mechanisms identified at various melt track locations.

Abstract

This study demonstrates the significant effect of the recoil pressure and Marangoni convection in laser powder bed fusion (L-PBF) of 316L stainless steel. A three-dimensional high fidelity powder-scale model reveals how the strong dynamical melt flow generates pore defects, material spattering (sparking), and denudation zones. The melt track is divided into three sections: a topological depression, a transition and a tail region, each being the location of specific physical effects. The inclusion of laser ray-tracing energy deposition in the powder-scale model improves over traditional volumetric energy deposition. It enables partial particle melting, which impacts pore defects in the denudation zone. Different pore formation mechanisms 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 are discussed. The results are validated against the experiments and the sensitivity to laser absorptivity is discussed.