Impact of beam shaping on melt pool behavior in laser processing of stainless steel 316L: Thermal analysis using multispectral imaging

Abstract

In Laser-based Powder Bed Fusion of Metals (PBF-LB/M), melt pool temperature distributions directly impact process dynamics and final part quality. While ring-shaped laser beam profiles promise improved melt pool stability, their effect on melt pool temperature remains unclear due to inaccurate absolute temperature measurements. To address this, we employ an in-house off-axial Multispectral Imaging (MSI) system (mean relative error less than 1.6%) to enable in-situ measurement of absolute melt pool temperatures and thermal gradients in 316L stainless steel. Comparing Gaussian and ring-shaped beams, we find that the Gaussian beam creates a concentrated heat zone with linearly increasing peak temperatures with increasing power under conduction mode. In contrast, the ring-shaped beam induces surface melting at lower power and full melting at higher power, resulting in a half-moon-shaped temperature distribution. Thermal gradient (indicative of Marangoni flow) reveals that the Gaussian beam generates stronger gradients (4–25 $K/\mu m$), driving circular Marangoni flow and bowl-shaped melt pools. The ring-shaped beam produces weaker gradients (2–18 $K/\mu m$), leading to flatter melt pools at low power and semi-elliptical melt pools at high power. This study provides critical insights into optimizing beam shaping strategies, broadening application possibilities, and deepening the understanding of melt pool dynamics in PBF-LB/M.