A Systematic Investigation of Laser Beam Shape Variation on the Thermal and Melt Pool Dynamics in Laser Powder Bed Fusion of 316l Stainless Steel

Laser Powder Bed Fusion (L-PBF) is a highly promising technique among Metal Additive Manufacturing (MAM) processes wherein a micron-size laser is used as a heat source that selectively fuses pre-determined regions of the metal powder bed to create a three-dimensional part in a layer-by-layer fashion. Despite the advantages offered by using L-PBF such as design flexibility, reducing the weight of parts, and producing less material waste, L-PBF parts are prone to defects such as porosity, cracks, delamination, and residual stresses which has led to the development of several multi-physics numerical models to predict the thermal-fluid conditions in the melt pool and capture these defects. In these advanced numerical models, the laser beam is assumed to be circular with a Gaussian intensity profile and is directed perpendicular to the powder bed. However, in large-scale L-PBF systems, due to a bigger build area and misalignment between the powder bed surface and the laser focal plane, the laser spot interacting with the powder bed is inclined and elliptically elongated. In this work, a multi-physics mesoscale numerical model is developed, and the thermal and fluid flow conditions are analyzed considering an inclined laser beam. The numerical model predicts that by inclining the laser beam, the melt pool depth is slightly reduced, due to lower energy density, and the melt pool width slightly increases. This change in melt pool dimensions affects the thermal gradient and solidification rate ultimately changing the as-built microstructure and resulting properties.