Enhancing productivity in Laser Powder Bed Fusion (PBF-LB/M) via layerwise Laser Remelting – proof of concept

Abstract

A limiting factor for a widespread application of laser powder bed fusion (PBF-LB/M) is the necessary compromise between quality and productivity resulting in high manufacturing costs. The productivity can be enhanced by increasing the layer height. However, this adjustment may result in either insufficient bonding due to inadequate laser energy input for complete melting or in an increased surface roughness and porosity through excessive energy density. The increased energy input required for complete melting of a high layer height induces the Marangoni effect which promotes an increase in surface roughness of the interlayer. Interlayer roughness peaks act as undercuts regarding the recoating process and result in local low density of the powder bed and thus porosity. Therefore, the requirements for a laser exposure are an adequate melt pool depth and a sufficient interlayer surface quality. For high layer heights and thus high productivity it is not possible to meet both requirements with a state of the art exposure strategy.
This work studied the feasibility of using layerwise laser remelting to smooth out roughness peaks after the first laser exposure with high energy density when using high layer height. A positive impact of the laser remelting on penetration depth and porosity was observed. Copper samples printed using the remelting strategy and a layer height of 60 μm achieved comparable values of porosity as samples with a layer height of 30 μm and a state of the art melting strategy. This approach resulted in time savings of 28 % while maintaining high part quality.