Dimensionless process windows in laser-based powder bed fusion of AISI 316L using ring-shaped beam profiles

Abstract

The research trend to investigate the influence of alternative beam profiles on the process and component properties in laser-based powder bed fusion raises the question of how to compare the processes and process results generated with various beam profiles in different sizes. The current state of research mainly examines the process simplified on a single-track basis or addresses isolated aspects, such as the change in beam profile and size with constant absolute process parameters, which neglects the cross-effects of these parameters. Therefore, this paper presents a new approach to consider varied process parameters and their cross effects. The approach is based on a simple heat conduction model and allows the creation of beam shape and size-independent process maps. These dimensionless process maps are created by replacing the common dimensioned process parameters (laser power and scan speed) with combined dimensionless parameters (dimensionless enthalpy and Peclét number, each extended by a dimensionless hatch distance). This way, the parameters consider material and beam properties. Within the process maps, the process boundaries are predicted by simple geometric conditions of the calculated melt pools using the introduced heat conduction model. The model is experimentally validated by conducting a comprehensive parameter study using a multidimensional design of experiments with seven different beam profiles in various sizes and varying laser power, scanning speed, and hatch distance processing AISI 316L. The relative density and surface roughness are evaluated in the experiments. The predicted and experimentally determined process limits are in excellent agreement.