Scan path resolved thermal modelling of LPBF

Abstract

Laser powder bed fusion product quality depends on process parameters (e.g. laser power, scan speed, etc.) and on the scan strategy. The accuracy by which a feature outline is printed defines the surface finish, workpiece fatigue behavior and the extent of post processing needed to achieve surface quality specifications. In this paper we develop a semi-analytic thermal model allowing the resolution of the scan strategy in detail while solving the energy equation to predict the thermal history of the printed component and its features. Experiments are performed using process parameters that have been shown to achieve an IN718 relative density larger than 99.5%. We study the influence of scan strategies on different features’ surface quality while keeping the process parameters unchanged. The model is driven by the build file provided to the 3D printer or using the more accurate in-situ process data describing the laser path and status. The model is verified using high-fidelity models as well as experimental results. We demonstrate both experimentally and numerically how the printer controller changes the build strategy, slightly affecting the quality of fine features. Laser scan dynamics and timing, particularly sky-writing, was shown to have a critical effect on the melt pool morphology and necessary to include in the models.