An investigation into the effects of contouring process parameters on the up-skin surface characteristics in laser powder-bed fusion process

Abstract

Laser powder-bed fusion (L-PBF) additive manufacturing is reshaping how parts are designed and built in the aerospace, automotive, biomedical, and other industries. However, in several applications, the quality of the components in terms of surface roughness, density, and mechanical properties is not comparable to that of parts made by conventional manufacturing processes. Multiple process parameters and associated uncertainties strongly influence the properties of L-PBF built parts. This study aims to understand the effects of contouring process parameters on the formation of up-skin surfaces and roughness variability in an inclined build scenario. Through Design of Experiment (DOE), the influence of the contour process parameters, such as the laser power, scanning speed, contouring offset, and incline angle (θ, between 30° and 60°), on upward-facing surfaces is investigated. Furthermore, a comprehensive multi-physics Computational Thermo-fluid model and Discrete Element Method (DEM) simulation framework is developed to shed light on how contouring scans affect the morphology of the upward-facing surface. The developed thermo-fluid model framework is used to perform multi-track multi-layer simulations of an L-PBF process. Numerical data suggests that a higher laser power enlarges the melt-pool size providing sufficient fusion at the border, hence, improving the density of up-skin regions. A higher density may primarily contribute to a better surface finish for up-skin features. The experimental result analysis shows that in the tested slope range (30° ≤ θ ≤ 60°), the up-skin surface roughness exacerbates with the increase of the incline angle and the scanning speed. On the other hand, a higher laser power will result in better surface finishes. The findings also indicate that a higher linear energy density (LED = Power/Speed) for contour scans is more favourable for the range of parameters tested in this study. Within the range of studied contouring process parameters, the maximum and minimum of average roughness (Ra) values for up-skin surfaces are 21.2 ± 2.9 µm and 8 ± 0.6 µm, respectively.