Effects of build- and scan-directions on magnetic field-assisted finishing of 316L stainless steel disks produced with selective laser melting

Abstract

Selective laser melting (SLM) is an additive manufacturing process, which allows for producing parts of very complex geometry. While SLM may produce the desired net-shape geometry, the surface conditions of as-built SLM parts are often insufficient. Also, the as-built state may yield undesired tensile stresses at the surface. Post processes such as magnetic field-assisted finishing (MAF) processes can yield the desired surface roughness and improve the residual stress state. However, in a part made by SLM, these processes will act on surfaces with various different orientations to the built direction, and, in particular, to the laser scanning direction. This paper analyzes the influence of laser scanning direction with respect to the surface to be finished by MAF using 316L steel disks produced with different orientations and scan strategies. The build plane of an as-printed disk has greater surface roughness and hardness but lower tensile residual stresses than the plane perpendicular to the build plane. These characteristics create difficulties in material removal and smoothing but do not impede MAF’s ability to increase hardness and impart compressive residual stresses to the surface scanned by the laser. The results indicate that material removal rate and hence optimal finishing time depend on the orientation of the surface with respect to the scanning direction, which should be accounted for in process planning.