Surface roughness in laser powder bed fusion – Interdependency of surface orientation and laser incidence

Abstract

Additive Manufacturing (AM) offers the opportunity for the manufacture of innovative parts with complex geometries and new possibilities regarding complex part design. However, the relatively high surface roughness of as-built parts is a considerable limitation and one of the challenges in AM. Laser powder bed fusion (L-PBF) is one AM technique for the manufacture of metallic serial parts. Although the effect of various process parameters on the surface roughness in L-PBF has been studied, a prediction of surface roughness at the pre-processing stage has not been achieved yet. The interdependency of the surface orientation and the laser incidence, although it is mentioned in literature, is still not yet analyzed or quantified. Therefore, the novel parameter surface laser relation angle ζ is introduced to quantify this interdependency and act as a parameter to predict surface roughness. By using a constant laser relation angle ζ the range of roughness parameter Ra on surfaces across the entire build platform can be decreased from 19 μm to 11 μm in comparison to the usage of a constant surface normal polar angle α. By this method the standard deviation is decreased from 5 μm to 2 μm as well with a constant arithmetic mean of 24 μm on both methods. Similar behavior can also be seen for the roughness parameter Rz in this work. The results achieved so far lay the basis for a homogenization of the surface roughness across the entire build platform.