Towards surface topography: Quantification of Selective Laser Melting (SLM) built parts

Reduction of surface roughness is one of the key research issues within the additive manufacturing technique Selective Laser Melting (SLM) since one of the major cost factors is the post processing of surfaces by means of milling, turning, etc. Time and resources needed for this post processing are most often directly related to the surface roughness. In order to effectively reduce roughness during the SLM-process, without reduction of melt pool size and therefore increase in production time, it is necessary to understand the physical processes responsible for roughness emergence. First necessary step in understanding the physical processes responsible for roughness emergence in Selective Laser Melting (SLM) is obtaining the surface topography of SLM built parts as exact as possible. Since the roughness of these parts can differ greatly between Ra approximate to 10-80 mu m with steep slopes partly >80 degrees obtaining the topography data is not trivial. Measurement methods are discussed with regard to the ability of mapping topography, using SLM built parts. Furthermore measuring specifications are discussed including measurement area and necessary sample geometry and finally the concept of roughness spectrum as an alternative to roughness value Ra is introduced and described. From this basis two possible measurements devices are chosen for further work, requirements for sample geometry are defined and first experimental results on single tracks and area measurements are shown.