Investigation on occurrence of elevated edges in Selective Laser Melting

Selective laser melting (SLM) is a layer-wise material additive process for the direct fabrication of functional metallic parts. During the process, successive layers of metal powder are fully molten and consolidated on top of each other by the energy of a high intensity laser beam. The process is capable of producing almost fully dense three-dimensional parts having mechanical properties comparable to those of bulk materials. However, one of the problems encountered in SLM process is the occurrence of elevated ridges of the solidified material at the edges of the successive layers. Those ridges reduce the dimensional accuracy and topology of the top surface. The edge-effect problem is encountered not only in SLM, but also in other production techniques applying melting processes such as LENS® (The Laser Engineered Net Shaping) and EBM (Electron Beam Melting). In this study, the reasons for elevated edges and solutions to this problem are investigated and reported. Different scan strategies as well as different hatching and contour parameters are tested to reduce the edge-effect problem. Besides, the influence of applying laser re-melting in combination to selective laser melting has been investigated. It turns out that re-melting layers deposited by SLM improves the part density and surface roughness, but creates on its own elevated edges.