Application of Laser Re-melting on selective laser melting parts

Selective Laser Melting (SLM) is an additive manufacturing process whereby a threedimensional part with almost full density and good mechanical properties is built in a layerwise manner. During the process, a laser source selectively scans a powder bed according to the CAD data of the part to be produced and the powder metal particles are completely melted. In this way, SLM is capable of producing functional metallic parts with a high geometrical freedom. However, there are some limitations to the process including insufficient surface quality, remnant porosity (~1-2%) and stair effect which is inherent to all layer manufacturing processes. In this study, laser re-melting is applied using a continuous wave Nd:YAG laser during SLM of AISI 316L stainless steel parts to overcome or to weaken these limitations. After each layer is fully molten, the same slice data is used to re-expose the layer for laser re-melting. In this manner, laser re-melting does not only improve the surface quality but also has the potential to improve density. The influence of laser re-melting on density enhancement, surface quality and stair-effect is studied varying the operating parameters such as scan speed, laser power and scan spacing. The laser re-melting method with optimized parameter settings greatly densifies the SLM part and improves the surface quality significantly at a cost of longer production times. The stair-effect is also greatly eliminated when laser re-melting is applied on the inclined surfaces after the process is completed and the surrounding powder particles are blown away.