Laser polishing of parts built up by selective laser sintering

Abstract

In this work, a surface finish method for parts built-up by selective laser sintering (SLS) is presented. One of the main drawbacks of the SLS technique is the high surface roughness of resulting parts. Therefore, parts have to be polished to be valid for operation conditions. Polishing processes are usually based on manual abrasive techniques. However, in the present paper, a surface polishing method based on laser irradiation is presented. The laser beam melts a microscopic layer on the surface, which re-solidifies under shielding gas protective conditions, resulting in a smoother surface. Laser-polishing tests for lines, planar surfaces and inclined planes have been performed, with satisfactory results in all the cases. The experimental tests were carried out on sintered test parts with an initial roughness of 7.5–7.8 μm Ra. The tested material is a commercial alloy denominated LaserForm ST-100 ©, composed by sintered stainless steel and infiltrated bronze that it is used mainly for the constitution of injection moulds. Experimental results present final surface roughness below 1.49 μm Ra, which represent an 80.1% reduction of the mean roughness. Finally, a complete analysis of test probes and its metallurgical composition is presented. Considering that the material presents a non-homogeneous structure, the polished surfaces present slightly higher hardness values and are more homogeneous than the initial ones. Thus, polished surfaces do not present any heat affected zone or cracks, which could cause failure during the part operation.