Surface Polishing of Additively Manufactured Ti6Al4V Titanium Alloy by Using a Nanosecond Pulse Laser

Several studies have found that the laser polishing process is exceptionally effective in smoothing metal surfaces with an initial roughness of less than 10 μm. However, the laser polishing performance for the surfaces of additively manufactured parts having different levels of morphology and roughness greater than 10 μm has not been comprehensively investigated. This paper therefore aims to unveil the viability of the laser polishing process for smoothing the additively manufactured surfaces possessing different degrees of morphologies and initial roughness. Three-dimensional printed sample and shot-peened Ti6Al4V titanium alloy sheets having various levels of surface roughness were polished by a nanosecond pulse laser under different processing conditions. Three experimental sets were performed to investigate the effects of initial surface roughness, laser scanning speed, laser pulse repetition rate, number of scanning passes, and flow rate of argon gas on the roughness and morphology of the polished surface. A smooth surface was achievable by using slow laser scanning speed, high laser pulse repetition rate, and multiple-scanning passes. Besides the initial roughness, the improvement was substantially subject to the initial surface morphology. The roughness of the laser-polished surface was improved by up to 73% when a suitable polishing condition was applied. The findings of this study have provided better insight into the laser polishing process and its ability to smooth the rough 3D-printed surfaces. The post-processing of additively manufactured parts, whose surface roughness is a critical concern, will benefit from the laser polishing guidelines suggested in this study.