Laser polishing of additive manufactured CoCr alloy components with complex surface geometry

Laser polishing, capable of polishing selective nonplanar areas, is exploited to improve the surface roughness of additive manufactured metal components. It offers a highly repeatable, higher speed polishing process as well as low labor costs compared with traditional mechanical abrasive polishing. In spite of the fact that many studies can be found on laser polishing processes, few have reported that focus on metal components, manufactured additively by selective laser melting (SLM) technology, with geometrically different complex surfaces. This paper presents a novel method to reduce the surface roughness of Cobalt Chromium (CoCr) components with complex surface geometry by using a layered polishing method which can constantly adjust the defocusing distance of the laser along with the surface shape of the components. The optimized laser polishing parameters used were firstly obtained from the test results on planar surfaces of CoCr alloy samples and samples with complex surface geometry were then polished based on the laser parameters. Characterizations for the laser polished samples were conducted using optical profiling and scanning electron microscopy, showing that the surface roughness was reduced significantly in comparison with the as-received samples. A reduction of up to 93% in surface roughness was achieved. The mechanical hardness was also characterized by testing for Vickers hardness, which indicated the surface hardness of the laser polished samples was enhanced by 8%. Moreover, a simple and effective model was developed to illustrate the method of laser polishing on the complex surface geometry of additive manufactured CoCr alloy components. The analytical model is helpful in understanding and evaluating the underlying mechanisms of laser polishing.