Reducing Surface Roughness of Selective Laser Melting of 316 Stainless Steel Component by Electropolishing

Additive manufacturing (AM) is widely used in the fields of aerospace, automotive, and biomedical. Because it enables to fabricate and customize parts with complex geometrical features. However, due to the layer-by-layer deposition and the partially fused raw material, AM part suffers from the step and balling effects, which shows inadequate and poor surface quality. Conventional polishing methods such as grinding, milling, and sandblasting have been applied to meet the requirement of well surface quality. But these contact polishing techniques usually introduce extra residual stress and surface damage, which are unsuitable for workpieces with complex shapes. In this study, we propose an environmentally friendly electrochemical polishing method for AM 316L stainless steel parts based on a combination of positive and negative pulses. Unlike the traditional phosphoric acid or sulfuric acid electrochemical polishing liquid system, the sodium chloride electrolyte adopted in this study avoids the pollution problem of waste liquid. A negative pulse was introduced to avoid the impaction of Cl- ions to the passivation film generated during the electrochemical polishing process. The effects of voltage, polishing duration, temperature, and duty cycle were analyzed by orthogonal experiments. Under the optimum reaction conditions, a surface roughness Ra of 0.421μm without pitting corrosion is achieved and the balling effect was eliminated.