Improving the surface integrity and mechanical properties of additive manufactured stainless steel components by wire electrical discharge polishing

Abstract

Metal additive manufacturing (AM) is gaining momentum among modern manufacturing techniques due to its flexibility in fabricating complex shaped components with minimum scrap. However, the technology cannot be directly employed in producing parts on a larger scale because of the poor surface integrity and average mechanical properties. This highlights the importance of post processing AM components with suitable methods that can overcome these limitations. The existing finishing methods for AM components such as laser polishing, chemical polishing, abrasive finishing, mechanical polishing and other hybrid combinations have their own limitations. Difficulty in accessing complex part surfaces, loss of dimensional accuracy and deterioration in material surface and properties are some of the major challenges related to existing finishing methods. In the present work, wire electrical discharge polishing (WEDP) technique has been proposed in improving the surface integrity and mechanical properties of metal AM components. Experiments were carried out on selective laser melted (SLM) stainless steel (SS316 L) specimens at different settings of pulse duration and servo voltage. A detailed investigation into surface finish and morphology was performed to determine the enhancement in surface integrity after WEDP. In addition, investigations were conducted to evaluate the improvement in mechanical properties such as microhardness and tribological performance. The irregularities/defects over the SLM surface were removed and a maximum finish of 0.739 μm was achieved. A negligible amount of wire material was migrated to the SS316 L workpiece surface after WEDP process. Moreover, reduction in crystallite size and microstrain was obtained based on results from XRD analysis. Martensite formation and shift in peaks were also evident from XRD pattern after WEDP process. An increase in microhardness (∼ 317 HV) at the subsurface and reduction in coefficient of friction (∼ 0.35) were also achieved. Based on aforementioned results, WEDP showed excellent capability in improving the surface integrity and mechanical properties thereby providing a promising hybrid option for combining with metal AM technology.