Surface finish control of additively-manufactured Inconel 625 components using combined chemical-abrasive flow polishing

Little is understood about how to improve the interior surface quality of complex parts produced using additive manufacturing techniques, such as selective laser melting (SLM) and electron beam melting (EBM). Two surface-related problems can be highlighted in this context: the presence of semi-welded particles and a significant surface roughness and texture. Semi-welded particles could cause pollution in the fluid system of an engine part, while a significant surface roughness and texture could compromise fluid flow. This study aimed to design, manufacture and validate an innovative finishing technique combining chemical and abrasive flow polishing of interior surfaces of tubular IN625 components designed for the aerospace industry. The synergistic effect stemming from a combined use of the chemical and abrasive flows was investigated by studying: a) the flow of abrasive particles suspended in water, b) the flow of a chemical solution without abrasives, and c) the flow of abrasive particles suspended in a chemical solution. Considering the complexity of additively-manufactured components, the effect of the SLM build orientation on the internal surface finish was also characterized. The roughness and three-dimensional topography of the polished surface of IN625 parts for two SLM building orientations were assessed using the profilometry and confocal laser scanning microscopy techniques. The results obtained show that by employing the combined chemical-abrasive flow polishing technique, semi-welded particles on the interior surfaces of IN625 components can be completely removed and the surface roughness and texture, significantly improved.