Porosity, Surface Quality, Microhardness and Microstructure of Selective Laser Melted 316L Stainless Steel Resulting from Finish Machining

Abstract

Among additive manufacturing (AM) techniques, Selective Laser Melting (SLM) is widely used to fabricate metal components, including biocompatible bone implants made of 316L stainless steel. However, an issue with the components manufactured using this technique is the surface quality, which is generally beyond the acceptable range. Thus, hybrid manufacturing, including AM and finish machining processes, are being developed and implemented in the industry. Machining processes, particularly finish machining, are needed to improve surface quality of additively manufactured components and performance. This study focuses on the finish machining process of additively manufactured 316L stainless steel parts. Finish machining tests were carried out under dry conditions for various cutting speeds and feed rates. The experimental study reveals that finish machining resulted in up to 88% lower surface roughness of SLMed 316L stainless steel; it also had a substantial effect on microstructure and microhardness of the additively manufactured components by creating smaller grains and strain-hardened layer on the surface and subsurface of the SLMed part. The finish machining process also significantly decreased the density of porosity on the surface and subsurface, compared to an as-built sample. The created strain harden layer with less porosity is expected to increases wear and fatigue resistance of these parts.