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.
Highlights
Additive manufacturing enables the production of complex-shaped parts and rapid prototypes that cannot be produced by machining methods [1,2]
The Selective Laser Melting (SLM) process provides many advantages as compared to conventional machining, its one of the major drawbacks is the low surface quality resulting from this process [10,11]
The surface quality of metallic selective laser melted (SLMed) parts is influenced by many factors; such as-built orientation [13] laser parameters—laser power, scanning speed, hatching distance, etc. [14]—and powder size [15]
Summary
Additive manufacturing enables the production of complex-shaped parts and rapid prototypes that cannot be produced by machining methods [1,2]. As hybrid method includes both SLM and finish machining, and finish machining is being used to improve the surface property, it is inecessary to investigate the effects of the finishing process on the surface and subsurface characteristics of additively manufactured parts. Few studies have reported that post-finishing processes such as laser re-melting [10], electrochemical and abrasive flow machining [27] and milling processes [28] have improved surface characteristics of SLMed parts. As a post-processing operation, finish machining processes, including turning and milling, can be utilized to improve surface characteristics and control subsurface properties. The influence of the finish turning process on surface and subsurface characteristics of additively manufactured 316L stainless steel is investigated and presented.
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