Influence of milling and non-traditional machining on surface properties of Ti6Al4V EBM components

With growing range of alloys that are processed in metal Additive Manufacturing (AM), especially for applications in the aerospace and biomedical industry, the development of post-processing strategies to economically achieve the desired surface finish and part feature tolerances are emerging as key challenges. This study focuses on implementing machining and fine-abrasive finishing processes to understand the impact of specific post-processing recipes on surface morphology and mechanical properties of AM components. Ti6Al4V components fabricated via Electron Beam Melting (EBM) process was subjected to a traditional machining and multi-step fine-abrasive finishing process. The white light interferometry, optical microscopy and microhardness testing studies demonstrated that multi-step finishing process can achieve an ultra-smooth surface finish of S_α < 50 nm. More importantly, the developed post-processing strategy increased surface density (and hence, bearing characteristics) by minimizing surface void volumes to less than 0.2% of as-fabricated EBM component, and a 20% improvement in surface hardness. A major implication of this first reported study on combining machining and polishing of metal AM part is that, orders of magnitude improvement in surface roughness and surface porosity can be achieved from a fine-abrasive finishing process, but the surface improvements are highly dependent on build orientation (58% in X-direction and 24% in Z-direction).