Effect of anisotropic property on machining response of selective laser melted Ti6Al4V alloys in high-speed milling

Abstract

Selective laser melted (SLMed) technology provides an advanced manufacturing method for many complicated and sophisticated components due to the advantage of near-net shape and high-efficiency. However, post-machining SLMed parts is greatly essential for obtaining high-quality surface due to their poor surface integrity. This paper studies the effect of anisotropic property on machining response of SLMed Ti6Al4V alloy fabricated by three laser scanning strategies (0°, 67.5° and 90°). Especially, the effects of needle-like martensitics α′ and melt-pool boundary are considered in this study. High-speed milling experiments are conducted on the top and front surfaces of samples for studying the relationship among anisotropic microstructure, mechanical property and machinability. The cutting force, surface and chip characteristic are applied to evaluate the anisotropy of machinability. The results show that the cutting forces of top surface are larger than those of front surface, which leads to higher surface quality and lower surface roughness of front surface. This can be associated with the distinct melt-pool boundary of similar block grain boundary (top surface) and columnar grain boundary (front surface). The laser scanning strategy changes the distribution of needle-like martensitics α′ and further influences the evolution of microstructure, mechanical property and machinability. The surface formation experiences a coordinated deformed process of melt-pool boundary, plastic flow, grain distortion, dislocation accumulation and entanglement induced by complex thermo-mechanical coupled effect. This paper systematically revealed the underlying mechanism of the surface integrity during milling SLMed Ti6Al4V alloy with different laser scanning strategy and machined surface. The researched results can provide in-depth insights for improving the surface quality and performance of additive manufactured (AMed) parts by post machining technology.