Micromilling-induced Surface Integrity of Porous Additive Manufactured Ti6Al4V Alloy

Abstract

Surface integrity refers to the condition of the workpiece surface modified by a manufacturing process. Surface integrity plays an equally important role in the functional performance and quality of the components as the dimensional accuracy, especially for applications such as load-bearing components and energy absorbers. With the rise in additive manufacturing technologies, the components where surface characteristics play an important role are being manufactured by a combination of additive manufacturing process followed by a finishing process. A secondary finishing process such as machining is essential for components produced by additive manufacturing or powder metallurgy as these processes exhibit poor surface finish, dimensional inaccuracies, and other internal/surface defects such as porosity. High strain rates and cutting temperatures involved in the machining process affect the surface characteristics of the machined component. It is envisaged that the cutting mechanism of porous parts produced by additive manufacturing could be significantly different from that of the continuous material. Therefore, the machining parameters, depending on their interaction with the inherent part porosity, could give rise to different surface characteristics and could be critical in determining the functional performance of the part. This work investigates the effect of micro-machining on the surface integrity and cutting force of additive manufactured Ti6Al4V alloy. Experiments are carried out at different levels of porosity and depth of cut to explore their effects on the cutting force, roughness, micro-hardness, residual stress of the resulting surface. It is seen that the mean cutting force was minimum during machining of porous materials and was maximum during machining of continuous materials. As the depth of cut increased, cutting force increased for continuous and porous materials. Whereas cutting force decreased as the porosity increased and was minimum during machining of most porous material (46 % porous). The surface finish was better for wrought alloy compared to additively manufactured Ti6Al4V alloy. As the porosity increased, the surface finish reduced initially and improved later.