Comparative analysis of micro-milling performances of conventionally and additively manufactured Ti6Al4V alloys: Experimental investigation and 3D modelling

Abstract

This study comprehensively investigates the micro-milling performance of Ti6Al4V alloy fabricated by laser powder bed fusion (LPBF) in comparison to wrought one. For that purpose, a series of micro-milling tests were performed at several spindle rotational speeds (12 000 and 24 000 rpm), feeds per tooth (2 and 4 µm/tooth), and a constant depth of cut (100 µm) under dry cutting conditions. The micro-milling performance was evaluated in terms of machining forces and temperatures, surface quality, subsurface microstructural characteristics, residual stresses, burr formation, and chip geometry. A 3D micro-milling model including both constitutive and friction models whose coefficients were determined experimentally was developed. The micro-milling model was validated based on the comparison between simulated and measured forces and surface residual stress. The model can simulate quite well both the feed force (Fy) and the transverse force (Fx) with an error in the range of 6.16–14.53% and 2.51–13.45%, respectively. In most cutting conditions, reasonably well prediction of surface residual stress was achieved in both longitudinal (1.4–29.3%) and transverse (0.7–19.5%) directions. In comparison to the wrought work material, LPBF Ti6Al4V showed higher forces and temperatures, lower surface roughness, higher compressive residual stresses, and lower burr formation. In the case of LPBF Ti6Al4V, subsurface deformation and a higher reduction in microhardness beneath the machined surface were observed after micro-milling. The different micro-milling performances obtained by wrought and LPBF Ti6Al4V alloys were mainly associated with the specific microstructure characteristics of these materials.