Constitutive modelling and micro-machinability evaluation of wrought and additively manufactured Ti6Al4V alloys: Experimental characterization and numerical simulation

This study presents the experimental determination of the coefficients of the Johnson-Cook (J-C) constitutive model and the numerical simulation of orthogonal micro-cutting and 2D/3D micro-milling processes of Laser Powder Bed Fusion (LPBF) Ti6Al4V. Besides, the results were also compared to the wrought Ti6Al4V. For that purpose, quasi-static and dynamic behaviors of wrought and LPBF Ti6Al4V were investigated by quasi-static tensile tests at several temperatures (0.001 s−1 at 20, 400, 600 °C) and at high strain rates using the split Hopkinson pressure bar (SHPB) tests (∼1000-5000 s−1 at 20, 400 °C). Sliding speed-dependent friction coefficients between WC-Co tool and workpiece material under open tribometer conditions were determined with tribological tests combined with numerical simulations. Micro-cutting simulations were performed using experimentally obtained J-C models of wrought and LPBF Ti6Al4V. A series of orthogonal micro cutting tests at different cutting speeds (75, 100, 150 m/min) and uncut chip thickness values (2.5, 5, 7.5, 10 μm) were performed to compare the measured forces and chip compression ratio (CCR) with those obtained by simulation. Micro-milling tests at different feeds (2, 4 µm/tooth) and spindle speeds (12000, 24000 rev/min) were carried out and cutting performance was evaluated in terms of surface integrity and tool wear. Good predictions of cutting forces, CCR, and average surface residual stresses were obtained for both materials. According to test results, due to its higher strength, more brittle behavior, and specific microstructure, LPBF Ti6Al4V showed higher cutting forces, tool wear, top burr width, compressive residual stresses, more affected subsurface microstructure, and lower surface roughness compared to wrought one.