Mechanism-Oriented Thermo-Mechanical FEM of Surface Residual Stress Formation in Ti-6Al-4V Machining with Experimental Validation

This study investigates the formation mechanisms of residual stress during the orthogonal machining of Ti-6Al-4V alloy using a coupled thermo-mechanical finite element model (FEM). The model was validated against X-ray diffraction (XRD) measurements, achieving a quantitative agreement with a Mean Absolute Error (MAE) of approximately 45 MPa for surface residual stresses. A novel continuous analysis path was introduced to track the temperature evolution from the chip formation zone to the machined surface. The study systematically quantified the effects of cutting speed ( =30–180 m/min), feed rate ( =0.1–0.5 mm/rev), and tool geometry on stress distribution. Simulation results reveal that increasing the cutting speed from 30 to 180 m/min causes a transition in surface residual stress from compressive to tensile due to dominant thermal softening effects. Conversely, increasing the feed rate and cutting edge radius ( = 0.01–0.05 mm) promotes deeper subsurface compressive stresses driven by enhanced plastic strain accumulation. Furthermore, the use of positive rake angles (up to 20°) was found to significantly reduce both temperature gradients and stress magnitudes.