Theoretical investigation of machining-induced residual stresses in longitudinal torsional ultrasonic–assisted milling

In order to realize the compressive stress and antifatigue manufacturing of titanium alloy TI-6Al-4V, a compound processing of longitudinal-torsional ultrasonic vibration and milling (LTUM) is proposed, a theoretical prediction model of machining-induced residual stress (RS) is established, and it is validated by experiments. The trajectory model of cutting edge in LTUM is constructed; furthermore, the undeformed chip thickness (UCT) model of LTUM is structured; The mechanical stress model of LTUM is established from the shear stress and plow stress; the thermal stress model of LTUM is established from shear thermal stress and plow thermal stress; Considering mechanical and thermal stress, the residual stress of longitudinal-torsional ultrasonic milling is established by loading and releasing stress. From numerical simulation of mechanical stress and thermal stress model, it shows that in LTUM, stress fluctuates with ultrasonic vibration, and mechanical stress absolute value is larger than that of traditional machining (TM); thermal stress absolute value is less than that of TM. A series of experiments are carried out to verify the RS model of LTUM. From present work, through theoretical prediction and experimental verification of machining-induced residual stress, it is concluded that established theoretical model predicts properties, and distribution of residual stress with high accuracy and the LTUM significantly increases surface compressive stress and compressive stress layer depth. It lays a foundation for the compressive stress and fatigue resistance of titanium alloys.