Residual stress prediction in ultrasonic vibration–assisted milling

In the current study, an analytical predictive model on residual stress after ultrasonic vibration–assisted milling is proposed in an effort to provide an accurate and reliable reference. Three types of tool-workpiece separation criteria are checked based on the tool center instantaneous position and velocity. Type I criterion examines the instantaneous velocity of tool tip under combined effects of feed movement and vibration. Type II criterion examines the position of tool center. Type III criterion describes the smaller chip size due to the overlaps between current and previous tool paths as a result of vibration. If none of these criterions is satisfied, the mechanical and thermal stresses are nonzero. The residual stress is then predicted through the calculation of stress distribution in loading process, incremental stress change considering kinematic hardening in plasticity, and the elastic stress release during relaxation process. The proposed predictive residual stress model in ultrasonic vibration–assisted milling is validated through comparison with experimental measurements on AISI 316L alloy. The proposed predictive model is able to match the measured residual stress with high accuracy of 6.4% average error and 23.6% maximum error among all cases. In addition, a sensitivity analysis is conducted. Higher axial depth of milling results in less compressive residual stress. Moreover, both higher ultrasonic vibration amplitude and higher spindle rotation frequency result in more compressive residual stress for AISI 316L alloy.