Investigation on cutting forces and tool wear in high-speed milling of Ti-6Al-4V assisted by longitudinal torsional ultrasonic vibrations

The advantage of ultrasonic vibration-assisted milling of titanium alloys has been reported generally under low material removal rate. In this study, high-speed longitudinal-torsion ultrasonic vibration milling (LTUVM) of Ti-6Al-4V was adopted to investigate the cutting forces and tool wear in contrast to conventional milling (CM). In ultrasonic milling, the tool and the workpiece will produce short-term separation, when the cutting speed reaches a critical speed, the tool and the workpiece are no longer separated but always in contact, at which time the cutting speed is called the critical speed. First, the kinematic equation of LTUVM method was constructed, and the critical speed for the cutting separation phenomenon generated by LTUVM was calculated by using the equation of tool tip trajectory. The effects of linear velocity and feed per tooth on the ultrasonic duty cycle were analyzed, and the fitted curves were constructed. Afterwards, the LTUVM system platform was constructed to carry out single factor experiments, exploring the difference of CM and LTUVM processes on the cutting force. The tool wear behaviors of CM and LTUVM were compared under high speed and extensive feeds. The experimental results demonstrated that as the linear velocity increased, during which the ultrasonic cutting separation gradually disappeared, the cutting force improvement effect decreased; however, the tool wear improvement effect was still significant. Such effects of cutting force and tool wear during LTUVM were discussed to reveal its conducive efficiency in high-speed milling of titanium alloy.