Micro/nano incremental material removal mechanisms in high-frequency ultrasonic vibration-assisted cutting of 316L stainless steel

Although the intermittent contact by the ultrasonic vibration-assisted cutting explained the machinability advantages, there exists a research gap in concentrating the effects of high-frequency ultrasonic vibration-assisted cutting (HFUVAC). This work clarified the differences of the micro/nano incremental material removal mechanisms between conventional cutting (CC) and high-frequency ultrasonic vibration-assisted cutting of 316 L stainless steel. The machinability advantages and microstructure features were compared and analyzed through the ultra-precision cutting experiments. Compared with the continuous contact mode of the conventional cutting, the incremental effect of the high-frequency ultrasonic vibration-assisted cutting achieved superior machinability, which included cutting force decreasing, tool wear reduction, surface defects suppression, and chips undergoing from discontinuous quasi-shear state to continuous multiple-shear state. As the nominal cutting speed increased in the high-frequency ultrasonic vibration-assisted cutting, the surface defects and surface roughness showed an increasing trend, which was indispensable to control the normal cutting speeds below 5 m/min, or the cutting stroke in each vibration cycle less than 800 nm to obtain the defect-free surface. The grain refinement and severe elongation deformation were observed at the chip bottom and machined surface of the conventional cutting due to strong mechanical friction loads. While the microstructure features of chips and the machined surface in the local deformation layer were the results of friction reduction, dynamic recrystallization, and twinning/stacking formation induced by the incremental effects of the high-frequency ultrasonic vibration-assisted cutting. The results help to improve surface quality and optimize the ratio of cutting speed to vibration frequency to enhance the efficiency.