Groove bottom material removal mechanism and machinability evaluation for longitudinal ultrasonic vibration-assisted milling of Al-50wt% Si alloy

The anisotropy, inhomogeneity, high brittleness, and hardness of Al-50wt% Si alloy challenge its machinability in conventional processing. To solve the problem of serious machined surface defects on the groove bottom, the longitudinal ultrasonic vibration-assisted milling (LUVAM) technique was developed for Al-50wt% Si alloy groove machining. Based on the characteristics of tool-workpiece separation and frictional reversal, the variation of cutting force and cutting temperature with amplitude was studied. The influence of amplitude on the material removal mechanism and surface formation characteristics of Al-50wt% Si alloy groove bottom under different material removal rates (precision and non-precision milling (PM and NPM)) were the focus of this paper. The results show that the probability of Si particle breakage and spalling in PM decreases with the increase of amplitude, and the particles are sheared instead. The ultrasonic dressing effect reduces the anisotropy of Al-50wt% Si alloy. However, in NPM, the ultrasonic dressing effect weakens and the dynamic impact effect increases when the amplitude exceeds the critical value 2.5 mu m. Additionally, the groove bottom surface features are related to the down milling (DM) and up milling (UM) methods. UM is the better method for PM of Al-50wt% Si alloy, and DM is the better method for NPM of Al-50wt% Si alloy. This work suggests that under different material removal rates, the machined groove quality of Al-50wt% Si alloy can be improved by selection of optimized amplitude in LUVAM.