Surface roughness prediction in ultrasonic vibration-assisted milling

Abstract

Better surface finish is believed to be one of the most important benefits of ultrasonic vibration-assisted milling. Many studies have shown that this benefit is most significant during slot-milling of a part when the vibration is applied in feed direction. To explicitly explain this phenomenon, an analytical model is proposed to predict surface roughness based on the trajectory of tool and the response of machined surface. The overall machined surface profile under tool trajectory depends on the tool tip movement, in addition to the tool deformation under cutting force and tool tip geometry. The movement of tool tip is governed by feed, spindle rotation, and ultrasonic vibration. The tool deformation depends on the milling force and stiffness. The geometry of tool tip is characterized by the tip radius and angle. Besides surface profile under tool trajectory, the response of machined surface is considered by assuming pure elastic deformation when the actual instantaneous cutting thickness is smaller than a critical value. In that case, part of the material is recovered so the actual machined surface profile is different from the profile under tool trajectory only. Surface roughness is then calculated based on the actual surface profile. Experiments are conducted on Aluminum alloy in both conventional and ultrasonic vibration-assisted milling under different spindle speed, feed, and vibration amplitude. Through the comparison between the analytical predictions and experimental measurements, the proposed model has high accuracy in all cases with average percentage error of 15%.