Study on force reduction mechanism in ultrasonic-assisted grinding based on single-grain scratching

Ultrasonic vibration-assisted grinding (UAG) has been proven to be a promising grinding ability improvement technique due to the grinding force reduction. However, the reduction mechanism is still unclear due to the lack of knowledge on material softening and grain-workpiece contact conditions in UAG. In this paper, we present a numerical and experimental study on ultrasonic vibration-assisted scratching (UAS) to understand the force reduction mechanism for UAG from a single-grain perspective. Based on crystal plasticity theory and dislocation density model, the constitutive model for ultrasonic-assisted deformation is established, in which the influence of vibration amplitude and strain rate is considered. To further study the acoustic softening effect, the ultrasonic assisted tensile test is conducted. The finite element model for UAS is developed with the kinematic analysis and the consideration of acoustic softening effect. The comparison between the simulated and experimental results indicates that the process force reduction under ultrasonic vibration can be attributed to (1) the reduction of contact area due to the path interference effect and (2) the yield stress reduction due to the acoustic softening effect. This research can deepen the understanding of the beneficial effect of ultrasonic vibration in UAG and offers new insight for studying other ultrasonic-assisted machining method.