Towards understanding the ploughing friction mechanism in ultrasonic assisted grinding with single grain

Despite the widespread use of ultrasonic vibration in machining (i.e., grinding) due to friction reduction, the friction mechanism at the tool-workpiece contact is still unclear. Most of the explanations focus on the kinematic analysis, but few attempts have been made to understand the deformation process of the tool-workpiece contact under ultrasonic vibration. This work presents a novel prediction model to calculate the ploughing friction co-efficient with the two-dimensional ultrasonic vibration assistance (imposed transverse vibration and additional normal vibration). Considering the ploughed surface generation, the actual contact area and the distribution of friction stress could be predicted. Particularly, the instantaneous contact area with a complex motion path was solved by generating the ploughed surface and calculating the overlapping area of the particle geometry engaged with the generated groove. Experimental results agree well with the predicted results. In addition to the deflection of resultant velocity, the friction reduction is also attributed to the change in friction stress distribution due to three special contact states. This research can deepen the understanding of tool-workpiece friction reduction mechanism in ultrasonic assisted grinding and might provide an important reference for studying other ultrasonic assisted machining processes.