Effect of crack propagation on surface formation mechanism and surface morphology evaluation of longitudinal–torsional composite ultrasonic mill-grinding of Si3N4

Abstract

Abstract Crack extension is critical in determining surface forming process and machined surface quality of hard brittle materials. However, there is still a lack of research on this subject. In this work, the effect of crack extension on surface formation mechanism and surface morphology of silicon nitride ceramics was investigated via longitudinal–torsional composite ultrasonic-assisted mill-grinding, and reconstruction model of machined surface morphology considering crack extension was proposed. This model was quantitatively characterized and evaluated by the average roughness Sa and the kurtosis Sku. It is found that simulation results considering crack expansion were in good agreement with experimental results. Average relative errors in average roughness and kurtosis were found to be 7.95% and 9.46%, respectively. Primary effect analysis was performed to understand the influence of process parameters on machined surface morphology. It is found that ultrasonic vibration leads to changes in shear angle and shear velocity of abrasive grains, thereby changing machined surface morphology. Results presented here provide practical method for predicting and controlling machined surface quality during precision machining of ceramic materials.