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

Abstract

Crack propagation is critical in determining the 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 propagation on the surface formation mechanism and surface morphology of silicon nitride ceramics was investigated via longitudinal–torsional composite ultrasonic-assisted mill grinding, and a reconstruction model of the machined surface morphology considering crack propagation was proposed. This model was quantitatively characterized and evaluated by the average roughness Sa and the kurtosis Sku. It was found that the simulation results considering crack expansion are in good agreement with the experimental results. The average relative errors in the average roughness and kurtosis were found to be 7.95% and 9.46%, respectively. A primary effect analysis was performed to understand the influence of the process parameters on the machined surface morphology. It was found that ultrasonic vibrations lead to changes in the shear angle and shear velocity of abrasive grains, thereby changing the machined surface morphology. The results presented here provide a practical method for predicting and controlling the machined surface quality during precision machining of ceramic materials.