Formation mechanism and modelling of exit edge-chipping during ultrasonic vibration grinding of deep-small holes of microcrystalline-mica ceramics

Finite element simulation was used to analyse the edge-chipping mechanism of the hole exit during ultrasonic vibration grinding of deep-small holes of microcrystalline-mica ceramics, which indicated that there were two causes of edge-chipping during the grinding process. The first edge-chipping phenomenon was caused by the abrasives on the bottom of the wheel, while the second edge-chipping phenomenon was caused by the abrasives on the circumference of the wheel. A model of the exit edge-chipping was developed based on the indentation fracture mechanics, and an edge-chipping index was proposed to evaluate the integrity of deep-small holes. Ultrasonic vibration grinding experiments of deep-small holes for microcrystalline-mica ceramics were performed on a five axis ultrasonic vibration precision machining machine. Single-factor experiments were designed to investigate the influences of grinding parameters on the edge-chipping size, and orthogonal experiments were designed to verify the reliability of the theoretical model of the edge-chipping size. The morphology of the hole exit was determined using a laser confocal microscope. Median filtering and “Robot” algorithms were used in the image enhancement and edge detection of the machined holes, respectively. The experimental results demonstrated that the edge-chipping index decreased as the spindle speed and ultrasonic amplitude increased, but it increased as the feed speed increased. Compared with common grinding, ultrasonic vibration grinding was beneficial to improve the machining quality of deep holes of hard and brittle materials. The experimental results for the edge-chipping index were close to the predicted results, with an average error of 13.3% between them, thereby indicating that the theoretical model of the edge-chipping index was reliable. In addition, the predicted values of the grinding force were also close to the experimental results. This work could provide theoretical and process guidance to aid in realising the high-efficiency and precision-machining of deep-small holes of hard and brittle materials.