Longitudinal-torsional compound ultrasonic vibration end grinding sapphire: A study on surface topography and roughness

Owing to excellent physical and optical characteristics, Sapphire has wide applications in detection, military, photoelectric and other industries. Nevertheless, it's difficult to use the conventional processing methods to process sapphire with high precision and efficiency due to its hardness and brittleness. This study adopted longitudinal-torsional compound ultrasonic vibration end grinding (LTUEG) method to grind sapphire. Firstly, the grinding trajectory equation of single grain under LTUEG was established. Then, combining with the motion state of single grain, the removal mechanism of sapphire under LTUEG was clarified. Finally, a comparative experiment between LTUEG and conventional end grinding (CEG) of sapphire was conducted, and the effects of processing parameters on surface topography and surface roughness were investigated. Results showed that surface roughness declined with grinding speed, enhanced with feed rate and grinding depth, declined first and then went up with amplitude, and the minimum value was 0.522 mu m. Compared with CEG, LTUEG could significantly reduce the surface roughness, with a maximum reduction of 20.98 %. LTUEG could reduce the pits size. Meanwhile, when the longitudinal amplitude AL was 0.8 mu m, the average pits length and pits depth reached the minimum, which were 33.13 mu m and 5.296 mu m, respectively. The research found that LTUEG could reduce block spalling, increase the ratio of plastic domain removal as well as improve the surface flatness of workpiece.