Research on removal mechanism of longitudinal-torsional compound ultrasonic vibration end grinding sapphire

Owing to its high hardness and brittleness, as well as the increasing demand in high-tech field, sapphire in conventional processing can hardly seek the balance between high efficiency and high quality. Ultrasonic vibration assisted grinding (UVAG) provides a perfect solution for sapphire grinding. Longitudinal-torsional compound ultrasonic vibration end grinding (LTUEG) as a mature UVAG technology, has the merits of reducing grinding force and improving surface topography in sapphire processing, but the removal mechanism of sapphire under LTUEG is still plain. Therefore, this paper based on kinematic analysis, developed grinding mechanism models of LTUEG and axial ultrasonic vibration end grinding (AUVEG), and discussed the differences of grinding mechanism between LTUEG and AUVEG. Then, single-factor experiments of conventional end grinding (CEG), AUVEG and LTUEG on sapphire were conducted, and the removal mechanism of sapphire under LTUEG was investigated, and the effect mechanism of longitudinal amplitude and torsional amplitude on the machined surface was analyzed emphatically. Results showed that grinding force and specific grinding energy were reduced after ultrasonic vibration applied; Compared with CEG, normal force and tangential force under LTUEG was decreased by 31.34 % and 20.99 %, respectively. Compared with AUVEG, LTUEG could decrease block spalling, increase the area of small broken area. It was found that within the test range, there was an optimal interval for A_L to affect the processing effect. A_L that was too low (0.5 µm) or too high (3 µm) would both lead to a decline in effect. Compared with AUVEG, the optimal interval for A_L to affect the processing effect in LTUEG was larger and the processing effect was better.