Rotary ultrasonic machining (RUM) is a hybrid machining process which combines the material removal mechanisms of diamond grinding and ultrasonic machining (USM), resulting in higher material removal rates (MRR) than that obtained by either diamond grinding or USM. The experiments with calcium aluminum silicate and magnesia stabilized zirconia have shown that the MRR obtained from rotary ultrasonic machining is six to ten times higher than that from a conventional grinding process under similar conditions (Prabhakar, 1992). In comparison with USM, rotary ultrasonic machining is about ten times faster; it is easier to drill deep holes with rotary ultrasonic machining than with USM; and the hole accuracy is improved (Cleave, 1976; Graff, 1975). Other advantages of this process include superior surface finish and low tool pressure (Cleave, 1976; Petrukha et al., 1970).

The effects of process parameters (applied static pressure, rotational speed, ultrasonic vibration amplitude, ultrasonic vibration frequency, diamond type, abrasive size, diamond concentration and bond type, etc.) on the process performance (material removal rate, tool wear, surface roughness, etc.) have been investigated experimentally (Kubota et al., 1977; Markov and Ustinov, 1972; Markov et al., 1977; Petrukha et al., 1970; Prabhakar, 1992; Prabhakar, et al. 1992; Wang and Lin, 1993). The major conclusions are summarized as follows.

      Effects of grit size

Analytical models for rotary ultrasonic machining would help in understanding the mechanism of the material removal and in optimizing the process parameters to obtain the required output. This section will present two models developed for predicting the MRR in rotary ultrasonic machining.