Abstract: The effective cutting time, cutting depth, cutting speed, and cutting length of single particle in rotary ultrasonic drilling are determined by examining mechanism of hard and brittle material brittle-fracture removal and analyzing characteristic of diamond tools’ rotary ultrasonic machining. A mathematical model is presented to predict the cutting force in rotary ultrasonic drilling. The experimental investigations of optical glass show that cutting force increases with the increase of feedrate and decreases with the increase of spindle speed, and the effect of spindle speed on cutting force is much stronger at high feedrate and the effect of feedrate on cutting force is much stronger at low spindle speed, which verify the developed mathematical model. Comparative experiments on rotary ultrasonic drilling and conventional machining show that the former can reduce cutting force and machined hole exit chipping sizes, improve machining efficiency and lower machining cost. From the phenomenon that the surface roughness resulted from rotary ultrasonic drilling is higher than that from conventional machining, it is concluded that the particle effective cutting depth is the most important factor influencing surface roughness when hard and brittle material is removed by brittle fracture.

Key words: Chipping size, Cutting force, Drilling, Mathematical model, Rotary ultrasonic machining, Surface roughness