Development of a Novel Ultrasonic Drill Using Longitudinal-Bending Hybrid Mode

Machining of hard and brittle materials is usually troublesome due to their high stiffness. In order to improve the processing speed of hard and brittle materials, ultrasonic assisted processing was developed. This paper reports a novel ultrasonic drill method, where longitudinal-bending hybrid ultrasonic vibration is used instead of single longitudinal or bending vibration. The cutting tool in this process is a core drill attached to an ultrasonic transducer, which generates longitudinal and bending vibrations. Thus an elliptical movement with ultrasonic frequency that is vertical to the working surface is formed at the cutting edge. The longitudinal vibration can help the cutting edge impact the workpiece and thus crush it. With the rotation of the cutting tool, the cutting edge scratches a groove on the working surface. While the bending vibration speeds up the movement of the cutting edge toward the workpiece in the working surface so as to amplify the fracture region. Moreover, a radial clearance assisting chip removal is made by the bending vibration. Merits of this machining method, including improved processing speed and avoidance of jamming are verified by experiment.