Abstract: An axial ultrasonic vibration assisted drilling method was proposed for solving problems such as difficulties in chip breaking， chip removal and poor processing quality in traditional drilling process. Motion characteristics and chip breaking mechanism were studied， and the comparative tests of conventional drilling and axial ultrasonic vibration assisted drilling were performed on the 45^# steel using an own-designed axial ultrasonic vibration assisted drilling system. Investigations were done toward the machining precision of holes， surface morphology and the shape of chips. The experimental results demonstrate that axial ultrasonic vibration assisted drilling can effectively reduce the surface roughness and improve the microscopic morphology compared with the traditional processing. In addition， variance analysis is used for data processing， indicating that the spindle speed and ultrasonic amplitude have significant influences on the surface roughness， and the processing effect is best when the amplitude is 20μm and spindle speed is 450r/min.

Key words: axial ultrasonic vibration, assisted drilling, 45^# steel materials, movement characteristics, mechanism of chip broken, machining quality