Cutting force and specific energy for rotary ultrasonic drilling based on kinematics analysis of vibration effectiveness

Rotary ultrasonic drilling (RUD) has become an effective approach for machining advanced composites which are widely using in the field of aeronautics. The cutting kinematics and the corresponding material removal mechanisms are distinct in different drilling areas during RUD. However, these fundamentals have not been fully considered in the existing studies. In this research, two distinct forms of interaction induced by ultrasonic vibration were considered as impact-separation and vibratory lapping between the abrasives and workpiece. And the conditions to guarantee the effectiveness of these interactions were obtained to eliminate diminishing effects of ultrasonic vibration. Based on indentation fracture theory, the penetration depth of abrasives and the axial drilling force model was derived for RUD. The verification tests of C/SiC composites resulted in a prediction error within 15%. Due to the minimal volume of material removed during each vibration cycle, the drilling force was more stable in vibration assisted mode. The specific drilling energy of RUD was firstly calculated based on the measured drilling load. It was found the drilling parameters should be matched with vibration frequency and amplitude to make better usage of the advantages of ultrasonic vibration, which is critical in the vibration assisted processing of advanced materials.