Comparison of drill wear mechanism between rotary ultrasonic elliptical machining and conventional drilling of CFRP

Carbon fiber-reinforced plastic (CFRP) is widely used as aircraft structural components for its superior mechanical and physical properties. Meanwhile, the rotary ultrasonic elliptical machining (RUEM), as a new drilling method in which an elliptical ultrasonic vibration is imposed on the end of the drill, can reduce tool wear effectively. In this paper, we firstly presented an investigation on the wear mechanism of diamond core drill in RUEM of CFRP in comparison with the conventional drilling (CD). A series of drilling experiments were performed including the drilling force measurement, the observation of drill topographies, and machined hole surface. The experiment results indicated that the drill performance in RUEM of CFRP was improved significantly in comparison with that in CD. Because the length of steady region rised by 39% and the tool life increased by 28% in RUEM than those in CD, respectively. With the observation of drill surface under a microscope, it was validated that less chip adhesion and more grain micro-fracture appeared in RUEM, which had a positive effect on the better drilling performance, such as lower drilling force, smoother hole surface.