Critical force of separation effect behaviors in rotary ultrasonic drilling for SiC

The machining mechanics of the rotary ultrasonic drilling (RUD) is investigated based on the separation effect of ultrasonic vibration (SEUV), by quantifying the critical force at a certain ultrasonic vibration amplitude. Firstly, the SEUV principle is explored by establishing the kinematic trajectory of the tool. Then, the critical force of SEUV at certain ultrasonic vibration amplitude is modeled. The simulation shows that as the tool interference displacement caused by the axial force is larger than the ultrasonic vibration amplitude, the tool vibration is in a suppressed state and the SEUV effect cannot be achieved. Third, the principles of standard drilling and peck drilling are proposed. The essence of peck drilling in step motion shows advantage to assure SEUV of RUD. Last, the critical force of SEUV is measured in experiments and proves that the SEUV is suppressed as the force exceeds a certain value. The RUD verification experiment on SiC of standard drilling and peck drilling is conducted. It is found that when the cutting force exceeds the critical force in standard drilling, the SEUV is suppressed and there has no significant improvement on the drilling performance. In peck drilling, the cutting force is lower than the critical force periodically, where the SEUV is achieved and the ultrasonic vibration can make effective impacts on the material and improve drilling performance.