Modeling the load capacity of frequency-tracked rotary ultrasonic machining system

Abstract

Rotary ultrasonic machining (RUM) is a superior processing method for difficult-to-cut materials. It employs a large enough ultrasonic amplitude of the tool to enable its unique intermittent cutting mechanics. The critical cutting force is a vital performance indicator to characterize the load capacity for the RUM system. If the cutting force exceeds a critical value, the ultrasonic amplitude of the tool will be restrained as a minimal value due to the deviation of resonant frequency, resulting in the performance loss of RUM. However, the current understanding of critical cutting force only applies to the RUM system without a frequency-tracking module. This study tries to fill the knowledge gap regarding the load capacity of the frequency-tracked RUM system. First, the dependency of actual ultrasonic amplitude on the cutting force is modeled based on the RUM system's input-output relation that uses a frequency-tracking module. Then, the critical cutting force is derived by inverse solving the above model Afterward, we propose a measurement method of the actual ultrasonic amplitude under load by observing the tool vibration trace on the machined surface using a diamond indenter. Moreover, an easy-to-operate experimental method to measure the critical cutting force is developed. Finally, serial load experiments of the RUM system under different driving voltages are performed. The experimental results verified the models of actual ultrasonic amplitude and the critical cutting force. Based on the model, the influences of the electrical and mechanical design of the frequency-tracked RUM system on the critical cutting force are analyzed.