Abstract: Based on the mode conversion theory of ultrasonic vibration, an ultrasonic torsion welding vibrator with a resonance frequency of 20 kHz is designed by combining the finite element method. The vibrator mainly consists of sandwich-type piezoelectric transducers and a mode conversion horn, with the mode conversion horn's mutual push rod and the vibration-transmitting rod connected by bolts. In order to reduce the leakage wave of the vibrator, a special structure vibration-dampening flange is designed to ensure torsional vibration at the output end of the mode conversion horn. The finite element analysis software is used for modal analysis and harmonic analysis. The torsional frequency of the simulated vibrator is 19.877 kHz, and the frequency response curve of the vibrator is obtained. The vibration mode conversion is completed at the mode conversion horn. Finally, the resonant frequency of the developed vibrator is 19.69 kHz measured by the impedance analyzer, which is less different from the theoretical value and simulation value. The longitudinal amplitude measured by the laser vibrometer at the end face of the mutual push rod of the vibrator is 10.2 μm, which is close to the simulation value. The feasibility of the design method is verified, and it can provide a reference for the design of other ultrasonic torsional welding vibrators.

Key words: mode conversion, ultrasonic vibrator, torsion welding, vibration-dampening flange, finite element analysis