Design optimization and eigenfrequency tuning of ultrasonic oscillator of one-dimensional longitudinal vibration at high temperature for laser welding.

Ultrasonic vibration-assisted laser welding is a very promising and innovative method, which uses the ultrasonic cavitation effect to suppress weld pool defects and improve weld quality. During ultrasonic-assisted laser welding, the high temperature of the weld will transfer to the ultrasonic system due to the long-time contact between the tool head and the weld, and the high temperature will cause the eigenfrequency of the ultrasonic oscillator to drift and unstable energy output. So, it is a very important and urgent problem to be solved. A frequency model of the ultrasonic oscillator is first established, and an optimization design method coupled finite element genetic algorithm and heat for the ultrasonic oscillator is proposed. This method can quickly predict the frequency mode and solve such problems as ultrasonic oscillator eigenfrequency drift and the existence of multiple resonance peaks in the design. Numerical simulation indicates that both sizes of the composite Ti-6Al-4 V conical horn and the tool head are negatively correlated with the eigenfrequency. The optimized total lengths of both the horn and the tool head are 77 mm and 65 mm, respectively. The eigenfrequency of the optimized ultrasonic oscillator satisfies the frequency tracking range (35 ± 0.5 kHz) in a wide temperature range. The experiment shows that no other non-working modes appear near the working frequency, which improves the output properties of ultrasonic energy, and the eigenfrequency of the optimized ultrasonic oscillator is 34, 790.3 Hz, which is agreement with the optimization, and the mechanical quality factor is up to 2899.2. The experimental and simulation results show that the theoretical and numerical optimization methods proposed in this paper can be applied not only in the structural design of the ultrasonic system for assisted laser welding, but also in the design and optimization of ultrasonic structures under other complex temperature conditions (glass molding, fouling removal, etc.). [ABSTRACT FROM AUTHOR]