Design, Fabrication and Characterization of L&T Hybrid Mode Transducers for Thermoplastic Welding

Abstract

Objectives This study aims to present a systematic approach for designing, fabricating and characterizing ultrasonic transducers for thermoplastic sheet welding capable of operating in longitudinal-torsional (L&T) hybrid vibration modes at 20 kHz, driven by an axially poled piezoceramic stack. Methods Multiple horn models featuring circumferential deep helical grooves were designed to generate longitudinal and torsional vibratory displacements. Modal analyses were conducted to determine the appropriate dimensions for the desired mode shape and resonance frequency. The selected horn geometries were integrated with transducer bodies in a CAD environment to build 3D models of ultrasonic transducers. Modal and harmonic analyses were performed to evaluate their mode shapes, resonance frequencies, and displacement amplitudes under various excitation conditions. Prototypes of the optimized designs were fabricated using predetermined materials and geometries and characterized experimentally for resonance frequencies and tip displacements. The experimental results were compared with numerical analyses to validate the approach. Results The developed transducers demonstrated successful operation in L&T hybrid vibration modes at the targeted frequency, with displacement amplitudes and resonance frequencies aligning well with the numerical predictions. Combining exponential area reduction and helical grooves in the horn appears to be a highly effective method for achieving longitudinal-torsional vibration from a longitudinally vibrating transducer. Finite element analysis proved to be a valuable design tool, facilitating accurate dimensional optimization of the horns to achieve the desired L & T hybrid vibrational mode shapes. The apparent longitudinal and torsional (spring) stiffness of the horn significantly influences the longitudinal displacement amplitude and angular displacement at the horn tip. The resonance frequency of the transducers shifted to higher frequencies with increasing excitation voltage. Conclusion This research provides a comprehensive and validated framework for designing ultrasonic transducers capable of operating in hybrid vibration modes. The methodology reliably achieved the desired vibratory performance, with prototype results aligning closely with design objectives.