Development of torsional-vibration systems used for high frequency ultrasonic plastic welding

The authors have developed a compact torsional-vibration system used for ultrasonic plastic welding at a frequency of approximately 38 kHz. It comprises two low-aspect-ratio vibratory elements, namely a "stepped horn" (a simple mechanical transformer of torsional vibration) and a hollow cylindrical bolt-clamped Langevin-type transducer, both of which are designed to maintain a sufficient area of radiating face and a high-amplitude vibration of the system even at its high resonance frequency. Several crucial points for construction of the system are detailed with the results of numerical simulations and measurements. The feasibility of this welding technique has been qualitatively examined by experiments. Also proposed is construction of another bolt-clamped Langevin-type transducer for the welding which can excite high-amplitude torsional vibrations at a frequency over 45 kHz. The measured characteristics of the trial-made transducers of this type are described.