Improvement of welding characteristics of ultrasonic plastic welding using high and low frequency vibration systems of 90 kHz and 27 or 20 kHz

To improve welding characteristics of 90 kHz two-vibration-system which can weld plastic sheets under one-third velocity amplitude compared with that of 27 kHz systems but can not weld large specimens successfully, an ultrasonic welding equipment using the combination of high 90 kHz and low frequency 27 or 20 kHz vibration systems with rather small and large vibration displacement amplitude (not velocity) is studied and shown its effectiveness. Welding specimens used are soft (poly-vinylchloride; shear vibration loss is large) and hard (polypropyrene) sheet materials, and both specimens were joined successfully with smaller total vibration velocity amplitude, similarly in both cases where (1) parallel and (2) normal direction vibration systems are driven simultaneously.