Welding characteristics of ultrasonic plastic welding using two-vibration-system of 90 kHz and 27 or 20 kHz and complex vibration systems

Abstract

To improve welding characteristics of ultrasonic plastic welding, a 90 kHz two-vibration-system, which can weld plastic sheets under one-third velocity amplitude compared with that of 27 kHz systems, is effective. However, this system cannot weld large specimens successfully because high frequency vibration stress cannot be transmitted uniformly through the large specimens due to the stress relaxation effect by the small vibration displacement of the high frequency welding tip. The ultrasonic welding systems using the combinations of (1) a high frequency 90 kHz longitudinal vibration system with small displacement amplitude and a low frequency 27 kHz longitudinal vibration system with large displacement amplitude (not velocity amplitude), (2) a 90 kHz longitudinal system and a 20 kHz torsional vibration system with large displacement, and (3) the complex vibration welding system using 27 kHz complex vibration welding tips vibrating in elliptical to circular locus are studied. The welding specimens used are soft (polyvinyl chloride: shear vibration loss is large) and hard (polypropylene) sheet materials, and both specimens were welded successfully with smaller velocity amplitude than that of the conventional welding method, similarly in both cases where (1) parallel and (2) normal direction vibration systems are driven simultaneously. The complex vibration welding systems of 27 kHz which has elliptical and circular vibration loci were revealed also effective for plastic welding.