This is a solid state welding process for joining similar or dissimilar metals by application of high frequency vibratory energy to work pieces held together under moderate static pressure. The equipment consists of a frequency converter, which changes 50 Hz power to the high frequency 15 - 60 kHZ required by ultrasonic head. The head has a piezo - electric transducer, which converts the high frequency electrical output into vibratory mechanical motion and wave guides, which transmits the vibratory waves to the tools and into the weldment. The job is tightly clamped while welding. The process is used to weld plastics, thin foils and dissimilar metals. The process is employed for manufacturing of toys for children.