During the ultrasonic welding process mechanical vibrations with defined amplitude, force and duration are applied to the materials to be welded. Due to intermolecular and surface friction heat is generated and melts the material.
The core of the ultrasonic welding system is the stack. It is made up of the piezoelectric converter, the booster (amplitude transformer) and the sonotrode. The stack contracts and expands with the ultrasonic frequency. The resulting vibrations are longitudinal waves. The travel of the weld tool, meaning the distance between the peak position and the zero position, is referred to as amplitude - in ultrasonic welding the amplitude is between 5 and 50 μm.
The wave length λ is calculated from the sound velocity, which is a material characteristic, and the frequency.