Ultrasonic plastics assembly is the joining or reforming of thermoplastics through the use of heat generated from high frequency mechanical motion. It is accomplished by converting electrical energy into high frequency mechanical motion (vibrations) that creates frictional heat at the joint area. The vibrations, when applied to a part under pressure/force, create frictional heat at the interface and cause the plastic in the joint area to melt, creating a molecular bond between the plastic components.

Most people are familiar with what happens when a metal object is repeatedly struck with a hammer. If the impact is hard enough and occurs often enough, the metal object begins to get warm. If this beating action continues, the metal can become surprisingly hot. The metal object gets hot because its molecules are moving, or vibrating, at a rate that causes an increase in temperature.