The process involves an ultra-high speed ultrasonic vibration frequency of 20,000-40,000 times/second at the ultrasonic welding head accompanied with an ultrasonic pressure, where the energy is transmitted to the workpiece. Meanwhile, the other side of the workopiece will remain stationary. The high-frequency friction will cause the surface contact of the workpieces (conduction melting) to melt, allowing the plastic parts to fuse together immediately. When cooled, a firm and uniform fusion can be obtained.