1. Ultrasonic Plastic Welding Machine When ultrasonic acts on the thermoplastic plastic interface, it produces tens of thousands of high-frequency vibration per second. This kind of high-frequency vibration reaches a certain amplitude. The ultrasonic energy is transmitted to the welding area through the upper welding parts. Because the acoustic resistance of the welding area, i.e. the interface between two welding parts, is high, local high temperature will be generated.