When ultrasonic waves act on the thermoplastic plastic contact surface, high-frequency vibrations of tens of thousands of times per second are generated. This high-frequency vibration reaches a certain amplitude, and the ultrasonic energy is transmitted to the weld zone through the upper weldment. At the interface of the weld, the acoustic resistance is large, so local high temperatures are generated. Moreover, due to the poor thermal conductivity of the plastic, it can not be dissipated in time and gather in the weld zone, so that the contact faces of the two plastics melt rapidly, and after a certain pressure, they are integrated into one. When the ultrasonic wave stops, let the pressure last for a few seconds to solidify it, thus forming a strong molecular chain for welding purposes, the welding strength can be close to the strength of the raw material. The quality of ultrasonic plastic welding depends on the amplitude of the transducer welding head, the applied pressure and the welding time. The welding time and the welding head pressure can be adjusted. The amplitude is determined by the transducer and the horn. The interaction of these three quantities has a suitable value. When the energy exceeds the appropriate value, the melting amount of the plastic is large, and the welding material is easily deformed; if the energy is small, the welding is not easy, and the applied pressure is not too large. This optimum pressure is the product of the side length of the welded portion and the optimum pressure per 1 mm of the edge.