The Specific Features of Heat Generation in Ultrasonic Welding of Rigid Plastics

The specific features of ultrasonic welding of rigid plastics are considered in this paper. The results of plastic weldability by ultrasound are shown. The core principles of contact and transfer ultrasonic welding are described. Ultrasonic welding is performed by heat, without heating up the entire thickness of the material, which enables welds of large thickness. The paper describes the thermal cycles of ultrasonic welding of polystyrene and the mechanism of welded joint formation when welding plastics by ultrasound. It is shown that heat on the welded surfaces is released due to internal friction. To increase the concentration of energy on the abutting surfaces, the welding groove is beveled to a V-shape. The thermal conditions of welding rigid polymers and the kinetics of the welded joint formation are analyzed. It has been established that V-shaped beveling leads to predominant heat buildup at the interface. This is caused by an increase in the level of dynamic stress, which contributes to the acceleration of the ultrasonic welding process. Beveling increases the welded joint strength, improves its appearance and reduces welding time. As a result, an equation is derived that allows the calculation of the melting time of the V-shaped groove. It is concluded that the maximum release of the ultrasonic energy corresponds to the resonant mode of operation of the welded assembly.

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