In contemporary society, various plastic products have penetrated into various fields of people's daily lives, and are also widely used in industries such as aviation, ships, automobiles, electrical appliances, packaging, toys, electronics, textiles, etc. However, due to limitations in injection molding technology and other factors, a considerable number of plastic products with complex shapes cannot be molded in one go, which requires bonding. The plastic bonding and heat sealing processes that have been used for many years are also quite outdated, not only low in efficiency, but also toxic in adhesives, causing environmental pollution and labor protection issues. The traditional process is no longer suitable for the development needs of modern plastic industry, so a novel plastic processing technology - ultrasonic plastic welding - stands out with its advantages of high efficiency, high quality, aesthetics, and energy conservation.

    Ultrasonic welding is a solid-state welding method, and the connection between welded parts is achieved through high-frequency elastic vibration of the acoustic system and the clamping effect of static pressure between workpieces. When welding plastic products, ultrasonic plastic welding machines do not add any adhesives, fillers or solvents, nor consume a large amount of heat sources. They have the advantages of simple operation, fast welding speed, high welding strength, and high production efficiency. Therefore, with the widespread application of thermoplastic and its composite materials, ultrasonic welding technology is becoming more and more widely used.

    Introduction to Ultrasonic Plastic Welding Process

    Ultrasonic plastic welding technology has developed from metal ultrasonic welding. It was first proposed by Jones and others in the United States in 1950.

    After the 1860s, the United States, Japan, Switzerland, the United Kingdom, Germany, and the former Soviet Union began using this technology in actual production processes.

    Ultrasonic welding can generally weld all thermoplastic materials. According to the functional characteristics of welding technology, polymer materials can be divided into three categories: (1) flexible materials, referring to soft and low elastic modulus materials; (2) Rigid materials refer to materials with high elastic modulus and low mechanical vibration damping factor, such as polystyrene (PS), polymethyl methacrylate (PMMA), and polyamide (PA); (3) All polymer films, polymer synthetic fibers, and fabrics composed of films and fibers.

    Due to the different types and properties of thermoplastic materials, sometimes it is easy to perform ultrasonic welding while others are not easy to weld.

    Research progress on plastic ultrasonic welding technology

    The mechanism of plastic ultrasonic welding is complex, and the welding quality is influenced by multiple factors.

    When welding materials, the first consideration should be the selection of welding equipment. High frequency welding equipment can achieve better welding quality. Secondly, the weldability of the material should be considered. Materials with low melting point and high surface friction coefficient can achieve better welding quality. Adding an appropriate amount of reinforcing materials can improve welding quality; Thirdly, the amplitude of ultrasonic waves, welding time, and welding pressure are the main process parameters that affect welding quality, and the three process parameters for obtaining better welding quality all have a certain range.

    With the increasing application of ultrasonic welding technology in the field of plastic connections, it is gradually receiving attention from plastic processing and forming workers.

    However, due to the short time and complex welding mechanism of plastic ultrasonic welding, the welding quality is difficult to control, which limits the further use of ultrasonic welding technology in the plastic field. Further research on ultrasonic welding technology needs to be strengthened from the following aspects:

    1) Research new welding equipment and develop welding equipment with high frequency and high power;

    2) Conduct in-depth research on the state of different material welding areas, including the thickness of the melt zone, crystallinity, degree of orientation, chemical composition, etc., and investigate the mechanism of plastic ultrasonic welding technology in depth;

    3) Optimize welding processes for different materials, establish corresponding relationships between welding equipment, process parameters, and commonly used materials, reduce the number of experiments, and lower costs;

    4) Further improve the quality testing methods for plastic ultrasonic welding, especially the development and improvement of real-time tracking and monitoring methods