Research Progress of Ultrasonic Spot Welding of Metals

Ultrasonic spot welding, as a solid-state welding technique, has attracted the attention of scientists and industry owing to its superiority of small affected zone, high welding strength, low energy consumption and excellent electrical conductivity of joints. However, this technique also has some obvious defects. With the workpiece thickness and hardness increasing, the welding system will become unstable and require greater surface grip and welding power. On the other hand, when conducting a dissimilar welding, the interfacial mechanical properties are susceptible to the generation of intermetallic compounds by interfacial diffusion. In the past few years, researchers attempted to develop the ultrasonic spot welding technique mainly by optimizing welding tools to improve the surface grip, creating high power ultrasonic spot welding equipment to improve stability, deeply studying welding bonding mechanism, and implanting intermediate layer to inhibit the diffusion layer. Up to today, high power ultrasonic spot welding has become the research focus and the object of the research has changed from wire and foil to sheet with a certain thickness and hardness. The key research issues include optimization of welding tooth profile, resistance heat assisted ultrasonic welding, ultrasonic softening theory and microwelds expansion theory, the strengthening mechanism of intermediate layer, etc. A series of achievements help enhance the mechanical properties of ultrasonic joints and further the industrial application of this technique. This review on ultrasonic spot welding technique mainly includes the principle and characteristics of ultrasonic spot welding, the optimization and improvement of welding tools, the bonding mechanism of welding interface, the simulation of welding interface temperature, and the process, structure and performance of welding. © 2020, Materials Review Magazine. All right reserved.