Ultrasonic welding process and strategies for performance regulation of Fiber reinforced thermoplastic composites: A review

Fiber-reinforced thermoplastic composites (FRTP), characterized by their lightweight nature, high specific strength, and recyclability, are increasingly adopted as core materials for structural components in aircraft and spacecraft. They are driving its leapfrog development from structural weight reduction to functional integration. Ultrasonic welding, as an efficient, clean, and automation-friendly technique for joining method, has become a focal point attracting significant attention from researchers. This review presents a comprehensive analysis of the ultrasonic welding of FRTP from four interrelated dimensions: interfacial bonding mechanisms, welding processes, defect influencing factors, and performance regulation strategies. Although a complete ultrasonic welding process involves both frictional heating and viscoelastic heating, it can be meticulously divided into five distinct stages. Quantitative findings from recent studies are summarized: under ultrasonic spot welding process parameters (amplitude 50–85 μm, welding energy 500–1500 J, and welding time 0.3–1.5 s), lap shear strengths of 20–35 MPa have been achieved for FRTP, while innovative energy directors (EDs) can further enhance joint strength by 20–40 %. Continuous ultrasonic welding holds significant development potential. Although it can achieve a maximum welding speed of 3.6 m/min, it still faces challenges such as localized overheating and porosity, resulting in joint strength lower than that of spot welding. The review identifies that controlling interfacial melting behavior and resin flow is crucial for defect suppression and performance optimization. Strategies such as welding parameters optimization, innovative ED design, and the application of auxiliary processes are discussed as promising avenues to enhance weld integrity and reproducibility. Finally, key research directions are proposed, including continuous ultrasonic welding for curved thick plates, multiscale modeling of ultrasonic energy transmission, and intelligent process monitoring.