Towards ultrasonic welding of robust thermoplastic composite joints without the use of energy directors

The development of an advanced ultrasonic welding process for thermoplastic composites (TPCs) without the usage of energy directors (EDs) represents a significant challenge and a highly desirable innovation for aerospace applications. A major obstacle in ED-less ultrasonic welding is the non-uniform heat generation and distribution at the welding interface, leading to inconsistent weld quality. This study addressed this challenge by introducing a novel strategy of co-consolidating an extra resin layer (eRL) onto the CF/PEI surfaces prior to the welding. The results demonstrated that applying eRLs with an optimal thickness on the CF/PEI adherends enhanced heat generation efficiency and ensured sufficient melt flow at the welding interface, while effectively eliminating carbon fibre squeeze-out. This approach significantly improves weld uniformity and mechanical performance, achieving a maximum lap-shear strength of 43.2 MPa. Overall, the incorporation of eRLs offers a promising pathway for the cost-effective, high-quality ultrasonic welding of large-scale and complex TPC structures without the usage of EDs.