Conduction welding of thermoplastic composites : An experimental study towards specifying the process window for process time and temperature.

The aerospace industry is increasingly incorporating thermoplastic composites into structures to improve the sustainability of the aircraft. These materials offer high strength-to-weight ratios and are weldable, mak-ing them preferable over traditional aerospace materials. This study focuses on the effects of the process parameters on the weld quality of conduction welded thermoplastic composites, thereby establishing a process window for consistent weld quality for a range of process time and temperature settings. Experimental investigations were conducted using a conduction welding setup developed at the TPRC. Spot welds were produced on lap joints using unidirectional quasi-isotropic carbon fibre-reinforced low-melting polyaryl-ether-ketone laminates. Non-destructive and destructive inspections were performed to analyse the weld quality across various process time and temperature settings. This included monitoring temperature cycles during the process, ultrasonic scanning of the welded samples, shearing the welded material, inspecting the outer surface and weld interface, and inspecting the thermal behaviour of the welded material. The results indicate minimal impact of process time on weld quality, whereas process temperature sig-nificantly influences the weld properties and quality. Higher temperatures produce larger, more uniform welds, which may result in thermal degradation of the material. Concluding that to achieve consistent welds on a lap joint of quasi-isotropic CF/LM PAEK laminate with a thickness of 1.2 mm using the current conduction weld setup at a process pressure of 370 kPa, the process window for process time and temper-ature spans from 0 to 60 s and from 370 to 430 °C. Beyond this window, weld quality may be limited. This study advances the understanding of conduction welding processes, offering insights for optimising the conduction weld quality of thermoplastic composite joints. Further research avenues include further exploring the effects of process and material parameters, refining the inspection methods, and optimising the welding setup.