Enhancing joint efficiency in friction stir welding of PA66 using an induction-heated threaded pin and glass fiber reinforcement

This study investigates the friction stir welding (FSW) of polyamide 66 (PA66) sheets using an induction-heated threaded pin tool with a stationary shoulder. A novel approach was implemented by inserting a 3 mm-thick PA66-GF30 (glass fiber-reinforced polyamide) strip within the welding zone to improve joint performance. Process variables including tool rotational speed, welding speed, and preheat temperature were systematically varied to study their effects on fiber distribution, weld morphology, and mechanical strength. Among the tested conditions, a rotational speed of 1000 RPM and welding speed of 20 mm/min resulted in optimal heat input, promoting uniform fiber dispersion and stable vortex flow within the nugget zone. The microstructural analysis identified five distinct regions in the stir zone, each exhibiting unique material flow behaviors. The inclusion of the PA66-GF30 strip significantly improved mechanical properties, with the best-performing sample achieving 91% joint efficiency. In contrast, higher rotational speeds caused fiber agglomeration, matrix degradation, and oxidation, leading to reduced weld quality. These findings underscore the importance of optimized heat input and reinforcement integration in enhancing the performance of polymer FSW joints.