A framework for friction stir multi-spot welding for thermoplastics.

Friction stir spot welding (FSSW) has shown promising potential for joining sheets and other geometries of metals as well as polymers. For thermoplastic materials, especially carbon black reinforced high-density polyethylene (HDPE-CB), the FSSW technique has shown promising results. However, in the published literature, most of the FSSW studies on thermoplastic materials have focused on single-spot joints. The current paper aims to investigate and develop a framework for multi-spot based FSSW joints. Based on the study, it is evident that the strength of the weld increases with the number of weld spots, and the weld direction plays a crucial role in determining weld performance. The double-side weld configuration of T4 weld spots achieved the maximum peak load of 5207 N. Additionally, edge distance and weld spacing were found to significantly influence peak load, demonstrating a proportional relationship. Overall, this study pioneers the investigation of weld spot inclination and spacing in multi-spot based FSSW of thermoplastic polymers, providing insights into their influence on joint strength and failure mechanisms. The findings highlight critical role of weld alignment and optimized spacing in enhancing load distribution and maximizing the tensile performance of lap joints.