Effects of welding process parameters on the mechanical properties of dissimilar PP and PE polymers joined via FSSW

This study investigates the effects of welding process parameters and specially designed tools on the joint strength of dissimilar polypropylene (PP) and polyethylene (PE) components joined by friction stir spot welding (FSSW). The experimental framework utilizes a Taguchi design of experiments to evaluate three variable parameters: tool geometry (T1-flat and T2-spiral), rotation speed (900, 1200, and 1500 rpm), and stirring time (60, 75, and 90 seconds). The welding operations are carried out on a Computer Numerical Control (CNC) three-axis vertical machining center under the same conditions using a CNC program. The results show that PP and PE polymer specimens can be successfully joined by the FSSW method. Each joined specimen is mechanically evaluated by lap-shear tensile testing; accordingly, peak forces were determined and analyzed. According to the signal-to-noise (S/N) ratios and statistical analysis, the T2 spiral tool, rotation speed of 1200 rpm, and stirring time of 90 seconds were determined as the optimal welding process parameters. These optimum combinations significantly improve weld quality and mechanical performance. This study confirms the feasibility of reliably joining low-melting thermoplastics such as PP and PE using the FSSW method and contributes to advancements in polymer welding technologies.