A novel combined MCDM approach for parametric optimization of friction stir lap welding of dissimilar polycarbonate to nylon-6

The fabrication of dissimilar thermoplastic polymers are often essential for wings and fuselage panels in aircraft and lighting systems of automobile parts. Several solid state welding procedures are generally recommended for the joining of amorphous and semi-crystalline unlike polymers. The present work addresses the influence tool motion and its positioning on dissimilar bonding of polycarbonate to nylon-6 by using different tool pin profiles such as hexagonal, square and cylindrical in friction stir lap welding. The optimal process variables to achieve high joint strength with adequate ductility and hardness in the weld was found through different multi-criteria decision making (MCDM) approaches. The weld undercut towards advancing and hardness deviation over rear side along dissimilar joint interface at very high or low tool revolving speed, respectively were the primarily indicators of the weld quality. The weld strength was 31 MPa (i.e. joint efficiency 67.5%) at high tool revolving speed (2400 rpm), low traverse speed (15 mm/min) and low plunge depth (0.1 mm) using cylindrical tool pin due to greater stirring torque. In contrary, it was marginally improved (joint efficiency 68%) even at low tool spinning speed (1600 rpm) because of necessary material flow using higher swept ratio hexagonal pin. The evaluation using three MCDM approaches such as CoCoSo, MABAC, and GRA revealed intricate relationships and varying degrees of agreement. CoCoSo and GRA exhibited moderate similarity, indicating a noteworthy alignment in their outcomes. A comparative analysis showed some noteworthy accomplishments with significant correlation (0.988) between CoCoSo and MABAC approaches.