Improving the Resistance Welding Quality of CF/PA6 Composite by Adjusting the Mesh Size of a Perforated Heating Element.

During resistance welding of fiber-reinforced thermoplastic composites (FRTP), lower temperatures are observed at the edge of the welding area that is vertical to the direction of the current (longitudinal edge, L-edge). This paper proposes a perforated heating element (HE) with reduced edge mesh size to increase the temperature in the L-edge, thereby mitigating the edge effect during the resistance welding of FRTPs. By reducing the mesh size in the L-edges of the welding area, a temperature gradient can be created during the heating process, thereby increasing heat generation at the L-edges of the HE. Through experimental and numerical investigations, the influence of this HE on temperature evolution and joint performance during FRTP resistance welding was investigated. A resistance model was proposed to analyze the resistance and heat generation of regions with different mesh sizes. The results show that the tailored HE increased the temperature in the L-edge area. Furthermore, the reduced mesh size decreased the resistance of the HE in the welding area, mitigating the excessive temperature in the transverse edge (T-edge) (parallel to the current direction) of the welding area. The joints welded with the tailored HE achieved a lap-shear strength (LSS) of 26.6 ± 0.8 MPa, which is 31% higher than the LSS of joints welded with unmodified HE. The proposed resistance model could predict the changing trends of resistance and heat generation in regions with different mesh sizes at the qualitative level. Further work needs to be carried out to improve its quantitative prediction ability.