Automotive body structures are being increasingly made in multi-material system consisting of steel, aluminum (Al) and fiber-reinforced plastics (FRP). Therefore, many joining techniques such as self-piercing riveting (SPR) and adhesive bonding have been developed. On the other hand, OEMs want to minimize the number of joining techniques to reduce the manufacturing complexity. Amount all joining methods, resistance spot welding (RSW) is the most advanced and cost-effective one for body-in-white.
However, RSW cannot be applied for joining dissimilar materials. Therefore, a novel Rivet Resistance Spot Welding method (RRSW) was developed in which Al or FRP components can be directly welded to steel structures with existing welding systems. RRSW uses rivet-like double T-shaped steel elements as a welding adapter which are formed or integrated into Al or FRP components during their forming process. After that, they are welded to the steel components by RSW.
This paper shows at first the development results on Steel – Al RRSW. An appropriate rivet geometry was developed using FEM simulation and made mechanically. The corresponding welding parameters were determined experimentally. Tests on different specimens and components were conducted. The static and fatigue strengths of RRSW are mostly better or equal to that of SPR. The corrosion resistance is superior to SPR. Finally, a section of a car roof made of Al sheet was stamped and welded with the steel structures in neighborhood using RRSW proofing the technology.
In next step, RRSW was extended for long fiber reinforced thermoplastics components manufactured by compression molding. A 2nd rivet was successfully developed using FEM welding simulation with the target of minimal temperature in FRPs to avoid their thermal damage, and wide welding process window. The entire process was proved on an FRP seat cross member welded in steel floor panel. The strength of this RRSW is also equal or better than SPR.