Friction spot welding of lap joints on wrought and cast aluminium alloys in comparison

Friction spot welding is a new joining process with small heat influences for lap joints, as an alternative and as an application extension to the resistance spot welding or mechanical joining of aluminium materials.

For wrought, cast and PM aluminium materials with different sheet thicknesses and surface finishes, the process technology sequences were investigated and optimised and the attainable joint properties were established. No tool changes were required for material combinations (Fig. 1) or sheet thickness variations (even three-sheet joints) but instead only an altered welding program sequence. With regard to the strength parameters, friction spot welding performed well in comparison with resistance welding and clinching (increased tensile shear and cross-tension forces and comparable fatigue strength).

With the investigation results, it was possible to achieve a distinct rise in the quality, the productivity and the economic viability for an extended application spectrum of spot welding, particularly for Al alloys with restricted suitability for fusion welding or cold forming, or with very different sheet thicknesses. The mobile design of the friction spot welding installation as a C‑shaped gun permitted flexible robot utilisation.