FEM model for the thermo-mechanical characterization of friction stir spot welded joints

A simulation study of the Friction Stir Spot Welding process for the lap-joining of thin aluminum sheets was carried out using the FEM code DEFORM 2D. The special feature of the developed FEM model is a 2D approach used for the simulation of a 3D problem, in order to guarantee a very simple and practical solution able to achieve results in a very short time. A set of experiments was performed by means of a CNC machine tool and FSSW lap joints on AA6060-T6 aluminum alloy plates were obtained. The experimental results were used as reference cases for the model validation. A set of tests was carried out by varying the process parameters, namely rotational speed, axial feed rate and plunging depth. Axial welding forces and temperature distribution in the joining region were recorded during the tests and their dependency from the welding parameters was studied. Shear tests were also performed to evaluate the quality of the joints as function of the welding conditions. A satisfactory matching between numerical and experimental data was found (average errors ranging around 10 %), confirming the good predictive ability of the FEM model. The FEM simulations were finally used for the prediction of the joint shear resistance.