Friction stir welding (FSW) is a solid state jointing technology, in which the butted plates are heated, plasticized and jointed locally by the plunged pin and shoulder moving along the joint line. The residual stresses due to the thermomechanical performance of the material and the constraint of the welded plates by the fixture are one of main concerns for this process. A prediction of the clamping force applied on the plates during FSW is expected to be helpful in controlling the residual stresses and weld quality. Furthermore, the prediction of the force history in FSW will be beneficial to understand the mechanics of the process and provide valid models for controlling the process, especially in the case of robotic friction stir welding. In this paper, a three-dimensional model based on a finite element analysis is proposed to study the thermal history and stress distribution in the weld, and subsequently to compute the longitudinal, lateral, and vertical forces. The model includes a coupled thermomechanical analysis. The parametric investigation of the effects of the tool rotational and longitudinal speed on the longitudinal, lateral, and vertical forces is also conducted in order to compute the appropriate clamping force applied on the plates. Measurements by the load sensors in the longitudinal, lateral, and vertical directions are presented and reveal a reasonable agreement between the experimental results and the numerical calculations.
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