A numerical process model for Friction Stir Welding with bobbin tool has been developed. The model is implemented in the FEA code Comsol?using Matlab?scripting. It includes a 3D representation of the work piece, clamping and the bobbin tool. The tool is translated through the work piece by discrete regeneration of the geometry and FE mesh for every time step of the simulation. A custom mapping algorithm is applied between time steps to guarantee physically sound results. The transient effects at the beginning (dwelling) and the end of the weld can be captured. The computational effort for the solution of this model is greatly reduced by the fact that only the current vicinity of the moving tool is enmeshed finely. The heat transported by the tool's rotation and the material in the shear layer around the tool are considered in the model using prescribed convective flow in an Eulerian frame. For this purpose a fast analytical shear layer model has been implemented which is calibrated with the output of a CFD Model of the material flow around the tool. The heat generation is governed by a pseudo mechanical heat source formulation (TPM) using only the material's temperature dependent yield stress data σ_y(T) as an input parameter. This robust approach can correctly predict the heat generation for any contact state condition δ > 0 without the need to provide experimental input data on machine power P(t) or torque M_T(t), frictional coefficient μ(T,sliprate,...) and contact pressure distribution p(t). The model's output includes the thermal history T(i) of the weld as well as the predicted machine torque Mr(t) for a given set of welding parameters (rpm, welding speed, plate thickness and geometry).
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