Friction Stir Welding Analysis by Using CFD Heat-Flow Analysis and Inherent Strain Method

Abstract

Friction stir welding (FSW) is a new technology which makes it possible to join two materials such as aluminum alloy, magnesium alloy and dissimilar materials at a solid state. Nowadays, FSW is mainly used for vehicles like vessel, aircraft, railcar and automobile. In this study, a three dimensional numerical model is constructed for the heat transfer analysis of the FSW using a commercial computational fluid dynamics (CFD) software Fluent and finite element analysis software ANSYS multi physics. The heat transfer analysis result is used to calculate welding deformation and residual stress. Before the simulation, several simplifying assumptions are made to the model. Three different heat transfer analysis were carried out and compared with each other. Especially, a rotation affected zone concept is imposed for CFD analysis. The rotation affected zone is a constant volume. In this volume, flow is rotated the same as the tool rotation speed and so plastic dissipation occurs. The CFD analysis is good to gain better understanding of the flow pattern regarding the vicinity of the tool. Also, the result of the asymmetric temperature distribution is remarkable as compared with other analysis. Also, the asymmetric feature of FSW are considered using a coupled CFD-FEM simulation. Heat transfer analysis was carried out by using CFD commercial program Fluent and the results were used finite element structural analysis by using ANSYS multi physics. The calculated residual stresses were compared with an experimental value by using X-ray diffraction method. Finally, inherent strain method was developed considering external constraint and features of FSW. At this time, external constraint was defined as reaction force and it was predicted using neural networks. This method result of the residual stress was verified by comparing the thermal elasto-plastic analysis, and experimental result.