Technology And Thermal Finite Element Analysis Of Friction Stir Welding

Friction Stir welding (FSW) is a relatively new solid state joining process. It is said to be "the most revolutionary joining method after Laser Welding". Compared with the conventional welding processes, friction stir welds show little deformation and low residual stress, and has good mechanical properties. Therefore, a lot of FSW experiments on many materials were carried out to obtain more powerful welds. Because of high thermal conductivity, welding of copper and its alloys is usually difficult by conventional fusion welding processes. The heat input required is much higher than that in almost other materials, and the welding speed is quite low. Thus, studying the feasibility of FSW for joining copper and its alloys is of great importance. In the study, pure copper (T2) and brass (H62) which has 3mm in thickness were welded by FSW. With the microstructure of the welds, micro hardness profile through the weld zone and corresponding tensile strength test data, the shape and dimension of the tool, the travel speed, the tool rotation speed and the welding pressure were optimized. The stir zone showed fine and equaxied grain structure, and the tensile strength of the weld is equal or higher than that of the pure copper base metal.The heat transfer process determines the thermal cycles in the work piece during the FSW, which affects the microstructure and mechanical properties. A good understanding of the heat transfer process in the work piece can be helpful in predicting the residual stress in the welding work piece and the hardness in the weld zone. A three-dimensional heat transfer model based on the tool shape for FSW is present in this paper. With the ANSYS finite element software and the limited measured temperature data, the temperature distribution of 6mm thick pure copper (T2) friction stir weld was analyzed. Heat transfer at the bottom surface of the welding work piece and the temperature-dependent thermal conductivity of the material were considered in the model. The numerical results are in good agreement with the experimental results.