ABSTRACT

Friction stir welding (FSW) was invented in 1991 at The Welding Institute, and nowadays is widely utilized in the shipbuilding, automobile, aerospace, construction, electrical, machinery and equipment industries. FSW is applied to various structures due to its many advantages like high quality or no need for protective gas. Furthermore, the welding temperature is not over the melting point. Thus, the deformation and residual stress of FSW is less than fusion welding. Recently, consumption of aluminum is increasing in order to reduce vehicle weight which can influence carrying capacity and velocity. However, when the size of the applied structure increases, deformation must be considered. Particularly, in the case of the thin plate, there is almost no temperature gradient at the top surface and the bottom surface, so that the shrinkage occurs after cooling to room temperature. In this study, 10 plates of 2.5 mm thickness used in aluminum battery housing were welded by friction stir welding. If the deformation is not taken into consideration, the problem arises that the tool cannot be positioned at the welding center line from the second welding line. In addition, the analysis is performed using the inherent strain method because thermal elasto-plastic analysis takes a long time to calculate the welding deformation. Finally, the welding deformation calculated by using the inherent strain method was verified by comparing with the thermal elasto-plastic analysis and experimental results.

INTRODUCTION

Friction stir welding (FSW) was invented in 1991 at The Welding Institute, and it has been applied to non-ferrous metal. Also, it has a lot of advantages. FSW is not fusion welding but solid-state welding. Therefore welding deformation and residual stress are small. In addition, it has excellent mechanical strength and welding process is not dependent on worker skill. Thus standardization and automation are possible (Kang et al. 2014).

The principle of FSW is as follows. A pin on the tip of the rotating tool is probing into the joint part of the work piece, which is referred to as a stirring or mixing process, and then the work pieces are melted and joined. The rotating tool generates frictional eat by rotating at a constant speed while applying a constant downward force to the work piece. The downward force is sometimes replaced y tool plunge depth control. Fig. 1 is a schematic view of the FSW process. Advancing side means surface motion (due to spinning) is the same as the travel direction and retreating side means surface motion opposes the travel direction.

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