Welding Deformation Analysis, Using an Inherent Strain Method for Friction Stir Welded Electric Vehicle Aluminum Battery Housing, Considering Productivity  
[PERSON]  
1 Transport Machine Components R&D Group, Korea Institute of Industrial Technology, Cheonan 31056, Korea 1  
[PERSON]  
2 Smart Manufacturing Process R&D Group, Korea Institute of Industrial Technology, Cheonan 31056, Korea 2  
[PERSON]  
3 Ship Structure Research Department, Hyundai Heavy Industries, Ulsan 44032, Korea 3  
[PERSON]  
4 Carbon & Light Materials Application R&D Group, Korea Institute of Industrial Technology, Cheonan 31056, Korea 4  
Correspondence: [EMAIL_ADDRESS]; Tel. : +82-63-210-37114  
cracks. Solidification cracks are caused by the tensile stress due to shrinkage or external factors during solidification at low temperatures within the solidification temperature range when the weld metal solidifies. Liquefaction cracks occur due to shrinkage when the intergranular area is locally melted and solidified by heating the heat affected zone to a high temperature. Porosity is also a significant problem with fusion welding aluminum compared to other metal materials. The pores are caused by the dissolution of gas into the weld metal during welding, the release of gas in the solidification process, the gas generated by the chemical reaction in the molten metal during cooling, and the release of gas due to the decrease of solubility. The purpose of this study is to solve the problems of arc welding by applying friction stir welding (FSW), which minimizes welding deformation and provides high weld quality when welding thin nonferrous metal plates, in order to produce high-quality battery housings. Figure 1 shows the welding deformations of arc welding and FSW tested by Hitachi, in which FSW shows a deformation on tenth that of arc welding [4]. Developed by TWI (The Welding Institute) in 1991, FSW is a solid-state joining process which does not apply greater heat than the melting point to the base metal. The operating principle of FSW is shown in Figure 2. A cylindrical tool--made of rigid material with a profiled probe--rotating at a high speed, is inserted into the joint of the workpiece. The welding region is softened by using the mutual frictional heat between the rotating tool and the workpiece, and the stir zone is formed with the forced plastic flow by the tool's rotation. The advantages of FSW include the following. The process does not generate hazardous substances, such as toxic fumes or hazardous rays during the work, and the work environment is good because there is little noise. FSW consumes less power and does not require welding rods, flux, and shielding gas. In addition, the welds are free from pores or cracks, which are likely to occur when using conventional fusion welding methods. FSW can be easily automated and maintains uniform quality because it does not rely on the proficiency and skills of the worker. The welding deformation is small and the dimensional precision is high because there is little thermal effect on the base metal. Figure 1: Welding deformation of arc welding and friction stir welding (FSW). Figure 2: Schematic view of the FSW process: (**a**) plunging into material stage; (**b**) dwell stage; (**c**) welding stage; (**d**) end of welding and tool retraction stage. In addition, it is easier to bond dissimilar materials, and the mechanical strength of the weld is 90% of the base metal, which is higher than the 80% of conventional TIG welding [5; 6; 7; 8]. Stationary shoulder friction stir welding technology can improve the weld surface quality and minimize the reduction of cross-section [9]. Due to such advantages, FSW is being applied to various industrial fields (aerospace, automobile, railroads, shipbuilding, etc.) and a wide variety of research is being performed. One of the great advantages of FSW is automation, as mentioned above. In reality, industrial sites have multiple welding lines and this process can be automated using FSW.