## 5 Conclusions  
Currently, welding technology is actively applied in most industries except the aerospace industry. In particular, the proportion of welding is quite high in the shipbuilding industry. In other industries as well, the application of new welding technology is increasing due to the desire to overcome the disadvantages of existing welding technology, thus the development of new welding technology is being pursued. In addition, the application of welding automation technology is increasing. Failure to properly predict the welding deformation in each process can lead to problems not only in product quality but also in the process. Therefore, welding deformation must be predicted and reflected in the process. Analysis using the inherent strain method, before performing expensive experiments, is a more efficient way to predict the welding process.  
This study was performed on a large structure (aluminum alloy battery housing for electric vehicle) with multiple FSW lines. In the case of FSW, a small amount of the transverse shrinkage  
Figure 17: Transverse shrinkage according to each welding step.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Welding Step**} & \multicolumn{2}{c}{**Inherent Strain Method**} & \multicolumn{1}{c}{**Experiment**} \\ \cline{2-3}  & **Each [mm]** & **Accumulation [mm]** & **Accumulation [mm]** \\ \hline
1 st & 0.24 & 0.24 \\
2 nd & 0.25 & 0.49 \\
3 rd & 0.16 & 0.65 \\
4 th & 0.19 & 0.84 \\
5 th & 0.13 & 0.97 \\
6 th & 0.18 & 1.15 \\
7 th & 0.13 & 1.28 \\
8 th & 0.18 & 1.46 \\
9 th & 0.14 & 1.60 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Transverse shrinkage of aluminum battery housing model.  
mode occurs after welding, and therefore, the tool and the workpieces are not placed in the correct position at each welding step. This problem has a significant influence on the quality of the final product (especially, the tensile strength, elongation, and hardness at the joints). In order to resolve these issues, we calculated the welding deformation of each welding step using the inherent strain method. The factors affecting inherent strain values are maximum temperature, temperature gradient, and reaction force. The calculated welding deformation (transverse shrinkage) was used as a value to correct the positions of the tool and the test piece at each welding step in the actual process, to solve the problem.  
In addition, since the thermal elasto-plastic analysis method is not suitable for large structures, because it requires a long time for analysis, we applied the inherent strain method and reduced the analysis time to 1/30. As the numerical results also showed an 11.1% error compared to the experimental results, the method proposed in this study was confirmed to be reasonable.  
The inherent strain method proposed in this study has a great advantage for calculation of the welding deformation of large structures, such as those for the automobile, shipbuilding, aviation, and railway industries. The analysis time is greatly reduced, and the analysis results are similar to the experimental results. In the future, it will be very helpful to improve the quality by applying the inherent strain method to various industrial fields, and predicting the welding deformation and correcting it.  
Conceptualization, S.K. and J.K.; methodology, S.K. and J.K.; software, S.K. and Y.J.; validation, S.K. and K.L.; formal analysis, S.K.; investigation, S.K. and Y.J.; resources, S.K. and K.L.; data curation, S.K. and K.L.; writing--original draft preparation, S.K.; writing--reviewing and editing, Y.J. and K.L.; visualization, S.K.; supervision, K.L.; project administration, K.L.; funding acquisition, K.L.  
This research was supported by the Ministry of Trade, Industry and Energy (MOTIE), Korea Institute for Advancement of Technology (KIAT), through the Encouragement Program for The Industries of Economic Cooperation Region. (No. P0002251). The authors declare no conflict of interest.