In this study, DD13 sheet materials used in automobile swing manufacturing were welded with GMAW (Gas Metal Arc Welding) welding method with different parameters such as welding method, welding amperage, and welding speed. The optimized value of the welding parameters, which will give the lowest hardness value in the weld seam hardness, was calculated by the Taguchi method. In addition, the heat input values that are thought to affect the hardness change were calculated, and the results were used to interpret the hardness change and Taguchi optimization values. After the experimental studies, the optimized value was compared with the actual results, and the verification test was performed. As a result of the optimization process, the lowest hardness value was estimated as 172.98 HV0.1 in MAG welding performed at 420 min/mm welding speed, 290 A, and 33.6 V parameters. The validation test result was found to be consistent with 173.4 HV0.1. Based on these values, finite element analysis (FEM) was performed with Simufact Welding 8.0 software. As a result of the investigation, the weld macrostructure, thermal changes, and the amount of distortion were examined. The results obtained are in agreement with the validation experiments.