In this study, the mechanical properties of the weld metal applied to the joints between the cold press formed steel tube and the through diaphragm were investigated by the welding test and the heat conduction analysis. The parameters of the welding test were the welding conditions such as the heat input, the type and shape of weld joint. The characteristic point was that the maximum heat input was set to 60 kJ/cm which was the upper limit for the welding robot as opposed to normal 30 kJ/cm. From the test and analysis results, it was clarified that the welding conditions affected the inter-pass temperature and the cooling time of weld metal. There was a correlation that the strength of weld metal increased with the increase the cooling speed.
