Estimation of temporal temperature distribution in blue laser welding of copper using thermal radiation imaging

The increasing demand for electric vehicles has highlighted the need for high-speed, high-quality welding of copper components used in motors and batteries. Blue laser welding, offering high optical absorption in copper, is a promising alternative to arc welding. However, quality monitoring methods remain underdeveloped. In this study, we developed a laser welding system integrating a high-power blue laser, galvanometer scanning, and thermal radiation imaging to evaluate the temperature distribution during welding. Two wavelengths in the near-infrared wavelength range were measured to estimate the temperature using two-color pyrometry. The thermal radiation distribution was found to correlate with the molten pool size, while temporal fluctuations in radiation intensity were attributed to dynamic changes in the shape of the molten pool surface. Notably, inconsistencies were observed between thermal radiation intensity and temperature values derived from separate single-wavelength measurements. This result indicates that thermal radiation imaging using a single wavelength band is insufficient for accurately evaluating absolute temperature or temperature distributions and confirms the importance of multiwavelength measurements for reliable temperature estimation.