Electromobility has been a strongly growing market for years. This is the reason for the demand for battery technology and electric components continue to increase. In these technologies, the material copper is indispensable due to its high electrical conductivity. With the same electrical conductivity, substituting aluminum to copper leads to a reduction in costs and weight. For example, substitution is not possible at connecting points, therefore dissimilar aluminum-copper joints are highly important. In micro processing, pulsed laser beam welding is applied to achieve a slender weld seam. However, the mixing of both joining partners leads to the formation of intermetallic phases during welding. This requires a precise detection of the process stage in order to limit the weld seam depth close to the interface between both materials.
In this paper, a pulsed laser welding process between aluminum and copper was tested by using a fiber laser (IPG-YLM- 450/4500-QCW, pulse duration < 10 ms). The optical spectrum of the welding process was detected by spectrometers in the visible light range. When aluminum is welded with copper, the wavelength spectrum changes due to the material dependent emission. The maxima within the wavelengths of each joining partner could thus be determined and transferred to photodiodes with suitable bandpass filters. This leads to an increase of the temporal resolution during the measurement compared to spectrometers, allowing the analyzation of the time-related signal characteristics. A difference between heat conduction welding and deep welding as well as the transition from upper to lower sheet metal could be determined.