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.
Spatter formation is a major issue in deep penetration welding with solid state lasers at high welding speeds from 8 up to 20 m/min. One approach to describe spatter formation is based on the assumption of an unstable keyhole. This leads to a temporary constriction of the keyhole due to the melt pool whereby the keyhole pressure increases. Finally, the keyhole collapses and spattering occurs. Therefore, the stabilization of the capillary is a possible way to limit spatter formation. For this purpose, several potential solutions have been tested in the past. However, investigations regarding a precisely local adjustable shielding gas flow on the keyhole stability under the condition of high welding speeds (≥ 8 m/min) is not given in the state of the art yet. To investigate these interactions, a shielding gas supply was developed, which can be adjusted in four axes with a reproducibility of 0.02 mm. Furthermore, the assembly was provided with a coaxial alignment laser for determining the interaction region of the gas. Under the processing of stainless steel (1.4301), different flow rates of argon, helium and nitrogen were tested. Additionally, Schlieren videography was used to visualize the gas flow. The spatial orientation has been varied in angles from 20° up to 48°. The experiments were recorded by means of HV-camera and subsequently analyzed by image processing (number, velocity and trajectory of spatters). Thereby, it was possible to reduce spattering by up to 91 % at welding speeds of up to 16 m/min.
This paper investigates laser welding of AA 6082 by superimposing a pulsed Nd:YAG laser with a continuous wave diode laser in order to reduce the hot-cracking susceptibility. Conventional pulsed laser welds exhibit severe solidification cracking on the application of a conventional rectangular laser pulse shape. Through the superposition of a Nd:YAG and diode laser beam crack-free welds can be realized without the use of an additional filler material in the case of sheet thickness of 0.5 mm. The diode laser beam simultaneously heats the base metal and weld metal during the melt-pool solidification and compensates solidification shrinkage and thermal contraction. Furthermore, the superimposed diode laser reduces the cooling rate during the melt-pool solidification. Hot-cracking can be eliminated by using an additional diode laser with a low output power of approximately 300W. A major impact of the diode laser superposition on the hot-crack suppression is expected to be achieved by reducing the solidification rate during the melt-pool solidification. These thermal changes result in coarser microstructure and therefore enable the easier feeding of liquid into the interdendritic cavities.
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