P 1256 – Advanced manufacturing of laser beam welded powertrain components using dynamic beam oscillation at reduced ambient pressure
Due to the high beam quality, energy efficiency, availability, and more flexible beam guidance, modern solid-state lasers offer numerous advantages for joining processes in automotive industry and especially gearbox manufacturing. However, at the same time, the high beam qualities and small focus diameters place higher demands on the manufacturing and positioning accuracy of the components to be joined. Therefore, the overall objective of the research project is to extend the application limits of laser beam welding with solid-state lasers by increasing the process stability to compensate for
The research project is based on the working hypothesis that in laser beam welding with solid-state lasers, the use of beam oscillation in combination with reduced ambient pressure leads to a significant improvement of gap bridging ability while simultaneously achieving high weld seam qualities. By the example of the case-hardened steel 1.7131, the influence of a reduced ambient pressure on the resulting gap bridging properties is investigated. Furthermore, suitable oscillation figures are evaluated as well as their influence on the process limits with regard to an improvement of the gap bridging properties. Building on these basic investigations, the effects of the gap bridging properties on joint strength, a process transfer to axial welds and welding of quenched and tempered steel are considered.
The resulting weld width has been found to be the main parameter influencing gap bridging in laser beam welding. Here, a reduced ambient pressure, due to the generally narrower weld seam geometry, leads to a decrease in gap bridging. On the other hand, the reduced ambient pressure causes a decrease in weld spatter formation and thus an increase in process quality, especially for the production of transmission components. To extend the process limits for the bridging of gaps, it is advised to widen the weld geometry. Therefore, more material is molten at the weld flanks and available for filling the gap. This can be achieved by positive defocusing of the laser beam as well as line oscillation transverse to the welding direction. As a result of the wider molten zone, lower undercuts and flat flank angles are formed. The transfer of the results to the welding of heat-treatable steel also showed a positive influence of the reduced ambient pressure on welding-induced crack formation, which thus contributes to increased process reliability and an expansion of the processing range for laser welding of difficult-to-weld materials.
Prof. Dr.-Ing. K. Dilger