Laser welding of die-cast aluminum

The advantage of aluminum die casting is that it is very cost-efficient for large quantities. At the same time, the component geometry can be highly complex. However, the greatest advantage for cooling aluminum is the material's high thermal conductivity. As the weldability of die-cast aluminum has so far been inadequate, the housings are encapsulated by glued or screwed-on covers and plastic connections, but this is relatively expensive. The difficulties in welding die-cast aluminum are caused by gas inclusions in the surface layers of the component, which occur as soon as the material melts and sometimes outgas abruptly on contact with the capillary.

Advances in laser sources and beam guidance systems

In recent years, there have been major advances in laser sources and beam guidance systems that have pushed the boundaries of what is feasible: It has been shown, for example, that high laser powers with the smallest spot diameters in conjunction with double-core fibers ("2-in1 fibers"), oscillating beam guidance ("wobbling") or even pulsed laser radiation make it possible to weld joints with aluminum and copper in particular. Higher process speeds can also be achieved. This is achieved through increased capillary stability and improved melt flow. For aluminium die casting, however, these technologies are often still not sufficient to achieve reliable quality in series processes.

So-called multi-spot optics have come into focus as a possible solution to this problem. These form three or even four individual beams from one laser beam, which are fixed in relation to each other and are guided together across the joining gap. However, the disadvantage of these complex and expensive optics is that the individual spots cannot be easily adapted to the process. The temporal and spatial distribution of the laser beam is therefore not variable.

Dynamic beam shaping as a solution for laser welding of die-cast aluminum

This is where the new technology of dynamic beam shaping comes in: Instead of using a single laser beam, these beam sources enable rapid temporal and spatial distribution of the laser beam within a specific field by superimposing and phase-adjusting 32 individual single-mode lasers. The field size can be adjusted by the optics and can be between a few hundredths and a few millimeters. In the current generation of lasers, the laser spot diameter itself is one sixth of the field length and can change position within this field around 50,000,000 times per second. This means that any quasi-static beam shapes can be generated and flexibly adapted to the respective process - without the use of mechanical components. This makes it possible to adjust the capillary shape, the melt pool flows and the temperature field to the joining task. The technology also makes it possible to dynamically change the focus position along the optical axis. Welding defects such as pores, cracks and humping can potentially be avoided and currently restricted process windows can be significantly extended.

It is also possible that the rapid temporal and spatial distribution of the laser beam enables better stabilization of the vapour capillary than static multi-spot optics. This makes it possible for the first time to set the ideal beam shape and deflection frequency for the process for demanding joints such as with aluminum die casting - completely flexible and adaptable.

BBW Lasertechnik is already using dynamic beam shaping and is already seeing promising results for laser welding of die-cast aluminum. By using a high-speed camera, the effects of the various process parameters can be analyzed in a targeted manner and adjusted if necessary. The results can also be examined in detail and further optimized in an internal metallographic laboratory. BBW Lasertechnik is therefore able to meet the challenges of this critical process and offer customers a service of the highest quality.