Successful demonstration Fraunhofer researchers construct complex casting tools using 3D printers

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Fraunhofer-Institut für Lasertechnik

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Fraunhofer ILT and MacLean-Fogg have manufactured a complex die-casting tool inlay for large aluminium parts using laser powder bed fusion (PBF-LB/M). This was made possible by the special steel L-40.

The automotive industry is currently undergoing a comprehensive transformation. Rising cost pressures and the transition to electromobility are forcing many manufacturers to rethink vehicle architecture and production processes. One way out of this problem area is to reduce the number of individual pressed parts. The aim is to use as few structural components as possible, but ones that are highly complex. This applies especially to large aluminium components, such as frame or transmission components. However, according to experts at the Fraunhofer Institute for Laser Technology (ILT), this strategy also places greater demands on the tools. They must be thermally resilient, allow for variants and therefore be adaptable to new geometries as quickly as possible. This change therefore brings with it new challenges. According to the researchers, the moulds required for this purpose must not only be larger than before, but also more durable, with more complex geometries and shorter development times. This is where the ILT and MacLean-Fogg, the manufacturer of the innovative L-40 tool steel powder, are focusing their efforts on improvement. With the help of a PBF-LB/M machine developed at the ILT in a gantry design, which offers a scalable build volume, and the L-40 powder, it has been possible for the first time to additively manufacture very large die-casting moulds with close-contour cooling. As emphasised, the moulds are suitable for large-volume components to be manufactured by high-pressure die casting (HPDC) because they can withstand the process conditions.

3D printing was previously not applicable for casting moulds

Two key problems have previously held back additive manufacturing when it comes to large-format die-casting moulds, explain the experts from Aachen. Firstly, the available build volume of classic PBF-LB/M machines was too small to produce mould inserts measuring 600 × 600 millimetres or more in one piece. Secondly, the tool steels used to date – in particular H11 (1.2343), H13 (1.2344) and M300 – cannot be processed reliably at this scale (>20,000 cubic centimetres). Even with optimal parameters, there was a risk of cracks in the part, thermal distortion and poor mechanical properties. This applied both during laser-based construction and downstream heat treatment. The risk is also greater the more pronounced the temperature gradients within the component are during the manufacturing process – an effect that is particularly pronounced in large-volume workpieces. To overcome these hurdles, new 3D printing machines and materials that do not cause problems with large component volumes were needed. However, the gantry-style machine and the new powdered tool steel have now solved the problem. And the production of large casting moulds using additive manufacturing addresses several key challenges in automotive production – particularly in the context of the transformation to electromobility. A decisive advantage is the contour-close cooling systems that can be implemented, which can be freely designed for the first time thanks to 3D printing. Contour-close cooling is effective and reduces local temperature peaks, reduces thermomechanical wear and significantly extends the service life of the mould.

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