Additive manufacturing for complex die-casting moulds

Thanks to a newly developed tool steel for 3D printing and a machine with a scalable build volume developed at the Fraunhofer ILT in Aachen, large-volume moulds can now be produced using additive manufacturing for the first time – a major advantage for the series production of large die-casting moulds. The scalable process has already been successfully demonstrated.

The automotive industry is in the midst of a profound transformation. Cost pressures and the transition to electromobility are forcing many manufacturers to fundamentally rethink their vehicle architecture and production processes. Many manufacturers are currently reducing the number of individual stamped parts and aiming for as few, yet highly complex, structural components as possible. Particularly in the case of large aluminium components, such as chassis or gearbox parts, this also places greater demands on the moulds: They must be able to withstand high thermal loads, accommodate variants and be adaptable to new geometries as quickly as possible.
This transformation brings with it new challenges: the casting moulds required for this must not only be larger than before, but also more robust, whilst featuring complex geometries and shorter development times. This is precisely where a project at the Fraunhofer Institute for Laser Technology ILT, in collaboration with the L-40 powder manufacturer MacLean-Fogg and Toyota as the end user, comes into play.
Through the use of a gantry-based PBF-LB/M machine developed at Fraunhofer ILT, featuring a scalable build volume, and the tool steel developed by MacLean-Fogg for additive manufacturing, it has been possible for the first time to additively manufacture very large die-casting moulds with contour-following cooling – suitable for large-volume high-pressure die-casting (HPDC) components. Initial results from smaller moulds, which Toyota is already using in series production, indicate a significantly extended service life for the additively manufactured moulds, as reported by Fraunhofer ILT. In the current project, a hybrid, large-volume mould was produced for the gearbox housing of the Toyota Yaris Hybrid. The combined process, involving a conventional preform plus additively manufactured structures, shortens production time, reduces costs and allows for a wide variety of variants on a single mould platform.

To date, solid geometries have led to internal stresses and critical defects in PBF-LB/M

As large-scale casting processes become increasingly established, the demands placed on the moulds used in HPDC are also rising. The moulds must enable precise, reproducible component quality at very high production volumes whilst withstanding extreme mechanical and thermal stresses. To ensure a sufficient service life for the mould inserts, complex internal cooling structures are essential, which cannot be achieved using conventional manufacturing methods.
Two key issues have so far limited the additive manufacturing of such large-format die-casting moulds: Firstly, the build volume available on conventional PBF-LB/M machines is too small to produce mould inserts measuring 600 x 600 mm² or more in a single piece. Secondly, the tool steels used to date – in particular H11 (1.2343), H13 (1.2344) or M300 – cannot be processed reliably at this scale (>20,000 cm³). Even with optimal parameters, there is a risk of cracking, thermal distortion and inadequate mechanical properties, according to Fraunhofer ILT.
This applies both during the laser-based deposition process and in the subsequent heat treatment. The risk is all the greater the steeper the temperature gradients within the component during the manufacturing process – an effect that is particularly pronounced in large-volume workpieces.
“To overcome this limitation, a new generation of machines and materials is needed, specifically tailored to the requirements of large-format HPDC tools,” explains Niklas Prätzsch, group leader for LPBF process technology at Fraunhofer ILT. “It is precisely this combination that has been the focus of the developments now realised.”
For the first time, this new material and machine technology makes it possible to manufacture even large-volume tools with free-form cooling structures. This not only allows local temperature peaks in the casting process to be specifically reduced, but also increases the range of variants whilst maintaining a long service life. This means that different components can be manufactured on a single mould platform without having to produce new moulds each time.

Scalable LPBF production for crack-free large components

To this end, the gantry-based-based 5-laser PBF-LB/M machine, developed at Fraunhofer ILT, with a current build volume of 1,000 x 800 x 350 mm³, has been further developed. Unlike conventional systems, it features a movable processing head and local shielding gas supply, meaning that the build volume can be scaled linearly along the machine axes whilst maintaining the same process boundary conditions (shielding gas flow rate, laser beam deflection angle, etc.). According to Fraunhofer, this means that, in the future, even larger tools can be manufactured using additive manufacturing than the tool insert considered in this project, which has a volume of over 20,000 cm³ and a bounding box of 515 x 485 x 206 mm³.
To minimise the temperature gradients that are critical for large-volume tools, a heatable substrate module was also developed. The build platform now reaches a temperature of 200 °C, meaning that each new layer cools not to room temperature, but only to a predefined thermal plateau. This approach reduces thermally induced stresses and the risk of cracking during the build process. The combination of a large build volume, high process stability and active pre-heating makes this system one of the first LPBF systems worldwide to be suitable for the cost-effective production of near-net-shape die-casting moulds, including those for mega or giga casting.
“The key to success lies in MacLean-Fogg’s L-40 material, which is tailored to the requirements of PBF-LB/M,” comments Prätzsch. This steel is characterised by a significantly reduced susceptibility to cracking compared with conventional tool steels – both during manufacture and during heat treatment. Even in its as-built condition, L-40 achieves high dimensional stability and outstanding properties in terms of hardness (48 HRC), tensile strength (1420 MPa) and notch impact toughness (>60 J). Comprehensive investigations have successfully validated both the transfer of parameters to the new machine concept and the performance in complex geometries – such as round or cantilevered cooling channels.
Overall, the combination of a scalable PBF-LB/M machine and a specially developed material enables, for the first time, the cost-effective, reproducible production of large-format die-casting moulds with contour-following cooling. Initial applications show that the service life of tools manufactured in this way can be significantly extended compared to conventional moulds.

Hybrid manufacturing for series production tools

As part of the project, the partners have produced an additively manufactured tool insert for a gearbox housing, which is already in use at Toyota today. The die-casting insert features a complex network of cooling channels that closely follow the contours; this alone is a clear advantage of additive manufacturing that would be impossible to achieve using conventional machining. For the additive mould construction, the project team opted for a hybrid process using a specially manufactured preform that already featured vertical cooling channels. The precise positioning and reliable joining of both components placed high demands on machine calibration, precision and process control. Such hybrid structures offer the potential to further reduce production time and costs, as the more cost-intensive PBF-LB/M process is only used in those component areas that cannot be produced conventionally.
The researchers have designed the complex cooling structure in such a way that critical zones of the mould are effectively temperature-controlled during die-casting. This reduces thermal stress, resulting in a significantly longer service life for the mould. In previous projects, a comparable additive-manufactured mould had already achieved a service life up to four times longer than that of a conventional H13 mould.
Following the construction of the HPDC mould, standard industrial heat treatment involving stress-relief annealing and hardening was carried out, followed by conventional milling of the functional surfaces. The high dimensional accuracy of the additive-manufactured base body required only precise finishing without any additional material input.

Pioneering efficient and durable casting moulds in the automotive industry

The manufacture of large-format casting moulds using additive manufacturing addresses several key challenges facing today’s automotive production, particularly in the context of the transition to electromobility. A key advantage lies in contour-following cooling, which, thanks to 3D printing, can be freely designed for the first time. The cooling channels can be optimally adapted to the areas of the mould subject to high thermal stress. This reduces localised temperature peaks, minimises thermomechanical wear and significantly extends the mould’s service life.
At the same time, additive manufacturing offers the potential to drastically reduce lead times. Instead of the labour-intensive machining and assembly of multiple mould components, a consolidated, fully additive structure is sufficient. The die-casting mould for Toyota was manufactured in less than ten days, including all preparatory steps. For OEMs, this means shorter development cycles and faster time-to-market for new vehicle platforms.
The ability to construct large-volume tools using a hybrid approach creates additional flexibility. Components with defined interfaces can be efficiently supplemented using additive manufacturing and functionally optimised without having to remanufacture the entire component. This reduces both material usage and the cost per mould. “With L-40, we have set out to push the boundaries of additive manufacturing for hot and cold forming tools in general, and for die-casting moulds in particular. This project demonstrates that it is possible to produce large, complex and, at the same time, highly durable inserts, and sets clear milestones to ensure it is also economically viable. Additive manufacturing is ready to tackle real challenges on an industrial scale. For OEMs, this is a decisive advantage: shorter development times, longer tool service life and greater flexibility in tool design,” says Harald Lemke, Director of Product Management at MacLean-Fogg Component Solutions.
According to Fraunhofer, for vehicle manufacturers such as Toyota, which are moving towards fewer individual parts and more complex structures, these developments offer new possibilities in tooling strategy: reduced effort in tool production, longer service life and the ability to produce multiple variants using just a single tool. ##The manufactured component impressively demonstrates that the developed process chain – comprising a large-scale LPBF system, an innovative material and hybrid manufacturing – meets the requirements of real-world industrial applications, even in the context of giga casting.
The potential extends far beyond this individual case: the process chain developed is suitable not only for large aluminium HPDC tool inserts, but also for most other hot and cold forming tools and inserts, such as stamping, threading or injection moulding inserts. Wherever high-stress tools with complex cooling systems and limited batch sizes are required, additive manufacturing can offer significant advantages.
Source: Fraunhofer ILT