"Megacasting is the logical development for us"

Megacasting is seen as groundbreaking by some OEMs because it can reduce complexity in production. A conversation between Martin Lagler from Swiss die casting expert Bühler and editor Götz Fuchslocher about the present and future of the process.

Mr Lagler, how is the automotive industry positioned in terms of die casting?

Die casting has a tradition of more than a hundred years and has been used in the automotive industry for decades, mainly for powertrain housings, such as crankcases or gearbox housings and oil pans, as well as for chassis components. With e-mobility, motor housings and inverter housings are also being added. Regardless of the drive system, die casting remains state-of-the-art for housings for steering gears and air-conditioning compressors.

Structural components in body-in-white were added, a topic that did not just start with Tesla, but already in the 1990s with Audi's aluminium space frame construction. This was accompanied by the development of corresponding alloys as well as vacuum technology, i.e. the extraction of air before aluminium is cast in. On the one hand, this ensures high quality, allows the cast part to be welded and enables high elongation values that were previously unthinkable in casting.

This laid the foundation for what we now call megacasting. The technology took off among German OEMs. Other brands joined in, and today numerous Chinese start-ups also rely on die casting in body-in-white.

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Megacasting has gained a lot of momentum. Last year in particular was an outstanding one.

Martin Lagler, Director Global Product Management and Marketing Die Casting, Bühler Group

How does Bühler position itself around megacasting?

According to our definition, the components just mentioned are those on machine sizes up to about 4,000 tonnes clamping force, for example those for the production of longitudinal members and suspension strut supports for the front end of the car. If you want to make the switch from sheet steel to aluminium, these components are a good introduction to die casting.

Apart from the OEMs, there are usually numerous foundries involved in this, which then supply these components to the car manufacturers. So, the tradition is great. However, regarding the use in the car body and here again with quite large components, die casting is still quite new. For us, megacasting is the logical further development in the area of structural components.

With large-dimensioned plants it is now possible to combine several structural components, as well as to completely substitute numerous steel components in a direct changeover. We typically speak of mega-casting when we go beyond the 4,000 tonnes of clamping force mentioned, for example into the 6,000 to 9,000 tonne range, values with which entire rear or front carriages can now be produced in one part.

Your company's machines bear the designations Carat 105 to 920. What distinguishes the systems?

The numbers are an indication of the sizes. The Carat 105, for example, has a clamping force of 1,050 tonnes, while the Carat 920 has more than 9,000 tonnes or - to put it more precisely - a clamping force of 92,000 kN. The machines are identical in concept, although there is a second important aspect, which is the casting unit.

It determines how much mass of aluminium can be cast, because a key feature in megacasting is whether the mould can also be filled with liquid aluminium within about 70 to 90 milliseconds. To ensure this, the machine must offer a correspondingly high filling force. Our model 610 Extended as well as the 840 and 920 have even larger casting units for this than the other models. Up to 200 kilograms of aluminium are possible in one pouring unit.

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Bühler die casting machine of the type Carat 840 — Volvo plans to use two Bühler Carat 840 die casting cells at its Torslanda plant.

Volvo wants to use two Carat 840 die casting cells at the Torslanda plant. What quantities and in what cycle times can the Swedes produce with them?

In general, we assume about 120,000 parts per year for these components and system sizes. Of course, this is a guideline and not an exact figure because there are other factors to consider. For example, it is relevant how thick-walled the components are, because thinner parts naturally solidify earlier than thicker ones. The shape of the component also plays an important role. The cycle times are around two minutes per component.

With all the changeover times and assuming complete availability of the plant, you then arrive at the number of parts mentioned. If an OEM wants to produce half a million vehicles per year, each with one part for the rear end, he will need four or five such machines. If he wants to equip the front of the car at the same time, the number doubles. It should be emphasised, however, that different components can also be produced on one machine if the moulds are changed.

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Volvo will use the systems for parts of the rear floor area of its new vehicle platform. What challenges does this pose, for example regarding wall thicknesses?

Since we are also active in the field of component design and processes, we know very well about the specific requirements. As a rule, body components are not uniform, they have to offer different thicknesses locally. It is important to design according to the flow direction of the aluminium. So the component design and the production processes are very much interrelated.

There is a lot of freedom, but the main question is how to meet the requirements with as little aluminium as possible and how to produce the component ideally. Only when design and process are ideally matched can the OEM achieve maximum lightweight construction with high-cost efficiency.

To give you a figure: In terms of wall thicknesses, we can technically go down to 1.8 millimetres. This is not an average value, but rather one for the edge of a body component. Where we cast in, the material thicknesses are of course higher. A strategic question is therefore also where to position the sprue. Magnesium offers even more potential in terms of reducing wall thicknesses because it is even easier to cast.

What prospects does magnesium offer?

In any case, magnesium is not yet an issue in the body-in-white. The lightweight material is more likely to be considered for structural components for the vehicle interior, such as the instrument panel or the steering wheel. Megacasting is cold-chamber die casting. It allows the two materials aluminium and magnesium to be processed, with aluminium accounting for well over 90 per cent. On smaller machines, there are also applications with copper or brass.

Read the full interview in German at automobil-produktion.de

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