Interview: “Rheocasting is no longer a ‘science-fair project’.”

Which questions were asked most frequently?

Fabian Niklas: The most common questions were: how exactly does it work? And what is the difficulty if I want to switch from conventional die casting to rheocasting? Very quickly you arrive at one of the biggest hurdles: alloy selection, because near-eutectic alloys cannot be cast in rheocasting.

Of course, the typical counterarguments also came up: cycle time, costs, and process stability. But these are topics that can be explained technically – and if you know what you are doing, rheocasting can be a real alternative with clear cost advantages. However, it is not suitable for every application.

How do you assess the willingness of the die casting industry to invest in rheocasting? Do you see concrete implementation projects?

Fabian Niklas: Investment willingness is a complicated issue. Rheocasting is no longer a “science-fair project”. There are applications already running in series production. Even so, many foundries, design owners, OEMs, and Tier-1 suppliers find it extremely difficult to approach the topic, simply because it is complex.

Just because something is labelled “rheocasting” does not mean it always contains the same process. A key factor, for example, is how stable you can control the solid fraction. With a solid fraction of 15 per cent you still have turbulent filling, while at 35–45 per cent you can achieve laminar filling – and those are two completely different worlds in terms of casting quality. This means you really need to understand the process in advance if you want to produce components successfully using rheocasting.

Can you give an example?

Fabian Niklas: A Japanese Tier-1 supplier that operates its own foundry looked at this issue and concluded that with rheocasting it could produce CO₂ compressors that are about three times more efficient. The components are helium-tight at 180 bar without any impregnation. In addition, you can move from a single-cavity to a dual-cavity design and achieve significant efficiency gains. But in Europe, hardly any Tier-1 currently dares to take such a decisive step.

And this is not only about willingness, but also about the consequences. In the Japanese example they had used the same standardised gating system for more than 25 years across all moulds. After two simulations it was clear that this design would not work for rheocasting. At that point you need to decide on a completely new gating concept, a new mould design and new process windows. Those are far-reaching decisions that must be taken if rheocasting is to be profitable in series production.

Do you see regional differences here?

Fabian Niklas: Yes, very clearly. Such decisions are more often taken in North America, China and India, partly because competitive pressure is extremely high and partly because there is a stronger entrepreneurial mindset. These Companies are using technology to their advantage. You could also see this at EUROGUSS. At the Casting-Campus booth, about 40 per cent of visitors seemed to come from India, and they asked very concrete questions about how to implement rheocasting properly. Visitors from European foundries were in the minority.

Why do you think Europe is more hesitant?

Fabian Niklas: The reasons are quite clear. Europe depends heavily on automotive volumes, and that sector is currently under enormous pressure. Margins have been declining for years, volumes are uncertain, and many foundry locations are expensive while often producing relatively standard components. A shock tower, for instance, is not a component that necessarily requires a high-end manufacturing location in Western Europe. It can be produced elsewhere with the same quality. In that context, “more automation” alone does not solve the problem if volumes are falling.

The common attitude is often: “This is not the first crisis. Let’s conserve cash and wait – we will get through it.” But this time the change is structural. European vehicles have become too expensive for many buyers, and competition from China is enormous. In such an environment it is very dangerous to postpone technology investments.

And something else I often see: companies “test” rheocasting by taking an old die casting mould and running it on some trial machine. They produce a few shots, quality is predictably poor because the mould was never designed for the process, and then they say: “See, we are not missing anything.” But that is not a fair test of the technology.

Which of the well-known advantages of rheocasting attracts the most interest from companies?

Fabian Niklas: There is not just one application for rheocasting. It is more like a bouquet of applications where it makes sense, and many fail because they start from the wrong point.

Many companies come from the automotive sector and say: “Here is a die-cast component – let’s convert it to rheocasting.” That usually fails, because the component already works as a die-cast part. Take a typical shock tower: it is designed for an alloy such as AlSi10. If I want to produce it by rheocasting, I may have to switch to AlSi7. That means new material specifications, new approvals – everything starts again from scratch. In the end, you get higher strength and elongation, but the application may not actually need those properties. In such cases, “rheocasting as a substitute” is simply not the right approach.

The most concrete discussions were about helium-tight components without impregnation. For many companies this is the real gamechanger. If components can be helium-tight at 180 bar without impregnation, you avoid having to “rescue” parts through impregnation – which does not work reliably at such pressures anyway. This opens the door to new applications, such as compressor or pump housings.

In addition, many companies are attracted by the overall package of measurable advantages:

• long flow lengths and improved filling behaviour thanks to the thixotropic properties of the slurry
• machine size reductions of often 20–30 per cent, because less pressure is required and the gating system can be optimised
• design freedom in wall thickness – from extremely thin sections of around 0.4 mm with almost no draft angles to very thick sections of 80–100 mm, sometimes within the same casting
• depending on the application, fewer pores, less post-processing, and in some cases, a T5 instead of a T6 heat treatment, which reduces both energy consumption and CO₂ footprint

In the end, the strongest interest always arises when rheocasting is not just “nice to have”, but an enabler – because it delivers properties that would otherwise be impossible or far more expensive to achieve.

Read the second part of the interview on EUROGUSS 36