The Cost Savings behind Rheocasting

When thinking about applications for Rheocasting, most people first consider using an HPDC part and casting it with Rheocasting. And for many parts this technically works, but is a business development disaster.

On the one side, you’re taking away a perfectly suited HPDC part from your portfolio. On the other hand, you’re now requiring the OEM to change the material specification and to validate the Rheocasting process for this part.

That is asking a lot for a part that works perfectly well in HPDC. The better properties don’t affect usage, and the purchasing organisation doesn’t pay extra for them. They would rather have the cost savings and compensation for the validation costs.

So, you now have to implement a new process and deliver parts at a lower margin than before in HPDC. That is the wrong way to implement Rheocasting.

There is a better way!

The biggest bottleneck in most transitions is the lack of a need to switch processes. It just works as it is. But there are examples where this transition unlocks massive advantages. In the picture, you see a transmission valve body.

It is cast on a 600- or 800-ton HPDC machine, and the alloy used for this part is AlSi9Cu3, or 226. There are drastic variations in wall thickness throughout the part. And these changes are the reason for countless issues in conventional HPDC, as the part must be porosity-free and leak-tight.

The Issues in HPDC

Most of the problems come from changes in wall thickness. Thick areas are prone to shrinkage porosity because feedability is limited. One mitigation strategy is to fill the cavity at the highest speed, then apply the maximum pressure afterward. This shotcurve causes massive tool wear. Intensifying this tool wear are all the hot spots throughout the casting. Tool wear is visible as heat cracks, leaving an imprint on the casting surface that must be manually ground off.

Shrinkage porosity isn’t solvable in HPDC for this type of part. Therefore, an impregnation step is required to make it leak-tight.

How Rheocasting improves the Part

The first thing in the transition is to adjust the internal specification to target the lowest end of the official EN AC-46000 spec, which is 8.0%. This step alone saves 1-2% on alloy costs.

The next step lay in the Rheocasting process. The slurry is around 100°C cooler than the liquid metal. This reduces the thermal load right from the start. Additionally, it already contains around 40% of the solid fraction, further reducing the latent heat during solidification. However, during the filling and feeding process, the latent heat remains within the slurry, allowing it to cast much more slowly and feed the shrinkage porosity.

Just this switch increases the tool lifetime over the calculated 100.000 shots for such a part. In HPDC, 1 to 3 people were behind the machine grinding the heat cracks after 30.000 shots. These tasks are no longer needed, and the associated hourly costs are back in your pocket. The 100% leakage test remains, but the impregnation step is no longer needed, as the parts are leak-tight from the casting process. This saving is another 3 to 8€ per part in your pocket.

The biggest advantage comes when a new tool is ordered. In Rheocasting, the machine size can be reduced, or a second cavity can be added to the same machine size. Instead of a single-cavity part on an 800-ton machine, they were now producing the part in a dual-cavity design on the same machine. That is the biggest efficiency booster!

Summary

When outstanding properties in complex castings are required, Rheocasting is the perfect tool to deliver higher margins and lower total cost of ownership. It eliminates many rework tasks that customers don’t pay for, making your foundry more profitable.

However, the changeover is not trivial. For a successful implementation like the one described above, you need to be experts in metallurgy, rheology, process knowledge, and all the small details that ensure the process runs smoothly.

Or you hire experts who show you how everything works, and then you collect the rewards. The Rheocasting Expert on Demand is the perfect service for you. Casting-Campus awaits your call! Schedule right below this article.