The Permanent Mold Killer Approach

The article numbers in HPDC are expected to drop by up to 75%. This process will, in particular, hit the smaller DCMs that produce powertrain parts, which will become obsolete due to vehicle electrification. So, it is time to look left and right for new parts to cast and fill the production line.

So, where can you find these new parts?

Great opportunities arise when you look at sand castings or die castings that run in large numbers. There are hundreds of such parts in the suspension systems of various cars. It gets especially interesting when you also consider truck beams and brackets. OEMs have reduced the weight of the trucks to increase fuel/power efficiency.

What is different for these sand or gravity castings?

There are several things to consider. The obvious one is that 90% of them are made of AlSi7Mg (A356), an alloy that is not usable in HPDC due to its soldering tendencies. The second aspect is that they have high wall thicknesses due to the necessary properties (10 mm plus).

That is a big issue for HPDC; Let me explain why:

Solidification phenomenon in thin-walled castings: Thin-walled castings experience rapid cooling due to their high surface area-to-volume ratio. The latent heat from the solidification can quickly be transferred out of the casting, leading to significant undercooling and promoting the formation of numerous nucleation sites and fine-grained microstructures. Dendritic growth is limited due to the short solidification time, resulting in good mechanical properties.

Solidification Behavior of thick-walled Castings: Thick-walled castings cool more slowly due to their lower surface area-to-volume ratio. The latent heat cannot be transferred out of the casting. Undercooling is less pronounced, resulting in fewer nucleation sites and coarser microstructures. Dendritic growth is more prominent in thick-walled castings, leading to larger dendrites and drastically reduced mechanical properties, particularly in terms of ductility.

In addition, aluminium shrinkage during the phase change is 6.6%. This increases the problem for thick-walled permanent mold castings, as more alloy is needed to compensate for the shrinkage, and the dendrite structure prohibits adequate feeding.

What’s the solution to this problem when you cannot use HPDC?

Rheocasting is the solution. The globular microstructure installed during the slurry-making process prohibits dendrites from forming. With its thixotropic properties, it can laminar fill thin- and thick-walled castings of outstanding quality. The pocket warmer effect allows for an extended feeding time to ensure the highest properties. But be aware that you need a high solid fraction of around 40-45% to get these parts successfully cast.

The cherry on top is that the high efficiency of an HPDC cell allows for a lower part price for the customer and a higher profit margin for the foundry! Schedule a Free Consultation Call, and let’s discuss whether Rheocasting of permanent mold castings is a solution for your foundry!