A Semi-Solid Casting Roundup

In my last article, there was confusion. Not because the article needed more information. It was because the differentiation within the category of Rheocasting is not clear for everyone.

But let’s start from the beginning. The world of semi-sold casting is divided into two processing routes. Thixocasting relies on controlled heating and shearing to achieve a thixotropic, globular microstructure, enhancing flow and mechanical properties. In contrast, rheocasting employs various techniques to create a non-dendritic, semi-solid slurry from a liquid.

The most often used method is mechanical steering. Melt is agitated by screws, impellers, paddles, or some other form of agitator. The shear forces on the melt from the steering create non-dendritic structures. An improvement to that process is the Comptech Rheometal process, which uses the steering of melting aluminium “ice cubes” to make the slurry. You can see how it works in the video.

Magneto-hydrodynamic or electromagnetic steering is similar but different. Initially, it was used to overcome the unfavourable effects of steering agitators, like sticking or the solution of iron from the steel. The new Rheocasting process from Meltec uses this method. Another variant of this is the Hitachi process. An electromagnetic field is applied in the shot sleeve.

Another method is the preparation of a slurry via some type of cooling slope and a holding/transport vessel. The UBE and cooling slope processes use this method to produce the slurry.

Combining methods already listed is the Semi-Solid Rheocasting SSR. It uses a copper or graphite rod to agitate the near-liquidus melt. Because of the localized heat extraction, the slurry arises. The GISS process developed from this method. It uses a graphite diffusor and nitrogen gas instead of a solid rod.

Another method is applying centrifugal forces to a container to introduce shear forces. This is used in the SEED process. There is even a flap to release the liquid to produce high-solid fraction billets.

The last method is ultrasonic sound waves. Inserting them into the melt while cooling generates a non-dendritic slurry because of cavitation and acoustic streaming.

As you can see, there are many faces to Rheocasting, and these are just a sample of all methods ever developed. So, it is quite clear that they cannot get all the same results. Still, 80% of the work of a good Rheocasting part is “normal HPDC stuff”, like tool design, cooling, spraying, and venting.

The Rheocasting Workshop is the best place to learn about Rheocasting and how to implement it in your foundry profitably. Schedule a free Consultation Call for more information on Rheocasting!