Hot Tearing in Gigacastings

Tesla started with its gigacastings, a trend toward larger castings. The Model Y is cast on IDRA Group’s 6100-ton machines. Volvo Cars started this year with its Gigacasting program for the EX90. They use Bühler’s 8400-ton machines.

HPDC casting processes do not scale well. It is not that double the size is double the cost and complexity. It is more than double. One major topic for these large castings are hot tearing effects in certain areas.

What are hot tearings exactly? Let’s start with a definition. Hot tearing is the undesired formation of irregular cracks in metal castings that develops during solidification and cooling, typically while the casting is still inside the mould or die cavity.

Hot tearing isn’t new. Casting alloys like AlCu5, with their large solidification range, hot tearing is not uncommon. However, for Gigacastings, several factors come together that make it more dramatic than for “normal” structural castings.

The flow length is much longer. Aluminium alloys have a volume deficit of 6.6% when solidifying. This has to be compensated with a new melt, which has to be fed through meters of casting. That is tough to do, even with the correct temperature settings of the die.
Also, the melt front is cooler at long flow lengths, making recombining less likely. Another aspect is that the residue in the die from the spraying process accumulates on the surface and harms the recombination even more. You won’t see these issues in casting simulations.

In summary, when you combine the worst feeding possibilities at the end of the filling with not-ideal recombined surfaces, you will end up with hot tearing.

Solutions to that problem are:

• Improve the thermal management of the die
• Increase overflow volume
• Fine-tune the spraying process
• Adjust the melt processing

When you are facing these or similar issues in your casting process, schedule a free consultation down below that you can get experienced support in your troubleshooting activities.