Forget Battery Hyper-Castings!

The way we build EVs is often totally different from that of classical ICE cars. The structural design of an EV is vastly different. It can be reduced to three major parts: the front Gigacasting, the Rear Underbody, and the Battery Box in between.

The entire car is built like a skateboard, with all relevant components positioned low to the ground. This enables the low center of gravity and excellent manoeuvrability. The rest of the car is build on top.

Battery Hyper-Casting

Casting the entire battery in one shot is far beyond the capabilities of current HPDC cells. Just by calculating the projected area and neglecting the solidification pressure, you end up with more than 20,000 tons of clamping force.

Totally unrealistic to cast it in one piece. It doesn’t matter if you use Rheocasting, Thixocasting or conventional HPDC. Besides having a closed surface on the casting, you also need good mechanical properties to absorb crash loads, ensuring the passengers’ safety. Additionally, the battery needs to be protected in that situation as well. No parts of the toxic chemistry of the battery are allowed to escape the enclosure. This also needs to be handled by the battery box.

Therefore, these enclosures must be leak-tight for any media, and that is the last nail in the coffin of Battery Hyper-Casting, at least for now. Who knows what the die-casting machines of the future will look like?

Battery Manufacturing in Reality

It is clear that a Battery Hyper-Casting is off the table. Some OEMs have taken efforts to cast the frame of the battery in HPDC and weld in the sheet metal later. However, most battery boxes are built with extrusion profiles and large stampings. In that way, it is easy to build large structural battery enclosures with a minimal amount of parts. These parts have uniform properties and can be welded, riveted, and/or glued together to build the hull that will house the actual batteries. Then, another piece of sheet metal is placed on top to close the enclosure.

The End-Plates are the Pain Point

The keen readers noticed that the front and rear ends of the battery have been left out of the discussion. It is precisely on these points that the extrusions fall short in their functionality.

These batteries require numerous connection points to the outside. All the wall power comes through these plates to charge the battery. The climate system has to pump the cooling media in and out. During winter, the battery requires heating. In the summer, it needs to be cooled. Additionally, the power lines for the front and rear motors must pass through there. And last but not least, all the wires for the sensors and the battery status.

Numerous connections must pass through the enclosure without compromising the integrity of the entire battery box. Still, no leakage is allowed, and excellent weldability is required. All these holes weaken the structure; additional strengthening is required.

Here comes casting into play. Casting these end plates in HPDC enables you to add functionality and strengthening features. However, reality soon reveals its weaknesses. Turbulent fill leads to leakage points in the casting, compromising the integrity of the whole battery box. Impregnation helps to close these points. This step is quite costly and also forbids welding the part into the battery box.

Rheocasting fullfils all Requirements

By utilising Rheocasting, a leak-tight casting can be produced that allows for large jumps in wall thickness. You can implement the same features as in the HPDC design; you don’t need the impregnation.

The lower defect amount and the laminar filling of the cavity during castings increase the weldability. In addition, the lower silicon alloys are closer to the sheet metal’s chemical composition, allowing for higher properties inside the weld seam. This increases the overall production efficiency of the battery plant, as you will find out, if the casting is tight after welding, when the battery is fully assembled. Repairing or rebuilding the battery is a costly process.

Avoid the constant fear of faulty or leaky batteries; choose the Rheocasting parts directly. This gives you another unfair advantage in today’s foundry market. Learn about Rheocasting in the Rheocasting Workshop from Casting-Campus GmbH and find out where else new applications are waiting for you!