Finding the Right Combination

In the automotive industry, companies like SGL Carbon and Katcon are designing and producing multi-material battery enclosures for electric vehicles (EVs).

One of SGL’s first projects was the development and prototype production of the battery case for the NIO electric smart car. The materials included extruded aluminum for the side rails, composites for the top and bottom plates, and steel for the mounting parts. The combination was chosen to meet weight targets, performance requirements and crash behavior.

“In general, in the field of battery enclosures, metallic parts are used for the load introduction as well as for crush zones, while the composite overtakes the load distribution,” says Dan Gillig, SGL’s North American technical sales manager.

When developing a mixed material component, SGL considers not only the process of combining the different materials but also how to prevent problems like galvanic corrosion during the vehicle’s lifetime. The design takes into account the different materials’ properties, how they react to specific forces and the load transfer/distribution between parts.

SGL varies its joining technologies according to the materials used and the specific part’s function. Liquid adhesive technology, for example, is important not only to attach the parts to each other but also to carry loads and avoid the creation of weak spots in the assembly. Some assemblies are supported by bolting or riveting, which provides a local mechanical connection in an area where adhesive bonding is carrying the load transfer. Inserts directly integrated into the composite structure or easily bonded threaded studs are often used for mounting points in the assembly when lower loads are being transferred.

Katcon, based in Santa Catarina, Mexico, has worked with Forward Engineering in Munich, Germany, to develop a toolbox of materials, processes and design knowledge that’s intended to help manufacturers achieve the best configuration for their specific battery electric vehicle (BEV) platforms. “The goal is to have a lighter battery enclosure that is also economically feasible, safe and sustainable and that can be mass produced,” says Juan Armendariz, Katcon’s general manager.

“We found that steel and composites make a great combination,” he says. “We use the steel in the structural members. We use the composites for large panels that are typically expensive to produce in steel due to machinery, tooling and the associated capital expenditures. We can produce those parts more effectively with composites, and the composites are very well suited for intrusion resistance and fire resistance.”