AUBURN HILLS, MI—Continental Structural Plastics (CSP) has developed a patent-pending clip system that replaces the need for bolts to join the top and bottom of an electric vehicle battery case. It improves the seal, reduces assembly costs and makes the batteries easier to service when needed.

The steel clips affix to the company’s multimaterial battery enclosure via molded-in features instead of using secondary machined holes and welds to join the top and bottom sections of the box.

“Unlike a point load created by using a bolt, the clips spread the seal load more evenly across the upper and lower flange,” says Hugh Foran, executive director of CSP’s Advanced Technologies Center. “On [our] multimaterial battery enclosure, 68 clips designed to hold 3 PSI of internal pressure replace 72 bolts that would all need to be torqued to a specified value. Each clip provides 950 Newtons of clamp force.

“By eliminating the need for bolts or bonding of any sort, a box assembled with these clips is easier to assemble and is much easier to service if the internal cells need repair or replacement,” claims Foran. “By using these clips in place of multiple fasteners and different types of welds, we can reduce assembly cost, complexity and the amount of scrap involved in the production of each enclosure.

“Our customers come to us with a number of challenges when it comes to developing the most efficient EV battery enclosures,” explains Foran. “This clip idea is just one example of how we are constantly searching for ways to improve both manufacturing processes and the end product.”

CSP’s multimaterial battery enclosure consists of a one-piece composite cover, one-piece composite tray with aluminum and steel reinforcements, and a mounting frame utilizing structural foam for energy absorption. This enables reduced frame thickness and weight, while improving crash performance.

“By molding the cover and the tray each as one piece, [we have] created a system which is easier to seal and can be certified prior to shipment,” says Foran. “[Our] multimaterial battery enclosure is 15 percent lighter than a steel battery box. Although it is equal in weight to an aluminum enclosure, [our] enclosure offers better temperature resistance than aluminum, especially if phenolic resin system advanced composite is used.”