Getting a Grip on EV Fasteners

December 12, 2019

Stuart Birch

It may not get much R&D fanfare, but fastenings and their coatings will play an essential engineering role in electrified vehicles (EVs). There is an increasing demand from the auto industry for innovative fastener engineering techniques to be applied throughout the design and manufacturing process. “Fastening innovations are crucial for EV and EV battery (EVB) manufacturers,” said Sven Brehler, engineering project manager at TR Fastenings.

Particularly relevant for EVB assembly according to Brehler are fasteners with electrically isolating coatings; lightweight, non-magnetic fasteners; battery retention bolts; cable management hardware; and compression limiters. All require robust and secure settings for the costly battery. Fasteners are also essential in charging units, battery casings and general infrastructure equipment.

According to Brehler, an EV’s battery module can be secured with plastic inserts. Designed to incorporate various coatings, inserts are fitted into the plastic during the injection-molding process. “Component suppliers are beginning to work closely with battery module manufacturers,” Brehler explained, “to develop and apply coatings which protect the inserts from corrosion to maintain good electrical connectivity or retain isolation where needed to avoid unwanted electrical resistance or potential short circuits.”

Along with the materials used in battery casings and structures, varying conditions must be considered when applying coatings, and there’s no single solution. "Many coatings and parts need to act as conductors to move electricity and current around the battery to ensure it reaches the right destination,” Brehler said, “with minimum resistance causing potential hotspots."

Managing battery heat

Brehler explained that conductive coatings can be applied to materials such as plastic fasteners or fasteners prone to corrosion. An increase in resistance increases losses and generates heat. “EV batteries can generate high levels of heat, so it’s essential that it is distributed over the assembly to provide general cooling and avoid localized overheating,” Brehler noted. “Busbars can support the distribution of heat from local hotspots to heat sinks when correctly tightened to optimize heat transfer between the various elements. Using fasteners with thermally and electrically conductive coatings will aid an effective service life.”

Insulating coatings are used to stop electricity from going where it shouldn’t. Specific coatings include PTFE (polytetrafluoroethylene) because it is highly heat resistant, able to retain its properties across a temperature range from -200 to 260°C (-328 to 500°F). “It also has low predictable friction,” Brehler said, “which can help to create secure joints through torque control essential when assembling the battery module.”

Plasma spray or High Velocity Oxygen Fuel (HVOF) spray techniques used in the aerospace and defense industries (facilitating lightweight materials while still maintaining hard, heat resistant and easily polished surfaces), are now being adopted by engineers within the auto industry to help solve specific challenges. Particularly in application to fasteners, Brehler noted this is a demonstration of the use of “sophisticated and advanced solutions to deliver efficiency and safety.”