Joined-up thinking for electric vehicle construction

Jon Lawson
Sven Brehler discusses an often-overlooked part of electric vehicle construction

The global electric vehicle (EV) industry is expanding rapidly, with 60% year-on-year increases and sales growing to 2.1 million units in 2018 according to McKinsey. As a result, advanced technology is now a top priority for competing OEMs and the role of fasteners is crucial.

Transport technology companies around the world are under pressure to innovate as a result of rising cost pressures, with trends such as lightweighting, autonomous driving and electromobility growing apace.

Suppliers into Tier 1 are increasingly required to come up with technical innovations for fasteners that work harder and ‘smarter’ that can be produced quickly and cost-effectively.

The key fastening applications within the automotive market include sub-Tier 1 manufacturers such as those within seating, powertrain, thermal management and HVAC, including high-end performance cars and the EV market - the latter being the fastest growing. It’s an evolving application that is leading the fastener industry to greater sophistication.

Achieving fastener weight reduction whilst maintaining high torque demands has become an important requirement in automotive applications. Industrial drive systems such as the Mortorq screw require up to 25% less material in the head yet still provide super high strength internal drive – an example of an innovative system providing the lowest head possible without compromising on fastener assembly performance.

One of the heaviest components in an EV is the battery, which runs the risk of negating the idea of carbon emission reductions if the vehicle’s weight dramatically increases energy consumption. As a result, fastener companies and their supply chains are constantly looking to innovate and are inspired by other transport industries such as aerospace.

Batteries, motors, transmissions and all their associated electronics are the leading technology areas of EV R&D and the fastenings and their coatings play an essential role. Innovative engineering techniques are now being applied throughout the design and manufacturing process to meet customers fast-changing needs.

Innovations are crucial for EVs

There are a number of components that are particularly relevant for EV battery assembly - fasteners with electrically isolating coatings - lightweight, non-magnetic fasteners, battery retention bolts, cable management hardware and compression limiters.

All these require fasteners to provide robust and secure settings to keep the costly battery safe. And fasteners are essential, not only in the EVs themselves but also in supporting technology and applications including charging units, battery casings and general infrastructure equipment.

An EV’s battery module can be secured with inserts for plastics that are used to maintain either good connectivity where required or avoid unwanted short-circuits due to corrosion or product failure. Fasteners for the EV batteries are designed to incorporate various coatings to suit the functionality of the joint. Examples of these include silver plating to improve connectivity or a high temperature resistant organic top-coat to provide an electrical barrier.

Component suppliers are beginning to work more closely with battery module manufacturers to develop and apply functional coatings to fasteners including protection from corrosion. These help to either maintain good electrical connectivity or retain isolation where needed to avoid unwanted electrical resistance or potential short circuits.

Coatings for EV heat management

Highly conductive coatings can be applied to certain materials such as plastic fasteners or fasteners prone to corrosion so they can act as electrical conductors, being part of the electrical circuitry. Increase in electrical resistance causes generation of heat together with loss of energy.

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 localised overheating. Busbars can support the distribution of heat from local hotspots to heat sinks, but only when correctly tightened to optimise heat transfer between the various elements. Using fasteners in thermally and electrically conductive coatings will aid an effective service life.

In certain cases, electrical currents must be contained. Barrier coatings avoid electricity from going where it shouldn’t and causing interference or a risk to safety through electrocution or fire.

Specific coatings used include PTFE (Polytetrafluoroethylene) because it is highly heat resistant with the ability to retain its properties across a temperature range, from -200°C to 260°C. It also has low, predictable friction, which can help to create secure joints through torque control, essential when assembling the battery module.

Manufacturers and sub-contractors must work together from the start to ensure the correct design for manufacturing (DfM) considerations. When cost-efficiency, sourcing, materials and product lifecycle concerns are discussed early on at the design table, costly delays later on can be avoided.

As an emerging transport sector, the fasteners needed in EV charging units and their associated structures require manufacturers and their supply chain to have technical knowledge and experience. There are increasing pressures and opportunities involved working within intricate global supply chain networks, and manufacturers servicing the automotive, electronics and technology sectors will be best placed to work with emerging EV-related businesses.

Looking ahead at electric vehicle construction

The EV sector is a fascinating one to watch as it develops and gains momentum. As the requirement for robust EV charging points grows, the automotive industry continues to innovate, with fasteners playing a major role in the EV revolution.

It is a rapidly accelerating market with huge potential for manufacturers and suppliers. It is therefore essential the supply chain has the infrastructure, technology and solutions in place to meet future demand for electric car use.

Sven Brehler is engineering project manager at TR Fastenings