Driving forward - materials solutions for future cars

Materials World magazine
,
5 Feb 2012
electricity cable in shape of car outline

Cars of the future will be different in many ways. Their drive systems, design and materials are set to change fundamentally. The push towards electric mobility presents carmakers with new challenges, creating a need for innovative materials and comprehensive solutions.

A future with electric cars quietly and cleanly humming around our streets is likely to remain somewhere beyond the horizon until vehicles are capable of travelling longer distances without having to stop for a battery recharge. The capacity and weight of batteries in electric cars (e-cars) will need to be much improved before they can move into the fast lane in greater numbers. But in the laboratories of the world’s materials scientists, better batteries are just one area of e-mobility R&D.

Consider, for example, efforts to cut the weight of other parts of a vehicle. While the main material of construction in conventional cars continues to be heavy steel, parts of the bodywork in some cars are already using new, lightweight materials. One thing is certain – there will be more to come.

The use of innovative and sustainable solutions based on plastics such as polycarbonate and polyurethane, particularly in glazing and in the roof structures of vehicles, are bound to be a part of this future. Polyurethane, for example, weighs much less than steel and about half as much as aluminium. Plastic windows, which can enable weight reductions of up to 50% compared to glass, are already being used in polycarbonate panoramic roofs or fixed  side windows in some vehicles. A prototype roof module with glazing and integrated solar modules, unveiled at a recent exhibition, weighed in at just 20kg, achieved through the use of transparent polycarbonate (see right). The module was not necessarily targeted at the e-mobility market, but the benefit in offsetting the weight of batteries in e-cars is obvious.

Auto manufacturers are understandably keenly interested in these new glazing systems, but it is not just advances in glazing that are attracting their attention. Plastics are particularly robust when reinforced with carbon fibres, and with carbon fibrereinforced plastic (CFRP), carmakers can achieve weight reductions of up to 80% compared with steel.

The material is already tried-and-tested in Formula 1, where the safety cell of race cars – the monocoque – consists entirely of CFRP, and has already saved many drivers’ lives in crashes. In the future, a conventional or e-car’s cell could also be made of CFRP, enhancing safety as well as helping to cut fuel consumption and emissions. Yet although composite materials such as CFRP are promising, they are still very expensive to produce.

Aluminium has great potential as a material for lightweight construction in specific applications because its existing strength can be increased significantly through the possibilities of nanotechnology – a real box of tricks that offers so much opportunity for materials scientists. Batteries are included in this, for example carbon nanotubes can extend the lifespan of lithium-ion batteries of e-cars because they conduct electricity extremely effectively.

A shift in production

New materials are also changing production processes, as more plastic in exterior automotive components is leading to the increased use of new bonding technologies. In time, bonding may be used more than welding or riveting as development engineers work on eco-friendly, highperformance, polyurethane-based adhesives for plastic components.

Polyurethanes, too, are set to play an even greater role in coating car bodies, helping to cut energy consumption in vehicle production. Much energy used in auto manufacturing goes on coatings because they cure at temperatures of up to 200ºC – but plastics are processed at much lower temperatures. With polyurethane-based coating systems, materials experts can reach the required quality at just 80ºC. In addition, plastics do not need a layer of anti-rust protection, so the number of paint coats can be cut, markedly decreasing CO2 emissions in car production. These benefits are clearly applicable to the e-car manufacturing lines.

Drive systems are another area of development. With polycarbonates, new design freedoms are being opened for developing e-vehicles to the extent where the traditional engine compartments in conventional vehicles can be forgotten, allowing completely new vehicle designs.

The moulding properties of polycarbonates are more extensive than glass and metal, and as a result, distinctive elements of style are possible through the use of polycarbonates to the extent where they can direct the brand appearance of vehicles. For example, they allow large, complex mouldings of 3D external bodywork parts with integrated glazing elements, such as the prototype concept for a complete, one-piece tailgate developed by Bayer MaterialScience of Germany pictured right. The rear window is part of the component’s joint-free polycarbonate outer shell, which clever integration of a rear spoiler and two styling lines – problematic if metal and glass were used. The spoiler, for example, would have otherwise had to have been a separate assembly operation. Tail and brake lights, directional indicators, licence plate lights and high-mount brake lights are fitted behind the transparent outer shell so there is no need for individual sealing of all these lights. The fixings and guides can be integrated using the two-component back-injection method, which eases assembly costs.

Freedom to design

Further freedom in design comes from the virtually unlimited choice of options for polycarbonate colouring (conventional glazing for cars is currently only available in standard colours). Bayer MaterialScience has developed transparent tinted colours specifically for polycarbonate glazing that filter out a large proportion of the sun’s infrared (IR) rays, resulting in a cooler vehicle interior. Treated polycarbonate glazing enables IR light and energy transmission values for dark colours that are at least as low as commercial thermal insulation pigments for glass. As a result, ventilation and air conditioning systems do not need to work so hard to counter the sun’s heat, which cuts power consumption and extends the distances e-vehicles can travel before needing a charge.

It is something of a curiosity that while all these developments are going on, the design of e-cars remains little different to that of the combustion engines of conventional vehicles, and e-vehicles continue to be developed and produced in the traditional way. Herbert Radunz, who coordinates Bayer MaterialScience’s focus in the automotive industry in the Europe, Middle East, and Africa region, says this will change, ‘We expect to see fundamental changes in material usage and production processes in the long term as a result of completely new vehicle concepts’.

And on the road to this new horizon of increased capacity in electric cars, the materials scientists of today must be having fun, knowing they are working towards tomorrow’s solutions.  

Further information

Rachel Owen, Bayer MaterialScience AG. Tel: +44 (0) 1635 563410. Email: rachel.owen@bayer.com Website: www.bayermaterialscience.com