Taking the weight off

Plastics are beginning to replace metals in some 'impossible' automotive applications – such as the chassis and even the wheels. Lou Reade reports.

Plastics continue to march into new automotive applications, thanks to a number of emerging materials and processing techniques. Designers are now able to specify and process materials such as long-fibre reinforced thermoplastics (LFRTs) and carbon fibre-based materials, allowing the production of lighter, stronger parts.

Some automotive components – such as fuel tanks and bumpers – are routinely made from plastics. It seems quaint to think that they were ever made of steel. But plastics are also finding their way into areas that are still considered 'no go' – such as external body panels, wheels and even the chassis.

A good example is JSP, whose Arpro material – a closed-cell polypropylene (PP) foam – has made inroads into several areas of the car, delivering substantial weight savings.

"Arpro is ideally suited for absorbing compression impact energy," says Bert Suffis, application sales manager at JSP. "Its original application was in bumper cores."

Arpro has since moved some way beyond this initial application. UK company Inrekor has used Arpro in combination with thin metal sheets to construct a very light car chassis. The structure comprises of a relatively thick Arpro core joined to two thin outer sheets of steel or aluminium, which is around 30% lighter than a traditionally made chassis.

The structure has since been incorporated into a new generation of electric vehicle, the QBeak, developed by Danish car manufacturer EcoMove and due for commercial launch later this year.

"Inrekor is very scalable: there's no need for huge upfront investment in stamping and metal forming," says Suffis. "That's usually a very large hurdle for a small company."

Arpro parts themselves also require relatively inexpensive tooling – aluminium-based tools rather than the hardened steel needed for injection moulding tools. This is because Arpro parts are foamed and are generally not made in such immense volume.

Because Arpro is made from a single material, it is more easily recyclable. But JSP has launched a variant, called Arpro Recycled. This contains 15% recovered PP – but is guaranteed to have the same mechanical performance as its 100% 'virgin' grade. "One manufacturer is already using it in a rear bumper," says Suffis.

He thinks that the Inrekor chassis will be crucial in the development of the emerging generation of small electric vehicles.

JSP's main focus remains the automotive industry, but it has set its sights on other sectors too: Inrekor lists logistics containers, caravans, ship bulkheads, railway carriage components and furniture as potential non-automotive applications.

"We could also use these panels to make modular buildings, such as for emergency relief," says Suffis.

The emerging generation of smaller vehicles, including electric cars, will be a key proving ground for plastics. And many will rely on a surprising material for weight saving: carbon fibre-reinforced plastic (CFRP), usually the preserve of F1 cars or aircraft.

In 2013, BMW will begin making two new mass-production cars that rely heavily on CFRP: the i3 'Megacity' electric vehicle, and the i8 hybrid 'supercar'.

"There is a need to reduce vehicle weight in order to meet emissions standards," says Joerg Pohlman, joint managing director of SGL-Automotive Carbon Fibers, a joint venture between SGL – Europe's leading carbon fibre producer – and BMW.

BMW uses carbon fibre to make flat 'carbon fibre textiles', which are then used to produce shaped CFRP parts. It is in these two areas that BMW claims a lead on its competitors, by automating the processes to make them suitable for mass production.

"We've taken textile production to an industrial scale for the first time," he says.

BMW uses resin transfer moulding (RTM) to reduce production time for each CFRP part to less than 10 minutes – much faster than the 20 to 30 minutes that was needed just a few years ago. The CFRP part in the Megacity car will be the 'passenger cell', which sits on top of an aluminium chassis. The CFRP part is half the weight of an equivalent steel part, says Pohlman.

Although this work is unlikely to transfer to other industries, BMW has definite plans to transfer it within the company.

"More and more car projects, starting from 2105 and 2016, will use carbon fibre as a structural element to reduce weight," says Pohlman.

Some of these vehicles may still be on the drawing board, but others are likely to be existing BMW models, he says.

And what about a plastic wheel? BASF, in collaboration with Daimler, has developed a thermoplastic wheel for use in a small car.

Heiko Hess, who leads wheel rim development in BASF's engineering plastics division in Europe, says the design relies largely on the company's Ultramid Structure material – a polyamide that is reinforced with long glass fibres.

"A three-dimensional glass-fibre network forms during injection moulding, imparting the end product with its outstanding physical properties – even at elevated temperatures," he says. "This forms the skeleton of the component, and is the reason why the warpage, creep and energy absorption all approach the behaviour of metals."

Although the wheel rim has been tested for serial applications, it would need to undergo far more rigorous testing before it could be allowed on the road.
"We don't expect to see it used commercially for another three to five years," says Hess.

Plastics have made a lot of headway in the automotive industry, removing weight from a variety of components. Now, it seems that they are making that vital next step — replacing some of those parts that it was said they never could.

Author
Lou Reade

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