Design Chain – Shedding pounds and adding value in automotive
By Lou Reade
Posted 15 November 2012
Materials suppliers are still providing weight-saving options to auto makers - with techniques ranging from foaming to composite processing.
Composites, once the preserve of high tech and high spec applications, are finding their way further down the automotive chain. At one time, composites could only be found in F1 cars, trucks and high end cars - where price was no object.
But the relentless need to cut weight has brought composites into the realm of the automotive mass market, helped in part by automation techniques that lower production costs and reduce cycle times.
It's true that many of these applications are still focused at the higher end of the market. But a number of 'on the road' cars now use materials that would once have been unaffordable in these applications.
Cutting weight means composites becoming mainstream
For example, at this year's JEC composites show, held in France, a number of companies showcased their composite efforts to help automotive companies cut the weight of components. Axon Automotive of the UK won an Innovation Award at the event for its Axontex carbon fibre composite system.
At the show, Axon exhibited its completed city car, which uses Axontex to make lightweight composite structural beams with high strength and stiffness - the 'B' size car, with dimensions close to a Citroen C1, has a frame that weighs just 50kg.
Axontex has a 3D woven structure, comprising a carbon fibre braid over machine-laid multiple preforms made of closed-cell low density polyethylene (LDPE) foam. The carbon fibres and LDPE are then infused with Scott Bader's Crestapol 1250 LV urethane acryl ate-based resin, using vacuum assisted resin transfer moulding (VARTM).
During this process, the foam expands to take the shape of the tool. The moulded Axontex carbon fibre composite beam incorporates shear webs into its internal structure. This, combined with the mechanical properties of the Crestapol resin, provides the necessary strength and stiffness.
Test pieces have consistently achieved an ultimate tensile strength (UTS) of up to 1000MPa, combined with a heat deflection temperature (HDT) of over 130ûC. The Axontex system also passes the seat belt load test according to ECE regulation 14, resisting up to 1350 daN (+/- 20 daN) per attachment.
At the same time, it can provide up to 1.5 times the specific energy absorption (SEA) - the ability of a material to absorb energy from a crash impact loading - of aircraft grade aluminium.
Crestapol 1250LV is an ambient curing urethane acrylate based thermosetting resin that is compatible with carbon fibres. Its developer, Scott Bader, says it is a cost-effective alternative to epoxy infusion resin systems. Scott Bader won a JEC Europe 2012 Partnership Award for its role in the Axontex project.
Axon is also leading a UK project to develop materials for lightweight car components. Composite Ultra Lightweight Automotive Suspension Components (or Cusp), is one of 16 projects that will benefit from a combined funding of £10m from the Technology Strategy Board and the Department for Business Innovation and Skills.
Each project aims to develop technologies that will help to cut CO2 emissions in low carbon vehicles. Others are studying lightweight engine designs, advanced battery management systems and next-generation electric motors.
Cusp's other project partners are Tallent Automotive and Warwick Manufacturing Group.
Among the 16 projects, there is one more that is composites-related: Acomplice (Affordable composites for lightweight car structures), a two-year project led by materials producer Umeco, aims to develop composite materials that could one day be used in mainstream cars.
"The targets we've set are vehicles like BMWs or high-end Toyotas," says Elaine Arnold, collaborative R&T project manager at Umeco and the project's co-ordinator. "We hope to be there in a few years."
Composites are usually restricted to high-end cars, as they far too expensive to be used in mass market models.
"We've seen SMC short fibre materials fitted in some cars - for applications like parcel shelves - but nothing really structural," she says.
Automation is lowering composite component costs
The manufacturing partner in the project is Aston Martin - due mainly to it being a UK-owned car manufacturer, as it is hardly a producer of mass market vehicles. Another partner is Delta Manufacturing, which will handle design for manufacture of components.
The partners have identified two specific components - both of them semi-structural - that will be redesigned in composites in order to save weight. However, Arnold says it is too early to reveal any details about them.
Automation is a key factor in reducing the cost of composite component manufacture, but material development will also play a role in the project.
Arnold says that Umeco is working on fast-curing resins, which would allow cycle times to be reduced. Work on the project will focus on the company's pre-impregnated DForm material - which, says Arnold, maintains unidirectional fibre orientation while being highly formable.
"It's not currently optimised for automated manufacturing, but that's what we'd like to do in this project," she says.
Meanwhile, Danish researchers are looking to identify ways of making carbon fibre automotive components more quickly.
The House of Composites (HOC) - a composite materials R&D company - will collaborate with Morten Rask, a postdoctoral student at the Technical University of Denmark (DTU), on a three-year project to identify mass production techniques for lightweight components.
The project is based on an HOC patent application, and aims to be able to produce carbon fibre parts in prepreg quality with a tool cycle time of five minutes using an automated autoclave-like manufacturing process.
Biodegradable solutions are also expected to be achievable.
Car manufactures have been invited to join the project. The first goal is develop a low volume manual process, for sports and exclusive cars, followed by an automated, high volume version that is suitable for mass production.
The Danish National Advanced Technology Foundation has provided a grant of around €210,000 (£167,000). This has been matched by the two project partners.
In fact, the use of carbon fibre reinforced plastics (CFRPs) in the automotive industry is expected to accelerate faster than an F1 car: consultancy Frost & Sullivan estimates an annual growth rate of more than 30%. This would take the market from its current position - just below $15m (£9.3m) - to nearly $100m (£62m) by 2017.
"CFRPs provide a better alternative to metals and glass-reinforced plastics, while innovative fabrication methods should enable high-throughput production," says Sandeepan Mondal, senior research analyst at the company.
And this fast growth comes despite the fact that several factors will restrain the adoption of the technology by the automotive industry.
"We identified four factors that could restrain the market," he says. "These are: high cost; long cycle times; a lack of engineering expertise with these materials; and recyclability issues," he says.
'Low modulus' grades of carbon fibre, as used by the automotive industry, typically cost up to $25(£15)/kg, he says. This is lower than the $35(£22)/kg for high modulus grades used in the aerospace industry. But the fact that the aerospace industry makes larger parts leads to better economies of scale there.
"There is also a lack of general engineering expertise among automotive OEMs," he says. "Most have invested in metal assembly plants, and are not keen on making more capital expenditure on a new technology."
Some 'mass market' car companies - notably BMW and Daimler - have already begun to adopt CF technology, but they are in a minority.
Mondal says that automotive companies are likely to adopt a 'hybrid approach', and use a range of materials - including aluminium, high strength steels and thermoplastic composites - to deliver weight savings.
The final factor is recyclability. While CF materials are most likely to deliver the crucial weight savings needed - in order to meet tough future emissions targets - they are notoriously difficult to recycle. The End of Life Vehicles (ELV) Directive insists that 85% of all vehicles must be recyclable by 2015. The use of CF composites would make this more difficult, he says.
Mondal estimates that 90% of CFRP automotive applications will use carbon-epoxy composites, with the rest composed of carbon fibres embedded in thermoplastics such as polyamide, polyurethanes and PEEK - depending on the application.
"Under-bonnet parts are most likely to use CF-reinforced PA, because epoxy does not have high enough chemical or heat resistance," says Mondal.
Beyond 2017, he believes that efforts to reduce cycle times for CF parts will continue to improve.
"Many carbon fibre producers are looking to bring cycle times below five minutes," he says. "This is still long compared with steel, but at the same time the cost of carbon fibre is likely to come down."
Europe is leading the efforts to adopt CF technologies, he says, followed by Japan - which is a global centre of CF production. The US, whose automotive industry has been very hard-hit, will be slowest to adopt these measures, he believes.
In the next feature: Foam in the automotive sector
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