The Lexus LFA features a carbon fibre composite cabin.
The Lexus LFA features a carbon fibre composite cabin.

In October, the BMW Group announced the establishment of a joint venture with the SGL Group for the production of carbon fibres and fabrics for use in construction of the Megacity Vehicle, which will be introduced in the first half of the next decade, says the automaker. Carbon fibre reinforced plastic (CFRP) materials will make up a significant portion of the vehicle’s structure.

“The combination of the advanced CRFP fibres developed by the SGL Group and BMW Group’s expertise in the industrial manufacture of CFRP components is making it possible, for the first time, to install CFRP on a large scale in a series vehicle at a competitive cost,” notes BMW.

Carbon fibres will be produced in North America, processed into a reinforcing fabric in Germany, and used to make CFRP parts within the BMW Group.

BMW has been using composites, including carbon fibres, in its vehicles for years. The roof of the M-series car is produced using Hexcel’s HexForce® NC2® carbon fibre reinforcements, manufactured with patented non-crimp technology that uses unidirectional tapes to provide strength and stiffness where required. In addition to NC2, Hexcel also supplies BMW with HexForce PrimeTex® 3K spread fabrics for the outer skin of the carbon fibre roof. Hexcel’s unique weaving experience combined with new spreading technology allows the aesthetic specifications of BMW to be met, reports Hexcel.

In Japan, Mitsubishi Rayon Co, along with the Japanese government’s New Energy and Industrial Development Organization (NEDO) and the University of Tokyo, has purchased a Fiberforge RELAY® station and R&D license to develop thermoplastic carbon fibre composites for automotive applications. The Fiberforge equipment creates tailored multi-ply preforms or tailored blanks using unidirectional tape and compression moulds them to produce parts.

In a separate development reported recently, Mitusbishi Rayon and SGL Group have formed a joint venture company to produce PAN-based precursors for the production of carbon fibres for automotive applications.

Supercars

Race cars and high-end supercars have been using CFRP materials for decades and continue to increase the carbon fibre content in their construction. The Lamborghini Murcielago 12-cylinder sports car makes extensive use of CFRP – 31% of total weight – including the body, floor, transmission tunnel, wheel housings and bumper section of the chassis. About 500 cars per year are manufactured, but the company’s goal reportedly is to increase output to as many as 3000 cars per year. Lamborghini is said to be moving away from prepreg construction to compression moulding and resin transfer moulding (RTM) processes.

The new Lexus LFA premium sports car has been designed with a carbon fibre cabin that weighs 100 kg (220.5 lb) less than a comparable aluminium cabin and retains the same rigidity, the company reports. CFRP represents 65% of the chassis structure, while aluminium alloys are used in the rest of it. The LFA team also developed an advanced joining technology to bond carbon fibre and metal components: flanged aluminium collars, used to link the two materials, require no inserts in the CFRP components.

Three different moulding processes are used to produce the LFA CFRP parts, the automaker explains. In the first, prepreg is laid up by hand to form the main cabin frame. In the second process, RTM is used with preforms impregnated with thermosetting resin to produce the transmission tunnel, floor panel, roof and hood. The third process is compression moulding, using short carbon-fibre reinforced sheet moulding compound (SMC). CFRP is also used for the diffuser, speed-controlled rear wing and interior components, contributing to additional weight savings.

The CFRP components were developed by Toho Tenax, the core company of the Teijin Group’s carbon fibre business, in cooperation with Toyota group companies, parts manufacturers and the Teijin Composite Innovation Center (TCIC). Toho Tenax supplies most of the carbon fibres used in the LFA.

“As the market steadily shifts towards electric vehicles and other environmentally friendly, next-generation automobiles, robust demand is envisioned for high-rigidity, ultra-lightweight carbon fibre composite materials,” predicts Toho Tenax. “Going forward, the company will collaborate with TCIC to further develop carbon fibre composite materials and related technologies, focusing on automotive applications targeted at both high-end and mass-production vehicles.”

Tesla EV still going strong

Still making waves in the automotive industry is the award-winning Tesla Roadster, manufactured by Tesla Motors, which reported in July an overall profit of US$1 million on sales of $20 million.

The $109 000 all-electric sports car with a CFRP body is the first production EV to travel more than 200 miles (321.9 km) per charge (at a cost of $4 to fully recharge) and the first US and EU-certified lithium-ion battery-powered vehicle, the company states. In July, the new Roadster Sport was introduced, demonstrating blazing performance of 0-60 mph in 3.7 seconds.

Tesla Motors continues to develop the all-electric Model S five-passenger sedan, which will carry a base price of $49 900, roughly half the price of the Roadster. With a 2011 launch date, the new model will shed the CFRP body panels in favour of metal in order to meet the expected ramp up to a volume of 20 000 cars per year, the company says. The carbon fibre/epoxy RTM process, which was chosen to produce parts for the Roadster, cannot meet the higher production volumes planned for the Model S, adds Tesla.

Production capacity and tooling for the Roadster is 1500 vehicles per year. Tesla describes the layup schedule of the body panels as follows. An outer layer of continuous non-woven glass fibre veil or tissue, covers a second layer of Zoltek Panex 35 carbon fibre +45°/-45° unidirectional 50K tow fabric, tricot stitched. The third layer is continuous nonwoven glass for infusion. The fourth layer is the same as the second. Upper and lower carbon fibre unidirectional fabric layers mirror each other to balance stresses and minimise distortion. The cure time for the RTM epoxy, mixed at the tool injection port with amine hardener, is 20 minutes.

Alternative energy vehicle manufacturer Velozzi and Bayer MaterialScience announced that they would collaborate with Nanoledge, a leading epoxy resin formulator to provide a full range of high-performance epoxy-based materials to the composites market in North America. Bayer’s Baytubes® multi-walled carbon nanotubes will be used to produce lightweight components for Velozzi’s SOLO crossover vehicle, now under development. The vehicle is expected to achieve 100 miles (160.9 km) per gallon of fuel. The car maker plans to make body and interior components using epoxy, carbon fibres and nanotubes.

 


This article is an abstract of the feature: Carbon fibre producers optimistic in downturn, published in the January/February 2010 issue of Reinforced Plastics magazine. Read the complete feature here.