The suitability of Carbon Fibre Reinforced Plastic as a material to produce car vehicle bodies on a mass scale.
The Automotive industry faces a crucial weight problem as a direct result of ever increasing customer demands in terms of both safety and performance. At present even modest small cars have, for example, power steering and air conditioning fitted as standard. It should also be noted that customers now pay particular attention to vehicle safety features such as airbags and side impact protection adding further to gains in vehicle weight.
Given recent advances in the processing time used to manufacture products with CFRP, is it now possible to manufacture vehicle bodies on a mass scale using this material, and thus take advantage of the strength to weight ratio it offers?
This article provides a complete research investigation covering topics such as Material properties, cost and environmental considerations, Manufacturing process and future material developments, all of which are used to derive a conclusion; is it possible, now or in the future, to manufacture automotive vehicle bodies on a mass scale using CFRP
The need for lightweight vehicles
Although there is seemingly much debate among experts regarding the global warming crisis, there seems to be a common acceptance that there is a need to change human lead emissions habits worldwide. The Climate Change Bill (Department for Food Environment and Rural Affairs, 2007) which became law on 26 November 2008 provides proof of the UK Governments commitment to change.
More and more pressure is being applied to automobile vehicle manufactures to reduce the CO2 emissions of the vehicles which they produce. The European Parliament (2005) passed a resolution which supports the need for mandatory vehicle C02 emissions standards. Since the passing of this resolution a response from the European Federation for Transport and Environment (2006) has documented a lack of success in the achievement of voluntary targets. The European Commission (2007) is now working towards legally binding vehicle CO2 emissions limits.
According to the US Transportation Research Board (Hailing, 2007), ‘the relationship between fuel consumption, (and therefore vehicle CO2 emissions) and vehicle weight is now linear. Thus, if we assume that a manufacturer reduces the weight of a vehicle by 10%, a corresponding fuel consumption reduction of 10% will occur’.
With this in mind it becomes clear that CFRP, based on its weight advantage alone, provides scope for further research as an alternative to the conventional materials used in car vehicle body structures; Mechanical testing has shown (Turner, Harper, Warrior, & Rudd, 2008) ‘that carbon fibre composite solutions can provide 40-50 per cent weight saving for an equivalent bending stiffness to steel panels’.
The requirements for mass production of vehicle bodies produced using CFRP must include the existence of a market large enough to justify substantial investment. A production/process chain development that allows the division of labour who can then perform simple, short, and repetitive process steps; and a product design that makes absolute use of standardised parts.
Review of previous research
There is limited, reliable, literature pertaining to the use of CFRP as the predominant material in automotive vehicle bodies. However CFRP is now the choice material for most exotic, high end performance vehicles having descended from the prototype racing series - Formula one. In an interview with Toyota Team President John Howett (Formula1.com, 2007) he explains... “We use so much carbon in Formula One because it is light, it’s strong, it’s extremely stiff and it adds to driver safety,”
The transition of CFRP vehicle body structures from Formula one into exotic, rare, expensive and niche motor vehicles into affordable mass produced motor cars is of primary concern in this article. Research has proven that the move from Formula 1 into the exotic cars is a reality; there is however no evidence that any motor vehicle manufacturer is using CFRP to produce whole car body structures on a mass scale.
BMW Group establishes joint venture with SGL Group
A BMW Press Release (2009) details... ‘The BMW Group and the SGL Group have agreed on the establishment of a joint venture for the production of carbon fibres and textile semi-finished products (CFRP) for use in vehicle construction. The total investment volume is € 90 million in the first development phase’.
The joint venture is ran by two companies, the first based in Germany (SGL Automotive Fibres GmbH & Co KG), and the second based in North America (SGL Automotive Carbon Fibres LLC).
The press release goes on to detail that the primary purpose of the venture is... ‘To acquire pioneering future technologies and raw materials that we need for our Megacity Vehicle on competitive terms’.
Robert Koehler, CEO of the SGL Group, stated: "This joint venture with the BMW Group is a milestone for the use of carbon fibres on an industrial scale in the automobile industry. For the first time, carbon fibres are taking on an important role in series vehicle manufacture. This confirms our strategy and shows that carbon fibre technology is becoming increasingly important in the materials substitution process to lighter material. This material will help to reduce CO2 emissions and save our natural resources“.
BMW's Megacity vehicle
The Megacity Vehicle , is said to be launched under a sub brand of BMW with CFRP making up a significant proportion of the construction materials. The joint venture between SGL Group and the BMW Group make calims that it is possible for the first time, to use CFRP on a large scale in a series vehicle at a competitive cost.
In advanced composite production there are a number of different methods of automation, which used to avoid the time consuming and costly nature of manual lay-up. To make true their claims, BMW will likely embrase one if not many of the following methods, although it is remaining tight lipped about the exact details.
An Automated Tape Laying (ATL) machine equipped with a Computer Numerical Control (CNC) system places Pre-impregnated (Pre-preg) carbon fibre material onto a tool. Fibre Placement Systems (FPS) also equipped with CNC systems place Pre-impregnated tows of continuous carbon fibre onto a mandrel to build up parts. Filament winding technology is another method now more widely used. Another likely candidate is compression moulding of sheet product
One important environmental consideration in the CFRP industry, concerns the waste produced during construction, and also how best to reuse the material at the end of its service life. These considerations become especially poignant in the light of new environmental regulations. Roberts (2006) estimates ‘that more than 1800 tonnes (4 million lb) of CFRP are produced in the USA every year; Europe is lower at about 900 tonnes (2 million lb), but even so this is still significant’. A new technology currently in development may prove to solve this problem; thermo-set based carbon fibre composites are converted into recycled chopped fibres. This process maintains nearly 100% of the materials modulus and 93% of its strength.
So, is it possible?
Davies (2007) suggests that the choice of material used in automotive body structures for mass production is conservative in nature. Davies goes on to theorise that... ‘Exceptional circumstances will be needed to bring about any significant change’.
Economics are of primary consideration in all systems of mass production, and it is commonly recognised that steel is still the main material of choice in mass produced vehicle body structures. Davis (2007) believes that significant changes in manufacturing strategy or raw material cost are needed to affect any real shift from this preference. He goes onto imply that... ‘Unless an economic breakthrough is made, even carbon fibre composites will struggle to find a wider application’.
The Author, having reviewed his initial research findings, believes there to be enough evidence to support the idea that CFRP vehicle body structures produced in mass volumes will become a technical reality in the next decade. However at this stage the author feels that further empirical proof is required to back up this claim and thus is still open to the potential of a ‘changed mind’.
Even if however, CFRP vehicle body structures can successfully be produced in mass volumes (which for the purposes of this article are considered to be volumes of over 50, 000 units), the question still remains as to whether or not the automotive industry will make the radical shift and begin to manufacture ‘normal every-day, mass produced vehicles’ using this material.
The author believes there to be a number of primary influential factors surrounding this question. The first of which are ELV (End of Life Vehicle) regulations. In the UK (The Environment Agency , 2009) regulations were first issued in 2003 and 2005 through the ELV directive and through the Environmental Permitting (EP) regulations 2007. The 2003 regulations deal predominately with the restricted use of hazardous materials, the 2005 regulations cover recycling. The regulations issued in 2007 serve to extend the treatment requirements to cover most automotive vehicles. It is therefore imperative that a suitable recycling infrastructure exists prior to the use of CFRP in vehicle structures on a mass basis.
Fuel availability and type, which is linked to emissions control and legislation is deemed another of the primary influential factors which may affect a move to mass produced vehicle bodies made from CFRP.
Secondary influences such as engineered vehicle safety may become an even more important factor, as historically, safety testing and legislation becomes more stringent with time.
Material cost is still regarded as the biggest prohibiting factor. However with advances in precursor technology, material costs may be set to fall quite dramatically. The ability to process a body panel made from CFRP as quickly as stamping a panel from steel is another technological challenge which needs satisfying. Therefore it can be argued that advances in manufacturing technology may favourably influence material selection and contribute to significantly lower manufacturing costs.
Ultimately all of the influential factors discussed need to be successfully resolved to make CFRP mass produced vehicle body structures a reality. We wait with baited breath to see if BMW live up to their promise of delivering a vehicle with a body made completely from CFRP - I for one hope that they do!
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