Automotive Applications Division Features

New Materials for Automotive Engineering - No Thanks!
by Tom Chatterley, Head of Materials Engineering Department, MIRA

Introduction and Background

This somewhat controversial title needs to be put into context. As part of the input into the DTI's Foresight Materials Initiative, the author, who is also Chairman of the Institute of Materials Automotive Materials Board, carried out a survey to determine what new materials would be needed by the industry in the new millennium. The somewhat surprising answer - which prompted the title of this article - was that in general no new materials were needed to be developed as there were plenty of materials already "out there". Transferring the technology from other industry sectors to the automotive sector was considered to be a higher priority.

The emphasis should therefore be on developing or improving the methods of processing these existing materials to allow the forces that are currently driving the industry - such as light-weighting, improved fuel efficiency, safety and energy absorption, improved manufacturing efficiency, concurrent engineering and reduced time to market, and ultimate recycling - to be cost-effectively addressed through material choice. Some of the processes and materials highlighted in this survey are briefly described below.

Metal Forming and Casting

Vehicle weight reduction is really taking place at a fast rate, at last, though this trend does not necessarily relate specifically to the greater use of light alloys. There is still a place for ferrous-based castings and forgings but these will need to be refined somewhat. High strength, thin-walled, steel castings are of some interest in order to replace current forgings and thicker-walled iron castings and associated casting processes are in need of further development. In fact, process improvements are needed in all casting operations to reduce waste and to improve dimensional control to net-shape or to near net-shape in order to reduce post casting machining.

Magnesium is already having an impact here and several components are in serial production. Closed-die, semi-solid, or thixo-forming of magnesium alloys is of great interest to the industry. But it was considered that there needs to be some "tweaking" of the alloys in order to reduce dendritic formation thus slowing down the solidification process at the pre-forming stage and increasing production rates.

This latter alloy development is typical of the type of work that will be undertaken by MIRA, as the main partner in the recent Faraday Partnership agreement with Oxford University, Oxford Brookes University, Cranfield University, Business Link Heart of England and The Oxford Trust. Entitled, "The Faraday Partnership in Automotive and Aerospace Materials". The collaboration has the declared mission to: Develop lightweight, high temperature and sensor materials for low pollution, high efficiency transport systems via an integrated programme of research, training and technology transfer for the benefit of the UK automotive and aerospace sectors. An exciting period is in the offing for all the main partners and collaborating Companies.

One of the most attractive aspects of using magnesium in the near future is that demand for the metal is actually driving down the price of the material. Because suppliers are able to produce magnesium in larger, more-cost-effective quantities, its application has become more competitive with plastic mouldings. Evidence of this critical downwards movement of raw-material price was first seen during the early part of 2001 and I am optimistic that further demand with further reduce prices.

Plastic Moulding

The increasing use of, and improvement in, plastic materials will continue at a fast pace. Further developments are needed though to bring, for example, in-mould colouring technology to a wider range of components (the no-paintshop option), for both interior and exterior applications. FIAT have recently demonstrated this technology in their "Ecobasic" concept car with the declared aim to bring the vehicle, and the majority of the new technologies that it highlighted, to serial production. Multi-layer sandwich moulding to optimise the surface properties and core strength has also been demonstrated with good results. But further development in this area is still needed.

Low-cost tooling needs further development too as this is a key aspect of plastic moulding technology and would allow a more cost-effective approach to different model iterations - and therefore marketing opportunities - by the OEMs. Spray-formed tooling, using plasma sprayed molten steel on to a ceramic tool form, would seem to be the way forward as this innovative process greatly reduces the number of steps and, by implication, the time taken to tool production.

Race Car Technology Transfer

Weight reduction is again the main driving force here. Lightweight, ultra-stiff, carbon fibre composite materials used in race car body structures are a clear example of where this established technology could be transferred into the mass market. The benefits of composite material properties are of great interest to vehicle engineers. The technology transfer has already taken place to some extent with some very low volume, esoteric models, such as the McLaren F1 road car and the proposed Mercedes-McLaren road car. The interest appears at present to be the movement of these materials further down the production chain into the higher volume areas. The main drawback at present, according to those particularly wanting to employ carbon-fibre, is cost. For example, a reduction of processing costs by switching from PAN-based fibres to cheaper produced Pitch-base fibres, offering similar properties to those of the PAN-based material, would be one way to move the technology forward. Other necessary developments would also drive down the cost of this high-performance material.

Other established technologies in this field, such as safety-related features with regard to energy absorption in the impact situation, could also be transferred as could sensor and monitoring technology, and low-friction coatings used in the engine. This latter technology is already beginning to be employed in a number of new engines to replace traditional cast iron liners and high silicon surfaces in the block cylinder bore. Here plasma coating of the bores using special alloy powders, or arc coating of bores using alloy wires, are being employed in certain new engine models by VW and DaimlerChrysler to offer reduced friction, high wear resistance and good oil-retention properties.

Multi-material Manufacture

Multi-material manufacture, sometimes known as hybrid construction, incorporating a whole raft of materials, including steel, aluminium, magnesium as well as plastic mouldings for application in the vehicle body structure is gaining ground over single metal body systems either in steel or aluminium. For example, the latest Mercedes CL body-in-white has been constructed in the way. Steel has been used in regions highly stressed in the frontal and side impact situation, such as the roof pillars, and longitudinal and body cross members. Aluminium has been used for large surface panels for the roof, bonnet, rear panels and rear wings. Magnesium has been employed for the inner door panels and seat frames and plastics mouldings have been used for secondary components such as the boot lid, spare wheel well and front wings. A weight saving of 50kg over the previous version of the model was achieved whilst the whole vehicle is 340kg lighter than its predecessor. An impressive endorsement for the construction technology and the performance and engineering requirement for weight reduction.

Clearly, this approach to body construction also brings joining technology to the fore. This would allow novel welding techniques such as "Friction Stir Welding", which has the ability to weld dissimilar materials together, to be investigated further. The hybrid construction method also allows the adaptation of other more common joining techniques like adhesive bonding, riveting and even old fashioned bolting techniques to be developed to a new level.

Conclusions

Clearly, there will be new materials needing development in the coming years, but for the moment there are a whole range of current materials that can be used or further-developed in terms of performance and cost for automotive use. Since the use of new materials will always depend on how they can be processed and on the process technology employed, successful application of these materials will only come to those who are able to integrate new materials technologies with engineering designs and new production techniques.