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09/02/2008
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Tom Shelley reports on radical design technologies developed in Formula 1 and now being made available for mainstream engineering
Five ex-Formula 1 engineers are offering their materials skills – including how to combine metal matrix composites and carbon fibre composites in the same component – to the wider engineering market.
F1 regulations outlawing costly and exotic materials have seen the engineers – who operate under the collective ‘XF1Tech’ – acquire particular expertise in producing cost-effective and serviceable solutions. And while many of these are aimed at improving mechanical performance per unit weight, they also have unique solutions to offer for stepping up impact performance. These were developed in F1 for the greater safety of drivers, but are also of relevance to the growing market for armouring civilian cars. The team also boasts a particular skill in solving design problems quickly, with the help of advanced CAD.
The XF1Tech team, soon to expand to seven, inhabits facilities within the heart of the UK’s high-tech racing community and still undertakes some of its work for F1 teams.
“We’ve all had about 20 years in Formula 1,” says design director Tim Robathan, who has seen the business of F1 change a great deal during that time. “These days, it can be restrictive to pioneer new ideas in the way we did in the past; so while maintaining an F1 exposure, we want to take the technology and mind set into other places.”
Formula 1 has, for some years, been developing expertise working with constructions made of carbon fibre.
“We believe that carbon fibre is now to the automotive industry what aluminium was a few years ago” states Robathan, who recognised that it would become the material of choice for performance cars – if not yet for mainstream cars. The automotive industries, he notes, “prefer dry cloth without resin on it” – in other words, fabrication by resin transfer moulding, without the time-consuming need to use autoclaves for curing.
One of the big technical challenges was preventing the fibre weaving patterns from showing through paint finishes.
“Paint manufacturers have put a lot of time and work into better paint finishes”, he adds, and there is also ongoing research on using chemical vapour deposition to create a smooth surface that could be used as a substrate to produce a smooth paint finish. This, he states, is a technique that’s already quite common for generating smooth, polished surfaces on rapid prototyped parts.
Meanwhile the latest designs of Formula 1 monocoques – which typically incorporate 6mm of aramid fibres on the outsides to prevent penetration of the driver compartment during a high speed crash – are finding other commercial outlets. Politicians and the very rich, for example, figure high on the list of those who want to be able to drive around in armoured limousines that still fall within European emissions regulations.
But while carbon fibre composites are immensely strong, they do not function well as recipients of screws or supports for gearbox shafts, and so optimum constructions often turn out to be combinations of composites and metal inserts. The ideas are not at all new in F1, even if they are not much used elsewhere as yet. Robathan describes how, when working in a previous employment in the 1990s, the technology was applied to steering columns. The composite plies were blown into female moulds, with metal inserts wrapped in film adhesives at the top and bottom.
“We achieved good weight savings and stiffness gains, crucial to centre of gravity and driver feel. Typically, they had been made of steel and titanium before that,” he says.
Wrapping metal parts in film adhesives is appropriate for bonding to composite constructions that are to be autoclave cured. If the composite construction is to be made by resin transfer moulding – increasingly popular in mainstream automotive manufacture due to its higher production speeds – the bonding medium might well be epoxy adhesive ideally, spread as a film only 0.25mm thick.
Specialist suppliers make the film adhesives, with managing director Paul White citing 3M, Cytec, Hercules and Advanced Composites Group.
As for using metal matrix composites for the metal parts in F1, Robathan says: “I have always regarded MMCs as titanium replacements.”
While stiff and very strong, he points out, they are relatively difficult to machine, notch sensitive and lead to differential wear problems – to which Paul White adds that they are also as light as aluminium, but strong as titanium, with very low coefficients of expansion.
Looking to the future, Robathan states: “We have worked with Tier 1 suppliers to Airbus on their new carbon fibre projects – it’s composites on a biblical scale.”
He explains that, at first, aircraft companies thought that making composite airliners would mean working in the same way as before, but using different materials. However, they are now coming to realise that making best uses of composites means completely re-thinking designs and production methods. For example, he asks: “Does a composite wing really need a wing spar? Could it not best be made as a sandwich construction, with a section making filling, rather than post bonding on the structure – as is the case with aluminium?”
XF1Tech are also very much into rapid manufacturing, particularly Windform XT, which is a carbon and nylon powder mix, developed by CRP Technology in Modena, Italy, for Selective Laser Sintering. Robathan accepts that the technology has its limitations, but is okay for making lightly loaded parts.
He adds: “We think there is a bigger potential for rapid manufacturing metal sintering”, citing electron and laser beam melting machines. He also comments that there is not yet a metal matrix composite powder yet.
He also sees a big future for an idea that has been described in Eureka in the past, but which has still not made it into the world of production – namely to make products from powders whose composition varies across the width of the component. He points out that metals, adhesives and carbon fibre all have different levels of stiffness that, when metals and composite are combined, can lead to failures in the adhesive. He feels that a much better way would be to “play with the metal properties”, so the stiffnesses are the same on each side of the interface between metal and composite.
“There is a good opportunity to be had there,” he concludes.
Pointers
* Carbon fibre composites can be combined with metal parts, including those made of metal matrix composites, in order to support screw fixings, shaft bearing supports and other localised loads
* Film adhesives are best, if the carbon fibre element is to be autoclave cured, but epoxy films are best in combination with low-temperature resin transfer moulding.
* New technologies and materials are constantly being developed, especially as regards rapid manufacturing
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Author
Tom Shelley
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