The continued emphasis on reducing emissions and improving fuel efficiency and performance has kept lightweighting – reducing the mass of vehicles – high on the agenda of automotive manufacturers.
“Lightweighting gives you better fuel economy and performance – the things a customer is looking for,” says Dr Geraint Williams, project manager in lightweight technologies at Warwick Manufacturing Group (WMG). “With the electrification of engines there’s also a lot of concern regarding ‘range anxiety’ so, whatever type of vehicle you’re looking at, a weight reduction initiative is always welcome.”
Much of the relevant research is around new and alternative lightweight materials. Manufacturers are especially interested in what these can offer in two “hot areas”: chassis and body-in-white.
Kieron Salter, managing director of consultancy KW Special Projects, says: “Lightweighting is a challenge for both these areas, as well as powertrain and other structural components. Any components that were traditionally cast or forged are coming under scrutiny to see if new materials can provide the same level of performance with less weight.”
There are challenges around the introduction of new materials, though, such as cost and manufacturing processes. “Trying to change processes may prove difficult – you can’t just take a part and replace it with a 3D-printed alternative,” says Salter. “You may have to change the whole system. But there’s less risk in introducing new processes when developing a new product.
“Unlike their established competition, emerging manufacturers don’t have the significant capital investment in traditional production infrastructure and are therefore better placed to explore new manufacturing techniques.”
According to the Center for Automotive Research in Michigan, major trends include, surprisingly, an increase in use of high-strength steels for body-in-white structural components. But the center’s research engineer Shashank Modi says: “In general, the larger the reduction in vehicle mass, the less likely conventional steel will be used for both body-in-white and closures”. The center forecasts that, by 2025, most closures, including doors, will be made of aluminium.
Steel is increasingly being replaced by aluminium but that doesn’t mean this lighter material is without its own issues. Professor Carl Perrin, director of the Institute for Advanced Manufacturing and Engineering at Coventry University, explains: “Aluminium has probably been the biggest winner, with all vehicle manufacturers keen to use it more in powertrain, structural components and body panels. The challenge for industry is finding processes that can take this material and still produce parts that offer the same or better performance and do not take part prices through the roof.”
Gear change
Steel will continue to have a role in a variety of forms, says Geraint, such as advanced high strength steel strip grades, as well as low density steel, which is on the horizon. WMG’s Ultran project – in partnership with organisations including Jaguar Land Rover – is working on the development of high-strength gear steels that can carry more load than traditional steel to allow drivetrains to become more compact and lighter.
Then there’s the development of a lightweight steel exhaust that offered a 50% weight saving. Perrin says: “The Prove (Production Readiness of Very Light Exhaust) project for Aston Martin involved designing and testing a lighter prototype exhaust system and secondly developing an innovative production process to overcome the challenges of manufacturing lightweight technology that is productive and competitive.
“Working hand-in-hand with the Institute for Advanced Manufacturing and Engineering and project partner MetLase, Unipart’s Powertrain Application business engineered a lightweight exhaust that offered a 50% weight saving yet still delivered the same durability, acoustic and driving performance as its standard, heavier counterparts. It was fitted to a luxury sports car and tested over 5,000km, which conclusively delivered fuel savings and an improvement in handling.”
We are going to see more diversification in materials used in the automotive sector, as Dr Remi Zante, senior technology officer at the University of Strathclyde’s Advanced Forming Research Centre, explains. “Not only will we see the introduction of different metal types, such as aluminium, steel and magnesium, there’ll also be a greater mix of metal grades as they are optimised for each location in the vehicle,” he says.
Bert Suffis, innovation manager at Arpro, says: “Hybrid solutions is a big area for new materials.” Arpro produces a lightweight material used in components for manufacturers including Peugeot and BMW. Suffis adds: “To create a hybrid concept, it is important to start from scratch at the design stage in order to be able to use material in line with the concept. And raw material suppliers need to master the product and also its production to get the best cost savings by reducing assembly steps, the number of parts, post-process steps and extending part life.”
One of the challenges for mixed-material body structures is joining – for example, it’s not possible to attach steel and aluminium with conventional welding owing to melting point differences, although research is being conducted in this area. General Motors recently patented a steel-to-aluminium joining process that’s being used on its Cadillac CT6. Other studies are leaning towards adhesives as being the primary joining tool in mixed-material vehicles.
There is also an interest in using composites, especially at the luxury end of the market, which is helping additive manufacturing to gain traction. Salter says: “One of the huge advantages of using composites is the ability to produce small batches without the need for intensive tooling. Also, additive manufacturing allows for the low-volume production of parts that could never have been achieved profitably using the diecast method.”
Iain Bomphray, chief specialist in lightweight structures at Williams Advanced Engineering, says: “New resin systems are being developed that can be cured very quickly, therefore speeding up manufacture. There are also some innovations around processes to get lots of fibre down quickly.”
Investments in materials design continue to happen. McLaren is working with Sheffield University’s Advanced Manufacturing Research Centre on a composites technology centre to develop a chassis production facility for its new models. And last year Daimler made several innovations in the area of carbon-fibre reinforced polymer (CFRP). Karl-Heinz Füller, head of hybrid materials at Daimler, says: “One example is the Mercedes-AMG S-Class CFRP rear panel. The greatest advance here is the new moulding and hardening process that makes it possible to manufacture complex CFRP components in minutes.
“Another example is the CFRP hybrid struts used in Mercedes-AMG cars such as the Cabriolet and the S-Class. Thanks to an innovative CFRP pultrusion process, carbon fibres and metal can be pultruded in profile form. The composite components, which boast optimised functionality and costs, can now also be economically produced in larger volumes.”
Research is also under way into new applications for lesser-used materials such as titanium and magnesium.
Working with Meridian Lightweight Technologies, Birmingham City University’s Institute of Sustainable Futures is researching magnesium as a potential next phase in automotive lightweighting, as the material is lighter than aluminium by 33% and steel by 75%.
The institute’s development manager Makhan Singh says: “It’s a fascinating material even aside from its great lightweighting properties – it has challenging corrosion behaviour, but it also gives great potential. We’re looking at what can be lightweighted, how to get magnesium parts to low-volume companies, and the recycling of magnesium scrap.”
Recycling potential
Several aluminium grades have been developed to assist in recycling, and Singh is keen to highlight the benefits of magnesium in this area. He says: “If you’ve got a vehicle with a lot of magnesium in it, the depreciation would be less because so much could be recycled. You could crush, re-melt and reproduce it.”
The automotive future is going to be multi-material and it is unlikely that any major component will be left unchanged. Technologies and processes are evolving to improve properties of certain materials once seen as not suitable.
Salter says: “Materials that heal themselves, that change to suit their environment and that have diagnostic capacities are all likely to be seen on vehicles within the next decade. But throughout all this change, the one constant will be the need for safe, cost-effective and sustainable vehicles.”