Governed by increasingly stringent legislation, vehicle manufacturers have clear objectives when it comes to reducing emissions and improving the efficiency of vehicles. Most companies agree on the notion that these targets will not be met by focusing on one aspect of vehicle development, like aerodynamics or the powertrain, for example. Instead, a holistic approach is necessary, and according to Jean-Luc Thirion, Head of Global R&D for Automotive at ArcelorMittal, lightweighting is a key piece in the puzzle.
Quarter of the whole
When preparing for future fuel economy and emissions regulations, two numbers in particular stand out for OEMs and suppliers: 54.5 and 95.
In the US, the US Department of Transportation (DOT) has proposed a 54.5mpg fuel economy target for 2025, although this is not set in stone and could be subject to change. In Europe, the target is based upon CO2 emissions, the fleet-wide average of which must be lower than 95g/km. This rule will start to be phased in during 2020.
All OEMs have been working towards these targets for a number of years, a fact which Thirion believes has seen lightweighting remain a continuous trend in vehicle development.
“Weight saving is one of the ways of reaching these objectives, but certainly not the only one,” he told Automotive World. “ArcelorMittal thinks that savings in weight will account for roughly 25% of the potential in improving vehicle efficiency and decreasing emissions.”
One of the main issues that we have in saving weight is that when you increase the strength of the material, the steel, you could theoretically deteriorate some key properties, such as joinability
Lightweighting has also become prominent in an increasing number of parts and components. The body-in-white (BIW) – the stage of manufacturing during which the unpainted sheet metal components are welded together to form the vehicle’s body – accounts for around 50% of weight saving potential.
“Increasingly, we are working with OEMs on the chassis, the rolling gear, mechanical units, interior and engine parts,” Thirion noted. “The seats, for example, can utilise high added value steel grades, which can further help to reduce weight. Essentially, reducing the weight of cars must be as comprehensive as possible.”
The process of saving weight in a vehicle involves two main approaches: the elimination of components and the reduction of material mass. The latter is typically achieved through reducing the thickness of the material in question, which for ArcelorMittal is of course steel.
“Reducing the thickness means increasing the tensile strength of the material,” observed Thirion. “This is a trend not just in the development of steel, but also for other materials used in vehicles too, and one of the main issues that we have in saving weight is that when you increase the strength of the material, the steel, you could theoretically deteriorate some key properties, such as joinability.”
He notes that both the formability and joinability of the material could be compromised when reducing thickness and increasing strength. It could also lead to issues with noise, vibration and harshness (NVH). Achieving the right balance between thickness and strength is an on-going part of research and development programmes at ArcelorMittal, said Thirion – but could this cause the cost of the steel to rise?
Control the cost of lightweighting
ArcelorMittal is working with OEMs to “propose solutions that keep the cost of the vehicle very low,” he said. “The idea is to introduce new materials with higher strength and good properties in terms of joining and forming, but it is crucial that the cost of lightweighting remains below €2 (US$2.18) per kilogram (2.2lbs) saved. In contrast, aluminium solutions can mean cost increases of up to €15 per kilogram of weight saved.”
Steel manufacturers can often adapt their plants to integrate new products with relative ease, so the solutions that we propose to customers are generally global in nature, and can allow both OEMs and final consumers to save money
One of the key manufacturing processes promoted by ArcelorMittal is hot stamping, which is used to produce its Usibor UHSS products for bumper beams, reinforcements for doors, A and B-pillars, as well as for parts in the floor and roof of the vehicle.
Replacing conventional cold formed grades with hot stamped parts can reduce the weight of the part by up to 50%, and the process does not cause a significant rise in the price of the end product.
Aside from keeping the cost of the material itself down, Thirion thinks that OEMs can save money as steel has an advantage when it comes to design and production trends in the automotive industry. An increasing number of companies, led by Volvo Cars, Volkswagen and GM, are looking to take advantage of global vehicle platforms. By using a single platform for numerous different models, companies are able to minimise investment from the design process through to vehicle production while maximising profit margins and maintaining a limit on the cost passed on to the consumer.
“When we propose a new solution, it is normally available in many different areas of the world fairly quickly,” said Thirion. “Steel manufacturers can often adapt their plants to integrate new products with relative ease, so the solutions that we propose to customers are generally global in nature, and can allow both OEMs and final consumers to save money.”
The fact that these platforms are global, and the cars using them are sold in different countries across different continents, means that OEMs must be able to obtain a supply of the materials used to construct these platforms. Thirion is adamant that steel has the advantage over alternative materials in this respect.
The melting pot
Essentially, where cost is paramount, Thirion is certain that steel trumps the competition: “Price is a factor on which we are fully convinced of the advantage of steel. We are quite aware that the automotive material mix of the future will be made of several materials, notably aluminium, carbon fibre and magnesium. The key is to determine what proportion the alternative materials will account for, which will be governed by cost.”
Some people imagine that autonomous vehicles might have less of a requirement for passive safety. And some imagine then that strength of material would be less important. However, we are not convinced
Materials like aluminium and carbon fibre are likely to be exclusive to the premium vehicle segment if their cost remains high, Thirion continued. He also thinks that some low volume production models may use these alternative materials. However, there are two main megatrends governing the automotive industry that will allow steel to retain its position over aluminum and carbon fibre in the automotive industry.
Currently the less influential of these two trends is the rise of the autonomous car, which could result in reduced demand for passive safety attributes. “Some people imagine that autonomous vehicles might have less of a requirement for passive safety. And some imagine then that strength of material would be less important,” he admitted.
“However,” he added, “we are not convinced.” Some of the most optimistic predictions suggest that 15% of vehicles on the road in 2030 will have some form of autonomous drive technology. This means that safety regulations could change, but are unlikely to become more lenient. Therefore, protecting passengers using passive safety measures will still be crucial.
“That’s why we don’t think autonomous driving will have a huge impact on the material mix, at least for the foreseeable future,” said Thirion. “In fact, ArcelorMittal predicts that AHSS will make up more than 50% of its automotive sales by 2030, as safety grows in importance. Emerging markets, like India and Brazil for example, could soon become huge consumers of AHSS.”
The second megatrend identified by Thirion is car sharing, and the decrease in vehicle ownership; this, he said, could have a greater impact on material mix. “The car is no longer part of the dream, but is becoming something based upon convenience. Today’s generation is less interested in ownership, but needs to use vehicles to get from A to B, so the cost of the vehicle must come down.”
Switching from steel to an alternative material not only creates a huge level of investment from an OEM point of view, but also causes issues with design. Unlike steel, these materials have not been used extensively in the automotive industry for a century, so the design processes are far slower
Thirion predicts around 10% of cars sold in 2030 will be shared vehicles. To succeed, said Thirion, cost must remain low, and OEMs must use the vehicles to push the boundaries of innovation, making them increasingly intelligent, connected and efficient. Design and development will not slow down, but will “grow at an alarming rate,” and Thirion suggested that this is difficult to do when using materials like carbon fibre and aluminium: “Switching from steel to an alternative material not only creates a huge level of investment from an OEM point of view, but also causes issues with design. Unlike steel, these materials have not been used extensively in the automotive industry for a century, so the design processes are far slower and typically require much more research. That translates to more manpower, more hours and more money.”
With this in mind, he thinks that steel will remain the dominant material of choice in the automotive industry over the next 15 years, accounting for approximately 88% of the material mix.
Demand on the horizon
To keep up with trends like autonomous driving and car sharing, Thirion believes R&D in the steel industry will accelerate, with a new wave of next-generation steels soon to reach the market. He hinted at some new products that ArcelorMittal intends to launch during 2016, and is confident that the company will continue to bring innovative products to market.
Global vehicle production is also set to gain momentum. In 2015, around 87 million vehicles were sold, a figure which some analysts predict will rise to 115 million by 2030. “Cost will become more important than ever as OEMs produce greater numbers of vehicles. The advantages of steel in terms of saving money for OEMs in the vehicle design and production processes, in terms of reducing the price tag and reducing weight to allow consumers to save fuel, will be even more integral to the automotive industry than they are today,” Thirion concluded.
This article is part of an exclusive Automotive World report on lightweighting. Follow this link to download a copy of ‘Special report: Vehicle lightweighting‘