The automotive industry is investing heavily in R&D to make vehicles more fuel efficient, improve performance and make them lighter. There is an unending quest by OEMs and suppliers to find ever lighter materials in automotive production. However, lightweighting strategies involve a combination of substitution of materials, innovation in manufacturing process and component design. Lightweighting also aims to make vehicles greener by reducing emissions without any compromise on safety.
Today, several advanced materials are being considered for almost all parts of the vehicle. Aluminium, plastics, high-tensile steel, titanium alloys, carbon fibres, polymer composites, amongst others, are replacing components made from cast iron and conventional steel. Most OEMs are considering steel for key body structures, body panels and body frame end modules. The use of carbon fibre composites has made its way into body panels but it’s mainly the automakers in North America and Europe who are considering carbon fibres in body structures, whereas OEMs in Asia are looking at carbon fibres primarily for interior applications. Aluminium and magnesium and titanium alloys are also widely being considered across small body parts, powertrain and chassis in North America, Europe and Asia.
Advanced and ultra-high strength steels
Application of advanced high-strength steel (AHSS) and ultra high-strength steel (UHSS) can make vehicles stronger to protect the cockpit and passengers in the event of crash. According to the Office of Energy Efficiency & Renewable Energy, AHSS could reduce component weight by up to 25%. OEMs and suppliers have used AHSS and UHSS to produce components which are critical for safety. This has helped them to reduce fuel consumption and meet CO2 emissions as an effect of the reduced weight. Both UHSS and AHSS steel are being considered beyond today’s use in Body In White (BIW). Even in applications which are weight-sensitive, steel is preferred over aluminium. For example, BMW has found that CO2 reduction of 10-15g/km can be achieved for each 100kg (220lbs) of weight reduced and by using high-strength steels (HSS), weight reduction of 20% can be achieved.
Steel companies are actively involving themselves in HSS, with many exploring savings of additional 2%. UHSS comes at high cost per tonne (approximately US$250-US$300) compared to conventional steel grades, but as less material is used for making the part or component, these are widely gaining popularity as a cost effective alternative. Also, with established manufacturing infrastructure for steel (welding and stamping machines) OEMs and suppliers are in no rush to invest in replacements.
During the last decade, OEMs’ use of aluminium has grown exponentially across the entire spectrum of the automotive component value chain. Today, aluminium is widely recognised as the best alternative to steel due to the emphasis on fuel economy, carbon footprint by both consumers and industry as a whole. According to a study by Ducker Worldwide, the use of aluminium by OEMs is expected to grow from an average of 147kg per vehicle in 2008 to 249kg by 2025, saving 81-92kg of direct kerb weight and 35kg of secondary kerb weight. For example, Ford reduced the weight of its F-150 truck by 318kg by replacing the vehicle’s steel body panels with aluminium sheet metal.
Using aluminium is not very different from steel in terms of designing. Vehicle manufacturers have used aluminium in engine cradles, rear axle sub frames, suspension parts and body shells, and have launched models with all-aluminium bodies. For example, the third-generation Range Rover weighs an impressive 20% less than its predecessor, and its aluminium monocoque is reported to be 39% lighter. Bentley also uses aluminium in its bodywork, engines, sub frames, and wheels. In short, aluminium has enabled the new cars to be bigger, cleaner and crucially, lighter.
Although the alloy has been around as a structural material in the aerospace industry for years, OEMs have had trouble combining aluminium with other metals. Currently, spot welding is the most prevalent robotised joining method used in the industry and riveting and adhesives are being used for joining aluminium sheets. With improvements and adoption in joining technologies, we should hopefully be able to join aluminium with steel, composites and even to plastics in the years ahead.
Another problem that looms around the use of aluminium is in recycling. A few OEMs have collaborated and built a closed loop ecosystem for recycling aluminium. The entire automotive ecosystem still needs to evolve to recycle its own scrap, something which could turn out to be an expensive affair.
Carbon fibre composites
While HSS and aluminium have their own benefits, carbon fibre (CF) composites may have a larger chunk to contribute in reducing the weight of a vehicle. However, the cost at which it can be done continues to pose a major challenge.
While on one hand, the share of carbon fibre has been increasing in the aviation industry (mainly driven by reduction in fuel costs and an intent to increase the number of people and goods carried by a flight), its usage in automotive applications has been restricted to passenger enclosures, hoods, frames, and interior panels. While premium OEMs have been using carbon fibres to reduce weight in high performance cars to improve efficiency, the cost of input and processing of the material, along with complicated recycling of the material, makes it less attractive for mass produced cars. Resistance and rigidity of the material are also a disadvantage, which is more likely to deform it more quickly rather than absorb energy during collisions.
Other advanced materials (titanium alloys, Ni-based alloys, metal matrix composites)
Research into advanced materials like titanium alloys, Ni-based alloys and metal matrix composites has shown that these materials have unique properties that cannot be achieved by other materials such as aluminium, steel or composites. This makes them ideal for use in engine and transmission parts. With most of the research into these materials (still in powder form) restricted to research labs, there is limited commercial capability for mass production of parts made from these advanced materials.
Challenge ahead – commitment to the right material
Vehicle manufacturing today consists of using a mixture of different set of materials within the body structure. The challenge of joining these materials implies OEMs have to think long and hard before switching to these lightweight materials. Companies have to invest in new technologies and machinery – a double-edged sword to effectively integrate these materials into already existing manufacturing process and value chain. On the one hand, there is growing resistance to new capital investment amid ongoing economic uncertainty. On the other hand, evolving industry trends such as improved fuel economy and emission controls with a greater focus on environment make it imperative for the use of lightweight materials.
The automotive industry also has to leverage learnings from the aviation industry to improve its adoption of advanced materials. There is a huge learning curve for industry stakeholders to understand crash simulation, material
failure mechanisms, assembly technologies, engineering and knowledge of composite designs. OEMs also need to understand sustainability of repair costs and vehicle life cycle assessments to determine the benefits of these advanced materials.
While OEMs are investing in R&D with producers of steel, aluminium and other materials, they must also collaborate with suppliers to maximise the opportunity for usage of these lightweight alternatives. While high strength steels and aluminium seem to be the best alternatives in current scenarios, efforts to find their replacements should never stop.