While lightweighting will remain an important element to the design of electrified vehicles, improvements to battery technology are expected to have a greater impact on driving range. As such, a focus on cost-efficiency could see a change in preference for body structure materials, with additional weight savings afforded by more exotic materials no longer warranting their premium to the same degree.
For example, elements of an electric vehicle (EV) that have more recently been constructed with aluminium for weight saving purposes – such as doors, wheels and the body-in-white (BIW) – could be monopolised by steel for mass market platforms.
The argument follows a steady trend by automakers to closely integrate e-mobility into their future strategies, with electrified vehicles no longer residing as just a premium option.
In July 2017, Volvo Cars stated that from 2019 the brand would go ‘all electric’, and was one of the first major steps to embrace e-mobility across an entire portfolio. This was admittedly a widely misinterpreted statement, which suggested that all future vehicles would be fully electric. In fact, all new Volvo cars would simply feature electrification of some sort, and thus most are still likely to carry an ICE. Three fully electric Volvo models and two fully electric Polestar models will launch between 2019 and 2021.
Following the fallout of the dieselgate scandal, Volkswagen too directed its focus toward EV leadership, and in February 2018 established a dedicated e-mobility division. It has also been developing the Modular Electrification Toolkit (MEB) – a scalable platform designed specifically for mass market EVs. Various other automakers have made similar moves, with Hyundai and the Renault-Nissan-Mitsubishi Alliance also making prominent steps to develop battery electric solutions. Then there are automakers that have built their entire business around the electrified and fully electric powertrain, such as BYD and Tesla respectively.
With the higher weight of the batteries we foresee more advanced high strength steel solutions – and in particular hot stamping – in the underbody structure
“The arrival of EVs is confirmed for coming years, and we see this impacting the pipeline of BIW architecture,” observed Jean-Martin Van der Hoeven, Chief Marketing Officer, Global Automotive & Mobility Solutions at ArcelorMittal. One of the largest steel producers globally, the company projects that by 2025 roughly 50% of the European new car market will consist of electrified vehicles, which include mild hybrids, full hybrids – such as those popularised by Toyota – plug-in hybrids, and battery electric vehicles (BEVs).
For all plug-in vehicles, there are a number of challenges facing automakers, namely range and charging efficiency. ArcelorMittal believes improvements to battery technology could reduce the emphasis placed on lightweighting, and instead direct automakers to utilise materials that offer the most cost efficient solution for the vehicle structure. Those body structures may also be designed to house various electrified powertrains for the same reason.
The challenge facing automakers
Regulatory pressure is forcing the industry to make significantly cleaner vehicles. Current targets from the European Commission require automakers to meet a fleet average of 95g CO2/km by 2025, with proposals for a further cut to 66g C02/km by 2030. In China, the current new energy vehicle (NEV) mandate rewards manufacturers for producing electrified vehicles, and penalises those that fail to meet an NEV score of 10% in 2019, and 12% in 2020.
The industry has found this compliance a challenge, and many of the cleanest combustion engines today struggle to get below 100g CO2/km. Mild hybrids can improve figures to somewhere between 80-90g CO2/km, but in order to achieve 66g CO2/km and below, plug-in hybrids and BEVs are deemed necessary. “With an internal combustion engine, you can only get your CO2 emissions down to a certain level before you have to start electrifying the engine,” commented Nick Molden, Chief Executive of Emissions Analytics. “The CO2 dynamic will be the strongest thing to push manufacturers toward EVs.”
The arrival of EVs is confirmed for coming years, and we see this impacting the pipeline of BIW architecture
The UK government recently introduced an online vehicle check that lists official CO2 emissions for ‘newer’ cars that have hit the market over the last five years or so. The 2018 Audi A3, fitted with a 2.0-litre gasoline engine, can emit between 128g and 156g CO2/km depending on the power rating, transmission and body style. By comparison, the 2017 gasoline plug-in hybrid A3 has an official CO2 emissions rating of just 38g/km, according to the online checker. “There is no other option than to have a certain minimum percentage of PHEVs or BEVs in the fleet to meet these CO2 numbers,” said Van der Hoeven.
The multi-energy platform
A wide variety of products fall under the umbrella term of ‘electrified vehicles’, and accurately forecasting how both consumer demand and automaker strategy will accommodate these powertrains is a tall order. Van der Hoeven predicts a ‘one platform fits all’ solution for new energy vehicles. “It will be very difficult to see how the market develops in the coming years,” he said. “We know that various options are available, and believe this will lead to a mainstream solution for the BIW architecture known in the industry as the ‘multi-energy platform’.”
‘Multi-energy’ is a phrase used by various stakeholders in the industry, most notably Citroen and Opel under the wider PSA Group strategy for flexible electrified vehicle platforms. A multi-energy platform accommodates the full range of electrified powertrains: anything from a 48-volt mild hybrid to a pure BEV. A tunnel in the underbody structure caters for both the ICE and its driveline, but also for the battery packs of an EV or PHEV. However, due to the weight of these batteries, the gravity point of the BIW is lowered, and the underbody structure must be redesigned to optimise crash safety.
“With the higher weight of the batteries we foresee more advanced high strength steel solutions – and in particular hot stamping – in the underbody structure,” explained Van der Hoeven. “It also probably leads to a situation where, due to the higher weight of the underbody structure, you need to reinforce the wheels and chassis.”
While such examples are scarce today, Van der Hoeven is confident that automakers will reconsider steel wheels as a primary option on mass market EVs in order to keep costs to a minimum. This again depends on the continued improvement of battery technology, which takes some of the pressure away from lightweighting. “There are some very attractive steel designs for wheels, which can easily compete with the beauty of aluminium,” he said. “You may see that aluminium wheels turn back to steel for passenger cars.”
ArcelorMittal believes that BIW solutions will utilise higher volumes of steel in future as OEMs weigh up the benefits of either buying more advanced batteries, or instead paying for more complex lightweighting strategies. Van der Hoeven suggests that as the dollar per kilowatt hour cost of a battery pack falls in coming years, extremely light materials such as carbon fibre reinforced plastic (CFRP) and aluminium are likely to fall out of favour. Steel, he says, is an attractive option for mass-market platforms.
With the arrival of more efficient batteries, weight saving to improve electric driving range will become less important. This means that efficient steel solutions are in, and aluminium and carbon fibre are out
“When considering the cost of materials for a pure BEV, carbon fibre is totally out of the picture, because the cost is US$15 per kilogram of weight saved. Aluminium is also out because the cost is US$5/kg, but steel is still in because it is about US$2.5/kg,” he explained. “With the arrival of more efficient batteries, weight saving to improve electric driving range will become less important. This means that efficient steel solutions are in, and aluminium and carbon fibre are out.”
Numerous reports suggest that the next generation BMW i3 is set to return to a steel-intensive design under the guise of the iX1, a similarly sized five-door crossover EV. The Volkswagen ID hatchback, slated to enter production in 2019, will be based on the brand’s new MEB architecture with a mix of steel, aluminium and magnesium. The Tesla Model 3 also features a steel-intensive body structure in contrast to the primarily aluminium Model S. “This is interesting because given the CO2 challenges facing ICEs, some of the exposed panels in premium vehicles have been aluminium in order to save additional weight. But with the EV, they will be going back to steel,” observed Van der Hoeven. “Steel has a strong outlook for years to come.”
It is worth noting, however, that current plans do not suggest a unanimous shift toward steel-based EVs; the NIO ES8, a seven-seat electric SUV for the Chinese market will feature an aluminium-intensive body, for example. The current Hyundai Ioniq platform, which is offered with both hybrid and EV powertrains, features an aluminium and steel body structure.
“For the next eight to ten years, CO2 emissions will remain an important consideration, especially when ICEs make up a significant part of the vehicle parc, be it via a mild hybrid or a PHEV,” concluded Van der Hoeven. “OEMs will strive to have the most efficient BIW architecture in terms of weight saving at the most affordable cost – that pushes us into a direction where the development of steel solutions will accelerate.”
This article appeared in the Q4 2018 issue of M:bility | Magazine. Follow this link to download the full issue