Jaguar Land Rover describes itself as a world leader in aluminium car body construction. JLR has used aluminium body structures in the all-new Range Rover, Range Rover Sport, Jaguar F-Type and the XJ – and in 2016, the OEM is expected to launch its tenth aluminium-bodied car. “The use of aluminium in an automotive application brings many benefits in terms of weight savings, improved fuel efficiency, lower emissions, increased crash safety and even better vehicle dynamics,” says the company on its website.
Lightweighting is crucial for performance, as well as for meeting fuel economy and CO2 targets, explains Dr Mark White, Chief Technical Specialist, Complete Body at Jaguar Land Rover. Here, White discusses the OEM’s use of aluminium, and outlines how a successful automotive lightweighting strategy hinges on efficient design and the use of the right material in the right place.
Body systems – half the vehicle weight
The body system accounts for nearly half of a vehicle’s weight, explains White. The body system includes the crash structure, all closures, sheet metal, exterior trim, doors, hood, tailgate, bumper systems, grilles and lights. Also included are interior systems like seats, instrument panel, trim, climate control and glass.
The chassis is the next biggest contributor, accounting for around 25%, followed by powertrain and electrical systems. Although the latter currently accounts for only around 5% of the total vehicle weight, the growth of in-vehicle infotainment is increasing that figure. “We’re asking for infotainment and wiring to remain weight-neutral,” says White, “while body, powertrain and chassis, amongst others, try to save weight.”
We only saved 200kg on the Range Rover body structure, but we managed to take another 200kg out of related weight saves
Secondary weight saving
Weight saving has a knock-on effect: a lighter vehicle can be powered by a smaller engine, meaning smaller brakes. A smaller engine delivers better fuel economy, meaning a smaller fuel tank. “A litre of fuel weighs about a kilo. If you can reduce the tank by ten litres, because you can maintain the same vehicle range with a more efficient engine as a result of the lightweight body systems, you get what we call secondary weight saving.”
Such secondary weight savings were exemplified in the Range Rover, unveiled in 2012 and launched in 2013. Weighing in at 420kg (926lbs) lighter than the previous generation, less than half of that weight was saved in the body structure. “We only saved 200kg on the Range Rover body structure, but we managed to take another 200kg out of related weight saves. More lightweighting in the suspension, and more powerful and fuel efficient engines meant secondary weight saves like a smaller fuel tank.”
The cost-per-kilo weight save
Crucial to lightweighting is efficient design and the use of the right material in the right place, says White. “When we first started on our aluminium programme, our body sides were 1.5mm thick. We’re currently at 1.2mm thick. We’ll be launching a next-generation car this year with a body side 1.1mm thick. And we know we can get to 1mm.”
At 1mm, JLR will have reduced the material thickness by 50% through design efficiency. “And that’s by developing the material to get stronger, more formable materials, and looking at optimisation techniques to make sure we’re putting the right material in the right place. We can do the same thing with our body structural castings. Back in 1998, our casting wall thickness was at 4mm. Our latest generation castings are at 2.5mm, and ultimately my goal is to get to 2mm. On smaller castings, I think I can even get to 1.6mm.”
When developing the business case for a new material, White says the aim is to offset any cost increase with an equivalent gain in design efficiency. Were a 10% cost increase for the base material to be offset by a 10% reduction in material thickness, for example, it would be considered cost neutral.
A litre of fuel weighs about a kilo. If you can reduce the tank by ten litres, because you can maintain the same vehicle range with a more efficient engine as a result of the lightweight body systems, you get what we call secondary weight saving
Developing a business case also involves assessing whether a lightweight material like aluminium, carbon fibre, magnesium, or a lightweight plastic, could be used in place of a conventional material. That may come at a cost but as that cannot be passed on to the customer, JLR uses what White calls the cost-per-kilo weight save calculation: “We target between £1 – £3 (US$1.4-US$4.3) per kilo (2.2lbs) of weight saved. We will buy a weight saving if it’s substantial enough for the vehicle, but only up to a limit of about £3/kg.” The goal, he emphasises, is for weight saving to be cost neutral.
Safety and fuel economy..?
Fuel economy and emissions targets require OEMs to reduce vehicle weight, but the lightweighting work is hampered by the need to meet increasingly stringent safety regulations that often require additional equipment – which adds weight. And the addition of crash-related equipment is the principal driver for lightweight materials, says White.
Were the ultimate, non-crashable autonomous car to exist, the money and effort expended on developing crash structures could be spent elsewhere. “But we don’t think that’s going to happen for at least the next decade. In fact, we’re going to continue to put crash structure and both passive and dynamic safety measures into our cars over the next decade. We’ll have advanced braking systems and collision avoidance systems. We’ll have more airbags both inside the car and externally, and we’ll have to find offsets for all of those.”
Aluminium – the easy switch
Asked what choices exist, White suggests that all OEMs begin with steel as a benchmark. “We’ll all explore the high-strength steels and the new high-strength formable steels, but we can’t change the laws of physics. The density of steel cannot change, limiting how much weight save we can get out of steel, and that’s between 5% and 10% of the current component weight. If a component weighs a kilo today in steel, I think the lightest you could get that same component using the latest technology steels would be 0.9 kg.
We will buy a weight saving if it’s substantial enough for the vehicle, but only up to a limit
“We don’t see high-strength steels giving us 20%, 30% or 40% weight savings over conventional steels. Over the last 15 years that we’ve been talking about lightweight steels, we’ve at best stayed static, and in fact most bodies have increased in weight if they’ve remained with steel.
“With aluminium, we think we can get between a 40% and 50% weight save over conventional steel.”
The lightweight alternatives, says White, are essentially aluminium, magnesium and composite material, adding that the easiest switch for a production line is from a steel spot-welded business to an aluminium riveted business. “You can use your press shop, body shop and paint shop, and your trim and final assembly doesn’t even notice the difference. And those are the four key capital investment areas in manufacturing a body today.”
White provides cost and weight context: “If we had a part that weighed a kilo in steel, we could get it to 0.9kg in high-strength steel and to between 0.5kg and 0.6kg in aluminium. By nearly halving the component weight, we’re no longer buying a kilo of material, we’re only buying between 0.5 and 0.6 of a kilo. Aluminium is about double the price of steel, but if you’re only using half of it, then you’re not doubling the price of the component. I’m not going to say we’re absolutely cost neutral, but our goal is to be as close to cost neutral as possible.”
Other material options: magnesium and composites
JLR’s use of magnesium includes front-end carriers, cross-car beams, parts for steering columns and steering armatures. Despite its weight advantage, White lists the considerable challenges that magnesium presents: most of the world’s magnesium is made in China using a coal-intensive process. In addition to the long supply chain and carbon footprint issues, the manufacturing process is dangerous, due to magnesium’s highly volatile nature. Due to its low melting point, magnesium will react with air and water, and thus needs to be coated and used inside the car, away from any thermal or galvanic risk. Furthermore, it cannot easily be joined to other materials, or even to itself. As a result, it requires bolting and bonding rather than welding.
With aluminium, we think we can get between a 40% and 50% weight save over conventional steel
Nonetheless, says White, use of magnesium looks likely to increase, particularly for lightweight bolt-on parts. “We could use it for seat structures, and potentially for window frames and decorative trim. But its usage is limited.”
As for carbon fibre, White’s concern is affordability. “I refer to composites rather than carbon fibre, because right now carbon fibre is not affordable. If you asked how much weight I could save if I went to composites instead of steel, a kilo part would only weigh between 0.3 and 0.4 kg. We could get a 60% to 70% weight save versus steel, but that would be at ten times the cost of steel.” And compared to aluminium, says White, carbon fibre would be a third of the weight but ten times the cost, making it at least three times as expensive as aluminium.
The automotive material mix of the future
As a result, White expects to see an increase in the number of aluminium cars on the road between now and 2020, by which time OEMs will have produced at least one generation and, in JLR’s case, at least three generations of aluminium cars.
Beyond 2020, White expects to see a combination of high-strength steels, aluminium and composites on new architectures.
As for what consumers think of the automotive industry’s lightweighting efforts, White chuckles: “I genuinely don’t think the consumer cares. People want more environmentally-friendly cars. We have a corporate responsibility to make our cars are as efficient as possible. But we’ve also got a responsibility to give our customers the cars they want. If we can make cars that are great for the environment, that our customers love, then it doesn’t matter what they’re made from.”
This article is part of an exclusive Automotive World report on lightweighting. Follow this link to download a copy of ‘Special report: Vehicle lightweighting‘
