With government legislation putting vehicle manufacturers and suppliers on a deadline to raise fuel efficiency and lower carbon dioxide emissions, lightweighting technology is taking further strides forward.
Lightweight aluminium bodies and ultra-high strength steels are among a variety of new materials and manufacturing techniques that are enabling the automotive industry to replace traditional parts with lighter alternatives. Until recently, lightweighting technology has struggled to take off in the volume segment, but the launch of the Ford F-150 will see a significant deviation to this trend; its radical aluminium body construction has cut out 700lbs from its the best-selling pick-up.
But it isn’t as simple as hacking away excess bodyfat in the quest for leaner bodies; the challenge continues when it comes to joining these new materials together, as Swamy Kotagiri, Chief Technical Officer at Magna, told Megatrends.
Challenges of joining
One of the challenges of using a variety of lightweight materials is the joining technology, and how to join them together in volume at a speed at which the industry is accustomed. This is why Magna thinks ahead to the manufacturing process before designing, as Kotagiri explains: “I think the most important thing is to have the strategy ahead of time, to define what the different materials, joints and slip planes are going to be and how the vehicle goes together. For example, we could be designing an aluminium body where the important thing would be to look at the different combination of joints, whether it’s a two-metal thickness joint or three-metal thickness joint.
“You may also want to minimise the variety of rivets so that you don’t have 12 different types being handled, for example, and if you have this in mind you can minimise the cost significantly, rather than just design it and then go through the manufacturing process later.”
Legacy constraints are one consideration for Magna, says Kotagiri. Another is corrosion: “Aluminium and steel is one challenge, but if you take it up to the next level which is magnesium and steel, the potential difference is so much more and so the corrosion issues become further magnified.”
Joining techniques driven by lightweighting
Lightweighting, Kotagiri says, will drive new joining techniques as the product is evolving: “For example, friction welding was not as common as it is today, and we have been seeing a lot of one-sided joining methods. With a spot weld you need to have access from both sides, and in the future as you join castings for different types of components you might only need access from one side to join the two materials. There is a big push coming up with different joining methods. I think it will get to a point where it will be as common as how we make steel bodies today.”
The end consumer will not see how the car has been joined or what mechanism has been used. In the end, it comes down to how it feels when they are driving the car, or whether it is “cheaper at the gas station or not,” Kotagiri says.
Material merits
The joining process is defined by which materials are being used, and one of the key things Magna believes is that the three factors of a vehicle’s design, segment and region, will dictate which material is used, with what alloy and in which part. A vehicle with a performance requirement to have a lower centre of gravity or to have a better weight-split between the front and the rear would provide one directive on where materials are used, and how.
“The premium you would pay in this case to have a lightweight roof would be a little bit more than just general lightweighting because we have to keep the centre of gravity down. Obviously there are specific advantages of one material over another, for example one kilogram of aluminium will have so much more energy absorption than steel. But, I don’t think there is an answer to say that one material is best, and that was one of the reasons why we looked at a multimaterial concept for keeping lightweighting in mind.
Multi-Material Lightweight Vehicle concept
Ford and Magna recently unveiled their jointly-developed Multi-Material Lightweight Vehicle (MMLV) concept; the MMLV uses advanced materials to explore future weight-reduction solutions.
“One of the key drivers for us is that we have such a broad base of products we offer in a car,” Kotagiri told Megatrends. “The features in a car are significantly increasing over time, and there is a pressure from the industry to keep weight down. The idea was not to take certain materials as the target to use throughout the vehicle, but to reduce the most weight out of the platform chosen, keeping in mind the premium of parts. Overall we were able to reduce just over 23% weight without reducing performance or durability.”
During the process Magna approached the US Department of Energy, and worked with Ford side-by-side as an OEM partner. Seven prototype vehicles were built, some used as demonstrators and some for durability and crash testing, which they passed.
“We asked the question: Where do we require stiffness, where do we require strength and how do we integrate different components. Based on all of these constraints, we used roughly two-thirds aluminium using casting, extrusion, and tapping. The remaining 33% used different processes of steel; hot stamping, cold stamping and so on. The intention was to pick materials, assembly and forming processes that are available today, and we ended up taking the 2013 Fusion and brought it to the weight of the Fiesta.”
Cost of lightweighting
After a vehicle has been lightened, most of the reduction in weight is then taken up by new features that keep adding themselves to a car, whether it is for comfort, safety or convenience features. Looking at cars from 2010 to the current range, overall vehicle weights have not dropped significantly, Kotagiri comments.
“If you look at the content that cars have now compared to 2010 it is significantly more, so what you’re substituting weight for will define the premium you’re willing to pay. There isn’t an answer to say that lightweighting is cheaper, but the obvious objective is to take away as much weight as you can without adding a premium.”
Varied strategy
Lightweighting is one of a number of possible strategies available to vehicle manufacturers seeking to reduce CO2 emissions. Magna’s broad portfolio of capabilities and its global reach mean it can offer a variety of solutions that include lightweight metals, composites and smart systems; concluding, Kotagiri says he believes it is this which makes Magna more than just a typical Tier 1 supplier.
