No Silver Bullet for Lightweighting

Lightweighting struggles will continue to weigh on the industry in the absence of new materials, and any dialing back of the CAFE 2025 goals will have no impact, say panelists.

September 28, 2017

8 Min Read
SGL carbon fiber yarn gets spooled on bobbins
SGL carbon fiber yarn gets spooled on bobbins.

DETROIT – How to get weight out of vehicles that already have been made significantly lighter is a conundrum facing suppliers and automakers alike.

Unfortunately, there is no silver-bullet solution that will make the process easier going forward, say panelists at a Society of Automotive Analysts Lightweighting Summit here.

“It’s unlikely there are any breakthrough materials awaiting discovery,” says Abey Abraham, director-Ducker Worldwide at the conference.

In the face of increasingly stringent global fuel economy and emissions regulations, including in the U.S. where a 54.5-mpg (4.3 L/100 km) fleet fuel-economy bogey is set for 2025, suppliers and automakers already have been able to remove tens – in some cases, hundreds of pounds of mass when creating new vehicles. One or more alternatives to traditional grades of steel – aluminum, magnesium, carbon fiber, and most commonly ultra-high-strength steel – make up a growing percentage of the bodies of most new cars and light trucks in the U.S.

But continuing to put vehicles on a diet to improve economy and emissions is making some industry players lightheaded.

“We can’t turn around next year and make a brand-new version of (an existing vehicle architecture),” says General Motors’ Rob Peckham, technical integration engineer-mass strategy and tool development. Using the Chevy Equinox as an example, he says GM removed nearly 400 lbs. (181 kg) from the vehicle with the latest generation. “We just came up with a brand-new car. Several years later, if you were going to do a facelift, how would you find enough mass to get out 125 lbs. (57 kg), or up to 500 lbs. (227 kg), for SUVs and trucks?”

While Peckham’s question has no easy answers, many panelists say a mixed-materials strategy, and optimizing designs will continue to be the way forward.

By using topology optimization software to determine the most effective load paths, suppliers and automakers are able to remove material that is unnecessary to the structural integrity of even the smallest parts.

Ford’s Shawn Morgans, global manager-systems architectures, says optimization software led his engineers to determine “40% of the material wasn’t serving any purpose” in a small, boxy reinforcement part, designed to transfer load from the outside to the inside of the rocker. “And on a small part that fits in the palm of my hand we took out over a kilogram (2.2 lbs.) of mass per vehicle,” he says. “So it’s the small steps, and the big steps, that are getting us where we need to go.”

For areas where mass cannot be removed, use of steel alternatives will continue to gain ground, panelists says.

Mixing materials is not new – Morgans reminds the crowd the Model T had steel panels, an aluminum hood and a wood frame – but the trend will become more popular, says Abraham. “Mixed materials is really the pathway (to mass reduction),” he says.

Ducker sees aluminum as the fastest-growing automotive material, going from 397 lbs. (180 kg) per vehicle in 2015 to 565 lbs. (256 kg) per vehicle by 2028, when it will comprise 16% of total vehicle weight.

While Ford probably is the automaker most closely associated with aluminum – after famously taking as much as 700 lbs. (318 kg) out of the F-150 pickup by switching from steel to aluminum body panels, others also have been using the durable, lightweight material extensively.

Aluminum has been a popular replacement for steel for hoods but also is being employed in other areas.

While Peckham notes the Equinox, Chevy Malibu and Bolt all have aluminum hoods, the Bolt also has an aluminum liftgate and doors. The Chevy Camaro employs cast aluminum shock towers and both the Bolt and Malibu have select chassis components made of the material.

The fast growth of aluminum should be music to the ears of supplier Novelis, but Gary Gallo, manager-automotive recycling for the aluminum powerhouse, notes the increase isn’t without downsides.

“The aluminum industry has never seen the volume of aluminum-scrap generation that we’re seeing today,” he says, driven by the rapid growth in the use of aluminum for closures.

The scrap, being generated largely by GM, FCA and Toyota and not part of Novelis’ closed-loop recycling program in which Ford and Jaguar Land Rover participate, could put downward pressure on pricing.

“There is no historical reference for what may happen to pricing as a result of that,” Gallo says. “We do believe that scrap sales going forward, that are left to a spot market, will be at significant risk.”

Carbon Fiber Still Too Expensive

As for alternatives to aluminum, some here say carbon fiber – strong, light and corrosion-resistant – is declining in price, but still is too expensive to be a viable alternative to steel.

Even early adopter BMW, which operates with supplier SGL a carbon fiber plant in Moses Lake, WA, to supply the i3 and i8 electric cars, has limited use of the material in some of its redesigned, higher-volume models, including the 5-Series, to increase their profitability.

BMW’s Florian Schek, head of lightweight design and vehicle weight, told an industry conference in August: “The cost (of carbon fiber) is still too high, and it’s a difficult technology.”

However, Ducker’s Abraham notes the cost of carbon-fiber composites is coming down, now 16 times the price of steel compared with 60 times the price of steel for aerospace grades of carbon fiber.

Aluminum as well as magnesium is seeing increased use in die-cast parts, says Morgans, who notes die-casting is an increasingly popular means to reduce the number of pieces in a given part.

Through use of die-casting, shock towers, typically multi-piece stamped designs, can be made singular.

Die-casting shock towers “offers a lot of advantages,” he says. “You get rid of all the joints, you get rid of any redundant material. And the other thing the casting allows is, you can tune that part in by putting ribs where you need it. And again you’ve got more control over the thickness and variation in your walls as opposed to stampings.”

Despite the growing popularity of new materials, steel continues to make up the vast majority of body and frame content.

“We’ll continue to build steel vehicles. I do not doubt that at all,” says Morgans, noting Ford is seeking the strongest grades of materials it can find.

Blake Zuidema, director-automotive products application for ArcelorMittal, promotes third-generation steels, such as his company’s Fortiform ultra-high-strength steel, as having the lighter weight and higher ductility automakers and suppliers want.

“The third-generation steels, whether it’s the Fortiform or the Fortiform S, provide a lot more ductility at a similar strength level (to second-generation steels),” he says. Fortiform S is in development at ArcelorMittal and has more ductility, the ability to stretch without breaking, than do traditional dual-phase steels.

Using the example of a front-motor compartment rail, Zuidema says third-generation steel can reduce weight about 10% but maintain the same level of formability.

Front rails and rear rails, which must absorb energy in front and rear collisions, as well as rockers and lower parts of B-pillars, which need to deform in side impacts, are the likely first candidates for third-gen steel, he says, adding some rear roof rails also could be candidates.

Beyond the usual suspects, Abraham says glass/glazing, coatings and interior components are the next areas from which weight will have to be removed.

The panelists say neither the midterm review of the 2025 CAFE standard nor the predicted coming of autonomous vehicles are derailing their march toward developing lighter, more efficient vehicles.

On the topic of CAFE, all say any possible change as a result of the midterm review, expected to be completed in April, is irrelevant given even developing countries, such as India, are toughening fuel-economy and emissions standards.

“I don’t think it really changes what we do,” Morgans says. “We’re producing vehicles for the global market. A lot of those vehicles get produced in the same plants. To manage the complexity that would be introduced if we did a different vehicle for each market, it’s too cumbersome to deal with.”

Zuidema agrees, adding the challenges of lightweighting are going on unmitigated around the world. “Frankly, we’re not really changing our strategy on the basis of the outcome (of the review),” he says.

Zuidema also says he is unconvinced autonomy will bring about accident-free transportation and therefore believes steel will be necessary to maintain the crashworthiness of the vehicle body.

“If you drive in Michigan in the winter time, you know all the sensors in the world don’t work if they’re covered with snow. All of the equipment in the world doesn’t help when the roads turn to ice.

“So in these situations, where technology is going to completely fail, you want a safe car,” he continues. “The crashworthiness has to be there, and under those circumstances all of the requirements of today are still going to be there in the foreseeable future.”

Stiffness will become more critical in later generations of autonomous vehicles, he says, as some models may use suicide doors that necessitate removal of the B-pillar.

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