Light is Right: How GM is Slashing Weight from its Cars

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Light is Right: How GM is Slashing Weight from its Cars

Fuel economy is a top priority and automakers are scrambling to reduce consumption. 

We were able to sit down with some GM insiders to get a glimpse at how it is working to lighten its entire product range to increase fuel efficiency.

Hybrid drivetrains, cylinder deactivation, stop-start systems and other technologies can help significantly, but eliminating mass is probably of the best way of boosting fuel economy.

“Every gram is important to find that maximum efficiency,” said Charles Klein, executive director of global CO2 strategy and energy center engineering at GM. This ethos has positively benefited much of this automotive giant’s diverse lineup.

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“The 2017 Malibu is the segment leader,” said Klein, noting that it’s some 300 pounds lighter than its predecessor, but that’s not all. Depending on trim, the Camaro has lost nearly 400 pounds; the 2017 GMC Acadia has shed 700 pounds; even the compact Chevy Cruze is down around 250 pounds.

All of this weight reduction has numerous upsides, including massive reductions in greenhouse gas emissions. Lighter vehicles can also offer more interior space, better safety and enhanced driving dynamics. Other efficiency-enhancing technologies don’t often provide such a broad range of benefits.

SEE ALSO: Why Mazda’s Miata is the Best Green Car

Unfortunately, none of this is easy; if it were, everybody would be doing it. The computer simulation time alone that’s required to optimize vehicle structures is unfathomable. Klein said the new Camaro represents some 9 million hours of number crunching; the Malibu took an extra million beyond that. But this is nothing.

Fifty-million computation hours were spent on the Cadillac CT6 alone, said Klein, time spent optimizing its structure to maximize safety while minimizing mass. But stepping outside the virtual world, there’s also plenty of work to be done.

Foundational Changes

“Structural efficiency is a relentless grind,” said Warren Parsons, chief architect of body structures and a GM Technical Fellow. This is because of the endless number of details they have to sweat while developing an automotive platform.

One would think that maintaining crash resilience while simultaneously reducing mass are mutually exclusive subjects, but with time and effort, they’re not. To deliver the best of all worlds, Parsons said they’re using ever more fancy high-strength steels in their vehicles. Of late, the press-hardened variety has gained notoriety. “The last decade they’ve become prevalent,” he noted.

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GM uses this material in its flagship Cadillac CT6 sedan, which features a mixed-material structure. There’s an abundant amount of aluminum, which saves an appreciable amount of weight, but they’ve worked a mélange of steel into the mix as well.

ALSO SEE: 2016 Cadillac CT6 Review

Aside from providing a rugged safety cage, good, old-fashioned ferrous metal can also help cut noise. Parsons said it was more efficient putting steel in the floor pan of the CT6 than using aluminum, which requires an extra helping of sound-deadener to keep unwanted ruckus at bay.

Welding the Future

Whether it’s Cadillac’s flagship sedan or the new Ford F-150, aluminum is slowly becoming more commonplace in the automotive business. GM is using it in a wide range of its products.

But this lightweight metal can be challenging to work with. Traditionally, it’s messy to weld, more expensive than steel, plus it doesn’t always play nicely with other materials, specifically galvanic corrosion can be a major issue.

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But GM has developed several groundbreaking ways of joining aluminum components together. They can arc weld, braze and even spot-weld them, technologies rival manufactures don’t necessarily have in their arsenals. But the biggest news is how scientists have figures out how to join steel and aluminum, two materials that normally want nothing to do with each other.

Perhaps the biggest hurdle of joining steel and aluminum involves their melting points; the difference between the two is some 900 degrees Centigrade. Aside from this, aluminum forms a very thin layer of oxide on its outer surfaces, which also makes welding a challenge. Finally, if you try to join these dissimilar materials, a glassy intermediate layer forms between them, something that Blair Carlson, lightweight material processing lab group manager, research and development described as being “really brittle” and having limited tensile strength, undesirable traits in an automobile structure.

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Still, researchers at GM have done what others have called impossible, welding steel to aluminum. “Our job is to understand the physics,” explained Carlson, which is exactly what they’ve managed to do, and in record time. Going from an initial idea to feasible prototype only took about two years, he said.

Several steel-aluminum components utilizing this technique will find their way into the Cadillac CT6 very soon, both in seatback assemblies and a hood-support piece.

Techniques like this eliminate the need for rivets. An aluminum-intensive body-in-white could contain as many as 4,000 of these mechanical fasteners, which add around 10 pounds of weight on their own, plus necessitate wider flanges, something that further increases weight.

Injection-Molded Metal

Another way GM is pushing its light-weight agenda involves magnesium, a metal that’s a 30 percent lighter than aluminum.

“We tried to push our research to more developing uses of magnesium,” Dr. Anil Sachdev, light metals systems lab group manager, research and development. And one of the items they’ve created is a unique prototype door structure.

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The innards of a typical automotive door are constructed of multiple steel stampings that are bolted, glued or welded together. Not only is this complicated, but having all of those joints is also an invitation for fitment issues and other problems.

Dr. Sachdev and his team have managed to create an entire door support made completely of injection-molded magnesium. Its benefits are numerous, including being just one piece, offering comparable strength and weighing an astonishing 50 percent less.

These molded frames are also quick and easy to make. “The total cycle time is about 90 seconds,” said Sachdev. “Every second is money,” he added, and simplifying components by using magnesium in this way could save untold dollars down the road.

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Unfortunately, for this technology there’s no clear-cut timeframe for when it could reach the market. Sachdev said, “We just keep the development very active,” though if GM is showing injection-molded magnesium door structures to the press, a market introduction probably isn’t too far off.

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  • Name

    Good write-up. Thanks.