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High-strength steels leading the race to lighten autos

Dec 31, 2013 | 08:00 PM | Anna Andrianova

Tags  Steel, high-strength, automotive, corporate average fuel economy, SMDI, Larry Sak, Ronald Krupitzer, Shawn Morgans Anna Andrianova

Pressure is building on automakers to make vehicles lighter. Federal regulations mandating improved fuel economy present automakers with the difficult task of cutting weight without sacrificing strength or safety.

“The new Cafe (corporate average fuel economy) law requires car companies to double their miles per gallon, or fuel economy, between now and 2025,” said Ronald P. Krupitzer, vice president of automotive applications at the Steel Market Development Institute (SMDI). That means automakers have to improve very aggressively—about 4 to 5 percent per year.

“Weight reduction is a very high priority and steel is about 60 percent of an average North American vehicle,” Krupitzer said. And while aluminum and plastic companies also are looking at ways to help automakers, steel companies have been working with the auto industry for 100 years and have sped up all their research projects.

SMDI has been working on a three-year project—FutureSteelVehicle—that developed a steel-intensive design for electrified vehicles that reduces the body mass by 39 percent using 97 percent high-strength and advanced high-strength steel grades. The new advanced grades of steel don’t change the metal density or weight, but their high strength allows parts to be thinner and lighter, Krupitzer said.

 In December, SMDI published the results of its lightweight steel twist beam study. It selected the “U-beam” design, which is based on a tubular shape using advanced steels. The project achieved a 30-percent mass reduction, and although the design came with a 15-percent increase in price, that is less than the cost of similar weight savings from materials like aluminum, SMDI said.

“The lightweight steel twist beam project is a great example of how currently available advanced steel technologies enable aggressive weight savings in the vehicle’s suspension, thus enabling better fuel economy for the automaker and the consumer,” Krupitzer said in a statement.

“Clearly there is a lot of pressure on all the automakers,” said Larry Sak, senior manager of materials, fasteners and material standards at Chrysler Group LLC. “We are trying to make cars lighter,” one of the key enablers that the Auburn Hills, Mich.-based automaker is looking at to meet the tougher fuel economy standards.

“Customers have really grown accustomed to certain extra features in cars that add weight,” Sak said. Some of the features are safety-driven, while others are conveniences—such as seat heaters and entertainment systems—that customers are now used to.

“We certainly have been shifting to the new grades—the advanced high-strength steels,” Sak said. But the new grades present challenges as well because they react differently to force or process differently—he said he has seen issues when panels made with the new grades split—and Chrysler has been doing a lot of work to overcome those issues.

Chrysler will use different materials in the future—maybe a combination of materials, including aluminum, magnesium and high-strength steels. Management always considers what makes sense at the moment, and for now steel will continue being a big part of production, Sak said. The whole infrastructure is set up for steel and it will be timely and costly to jump to another material.

Chrysler, in collaboration with Dearborn, Mich.-based Ford Motor Co., Detroit-based General Motors Co. and the Auto/Steel Partnership, last year started working on a four-year project called Integrated Computational Materials Engineering Approach to Development of Lightweight, Third-Generation Advanced High-Strength Steels. As a part of the project, which received a $6-million award from the U.S. Energy Department, the automakers are working on computer modeling tools to work out some of the material’s issues virtually while simulating welding and forming before moving a particular advanced grade into production.

Automakers already use advanced high-strength steels, but the collaborative project aims at creating a product that is high-strength, ductile and uses existing conventional infrastructure. “Advanced high-strength steels have demonstrated significant potential for increased vehicle lightweighting,” Lou Hector Jr., General Motors technical fellow and technical program leader on the project, said in a statement. “Since our existing infrastructure is built around conventional steels, it is critical to develop advanced steel grades that can be formed utilizing this very same infrastructure, thus reducing major overhauls of the manufacturing process.”

Currently, the cold-forming process is widely used for advanced high-strength steel, but in recent years more automakers and their suppliers have tried the hot-stamping process, said Shawn Morgans, body structures technical leader at Ford. “If you look at the industry trend, there are a lot more hot-stamp parts out there than there have been in the past,” and the demand for hot stamping is growing faster than capacity.

Hot stamping is especially valuable for components with complicated geometry and those that require extremely high strength, but the process has a big drawback—it costs significantly more than the traditional process, Morgans said.

“There is a lot of promise in what the steel companies call a third generation of advanced high-strength steel,” he said. The preliminary properties are very attractive, but all of it is still in the works, and while it may come to fruition in 2018, Ford is designing cars for 2018 now and has to use the materials that are available currently.

Ford is trying to move away from pricey hot stamping and use other processes, including hydro forming for its body structures, or other materials, such as carbon fiber. But it is not easy to find a way to reduce mass in a cost-effective way, Morgans said. Ford’s vehicles don’t carry a big margin, and it is not easy to justify switching to another material when the infrastructure is set for steel, he said.

It is easier to reach the weight-reduction goal for a smaller car, but Ford has a lot of large cars, Morgans said, which makes it harder to compete with automakers with an assortment of smaller cars.

Automakers can make vehicles smaller or lighter, but consumers don’t necessarily want to drive smaller cars, said Blake Zuidema, director of product applications for Luxembourg-based steelmaker ArcelorMittal SA. “We are very aware of the challenges the automotive industry is facing right now. The pressure is really to make today’s vehicles lighter (but) maintain the size and utility as much as possible.”

ArcelorMittal’s specialists spend a lot of time looking at metal properties and how components interact with each other, passing along that information to a product development team that works on a new grade of steel with unique and specific properties for each vehicle part, Zuidema said, whereas a few decades ago they used to create new grades and then look for applications.

Everybody in the industry is working hard to find new ways to meet the tougher fuel economy regulations, he said.

“I don’t see, as we go forward, it getting easier,” Morgans said. “I think mass is going to be a major issue because fuel consumption has got to be reduced.”

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