Automotive Design and Production

MAY 2014

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p The Cadillac ATS has a low curb weight that's a result of careful component-level design, as well as the use of high-strength steels. among the lightest sedans in its competitive set. The average strength of the steel in Cadillac's smallest sedan is in the range of 410 MPa. While steel developments continue—not only incrementally, as has been the case for years, but even fundamentally, as the steel makers begin to work hard even at the microstructure levels—Anderson observes, "Ford has made a revolutionary change with the shift to aluminum, but will others accept an equally revolutionary change with steel?" Says Krupitzer: "We're trying to get one or more of the OEMs to make an optimized steel pickup to go against the 2015 F-150. Companies like Toyota, Nissan and Honda all see the overall cost beneft in using steel to its ultimate, while some companies seem to be oddly frustrated with the incremental change as each new steel arrives." What Krupitzer and Anderson suspect is that there's insufcient appreciation for the fact that aluminum gets its strength via lower density, while steel does the same through stronger, thinner-gauge materials. This has led steel makers to invest heavily in computer- aided design and engineering. "Varying the architecture for greater efciency," says Krupitzer, "brought us to topology optimization; looking at the package space, subtracting that away, and optimizing the remaining structure. This results in some very interesting solutions that are quite efective. Even though the gauge is thinner, we use the geometry to restore or enhance stifness." This has resulted in what he describes as the front primary load path "elephant nose" structure of the Future Steel Vehicle that the WorldAutoSteel organization ( worldautosteel. org ) developed to show the possibilities that can be achieved with steel, and roof bows that travel diagonally instead of laterally from span-to-span. This is combined with weld bonding—welding and gluing panels at the same time—in order to get a continuous join that is many times less expensive than laser joining. Speaking of the Future Steel Vehicle's develop- ment, Anderson points out, "These modeling and computer tools, etc. are applicable to all OEM designs and materials, and those material providers would gain from the same clean- sheet approach and topology optimization we have used with our advanced steels." However, whereas aluminum still uses the same 5000 and 6000 series alloys they've traditionally ofered to both automotive and military users for years (Krupitzer likens referring to the alloys used in the 2015 F-150 as "military grade" in the Ford press release to the fshing industry's renaming of the Patagonian toothfsh as "Chilean Sea Bass"), steel potentially has more to ofer on the materials front. "Our current portfolio includes 45 advanced high-strength steels, and approximately 19 manufacturing techniques like roll-forming, tailor-rolled blanks and hydroforming that other materials can't match. And we don't need fve years to build extra capacity. We have it in place now." AD&P; > May 2014 > FEATURE > Steeling for Battle > Christopher A. Sawyer 32 0514ADP FEATURE Steel.indd 32 4/22/2014 1:32:31 PM

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