Steely visions of lightweight parts

  • 19-Aug-2009 10:54 EDT
rear diff (aisi).jpg
The cast-iron rear differential case is in a weight-reduction spotlight.

The steel industry is once again on a diet, and the weight-shedding targets include vehicle bulges known as "hang-on" parts.

"We have found that 'hang-on' parts represent our most serious threat because materials can be changed without affecting overall assembly joining methods," said Ron Krupitzer, Vice President of Automotive Applications for the Steel Market Development Institute (SMDI), a business unit of the American Iron and Steel Institute (AISI).

The material options for wheels, fuel tanks, closure panels, and suspension components are plentiful. "One can change the material and simply bolt that new part to the car," he said. With metals and nonmetals vying for application honors, the steel industry is in the midst of putting together a "good case study for choosing steel," according to Krupitzer.

AISI and Auto/Steel Partnership's Lightweight Suspension Project uses an aluminum front lower control arm as its benchmark. When the project wraps in late 2009, steel proponents expect to show that a stamped-steel front lower control arm and a forged-steel front lower control arm can net a 30% cost savings at equivalent weight and performance to an aluminum-made component.

"Suspension components have always been a challenge for steel in terms of lightweighting," said David Anderson, Director of Long Products for the SMDI. Many current vehicles have steel suspension components, but the mild-grade metal is thick and heavy.

Hot-rolled (mild) steel lower control arms typically represent thicknesses greater than 2 mm (0.08 in). "To achieve the weight targets, we will employ advanced high-strength steels (AHSS) with design optimization, and that may result in gauges less than 2.0 mm," said Jody Shaw, Manager of Technical Marketing and Product Research for United States Steel Corp.

AISI is no stranger to projects with a lightweight orientation. In 2000-2001, the UltraLight Steel Auto Suspensions (ULSAS) program focused on the rear suspension. The global initiative resulted in a steel-intensive design with 30% less mass than a conventional steel design equivalent.

"The steel industry, working with our automotive partners, has undertaken the Lightweight Suspension Project to prove that new steels have the potential to save weight, maintain or improve performance requirements, and do it cost-effectively," said Anderson.

Another ongoing project has the steel industry focused on producing near-net shape parts via a precision flow forming process. "Existing equipment can be used for the initial parts, but the operation may require a scaling up of the process for larger parts—such as rear differentials—and for mass production," said Krupitzer.

A 50% weight savings is projected.

"For the initial work, the focus is on front-drive components that weigh approximately 10 lb, so we're targeting a 5-lb weight savings. As the project moves forward, the focus will be on rear-drive components that weigh more and therefore can generate greater weight savings," said Krupitzer.

Linamar Corp. is supplying the prototype equipment for the project that involves AISI member companies, Chrysler Group LLC, Ford Motor Co., and General Motors Co., as well as the U.S. Department of Energy.

Steel industry representatives know that low-density materials are tough competitors. "But we feel that if high-strength steels can provide mass savings within 10 or 11% of that achieved with low-density materials, the lower cost of AHSS compared to those alternatives will encourage more use of AHSS for mass reduction," Krupitzer said.

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