Steel Kickin'

Superman might be worried that he needs a new nickname, judging from today's seemingly endless talk about alternative materials.

But thanks to ongoing innovations from the steel industry, it appears the "Man of Steel" can relax.

Two new engineering studies released in May by a consortium of steel companies - the American Iron and Steel Institute (AISI) - show traditionally "weighty" steel is evolving as a competitive option for designing lighter and safer vehicles.

The UltraLight Steel Auto Suspension (ULSAS) and the UltraLight Steel Auto Closures (ULSAC) are the second and third development efforts from AISI. The consortium sprang forth in the 1990s when it appeared steel would lose ground (actually, per-vehicle weight) to alternative materials as automakers continued to push for improved fuel economy in meeting stricter environmental standards.

The ULSAS and ULSAC reports follow AISI's 1998 UltraLight Steel Auto Body (ULSAB) and precede the ULSAB-Advanced Vehicle Concepts (AVC), due out in 2001. The closure panels and suspension will be integrated in AVC computer models in meeting goals of the Partnership for a New Generation of Vehicles.

Conducted by U.K.-based Lotus Engineering Services Inc., ULSAS focuses on one of steel's traditional strongholds, automotive suspension components - a bastion assaulted by aluminum in the last several years. The study claims mass reductions of up to 34% - importantly, at no additional cost - in four lightweight steel-intensive designs versus traditional steel suspensions. A fifth steel design actually showed a small mass reduction compared with a current aluminum design, with a 30% cost reduction as a bonus.

"There is a misconception that if you move to the higher echelon of steels, there's going to be a cost penalty. That's simply not true," says Peter Rawlinson, ULSAS program director.

Although some studies rely on future technologies, that isn't the case with ULSAS. "This program is doable today," says Nick Sampson, ULSAS technical manager and a Lotus engineer.

Lotus used five standard vehicle classes from every major automotive market to design five different rear suspensions: a traditional twistbeam, a strut-and-links arrangement, double wishbone, a multi-link design and the Lotus Unique concept.

Each one provided mass savings, reduced or didn't raise cost and met or exceeded performance targets. Of the five, only the multi-link suspension was benchmarked against aluminum. Because of its superior ride and handling characteristics, multi-link usually is more sophisticated and costly than other suspensions. However, it may be destined for more than luxury use via ULSAS' multi-link suspension, which delivered cost savings of 30% and a slight mass advantage over the aluminum-intensive design.

The Lotus Unique concept resembles a conventional double-wishbone system. It offers a simplified design with fewer components and performance results comparable to more complex suspension arrangements. It modestly cut cost and reduced mass by 34% compared to a standard-steel double-wishbone suspension.

Rear suspensions were chosen for ULSAS because they have a greater impact on luggage and occupant space, and there is a wider variety of rear suspensions than front suspensions.

Meanwhile, ULSAC's results were drawn from a three-year study of a frameless door that weighed and cost less than a variety of current production doors.

Pete Peterson, an executive at U.S. Steel Corp., one of 33 companies in ULSAC, called the closure panels study "the most creative project in the (UltraLight) family," compared to ULSAS and ULSAB, because ULSAC "achieved results that even surprised us."

The results included a door that is 22% to 42% lighter than benchmarked doors. Troy, MI-based Porsche Engineering Services Inc. conducted the study, which found the ULSAC door weighs 23.15 lbs. (10.5 kg) and would cost $66.50 to manufacture in a high-volume product program (225,000 units annually). A heavier "state of the art generic door," meanwhile, costs $69 to make, according to the study. Most of the savings were gained in material expenses and stampings.

By using high- and ultra-high strength steels and technologies such as hydroforming and tailor-welded blanks, ULSAC achieved a 33% mass reduction.

Compared to the average of three frameless doors now in production, the UltraLight steel door weighs 42% less and is 22% lighter than the lightest benchmarked framed door structure.

ULSAC's frameless door offering has only nine major parts and does not require the separate inner steel panel or intrusion beam typical of current designs. Instead, two horizontal tubes - one along the top of the door, the other along the bottom - provide stiffness and work together as side impact beams.

The outer panel is made of bake hardenable high-strength steel. It was chosen because tests showed it provides the best dent resistance, which often is considered a weakness of steel.

ULSAC components are production-ready, and the research will be shared with key suppliers. "They've seen it conceptually," says Mr. Peterson. "We're going to pitch it to them."

The steel consortium also continues its work on sheet hydroforming for outer body panels made of high-strength steel. Results are expected by year's end.