ULSAC: Steel Closures-Steel Industry Announces Results of UltraLight Steel Auto Closure (ULSAC) Study

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Steel Closures...Steel Industry Announces Results of UltraLight Steel Auto Closure (ULSAC) Study

Apparently saving weight and cost in a vehicle body structure wasn't enough for the steel industry. Now, the consortium that produced the UltraLight Steel Auto Body (ULSAB) program has set its sights on automobile closures: doors, hoods, decklids and hatchbacks.

The UltraLight Steel Auto Closures (ULSAC) project debuts as a phase one paper report, similar to the first phase of the ULSAB project. The validation portion of the ULSAC study is expected in the year 2000, according to Darryl Martin, director, Automotive Applications for the American Iron & Steel Institute (AISI). " Right now, we're taking our ideas, and discussing them with people to gauge their reactions. After that, we'll focus on building the demonstration hardware," says Martin.

But those ideas already are panning out on the statistics sheet and CAD models. The phase one review shows off closure design ideas that might cut vehicle weight by more than 50 pounds, and continue to offer low-cost, high-strength, recyclable and safe solutions for the steel industry's automotive customers.

Another Lightweight All Around

These designs could translate into significant mass reductions for automakers who typically use steel on their high-volume platforms. Collectively, closures can make up around eight percent of a vehicle's total body weight, making them a big target for automakers looking to shed pounds. ULSAC's initial numbers calculated by Porsche Engineering Services, Inc. (PES) in Troy, Michigan, show mass reduction on each closure relative to a benchmark created from eighteen '97-model-year vehicles.

Doors: A roof-integrated design showed a 23 percent drop in mass compared with the target 15.5 kg/m2. Another design concept - a frame integrated door - showed a 22 percent reduction in mass compared with the same benchmark target. A third frameless door design study saves mass by combining several features into one part, including the mirror patch, upper hinge and joint node. Calculations on this design show a 27 percent drop in mass compared with the benchmark target.

Hoods: Two hood designs, conventional and grille-integrated, showed a 32 percent and 29 percent drop in mass respectively. Both used a a 0.6 mm sheet hydroformed outer panel and feature lines to improve dent resistance in the thin material. Adhesive bonding in the hem flanges was employed to improve structural performance.

Decklids: ULSAC studied a conventional design with a tail. The traditional boot cover shows a 29 percent drop in weight and again uses a sheet hydroformed panel for dent resistance.

Hatches: PES used sheet hydroforming, thin gauge, stamped steel sheet and adhesive bonded hem flanges for this lift-gate hatch configuration. The design employs a tubular hydroformed frame to maximize section size and reduce part count. This helps to drop the weight 26 percent below the benchmark average.

Beating The Benchmark, and The Best

Pete Peterson, marketing director for U.S. Steel and ULSAC communications chairman, says the consortium isn't just relying on beating the average to impress automotive customers. ULSAC also is gunning for the best in class. "It isn't good enough to be better than the average because there may be somebody out there who is better than us," says Peterson. "So we have two objectives: to beat the benchmark significantly, and then to be 10% better than the best-in-class. So far, we hit that on every measurement," says Peterson.

Weight isn't everything though. During the next 12 months, the consortium will examine other critical issues like manufacturability, cost, dent resistance and safety.

And like the concepts presented in ULSAB, the ULSAC designs will be based on real-world technologies that are accessible in today's manufacturing environment. " We won't put ourselves in a position of coming up with something that is a really great idea, but not have it be realistic to produce," says Peterson.

Filling in The Gaps

Progressing from ULSAB to closures was a natural step forward, according to Martin. ULSAC not only helps automakers continue to shake weight out of steel applications, but it also helps reduce the continuing pressure on automakers to turn to more expensive alternative material applications for closures.

"As we all looked at (ULSAB), we recognized that if you don't do something about closure panels, that's the same thing as saying 'well were not worried about them. You guys can do whatever you want with them,'" says Martin. "And we know that closures are probably the easiest to replace with other materials, because they are bolt-on."

In recent years, automakers have turned to other materials to drop closure weight on vehicles that were just over their maximum rating for regulations like Corporate Average Fuel Economy (CAFE), says Peterson. These closures were an easy target because they were not part of the basic structure and not part of the crash-energy management system. "So, it is pretty easy to flip back and forth between materials on closures. But if you go back and research it, you will find that over time, many closure panels that went to aluminum or composite -- flipped back to steel," says Peterson.

Selling it Worldwide

The worldwide consortium of steel makers sponsoring the ULSAC project was not a reluctant host. In fact, Peterson says it was not a tough sell at all. "We simply pointed out, if we produced a body structure that has no closures on it, and somebody asked us the obvious question 'What are you going to do about closures?' and we said well we really haven't looked at that, it wouldbe a marvelous opportunity for our competitionto jump right in. They could say 'we will take care of the closures.' So it didn't take a lot of imagination to see the threat we had created for ourselves in not doing the closures in the first place."

The validation phase will begin with the introduction of one closure -- the one with the most demonstration potential, according to Martin. The other closures will follow, one by one, allowing the steel industry and its automotive customers time to absorb each element, and modify the technologies and material applications over time.

"The use and role of steel will be evolutionary," says Martin. "No one is going to make any radical changes right now. And as we've shown, the best time to make changes is when you have a clean sheet of paper."