When most people think of car and truck frames they think of steel stampings, but they might want to consider a more rounded perspective, according to some producers of tubular auto parts, who argue that the role of steel tubes in automobile frames could grow.
That's especially true in the wake of new emissions rules and more-stringent rollover standards in the United States as well as stricter crash survival standards in Europe, they say, because tubular structures are lighter, safer and more efficient to produce than traditional stampings for certain applications.
Increased U.S. fuel economy standards are scheduled to take effect in 2020, which means automakers will begin concept work by 2015 at the latest, according to Paul Schurter, principal engineer of advanced engineering at ArcelorMittal SA's automotive product applications unit. "But they will not wait until then. It's not the type of thing that can be accomplished in a normal product-design cycle," he said.
Hydroformed tubes are made by placing a steel tube in a die and then injecting liquid under high pressure, forming the tube into the desired shape and also to pierce or otherwise modify it.
Steel tubes traditionally have been used in a variety of automotive applications, including powertrains, exhaust systems, axles and trailer hitches. Several sources say the tubular content for those products isn't likely to grow much. But in auto bodies, the story might be different.
General Motors Corp.'s Pontiac Solstice and Saturn Sky feature hydroformed, advanced high-strength steel (AHSS) body tubes, running from the front end to the rear bumper on both sides of the vehicles to form the backbone of the body structure. They might also provide a glimpse of what the future holds, Rick Owens, general manager of sales at ArcelorMittal's Dofasco tubular products unit, said.
But while there is "tremendous opportunity" for AHSS tubes, especially in smaller diameters, there is also fierce competition from other technologies, Owens cautioned, noting that steel tubes are actually losing ground to stamped parts in door beams. Vehicle assembly lines generally are geared toward stampings, which historically have required a different type of welding than tubes. Tube makers have made efforts to integrate their products into traditional assembly line welding techniques. Still, tubes generally cost more than stampings and take more time to produce.
ArcelorMittal bills itself as one of the largest suppliers of steel tubing for automotive components. It also makes subassemblies and finished parts that eventually end up in automobiles. In addition, the company ships tubes directly to original equipment manufacturers and other companies that bend, pierce or hydroform them into auto parts.
One such company is Vari-Form Inc., Troy, Mich., which specializes in hydroformed tubular components.
Hydroformed tubes were "all the rage" in the early 1990s and the market matured in the mid- to late-1990s, according to Terry Nardone,Vari-Form's commercial manager, who adds that the industry has grown more modestly since then. "It's still a solid growth industry," he said. "Applications continue to be developed."
Vari-Form also has developed prototypes for hydroformed tubes made from aluminum and magnesium but none has gone into production, largely due to cost concerns on the part of automakers.
"Between stamping, roll-forming and even plastics, it's very competitive," he said. "No one can sit back and wait for something to happen."