Ask owners of the 1997 Chevrolet Corvette where their car was born, and they will likely answer Bowling Green, Ky.
Actually, the gestation began in a corner of Plant 14 at General Motors' Metal Fabricating Division in Pontiac, Mich. There, 14-foot-long steel tubes are bent and expanded with pressurized water - a process known as hydroforming - to create one-piece side rails.
Those rails are integral parts of the new Corvette's perimeter frame. They greatly increased the new sports car's structural stiffness. They also made it easier to enter the car. The previous Corvette had to be climbed into because of its high side rails.
For suppliers faced with conflicting demands of cutting vehicle weight and increasing structural stiffness, hydroforming is increasingly becoming the best choice for structural components.
And it almost always is a lower-cost alternative. A single piece typically replaces several stampings and their associated dies, welding and labor. For example:
The new Corvette's single-piece side rail eliminates 14 stampings.
A radiator support assembly made by Vari-Form of Warren, Mich., for the Dodge Ram has 10 components, vs. 17 for the stamped design. The change saved $6 million. A front subframe Vari-Form makes for another automaker has one component, vs. six for the stamped design, and saved $1.2 million.
In auto manufacturing, it does not get much closer to the Holy Grail than that.
'A lot of tubular products are going to hydroforming,' said Craig Cather, president of CSM Corp., an Okemos, Mich., consulting firm that specializes in auto suppliers.
Exhaust manifolds and frame pieces are among the prime candidates, he noted, because the technology offers weight and design advantages. 'We haven't seen any dark clouds being cast over the technology,' he said.
There is some concern, though, that supplies of tubing could be tight if hydroforming continues to grow.
The intense interest in the first all-new Corvette in 13 years has helped raise hydroforming's profile. The Corvette side rails are the largest single auto part to ever be hydroformed.
Magna International Inc. also made a big hydroforming splash last year. It won the contract to supply hydroformed frame rails for GM's full-sized light truck platform for the 1999 model year.
But hydroformed parts have been trickling into vehicles since the beginning of this decade. Many more examples will show up on vehicles in the 1998 and 1999 model years. The key is to get in early on the vehicle development program.
Many of the early applications, such as instrument panel support beams, merely took the design for a stamped part and converted it to hydroforming.
Vari-Form supplied its first hydroformed auto part in 1990 - an instrument panel support beam for Chrysler Corp.'s minivans. But only now is the company beginning to reap benefits from years of meeting with product development engineers and talking up the technology, said Terry Nardone, commercial manager.
'They had to rethink the way they design parts,' Nardone said. 'In the beginning they had lots of concerns. There were no flanges on the tube; they couldn't see a way to mount seals, or get inside access for welding.
'Now, there's a dramatic difference,' Nardone said. 'We're seeing more part designs come out intended for hydroforming.'
Some suppliers such as Vari-Form, a unit of Bundy North America, have been using the technology for almost a decade. Today Vari-Form makes more than 3 million hydroformed auto parts annually. Vari-Form does not release sales figures, but Nardone said its hydroforming sales have doubled in the last three years.
Others join in
Several other suppliers, such as MascoTech Tubular Products, have entered the arena within the last couple of years, primarily by buying the technology from German companies. MascoTech, for example, bought two high-pressure hydroforming presses from Huber and Bauer of Dillingen, Germany, and built a facility in Canton Township, Mich., large enough to hold as many as six hydroforming presses.
Rather than chase all kinds of hydroforming business, MascoTech is concentrating on exhaust products such as manifolds, one of its existing core competencies, said Jim Babiasz, general manager for the Tubular Products group. The company also has decided to branch out and seek working hydroforming pieces for seat
frames, particularly structural seats that incorporate the seat belt system.
'We want to stay out of areas where lots of people are making investments,' Babiasz said.
MascoTech also sees advantages by using a high-pressure system capable of forming tubes at up to 87,000 pounds per square inch. Many hydroforming systems, such as those used to make instrument pan-el support beams, operate at low pressures of 7,000 psi or less. 'With low pressure, you're just reshap- ing the part,' he said.
But with high pressure, he noted, the material is actually pushed around.
The high pressure also delivers a key benefit by enabling engineers to make extrusions on the hydroformed part. The hydroforming press pushes in on the ends of the tube, forcing the material to flow into cavities. Those extrusions could allow the pieces of a seat frame to clip together, for example, and reduce the need for welding.
MascoTech also has found that the process gives lower grades of steel tubing the hardening and strength properties of high-grade steel, said Mark Alcini, chief engineer of project engineering. That can help cut costs further.
But the company points out that hydroforming is still a developing technology for auto applications. 'Anyone who is doing this today is writing the textbook,' said Babiasz. 'The scary part is that we're doing things with metals that metallurgists don't understand.'
The auto world took notice last year when GM awarded Magna the contract to supply 1.2 million frames a year for its next-generation full-sized pickups and sport-utilities.
The new trucks, being developed under the GMT 800 code-name, are scheduled to be produced for the 1999 model year. GM's plans called for hydroformed frames -a testament to the automaker's growing confidence in the technology. The hydroformed frame reportedly weighs about 25 pounds less than the current frame, and costs about $60 less per piece.
In choosing Magna, which acquired its hydroforming skill by purchasing a German company, GSA, GM shunned longtime incumbent frame suppliers Dana Corp. and A.O. Smith. Each had limited experience with hydroforming.
'Magna was very, very aggressive on price in bidding for that project,' said a source at a company that worked with one of the incumbent bidders for the project. Said CSM's Cather: 'Magna's really got their hands full with that one. It's a new technology for them, and the program has many iterations.
'It's the biggest hydroforming contract that's taken place,' he said. 'And GM must have a lot of confidence because they've taken their biggest-selling platform and placed it with a supplier that doesn't have a lot of experience with the technology.'
Dale Jewett is engineering editor of Automotive News in Detroit.