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  Press Relase: How Hydroforming, or Water-Molded Metal, is Reshaping the Structure of Today's Vehicles
Posted by: Hydro_Publishing on Thursday, July 17, 2003 - 11:58 PM
News Water. It seems so innocent when flowing from a kitchen tap, but anyone who's ever dealt with the hysteria of a burst pipe recognizes its stunning power. Indeed, one of nature's most abundant and essential resources is also one of its most forceful.
Today, GM is harnessing the force of water to shape metal. The concept, called hydroforming, holds tremendous potential for the future of automotive design and manufacturing.

Image: General Motors

What goes around comes aroundů
Hydroforming has been around for about a century, but only recently has it been tapped for automotive uses. Long ago, metalworkers crafted items such as doorknobs, plumbing fixtures and musical instruments using hydroforming techniques.

Today, it offers automakers an alternative to conventional stamp-and-weld processes for body and structural components. Over the last decade, GM has invested in this new technology, and other automakers and even motorcycle manufacturers are following suit. Depending on the application, it can save weight, improve fuel economy, minimize waste, and result in stronger, stiffer components that require less welding. It also provides vast improvement in dimensional accuracy in certain applications. In addition, hydroforming is suitable for both low and high volume production.

The GM advantage
While drivers can't see hydroforming's advantages, they most certainly can feel them. Hydroformed frame rails increase a vehicle's strength and stiffness, resulting in better structural integrity, ride and handling.

"No automaker uses or manufacturers more hydroformed components than GM," said Charles Bruggemann, engineer and chief hydroforming expert with GM's body engineering center in Pontiac, Mich. "GM was the first OEM with hydroformed frame rails for cars, trucks and SUVs, and it has the most applications on the road today."

GM also is the first North American automaker to develop in-house hydroforming design, engineering and manufacturing capabilities. GM has pioneered much of the hydroforming technology it is using today, and has earned some 25 hydroforming patents in the process. It has a 3.6 million-square-foot metal fabricating plant in Pontiac that produces a variety of hydroformed parts, including frame rails for the Corvette. It also uses various suppliers for other applications.

In the hydroforming process, operators feed precut hollow, round steel tubes, called blanks, into a bender, where they are shaped into the general form of the final part. Robots place the bent tube into the lower half of a hydroforming die where the ends are sealed. A combination of water, mixed with a touch of oil and corrosion inhibitor, is fed through the seals into the blank and then highly pressurized to shape the steel into the desired configuration. Often, any required holes or slots can be pierced into the part while it is in the hydroforming die. The result is a finished part that may require only trimming before heading off to the assembly line. Depending on the part, the water pressure may range anywhere from 5000 psi to 30,000 psi - and in special cases, may even near 100,000 psi.

"Just about anything that's not really flat or really chunky offers potential for hydroforming. Anything that has curves, contours or shapely angles is a worthy candidate," said Bruggemann.

And as engineers explore this novel technique, they are finding new ways to use hydroforming, including in assemblies or with alternative metals such as aluminum. Over the next decade, the technology will likely find its way into dozens of new uses.

In 1997, the fifth-generation Corvette represented the first true breakthrough in automotive hydroforming technology with industry-first twin seamless hydroformed frame rails. Each rail began as a piece of 18-foot-long six-inch diameter tubing, and replaced the previous model's 14-piece stamped and spot-welded rails. The frame rails gave the Corvette unprecedented stiffness - a 450 percent improvement - and dramatically improved ride and handling while reducing weight and improving step-in height. It also saved GM some $25 million in tooling costs.

In the Chevy Silverado and GMC Sierra, GM's full-size pickup trucks, hydroforming has produced a significantly lighter, stronger frame, with vastly improved structural integrity. It's the toughest light-duty truck frame in GM history. The frame and engine cross-members also eliminate hundreds of inches of weld, improving the dimensional control of mounting brackets. Since its debut, competitors have adopted some of the elements of the frame.

It's not perfect, butů
Of course, hydroforming isn't always the perfect solution. Its critics claim it's a slower, more expensive process that doesn't work for every application. All true. But GM has been able to overcome some of these obstacles because it's been at the forefront of hydroforming development. For example, it runs the Corvette frame rails two-at-a-time to pick up speed and save on cost. It also runs the upper parts of the Chevy TrailBlazer motor compartment front in a way that produces six parts at a time. GM has the in-house equipment, and has worked independently as well as with suppliers to develop unique manufacturing techniques. In addition, judicious use of hydroforming, when the engineering and business case is strong, has helped GM make the most of the innovative technology.

Yet hydroforming's newfound popularity doesn't mean that traditional stamp-and-weld processes will become obsolete. Stamp-and-weld still remains the smartest method for making straight parts with minimal scrap around the edges.

As GM refines and perfects this old-technology-turned-new, it is also exploring creative new uses for hydroforming that in future years will appear on its vehicles. For now, one thing is clear: hydroforming holds enormous potential for the auto industry and is here to stay.

How GM is using hydroforming
Hydroformed components are a lot more common than one might expect. At GM, it began with the instrument panel beam on the 1994 Buick Regal and Oldsmobile Cutlass, and engine cradles for the 1995 Oldsmobile Aurora and Buick Riviera soon followed.

Since then, hydroforming has been used on an assortment of GM vehicles including Buick Park Avenue, LeSabre and Rendezvous, Cadillac CTS, Seville and DeVille, Oldsmobile Alero, Aurora and Bravada, Pontiac Grand Am, Bonneville and Aztek, Chevy Suburban, TrailBlazer, Tahoe, Silverado, Malibu, Corvette and SSR, GMC Envoy, Sierra, and HUMMER H2. Some of the components include frame rails, radiator supports, roof rails, roof bows and other under-the-hood components and assemblies.

Here's a closer look at how GM is using hydroforming in some of its vehicles:

Silverado and Sierra. Hydroforming produced an extremely strong foundation in the full-size pickup truck lineup. It offers a strong, stable skeleton for the body, powertrain and suspension. The modular, three-section, ladder frame features hydroformed front rails. Hydroforming eliminates approximately 300 inches of weld from the front section for increased rigidity and frame strength, more precise fit and finish, as well as 44 lbs. of steel scrap per frame. Suspension mounting points are also more precise, significantly improving factory front-end alignment consistency and precision.

TrailBlazer, Envoy and Bravada. During the 2002 model year, these mid-size SUVs introduced the first front-to-rear fully formed hydroformed SUV rail in the industry. The two piece hydroformed steel frame side rails, with eight cross-members, provide a rigid structural backbone for the body. This strong foundation improves the truck's overall strength and ride quality, and significantly decreases road vibrations and noise. Dramatic increases in torsional stiffness - to best-in-class levels at 23-Hertz - improve the performance of suspension components.

SSR. The Chevy SSR features a uniquely tailored frame with fully hydroformed steel side rails. It offers great strength and stiffness, relatively low weight and precise quality, great torsional rigidity and dimensional control. A traditional stamped frame with this amount of strength and rigidity would weigh roughly 20 percent more. The holes for the suspension attachments are laser-cut, providing great dimensional accuracy measured to meet minute standards. This gives engineers maximum control of suspension components, enabling them to tune the suspension to a more precise degree.

HUMMER H2. The H2 uses a fully welded ladder-type frame, with a modular, three-piece design that incorporates a number of hydroformed components, and provides outstanding strength, stiffness and dimensional accuracy for the H2's chassis. The hydroformed front section is a shorter, high-strength version of that used on GM 2500 Series (3/4-ton) trucks. Its reduced length helps create the H2's high approach angle(s). To offset a resulting reduction in the frontal crush zone, GM engineers added reinforcements in key box sections of the frame, ensuring that its ability to absorb energy, crush and collapse is at least as good as, if not better than, competitors. The hydroformed, rear-frame section, crafted off GM's 1500 Series utilities, has also been shortened to help create a high departure angle. It is heavily reinforced in key areas for the H2's higher 8,600-pound GVWR capacity. (The 1500 Series is limited to the 7,000-pound maximum GVWR of the GMC Yukon Denali.)

The hydroforming process
The hydroforming process varies slightly depending on the component, but here's a general look at the overall procedure.

1) First, a computer-controlled machine cuts a length of straight metal tubing, also called a blank, to the proper size and feeds it into a machine, where it is pre-bent into the approximate contour of the finished part.

2) Next, the blank is inserted into the die, which is pumped full of highly pressurized water.

3) The water fills the blank, which conforms to the die walls. The water shapes the blank into the desired form.

4) At the same time, the machine compresses the ends of the blank, which eliminates thin spots on the outer wall of the blank, and prevents wrinkling on the inner wall, as well.

5) The component is then removed from the hydroforming press, the ends are trimmed and mounting holes are pierced with lasers and cutting torches.

Source: General Motors Press Release 2003


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