04.08.2005, 14:25
Ist noch nicht erschienen. Kommt erst nächste Woche bei "Automotive News".
Aber da wir hier ja von der schnellen Truppe sind...
Aber da wir hier ja von der schnellen Truppe sind...
Zitat:Sometimes it's what you can't see that makes a car different. Consider the 2006 Corvette Z06. While it may look like a regular C6 Corvette, the Z06 that goes on sale in the fourth quarter will have a new 7-liter V-8 engine capable of producing 505 hp. That is 100 hp more than the previous Z06.
But a bigger engine means more weight, which in turn cancels some of the added horsepower. In addition, the Z06 required bigger brakes, more cooling equipment, sturdier powertrain components and bigger wheels than the standard Corvette.
So what did General Motors do to create its fastest Corvette, which is capable of reaching 60 mph in 3.7 seconds from a dead stop?
Dana Corp. of Toledo, Ohio, created an all-aluminum frame, which made a difference of 136 pounds compared with the steel frame on the 2004 Z06.
(There was no 2005 model.) It also helped keep the curb weight of the vehicle to 3,132 pounds, compared with 3,118 pounds for the 2004 Z06.
But to get there, Dana had to solve a problem: How do you make lightweight aluminum do the work of steel without varying one notch from the steel specs?
By the time Dana had found the answer, it had embraced two new manufacturing technologies and entered into another competitive arena with implications for future business on other vehicle programs.
GM set two hard parameters when it proposed the project in 1999. First, the frame had to be all aluminum - a material Dana had never used on a vehicle frame.
Second, the frame had to match the dimensions of the standard steel space frame the Corvette already was using.
GM, which makes the steel frame, would not accept a frame that required a re-engineering of the body. And it would not accept a frame that resulted in any changes to the existing Corvette assembly line in Bowling Green, Ky.
A millimeter off here or there, and the car's instrument panel, for example, wouldn't fit between the doors. And, according to GM's orders, to make the Z06 viable as a business venture, there could be no cost added to GM's operations. The expression GM's engineers used on the project was "same as steel," says William Kroppe, director of structural solutions product engineering at Dana's structural components plant in Reading, Pa.
"We had to make the aluminum product meet the same dimensional requirements as the steel product," Kroppe says. "And if you know anything about the nature of aluminum, that's easier said than done." On a standard frame, steel pieces are stamped and then welded together.
The Z06's frame would require aluminum components that were stamped, cast and extruded.
But aluminum reacts differently than steel when stamped. And it reacts differently when welded. As the processes add heat, the material properties change. Dimensions can be distorted.
Considering that the frame in question is nearly 13 feet long - similar in composition to a long ladder - the chances that something would move out of spec were great.
"Dana has 100 years of experience with stampings," Kroppe says. "We have are less experience with extrusions and castings. And in aluminum frames, this was our first experience."
Dana subcontracts all of the Z06 frame pieces. GM supplies the long aluminum side rails for the frame through its Metal Fabricating Division in Flint, Mich. That hydroforming line has the flexibility to turn out both steel and aluminum rails. Dana's role from the beginning was module integrator, bringing together the outsourced components and determining how to build them into a frame that met specifications. All of that happened at Dana's plant in Hopkinsville, Ky., an hour west of Bowling Green.
What Dana learned during development was that changing the material required two new solutions at the same time.
First, to maintain the right metal rigidity, Dana's engineers knew they would have to make changes in the gauge of the material at key points. And if no variances were permissible on the frame's outer edges, they would have to be made on the inside of the frame components. That is where the alterations would not affect how the frame joined the existing body. "Otherwise," Kroppe says, "it would start a domino effect, pushing
all the their components outward to where components would no longer fit."
Second, Dana would have to rely on something other than spot welding to hold it all together.
Spot welding, the traditional process of joining steel components, would be too much trouble for the aluminum.
Welding aluminum requires substantially more energy and results in a greater accumulation of material waste on the welding tips. That causes more labor, more maintenance, more production downtime and ultimately
lower productivity and higher costs.
Dana looked into two relatively new methods of bonding metals: laser-beam welding and self-piercing rivets. Dana, a global manufacturer with diverse industrial businesses, was well aware of the technologies. But it never had cause to use them.
The Z06 project gave Dana's engineers a good reason to begin experimenting.
Kroppe says the company began testing both technologies around 1999, experimenting with smaller components before tackling anything on the scale of a sports car frame.
Both approaches had the advantage of being "single-sided processes."
In spot welding, the components being bonded have to be manipulated from both sides. In the new processes, the work is done from only one side. That gives a manufacturer better access.
In the laser-based approach, two sheets of metal are positioned together, and two laser beams then are aimed at a point beyond the surface of the top component. They bond the two by burning a line through the top sheet
that scratches only partly into the second sheet.
Self-piercing rivets work in a similar way. That technology, developed in Australia, has been in commercial use at least since the 1980s. British-based Henrob Ltd. supplied self-piercing rivets on the aluminum Audi A8 in the early 1990s.
Textron Inc. supplies the technology, which is handy for bonding dissimilar materials such as steel and aluminum.
When two sheets of material are layered together, the rivets pierce the top surface but not the second. Instead, they deform into the second surface, bonding as they flare out.
The technology has been used on automotive body sheet metal, mostly in Europe.
Kroppe believes the Z06 application is the first time an automaker is
relying on it to hold together heavyweight chassis components. "We didn't invent a new technology," he says. "We just put it to a new application. And the reason we did that was to avoid spot welding. "The benefit for Dana now is that we look at these three processes - aluminum frames, self-piercing rivets and laser-beam welding - as new tools
in our toolbox," Kroppe adds. "That enables us to go talk to other customers. We can tell them we have this new technology, and let them decide what they want in their frame. It wasn't on the table before.
It is now."
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