The Corvette goes aluminum: for the high-performance Corvette Z06 GM defied tradition and switched from a steel to an aluminum frame.
Laser welding is used in the driveline tunnel area. To prevent road noise from intruding into the cabin, GM insisted that no holes be cut in the folded aluminum sheet that forms the tunnel, which ruled out MIG welding it to the frame since that would require access holes for the guns. Although laser welding is performed without the need for access holes, Kroppe admits that adjusting both the head speed and angle and re-focusing the laser's optics to deal with the thick panels was laborious. But he notes that now Dana has the knowledge base--and ability--to cost-effectively laser weld aluminum.
SWISS WATCH WORK. Dana has carved out a small cellular assembly area for the Z06 in its manufacturing facility in Hopkinsville, KY, that is otherwise dedicated to producing serious volumes of stamped and spot-welded steel frames. (Annual volume for the Z06 is projected at 7,000 units.) "Compared to the other frames we make in that plant, this is Swiss watch work," says Kroppe. To prove the point, the describes how the aluminum castings that provide the attachment points for the suspension components are CNC machined with a precision that exceeds steel frame fabrication techniques. To achieve the highest degree of dimensional accuracy, Dana found it best to assemble the body first and then machine it using a Tricept robot from ABB (Auburn Hills, MI; www.abb.com).
RELATED ARTICLE: MITSUBISHI GETS CENTERED
Far its 2005 Lancer Evolution MR Edition, Mitsubishi added an aluminum roof panel to what was already an aluminum-intensive vehicle featuring fenders, hood and suspension components made from the lightweight material. Why the roof? According to Bryan Arnett, manager of product strategy, Mitsubishi Motors North America, designers were looking for the best way to lower the center of gravity of the car to enhance its handling, and lightening its uppermost part gave them the most bang for the buck. By switching to aluminum from steel, the MR Edition shed 4 kg (8.8 lb.); the center of gravity is reduced by 3mm. Had the designers stuck with steel they would have had to lower the entire roof by 50 mm to achieve the same effect. To prevent a galvanic reaction between the roof panel and the steel frame on which it rests, Mitsubishi uses an adhesive as a separation layer, in addition to self-piercing rivets. Thermal warping resulting from aluminum's thermal expansion coefficient (twice that of steel) is countermeasured with a longitudinal design bead that essentially absorbs the differences.
By Kermit Whitfield, Senior Associate Editor
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|Title Annotation:||THE TECHNOLOGY; Structural Solutions Group, Dana Corp.|
|Comment:||The Corvette goes aluminum: for the high-performance Corvette Z06 GM defied tradition and switched from a steel to an aluminum frame.(THE TECHNOLOGY)(Structural Solutions Group, Dana Corp.)|
|Publication:||Automotive Design & Production|
|Date:||Apr 1, 2005|
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