Hydroformed drive shaft and method of making the same
 A tube-in-tube driveshaft has an inner tube extending coaxially within an outer tube. A dampening material such as polystyrene foam is injected into the space between the tubes to increase strength, and reduce noise, vibration and whipping. The driveshaft is made by placing the tube-in-tube assembly axially within a mold cavity, and injecting fluid into the inner tube under sufficient pressure to expand the inner tube to its final desired contour and the outer tube into pressure contact with the mold cavity. The expanded tube-in-tube assembly is then placed in a second mold cavity. Fluid is injected into the inner tube and also between the tubes under sufficient pressure to expand the outer tube into contact with the second mold cavity, thereby forming the outer tube to its final desired contour, while retaining the inner tube in its final desired contour. The tube ends are welded together and the dampening material is injected into the space between the tubes through holes in the inner tube. 
Daimlerchrysler Corporation
Y B F B F F
Y10S B21D F16F B21D F16F F16C
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James D.
Hill