| 摘要 |
A method of forming a tubular, double wall, air gap, exhaust duct component for an internal combustion engine, the resulting exhaust duct component, and the blank for such, involving providing an inner membrane duct element, with orifices therethrough spaced along its length, providing an outer structural duct element in 360 degree engagement with the inner duct element in the areas where forming and bending operations are to be performed, conducting such forming and bending operations, securing the resulting blank in a hydroforming die cavity, sealing the ends of the inner element to the ends of the outer element, plugging the ends of the inner element, injecting a liquid, preferably water, into the inner duct element and increasing the pressure on the liquid to expand the outer element away from the inner element and ultimately into conformity with the die cavity while the inner element floats in place, in a manner to create an air gap substantially over the full length of the duct component, i.e., except at the ends.
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