Patent ID: 7788960

Claim:
A method of making dual-wall tubes from single-wall pieces of tube, comprising: providing a first piece of tube having a single wall with an inner surface and an outer surface extending between a first end and a second end; engaging the first end of the first piece of tube with a forming surface of a die shoe; moving the first end of the first piece of tube relative to the forming surface of the die shoe to form a curl until the first end of the first piece of tube substantially contacts one of the inner surface and the outer surface; continuing to move the first piece of tube relative to the forming surface of the die shoe to form a second wall as the first end traverses along at least a portion of the one of the inner surface and the outer surface; disengaging the first piece of tube from the die shoe to provide a first dual-wall tube; providing a second piece of tube having a single wall with a second piece inner surface and a second piece outer surface extending between a second piece first end and a second piece second end; engaging the second piece first end with the forming surface of the die shoe; moving the second piece first end relative to the forming surface of the die shoe to form a second piece curl until the second piece first end contacts one of the second piece inner surface and the second piece outer surface; continuing to move the second piece of tube relative to the forming surface of the die shoe to form a second piece second wall as the second piece first end traverses along at least a portion of the one of the second piece inner surface and the second piece outer surface; and disengaging the second piece of tube from the die shoe to provide a second dual-wall tube.