Extended jacket end, double expansion hydroforming

Abstract

Hydroforming double wall tubular stock into an air gap tubular element comprising providing a plural wall tubular workpiece having at least an inner wall liner and an outer wall jacket having adjacent open axial ends, causing at least one of the jacket ends to extend axially beyond the adjacent liner end and to be flared outwardly, placing the workpiece into a first mold cavity of a size and configuration to result in the desired size and configuration of the liner, sealing the open ends of said liner, injecting hydroforming fluid into said liner to fill it and applying pressure thereto to expand the liner and jacket in the first mold cavity, releasing the pressure, placing the workpiece in a second mold cavity of a size and configuration desired for the jacket on a resulting air gap tubular element, providing hydroforming end closures to seal off the jacket ends, at least one of the end closures having an annular shoulder aligned with the flared extended jacket end radially outwardly offset from the adjacent liner end, pressing the annular shoulder directly against the flared jacket end to seal the flared jacket end between the shoulder and an anvil surface, injecting fluid into the workpiece to fill it and applying pressure to expand only the jacket.