Liquid-operated molding with duplicated control time

TLDR: In this paper, the dual wall tubular exhaust conduit workpieces which are previously curved are successively arranged in a cavity 14 and are mechanically preformed by force mold clamping.

Abstract: PURPOSE: To obtain a hydroforming apparatus for rapidly forming a double wall conduit having the gap of a controlled size between the walls from dual wall tubular stock by providing the apparatus with a preform, semi-finish cavity and finish cavity. CONSTITUTION: The dual wall tubular exhaust conduit workpieces which are previously curved are successively arranged in a cavity 14 and are mechanically preformed by force mold clamping. A first pair of end plug sub-assemblies 20 exists at both ends of the cavity 14 and a hydroforming liquid is injected through the same. Both walls of the double wall workpieces are expanded up to the size of the cavity 14. The workpieces are thereafter arranged in the cavity 16 and the hydroforming liquid is injected from the end plug sub- assemblies 40. The pressurizing liquid equals the pressure acting on both of the inner walls and outer walls of internal elements through apertures. The external force is acted on the walls on the inner side of the external elements to expand the walls to the final dimensions of the cavity 16, by which these elements are arranged apart with the controlled exact spacings from the inner element.