Method for the production of hollow elements, hollow element, assembly piece, and follow-on composite tool for carrying out said method

Progressive tool for the manufacture of hollow body elements having a substantially polygonal outline and adapted for attachment to components comprising sheet metal hollow body elements by cutting individual elements to length from a section having a rectangular cross section and first and second broad sides, said section being present in the form of one of a profile bar and a coil after prior piercing of apertures into the section, optionally with subsequent formation of a thread cylinder, said progressive tool having a plurality of working stations, wherein in each case two operations are simultaneously carried out for each stroke of the progressive tool in each working station for the section, wherein an upsetting process is carried out in a first working station using upsetting tools each adapted to form a cylindrical recess having a diameter and a recess base at a first broad side of the section and a hollow cylindrical projection having an inner diameter and a space base at a second broad side of the section opposite to the first broad side, with said recess base and said space base being separated by a web of material and with the projection being surrounded by a ring recess, wherein said upsetting tools are adapted so that the diameter of each cylindrical recess and the inner diameter of each hollow cylindrical projection are made substantially the same,

• wherein piercing tools each comprising a cylindrical piercing punch having a diameter corresponding substantially to said diameter of said cylindrical recess and said inner diameter are provided in a second working station for piercing said web of material,
• wherein flattening and dilating tools are provided in one said working station and adapted to carry out a flattening and dilating process for the manufacture of an undercut surrounding each cylindrical projection and a piercing edge at said cylindrical projection, and
• wherein cut of punches are provided in a final working station for the separation of in each case two hollow body elements from the section by means of the cut-off punch.

A method for the manufacture of hollow body elements for attachment to components consisting of sheet metal, in particular for the manufacture of hollow body elements, having a substantially square or rectangular outline by cutting individual elements to length from a section present in form of one of a profile bar and a coil after prior piercing of apertures into the section, using a progressive tool having a plurality of working stations in each of which respective operations are carried out, said section having a first broad side and a second broad side, the method comprising:

• a) in a first step, starting from a section rectangular in cross-section, a forming process is carried out in which a hollow cylindrical projection having a hollow internal space with a base is formed at said second broad side as well as a recess surrounding said hollow cylindrical projection but without forming a cylindrical recess at the first broad side of the section and, said recess surrounding said hollow cylindrical projection being polygonal in plan view and having faces set obliquely to a central longitudinal axis of the hollow body element, said forming step being effected by forming said hollow cylindrical projection partly from the material displaced during the formation of the recess and partly from the material displaced during the formation of said hollow internal space,
• b) in a second step, a web remaining between said first broad side and the base of the base of the hollow internal space is punched out to form a through-going aperture, and
• c) in a third step, which is combinable with the second step b), the hollow cylindrical projection is flattened at its free end for the formation of a piercing section and an undercut at the outer side, whereafter the hollow body element is separated from the section.