Process and apparatus for producing a hollow body, and hollow body

Method for producing a hollow body made of metal, which comprises at least one first axial portion with a first cross-sectional area and a second axial portion with a second cross-sectional area and in which both first and second axial portions of the hollow body are connected to one another by means of a shape transition running in a radial plane, the method comprising:

• producing a preform body, which comprises at least one transition region extending in an axial direction and is arranged between a first and a second axial portion of the preform body, wherein, in the transition region, the cross-sectional area of the preform body continuously changes from a first cross-sectional area of the first axial portion of the preform body into a second cross-sectional area of the second axial portion of the preform body;
• selecting a length of the transition region of the preform body as a function of the wall thickness of the preform body, the change in shape in the shape transition, and as a function of material;
• accommodating the preform body in a die, wherein the die has a final external shape of the hollow body,
• inserting a shaping mandrel into the preform body, wherein the shaping mandrel has the internal shape of the hollow body;
• and
• axially moving the shaping mandrel to upset the preform body in the die to complete the production of the hollow body, so that a maximum sheet thickness change in the axial directions of the hollow body is +/−15%.