Analysis of Geometry and Thickness Distribution in a New Hydroforming Die for Cylindrical Stepped Tubes

Seamless tubular components with various cross sections, such as cylindrical, conical, and square cross section stepped tubes, are mainly produced in a tube hydroforming process. In forming those parts with this process, achieving shapes with sharp corners, requires an increase in the internal pressure. This may cause local thinning and bursting at the tube corners. The authors propose a new hydroforming die set in which the die corner filling is improved for cylindrical stepped tubes. In the new die, the forming of tube consists of two steps of bulging and final forming. In this paper, the effect of pressure path on thickness distribution and geometry of stepped tubes are studied by finite element simulation and experiment. The results in this paper illustrate that the bulging pressure and the pressure-axial feeding of the final forming stage influence the desired final geometry and that the proper selection of these parameters affects on the deformed part geometry. It is also shown that in the new die set it is possible to produce a sound part with uniform thickness distribution along the wall side.