Cold Forging of Hollow Shafts with Variable Wall Thickness by Means of an Adjustable Forming Zone

Hollow shafts are widely used due to their high weight saving potential and only slight reduction of their bending and torsional stiffness compared to solid shafts. Additional weight savings can be achieved by a specific material allocation within the hollow shaft, which can be achieved by varying their wall thickness. The production of such hollow shafts by conventional forming processes and multiple forming stages appears quite costly today. Alternatively, incremental forming processes could be used, but those are very time-consuming. In order to overcome these disadvantages, this paper proposes a special cold forging process characterized by a locally adjustable forming zone, which allows the production of hollow shafts with variable wall thickness within one single press stroke. In previous numerical investigations, the potential of this cold forging process for the production of customized hollow shafts with predefined wall thickness locations or internal splines has already been demonstrated. However, experimental validation has not yet been carried out. In this paper, the first experimental results on hollow shafts produced with wall thickness changes along their longitudinal direction are presented. The experimental setup and the results of the tests carried out so far are described. Furthermore, the experimental results are compared with the numerical calculations of this new forming process.