New incremental methods for springback compensation by stress superposition

The paper deals with two new process variants invented by the authors. Both use the principle of stress superposition to reach an additional plastification of the material for a controlled influencing of the forming zone. By the superposition of an additional load on a forming process it is possible to compensate the springback effect e.g. of bending angles or bending radii to extend the forming limits of the material and to reduce the forming forces. The first process is the new process of incremental tube forming. This process is based on the combination of a spinning process with the free forming of tubular semi-finished products. This process is suitable to bend tubes two- and threedimensionally to an arbitrary contour and to manufacture tailored tubes. The process is useful to bend tubes without a die with full springback compensation. The second process is an advanced sheet metal air bending process using a roll which is pushed against the bending part after the loading operation and before unloading. This results in an incremental superposition of stresses along the bent part leading to a springback reduction and improvement of the crash properties. The paper shows the principles of both procedures and presents the results of the experimental investigations.