Analysis of process limits for open-die forging with superimposed manipulator displacements in vertical direction

Open-die forging is an incremental bulk metal forming process providing excellent mechanical properties and lifetime. Therefore, open-die forged parts are used for highly loaded application purposes e.g., in energy technology. However, the range of producible geometries in open-die forging is limited mainly to long and straight workpieces with simple cross-sections. Here, open-die forging with superimposed manipulator displacements offers a large potential for the production of curved workpieces. The new process concept is based on the idea, that the manipulator, originally designed as a handling device, is now actively used to control the material flow towards an intended final geometry. The idea was successfully realized for the production of curved workpieces by open-die forging. The hereby-presented investigations now aim at an analysis of the process limits for bending in vertical direction. Based on a fundamental analysis, a tilting of the samples between the forging dies and an undesired contact of the curvature with the forging die were identified as main process limits leading to a reduction of the curvature. By numerical simulation and fundamental geometric analysis, a process window was identified, where the occurrence of process limits and thus a reduction of curvature can be avoided. Finally, experimental validation was carried out at the industrially scaled open-die forging setup at IBF proving that the identified process window can successfully be realized.