A combined approach to determine workpiece-tool-press deflections and tool loads in multistage cold-forging

Press and tool deflections have significant influence on the accuracy of products and tool service life in cold-forging processes. This paper presents a combined experimental–numerical approach to determine the deflections of the workpiece-tool-press (WTP) system and tool loads to improve product accuracy in a multistage cold-forging process. The measurements of deflections of the vertical mechanical press for the determination of the press flexibility matrix were performed in dynamic operating conditions. Numerical modelling of the vertical mechanical press and a multistage forging system was performed in order to evaluate the tool loads, the displacements and the rotations of the entire WTP system. The press flexibility matrix in combination with finite element (FE) model of the press and multistage process enable predictions of the elastic displacements and rotations of the tool and the press ram as well as determination of the evolution of the resultant force in order to design a reliable multistage cold-forging process. By redesigning the time sequences and evolution of the multistage forming operations during the press stroke, the evolution of the resultant force and the torque are optimized. This approach has been successfully applied to improve the prediction of tool loads, WTP deflections and rotations for the production of the automotive starter side plate.