Accurate cold forged parts through adjustable dies

Abstract In response to the growing demands for both sustainability and precision in metal forming, this study investigates the potential of an adaptive die system for cold forging processes. The system allows of control of die preload during the main forming and ejection phases, thus offering two degrees of freedom to influence product properties. Through a combination of experimental and numerical investigations, the interdependence between the final part diameter, axial residual stresses, and ejection forces is systematically analyzed. It is shown that increasing the preload during forming reduces the final diameter. Conversely, preload applied during ejection has a direct influence on the resulting ejection force and surface stresses. This decoupling capability enables targeted tuning of individual product properties. To experimentally represent the variability of material batches, three different steel grades were selected, spanning a broad range of flow stresses. The resulting process maps reveal how fluctuations in material properties affect forming outcomes, and how the adaptive die system can be used to compensate these effects. The experimental trends were confirmed by finite element simulations, which support the physical interpretation of preload-related elastic and plastic interactions within the tooling system. The study shows that adjusting the preload intelligently enables dimensional corrections and residual stress or ejection force optimization. The primary focus is on understanding and modeling the process-property relationships. The results lay the foundation for potential control strategies, such as inline or part-to-part adaptation. These strategies can be integrated into future forming lines for increased robustness and flexibility.