Metamodel-based control algorithms for the correction of bending angle after springback in an industrial U-Bending process

The increased complexity of geometries and the improved properties of sheet metal components result in narrower process windows, highlighting the need for better process control to minimize deviations and to ensure the production of high-quality parts. In this context, this study focuses on controlling the bending angle of a seat rail component manufactured by a renowned TIER1 company. This angle changes due to material, process fluctuations and post-forming springback. Two types of material, a cold-rolled Dual Phase DP980 steel and a Complex Phase CP980 high-strength steel, are both employed interchangeably when manufacturing this component. Variations in the mechanical properties and thickness of these two materials result in significant differences in post-springback bending angle. To tackle this challenge, various control strategies have been developed including a classical controller and a controller enhanced with a metamodel-based feedforward term. For the latter, two approaches were used: a simulation-based metamodel and an experimental data-based metamodel. Heuristic-based disturbances, reflecting both material variability and process changes (tool mounting variations, tool wear, gap changes and temperature variations), have been considered. To calibrate the new controller parameters and gains, a constrained-based genetic algorithm approach has been utilized together with a numerical virtualization of the process. After this virtual set-up, the new controllers have been tested experimentally in a real environment, using an industrial U-bending tool and a 4000 kN servomechanical press. The new controllers have proven to be an efficient method for enhancing the process robustness. A classical controller, employing a feedback control system, enabled consideration of part-to-part variations. On the other hand, the addition of a metamodel-based feedforward term facilitated anticipation of material properties and sheet thickness changes, thereby preventing scrap production.