Local Heat Treatment in Draw Bending for Profiles of Manganese Boron Steel 22MnB5

Due to the increasing demand for vehicles with a low fuel consumption and consequently low emissions, lightweight construction is an important task in the automotive industry. High-strength profile parts reduce the total weight of the vehicle while maintaining a high bending-resistance. Draw bending combined with inductive sheet heating and subsequent cooling represents a cost-effective and economic concept for producing partially hardened profiles for small batch sizes. This paper deals with experimental investigations to optimize and examine heating and cooling in the process chain of draw bending. After designing the process by numerical simulation, the existing draw bending machine of the IFUM was expanded by an inductive heating unit and a cooling system. Subsequently, new experiments on the implementation of a heat treatment during draw bending were carried out with this machine. In the course of these experiments, the determined process limits were recorded based on the required drawing force, the temperature courses in the process and the respective hardness values. These values served to evaluate and validate the results of the numerical simulation. By means of heating the material before it enters the forming die, it could be shown that it is possible to form super high-strength-profile components through draw bending. The material was heated up to austenitization temperature by a surface inductor and cooled by the draw bending tool and the additional air cooling. The material used was the uncoated manganese-boron steel 22MnB5. Good results with regard to process and part quality were obtained by means of an upstream heating. The comparison with the simulation also showed a high degree of similarity and consequently confirmed the results of the numerical representation of the process. Thus the general feasibility of integrating a heat-treatment into a draw bending operation was successfully proved.