Model-based Design of Self-Correcting Strategy for a Punch Bending Machine

Abstract The precise reproduction of geometrical form often constitutes a challenge in manufacturing of metal parts. The reasons for form deviation can be e.g. varying properties of the semi-finished product as well as wear of the punch-bending machine or the punch-bending tool themself. Usually the process parameters are manually adjusted on the introduction of new production scenario or after the deviation between the actual form of produced pieces and the designed form become clear. The choice of new process parameters is normally based on the experience of the machine operators. It leads to a time-consuming and expensive procedure right on the early stages of production scenarios as well as during the established production process. Furthermore, the trend of miniaturization of part sizes along with narrowing tolerances and increase in the strengths of materials drastically pushes up the requirements on the production process. Aiming at reduction of scrap rate and setup-time of production scenarios, a self-correcting control strategy has to be developed. The strategy is designed by modeling the bending process. In the first step the bending model has to be analyzed by varying of process variables (e.g. the strength or the geometrical properties of the material) influencing the process significantly. It is done by corresponding simulations. After that, the correlations between input and output variables were defined and different self-correcting control strategies were designed and tested. In order to identify and validate the simulation and to test the quality of the self-correcting control strategies, a special experimental tool, representing the most important bending operations, was built up at the University of Paderborn. The experimental tool is equipped with an additional measurement device and can be operated on a universal testing machine. Finally, the self-correcting control strategies were tested under real production conditions on the original tool in order to address further influences of the punch-bending machine on the deformation process. In this paper, recent investigations of a collaborative project of the University of Paderborn and two industrial partners will be presented. The paper includes the results of model analysis and the influence of various process variables. Besides that, the paper focuses on the development of self-correcting control strategy and a suitable measurement methods. The first implementation of the developed control strategy on the basis of real production facility is described.