Model-based approach for self-correcting strategy design for manufacturing of small metal parts

The compliance of increasing requirements on the final product often constitutes a challenge in manufacturing of metal parts. The common problem represents the precise reproduction of geometrical form. 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 model-based approach is chosen to design a self-correcting control strategy. The strategy is designed by modeling the bending process. In the first step the bending process has to be analyzed on the model by varying of process variables influencing the process significantly. It is done by corresponding simulations. After that, the correlations between significant variables and geometrical deviation 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 was built up. 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 manufacturing process.