Robot-based incremental sheet forming - compensating for disturbances caused by a local heating and the inaccuracy of the metal forming device

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Incremental sheet forming (ISF) is a flexible, workpiece-independent procedure to manufacture sheet metal parts in small lot sizes. One of the major drawbacks of ISF processes is their low geometrical accuracy, which limits a widespread industrial application of these especially when it comes to forming asymmetric parts. The research Projects, which have been successfully advanced at the Chair of Production Systems (LPS), prove that robot-based ISF has high industrial potentials especially for prototyping. It has been possible to considerably reduce the geometrical deviations especially as a result of performing the forming processes at elevated temperatures. Therefore, the aim of this project is to use the positive results of hot forming achieved so far and react on the current causes of deviations resulting from inaccuracies of the forming device and from forming at elevated temperatures. To achieve this, the research focus shall be placed on the following:(1) compensating for the compliance of the forming device,(2) increasing the positioning accuracy of the forming device,(3) compensating for the shrinkage behavior as a result of local heating.To implement the compensation strategies, the first objective is to develop a process control system which makes it possible to centrally monitor the state information of the forming device and to influence the real-time forming process. Afterwards, the project integrates the stiffness model, which has successfully been implemented on the forming robot at the LPS, into the implemented real-time environment. This stiffness model is enhanced to include a combined operation of the forming and supporting robot to increase the stiffness of the entire forming device. In addition, the project is designed to develop a coordinated force control of both forming tools and to integrate it into the control system to increase the positioning accuracy of the forming device.Moreover, the project has the aim to analyze the geometric inaccuracies caused by local heating. A statistical experimental planning serves to thoroughly investigate the shrinking behavior of a hot formed sheet. To identify the characteristic of the shrinking behavior, it is necessary to determine the cause-effect relationships of varying process and geometry parameters and the resulting component shrinkage. Based on this, our project develops a model to calculate an optimized tool path in dependence of the actual process and geometry parameters in order to work against the shrinkage of the sheet. The developed compensation strategies are finally brought together in the process control.Our project lays the necessary basis for a successful realization of a procedure to manufacture sheet prototypes and small batch series; it aims at increasing the accuracy, at centrally monitoring and controlling the forming process as well as investigating the shrinking behavior of hot incrementally formed sheets.