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

增量式板料成形是一种灵活的、与工件无关的小批量板料成形工艺。ISF工艺的主要缺点之一是其几何精度较低，这限制了其广泛的工业应用，特别是在成形非对称零件时。已经在生产系统主席会议上成功推进的研究项目证明，基于机器人的ISF具有很高的工业潜力，特别是在原型制造方面。可以显著减少几何偏差，特别是在高温下进行成形过程的结果。因此，该项目的目的是利用迄今在热成形方面取得的积极成果，并针对由于成形装置不准确和高温成形造成的偏差的当前原因做出反应。为实现这一目标，研究重点应放在以下几个方面：(1)补偿成形装置的柔度；(2)提高成形装置的定位精度；(3)补偿局部加热引起的收缩行为。为了实施补偿策略，第一个目标是开发一个过程控制系统，使其能够集中监控成形装置的状态信息，并影响实时成形过程。随后，该项目将已在LPS成形机器人上成功实现的刚度模型集成到所实施的实时环境中。该刚度模型被增强以包括成形和支撑机器人的组合操作，以增加整个成形装置的刚度。此外，该项目还设计开发了两种成形工具的协调力控制，并将其集成到控制系统中，以提高成形设备的定位精度。此外，该项目的目的是分析局部加热造成的几何误差。统计实验计划用于深入研究热成形板材的收缩行为。为了确定收缩行为的特征，有必要确定不同工艺和几何参数以及由此导致的组件收缩的因果关系。在此基础上，我们的项目开发了一个模型，根据实际工艺和几何参数计算优化的刀具路径，以防止板材的收缩。我们的项目为成功实现板材原型和小批量系列的生产过程奠定了必要的基础，旨在提高精度，集中监测和控制成形过程，以及研究热增量成形板材的收缩行为。

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.