Manufacturing of combined convex-concave form elements by using active-medium support in incremental sheet forming

板料渐进成形是一种柔性高、适合小批量生产的制造工艺。然而，如果毛坯下面没有坚实的支撑，例如通过模具或反工具，就不能形成具有良好几何精度的复杂几何形状。活性介质渐进成形(IFAM)研究项目的第一个资助期通过在毛坯底部的液体或气体介质提供软支撑，从而满足了这一挑战。刀具路径和压力水平的结合使凸形和凹形零件的制造以及凸凹形零件的组合成为可能。第一个资助期的一个方面是通过分析、实验和数值方法分析凸起行为。为了准确地实现目标几何形状，必须考虑工艺参数和零件形状之间的复杂相关性，并导致与机器学习领域的跨学科合作。神经网络被训练来预测几何特性的在线闭环控制中所需的压力。与恒压加工工艺相比，采用动态调节压力级的加工工艺，几何精度有了显著提高。除了这种控制概念的巨大潜力外，它的缺点是被限制在一种特定的材料和一种预定的几何形状上。第二个资助期背后的动机是解决这个问题，并将控制概念的适用范围扩大到任何任意的材料和几何形状。扩展的控制概念是基于这样的研究假设，即靶材形状、成形能量和切向成形力之间存在很强的关系，并且可以用数学方程来表示。该分析模型包括上述数学方程，并通过数值结果进行了验证，作为本项目建议书的前期工作。在这种方法中，介质的压力水平作为关键的修正变量被切向力取代，因此需要进一步研究工艺参数之间的相互关系。为了确保扩展的控制概念包括所有依赖关系，与机器学习领域的多学科合作是必要的。这项合作的基本目标是开发在线闭环控制，以实现可靠和可重复的制造过程。控制成形过程将由设计指南完成，其中包括CAD文件的处理和通过调整凸凹组合零件的制造顺序和刀具路径来补偿几何偏差。

Incremental sheet forming (ISF) is a manufacturing process, which has a high flexibility and is suitable for producing small lot sizes. However, without solid support beneath the blank, for example through a die or a counter tool, complex geometries with a good geometrical accuracy cannot be formed. The first funding period of the research project on incremental sheet forming with active medium (IFAM) met this challenge by providing a soft support through a liquid or gaseous medium on the blank’s underside. The combination of tool path and pressure level enabled both the manufacturing of convex and concave elements as well as combined convex-concave parts. One aspect of the first funding period was analysing the convex bulging behaviour by including analytical, experimental and numerical methods. To achieve a target geometry accurately, the intricate correlations between the process parameters and the part shape had to be considered and led to an interdisciplinary collaboration with the field of machine learning. A neural network was trained to predict the required pressure in an online closed-loop control of the geometrical properties. Compared to the manufacturing process with constant pressure, the geometrical accuracy was significantly improved by using a dynamically adjusted pressure level. Beside the great potential of this controlling concept, it has the disadvantage of being restricted to one specific material and one predetermined geometry. The motivation behind the second funding period is to solve this problem and extend the applicability of the controlling concept to any arbitrary material and geometry. The extended controlling concept is based on the research hypothesis that a strong relationship between target shape, forming energy and tangential forming forces exists and can be expressed by a mathematical equation. The analytical model, which includes the aforementioned mathematical equation, was proven by numerical results as preliminary work to this project proposal. In this approach, the pressure level of the medium as a pivotal correcting variable was replaced by the tangential forces and thus requires further investigation of the interrelation between the process parameters. To ensure that the extended controlling concept includes all dependencies, the multidisciplinary cooperation with the field of machine learning is necessary. The underlying goal of this cooperation is to develop an online closed-loop control for a reliable and a reproducible manufacturing process. The controlled forming process will be completed by design guidelines, which include the processing of CAD-files and the compensation of geometric deviations through adapting manufacturing sequences of combined convex-concave parts and tool paths.