Joining by dieless hydroforming with outer pressurization

轻量化施工要求对结构和构件进行重量优化。这通常是通过集成功能或将不同材料特性组合在一个单一组件中来实现的。由于材料性能的高度多样性，对连接技术提出了很高的要求，这导致了传统连接工艺的技术或经济限制。无模液压成形连接是传统方法的合适替代方案。该工艺允许生产过盈配合和/或成形配合接头，这使其适用于混合化合物的连接。通过记录工作介质的压力数据，可以很容易地监控过程，这使其有资格实现过程自动化。目前，其应用范围受到内部可达性的限制。该项目旨在通过扭转成型方向来扩展工艺限制，以连接内部可访问性有限的部件，如强烈弯曲或特别长的型材，并密封旋转对称的容器。不是内部高压的径向膨胀，而是外部压力的径向压缩。潜在地，这将导致应用范围的扩大，并促进该技术的工业接受度。为了实现项目目标，有必要开发可靠增压的工具概念，并生成连接和工艺设计的方法。第一个原型工具被开发出来，并在成形技术和轻质结构研究所用于可行性研究。采用静态密封系统，工件公差对密封效果产生负面影响，或由于预紧力增加而导致高密封磨损。因此，必须通过数值和实验研究来改进工具技术。在不同的连接方向上，连接对端部的应力应变分布不同。由于它们影响粘结强度，因此它们的确定对于制定工艺和接头设计的方法和指南至关重要。工艺的最终比较(使用外部和内部高压启动)显示了各自的经济性，并允许定义整个工艺窗口。这些知识将通过向合作伙伴的示范部分进行工艺应用而转化为工业实践。最后，该项目通过成型工艺提供了经过工业验证的灵活连接，适用于具有不同材料组合和外部可访问性的干涉和/或成形配合接头。

Lightweight construction requires weight optimization of structures and components. This is often realized by the integration of functions or the combination of different material properties in one single component. Due to the high diversity of material properties there are high demands on the joining technology which lead to technological or economic limits of conventional joining processes.A suitable alternative to conventional methods is the process of joining by die-less hydroforming. This process allows the production of interference fit and/or form fit joints, which makes it suitable for joining mixed compounds. By recording the pressure data of the working media it is easily possible to monitor the process which qualifies it for process automation. At present, the application range is limited by the inner accessibility. The project aims at extending the process limits by reversing the forming direction to join parts with limited inner accessibility like strongly curved or especially long profiles and also to seal rotationally symmetric containers. Instead of a radial expansion by internal high pressure there is a radial compression by external pressure. Potentially, this leads to an increase of the application range and promotes the industrial acceptance of the technology. To achieve the project objective, it is necessary - to develop tool concepts for the reliable pressurization and- to generate approaches for joint and process design.A first prototype tool was developed and used for feasibility investigations at the Institute of Forming Technology and Lightweight Construction. A static seal system was used, with the workpiece tolerance negatively affecting the sealing effect or leading to high sealing wear because of increased preload forces. Consequently, the tool technology has to be improved by using numerical and experimental investigations. The stress and strain distributions in the joining partners differ at different joining directions. Since they influence the bond strength, their determination is essential for the derivation of approaches and guidelines for process and joint design. A final comparison of the processes (with external and internal high-pressure initiation) shows the respective economy and allows to define an overall process window. The knowledge will be transferred to industrial practice by process application to demonstration parts of the cooperation partners. Finally, the project provides an industrially proven, flexible joining by forming process suitable for interference and/or form fit joints with different material combinations and external accessibility.