Joining by dieless hydroforming with outer pressurization

轻量化结构要求结构和部件的重量优化。这通常是通过在单一组件中集成功能或组合不同材料特性来实现的。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局限性。一种适合替代传统方法的方法是通过无模液压成形连接。该工艺允许生产过盈配合和/或形式配合接头，这使得它适用于连接混合化合物。通过记录工作介质的压力数据，可以很容易地监控过程，从而使其符合过程自动化的要求。目前，其应用范围受限于内部可达性。该项目旨在通过扭转成型方向来扩展工艺限制，以连接具有有限内部可及性的部件，如强弯曲或特别长的轮廓，以及密封旋转对称的容器。不是由内部高压引起的径向膨胀，而是由外部压力引起的径向压缩。这可能会导致应用范围的增加，并促进该技术的工业接受度。为了实现项目目标，有必要开发可靠加压的工具概念，并为接头和工艺设计提供方法。第一个原型工具被开发出来，并用于成形技术和轻量化结构研究所的可行性调查。采用静密封系统，由于预紧力增加，工件公差会对密封效果产生负面影响或导致高密封磨损。因此，必须通过数值和实验研究来改进刀具技术。在不同的连接方向上，接头内部的应力和应变分布是不同的。由于它们影响粘结强度，因此确定它们对于工艺和接头设计的方法和指南的推导至关重要。过程的最后比较（外部和内部高压启动）显示了各自的经济性，并允许定义整个过程窗口。知识将被转移到工业实践的过程应用到示范部分的合作伙伴。最后，该项目通过成型工艺提供了一种工业验证的灵活连接方式，适用于不同材料组合和外部可达性的干涉和/或配合接头。

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.