Joining by dieless hydroforming with outer pressurization

• Applicant: Professor Dr.-Ing. A. Erman Tekkaya
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing ; Production Automation and Assembly Technology
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 350070123

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.

• DFG Programme: Research Grants (Transfer Project)
• Application Partner: Faurecia Autositze GmbH; Faurecia Emissions Control Technologies Germany GmbH; Poppe + Potthoff GmbH
• Co-Investigator: Professor Dr.-Ing. Noomane Ben Khalifa