Sandwich joining – Functional Sandwich Structures by hole-flanging with lost punches

This research project aims to reduce the processing effort involved in joining sandwich sheets by using special joining elements and thereby improve their marketability. Material-friendly load application can be achieved in a process-integrated manner by local stiffening through hole-flanging during the joining process.

Coordinator: Thiemo Germann M. Sc.
Duration: October 2020 – September 2022
Funded by: BMWK AiF EFB IGF


Modern semi-finished products such as sandwich sheets enable lightweight construction through stress-appropriate design of components at the material level. However, the wide range of different mechanical and physical properties combined in a single semi-finished product when using such modern composites poses new challenges for established manufacturing processes. These challenges and the additional effort involved in joining sandwich sheets impede their widespread industrial application.

Hole-flanging has the potential to create material-friendly joints in sandwich sheets. The present project investigates the use of special joining elements as hole-flanging punches which remain in the component after the forming process (see Fig. 1) in order to produce components which are ready for assembly. The aim of the project is to qualify hole-flanging with joining elements as an industrially suitable joining technique for sandwich sheets that meets common joint strength requirements for many applications.

[1] Cross-section of a hole-flanging joining element, process simulation


Based on the results of the previous research project (opens in new tab) , the existing parametric FE model will be extended to represent the joining process and non-axially symmetrical geometries. The optimization of the joining elements and the process design will be carried out on the basis of the model. An early validation of the concept is planned through tests with machined joining elements. Following the development and commissioning of the test tool, the influences of the essential geometry and process parameters are investigated experimentally. In order to qualify the joining elements for series production under the influence of weathering, specimens with the three most promising variants will be produced and subjected to fatigue strength and corrosion tests. The project will be completed with a final report and the application of the technology in a demonstrator component.


The research work presented here takes place within the framework of IGF project no. N10850/19 of the European Research Association for Sheet Metal Working (EFB). This is funded by the German Federal Ministry of Economic Affairs and Climate Action (BMWK) via the Arbeitsgemeinschaft industrieller Forschungsvereinigungen (AiF) as part of the program for the promotion of Industrial Collective Research (IGF) due to a decision of the German Parliament.

Furthermore, we would like to thank all industrial partners who support this research project:

  • Joh. Jean Weiler e.K.
  • LÄPPLE Automotive
  • PROFIL Verbindungstechnik GmbH & Co.KG
  • PROMESS Montage GmbH
  • RB&W Manufacturing
  • Tata Steel Technology