Flexible form-fit joining using incremental sheet metal forming

• Applicant: Dr.-Ing. David Bailly
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 459861167

The joining principle of hemming offers the possibility of creating linear joints with form- and force-fit and is widely used, especially in car body construction. The industrially established processes for hemming are tool-based machine hemming and roller hemming. The overarching motivation of the research project described here is the use of the process principles and tools of incremental sheet metal forming for the production of hemmed joints (ISF-hemming) as an alternative to the established processes. In addition to a greatly simplified tool design, the potentials include the extension of the process limits with regard to crack and wrinkle formation as well as the possibility of integrating forming and joining operations in a system design. In the first funding period, a fundamental understanding of the ISF-hemming process was established. An advantageous material flow was demonstrated, which is beneficial for the crack- and wrinkle-free production of curved hems. Previous findings relate exclusively to straight and curved contour lines of hems, which lie in a planar plane. In the requested second project phase, the process understanding developed is to be extended from two-dimensional to three-dimensionally curved hems. This broadens the range of applications because many real components also have three-dimensionally curved edges. However, the multi-directional curvature also results in new challenges, as material compression or stretching can occur in all spatial directions depending on the combination of curvatures. Even with a straight hem, material compression or stretching occurs in a curved sheet surface in the previously used intermediate stage of the 90° collar. If a surface curvature is then combined with an edge curvature, these material flow effects are superimposed, i.e. different material compression or stretching could be reinforced or even compensated for. The work program will initially focus on straight hems on convex and concave surfaces and then on the further development of three-dimensional hems. In each case, the conventional process strategy with a 90° intermediate stage will be investigated first and then new process strategies will be developed with the aim of achieving a more beneficial material flow. The planned investigations will be carried out experimentally and simulatively. Process simulations are used for process planning and material flow analyses as well as for the development of new process strategies and optimized blank shapes. Finally, the transfer of the findings to a realistic application component will be investigated.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr.-Ing. Junhe Lian