Falzen von Baugruppen aus FVK und Metall

Components made of fiber-reinforced plastics make an important contribution to reducing vehicle weight in the automotive industry. Recent developments show an increasing industrial interest in integrating fiber-reinforced plastics in existing metal structures. One challenge is the appropriate joining of these hybrid structures. It is important to avoid interrupting or damaging of the fiber flows, to take the forces in the joining area as homogeneous as possible, to ensure sufficient skin quality and to meet corrosion-technical requirements - especially when joining carbon fiber reinforced plastics with metals. This research project examined the joining of an CFRP structural component with a metallic outer skin part by hem flange bonding. Such hybrid FRP-metal assembly combines the outstanding properties of both materials in the composite, while the hem flange bonding ensures optimum connectivity. The embedding of the joining process in the existing process chains and the use of existing plant technology for the production of automobile hang on parts among OEMs and suppliers promise a rapid implementation of the results. The advantages mentioned are facing new challenges resulting from both the manufacturing process chain as well as from the operating conditions and material-specific properties. Within the project the following issues were examined: Joining process: According to the specified materials and process boundary conditions, suitable adhesives were chosen. These have been studied and characterized both in situ and in the hem flange. The hem flange bonding of steel-CFRP and aluminum-CFRP assemblies was studied in different model geometries using tabletop hemming and roller hemming. Here, the hemming result was evaluated and the CFRP inner part was examined for possible damage. The results show that the forces during the hemming process do not lead to any structural damage in the CFRP. Thermal stress: If the hem flange bonding of the hybrid assembly is implemented in the common process chain, there are heatings up to 200 ° C in the subsequent coating process. This results in the so-called delta-apha-problem because the coefficient of thermal expansion of the outer metal part is significantly higher than the FRP inner part, resulting in relative movements during heating and cooling of the assembly. The expansion of the parts, the relative movements in the composite and the warpage occurring after the adhesive curing were recorded and evaluated. In addition, the description of the processes in the furnace as well as forecasts of war page were carried out by numerical simulation. Then constructive measures were examined in order to reduce the warpage of hem flange bonded hybrid assemblies. Joint properties: The strength of the bonded CFRP-metal hem flanges was determined and evaluated in peel tests and 3-point bending tests. In 3-point bending test it was proved that the hem flange not fails even for large sample deformation. The corrosion of metal-CFRP hybrid assemblies is essentially affected by disbonding of adhesive at metal surface and defects or critical areas in the hem flange. Good corrosion protection performance could be achieved by optimization of hemming parameters and selection of suitable adhesives