Endless fiber-reinforced plastics offer outstanding mechanical performance with relatively low density and are therefore ideal lightweight materials for the realization of sustainable mobility concepts for the future. Resin injection processes such as resin transfer molding (RTM) are promising processes for the production of fiber-polymer composites from dry preforms. For the production of these preforms, textile semi-finished products such as fabrics or non-crimp fabrics are usually used. Due to their constant production width, however, a high proportion of waste is generated when cut into preforms close to the final contour, which on the one hand impairs the economic efficiency of the production process, but on the other hand also leads to high amounts of waste. It therefore makes sense to replace classic preforming processes with more material-efficient processes such as Dry Fiber Placement (DFP). In DFP, continuous fiber rovings, provided with a powder binder material, are placed directly on a tool in a robot-assisted laying process in order to create a preform close to the final shape with load-compatible fiber position and orientation.
In contrast to preforms made of classic textile semi-finished products, preforms manufactured by DFP have a lower permeability to the resin required for component manufacture. This makes both the achievable process speed for resin impregnation and the component quality a challenge.
Within the framework of a DFG-funded research project, approaches are therefore being investigated to understand the impregnation behavior of these DFP preforms in detail (i.e. down to the level of the individual fibers). In addition to a fundamental understanding of the impregnation behavior and its manipulability, the overall objective is to demonstrate approaches that raise the impregnability of preforms to a level comparable to classical textile semi-finished products such as fabrics. Only this way the advantages with regard to material efficiency can be used economically. For the evaluation of the effectiveness of the different structural variations with regard to the increase in permeability, a holistic approach is used which, in addition to the experimental investigation, includes the comparison and calibration with simulative and theoretical approaches (Figure 1).As a result, a large spectrum of possible structural variations can be evaluated in a time-efficient manner. The approaches for permeability control contain variations of the preform structure that can be applied on several levels. The micro level describes the spaces between individual fibers, which can be enlarged, for example, by introducing auxiliary materials such as binder particles with different morphologies. The meso level is a larger level in which spaces between entire fiber bundles or strands are considered. A possible example is the sewing of preforms for the insertion of meso flow channels into the preform structure as shown in Figure 2 and Figure 3. Overall, the project thus contributes to making dry fiber placement, which offers major advantages in terms of both mechanical and resource efficiency, competitive in terms of process technology.
The project "Fundamentals concerning impregnation of preforms manufactured by Dry Fiber Placement" is supported by Deutsche Forschungsgemeinschaft (DFG), (funding reference: BE 6334/1-1).
Dipl.-Ing. Oliver Rimmel
Institut für Verbundwerkstoffe GmbH
Telephone: +49 (0) 631/2017228