Abstract

Fiber reinforced polymers are characterized by a superior specific stiffness and strength. But the good material properties can only be found in preferential fiber direction. Therefore, it is indispensable to know the fiber orientation for the design of components and the evaluation of the mechanical component behavior. For long fiber reinforced polymers, such as sheet molding compound (SMC), the fibers are re-oriented due to the material flow during manufacturing. In this respect, the material flow is directly dependent on the component design. Accordingly, there is a direct dependency between design, material and manufacturing, which must already be considered during the initial design phase of SMC components. In order to be able to take the fiber orientations resulting from the manufacturing process into account in the component design, manufacturing simulations are used in the context of virtual product development. For this purpose, the flow behavior during compression molding of SMC has to be calculated. The resulting mechanical behavior of the component can only be predicted by accounting for a sufficiently accurate prediction of the fiber orientations. This contribution discusses the simulation of compression molding of SMC in Autodesk Moldflow 2019. Therefore, the modeling of characteristic flow properties is shown. In addition to the selection of appropriate manufacturing conditions (such as size and compressibility of the initial charge, press speed etc.), this also includes target-oriented modeling of the wall friction behavior in order to be able to represent wall-slip which is characteristic for SMC. The results generated in Moldflow for the fiber orientation tensors are compared with real fiber orientations in the component analyzed by optical evaluation methods. Additionally, compression force and cylinder displacements are compared to recorded press data. In a second step, the anisotropic material properties are provided for structural simulations in Dassault Systèmes Abaqus using a mapping procedure. The results of the mechanical simulations are also compared with experimental results. It was found that the friction at the mold wall, which is crucial for the material flow, was not sufficiently modeled in Moldflow 2019. Through direct cooperation with the responsible developers, the problem could be solved, and Moldflow 2021 could be used to calculate the resulting fiber orientations and compression forces with sufficient accuracy. The accuracy has been validated by evaluating the fiber orientations, predicted compression forces as well as the mechanical structural response.