Fraunhofer Institute for Microstructure of Materials and Systems IMWSLightweight construction is an indispensable approach, particularly for modern mobility and the achievement of climate protection targets. In vehicles with combustion engines, lightweight construction solutions ensure lower fuel consumption and thus a reduction in pollutant emissions thanks to the reduced vehicle weight. Lightweight construction also helps to save on materials and thus conserve resources. In electromobility, lightweight construction technologies increase the range because less mass has to be moved with the energy stored in the battery.
One technology already established in industry is plastic-based sandwich composites with continuous fiber-reinforced top layers and honeycomb cores. Due to their very good weight-specific mechanical properties, they are used in particular for large-area structural components in lightweight construction. In contrast, continuous fiber-reinforced sandwich composites are still rarely used for complex structural components, with previous areas of application including high-price segments such as the aerospace and sports equipment industries. This is mainly due to the fact that such components cannot yet be produced fully automatically in short cycle times. TS-Moulding offers a solution to this problem.
Previous limits of sandwich construction
The sandwich construction enables an optimum ratio of bending stiffness to component weight. This is achieved by a three-layer structure with two thin, highly rigid and high-strength cover layers, between which there is a core structure that is predominantly filled with air. This structure-optimized design ensures a high section modulus combined with low density, i.e. very high weight-specific stiffness of the sandwich composite.
When using fiber-reinforced plastic composites, the best results can be achieved with a structure that contains a fabric of unidirectional continuous fiber-reinforced plastic layers (UD layers) as cover layers and a honeycomb core as support structure, which enables ideal absorption of external surface loads due to its cell walls aligned orthogonally to the cover layers. While the surface layers are subjected to tensile-compressive loads, the honeycomb pattern represents a self-supporting load-bearing structure for absorbing in-plane shear stresses.
As important as the honeycomb core layer is for achieving weight advantages and material efficiency, the design and production of integrative structural components is just as challenging. For the production of high-performance sandwich structures with thermoset matrix materials, the joining of core and cover layers with simultaneous shaping is widespread, but requires upstream preparation steps and can result in total production times of several hours. For thermoplastic continuous fiber-reinforced sandwich components with comparable component complexity, only foaming processes have been used to date if the aim is to achieve cycle times suitable for large-scale production. However, the weight-specific mechanical performance of such sandwich composites with a foam core is not as good as that of sandwich structures with a honeycomb core. There are already solutions for the industrial and cost-efficient production of thermoplastic continuous fiber-reinforced semi-finished sandwich products with cover layers made of scrims and honeycomb cores. However, the products are merely plate-shaped semi-finished products that are difficult or impossible to shape into components with complex designs.