The success factor for innovative and at the same time economical lightweight construction of car body components is a holistic and particularly targeted use of fiber-reinforced plastics. However, the interaction with conventional materials such as aluminum and steel is also crucial. This can be achieved, among other things, by hybrid mixed construction methods. To expand competencies in the field of CFRP/metal hybrid lightweight construction, the MAI CC4.0 "HybCar" project has been launched with the aim of developing competencies in the field of hybrid lightweight construction along the entire value chain.
As part of the HybCar project, carbon fiber-based unidirectional (UD) tapes with a polyamide 6 matrix are deposited onto metallic substrates in a load-path-compliant manner using a fiber placement process. The mix of carbon fiber-reinforced thermoplastics and metal sheets enables the production of lightweight components while considering a particularly resource-efficient use of materials. An X-shaped technology demonstrator was developed as part of an underbody for electric vehicles, encompassing all the technological challenges of this specific hybrid application.
In addition to using UD tapes, pultruded thermoplastic flat profiles can also be used for local reinforcement. This can increase filing efficiency and thus improve the economics of the application.
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The very local reinforcement with fiber composites makes it possible to reduce the thickness of the steel sheet from 2.5 mm to 0.7 mm and structurally reduce the overall height throughout the vehicle floor. This gain in space can be used to further advantages in terms of aerodynamics, fuel consumption or comfort/interior space. In addition, the flexibility in the thickness of the fiber composite insert means that the floor assembly can be designed or scaled to suit requirements.
As a result, the underbodies can be used for both small batteries and vehicle models with large batteries thanks to the precise insertion of load-specific reinforcement structures. In the process, smart mold inserts can be used to produce the corresponding floor assemblies across all models using the same forming mold and the same production setup. This not only saves time, but also tooling and changeover costs.
Thanks to the flat design of the carrier structure, more than 18 millimeters of height have been gained in the front foot area. Furthermore, the weight was reduced by more than 10 kilograms, representing a weight saving of around 40 percent. Thanks to a fully automated manufacturing process, the cycle time for production was brought to under 90 seconds.
"CFRP/metal-based hybrid structures offer a good opportunity to combine the advantages of both material classes. In the HybCar project, we are developing a scalable component concept with an efficient use of materials in combination with a fully automated manufacturing process.", explains Michael Kropka, Product Developer Thermoplastics at SGL Carbon.
The HybCar project, which is funded by the Bavarian State Ministry of Economic Affairs, Regional Development and Energy, is being driven by a consortium comprising EDAG Engineering GmbH (EDAG), the company Automation W+R, the Institute for Materials Resource Management at the University of Augsburg (MRM), the Fraunhofer Institute for Casting, Composite and Processing Technology IGCV and SGL Carbon. The demonstrator component is manufactured at SGL Carbon’s production site in Meitingen near Augsburg. The production of the prototype is preceded by digital product development, which is also being developed as part of the project.
The pre-consolidated UD tape structure is heated together with the steel component in an infrared oven above the melting temperature of the polymer. In the next step, in addition to the 3D forming, an adequate bonding agent is used to produce a strong material bond between the two components.