Loadable inserts in CFRP lightweight design

Especially in the automotive, aviation and sports industries, metal assemblies are being replaced by fibre-reinforced composites in order to increase efficiency by reducing weight. Here, carbon fibre reinforced plastic (CFRP) is the preferred material, especially in sandwich structures with a foam core and CFRP top layers. Consequently, the demand for new resilient joints for metal and CFRP components is increasing.

State of the art

Conventional joining processes, such as welding or riveting, can only be used to a limited extent and they do not reliably apply the impacting forces, so that component failure is to be expected. As an alternative, metal force application elements are used, known as inserts, that transmit the forces over a large area into the core and the top layers of the CFRP components. However, the disadvantage here is that manufacturing them is time- and cost-intensive, since the inserts have to be fitted into the prefabricated CFRP sandwich component at a later stage in the production process.

Technology

Scientists at the KIT wbk Institute of Production Science have developed highly resilient inserts that are already fitted during the manufacturing of the CFRP sandwich structures using liquid composite molding (LCM). In designing the foam core, the form of core reinforcement is taken into account by specially selecting a cavity in which, e.g., a thread screw is later positioned.This cavity is filled during the injection of the liquid matrix, e.g. epoxide resin, whereby the screw shaft is anchored in the matrix. After curing, local reinforcement is achieved. Additional special plastic spikes seal the inserts and support the assembly process: They protect the screw thread from contamination or damage during positioning, for example.

Advantages

The new resin inserts are cheaper and lighter than metal reinforcements. Moreover, they can take a greater load since the carbon fibres of the top layers remain undamaged in the manufacturing process. Thanks to process integration, subsequent joining steps are not required.

Options for companies

The new method is suitable for large-scale series production. KIT is looking for companies interested in its industrial application to support its implementation in industry.