Lightweight construction with fiber-reinforced plastics has become indispensable in the automotive sector. Every gram of weight counts, especially in electromobility. In addition, carbon fibers allow design freedom and help to improve fire protection and crash safety. But how can component production with this still young material be made particularly efficient and optimally integrated into existing automotive processes? The experts at SGL Carbon have been working intensively on this challenge for years in close cooperation with customers. The decisive factors here are not only component design and innovative processing methods, but also optimum textile pre-processing of the material. One important variant is precisely tailored and customer-specifically assembled packages of carbon fiber layers, known as stacks.
A stack is a textile structure for further processing in the process chain for manufacturing CFRP components. The stack consists of different individual textile layers, which define the mechanical properties of the final component by material, number, orientation and grammage.
These individual layers are stacked, cut to size and joined together by different joining processes. Stacks are used as input material for the component-forming processes wet pressing and preforming/RTM.
Today, stacks are already the basis for almost all components manufactured using the particularly common wet pressing and RTM processes. However, the rule is still that most component manufacturers purchase the carbon fibers as textile rolls and manufacture the stacks themselves. This includes the layering of the textile layers, the cutting, the fixing and the provision of the stack at the preforming line or press. The problem here is that stacking and thus the handling of dry fiber materials are often not the core competence of the component manufacturer. The production of the stacks costs time and manpower and requires the development of know-how. At the same time, the manufacturer has to pay for, reuse or dispose of material waste.
SGL Carbon can and will take all this off customers' hands in the future. Our portfolio of textile reinforcement materials already covers numerous requirements of industrial applications. And what doesn't fit yet, we simply adapt, so that our customers get their CFRP components as cost-effectively and efficiently as possible. With our stacking systems, larger geometries can also be realized, allowing larger components to be produced from one piece.
Our SIGRATEX high-performance textiles based on carbon and glass fibers are optimized for automated stacking processes. We thus offer a complementary portfolio of composite solutions that improve the performance of the finished product and thus contribute to a smarter world.
To produce composite components, many upstream processes are necessary before a component is created. We take over the entire textile process steps, such as fabric production, layering and cutting, and supply the minimum necessary stacks for component production directly to the press.
When selecting the right textile, the customer benefits from the design freedom within our broad textile material construction kit: different fiber orientations or basis weights, carbon or glass fiber or a mix of both – each individual layer in the stack can be freely selected.
No defect leaves the factory - we guarantee 100% inspection of the individual layers by online measurement of the textile top and bottom. Defective areas in the material are communicated from the scrim line to the stack line. In the stack production, faults in the single layer in a stack are detected and the faulty stack is blocked for further processing. The stack contour as well as the position of labels and, if necessary, joining points are 100% monitored by optical measuring systems. Our certification according to IATF 16949 makes our quality performance transparent and proves our process capability and reliability over the entire value chain.
In our state-of-the-art plant park, we have created the ideal conditions for efficient stack production. We offer our customers the optimal solution here: from initial prototypes and small batches to large-scale production with quantities of up to one million units per year. The high degree of automation of the stacking line enables us to ensure product quality and production volume.
We offer our customers tailor-made solutions for their applications. For example, our stacks can make optimum use of lightweight potential and component performance by introducing local reinforcement, e.g. with fiber placement technology. In addition, carbon fibers are applied where they are needed, enabling load-path-compatible construction.
We take care of the annoying waste disposal: A waste-optimized stack is already generated during configuration. The near-net-shape stacks are delivered directly to the customer's press. This eliminates the trimming of textile semi-finished products and the storage and disposal of off-cuts for our customers.
Our stacks are the result of decades of experience. As a long-standing partner, we have been producing carbon fibers, semi-finished products, and stacks for the automotive industry for over 10 years. In the process, the joint venture together with BMW has advanced our expertise in large-scale production. Our material systems and production technologies are designed so that all components can be manufactured in large series.
1. Layer selection
At the beginning, the various individual layers for the stack are selected together with the customer from our extensive product portfolio of fabrics. The customer can choose between different textile types, fiber materials, fiber orientations and areal weights to achieve optimum component performance.
In the second step, the individual layers are stacked on top of each other according to the layer structure.
The layered individual plies are then cut to shape with a cutter. The layer structure and the contour are created after this step.
In the next step, the stack is joined by applying pressure and temperature. Depending on the process used, the stack can be joined over the entire surface or at specific points.
5. The finished stack
The customized SIGRATEX stack can now be delivered to the component manufacturer and used directly for further processing in the mold.