Composite manufacturing technologies
The braiding process is to be performed on special radial braiding machines. There, a robot guiding the braiding core controls the deposition of composite fibers via the braiding bobbins at defined angles and in several layers.
Additional fibers in the longitudinal direction of the component (UD fibers) are introduced along the braiding core axis around the machine's circumference. The resulting tube is formed on the braiding core. The outcome is a "preform" that already matches the final contours of the component to be manufactured.
The advantages of the braiding method at a glance:
- Flexibility in component geometry: can be used for hollow bodies of nearly any shape
- Flexibility in fiber structure: depending on the intended use, various types of fibers can be combined (carbon fibers, glass fibers, aramid fibers, etc.)
- Flexibility in component properties: variable braiding angles for each braided layer make it possible to adjust torsional stiffness with high precision. Feeding additional fibers into the longitudinal component axis (UD fibers) makes it possible to optimize bending stiffness. Additional braiding layers at the component surface help improve impact characteristics.
- Flexibility in process management: By applying dry fibers in the braiding process, the preform production process can be combined easily with other textile processes. For adjusting certain component properties, the braiding process is combined, for example, with the UD winding method as well as with local reinforcement by means of embroidering and laid mats. The fact that the braiding will not be closed until right on the braiding core surface makes it easy to integrate the pin structure of our T-Igel® connection.
- Low process costs: The high degree of automation, the high throughput in fiber placement, and the low amount of generated waste makes it possible to implement high-volume series at low cost. As a result, attractively low lightweighting costs become feasible, especially in combination with the RTM process.
- Long-standing experience: TEUFELBERGER is a braiding specialist because of its decades of experience as a rope maker (with more than 500 braiding machines installed at its various international branch operations)
In TEUFELBERGERs proprietary filament winding process, dry composite fibers from up to 4 winding bobbins are deposited in parallel at controlled angles as a UD layer structure onto a winding mandrel. Other than in the conventional filament winding process, the winding bobbin rotates around a stationary core that is guided through the winding eye by means of a robot. This process makes it possible to produce even complex component geometries, and it can be combined with the braiding process.
The advantages of filament winding combined with braided structures at a glance:
- Improved component properties: The unique combination of braiding and winding technologies produces improved component properties at low process costs. Higher fiber volume contents, tear-stopper function, increase in local torsional rigidity, and many others.
- Low process costs: The specifically developed automatic filament winder can be docked easily to our braiding machines, but also be operated in a standalone mode. This makes the automated production of complex components having quasi-isotropic properties (4-axial fiber structures) possible.
- New lightweighting applications: The possibility of creating layered braided and wound structures broadens the scope of lightweighting applications and the options for functional integration. It is now possible to cost-efficiently produce internal-pressure-loaded components having high longitudinal rigidity (see TEUFELBERGER crossmember with integrated pressure tank) or tie rods providing high resistance to buckling.
- Improved force transmission: Local compression layers make it easier to integrate metallic force transmission elements such as TEUFELBERGER's T-Igel®.
RTM – Resin Transfer Moulding
In the RTM process, the braided and/or wound preform is inserted into the cavity of the compression mold. The contours of the cavity correspond to the outer geometry of the finished RTM component. After closing the mold, applying the pressure, and reaching the necessary process temperature, the low-viscosity resin/hardener mixture is injected into the mold under pressure and at an elevated temperature.
Finally, the compression mold is opened after the curing phase, the component is removed from the mold and, if necessary, post-hardened in an oven up to final curing temperature. Depending on component requirements and core strategy (lost core vs. reusable core), the braided/RTM core is eventually pulled out or separated.
The advantages of the RTM process at a glance:
- Excellent component quality: Due to the use of compression molds, the inner surface of the RTM cavity is mirrored exactly in the component surface. Furthermore, special in-mold coatings can be used to adjust other surface characteristics. This way, one obtains true-to-contour and pore-free components having fiber volume contents up to 60%.
- Low process costs: Depending on the requirements and the number of pieces to be produced, different molds and different numbers of cavities are employed. Depending on injection pressure (at TEUFELBERGER up to 40 bar), temperature control, and resin system, process times within the range of 5 min are possible.
- Flexibility in manufacturing process: It is possible to use different resin systems (epoxy resins, PU resins) having different properties and curing temperatures and various core materials. At TEUFELBERGER, we also employ out-of-mold injections (up to component lengths of 4.5m) and RTM light processes.
- T-Igel®-capable: The RTM process ensures the optimum integration of the T-IGEL® connection.
Vacuum infusion constitutes a simple and cost-effective alternative, especially for low-volume component projects and the implementation of function demonstrators with low external tolerance requirements. TEUFELBERGER has optimized the infusion technology for three-dimensional hollow structures.
In the vacuum infusion process, the liquid resin impregnates the dry fibers while it is sucked into the fiber preform at negative pressure and at moderate temperature. Special vacuum materials permit controlling the motions of the resin front. In this process, the outside of the preform is sealed off with flexible membranes and sheets. Curing takes place in an oven.
The advantages of vacuum infusion at a glance:
- Low process costs: The vacuum infusion process offers excellent cost-effectiveness for prototypes and small series.
- Also suited for very large dimensions: This process can also be used for component lengths up to several meters.
- Flexibility in the manufacturing process: Due to the use of flexible membranes in the vacuum infusion process, there are almost no limits to component complexity.
For special components (e.g., for gusset plates, thrust plates, inner liners) TEUFELBERGER also works with prepreg materials. In this case, the pre-impregnated UD fabrics and woven mats are cut to size and draped manually onto steel molds according to a defined layer structure. The consolidation takes place for plates in temperature-controlled compression molds and for tubes via shrinking hoses in the circulating air oven.
The advantages of prepregs at a glance:
- Excellent component quality: The pre-impregnated prepreg material makes lowest pore contents and high fiber volume contents possible. The unidirectional layers and the use of high modulus fibers ensure a load-conforming fiber placement and the production of components of high specific mechanical properties.
- Low cost & flexible manufacturing: In the case of simple component geometries and mid-range piece numbers, the higher material costs of the prepreg materials can be compensated easily by fast and flexible manufacturing using simple means of production.