Automating Wet Fiber Placement

Additive manufacturing is becoming increasingly important in the production of complex structural components. Researchers around the world are continuously developing new processes, in which various materials made of polymers and metals are applied to produce three-dimensional objects from computer-aided models. Additive manufacturing processes that combine polymers with fibrous materials have been developed for quite some time; these processes mostly employ short fibers but also increasingly continuous fiber bundles. Thermoplastic resins are mostly used for these additive manufacturing processes and less frequently thermoset resins, despite them dominating the fiber-reinforced composites market. In contrast to thermoplastic materials that can be re-melted, thermoset resins solidify as a result of a chemical reaction which is why semi-finished products based on thermosets only have a limited shelf life and usually require cooled or even deep-frozen storage. The short shelf life can be circumvented via an in situ impregnation process for fiber bundles with a thermoset resin directly in the deposition process. Direct impregnation is currently being pursued at Leibniz-Institut für Verbundwerkstoffe (IVW). Wet fiber placement (WFP) has been developed in the TopComposite junior research group at the IVW.

In WFP, fiber bundles are drawn from a roving creel, impregnated with a thermoset resin and are then conveyed via a roving conveying system that exploits belt friction effects. The TopComposite interdisciplinary junior research group, funded by the German Federal Ministry of Education and Research (BMBF), is currently developing the process technology as well as product design methods and adapted resin systems. The focus so far has been upgrading the existing lab prototype to a fully automated system. Figure 1 depicts the automated system that was developed. The new system includes four axes which are divided into an X-Y table - on which the molding tool is mounted - and a Z-axis - on which a rotary axis is mounted. An end effector is attached to the rotational axis, through which the roving is conveyed to the molding tool. A pneumatically driven cutting unit is used to cut the roving in the end effector to the desired length, enabling discontinuous placement. The rotational axis can rotate the end effector to the correct fiber orientation, allowing straight as well as curved profiles to be placed. The new system also includes various dancer units to synchronize the various drive units in the system.

In the next step, the end effector will be further optimized and test specimens will be producedwhile, simultaneously, the influence of deposition defects is investigated.

The project "TopComposite – Topology-optimized and resource-efficient composites for mobility and transport" is funded by the Federal Ministry of Education and Research (funding reference 03XP0259).