Laser-based production of carbon fibers

Carbon fiber reinforced plastics are excellent materials for applications in lightweight constructions in the automobile or aviation sectors due to their 2.5-fold higher specific strength compared to aluminum. However, the high manufacturing costs of carbon fibers are one of the main limiting factors for the exploration of new fields of applications. The precursor fibers mostly consist of polyacrylonitrile which is transformed into carbon fibers in furnace processes. Almost one half of the manufacturing costs can be assigned to the stabilization and carbonization of the carbonaceous precursor fibers. The furnace processes takes up to 2 h and produces high energy costs due to the needed temperatures of about 1500 °C. In this paper, a new laser-based manufacturing process for carbon fibers is presented. The process is developed at the Fraunhofer Institute for Laser Technology (ILT) and shows potential for the implementation of a fabrication process with reduced energy and time costs compared to the conventional furnace based approach. Furthermore, the fiber stabilization can now be realized with higher heating rates. Thus, shorter stabilization times are potentially needed. The exothermal energy from the stabilization reaction can be extracted more efficiently via the cool ambient air which reduces the risk of thermal damage of the fibers tremendously. Furthermore, the excellent adjustability of the spatial and temporal energy deposition via laser allows an adaptive process control which has the potential to fabricate fibers with increased mechanical properties in shorter times. First investigations of the stabilization process indicate that a careful choice of the process parameters allows for inducing distinct temperature profiles in the fibers which influences the resulting carbon fiber structure. Furthermore, first investigations on laser-based carbonization show that the fabrication of fibers with tensile force of up to 8 cN is possible.