This study addresses the experimental investigation of the influence of the thread count of carbon fiber (CF) twill textile-reinforced polyamide 66 laminates on their inductive heating behavior. By means of stationary heating experiments of laminates, different twill 2/2 fabrics have been investigated. The used twill 2/2 fabrics differ only in thread count and consequently in their area weight. Due to the different area weight, the manufactured laminates differ in the number of plies to guarantee an equal fiber volume content in each plate. In order to evaluate the heating behavior of the different specimens, the heating rates of both surfaces of the specimens were measured and compared. Thus, it was found that a lower thread count promotes a faster inductive heating of CF twill 2/2-reinforced polymer composites. Further investigations based on microsection analysis and measurements of rovings cross-section shape revealed that the increase of heating rates at lower thread counts relies more on the number of fabric layers. Through a higher number of fabric layers, the total contact area will be higher due to more interply and intraply contact interfaces which occur in the laminate.
Continuous induction welding is particularly suitable for joining carbon fiber-reinforced polymer composites (CFRPC) with thermoplastic matrix, as the energy required for melting the thermoplastic matrix is introduced without contact and leads to intrinsic volumetric heating of the adherends. However, the great potential of fast heating cannot be fully exploited. Therefore, a process improvement of continuous induction welding was carried out, which follows three complementary approaches. The first approach provides for the development of an adapted laminate structure. Compared to a conventional CFRPC laminate, the adapted laminate shows a heating in the joining zone that is approx. 16 K/s faster. The second approach intends to improve the currently used cooling system to cool the induction coil faced laminate surface. Spray cooling proved to be the most suitable method. Compared to pressurized air cooling, it was possible to achieve a temperature difference between the joining zone and the inductor faced laminate surface that was approximately twice as large. The third approach aims at the simulation-based improvement of the consolidation phase. This model can be used to determine the joining pressure and pressure time required to achieve intimate contact.
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