Comparison of Different Joining Techniques as a Benchmark for Integrally Joined Thermoformed Components Based on Tailored rCF Organosheets

Climate-neutral aviation requires resource-efficient composite manufacturing technologies and viable solutions for the reuse of carbon fibers (CF). In this context, thermoplastic composites (TPC) can make a strong contribution. Thermoforming of TPC is an efficient and established process for aerospace components. But it’s efficiency could be further increased by integration of joining processes, which would otherwise be separate steps. In this work, a two-step thermoforming process for hollow box structures, particularly uplift structures, is presented. The starting point are two organosheets. First, one of the organosheets, intended for the bottom skin of the uplift structure, is thermoformed. After cooling, the press opens, the organosheet remains in the press and an infrared heater is pivoted in, to locally heat up just the joining area. Meanwhile, a second organosheet, intended for the top skin, is heated and thermoformed and simultaneously joined to the lower skin, thereby forming the box structure. I.e. the process can be referred to as co-consolidation with localized heating of the joining areas. This process concept was applied to a spoiler segment: In this case the two variable thickness organosheets were based on recycled CF (rCF) nonwovens. The variable thickness results from the different number of layers of rCF nonwoven. The result is a lower skin panel, where the spar is already integrated, therefore another subsequent joining processes is avoided. To evaluate the bonding strength that can be reached using the co-consolidation with localized heating of the joining areas, it was compared to other joining methods: (1.) Co-consolidation and (2.) resistance welding. Single lap shear samples were produced for comparison. The Resistance welding was the fastest process, followed by Co-consolidation with local heating of the joining area and co-consolidation with a variothermal mold. The shear strength was determined in the tensile test based on DIN 1465. The presented manufacturing process can increase the variety of products for established thermoforming and thus lead to more sustainable structures for aviation.