Resistance welding of high-performance reinforced thermoplastics in fuselage applications

Abstract

The amount of carbon fiber-reinforced plastics in modern aircraft is constantly increasing, with highperformance thermoplastics playing an important role in primary structures. The advantages of these materials include attractive mechanical properties and short process cycles. The use of new materials has also generated interest in high-performance and robust joining processes. In previous aircraft series, rivets have usually been the preferred joining method. In addition to setting the rivets, the method requires a large number of work steps such as pre-drilling holes and a subsequent costly cleaning. The process of resistance welding eliminates all these steps. Furthermore, this type of joining is more suitable for a fiber-reinforced structure, as the fibers of the components do not have to be drilled. The resistance welding process is as follows: An electrical conductor is placed between two components. The components are then pressed together under a defined pressure and the conductor is connected to electrodes on both sides, closing the circuit. The resistance of the conductor generates heat by means of an applied current, which melts the boundary layers of the components. The heating process is followed by a cooling process. After reaching the glass transition temperature of the polymer being processed, the pressure is removed and cooling continues to the initial temperature. This paper details work done on the resistance welding process of components made of carbon fiberreinforced polyarlyetherketone (CF-PAEK). Applications in the fuselage suitable for this welding method are the frame-to-skin, stringer-to-skin, clip-to-skin and clip-to-frame connections. For the welding combinations above, one type of angle is welded to one surface. In order to develop and adapt the welding process to the new material, trials were made on coupon level and an investigation of mechanical performance performed. Based on these results, a welding tool was designed to join L-shaped-angles onto a laminate.