Gap measurement for thermoplastic adhesive joining of aircraft frames

The assembly of frames into the structure of aircraft fuselages requires adhesive shimming to fill occurring joint gaps above 0.3 mm. Gap measurement and gap filler application tasks are time-consuming manual processes. Up to now, the frame elements form the interface between frame and shell adjusting any form deviations. Stiffness elements are added to support the shape of the frame. To save process efforts, new frames under development are thermoplastic integrals with main body, feet, and stiffness elements made of one part. These parts are easier to form and re-shape during production but have to be adequately produced to fit to the shell, avoiding joining forces and deformations. In this paper, it is presented that the gaps can be measured with an automated method. Novel developments are the automated gap body measurement of rigid parts in a pre- assembly station, the measurement method by avoiding joining forces and the automated procedure of measuring gaps for applying the gap filler. The gaps between two joining parts are reconstructed virtually by measuring the joining surfaces of the produced parts with a laser tracker and a line scanner (T-Scan) before joining. These points are combined with the CAD model of each part. The parts are then virtually joined. The exact opposite points of each joining surface are either in contact or have a distance resulting in the gap value. Virtual joining gives insight into the results of the process and helps decide on the gap-filling strategy. The effects of contact during assembly can be avoidable using a design gap or a shape best-fit. The resulting point cloud is then processed and transmitted to a robot-guided 3D printer reproducing the surface structure with thermoplastic PEEK gap filler material directly onto the frame feet surfaces.