Laser In Situ Joining as a Novel Approach for Joining Large-Scale Thermoplastic Carbon Fiber-Reinforced Polymer Aircraft Structures

Thermoplastic matrix composites are a viable option to reduce the carbon footprint during the life of an aircraft due to their ability to be molten and resolidified again. Tape-based layup processes, such as automated tape placement, are well-examined but have not seen extensive use in large-scale joining applications, since they have to be processed layer-by-layer. In contrast, the advanced laser in situ joining method (CONTIjoin) utilizes fully consolidated and cut-to-size multilayered laminates, enabling the continuous layup of tailored laminates aligned with the mechanical application requirements. Herein, sample joints are manufactured using CONTIjoin technology, describing the general process principle, and are compared with samples produced using a standard heat press process. The base material, carbon fiber-reinforced LMPAEK (low-melt polyaryletherketone) is characterized using infrared spectroscopy. Using a 3.5 kW carbon dioxide (CO2) laser (10.6 μm wavelength) coupled with highly dynamic beam deflection, multidirectional reinforced laminates with up to six plies are processed to produce 24-ply plates. The influence of joining temperatures up to 400 °C on the joint quality is investigated. Cross-cuts are examined and interlaminar shear strength tests are conducted. With CONTIjoin, maximum strengths of 48.5 MPa are observed, reaching over 90% of the heat press reference.