Direct deposition of CF/PEKK composite shims on CF composite laminates for aeronautics

A new deposition system, composed by a 4-axis robot (Epson SCARA T3-401S), an extrusion head (E3D Titan Aero Kit), a bench power supply and a controller (Duet 2 WiFi), was prototyped for layer-additive-manufacturing (LAM) of carbon fiber (CF) poly-ether-ketone- ketone (PEKK) composites. The extrusion device has been modified to allow the deposition of tapes instead of circular filaments used in fused deposition modeling (FDM), that represents the conventional technology for this kind of application. An elastic connection, composed by 4 springs, was placed between the robot end-effector and the extruder to guarantee tape agglomeration during manufacturing. Deposition tests of 20 layers of CF-PEKK thermoplastic composite were carried on a CF-epoxy laminate as substrate, at the extrusion temperature of 420°C and the rate of 60 mm/min. Adhesion was high even if the substrate had a thermoset epoxy matrix. The CF-PEKK composite showed a good surface appearance, irregularities and misalignments were not visible at the end of manufacturing process. Good adhesion of the 3D printed part is fundamental to evaluate the feasibility of the prototyped LAM machine to deposit aeronautic shims. Machining tests have shown that the deposited CF-PEKK composite is well bonded to the surface of the traditional CF-epoxy laminate. In fact, even with the small size of the deposited part, the CF-PEKK composite has been machined without any issue.