Effect of the feeding process on variable component printing of carbon fiber/polyether-ether-ketone composites

While fused filament fabrication (FFF) remains the predominant technique for polyetheretherketone (PEEK) composite printing, its inherent limitations in achieving interfacial-gradient composition control constrain the capability for variable component printing. Although 3D printing based on screw extrusion has recently emerged as a promising alternative for variable component composites, the key processes involved have not been systematically studied. This study employs a custom-designed screw extrusion system (16 mm diameter) with dual-material feeding capability (PEEK and 40 wt% carbon fiber/PEEK) to systematically investigate feedstock delivery mechanisms governing compositional gradient formation. Experimental results demonstrate three key findings: (1) Continuous carbon fiber (CF) content regulation (0–40 wt%) is achievable through the control of bilateral feeding ratios; (2) Complete melt chamber replacement occurs at a 2560 mm CF/PEEK feeding stroke, corresponding to the maximum fiber concentration; (3) Gradual feeding ratio modulation reduces the required transition distances by 50% compared to abrupt material switching. The optimised process successfully fabricates geometrically complex gradient components, significantly expanding the multifunctional engineering potential of PEEK composites.