Optimal design of an in-situ variable component 3D printhead for SCF/PEEK composite

Screw-based material extrusion 3D printing technology offers the potential for manufacturing fibre-reinforced composites with component gradients by mixing materials within the printhead. However, mixing composites with high fibre content sufficiently in a limited range for rapid component switching presented a challenge. Herein, an in-situ variable component screw-based printhead was developed. Pins with different geometries were added to 8, 12, and 16 mm diameter extrusion screws, to enhance the mixing efficiency. A particle tracking model based on computational fluid dynamics simulations was used to optimise the geometry and distribution of pins by taking 0-40 wt% short carbon fibre-reinforced polyether-ether-ketone (SCF/PEEK) as an example. The incorporation of pins enhanced the mixing efficiency but aggravated the dead zone, which decreased the variable component response rate. An optimal design of pins that balanced mixing efficiency and response rate was developed, by which the variable component response rate was promoted by 369%, while the degree of mixing was improved by 50%. Benefitting from the enhanced mixing, the tensile strength of in-situ mixed 20 wt% SCF/PEEK composites was increased by 23%. The in-situ variable component screw-based extrusion printhead developed and optimised in this investigation provided a novel approach to fabricating fibre-reinforced composites with variable components.