Variable filament strategy for high-speed additive manufacturing of continuous carbon fibre reinforced thermoplastic composites

The use of large-size continuous carbon fibre (CCF) reinforced filaments in composite additive manufacturing boosts printing speed effectively, while it also leads to low-precision and poor-quality curved sections. This study proposes, validates, and demonstrates a variable filament (VF) strategy for high-speed additive manufacturing of continuous carbon fibre composites, based on the mechanical and morphological characteristics of 1 K and 6 K filaments during straight and curved printing. For mechanical properties, compared to 1 K filaments, coupons printed by 6 K filaments exhibit a lower tensile strength by 15.8%, but similar interlayer strength. Morphologically, when printing straight paths, 6 K filaments require a width 1.5 mm larger than 1 K filaments, and the printable curvature radius for 6 K filaments is 3 mm larger than 1 K filaments. It indicates that 1 K filaments can provide higher precision compared to 6 K filaments. Therefore, the strategy involves selecting filament sizes based on the geometric shape of the structure by tool changing to preserve the geometric morphology and mechanical properties of the composites as much as possible, while improving manufacturing efficiency by up to 5 ∼ 6 times. A set of double shear coupons printed using the VF method show only a 17% reduction in shear strength compared to 1 K filament coupons. Moreover, it maintains the hole precision and improve the shear stiffness by 423% as compared to 6 K filament coupons.