Abstract: The 3D printing technology of carbon fiber reinforced thermoplastic composites is an effective way to realize the integrated manufacturing of advanced composite parts with complex structures. Due to the discontinuity of short fiber and the weak load transfer capability of the matrix between continuous fibers, the mechanical property enhancement of 3D printed single-form (short or continuous) fiber reinforced thermoplastic composites has entered a bottleneck period. In order to break through the technical bottleneck of high-quality manufacturing for advanced composite parts with complex structures, it is vital to develop the short-continuous carbon fiber synchronous reinforced thermoplastic composites (S/C-CFRTP) 3D printing technology. However, due to the high melt viscosity of the matrix containing short fiber and the rapidly changing temperature-pressure of the deposition material, it is difficult to make a full impregnation between continuous carbon fiber and matrix during the in-situ impregnation 3D printing process. Poor impregnation results in the weak mechanical properties of S/C-CFRTP parts, which can not meet application requirements. Improving the fiber-matrix impregnation percentage is the key to achieving high-quality 3D printing of S/C-CFRTP. Based on the offline impregnation method, the manufacturing process and 3D printing process of S/C-CFRTP prepreg filament are proposed. The influence of prepreg filament manufacturing process route and process parameters on its impregnation percentage, fiber content, and tensile strength were studied. A high-quality manufacturing strategy with a “mixing-impregnation-shaping” process route and “low filament-making speed and large outlet diameter” process parameters is proposed. The maximum tensile strength of prepreg filament reached about 448.70 MPa. Meanwhile, comparing the S/C-CFRTP parts printed by different printing processes, it is found that the towpreg extrusion printing process reduced the void fraction by nearly half and increased the fiber content by about 7%. The tensile strength and modulus of the S/C-CFRTP parts manufacturing by towpreg extrusion printing process increased by about 18.6% and 11.6%, namely about 430.45 MPa and 38.51 GPa.

Key words: short-continuous carbon fiber synchronous reinforcement thermoplastic composites, prepreg filament, 3D printing, impregnation percentage, tensile properties