Consumer fused filament fabrication (FFF) desktop 3D printers are used for prototyping, spare parts and even small-scale production, but produce parts with lower tensile strength than traditional manufacturing methods. High tensile continuous fibers increase filament composite strength, but poor fiber adhesion and pull-out are common weaknesses. The few commercially available continuous fiber reinforced (CFR) filaments are costly and only compatible with their manufacturer’s machines.
This work describes the development of a method and a prototype apparatus to produce standardized CFR filament, addressing the weaknesses of CFR thermoplastics while maintaining their compatibility with consumer 3D printers, and thereby achieving mechanical properties required for cost-effective small-scale productions.
A bundle of raw carbon fiber is impregnated with a solution of thermoplastic and compatible solvent, improving the adhesion of the fibers to the thermoplastic and reducing fiber pull-out. The pretreated fiber is then extrusion-coated with thermoplastic to achieve a standardized filament diameter. 1.75mm PLA filament reinforced with 12k continuous carbon fiber and pre-treated with an ABS-Acetone solution was produced.
Parts and products ranging from small consumer goods to meter-sized airplane wing sections were successfully printed using a standard FFF extruder. Tensile tests showed a yield stress increase of 535% compared to plain PLA, and a 70% increase compared to filament produced with raw, untreated fibers. Further work is needed to determine the ideal fiber content, its distribution within the filament and the concentration of the solution.