Large-format additive manufacturing (LSAM) of carbon fiber reinforced composites at high material deposition rates has recently gained much attention due to its applications in printing large-volume components with good mechanical strength. However, no research work on LSAM of composites reinforced with long carbon fibers has been reported. The mechanical and physical properties of fibrous composites largely depend on their reinforcing fiber orientation and length-to-diameter aspect ratio. With increasing fiber length, mechanical properties increase, such as strength, modulus, impact resistance and wear resistance. Thus, a new additive manufacturing (AM) approach to fabricate long fiber reinforced composites (LFRC) was proposed in this study. A high deposition rate was achieved by the implementation of a single-screw extruder, which directly used thermoplastic pellets and continuous fiber tows as feedstock materials. Thus, the proposed approach was also used as a large-scale additive manufacturing method for printing large-volume components with high efficiency. Using polylactic acid (PLA) pellets and continuous carbon fiber tows, the feasibility of the proposed AM method was investigated through printing LFRC samples and further demonstrated by fabricating large-volume components with complex geometries. The printed LFRC samples were compared with pure thermoplastic and continuous fiber reinforced composite (CFRC) counterparts via mechanical and microstructural analyses. With comparable flexural modulus, the flexural strength of the LFRC samples was slightly lower than that of the CFRC samples. An average of 28% in flexural strength and 50% in flexural modulus were achieved compared to those of pure PLA parts. Discontinuous long carbon fibers, with an average fiber length of 20.1 mm, were successfully impregnated into the printed LFRC samples. The carbon fiber orientation, distribution of carbon fiber length, dispersion of carbon fibers, and porosity were further studied. The carbon fibers were highly oriented along the printing direction with a relatively uniformly distributed fiber reinforcement across the LFRC cross sections. Meanwhile, a wide range of fiber length led to a large variation of flexural strength and modulus observed for the LFRC samples. With much lower void fraction, the void pattern in LFRC was found to be dramatically different than that of the CFRC samples printed under the same conditions. With further reduced fiber volume fraction, a much lower void fraction at 0.1% was achieved in the LFRC samples. With high deposition rate (up to 0.8 kg/hr) and low material costs (\< \$10/kg), this study demonstrated the potentials of the proposed method in LSAM of high strength polymer composites reinforced with long carbon fibers. 


Feasibility and Characterization of Large-Scale Additive Manufacturing With Long Fiber Reinforced Composites

Division / Sponsor: 
Manufacturing Engineering Division (MED)

International Manufacturing Science and Engineering Conference - Paper Proceedings: https://asmedigitalcollection.asme.org/MSEC/MSEC2020/volume/84256

JSME 2020 Conference on Leading Edge Manufacturing/Materials and Processing - Paper Proceedings: https://asmedigitalcollection.asme.org/lemp/LEMP2020/volume/83624

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