During its early development stages, 3D printing was primarily used for rapid prototyping, whereas it is currently employed to fabricate products in various fields, including aerospace, automobile production, dentistry, architecture, and food. The photopolymerization of the polymer used for 3D printing is precise and provides excellent surface roughness but has lower mechanical strength than traditional manufacturing methods. In this study, Multi-walled Carbon Nanotubes (MWCNTs) were blended with urethane acrylate-based resin as a filler. Mechanical strength enhancement was confirmed using a DLP 3D printer. The stabilities of MWCNT dispersions in resin were verified, and viscosity and curing depth measurements were conducted to establish 3D printing parameters. Tensile and flexural strengths were higher for an MWCNT length of 50 μm than one of 100 μm, and maximum values were obtained at an MWCNT content of 0.1 phr. Under optimal conditions, tensile and flexural strengths increased by 2.1 and 1.8-fold, respectively.

SFT, which has a high glass fiber content, is one of the effective methods to replace metal and secure weight reduction and price competitiveness. This study evaluated the effect of glass fiber shape on mechanical properties in injection molding by fabricating SFT with a glass fiber content of 60%. Three types of SFTs were manufactured by adding round glass fibers of Φ7 μm and Φ10 μm and flat glass fibers of 27 × 10 μm. DOE (Design of Experiment) conducts to confirm the change in tensile strength due to changes in significant injection conditions. As a result of the experiment, Φ7 μm SFT and flat SFT have similar tensile strength and Φ10 μm SFT showed the lowest tensile strength value. As for the standard deviation of strength value, the Φ7 μm SFT had the largest standard deviation, and the Φ10 μm SFT showed the slightest change in the injection conditions. In flat SFT, it confirms that the tensile strength increased as the molding temperature increased. The fracture surface observes using SEM. It founds that the tensile strength lowers due to the small glass fiber density and many pullouts at the fracture surface of Φ10 μm with weak strength.