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With the high precision requirements and the trend of large-scale composite parts, the development of composite molds is imminent. The short carbon fiber (SCF) composite mold is mainly prepared by the technological process flow of composite sheet injection, the bonding of composite plates, and machining. However, the current process optimization method has not matured adequately, and there are still many shortcomings, for example, low precision and high cost. In this paper, the optimization method of SCF/polyetherimide (PEI) composite molds is proposed. Many experiments have been conducted, and the results show that the coefficient of thermal expansion of composite samples can be effectively reduced and the mechanical properties can be improved by optimizing the SCF weight ratio and carbon fiber length. The bonding strength of composite joints in a high-temperature environment can be improved by optimizing the bonding process parameters and modification by carbon nanotubes. Based on the above optimization method, the SCF/PEI composite mold is prepared, and the C-shaped beam composite part is fabricated by using this mold. Compared with the part made by aluminum mold, the shape accuracy of the C-shaped beam composite part is proven high through digital measurement technology. [ABSTRACT FROM AUTHOR]

Continuous carbon fiber reinforced polymer composite 3D printing has drawn more attention due to its ability to manufacture composite structures with complex shapes. The surface treatment of CF is necessary to improve the combination between carbon fiber (CF) and matrix. In this work, polyurethane with nano‐SiO2 (PU/SiO2) was used to size CF to enhance the compatibility of CF and nylon 6 (PA6). The chemistry and morphology of the CF were characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The interface strength between CF and PA6 was tested by the fiber pull‐out test, and eventually obtained optimized concertation of PU/SiO2 sizing agents (with 25 wt% PU and 0.4 wt% nano‐SiO2). The results show that compared with untreated CF, the interfacial shear strength (IFSS) of CF and PA6 after sizing increased by 316.93%. In addition, several CF/PA6 composite specimens printed by a homemade composite 3D printer were used to do mechanical tests. The results show that the flexural strength increased by 33.87%, the tensile strength increased by 20.75%, and the interlaminar shear strength (ILSS) increased by 66.54%. [ABSTRACT FROM AUTHOR]