SUN Jian ¹, BIAN Jiamin ¹, GAO Liansheng ²

(1. School of Materials Science and Engineering, Jingdezhen ceramic institute, Jingdezhen 333403, Jiangxi, China; 2. Jingdezhen Branch, Jiangxi Research Institute, Beihang University, Jingdezhen 333403, Jiangxi, China)

Extended abstract:[Background and purposes] Advanced carbon fiber reinforced composites (CFRP) have been widely applied in the aerospace field, due to their outstanding properties, such as high specific strength, high specific stiffness, excellent weight reduction effect and superior fatigue resistance. In the manufacturing of aircraft structures, major load-bearing components such as wings and fuselage are commonly fabricated using the autoclave molding process. As a crucial tool for the curing of CFRP components within the autoclave, the surface temperature distribution of frame molds directly affects the curing quality of the final products. Enhancing the uniformity of the temperature field within the autoclave helps reduce residual stress and deformation generated during the curing process, thereby improving the mechanical performance and dimensional stability of the composites. Existing studies have primarily focused on optimizing internal heat transfer characteristics and local structural designs of molds. However, research on the regulation of the overall flow field within the autoclave remains limited, and the interaction mechanism between mold structures and internal airflow has not been systematically and thoroughly studied. In this work, a frame mold was designed and constructed to simulate the temperature and flow fields during the autoclave molding of composite components. Flow guide plates were incorporated inside the mold to regulate the direction of fluid flow, aiming to improve the temperature distribution within the autoclave. Additionally, the effects of fluid velocity and temperature regimes on the heat transfer characteristics were examined.[Methods] To address the issue of non-uniform temperature distribution on the mold surface, a physical and mathematical model of the autoclave curing process was established. Computational fluid dynamics (CFD) numerical simulations were conducted to analyze the temperature distribution within the autoclave during the molding process. The simulation results were validated against existing experimental data, with the simulation error controlled within 3%. A systematic study was carried out to explore the influence of fluid velocities, temperature regimes, and the addition of flow guide plates within the mold structure on the temperature field characteristics. By setting various fluid velocities and temperature processes and designing different types of flow guide plates (such as flat-type and concave-type), the effects of each factor on the temperature distribution were systematically analyzed using the controlled variable method.[Results] The simulation results show that increasing the working fluid velocity significantly improves the heat transfer efficiency between air and the mold surface. When the fluid velocity increased from 2.5 m·s⁻¹ to 7.0 m·s⁻¹, the maximum temperature difference decreased from 45.21 K to 31.46 K, achieving a reduction of 30%. Meanwhile, the average temperature standard deviation dropped from 5.67 K to 3.08 K, indicating a marked improvement in temperature uniformity. Setting appropriate holding times during the heating process also contributed to reducing the average temperature standard deviation. When the number of holding stages increased from one to three, the maximum temperature difference decreased from 45.21 K to 31.82 K, representing a reduction of 29.64%, while the average temperature standard deviation decreased from 5.67 K to 5.27 K. Furthermore, adding flow guide plates within the mold structure effectively regulated the internal fluid flow and improved the temperature uniformity. Compared to the original mold without guide plates, the addition of a flat-type guide plate reduced the maximum temperature difference by 20.56 K (approximately 45%) and the average temperature standard deviation by 2.72 K. When compared with the concave-type guide plate, the flat-type guide plate still demonstrated superior performance, reducing the maximum temperature difference by 15.92 K (approximately 39%) and the average temperature standard deviation by 0.92 K.[Conclusions] Th influence of fluid velocity, temperature regimes, and the addition of flow guide plates on the temperature field uniformity of frame molds during the autoclave curing process was systematically studied, while feasible optimization strategies were proposed. The results indicate that moderately increasing the fluid velocity and setting appropriate holding times during the heating phase can significantly improve the uniformity of the mold surface temperature. Furthermore, regulating the internal fluid flow by adding flow guide plates, particularly flat-type plates, can greatly enhance the temperature uniformity compared to concave-type plates, thereby improving the curing quality of composite products. This research provides a theoretical basis for the optimization of autoclave molding processes for CFRP components and offers valuable guidance for the high-quality manufacturing of complex structured composite products.

Key words: composite materials; autoclave; mold; temperature field