Application of Lost Foam Process in Development of Hollow Irregular Carbon Fiber Composite Structure

In the composite materials industry, hollow parts, which reduce product weight and improve bending rigidity, are generally manufactured through the bonding and blown film processes. However, the bonding process makes carbon fibers discontinuous, and the blown film process generates excessive wrinkles within tubes. To solve these problems, we developed a new manufacturing process. The difference between the coefficient of thermal expansion of the mold and the material created a difference in the internal and external pressures. Similar to the blown film process, a hot-melt core material was used to smoothen the interior of the tubes and make the shapes of hollow parts complex and diverse. On the basis of the difference between the coefficient of thermal expansion of the mold and the material, we covered the core material with carbon fiber composite materials. The carbon fiber composite materials provided internal pressure during molding. After the molding was completed, the composite structure was placed into a refrigerator to cool. Due to the core material’s thermal contraction properties, the core material contracted and could be easily removed. The core material could also be removed by melting and be reused. Through computeraided engineering (CAE), we simulated the thermal stress of the mold and the core material and verified the simulation results by conducting an experiment. We (1) simulated the heating curves and thermal stress through CAE, (2) conducted an experiment on thermal expansion pressure to measure the actual thermal expansion pressure of the core material and calculated the error between the experimental and CAE results, and (3) successfully manufactured well-structured hollow parts with irregular shapes and manifolds. The optimal processing parameters for the hollow last foam manufacturing process were obtained. The temperature was increased from 25°C to 120°C, maintained at 120°C for 60 min, increased to 150°C, and maintained at 150°C for 45 min. The process capability results revealed that the Cpk values for the core material temperature and pressure value were 1.49 and 1.52, respectively, which met the quality standard of the process capability indices. The manufacturing process we proposed in this study substantially improved the quality of current mold manufacturing. © 2023, Chinese Society for Quality. All rights reserved.