To deal with environmental issues, the gasoline mileage of passenger cars can be improved by reduction of the car weight. Carbon Fiber Reinforced Thermoplastics (CFRTP), which are superior in specific strength and specific modulus, is expected to be used for car body. Many pipe-shaped members have been used for structural materials for cars, and low cost and high-speed molding method for CFRTP pipe has been required. Although rapid heating process of mold has been developed by applying high-frequency direct resistance heating to the mold itself in previous studies, sufficient mechanical properties of CFRTP pipe could not be obtained because of the high viscosity of thermoplastic resin. In CFRTP molding, impregnation improvement of the resin is one of the important issues to be solved. In this study, carbon fiber thermoplastic resin preimpregnated sheet, which was impregnated with thermoplastic resin beforehand, is used as molding material to improve the quality of the CFRTP pipe. The CFRTP pipe molded with pre-impregnated sheet had less void and higher strength than the pipe molded with dry carbon and nonwoven fabric.

In the automotive industry, it is necessary to reduce the cost of molding process for an application of CFRTP in car component parts. Recently, a heating method of the mold by using the high frequency direct resistance heating is attracting a great deal of attention. With this method, electric current passes near the mold surface intensively by skin effect and heats the mold by Joule heating. By applying direct resistance heating to the flat mold for CFRTP molding, simplification of the equipment and facilities as well as high-speed molding can be expected. However, the uniform temperature distribution is one of the important issues to be solved for flat plate because of a current concentration at the corners. In this study, in order to apply the direct resistance heating to the flat mold for CFRTP molding, FEM analysis of the electromagnetic field and heat transfer was conducted and analyzed results were compared with the experimental results. Target part of the mold was efficiently heated by positioning the electrodes close to the molding surfaces, and the temperature rise in the corner part was remarkable under the higher frequency. For preventing a current concentration at the corner parts, a new feeding model, in which copper plates were positioned at the both sides of the mold, was proposed.

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