In the automobile industry, it is required to reduce the weight of cars for better fuel consumption. Recently, Carbon Fiber Reinforced Thermoplastics (CFRTP) are expected to be used for lightweight component parts. However, the cost of CFRTP is so high that the use of CFRTP is barely applied in the automobile industry. In order to lower the cost of CFRTP, simple equipment and low consumed power are necessary. High-frequency direct resistance heating to CFRTP molding dies becomes possible to solve these issues. High-frequency direct resistance heating is a method that alternating current is directly applied to a metal, and metal surface is heated by skin effect. When opposite directions of an alternating current flow in a pair of metal sections which face each other with a small gap, the proximity effect also promotes the concentration of current density on proximal surfaces of the metal and heats the metal surface intensively by joule heat. By applying high-frequency direct resistance heating to CFRTP molding, cost reduction as well as simplification of the facilities can be expected. In this study, in order to apply high-frequency direct resistance heating to CFRTP molding die, the effects of the proximity effect on the mold are evaluated to clarify the heating characteristics and conditions of the proximity effect, and the applicability of CFRTP molding is discussed. The experimental result reveals that the proximal surfaces can be heated by proximity effect.

Carbon Fiber Reinforced Plastics (CFRP) are expected to be used for lightweight component parts of automobiles. Considering recyclability and productivity, Carbon Fiber Reinforced Thermoplastics (CFRTP) have been getting attention. However, the cost of CFRTP is so high that the use of CFRTP is rarely applied in the automobile industries. In order to reduce the cost of CFRTP, a novel production process with short cycle time needs to be developed. Direct resistance heating of the mold for CFRTP thermoforming is the technology in which high speed heating can be obtained by using high frequency voltage. However, uniformity of temperature distribution is one of the important issues to be solved. In this study, in order to understand the proximity effect, effect of electrode shapes and the frequency of applied voltage on the temperature distribution of a flat type mold, FEM analysis of the electromagnetic field and heat transfer was conducted and analysed results were compared with the experimental results. When alternative current is applied to the facing surfaces of molds in different directions in FEM analysis, the current concentrates to the facing surface due to the proximity effect. The analysed temperature of the mold surface corresponds to the experimental results. When higher frequency is applied to the mold, higher concentration of current is obtained. When the electrodes are mounted to be close to the mold surface, the mold surface can be efficiently heated.