CFRTP (Carbon Fiber Reinforced Thermoplastics) are expected to be used for lightweight component parts in the automobile industry, due to their properties such as high specific strength and high specific stiffness. Because of their expensive cost, however, their application to mass-produced vehicles is limited and expected to be used based on the concept of multi-material combined with conventional materials such as aluminum and steel. For the adaptation of a multi-material body, joining technologies for dissimilar materials are required, and a reasonable and practical high performance joining method is expected to be developed. Resistance spot welding is the well-used method for joining panels and bodies in automobiles using metal materials. If the resistance spot welding can be used for joining dissimilar materials of CFRTP and aluminum alloy, there is no need to introduce new equipment and it promotes the adoption of CFRTP. In this study, in order to develop a resistance spot welding technology of CFRTP and aluminum alloy, the influences of current, welding time and electrode force on lap-shear strength were evaluated and the joining mechanism was clarified. In the resistance spot welding of CFRTP and aluminum, the dielectric breakdown of resin, which is a matrix of CFRTP, occurs at the initial stage of energization. After the decomposition of the resin by the high temperature with the dielectric breakdown, an electric path of carbon fibers in CFRTP was created, and direct resistant heating of the carbon fibers melts the surrounding matrix resin. Therefore, larger welding area and fracture load is obtained in the case of longer welding time, larger current and lower electrode force. The shear strength of 17.3MPa was obtained by the resistance spot welding of CFRTP and aluminum with silane coupling treatment.

In recent years, due to the serious environmental issues, the development of the gasoline mileage improvement technology has become essential in the automotive industry. Weight-saving of the car body can contribute to improving the gasoline mileage. CFRP (Carbon Fiber Reinforced Plastics) are widely used as structural material for airplanes, various kinds of sports gear and premium automobiles because of their low density and high performance in mechanical properties. In CFRP, CFRTP (Carbon Fiber Reinforced Thermoplastics) are expected to be used for lightweight component parts because of their high recycling efficiency and high productivity. Accordingly, a high-efficiency machining method of CFRTP has been needed; however, CFRTP are known as difficult-to-machine materials. Delamination and huge burrs are major problems in CFRTP cutting. Although a circular saw that can be used at high speed is usually used as a cutting tool, the internal damage of CFRTP resulting from machining has not been clarified yet. In this study, in order to evaluate the influence of cutting speed on the internal damage of CFRTP cut by circular saw, the internal damage depth and the temperature of specimens during cutting process were measured. The internal damage occurred by circular saw processing and the internal damage depth were decreased in the case of fast cutting speed. The temperature of the specimen was increased in the case of slow cutting speed because of the longer contact time of the circular saw with the specimen.