Continuous Fiber Reinforced Thermoplastics Molding by Melted Thermoplastic-Resin Transfer Molding Process

Abstract

The application of Fiber Reinforced Thermoplastics (FRTP), which have the advantage of high specific strength and high specific stiffness, is expected to reduce the weight of automobiles. As thermoplastic resin has difficulty in impregnation into fabrics of continuous fibers due to its high viscosity, FRTP products with complicated shapes are usually manufactured by secondary processing of FRTP laminates. As this method uses high-cost FRTP laminates, in which thermoplastic resin is pre-impregnated into fabrics of reinforcing fibers, it is necessary to develop a low-cost FRTP manufacturing process. In previous study, the molding method, by which FRTP can be molded by compression after injection of melted thermoplastic resin into fabrics, was developed. However, due to the high viscosity of thermoplastic resin, this method is limited to fabrics of discontinuous fibers. As the mechanical properties of FRTP depend on the length of the reinforcing fiber, it is necessary to use continuous fiber for superior materials. In this study, Melted Thermoplastic-Resin Transfer Molding (MT-RTM) process, by which FRTP using continuous fiber can be molded at affordable cost, was developed. The effects of molding condition in MT-RTM on the impregnation properties of injected thermoplastic resin into fabrics of continuous fibers were clarified and tensile tests of MT-RTM products were conducted. In MT-RTM, FRTP of complicated shapes with ribs and bosses can be molded integrally by press while keeping the low viscosity of injected resin at mold temperature near the melting point. GFRTP molded by MT-RTM showed good impregnation property and tensile strength equal to that of GF/PA6 laminates molded by press molding.

Effect of Press Displacement on Impregnation Properties in Melted Thermoplastic-Resin Transfer Molding of Continuous Fiber Reinforced Thermoplastic Composites

“…The barrel temperature of the injection molding machine is 280°C, the injection pressure is 120 MPa, the injection speed is 150 × 10 -6 m 3 /s, the press pressure is 5 MPa, the pressure holding time is 30 s, and the mold temperature is 200°C. After preheating the plain woven fabrics of glass fiber (0°/90°) 5 s for 90 s, the mold opening amount was set for 2.8 mm, 4.8 mm and 8.8 mm [6] and press to 2.8 mm after resin injection. The products molded in this way are referred to as IP2, IP4, and IP8, respectively.…”

“…On the other hand, for automotive applications, resin transfer molding (RTM), in which resin is impregnated into dry-type reinforcing fabrics, is used to offer affordable prices. We have been developing an melted thermoplastic-resin transfer molding (MT-RTM) method in which melted thermoplastic resin is injected and impregnated to continuous reinforcing fabrics using an injection-press hybrid molding machine [6]. In this study, we have clarified the effects of mold temperature and pressure holding time on the impregnation of continuous fibers using plain woven fabric of glass fiber as reinforcement and PA6 as matrix resin.…”