The press and injection hybrid molding system, which is a novel molding technology with the combination of press molding and injection molding, is expected for the production of FRTP (Fiber Reinforced Thermoplastics) with complicated shapes and high levels of stiffness and strength. Press and injection hybrid molded structures consist of an outer shell laminate of continuous fiber and injected short or long fiber reinforced thermoplastics which form the rib structure. The higher mold temperature was reported to increase the strength of the interface between the outer shell laminate and injected material. On the other hand, the penetration of continuous fibers of the outer shell laminate into the rib structure decreases the mechanical properties of the outer shell laminate. While the effects of mold temperature on the mechanical properties of hybrid molded composites were clarified, the effects of press pressure have not been clarified yet. In this study, the effects of the press pressure on the mechanical properties of the outer shell laminate and interfacial strength between the outer shell laminate and injected material were evaluated. As the lower press pressure decreases, the penetrated height of continuous fiber into the rib structure, higher in-plane tensile strength and lower interfacial strength, are obtained.
In the press and injection hybrid molding of GFRTP, short or long fiber reinforced thermoplastics or thermoplastics are injected on the continuous fiber reinforced thermoplastics, which allows us to obtain light weight structures with excellent strength and stiffness. In previous studies, it has been reported that the interfacial bonding strength between laminates and ribs was improved by supplying fiber of laminates to the interface. Although the interfacial bonding strength of the hybrid molded product was improved, its fracture occurred at the injected material or the interface between laminates and ribs. In the case of the fracture at the injected material, it is expected to improve the interfacial bonding strength by using fiber reinforced thermoplastic with higher mechanical properties as injection material. For the injection molding, forming a V-shaped interface by moving the melted resin was reported to improve the weld strength. This technique can be applied to the press and injection hybrid molding and may improve the interfacial bonding strength. In this study, GFRTP were molded by press and injection hybrid molding under different injection volumes using PP and the short glass fiber reinforced thermoplastics and the effect of injection material and injection volumes on the interfacial bonding strength was clarified by the tensile tests using T-shaped specimens cut out from the molded products. When larger volume of the short fiber reinforced thermoplastics was injected, fracture occurred mostly at the injected material and higher interfacial bonding strength was obtained.
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