Effect of Molding Condition on Mechanical Properties in Injection and Compression Hybrid Molding

Abstract

The advantage for discontinuous fiber reinforced thermoplastic composite is to form a complicated shape in a short time. On the other hand, the continuous fiber reinforced plastic (c-FRTP) has high mechanical properties, but its process ability is limited and it is difficult to produce complicated shapes such as ribs. Therefore, the hybrid molding method attracts attention. The hybrid molding method used in this study is a molding method combined the compression molding with continuous fiber and the injection molding with discontinuous fiber. Hybrid molding is a method of injecting and joining discontinuous fibers to a continuous fiber part. The part of requiring strength is formed by compression molding of intermediate material with continuous fiber, and the complicated shape part is made by injection molding of discontinuous fiber. However, there is a problem with the strength of the joint part between the intermediate material part molded by compression molding and the part molded by injection molding. Joining characteristics are affected by preheating conditions of c-FRTP, molding conditions such as temperature, pressure and speed of injection resin. Therefore, it was aimed to clarify the effects of the preheating condition for the intermediate material and the temperature of the injection resin on the mechanical properties of the molding and injection resin joint. In this research, a hybrid molding machine of a press machine and an injection machine was used. A heating test was conducted by using preheating devices, and the temperature distribution and the difference in temperature rise were investigated. In addition, the influence of the difference in the preheating condition of the intermediate material on the strength was examined by evaluation of mechanical properties, surface and cross sectional observations. From this study, middle infrared was found out to be the most suitable preheating device for hybrid molding, from its advantages that could preheat in a short time and improves mechanical property.