Prediction for the Configuration of Fiber Orientation in Injection Moulding

Abstract

Thermoplastics filled with short fibers have been used in injection moulding for more than ten years in order to improve or control mechanical properties of moulded parts such as mould shrinkage, stiffness, heat distortion, etc.. In the moulded parts of Fiber Reinforced ThermoPlastics (FRTP), the orientation of short fibers is determined by the flow of the molten resin and therefore their mechanical properties are highly dependent on the orientation state of fibers. For example, their elastic moduli and tensile strength in the oriented direction have been known to be greater than those in order directions. In FRTP composite industry, it is desired that the fiber orientation becomes predictable quantitatively and the mould design can be carried out to utilize the desirable orientation positively.
This paper shows how to predict the fiber orientation distribution in injection moulded parts, from the modelling study on the flow properties of composites. In this model, it is assumed that the behaviour of fibers is completely governed by the flow state of matrix. This prediction might be limited to simple thin products, since the flow of the molten resin is considered to have 2-dimensional isothermal properties and the fibers have an in-plane orientation. The experimental results for a simple injection moulded plate revealed the process of the fiber orientation in short-shot samples. The numerical prediction is quantitatively in good agreement with the experimental results.