Numerical Simulation Of Fiber Orientation In Injection Moulding Cavity

Short fiber reinforced composites have super properties due to high strength and low density, which are widely used in industrial manufacturing and daily life. However, the composites, whose mechanical properties have close relation with fiber orientation in final product, are made of matrix materials and short fiber. Industrially, people usually acquire what they want through injection-molding or roll-forming.Usually, the final fiber orientation and spatial distribution are badly complex but basically depend on the following factors, like process parameters,cavity geometry parameters physical parameters of matrix material and fiber. Therefore, based on the practical production and manufacturing, it will be of practical significance to predict the orientation by positively exploring the factors that affect the fiber distribution and seeking for accurate and seasonable computational model and numerical method. This study mainly made the following two improvements:First of all,it overcomes the errors caused by the traditional method during using the orientation closure approximation and improve the computation accuracy; Secondly, the prediction has been successfully realized to analyze the fiber spatial orientation. It has finished the analysis about effects on fiber orientation caused by temperature、filling time、cavity’s thickness and shape、fiber ratio aspect and matrix material properties Meanwhile, the prediction of fiber orientation have been done for three common geometrical structures (center inlet disk、cuboidal cavity and dumbbell cavity),and the analysis has been done about the composites’ rheological properties in cuboidal cavity and the comparison of orientation between numerical simulation and experiment in dumbbell cavity has also been finished. Finally, it draws the following conclusions:(1) the inter-fiber interaction coefficient is a key factor affecting the fiber orientation, with its increasing in shear flow field the fiber orientation will change from flow direction to isotropic distribution,and the fiber volume fraction hardly affects the fiber orientation when fiber aspect ratio is larger than140;(2) The orientation distribution in three cavity mentioned above is regular——fiber orientation has a layered distribution, when nearing the cavity walls it orientates along the flow direction, like near the up-and-down walls of center inlet disk and cuboidal cavity, fiber arranges in radial direction and length direction, and near walls of cuboidal cavity in width direction,the fiber does so. But in the neutral layer the fiber will orientate along the circumferencial direction of disk and width direction of cuboid,and Compared with them,a larger difference dose exist in other layers.What’s more, for dumbbell cavity with complex geometrical structure, fibers arrange in flow direction at the contracted locations, in the width direction at the divergent locations and in the thickness direction at inlet\middle\end location.(3)For cuboid cavity, when changing its geometrical dimensions and manufacturing parameters, fiber orientation will be affected more or less. Increasing the cavity thickness fiber orientation direction will divert from flow direction to planar distribution,and then changing wall temperature and inlet temperature will hardly affect the fiber orientation distribution,but the increasing of filling time will weaken the fiber orientation in flow direction, conversely it will strengthen the orientation in width direction.Then for different matrix materials, orientation arrangement is very different among them. Furthermore, adding fibers to the matrix resin will cause the complicated changes for the composite melt’s rheological properties like shearing stress near walls will be much more than that near neutral layer,and the former’s viscosity less than the later.(4) The cross-section photos of dumbbell-like sample show that the orientation will change from the cavity’s length direction in middle location to thickness direction near the wall, and trendence reflected is the same as the numerical simulation results.