Study On The Self-Interference Flo Of Polymer Melts In Cavity Based On CAE

When a special pin gate, called twin-gate, was applied in mold design, a kind of flow called self-interference flow (SIF) will be formed in cavity during injection molding process, which can control the aggregated structure of polymer and enhance the impact strength of product. It is difficult to describe the SIF with the traditional theory and experiment methods. However, SIF can be simulated though computer-aided engineering (CAE) technology, which enable us to study the cause and the effects of the flow for the theoretical research and production. In this paper the simulation theory of flow, packing and cooling stage during injection molding was described, and the numerical simulation model was established. The function of CAE software MPI 4.1 was introduced. By using MPI4.1, the filling process at different place of the gate of ABS angle fitting mold was simulated. Synthetically considering various such as place of the gate, number and distribution of the blister in the product, number and distribution of weld marks, temperature change of the flow front, etc. place 2 of gate was suggested. In this paper, factors affecting self-interference flow (SIF) of polymer melt were studied through MPI4.1. The results of simulation show that there is a strong interaction, which affects the flow process and aggregated structure of material, is present between the two streams of melt from two orifices during injection molding. This kind of interaction only depends on the distance between two orifices, d. When d is less than the critical distance ,dc, the streams of melt from two orifices can form the self-interference flow and the meeting angle of melts will exceed 120°so that weld line will not be formed in the product. Results obtained from simulation of SIF and conventional flow process (CFP) under same molding conditions show that the quality of SIF sample in terms of bulk temperature, shear stress, volumetric shrinkage and sink marks, is much better than that of CFP. But if d exceeds 2.0mm, volumetric shrinkage and sink marks of SIF sample may gave more worse than that of CFP sample. We thought the effect of SIF maybe have become very weak in this situation. Drawing from the results of simulation of SIF with various orifice diameter, injection time and materials, we come to the conclusion that the critical distance is a fixed value 1.2mm. But the proposition that the material property has no effect on the critical distance needs to be further proved by experiment. By using DOE (Design of Experiment) module of MPI4.1 the molding parameters most affect the quality of product in SIF can be determined. The results of DOE analysis show that the packing parameters are the most important factor for the volumetric shrinkage, sink marks of product and so on. A series of cool&flow&warp analysis with various hold pressure and hold time was carried out and the optimum parameter was decided, which is a hold time of 18s and a hold pressure of 50MPa.