Visualization Experiment Research For Filling Imbalance Of Injection Molding Of Plastics With Different Thickness

Filling imbalance is an important part of precision injection molding technology. Inter-cavity imbalance leads to differences of products in terms of weight, shrinkage, warpage, mechanical properties, optical properties and so on. As a result, injection molding of multi-cavity loses repeatability which is exceptionally important. Intra-cavity imbalance results in uneven molding quality in different locations of a product. Previous studies mainly focused on the filling imbalance of geometrically balanced runner system at conventional measures. In this paper, a two-cavity mold with T shape runner system serves as the study objects, the thickness of cavity is different, they are 3.5mm, 2mm. and 0.5mm. Aiming at the promotion for precision injection molding, numerical analysis, visualization means and cavity pressure field measurement method are performed to explore the impact of plastic thickness on filling imbalance.The results of numerical analysis are consistent with previous visualization experiment. But the degree of filling imbalance is generally weak. Therefore, further research is necessary; a rational model should be established to improve the accuracy of numerical analysis.A set of visualization experimental platform for injection molding was developed and visualization experiments were performed. Conventional visualization experimental results show that plastic thickness not only affects intra-cavity imbalance but also has impact on inter-cavity imbalance. By tracer visualization experiment, stream harness is concluded. Its morphology described the flow state of melt in the cavity vividly.According to the results of numerical analysis and visualization experiments, a resin flow behavior model is established to describe the intra-cavity imbalance of melt in freedom flow state. Fountain flow model is applicable to injection molding at low injection rate, while shear heat model is for the state of high injection rate. the difference between the two shear-induced thermogenesis in a significant degree.In most cases, the imbalance law of shrinkage visualization experiment, the measurement of cavity pressure distribution and the intra-cavity imbalance is corresponding. In a single cavity, for the faster filling side of cavity, more melt exists and its temperature is higher. As a result, the melt of this side shrink slower and thus get a higher pressure distribution.