Visualization Experiment Study On The Melt's Filling Behavior In Thin-wall Injection Molding

In recent years, electronic information products, medical equipment products and other products are designed towards weight-reduction, thin wall and minified size, as a result, thin-wall and micro injection molding technology becomes a research hotspot. Currently, the study on melt's filling behavior in thin-wall injection molding is not systemic. In this paper,-the injection molding process of multi-cavity mould and single cavity mould were studied. The research on the impact of part thickness and runner depth on filling imbalance in the multi-cavity mould was conducted. The influence of material and thickness of cavity on melt's filling rate in single-cavity mould was also researched. Meanwhile, with the application of sensor system, the pressure distribution of melt in the cavity was measured and the relationship between the melt's pressure and filling rate was obtained. The results can be provided as experimental evidence for the study of thin-wall or micro scale injection molding technology.To conduct the experiment of visualization and pressure measurement in single cavity mould during the injection molding process, two single-cavity inserts with the thickness of 3.5mm and 1mm and a sensor insert were designed and manufactured. Then, the multi-cavity insert used in previous experiment was modified with its depth of branch runner changed from 3.5mm to 0.5mm.The effect of runner's depth on melt's filling imbalance was studied by comparing the experimental results with those gained before.The visual experiment results of multi-cavity injection molding indicate that, the cavity thickness only changes the degree of the melt's filling imbalance but not the trend. However, the depth of runner has a great impact on both the degree and the trend of melt's filling imbalance.The visual experiment results of single-cavity injection molding show that, the material variety influences the melt's filling rate significantly. The input of glass fiber increases the viscosity compared with pure PP, which causes more shear heat generated and a larger filling rate at a high injection rate. While, at a low injection rate, condensate layers attached on the cavity wall is thick for the melt's high viscosity. With the decrease the cavity thickness, the resistance effect of condensate layer on the flow-up melts is strengthened, which causes a sharp increase of filling rate when the heated melts flow through the condensate layers. The pressure in the cavity is closely related with the injection velocity, for a high injection velocity, the pressure is low or vice-versa.