Research On Characteristic Size Effect For Injection Molding Of Micro-structured Thin-wall Part

Typical thin-walled parts with microstructures such as light guide plates and Fresnel lenses have been successfully produced by injection molding technology.However,due to the narrow cavity melt flow law and the unclear quality control mechanism of plastic parts,product quality cannot be guaranteed.The flow law and quality control mechanism are directly related to the size effect in the molding process.The size effects of thin-walled parts with microstructures during the forming process include wall thickness size effects and local microstructure size effects.In this paper,the size effect of thin-walled parts with microstructures during injection molding is studied.Among them,the wall thickness size effect mainly studies the influence of the ratio of wall thickness size to the overall size on the molding process and the quality of the part.Mainly analyze the effect of the microstructure interval size and the angle formed with the main flow direction on the forming process and the quality of the parts.The main work of this article is as follows:(1)Study the influence of feature structure size on the mapping relationship between molding process and plastic part quality.Based on the needs of experimental research,establish an experimental platform for high-speed injection molding process.In addition to high-speed presses and auxiliary oil temperature auxiliary heating equipment,design and manufacture a set of injection molding molds with V-grooves microstructure optical components.On the basis of the process experiment,combined with the analysis of the forming quality data of the parts,the mapping relationship model of the process and the quality of the plastic parts under the wall thickness size and the microstructure size is established.It provides support for further study and analysis of the size effect of the feature structure of the part and the filling behavior of the melt flow in the cavity.(2)The effect of sub-millimeter wall thickness of microstructured parts on melt flow filling behavior and the quality of the parts was studied.Based on the process experiment and mold flow simulation analysis,it was determined that the behavior of the mold filling behavior of the melt flow in the cavity with different wall thicknesses of the microstructured parts was affected by the shear flow and heat transfer rate.Appropriate increase in material temperature and injection pressure can effectively offset the adverse effects of flow resistance and heat loss,and ensure the complete molding of plastic parts.Combining the mapping relationship between the process and the quality of plastic parts,the process combination strategy for forming parts with different wall thicknesses is clarified.For the parts with thinner wall thickness,only the effect of increasing the mold temperature and the injection speed is limited.The appropriate process combination needs to give priority to the selection of injection pressure.(3)The study of the microstructure size of the part affects the flow-filling behavior of the polymer melt in the cavity.Combined with the experiment and mold flow simulation analysis,the difference in the behavior of the melt flow mold filling behavior in the cavity under the microstructure size of the part is determined.When the distance between the microstructures is large,the melt flow filling is sensitive to the injection pressure,and it has better filling in the thickness direction of the cavity.Under the conditions of small angle,the heat and pressure loss of the microstructure encountered by the melt are lower than those of the large angle,and the effective process is longer.As the angle increases,the flow resistance of the melt plane tends to fill in the thickness direction,but the volume of the melt flowing into the cavity is obviously reduced to weaken this trend.In summary,by studying the size effect in the injection molding process of thin-walled parts with microstructures,this paper analyzes the melt flow filling behavior and summarizes the quality control strategies and points of plastic parts,which is conducive to ensuring the quality of this type of device production.