Study On Methd And Process Optimization Of Multi-layer Counter-Pressure Injection Molding For Thick-Walled Optical Products

In recent years,with the pursuit of lightweight and molding efficiency in product application,plastic optical elements gradually replace high-density glass and have been widely used in the optical field.However,the optical properties of thick wall injection molded optical components are seriously affected by the residual stress caused by macro and micro geometric defects.How to improve the injection molding defects of thick-walled optical elements is a difficult problem to be solved.In actual production,thick-walled optical elements have a large wall thickness difference compared with ordinary products.When using conventional injection molding method to manufacture thick wall optical elements,the cooling rate of different thickness areas is significantly different,which will cause serious geothermal residual stress and shrinkage deformation defects.At the same time,the longer cooling time reduces the production efficiency and increases the risk of material degradation.In view of the above problems,this paper innovatively proposes layered back pressure injection molding,and explores the influence of process parameters of this molding method on the size shrinkage and optical performance of thick wall optical elements by using the mold flow analysis method,and further optimizes the molding process by using intelligent algorithm.The specific work is as follows:(1)The common forming defects and mechanism of thick-walled optical elements are summarized and analyzed.The multi-layer counter-pressure injection molding is proposed.Combined with the internal pressure law of injection molding cavity,the forming characteristics of multi-layer counterpressure injection molding in the process of thick-walled forming are analyzed in detail.The improvement of common forming defects of thick-walled optical elements by multi-layer counter pressure is analyzed theoretically.The shrinkage of the single layer can be significantly reduced by the layered back pressure injection method,so as to effectively suppress or eliminate the common defects of thick wall optical elements,so as to ensure the molding accuracy and optical properties.(2)The Taguchi test method was used to simulate and analyze the conventional injection method.The significant effects of common process parameters on the volume shrinkage and optical path difference of thick wall optical elements were determined,and the process parameters were preliminarily optimized.According to the different quality objectives,two groups of better parameter combinations were obtained.It was determined that melt temperature,injection speed and packing pressure had significant effects on the volume shrinkage and optical path difference of the products,which provided the basis for the subsequent full factor test.(3)Moldex3D was used to build the simulation platform of layered back pressure injection molding.Combined with the full factor test method,the layered back pressure injection molding was simulated and analyzed.The effects of different delamination methods,back pressure and key process parameters on the volume shrinkage and optical path difference of thick wall optical elements are determined.By comparing conventional injection molding with layered back pressure molding,it is verified that layered back pressure improves the forming quality of thick wall optical elements.Finally,a better layering method and back pressure are obtained,and the raw data are provided for the establishment of neural network.(4)BP neural network is used to establish the relationship model between process parameters and quality objectives,and the optimization scheme of process parameters of thick wall optical elements based on genetic algorithm is proposed.In MATLAB,BP neural network is used to establish the model relationship between process parameters and optical path difference and volume shrinkage,and genetic algorithm is used for multi-objective optimization.Finally,the optimal solution set of process parameters is determined according to Pareto curve.The results show that the molding quality of the products is improved significantly according to the optimization method.