Simulation Of Briefringence/Internal Stress Distribution Of Plastic Molded Lenses

Security lens is developing towards miniaturization,and plastic aspheric lens can meet the requirements of miniaturization.At present,plastic aspheric lens is processed by injection molding,but its molding process is very complex,so the molding process parameters are affected by many factors.Therefore,controlling the injection molding process parameters becomes the focus of attention.However,analyzing process parameters through actual processing is costly and inefficient,while analyzing process parameters through simulation is more economical and efficient,so simulation analysis is a more effective way to solve such problems.The purpose of this paper is to find the process parameters that meet the evaluation index by simulating and analyzing the plastic aspheric lens used in a security lens.The evaluation index of plastic aspheric lens is that the birefringence(light retardation)is less than 54.6nm and the internal stress is less than 32MPa.Firstly,the injection process of plastic aspheric surface is analyzed by using the physical model of injection molding,and the main process parameters that affect the molding quality are melt temperature,mold temperature,injection time,packing pressure and cooling time.Then,the performance of plastic lens with melt temperature of 200℃,mold temperature of 80℃,injection time of 1s,holding pressure of 40MPa and cooling time of 20s is simulated and analyzed by finite element method,which is 99.47nm light retardation and 39.15MPa internal stress respectively.The results do not meet the evaluation index,so it is necessary to optimize the parameters.Secondly,the orthogonal test with five factors and four levels is designed and simulated,and the influence trend of each process parameter on evaluation index is studied by range analysis method.The results show that with the increase of mold temperature,the internal stress first increases and then decreases,while the light hysteresis first decreases and then increases.With the increase of injection time and packing pressure,the internal stress also increases,while the light hysteresis first decreases and then increases.With the increase of cooling time,the residual stress and light hysteresis increase,then decrease and then increase.Thirdly,by analyzing the influence trend,the best combination of process parameters is obtained,namely melt temperature 300℃,mold temperature 90℃,injection time 1s,packing pressure 60MPa and cooling time 60s.Under this process combination,the internal stress of plastic parts is 14.70MPa and the light hysteresis is 51.58nm,both of which reach the best value of each group of tests and meet the evaluation index at the same time.Finally,the optical surface deformation data of finite element analysis is imported into the corresponding surface of optical analysis software by using interferogram interpolation method,and the best combination of process parameters is analyzed from the aspect of imaging quality.Through the simulation analysis of the process parameters of plastic molding lens,the evaluation index is achieved,that is,under the conditions of melt temperature 300℃,mold temperature 90℃,injection time Is,holding pressure 60MPa and cooling time 60s,the internal stress is 14.70MPa and the light hysteresis is 51.58nm.Through the data exchange between the finite element analysis results and the optical analysis software,it is verified that the imaging quality of the lens processed by the optimized process parameters is also the best,and the MTF reaches 0.869 at 1001p/mm,which has guiding significance for the actual processing and manufacturing.