Numerical Simulation On Stress State And Formed Shape Of Aspherical Glass Lens For Molding Process

Aspherical glass lens has a widespread application in recent years.Theconventional technique which involves grinding, lapping and polishing can notsatisfy requests of high-precision volume manufacturing. Glass molding processhas emerged as a promising way to produce aspheric glass lens with high precisionand efficiency. Although the molding process appears to a better alternative, thereare shortcomings that need to be studied before using the process for massproduction. From the point of view of the current study, the shortcomings includeboth appropriate process parameter choosing and mould shape compensation.Finite element simulation can be used to compute lens internal stress state andfinal lens shape as a reference of the process parameter choosing and mould shapecompensation.In this paper, the theory of glass molding process and glass material model attransition temperature region was introduced briefly. The results indicated thatlens internal stress relaxes faster at higher temperature. With the application of theadvanced nonlinear finite element software MSC.MARC, four steps includingheating, pressing, annealing and releaseing were all studied.To predict the heating and pressing parameters of a micro aspheric lensmolding process, a molding process model was established and all the boundaryconditions were set. Based on the finite element software numerical simulation,mold filling condition of glass D-ZK3at540℃～590℃was analyzed, and theoptimum molding temperature is about580℃.The results also show the higher themolding temperature, the smaller the residual stress, and the minimum heatingtime for this model is about155s at580℃molding temperature. Finally differentmolding velocities were analyzed, and the results show the average residual stressof lens increases with molding velocity increasing.In the stages of annealing and releasing, stress reduction at the beginning ofreleasing was analyzed. Stress distribution of lens for four steps was discussed,and at the time of mold closing, stress reaches its maximum value. The mechanismof process parameter and friction coefficient influencing stress distribution wasclarified. The minimum annealing time at different molding temperature andmolding velocities were all predicted. Annealing time estimation for this modelwere all clarified. Finally, lens shape after releasing was predicted, and the relationship betweenprocess parameter and lens final shape was studied by changing single processparameter. The results show the higher the molding temperature, the smaller theform error, and the quicker the molding velocities is, the form error grows larger.Annealing rate has little effect on the shape deviation, and when maintenanceforce increasing, shape deviation becomes smaller. At last, shape deviationbecome smaller when riction coefficient grows.