Experimental Study And Numerical Simulation Of Glass Molding Process For Optical Glass Lens

With the increasing demand of electronic products such as camera,camcorder etc,the micro-aspherical glass lens has been attracting more and more attention due to their better optical properties.The conventional techniques,e.g.ultra-precision grinding and polishing methods,are used to process aspherical lens individually.The glass molding process(GMP)can press glass perform into a shape of finished lens under high pressure and temperature conditions,and it is easy to achieve mass production.So,it has emerged as a promising alternative one.However,there are two major difficulties in current industrial practice as follows:Firstly,large residual stress results from the glass preform in GMP,which could cause glass lens to breaking in stripping process and affect the quality of products,resulting in reducing the service life and optical properties of the molded lens.Secondly,there is a profile deviation between the final shape and designed shape.The method of trial and error could improve the molding quality of molded lens,but it is laborious and time-consuming.In order to decrease residual stress of molded lens,a numerical simulation model for multi-steps GMP has been established to investigate the influence of molding parameters in different stages on residual stress in this paper.A new method of molding rate with segmented control is proposed,which may reduce the maximum residual stress effectively.In order to improve the geometrical precision of the molded lens,a numerical simulation model for predicting the profile deviation of molded lens is established,and the influence of glass molding parameters on profile deviation is also investigated.On the basis of the node geometric correction principle and curve fitting techniques,a new compensation method for GMP was proposed.The primary work and achievement are as follows:1)For the multi-steps ultra-precision GMP,the numerical simulation models for three-steps heating,molding rate with segmented control and three-steps annealing are established respectively based on the generalized Maxwell model.Finite element simulation is used to analyze the influence of glass molding parameters in different stages on residual stress,and is compared with the conventional single-step GMP.Based on the analysis of the variation of residual stress in pressing stage,this paper is focused on molding rate which is divided into four stages,and the influence of molding rate in different stages on residual stress is investigated.2)Based on the structure relaxation model,a numerical simulation model for predicting the profile deviations of molded lens is established.The relationship between molding parameters and profile deviation is analyzed with single factor analysis method.The traditional method with compensating the molds by the method of trial and error is very time-consuming.A new method of compensation technology for GMP is proposed which based on node geometric correction principle and curve fitting techniques.The method of trial and error used to modify the die contour curve in the numerical simulation model.When the geometrical precision of molded lens meets the design requirements,and then the die for GMP is machined according to the optimal curve obtained in numerical simulation.3)Based on B-axis controlling and the fixed-point grinding technology,the high precision aspherical die for GMP are machined.The glass molding experiment which using the glass preform of spherical DZK-3 is carried out on the multi-steps ultra-precision glass molding machine.The suitable range of molding temperature is obtained,and aspherical glass lens was machined.Then the profile deviation of molded lens is measured and compared with the simulate result.The validity of the simulation model is verified.4)Glass molding experiments for fabricating double-convex spherical lens are carried out on the multi-steps ultra-precision GMP machine.The influence of the variation of curvature on profile deviation is investigated by adopting a combined approach of experimental and numerical simulation.The experimental results show that the upper surface has larger profile deviation than the lower surface.The experimental and simulate results are similar,which verify the validity of the numerical simulation model further.