Viscoelastic Testing And Simulation For Aspheric Diffracted Optical Glass Lens Molding

Aspheric diffraction lens is widely used in wavefront shaping,infrared system,optical calculation,aberration correction,image recognition and so on,which can eliminate the aberration of optical system and reduce the imaging defects such as chromatic aberration.However,due to the great difficulty of processing,its applicaton is limited.As a hot pressing technology which can copy the mold shape to the glass sustrate at high temperature,high-precision molding technology has high production efficiency,low cost and high precision.It is a feasible technology to manufacture aspheric diffraction lens,but there are still some scientific and technical problems.This paper mainly studies the molding process of aspheric diffractive lens,including lens optical design,glass property measurement,molding simulation experiment,mold structure processing,involving optical design,material properties,program calculation,simulation,mechanical processing and so on.Firstly,under the premise of given optical index of the lens,the optical glass is selected,and the aspheric diffractive lens is designed and optimized by using ZEMAX.The aspheric diffractive lens’ contour equation was calculated according to the phase distribution function.On this basis,the relationship between the optical design index and the structural parameters of the aspheric diffraction lens is further explored.Secondly,the viscoelastic properties of K-LCV161 glass were measured.The creep curves of glass under different temperatures and different forces were measured by using the minimum uniaxial compression experiment.Then the stress relaxation characteristics of glass were described according to Maxwell model and WLF equation.The Prony series form and displacement factor for the input of molding simulation stage were given;The specific heat capacities of several groups of glasses under different temperature rise and fall rates are measured by differential scanning calorimetry.Based on this,two methods to solve the parameters of TNM model are explored.The specific parameters are obtained and converted into the form of simulation input in the molding annealing stage.The volume changes of glass during cooling process predicted by thermal expansion model and structural relaxation model are compared.Thirdly,according to the viscoelastic properties of glass,the accuracy of two-dimensional axisymmetric model commonly used in molding simulation is studied in MSC.Marc.On this basis,the three-dimensional simulation of heating stage is carried out,and the shortest heating time is given;the three-dimensional simulation of pressing stage is carried out,and the influence of forming temperature,pressing rate,holding time and glass shape on forming stress is revealed.Finally,based on the selection of mold materials and the characteristics of mold shape,by selecting appropriate machining machine tools,diamond cutting tools and process parameters and compensating for errors,the aspheric diffraction lens mold was obtained by using single point diamond turning on C71500 Cu-Ni alloy.The research contet in this paper can provide reference for the design of aspheric diffraction lens and the molding process.Meanwhile,the viscoelastic method and data presented in this paper can also be used as the basis for further research.