A Study Of Finite Element Simulation For Glass Molding Process Based On Thermal-structural Coupling

With the continuous development of optoelectronic communication,smart cars,security surveillance and other fields,the demand for optical lenses is increasing dramatically,and precision glass molding has become the mainstream technology for mass production of optical lenses by virtue of its high efficiency and environmental protection.In order to improve the development efficiency,finite element simulation is usually used to optimize the molding process parameters.However,the current finite element simulation model for precision glass molding has the following challenges:(1)the material properties of the glass have a great influence on the quality of the molded lens,and the accurate characterization of the material properties is the primary factor to decide whether the model is accurate or not;the existing models have only studied the material properties for some glasses,and less involve the material properties of the new low melting point glass;(2)the glass molding process contains The boundary conditions set by the existing finite element simulation models ignore the heat changes caused by the radiation and convection heat transfer factors,which are not sufficient to accurately characterize the complex thermal environment of the molding process.Therefore,this thesis considers the material characteristics of the new low melting point glass M-BACD5 N to analyze the heat transfer process of the lens and structural parts(heating plate and mold)under three heat transfer methods(heat conduction,convection heat transfer and radiation heat transfer)during the molding by GMP-211 V molding machine,establishes a thermal-structural coupling model,and builds a simulation model of aspheric lens glass molding based on the thermal-structural coupling model to analyze The simulation model of aspheric lens glass molding is established based on the thermal-structural coupling model,and the relationships between the molding process parameters(molding temperature,molding rate,annealing temperature),lens residual stress and face shape error are analyzed to obtain the optimization method of aspheric lens glass molding process for different geometric features.The main research work of this thesis is as follows:(1)For the new low-melting glass M-BACD5 N,considering its low transformation point and stable thermal properties,explore the change process of the glass in the transformation interval,calculate the viscoelasticity and structural relaxation parameters of the glass,and establish the molding process M-BACD5 N material model.The viscosity of the material is measured by a parallel plate and a bending beam viscometer.According to the relationship between the temperature and the viscosity of the material,the range of each temperature point and molding temperature of M-BACD5 N is determined;the stress relaxation parameters are obtained by the cylindrical compression experiment;The thermal expansion coefficient and specific heat capacity of the material were measured by scanning calorimetry,and the structural relaxation parameters were calculated based on the TNM model algorithm.(2)Based on the thermal analysis of the structure of the GMP-211 V molding machine and the molding process,a thermal-structural coupled finite element model is established.The experiments show that the thermal-structural coupled model can better characterize the glass molding process than the existing models.Firstly,the thermal analysis of the compression molding process is carried out by means of simulation and experiment,and it is proved that the main way of heat transfer in the heating and holding stage is radiation heat transfer,and the main way of heat transfer in the annealing and cooling stage is convective heat transfer.Then,according to the changes of the structural parts(heating plate,mold)and thermal environment involved in the compression molding process,a finite element model of thermalstructural coupling is established.Finally,the thermal-structural coupling model and the existing model are used to simulate the compression of the cylindrical sample.Through the compression experiment of the cylindrical sample,it is proved that the thermal-structural coupling model can better characterize the heat transfer process of the heating plate than the existing model;-The structural coupling model and the existing model are used to simulate the aspherical lens.Through the aspherical lens molding experiment,it is proved that the thermal-structural coupling model can better characterize the heat transfer process of the structural parts and predict the maximum residual stress of the lens than the existing model.It makes up for the problem of insufficient representation of boundary conditions in existing models.(3)Based on the thermal-structural coupling model,the influence analysis and process optimization of large-diameter aspheric lens molding process.Based on the thermal-structural coupling model,a simulation model for forming a large-diameter aspheric lens was established,and the effects of lens geometric characteristics and molding process parameters(molding temperature,molding rate,annealing temperature)on the residual stress were analyzed.The simulation model is verified: 1)The simulation results of the maximum surface error are close to the experimental results;2)The maximum surface error value is similar to the change trend of the maximum residual stress value;3)Within a certain range,increase the molding temperature,reduce the molding rate,The annealing temperature can effectively improve the size of the maximum residual stress,thereby reducing the maximum surface error and improving the surface accuracy.Therefore,the method of glass process optimization for aspheric geometric features by thermal-structural coupling model is effective.For the designed large-diameter aspherical lens,considering the factors of time efficiency and surface accuracy,the optimized process parameters are: molding temperature 580°C,molding rate 0.06mm/s,and annealing temperature 470°C.Its surface error PV value is reduced from 9.0232?m before optimization to 4.4512?m,thus improving the development efficiency of new products.