Ultra-precision Grinding Of Aspherical-cylindrical Lens Array Mold

With the development of optical system towards miniaturization,integration and intelligence,glass microstructure array optical elements with small structure,high integration and good optical performance have gradually replaced traditional optical elements as key components in optical systems.The process chain composed of ultraprecision grinding and glass molding technology is the most feasible way to realize high-quality,high-efficiency and mass production of glass microstructure array optical elements.At present,the mass production and manufacturing of simple spherical and aspherical glass optical elements has gradually matured.However,the characteristics of hard-brittle materials and complex geometric structure of the microstructure array mold bring challenges to its surface quality and high-precision surface control,which also limits its industrial application and promotion.The key technologies on ultra-precision grinding of micro-aspherical-cylindrical array(MACA)mold for the glass molding of the complex microstructure array optical elements are investigated in this study.The removal mechanism of the hard-brittle mold material,the monitoring of grinding process and the active control of the profile accuracy are discussed in detail.The main contents of this research are listed as follows:The on-machine spiral truing model of ultrathin arc-shaped diamond wheels was established.According to the model,the main error influencing factors in the truing process were provided.Theoretical models for these errors were developed to investigate their effects on the profile accuracy of the diamond grinding wheel.Based on the error analysis models,a compensation truing experiment was performed,where an ultrathin arc-shaped diamond grinding wheel with high accuracy was obtained.Nanoindentation and scratch experiments of WC and GC were carried out to investigate the difference of mechanical response characteristics between crystalline and amorphous materials under static and quasi-static loads.It was found that the micro-molecular structure of the material has a great influence on the mechanical response characteristics of the material.An analytical model of the elastic stress field of the two materials under static and quasi-static loads is established,and the difference of the main stress field distribution characteristics of the two materials during the scratching process was analyzed based on the model.Combined with the micromorphology of the indentation and scratching surface,the reasons for the differences in the nucleation and propagation of scratching cracks and material removal characteristics of the two materials were analyzed.The results can provide theoretical basis for revealing the characteristics of grinding surface crack damage and material removal during grinding.The evolution law of grinding wheel surface morphology and workpiece surface morphology during WC grinding was studied through grinding experiments,and the linear regression equation of grinding ratio of grinding wheel in stable wear stage was established.According to the actual distribution characteristics of abrasive grains,the grain distribution characteristics of the reconstructed grinding wheel are obtained by using the Johnson transformation the inverse Johnson transformation method.Then,the ultrathin grinding wheel is reconstructed by considering the distribution characteristics of abrasive grains and the complex wheel profile.On this basis,a theoretical prediction model of dynamic grinding force was established,which took the analysis of wheel wear characteristics and the change of profile structure characteristics into account in the process of microstructure grinding.The validity of the prediction model was confirmed by the comparative experiments of different grinding parameters.The grinding force prediction model could reflect the influence of grinding wheel wear and the change of microstructure profile structure on the grinding force to a certain extent.A comprehensive model is established to understand the mechanism of the generation of the MACS A surface,which considers the wheel topography,the kinematics model of abrasive grains and the complex geometric conditions between tool and local surface profile in envelope grinding.The surface morphologies of MACS A obtained by simulation and experiment were coincident with each other very well.The simulation model is further verified by comparing the power spectral density(PSD)of the experimental and simulated surfaces.Based on the simulation and the experimental results,the effect of three tool path planning methods(constant step,constant arc length and constant scallop-height)on surface uniformity and profile accuracy was investigated to obtain a more uniform microstructural surface.A new compensation method was proposed to improve the form accuracy of MACSA based on the real-time profile of grinding wheel.The envelope grinding method for MACSA using ultrathin diamond grinding wheel with high-order curve section profile was proposed to directly compensate the form-dressing error.The mathematical models of grinding wheel with high-order curve section profile and the wheel path model were established.Then,the mathematical model of instantaneous radial wear of diamond wheel in the grinding process of MACLA surface was established based on the grinding ratio and structural characteristics of aspheric surface.Finally,the normal residual error was obtained to generate a new diamond wheel trajectory for compensation machining.The active predictive control and automatic grinding compensation for the error factors before,during and after grinding are realized.System software of microstructure array ultra-precision grinding was developed to program NC program and simulation results for microstructure array grinding and compensation.The research provides theoretical and technical support for the engineering application of ultra-precision grinding of complex microstructure array molds.