Study On Key Technologies Of Ultra-precision Grinding For Complex Optical Surfaces

With the development of optoelectronic information technology,optical components used in astronomy,aviation,laser,medical and communication fields are constantly further developed.Compared with traditional planar and spherical optical components,complex optical surfaces have unique advantages in reducing the number of optical components and size of optical systems,simplifying the structure of optical systems,improving design freedom,and achieving special optical performance.The usage of complex optical surfaces has gradually become one of the trends in optical applications.Precision glass molding(PGM)technology is one of the most promising technologies for achieving high efficiency,high quality,low cost and mass production of optical components.It has been widely used in the bulk production of high precision micro aspheric surfaces.However,PGM has not been effectively applied to fabricate complex optical surfaces.The main constraint is because it is difficult to fabricate highprecision complex mold inserts for glass molding.The key technologies on ultra-precision grinding of mold inserts with complex optical surface for precision glass molding are investigated in this study.The material removal mechanism in ultra-precision grinding process,the ultra-precision grinding method and the corresponding PGM are explored in detail.The main contents of this thesis include the following aspects:(1)Fundmentall investigation on the removal mechanism of materials in the ductile regime grinding of brittle materials is performed.Large-scale molecular dynamics simulations are carried out to study single grit scratch and multi-pass scratch on single-crystal silicon and polycrystalline tungsten carbide.The simulation and experimental studies shows that the material is removed in ductile mode during ultraprecision grinding.The material deformation mechanisms of the domain include scratching,ploughing,extrusion,shearing,and reciprocating fatigue.(2)Based on the multi-axis ultra-precision machine tool,corresponding grinding methods are determined for micro-aspheric and cylindrical aspheric surfaces.The virtual spindle grinding method and slow tool servo grinding method are proposed to fabricate the aspheirc microlens array and the optical free-form surface,respectively.The arc profile grinding wheels used in the above mentioned grinding method are precisely trued with an innovative in-situ truing approach.The wheel path determination strategy for the typical complex optical surfaces are detailed.(3)The influence of ultra-precision grinding process errors on the form error of complex optical surface components are investigated.The error transmission mechanism is explored by the combination of Z-Buffer and multi-body theory.Through the analysis of simulated form error caused by process errors in grinding the toroidal and saddle surfaces,the mapping principle between the machined surface form error and the process errors is obtained.(4)The systematic grinding experiments of typical complex optical components are carried out.Profile error and compensation are performed on complex optical surfaces with contour compensation,and sub-micron surface precision and nano-scale roughness are achieved.The mold insert for glass molding is subjected to the corresponding compression molding experiment,and the complex optical lenses obtained by molding can meet the demands of industrial application.