Fabrication Of Large Aspherics Using Non-Newtonian Fluid Polishing Tool

Compared with the conventional methods,CCOS(Computer Controlled Optical Surfacing)is a much more effective way to make aspheric mirrors due to its deterministic material removal and high convergence rate.CCOS has made rapid progress with the development of some advanced techniques such as stress lap polishing?Magnetorheological finishing and ion beam figuring.However,the next generation large optical systems put forward with higher requirements to these CCOS techniques.Aspheric mirrors need to be fabricated in a more efficient way.In addition,controlling of mid-to-high frequency errors on the optical surfaces is becoming very important.The new requirements need CCOS techniques to have better figuring?smoothing and finishing abilities.However,the existing CCOS techniques cannot meet the above requirements at the same time.A good solution is to take their advantages into different stages of the fabrication process.Non-Newtonian fluid lap polishing is a new technique to process the aspheric surfaces.Due to the non-Newtonian fluid lap takes advantages of both rigid and compliant tool,it has a very flexible application in manufacturing large aspheric mirrors.In this paper,the non-Newtonian fluid lap polishing will be studied in detail.The paper is organized as follows:1?The research on the basic principles of the non-Newtonian fluid polishing tool.The visco-elastic property of the non-Newtonian fluid was studied based on the Newton's law of viscosity.The rigid and compliant performances of the non-Newtonian fluid lap in a real polishing work were defined in two time scales: long time scale and short time scale.The static mechanical analysis and dynamic mechanical analysis were used to explain the different performances of the non-Newtonian fluid lap in two time scales,respectively.2?Design and manufacturing of the non-Newtonian fluid lap.A general structure was designed based on the structure of a compliant tool.The dimension of the tool was analyzed based on the gradient pressure effect induced by the drive force,and the contact condition between the tool and the aspheric surfaces.Two factors that cause unstable tool influence functions were studied using finite elements analysis and Hertz contact theory,respectively.The unstable factors were also verified by experiments.A new structure was designed by finite elements analysis.The new structure was proved to be effective to have a high theory-like tool influence function.3?Research on the optimization of polishing parameters using non-Newtonian fluid lap.A series of experiments of polishing RB-SiC were made,which include the relationship between the removal rate and the polishing parameters,the relationship between the surface roughness and the polishing parameters,and the relationship between the removal rate and the polishing compound and so forth.Baes on the experimental results,the polishing parameters were optimized.A 360×300mm RB-SiC aspheric mirror was used to make the unique polishing experiment,the stability of the tool influence function of the non-Newtonian fluid lap was proved to be larger than 90%.An 800×300mm Si aspheric mirror was used to test the figuring ability of the non-Newtonian fluid lap.After 6 polishing period,the RMS value of the surface errors converged from 0.192?RMS to 0.073?RMS.The grinding ability of the non-Newtonian fluid lap was also be studied.A 1430 mm diameter ceramics glass was used to make the grinding experiment,and the result showed good potential of smoothing the mid frequency errors in grinding using non-Newtonian fluid lap.4.Research on the smoothing effect of the non-Newtonian fluid lap.The basic principle of the smoothing effect of the non-Newtonian fluid lap was studied.A time-dependent smoothing model was developed based on the classical bridging model and parametric smoothing model.An optimization strategy of improving the smoothing efficiency was made based on the time-dependent smoothing model.Two sets of smoothing experiments were performed.Based on the experimental results,the best smoothing parameter was gained.