Basic Research On Ultra-smooth Magnetorheological Polishing Process Of Fused Silica Components

Fused silica has excellent physical and optical properties and is widely used in strong laser field,but it is difficult for traditional optical processing methods to make the roughness of fused silica below lnm.In addition,the surface and subsurface defects caused by manufacturing are main factors for the reduction of fused silica anti laser damage threshold.Magnetorheological finishing(MRF)is a kind of advanced flexible polishing technology,which provides a new method to realize the ultra-smooth surface of fused silica.The parameters of magnetorheological finishing machine and magnetorheological(MR)fluid are main factors,determining the removal process and the effect of polishing process,and key to obtain the ultra-smooth surface.At present,evaluation indicators of the ultra-smooth surface are difficult to effectively characterize the influence of the magnetorheological finishing parameters on the smooth surface of the fused silica.Associated with the power spectral density(PSD),this paper studies main factors how to affect the smooth surface of fused silica.Firstly,based on the physical and chemical properties of fused silica,water in MRF plays an important role in the removal of fused silica.According to the characteristics of fused silica material removal and removal quantity control model,removal depth of fused silica material is the key to obtain super smooth surface and critical depth can be calculated by Hertz contact theory.The dispersion behavior of aggregation and combination of MR polishing and removal mechanism of micro nano particles show that solid particles of magnetorheological fluid in the normal load and the dispersion of MR fluid are main factors affecting the quality of ultra-smooth surface of fused silica.In addition,the particle size and pH value influence dispersion of MR fluid.2D contour root mean square(Rq)and 3D surface root mean square(Sq)are traditionally parameters to characterize and quantify the quality of ultra-smooth surface,namely they can only describe the morphology in one direction(z direction)of the amplitude,which is unable to effectively characterize the magneto rheological process of fused silica ultra-smooth surface in the plane direction(x direction and Y direction)effect.However,using the power spectral density to evaluate ultra-smooth surface of fused silica can make up the shortages.Electromagnetic simulation and related experiments were applied to study MRF immersion depth and excitation current how to influence ultra-smooth surface of fused silica.The results showed that both the immersion depth and the excitation current affected the polishing effect by changing the magnetic field gradient,and they had a linear relationship with magnetic field.Finally,based on the experimental results,chapter evaluates the relationship between the pH values of the magnetic particles with different particle size and the MR fluid.The results showed that the surface quality of the iron particle size mainly influenced spatial frequency at 100.1?102 mm-1 and space frequency of pH affecting ultra-smooth surface of fused silica was 100.1?102.6mm-1,alkaline enhancement will expand the influence of MRF anisotropy on the fused silica smooth surface quality of the premier league.