Theoretical And Experimental Study On Disc Polishing Technology Based On Center-Inlet Hydrodynamic Theory

The rapid development of optical technology is based on high quality optics.Due to their advantages,large aspherical optical elements are widely used in modern optical devices.In actual machining process,a variety of polishing methods are needed to finish manufacturing of optical components.After hundreds of years of development,modern optical processing system which contains a wealth of poilishing methods can meet the requirement of current optical processing.However,optical processing technology has been in constant development.At the same time,the exploration and attempt of new polishing methods have never been stopped.In this paper,in order to meet the machining requirements of large aperture optical components,new polishing methods are tried to perfect existing optical processing system.Based on center-inlet hydrodynamic theory,Contact Center-inlet Disc Hydrodynamic Polishing(CCDHDP)and Floating Center-inlet Disc Hydrodynamic Polishing(FCDHDP)are proposed.Then,studies on these two polishing methods are carried out by theoretical analysis and experimental verification.Firstly,removal function of CCDHDP is studied.According to the requirement of removal function study,a process experimental equipment with slurry supplied from the tool's center hole is designed.Then,the material removal process is studied based on single particle removal model.It is found that tool rotary speed increases material removal efficiency by affecting particle movement velocity,and tool load improves material removal efficiency by affecting effective contact area and cutting depth of halfembedded abrasive particles.However,change of tool load won't affect cutting depth of abrasive particles in full-embedded state.Experimental results show that center-inlet method can improve sufficiency and uniformity of abrasives supply,prolong life of polishing pad,and improve stability of removal function.Secondly,surface shaping ability of CCDHDP is studied.Removal function can be considered as a combination of different wavelengths in a certain bandwidth.Through simulative processing,it is found that removal function can not remove the surface error whose wavelength is less than its wavelength bandwidth,can partly remove the surface error whose wavelength is in its wavelength bandwidth,can fully remove the surface error whose wavelength is larger than its wavelength bandwidth.CCDHDP surface shaping experiments are completed to prove that the smaller the removal function is,the better its surface shaping ability is.At the same time,it is verified that surface shaping ability can be improved when slurry is supplied from the center hole.Therefore,CCDHDP is more suitable for the correction of medium and low frequency errors in rough polishing stage.Thirdly,slurry film of FCDHDP is studied.A polishing tool is designed,and feasibility of this polishing method is verified by experiments.A CFD model of slurry film is established,and the accuracy of this model is verified by slurry film thickness experiments.Pressure field and velocity field distribution of slurry film are analyzed based on this CFD model.For tool without grooves,tool rotary speed does not affect load-thickness curve.However,increase of input pressure will make load-thickness curve move up.For tool with grooves,increase of input pressure will lead to increase of load-thickness curve,and increase of tool rotary speed will also lead to increase of load-thickness curve.Finally,studies on FCDHDP are carried out by theoretical analysis and experimental verification.Based on CFD,A roughness prediction model is established,and maximum roughness of workpiece surface is proportional to maximum cutting depth of abrasives.Based on experiments,effects of abrasive particle size,tool load,tool rotary speed and input pressure on the polishing effect are investigated.It is found that for both kinds of polishing tools with or without grooves,the smaller the particle size,the tool load and the input pressure is,the smaller the surface roughness.At the same time,tool rotary speed does not affect surface roughness obtained by tool without grooves.However,due to hydrodynamic effect,surface roughness obtained by tool with grooves will become smaller with increase of tool rotary speed.FCDHDP can improve the surface roughness on the basis of maintaining the original profile.Therefore,this method is suitable for the correction of high frequency.