Study On The Key Technology Of Vibration-assisted Polishing For Optical Elements

The machining process of high precision optical workpieces generally includes four stages,namely grinding,grinding,rough polishing and deterministic manufacturing.The main goal of the rough polishing stage is to remove the damage layer produced during the grinding stage,and improve the surface shape accuracy and surface quality in some degree.In order to improve the efficiency of rough polishing stage,the main method for plane and spherical workpieces is to use a large polishing tool polishing the whole mirror.For aspheric workpieces,the global polishing method can not be applied because of different curvature radius of the workpiece surface.So we generally use small polishing tool for the polishing.However,this method has low processing efficiency,at the same time it will introduce more mid-high spatial frequency errors,which can not meet the optical workpiece requirements of modern optical system.Based on traditional small polishing tool,this paper introduces vibration to study the effect of vibration-assisted polishing on increasing polishing efficiency?control surface quality and suppressing mid-high spatial frequency errors,which will provide effective technical support for the fast rough polishing of aspheric optical workpieces.The major research efforts are divided into the following parts:1.The theoretical analysis of vibration-assisted polishing process is carried out.Through establishing mathematical model of the single abrasive grain impacting workpieces,we analyse the ductile-brittle transition mechanism of hard-brittle materials caused by vibration parameter changes.LY-DYNA simulation is used to analyze the process of spherical and conical abrasive particles impacting workpieces.Results show that the workpiece material can be removed under the condition of vibration machining.With the enhancement of vibration signal,the depth of processing gets higher,when the critical cutting depth is reached,the crack is generated and the workpiece material is quickly polished under brittle removal.2.The study of axial vibration-assisted polishing experiments are carried out on the ultrasonic vibration toolholder platform.The experiment results show that the vibration-assisted polishing has higher material removal efficiency,which proves the correctness of the theoretical analysis and simulation.According to the whole polishing experiments,the higher material removal rate is got by the process parameters with high amplitude and large depth of press;the better surface and lower damage of the workpieces are got by the reverse process parameters.3.In order to control the integrity of the surface quality,on the one hand the results from the experiment of the non-contact vibration-assisted polishing show that the workpiece surface quality can be improved effectively.On the other hand the press of the poishing is small in the process of vibration-assisted polishing through thetheoretical analysis,so the damage caused by the polishing is also small.The results of the experiments show the new damages are not generated on polishing the non-destructive exemplar by the vibration-assisted polishing.The subsurface damage depth is changed better than the non-vibration polishing when the K9 glass with the explicit subsurface damage is polished by the vibration-assisted polishing.4.According to the theoretical analysis,the machining path is diturbed by the radial vibration-assisted polishing and the removal efficiency is improved,therefore the mid-high spatial frequency errors are inhibitted.However the axial vibration-assisted polishing does not have the ability to suppress mid-high spatial frequency errors.The experiments are carried out on studying that the radial and axial vibration-assisted polishing inhibitted the mid-high spatial frequency errors,and the results of the experiments show the mid-high frequency spatial errors are inhibitted obviously by the radial vibration-assisted polishing.The axial vibration-assisted polishing cannot inhibit the same errors,which proves the correctness of the theoretical analysis.