Research On Precision Grinding And Measurement Technique For Low Subsurface Damage Of Monocrystalline Silicon Curved Optics

Curved optics of monocrystalline silicon play an important role in high power laser system and its form accuracy and subsurface damage(SSD)have a significant impact on the performance of the laser system.These are many problems in the fabricating process of curved optics,however,the mature fabricating process of plane optics of monocrystalline silicondoes not apply to the manufacture of curved optics.Normal grinding fails to control the depth of SSD due to the hard and brittle physical characteristics of monocrystalline silicon,and this makes it difficult to balance the efficiency,cost and the final machining precision in the following polishing process,thus the precision grinding is introduced between normal grinding and subsequent polishing process to solve this problem.In this thesis,the error sources which influence the form accuracy and the relationship between process parameters and the depth of SSD are investigated to decrease the depth of SSD and improve the form accuracy.The major research efforts include the following points.(1)Based on the ductile machining of precision grinding,the transformation between brittle and ductile machining is analyzed,and the critical grinding force,the critical depth of grinding and the minimum wheel speed are obtained to provide reference for optimized process parameters.(2)The factors which influence the form accuracy are investigated.By establishing the influence model of the pose error and the wheel wear on fabricating precision,the pattern of pose error and the law of wheel wear are obtained.The method of adjusting the pose and the process of iterative grinding based on the compensation of wheel wear are put forward.(3)The distribution law of subsurface defects in grinding is studied.Based on the relationship between grinding force,depth of subsurface defects and different process parameters,the optimized parameters which constrain the defects are obtained.(4)The processing experiment is carried out on a 195mm-diameter parabolic mirror of monocrystalline silicon.An on-machine measurement device is established and its detection characteristic is evaluated.The reasonable program of compensating machining is presented according to the on-machine measurement results.The values of the roughness of Ra,the form accuracy of Peak-Valley and the depth of subsurface defects of the final machining workpiece are 0.081μm,3.77μm and 3~5μm respectively.