Forecast And Experimental Study On Subsurface Damage Of Ultraprecision Machining Glass-ceramic

Glass-ceramic is a kind of optical material widely used in modern industrial development,occupying a decisive position especially in aerospace society. Glass-ceramic with high precision and low damage is an ideal material to manufacture large space telescopes and laser gyroscopes.In fact,machining itself will lead to subsurface damage within the workpieces,which will greatly reduce the optical performance of glass-ceramic.So it is necessary to explore the method to forecast subsurface damage before processing by doing system research,in hope of removing the damage effectively generated during the former procedure in subsequent processing.And it would improve the optical properties of glass-ceramic notablely,which will be of great significance for the development of the space industry in our country.This paper firstly researches the formation mechanism of subsurface damage of glass-ceramic grinded and polished.The depth of subsurface damage was determined for glass-ceramic ultraprecision grinded and polished with the method combinating atmospheric pressure plasma polishing and the advanced detection.Secondly,the nanoindentation experiments were simulated with help of the finite element software,which were designed to research machining process of single grit grinding glass-ceramic.The material plastic performance can be got,as well as the variation rule of residual stress with the change of tip radius and pressure depth,which will provide guidance for practical processing.Thirdly,research has been done to the critical pressure load of cracks caused by indentation before Vickers-hardness and fracture toughness of glass-ceramic were got through indentation test of Vickers.On this basis,the brittle ductile transition in fatigue state was researched by the experimental method of cycling nanoindentation for the first time,such as the variation rule of critical pressure load in fatigue state,and the influence of the fatigue factors on critical grinding depth.Finally,prediction model of surface roughness and subsurface damage depth, taking the processing speed and processing time as investigation factors,was obtained by optimizing polishing experiment through a general rotary combination design method of quadratic regression.What have been done above realized the forecast before machining,obtained process parameters after optimization,and also analyzed the influences of the processing speed and processing time on surface roughness and subsurface damage depth respectively.