| Glass-ceramics materials are widely used in aerospace,building industry and biomedical applications due to their advantages of low expansion coefficient,good thermal stability,and high mechanical strength.The optical applications in the aerospace field have higher quality requirements for the inner surface of the hole-shaped glass-ceramics.The traditional optical glass ultra-precision machining technology is mainly for the outer surface processing,and the research on the process technology of the inner hole for sustainable and high-efficiency precision machining less.The goal of this study was to achieve ultra-precision machining of square-glazed glass-ceramics with dimensions of 50mm×50mm×10mm.The research content and research results of this thesis have important theoretical significance and practical application value for promoting the development of ultra-precision machining technology for hard and brittle optical material special-shaped parts.A new slurry-assisted super-precision grinding process was proposed.The influence of grinding process parameters and slurry jet process parameters on the surface quality of the workpiece and the morphology of the grinding wheel was investigated.A micro-abrasive flow polishing method in the inner surface of the glass-ceramics was proposed.The abrasive flow numerical simulation of the solid-liquid two-phase flow in the process of processing was carried out.The flow cavity and processing parameters was optimized to acquire a high-quality surface of glass-ceramics.The specific main content and conclusions are as follows:(1)A slurry-assisted grinding system for grinding the square hole of glass-ceramic glass was designed.The slurry-assisted ultra-precision grinding experiment of the square hole of glass-ceramic was conducted using a small-diameter grinding wheel.The influence of the slurry base fluid,abrasive type and grinding process parameters on the grinding force,workpiece surface roughness,subsurface damage depth and wheel morphology was obtained.The oil mist cooling grinding can realize the ultra-precision machining of the workpiece in the plastic domain,and the surface roughness is small.However,the grinding wheel dulled quickly and the grinding force is large,it was difficult to obtain a high shape accuracy,and it was impossible to continue grinding for a long time.The cerium oxide slurry cooling can obtain a higher surface quality under the conditions of large grinding depth,but the dressing effect on the grinding wheel was not significant.When the silicon carbide slurry assists in grinding,the slurry has an online trimming effect on the resin-bonded grinding wheel,and the maximum grinding efficiency can be obtained,and the surface/sub-surface quality of the workpiece is stable,and the continuous high-efficiency precision grinding of the glass-ceramics can be realized.(2)The finite element model of the solid-liquid two-phase flow in the square hole of the abrasive fluid-polished glass-ceramics was established.The hydrodynamic numerical simulation of the viscoelastic abrasive fluid polishing process was carried out.The influences of different cavity clearances,processing pressures,and rheological characteristics of the fluid on the surface pressure,shear rate,near-wall velocity,and turbulent kinetic energy of the workpiece were obtained.The simulation analysis shows that the reduction of the slits in the runner cavity,the increase of the processing pressure,and the decrease in the viscosity of the fluid all increase the material removal rate,but the uniformity of the workpiece surface removal decreases.The cavity clearance of 3mm was determined,the processing pressure of 6MPa and the processing temperature of about 300C had the optimum processing effect.(3)Abrasive flow polishing experiment was carried out on the square hole of the microcrystalline glass assisted grinding with silicon carbide paste.Based on the ultraprecision machining theory,the results of the polished surface/sub-surface quality were analyzed,and the influence of the crystallized glass was obtained.Material removal rate and key factors of surface/subsurface quality were analyzed.The material removal mechanism under different processing parameters was analyzed.When using 2000#diamond and 3500#SiC abrasives for polishing,the surface of the workpiece after polishing was smoother.As the pressure increased,the surface quality of the workpiece increased first and then decreased.At the initial stage of polishing,the surface roughness decreased rapidly,with the increase of the number of processing cycles,the surface roughness tended to be stable.The processing mechanism of the 600#diamond abrasive was mainly the removal of the brittle zone.The abrasive surface of the 2000#diamond and the 3500#silicon carbide abrasive mainly removed the plastic zone on the workpiece.And the scratches and ploughs on the workpiece surface were more significant due to the high hardness of the diamond abrasive particles.Polished with 2000#diamond abrasive,the minimum surface micro-crack damage depth workpiece was obtained with the best sub-surface quality of the workpiece. |
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