Lapping And Polishing Mechanism Of Magnesium Aluminate Spinel Doom Cover By Fixed Abrasive

Magnesium aluminate spinel has been widely applied in civil and military fields,especially for doom cover of missile because of its excellent performance like high strength and hardness,good transparency and wear-resisting.But,it is expensive and inefficient to use the traditional loose abrasives for lapping and polishing owing to its brittleness and stable physical and chemical performances.In the thesis,a new solution of using FAP for lapping and polishing was proposed to avoid the above disadvantages of the traditional processing technology.The average cutting depth model and materials removal rate model of lapping and polishing for magnesium aluminate spinel with FAP was built.The materials removal mechanism was dicussed,the preparation technology of FAP for doom cover and the optimization of FAP's bulges distribution were researched,the suitable processing was selected and processing parameters were optimized.The main work is displayed as followings:(1)The average cutting depth of single abrasive and the materials removal model.The active abrasives number was estimated when lapping and polishing magnesium aluminate spinel based on the structural feature of FAP,the average cutting depth of single abrasive and the materials removal calculating model were built by considering mechanical relationships among abrasives,wafer and lapping pad.Effections of precessing factors on its were also discussed.(2)Materials removal mechanism when lapping and polishing magnesium aluminate spinel with FAP.The materials removal reasons were divided into three types: the pure mechanical action,the chemical corrosion of slurries and the coupling of them.The disjunctive model of materials removal rate was built and the measuring method was proposed.The experimental results show that the material is mainly removed by pure mechanical action when lapping and polishing magnesium aluminate spinel with FAP and it is about 67% of the whole materials removal.(3)Actions of slurry on wafer surface materials characters.The microhardness and fracture toughness of spinel wafer were tested under different slurries by employing microhardness tester,and critical cutting depths were estimated.The depth of soften layer formed on wafer surface under slurry was measured by XPS depth profile.The possible forming mechanism of soften layer and effects of soften layer on processability and critical depth of wafers were also analyzed.(4)The prediction and measuring method of subsurface damage on lapping and polishing magnesium aluminate spinel with FAP.The distinct element model of lapping and polishing magnesium aluminate spinel with FAP was built and the subsurface damage depth of magnesium aluminate spinel wafer was deduced according to the maximum cutting depth of single abrasive.The subsurface damage depths of wafers lapping and polishing with different abrasive sizes FAPs were measured by slops polishing.Predicted results and measuring reults were compared and analyzed.(5)The bulges distribution optimization and preparation technology of FAP for doom cover.The motion feature of abrasive on lapping and polishing magnesium aluminate spinel doom cover with FAP was explored,the equation for calculating trajectory length of abrasive was deduced.So,the wear calculating model of abrasive on FAP for lapping and polishing magnesium aluminate spinel doom cover was built and the bulges distribution optimization method of FAP for doom cover was proposed.The preparation process of FAP for spherical surface by two-stage building method was also proposed.(6)Processing of lapping and polishing magnesium aluminate spinel with FAP.Effects of processing parameters on material removal rate and surface quality of lapping and polishing magnesium aluminate spinel with FAP were researched.The suited processing route and parameters of lapping and polishing were also selected according to different stages,which would markedly shorten the processing time of magnesium aluminate spinel products.