Theoretical And Experimental Study On High Efficiency Grinding Process For Typical Rotary Curved Surface Workpiece Of Si₃N₄

Silicon nitride ceramic material has been widely used in aerospace, nationaldefense industry and other fields due to its advanced physical properties andmechanics characteristics. Grinding with diamond wheel is the most commonlymethod used to machining ceramic material. For its high hardness, high brittlenessand hard to machine performance, silicon nitride is prone to generate sub-surfacedamage in grinding process, which has important influence on the using properties ofthe workpieces. One typical silicon nitride workpiece with rotary curved surfaces isapplied to the aircraft radome, whose structure and surface quality have a directimpact on detection and guidance performance of the radomes. In this case, this papertakes the typical silicon nitride workpiece as research subject. Aiming at th erequirement of high precision and efficiency grinding without damage, the highefficiency and precision grinding process of the typical silicon nitride workpiece withrotary curved surfaces were put forward, combining precise grinding, ELID grindingand chemical-mechanical polishing(CMP). Through theoretical analysis,mathematical modeling and experimental, the influences of the process parameters onthe surface quality and material removal mechanism were analyzed, and the processparameters were optimized. The main research work mainly includes:High efficiency and precision grinding experimental table of the typicalworkpiece with rotary curved surfaces was founded based on the grinding CNCmachine. Based on the analyzing of the machining technology characteristics of thetypical workpiece, the fixture was designed, and the process routes and experimentprogram about precise grinding of the typical workpiece were made.Adopted the normal trace grinding method, the research on mathematical modelsof the grinding surface scallop height of the rotary curved surfaces (convex surfaceand concave surface) were set up. The influences of process parameters on grindingsurface roughness were carried out by using response surface methodology and singlefactor test method, and the mathematical model was founded to analyze the influencesof grinding wheel radius, wheel feed rate and workpiece radius of curvature onsurface roughness. The material removal mechanism of the silicon nitride ce ramicworkpiece with rotary curved surfaces was analyzed in grinding process. Grindingsub-surface damage depth model of the silicon nitride ceramic was founded. Thedetection method of rotary curved surface grinding sub-surface damage depth was put forward based on the circle section polishing. The experiment of grinding sub-surfacedamage depth of the typical workpiece was carried out.The ELID grinding experimental device for rotary curved surfaces workpieceswas designed. A model for the anodic dissolution thickness about voltage, duty cycle,conductivity ratio of electrolyte, interval between cathode and anode and thesharpening time was built. Using Taguchi method, the influence of the pulse frequency,duty cycle, electrolyte flow and wheel speed on the sharpening time was analyzed.Under the ELID dynamic grinding, a model for voltage, duty cycle and the grindingsystem parameters was established. Through the ELID experiment, the effect ofelectrolytic parameters and grinding process parameters on the surface quality ofrotary curved surfaces workpiece was studied.A CMP experiment process solution for workpiece with rotary curved surfaceswas put forward for the small size workpieces. Applying single factor experiment, theinfluence of polishing concentration, polishing flow, polishing wheel speed andpolishing time on surface roughness was discussed. The surface roughness ra as themain evaluation index, the process parameters of the CMP for rotary cured surfaceworkpiece was optimized using Taguchi method. The optimal process parameters onrotary surface workpieces of Si3N4ceramic were selected. The result showed thedescending order of selected process parameters impacting on surface roughness waspolishing wheel speed, polishing time, slurry flow rate and slurry concentration.The high efficiency and precision grinding process experiment was carried out onthe typical workpiece with rotary curved surfaces of silicon nitride ceramic, includingblank precision grinding forming, ELID grinding and CMP. A non-damage surfacewas obtained with ra3nm. By comparing the experiment results with single ELIDgrinding and CMP, the advantage of this comprehensive process on improving surfacequality and processing efficiency was verified. Based on the predictive control ofdepth of subsurface damage, the margin allocation scheme is proposed for theprocessing stages of efficient precision grinding. Using the fuzzy algorithm and thegenetic neural network, the evaluation and optimization model is established for thegrinding process parameters, and it has been verified by the experiment.