| Electronic ceramic materials and components are important part of the electronic information industry.They have important supporting role for the development of electronic information industry and technology innovation.Besides,they possess remarkable social and economic benefits.As a new multi-functional porcelain material,strontium titanate ceramic material(Sr Ti O3)has high dielectric constant,good thermal stability,high resistance to high pressure,it has become the preferred materials of the capacitor,varistor ceramics,and thermosensitive element.With the development of applications,the substrate size of SrTiO3 need to reach two inches,the thickness low to0.1mm and surface is smooth(Ra?0.01?m).However,the SrTi O3 was attained by pressureless sintering,it has the characteristics of thin,soft,crisp and warped,and it is difficult to machine effectively.Therefore,the broken rate of the substrate,obtaining the smooth surface without damage and ensuring the integrity of the machined surface are key technical problems need to be solved urgently.Based on the study of the cluster magnetorheological(MR)finishing,the MR finishing with dynamic magnetic fields is proposed.As permanent magnet rotate eccentrically,the static magnetic fields convert into dynamic magnetic fields and the direction of the magnetic lines of force proceed to change.The MR particles and abrasive particles carry on multi-dimensional movement with the axial,radial,tangential and redistribution in MR fluid.The shape and performance of polishing pad recovery quickly and the abrasive update,then the workpiece was machined by high efficiency,high precision and uniform MR polishing.The single point MR polishing device of dynamic magnetic fields was developed.The silicon was used as the experimental material,the surface roughness,surface morphology and material removal rate were used as the evaluation index.The main factors influencing the polishing effect were analyzed,and the processing effects were studied.After polishing,the ring shaped polishing belt zones appear on the surface.And the favourable polishing effects were obtained when silicon carbide abrasive was used to polish the workpieces for 50 to 70 min with the rotation eccentricities of magnetic polebeing 5mm and the machining gap being 1.1mm.By comparing the polishing effect of SrTi O3,monocrystalline silicon and single crystal 6H-SiC,the advantages and the feasibility of the MR finishing with dynamic magnetic fields were analyzed.Based on MR finishing with dynamic magnetic fields,the new cluster MR polishing device of dynamic magnetic fields of multiple poles rotating simultaneously was designed.The test platform was built by using piezoelectric sensor.It can measure the polishing force of the polishing pad into workpiece surface.By system experiment,the characteristics of MR polishing normal force of dynamic magnetic fields is analyzed.The influences of the revolving speeds of magnetic pole,the machining gaps,the movement ways of workpiece on MR polishing force were researched.The strontium titanate ceramic substrates were single point MR polishing by the cluster MR polishing device of dynamic magnetic fields.The influences of the abrasive types,machining gaps,revolving speeds of magnetic pole,rotation eccentricities of magnetic pole and other parameters on the processing effect were researched.The best processing parameters were achieved.Under dynamic magnetic fields,smooth and flat MR polishing was realized.By analyzing the surface of strontium titanate ceramic substrates that was polished through single point orientation MR polishing with dynamic magnetic fields,the behavior mechanism of the abrasive grains under dynamic magnetic fields was analyzed in detail,the material removal mechanism was studied,and it is found that all the surface materials were removed under elastic plastic deformation. |
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