Research On The Lapping Of Single Crystal Sapphire Dome Using Magnetic Control Finishing With Fixed Diamond Magnetic Abrasive

With high mechanical strength,good heat conductivity,resistance to chemical corrosion and broadband transmittance of infrared light,sapphire crystal is becoming the ideal fairing material for high speed aircraft and high-Mach missile.But with low efficiency and surface defects such as cracks,scratches and collapse,the traditional grinding technology seriously restricts the application of sapphire dome.Magnetic abrasive finishing has the advantages of strong adaptability,high precision and excellent surface quality,which can be used in the grinding process of sapphire dome.In this thesis,the magnetic abrasives with high content of diamond in the coating were prepared by electroless composite plating method.The magnetic abrasive finishing experiments of sapphire dome were conducted.The effects of main process parameters on the material removal rate and surface roughness were analyzed systematically.The sphericity and surface quality before and after magnetic abrasive finishing were studied.The main work and results are as follows:(1)An adsorption model was established to demonstrate the relationship between the metallic matrix powders and micro diamond particles during the electroless composite plating.The concentration of diamond particles suspended in the plating solution,the diamond grit size,the total surface area of the metallic matrix powders and the plating temperature,were taken into consideration.Electroless composite plating experiments were carried out and the influence of diamond concentration and grit size on the diamond content in the coating of magnetic abrasives were studied.(2)The overall structure of the sapphire dome finishing tool was designed.the 2D finite element model was established by ANSYS finite element software,and the influence of the magnetic pole thickness,the number of slots,the slot width and the slot angle on the magnetic field strength and its gradient were simulated and analyzed.The structure of the finishing tool was optimized by analyze the simulation results and the sapphire dome magnetic finishing tool was developed.(3)The effects of the buffer thickness,the rotation speed,ethylenediamine concentration and lapping time on the material removal rate and surface roughness were studied.Considering the MRR and surface roughness of the sapphire dome,the optimal process parameters were obtained.The material removal rate is 142?m3/min and the surface roughness is 93 nm.The sphericity of the dome decreases from 54.54?m to 11.64?m,and the surface quality is remarkably improved.