Study On The Cluster Magnetorheological Polishing Experiment Of Single Crystal Sapphire Substrate

Single crystal sapphire is multifunctional crystal material with excellent comprehensive performance and is widely used in various fields.With the improvement of product performance in various fields,the processing requirements of single crystal sapphire are also getting higher and higher,requiring that the surface quality after processing is good and no subsurface damage.At present,the methods of processing single crystal sapphire have certain defects.The cluster magnetorheological polishing technique is an optical surface planarization polishing method,which has the advantages that other ultra-precision polishing methods do not have.In this paper,the cluster magnetorheological polishing process of single crystal sapphire were systematically studied,the main research work is as follows:1)Combined with the material removal mechanism of the traditional polishing process,the material removal mechanism in the single crystal sapphire cluster magnetorheological polishing process is analyzed.The material removal mathematical model was established based on the Preston equation from empirical formulas in grinding.The relationship between material removal amount and polishing parameters was obtained by the model.The correctness of the model was validated by experiments and summed up the impact of polishing parameters on the material removal amount.2)SolidWorks modeling software and Ansoft Maxwell three-dimensional magnetic field simulation software are used to simulate the magnetic field generated by different structure of the polishing disc,different shapes of the magnetic poles and different magnetic pole arrangement.Based on this,the influence of the uniformity of the magnetic field and the magnitude of the magnetic induction on the polishing effect is analyzed.3)According to the process of rough grinding,fine grinding,rough polishing and cluster magnetorheological polishing,the experiment equipment was optimized in view of the problems existing in the experiment.The lapping fluid formulations and the polishing fluid formulations were improved.The cluster magnetorheological polishing process was carried out by using self-made silicon dioxide colloidal sol with a particle size of 70 nm.The effects of the concentration of the polishing fluid,the pH of the polishing fluid and the temperature of the polishing fluid on the surface roughness were studied.The experimental results show that the rate of decrease of surface roughness decreases with the decrease of abrasive concentration,increases first and then decreases with the increase of the polishing fluid temperature and pH.When the concentration of the polishing fluid is 45%,pH=11,temperature at 36 ?,the rate of decrease of surface roughness is 1.65 nm/min and the surface roughness is 0.8 nm.4)The formation mechanism of subsurface damage was analyzed.The feasibility of cluster magnetorheological polishing to remove subsurface damage was theoretically analyzed.Based on the theory of imprint fracture,the relationship model between subsurface damage depth and polishing parameters was established.The rationality of the model was verified by orthogonal experiments and the effects of polishing parameters on the depth of subsurface damage was studied.The experimental results show that the subsurface damage depth increases with the increase of polishing pressure and particle size.polishing pressure is a key factor in determining whether subsurface damage is occurring,when the particle size is 280 nm and the polishing pressure is 82 N,no subsurface damage occurs during polishing and the subsurface damage caused by grinding can be removed.After 100 minutes polishing,the subsurface damage depth is reduced to 0.9 nm.