Simulation Study Of Machining Quality Of Optical Sphere

As a kind of optical component,optical sphere is widely used in national defense,civil and scientific research fields due to its own special structure and good light transmission performance.However,the different shapes and sizes of the sphere and the properties of the materials used to create the sphere itself make the overall processing of the sphere complex and costly.Therefore,in this article,we designed a polishing machine with the basic processing principle of "two rotations + one oscillation",and simulated and analyzed the machining quality of the dome on this basis.The specific works are as follows:Firstly,we designed a sphere polishing machine based on the working principle of "two rotations + one oscillation" and analyzed the characteristics of the sphere material,size and process requirements.The overall working mode of the machine was introduced and the static and dynamic mechanical analysis of the designed machine was carried out to verify the stability and rationality of the machine structure design.Meanwhile,Comparing the free-mode and bound-mode,it was found that the constraints have a noticeable effect on the results of the modal analysis.Then,the trajectory equation of any point on the polishing head was established on the basis of the motion characteristics of the machine.At the same time,the positive icosahedron was selected as the ontology,and the sphere surface mesh was obtained by dividing and removing the redundant mesh by multiple iterations.The initial position of the polishing head as well as the termination position were discussed to get the best trajectory simulation time.Based on the single abrasive trajectory equation,the trajectory curve was drawn by Matlab,and the dispersion coefficient was used as the evaluation index to analyze the influence of each factor on the trajectory uniformity.The trajectory uniformity was found to be significantly better than the integer ratio when the speed ratio was an irrational number with a rational infinite loop fractional number.Increasing the radius of the polishing head,the dispersion coefficient gradually decreased and the uniformity becomed better.Increasing the pendulum speed,the length and density of the trajectory gradually decreased,and the non-uniformity gradually increased.Changing the initial phase of the abrasive grain motion had little effect on the trajectory uniformity,but only made the trajectory rotate by a corresponding angle.Also,It was found that the trajectory uniformity gradually became better as the number of abrasive particles increased.Based on the Preston equation,the wear amount at any point on the polishing head was studied to analyze the variation of speed,pressure and wear amount at different heights and at different bushes.It was found that the speed,pressure and wear at different busbars at the same height all fluctuated in the same range,with only slight deviations in phase.The fluctuation range of all three becomes larger at different heights on the same buses.Finally,the micro-element idea was used to decompose the dome surface into multiple infinitely small regions,each of which was equivalent to a small plane,a method combining nanoindentation and finite element was used to investigate the change of physical properties of the material and the internal stress distribution during the polishing process.Nanoindentation experiments were conducted on two typical optical materials,sapphire and quartz,and six different magnitudes of force were taken for loading to obtain the load-displacement curves under different loads.Based on the indentation test results,the hardness values were 32.49 GPa,8.67 GPa and the modulus of elasticity were 417.22 GPa,68.27 GPa.The relationship between the elastic work,dissipated energy and total energy during the indentation process and the maximum indentation depth,maximum force and residual depth were analyzed,and the liner distribution between the two was found.Meanwhile,the loading state function of loaddisplacement curve was established.The nanoindentation structure model was constructed by ABAQUS,and the P-h principal structure function was obtained by combining with the gauge analysis method.The function reliability was also verified by making a comparison with the experimental curve.Adopting various shapes of indenter to simulate the influence of different shapes and sizes of abrasive grains on surface of materials during polishing process,and the load-displacement curves,stress-strain and surface morphology after loading and unloading were obtained and analyzed.