Simulation And Experimental Of KDP Crystal Micro Surface Topography Formation In Solution Mechanical Polishing

Potassium dihydrogen phosphate(KDP)crystal is an important optical element(photoelectric switch and frequency doubled converter)in inertial confinement fusion(ICF)optical system.Because of its soft brittleness,easy deliquescence,sensitivity to temperature change and anisotropy,it is recognized as a very difficult material to process.At present,single point diamond flying-cutting is the main means of ultra-precision machining of KDP crystal,but the means will leave cutting marks on the surface and cause subsurface damage,which is an important reason to induce laser damage of KDP crystal.The results show that the abrasive free solution mechanical polishing based on the dissolution of KDP has obvious advantages in the removal of cutting marks and subsurface damage.However,the understanding of the formation process of surface micro morphology in KDP crystal solution mechanical polishing still needs further study.Therefore,the coupling mechanism of the microemulsion polishing slurry and the mechanical function of the polishing pad in the process of solution mechanical polishing will be analyzed in this paper by simulation and experiment,and establish the physical model and mathematical model of the formation process of the surface micro topography,and finally carry out the test to verify it.The main research contents include:(1)The effects of dissolution,mechanical action and dissolution mechanical coupling on the removal rate and micro morphology of the surface of flying-cutting KDP crystal were studied,and the mechanism of dissolution mechanical coupling in the polishing process was analyzed.The research showed that in the dissolution mechanical polishing of KDP crystal,material removal was mainly caused by dissolution.Mechanical action could accelerate the diffusion of water core in microemulsion and accelerate the removal of dissolving products from the surface of KDP crystal.For flying-cutting KDP crystal,all microemulsion on the surface would be affected by the polishing pad mechanically,and then the surface would be dissolved.The high and low points of cutting marks would be removed simultaneously.However,the dissolution rate of the high point was slightly faster,so with the polishing process going,the surface would drop and the knife marks would gradually disappear,achieving the controllable removal of the cutting marks.(2)The physical and mathematical models of the formation process of the micro morphology of KDP crystal surface in solution mechanical polishing were established.The main factors influencing the formation of surface micro morphology and the relationship between them were analyzed,and the physical model of solution mechanical polishing process was built.By kinematic analysis and contact theory calculation,the coordinate point calculation function of surface removal position in polishing process was established.By modeling dissolution,the removal function of removal point height was established.The simulation model of the formation process of the micro morphology of the polished surface was obtained,by coupling the coordinate function of the removal point and the high removal function.The surface micro morphology characteristic parameters(roughness RMS)and the calculation formula of the macro material removal rate were given,based on the mathematical model(3)The mathematical model was verified by polishing experiment.The model could simulate the formation process of surface micro topography under different parameters(speed,polishing pressure,polishing time and concentration of KDP solution in microemulsion)accurately.The polishing surface topography and roughness RMS could be obtained,and the macroscopic material removal rate and cumulative removal height of KDP crystal under corresponding conditions could be calculated.The simulation results was consistent with the experimental results well.