Simulation And Analysis Of Friction And Wear Of The Polishing Pad In Deliquescent Polishing Of KDP Crystals

Potassium dihydrogen phosphate(KH2PO4,or KDP)crystals have excellent optical properties and are key for multiplier conversion elements in inertial confinement nuclear fusion.KDP is recognized as an extremely difficult optical material to process due to its soft and brittle texture and its susceptibility to deliquescence.Currently,the primary methods for ultraprecision machining of KDP crystals are single-point diamond turning,ultra-precision grinding,and polishing techniques.Compared to other methods,deliquescent polishing of KDP crystals is regarded as one of the most promising processing techniques due to the absence of abrasives in the polishing fluid and the near absence of scratches on the workpiece surface.Deliquescent polishing of KDP crystals is a chemical-mechanical polishing without abrasives,and the polishing pad assumes many pivotal roles in the deliquescent polishing process.Studying the pad’s wear during this process can help improve the polishing efficiency and quality,prolong the polishing pad life,and reduce the cost of deliquescent polishing.The research in this paper is as follows.Firstly,the kinematic analysis of the deliquescent polishing oprocess of KDP crystal was carried out,and the equation of the trajectory of a single point on the surface of the KDP crystal relative to the polishing pad is derived through coordinate transformation.Based on the observation and analysis of the trajectories,the coefficient of variation was introduced as an index for discriminating the uniformity of the trajectories.The surface of the polishing pad is gridded,the distribution of trajectory points in each grid was counted,and the coefficient of variation of the trajectory at this time was calculated.At the same time,a regression prediction model of the coefficient of variation under the given conditions was established,which can make a more accurate prediction of the coefficient of variation of different polishing parameters under the given conditions.Next,the trajectories of a single KDP crystal relative to the polishing pad is plotted,as the trajectory of a single KDP crystal is formed by superimposing the trajectories of numerous single points on the surface of the KDP crystal.By comparing the plotted single crystal trajectories with the single point trajectories,the validity of the single point trajectory variation law is verified.Finally,in the case of polishing three KDP crystals at the same time in the actual process,the ideal conditions were assumed to ensure equal pressure on the contact surface between the KDP crystals and the polishing pad,and then count the accumulated number of trajectory points at each point on the polishing pad,and this was used to indicate the number of times the pad is worn by three crystals and a three-dimensional graph of the distribution of trajectory points was drawn.By analyzing the three-dimensional graphs,the effect of varying the parameters on the number of wears on the pad was investigated.