碳化硅陶瓷研抛的流场仿真及其摩擦磨损性能研究

发布时间：2018-02-13 14:20

本文关键词： 碳化硅陶瓷二维流场仿真三维电场仿真研抛摩擦磨损特性　出处：《哈尔滨工业大学》2015年硕士论文　论文类型：学位论文

【摘要】：碳化硅具有优良的物理化学性能,是制备空间大尺寸轻型反射镜的新材料。但碳化硅具有硬度高、脆性大、对缺陷敏感等特点,难以获得高表面质量和高效加工。传统加工方法以及化学机械抛光(CMP)因磨粒的存在易产生表面及亚表面损伤,摩擦化学研抛(TCP)不采用磨料,可获得高精度碳化硅表面,但效率低。摩擦电化学研抛(TECP)可实现金属表面高效、高精度加工,但对碳化硅陶瓷的摩擦电化学研抛机理尚不十分明确。论文通过对碳化硅陶瓷研抛的流场仿真和摩擦磨损实验研究,获得不同工艺条件对其研抛特性的影响规律,研究对实现碳化硅陶瓷的高效超精密加工具有重要的理论和指导意义。首先针对带孔抛光垫,利用Fluent软件建立研抛过程的二维有限元模型,并研究了研抛速度、抛光垫厚度、小孔尺寸及流体膜厚度对流体流场特征的影响规律。利用Ansoft Maxwell软件建立研抛副间电场分布的三维有限元模型,并研究了抛光垫电导率和厚度对电场分布的影响规律。然后,对原有的行星轮式圆平动研抛试验机进行结构改进,实现了载荷和电压的加载;开发了数据采集处理系统,实现了压力、摩擦力和摩擦系数的在线监测。最后,应用改进的试验机研抛碳化硅陶瓷,获得了不同外加电压、研抛液及研抛配副对其摩擦磨损性能的影响规律。仿真研究表明:带孔抛光垫的小孔直径和数量对流体的承载能力和摩擦力有重要影响。当抛光垫上小孔的数量一定时,随着小孔直径的增大,承载能力和摩擦力降低;当小孔间距和小孔直径的比值一定时,随着小孔数量的增多,承载能力先降低后增加,摩擦力降低。碳化硅上的外加电压对研抛液及抛光垫的影响范围和作用较小。增加抛光垫电导率、降低抛光垫厚度可提高研抛表面的电流密度。实验研究表明:碳化硅与铸铁盘配对研磨时,3%Na OH的研抛效率略高于去离子水的;对试件不加电或施加正电时的研磨效率是施加负电时的3倍左右。与砂纸配对研磨时,砂纸粒度越大,摩擦系数越大,机械去除作用越强,因而研磨效率越高。在与细砂纸研磨时,因其机械去除作用减弱,3%Na OH的化学去除作用,特别是电化学去除作用较为明显。此时,对试件施加正电的研磨效率是施加负电和不加电的1.5倍左右。不同加电状态下碳化硅与磨砂革配对抛光时,摩擦系数相近,但加正电时的抛光效率是负电和不加电时的8~10倍,电化学去除作用明显提高;打孔磨砂革因表面平整度差,抛光时比不带孔磨砂革的摩擦系数大、波动剧烈;不同抛光液性能影响实验表明,W5金刚石悬浮液抛光效率远高于3%Na OH溶液的,两者混合液的抛光效率介于其间。
[Abstract]:Silicon carbide has excellent physical and chemical properties and is a new material for the preparation of light mirror with large space size. However, silicon carbide has the characteristics of high hardness, high brittleness, sensitivity to defects, etc. It is difficult to obtain high surface quality and high efficiency machining. Traditional processing methods and chemical mechanical polishing (CMP) can easily cause surface and subsurface damage due to the existence of abrasive particles. Friction chemical polishing and polishing (TCPP) can obtain high precision silicon carbide surfaces without abrasive materials. But the efficiency is low. The friction electrochemical polishing and polishing (TECP) can realize the high efficiency and high precision machining of metal surface. However, the friction and electrochemical polishing mechanism of sic ceramics is not very clear. Through the flow field simulation and friction and wear experiments of sic ceramics polishing, the effects of different technological conditions on the polishing characteristics of sic ceramics are obtained. The research has important theoretical and guiding significance for the realization of high-efficiency ultra-precision machining of silicon carbide ceramics. Firstly, a two-dimensional finite element model of polishing process is established with Fluent software, and the polishing speed and the thickness of polishing pad are studied. The effect of pore size and film thickness on the flow field characteristics is studied. A three-dimensional finite element model of electric field distribution between polishing and polishing pairs is established by using Ansoft Maxwell software, and the influence of the electric conductivity and thickness of polishing pad on the electric field distribution is studied. By improving the structure of the original planetary wheel type circular flattening machine, the loading of load and voltage is realized, the data acquisition and processing system is developed, and the on-line monitoring of pressure, friction and friction coefficient is realized. The application of the improved testing machine to polishing silicon carbide ceramics has obtained different applied voltages. Simulation results show that the diameter and number of holes with holes have an important effect on the bearing capacity and friction force of the fluid. When the number of holes on the polishing pad is constant, With the increase of pore diameter, the bearing capacity and friction force decrease, when the ratio of pore spacing to orifice diameter is constant, with the increase of the number of holes, the bearing capacity decreases first and then increases. The effect of applied voltage on silicon carbide on polishing liquid and polishing pad is small. The electric conductivity of polishing pad is increased. Reducing the thickness of polishing pad can increase the current density of polishing surface. The experimental results show that the polishing efficiency of 3NaOH is slightly higher than that of deionized water when sic and cast iron disk are paired and ground. The grinding efficiency of the specimen without or with positive charge is about three times higher than that with negative charge. The larger the grain size of sand paper is, the greater the friction coefficient is, and the stronger the mechanical removal is when the sand paper is paired with sand paper. Therefore, the higher the grinding efficiency is, the more obvious is the chemical removal of NaOH, especially the electrochemical removal, due to its mechanical removal. The grinding efficiency of positive charge is about 1.5 times higher than that of negative charge and no charge. The friction coefficient of silicon carbide and polished leather is similar in different states, but the polishing efficiency of positive charge is 810 times higher than that of negative charge and no charge. The effect of electrochemical removal was obviously improved, and the friction coefficient of perforated abrasive leather was larger and fluctuated sharply than that of non-hole polished leather during polishing because of the poor surface smoothness. The results show that the polishing efficiency of W5 diamond suspension is much higher than that of 3NaOH solution, and the polishing efficiency of the mixture is between them.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ174.1

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