Research On Grinding Wheel Wear And Its Impact On Aspheric Surface Error Of SiC Ceramics

SiC ceramics can well satisfy the requirements of spatial optical field on the materials of optical elements and is more and more widely used in satellites, aerospace, advanced weaponry, space telescopes and other fields because of its material characteristics, such as high hardness, high wear resistance, low thermal expansion coefficient, high resistance to chemical corrosion, high specific stiffness and good dimensional stability. While the big problem which limited the use of SiC ceramics is the difficult processability. Precise grinding process using diamond grinding wheel is a common processing method, but the shortcomings such as serious wear of grinding wheel, low processing efficiency, bad surface/subsurface quality and poor form accuracy of aspheric surface become the serious problems in application of SiC ceramics. Therefore, the study of grinding characteristics of SiC ceramics, wear characteristics of grinding wheel and its impact on a spheric surface accuracy has very important theortical significance and application value.In grinding process of large scale aspheric surface of SiC ceramic, because of large removal amount of workpieces and high material characteristics, grinding wheel has been serious wear, which becomes an important factor restricting the aspheric surface accuracy. Grinding trajectory is a significant factor in SiC ceramics aspheric aspherical grinding process. The grinding wheel wear conditions was analyzed in several common way of grinding aspheric surface and a parallel method has been chosen to conduct the aspheric surface grinding of SiC ceramics. In this way the effective use of grinding wheel is greatly improve which can reduce wheel wear. A mathmatical model of scallop-height is built and the optional range of grinding wheel size, as well as the tilt angle of grinding wheel is determined with a purpose to maximize the effective use of the wheel area. The combination of constant removal rate grinding mathod and contant scallop-height grinding method is determined to control the grinding process of SiC ceramics aspheric surface.Metal bonded diamond grinding wheel has been chosen to carry out experiments according to material characteristics of high hardness and high wear resistance. It is found that it is more difficult for SiC ceramics to remove than glass according to the experimental results. Grinding wheel wear is a very complex phenomenon, which is produced under the influence of many factors. Single diamond abrasive scribing tests were adopted to study the scribing force, trenches quality, as well as abrasive wear, and to provide a reference of single grain life in grinding process using diamond wheels. Diamond grinding wheel wear experiments were engaged to study the variation trend of grinding force, surface roughness surface topography and subsurface damages with grinding wheel wear. The grinding characteristic of SiC ceramics as grinding wheel wear are analysed by the experimental results, including grinding force, surface roughness, surface topography and subsurface damages. According to the grinding characteristics and experimental data, the grinding ratio between removed volume of SiC ceramics and the wear volume of grinding wheel is essentially unchanged in the stable stage of grinding process. Therefore, a prediction model of grinding ratio is established based on experiments.The models of grinding wheel radius wear and form accuracy of SiC ceramics aspheric surface were built according to grinding ratio. Experiments were engaged to verify these two models and the results confirmed that the error between theoretical and experimental values is in the allowable range of less than 20%. And they can be used to predict the aspheric surface form error. In the end of this thesis, tactics of reducing form error and error compensation method were given and form error was reduced using this method and after several interations of simulation, the form error can be eliminated, theoretically.