Theoretical And Experimental Studies On The Honing Of Engineering Ceramics

Honing is one of high-efficient finishing operations for metals. The application of advanced ceramics in industry proposes new research work for ceramic honing. Systematical studies on honing of engineering ceramics are carried out theoretically and experimentally in this dissertation.As a low-speed grinding, honing owns the common laws of ceramic grinding processes. The indentation stress field and single-point diamond grinding stress field of ceramic materials are described with elasticity theory. Based on indentation fracture mechanics, the formations of indentation cracks and grinding cracks are analyzed. The median/radial crack system and the lateral crack system which are two kinds of indentation cracks, can be employed as fundamental theory concerning the study on grinding processes of ceramics. According to the stress analysis of grinding stress field, grinding processes are first theoretically studied in consideration of the formation reason of grinding cracks, the effect factors on the formation of grinding cracks and influence of machining methods on grinding processes. The second principal normal stresses can lead to grinding crack which generates forward beneath the abrasive grain in the plane of grain motion. The first principal normal stresses can lead to grinding crack which generates behind the abrasive grain in the plane perpendicular to grain motion. The mechanical properties of ceramics obviously affect the grinding processes. The machining properties of ceramics vary with different kinds of ceramics under the same machining condition. Brittle ceramics which have low critical indentation load generate high principal stress extreme values. So the ceramic material can generate grinding cracks and own good machining properties. On the contrary, ceramics with high toughness degree are difficult to machine. Another influence factor of ceramic grinding processes is machining method. Rough machining and finishing of ceramics can be achieved by suitable selection of machining methods. During finishing processes, to increase the ratio between tangential grinding force and normal grinding force can make machining plastic deformation zone lie close to the ceramic surface ahead of the abrasive grain. Hence ceramics can be removed through plastics flow. To increase component of grinding force ratio can increase principal stress extreme values in grinding stress field. Materials can be removed by brittle fracture. The foregoing statements establish basic theory for ceramic honing.The mechanism of ceramic honing is studied on the basis of honing characteristics. Systematical research on ceramics removal during honing process is first completed in three aspects: honing incidental tensile stresses, honing Crosshatch pattern and interaction of cracks among adjacent grits in ceramics. The unique feature of honing compared with other machining operations is that the honing bore contains honing incidental tensile stresses. The stresses have important influence on material removal of honing processes for brittle ceramics with low tensile strength. So the fracture criterion for crack propagation can be met easily. Because the honing incidental tensile stresses effectively decrease the critical grinding stresses and increase initial...