Research On Some Problems For Controllable Lapping Of High Precision Natural Diamond Cutting Tool

The ultra-precision machining technology rose in response to the pursue of high precision in mechanical manufacturing. It is a complex systematic technology, within which the cutting tool technology is doubtlessly of great importance for ultimately fulfilling the cutting of workpieces. So far, in the known engineering materials, diamond is the only proper tool material for ultra-precision machining. Seen from the economic benefit and the potential processing-level of tool made from the natural diamond, mechanical lapping has definite advantages. Lapping of diamond tool involves problems of process technical details and the related friction and wear theory. The lapping technology of high precision rounded natural diamond cutting tools, as a commercial secret, was emerged in the foreign company under the demand of modern state of the art technologies, such as aerospace science and technology.Diamond mechanical lapping is an age-old technique. The scientific research on diamond friction and wear originated in 1920 s. Limited by observation methods, the amorphization phenomenon of diamond carbon atoms was verified by experiment until the year of 1999. Up to 2010, researchers had explained the anisotropy of diamond wear rate essentially. The wear of diamond in tool lapping derives from the amorphization of carbon atoms which forms the amorphous layer removed ultimately. As a further study on the material removal mechanism and lapping techniques in diamond tool lapping, the research work of this dissertation on related theory and techniques is as follows:1) Through establishing the molecular dynamics simulation model for diamond lapping in nano scale, the anisotropy of amorphization rate is explained in terms of atomic resistance force, and the sublayer structure, lattice deformation and amorphization sequence of carbon atoms in the inner of the amorphous layer are revealed by analyzing the speed of carbon atoms, density of the amorphous layer and the ratios of different hybridization types of carbon atoms along the thickness direction of amorphous layer;2) The determination method of crystal direction for the lapping direction is presented. Based on this method, the diamond wear rates, i.e. the wear thickness of diamond per unit time, under different lapping velocities and pressures are measured on a certain crystal direction. The two wear stages, nonlinear and linear stages, are found. The effect of lapping velocity and contact pressure on the period of nonlinear stage is analyzed. By analyzing the linear stage of diamond wear, the model of the diamond wear rate is established based on the theories of carbon atom amorphization and contact mechanics, and then the model is verified;3) The effect of lapping direction on the morphology of diamond surface is studied by experiments, which is explained in terms of amorphization rate of diamond carbon atoms and the amorphization energy required. Based on this, a lapping motion design method using genetic algorithm that can obtain a better surface roughness is proposed. Moreover, the wavelet analysis is adopted to compare and analyze the surface morphology formed by 3 types of lapping motion(basic type- only rotation movement of the spindle, 2-degree of freedom type- the reciprocation motion cooperated with the spindle rotation and 3-degree of freedom type- the planetary motion and reciprocation motion involved besides the spindle rotation);4) Based on the understanding of diamond wear rate obtained by research work narrated above, a new lapping method of anisotropic control of material removed on flank face is presented. This method is directed at the characteristic that each point on the flank face of the round nose diamond tool has a different crystal direction. Meanwhile, the measuring method of material removed on flank face in lapping is provided, and the measring error is analyzed. Moreover, an experiment is carried out to verify our method.Based on the study on the theory related to diamond friction and wear, this dissertation was carried out by using the lapping motion design as an entry point. Our work deepens and expands the understanding on diamond friction and wear theory and provides necessary support to the motion design of diamond cutting tool lapping process.