Analysis For Spectrum Involved In Diamond Turning Of Single Crystal Silicon And Mechanism Of Tool Wear

Single crystal silicon is a critical infrared material, which has been employed in the optical systems increasingly because of its unique optical properties. It is hard and brittle,its fracture strength is close to the yield strength. So it is very difficult to obtain high-quality surface by using the traditional machining technologies. In recent years, single point diamond turning technology has been greatly developed. The higher geometric precision and efficiency, lower cost, easier to be controled to generate the complex surfaces make it more advantageous than the ultraprecision polishing. The excellent properties of diamond turning in machining the brittle materials have attracted lots of attention. However, the mechanism of brittle-ductile transition,diamond tool wear as well as the material removal at micro/nano scale have not yet formed a unified understanding in diamond turning of single crystal silicon. So it is necessary to make more exploratory work.Firstly, this work resorted to the scientific experiments, theoretical analysis and cutting simulations to research the distribution of tool vibration spectrum due to the fluctuations of cutting forces. Through modeling on the relationship between the distribution of tool vibration spectrum and the cutting parameters, this work explored the reasons for the change of spectrum distribution, micro-deformation remove mode and the mechanism of brittle-ductile transition. The distribution of tool vibration spectrum vs. cutting length had been set up. As expected the wear state of diamond tool can be monitored on-line by observing the change of characteristic frequency.Secondly, considering that the surface quality has been one of the most important indicators to affect the application performance of single crystal silicon,this work discussed the variations of surface roughness and mechanical properties with the change of cutting speed and cutting length by means of nano-indentation experiments. In terms of the observed phenomena, the changing rules were analyzed. It is helpful to select the cutting parameters in diamond turning of single crystal silicon.Finally, this work employed SEM to analyse the wear pattern of diamond tool with the increase of cutting length and cutting speed. It was found that the micro-groove was the main factor to result in the heavy wear of diamond tool. Then the models of diamond tool wear with the cutting length and cutting speed was established. There were three stages in the process of diamond tool wear, i.e. the initial wear, slow wear and severe wear. The wear extent was slight under higher cutting velocity. Moreover, the mechanism of diamond tool wear was analyzed by inspecting the chemical compositions of processed silicon surfaces using XPS (X-ray photoelectron spectroscopy). The results indicated that formation of SiC and diamond-like carbon hard particles were the main reason for the micro-groove wear of diamond tool. Comparing the concentration of carbon, the hard particle of SiC was a few more than the diamond-like carbon.