Study On Reliability Of Sintered Diamond Cutting Tools For Sic Ceramics

Silicon carbide ceramics is a typical non-metallic material that is difficult to process.It has the advantages of high temperature resistance,thermal shock resistance,high hardness,corrosion resistance,oxidation resistance,abrasion resistance,creep resistance,high thermal conductivity and excellent thermal stability,which makes it the most valuable high-temperature structural ceramics above 1400?C,having a very wide range of applications.The drilling process of high-hardness silicon carbide ceramics is difficult to process.There are many problems such as tool wear,machining time,cost limitation and difficulty in obtaining large amount of degradation data.In view of these problems,this paper took the hole processing process of pressureless sintered silicon carbide ceramics as the research object,and conducted single-factor hole drilling experiment on pressureless sintered silicon carbide ceramics with a 5mm diameter sintered diamond bit.The main research of this paper includes the following four aspects:(1)Determine the tool degradation cumulant distribution model.On the basis of Bayesian theory,a reliability modeling and analysis method based on degradation distribution is proposed.Firstly,according to the degradation data of the tool acquired in the grinding and drilling process of silicon carbide,the exponential distribution,normal distribution,Weibull distribution,logarithmic normal distribution and Gamma distribution of the degradation data were fitted respectively to determine the distribution model of tool degradation,and the non-parametric test method was used to test the distribution.Then,based onthe distribution model,the least square method was used to estimate the distribution parameters,and the obtained parameters were taken as known values to expand the samples.The least square method was again used to obtain a large number of parameter estimates,and the final parametric posterior distribution model was obtained with the combination of Bayesian theory,and the tool reliability change curve was finally determined.(2)Determine the tool degradation increment distribution model.On the basis of Bayesian theory to determine the distribution model of tool degradation increment,an analysis method based on Gamma process reliability modeling was proposed.Similarly,the regression data was optimized to determine the distribution model of the regression data,and the estimated value of the parameters was determined by experts' experience.Then based on Bayesian theory,Markov Chain Monte Carlo method is used to update the model parameters,and finally the tool reliability function is obtained.(3)Modeling tool degradation increment considering tool individual Difference.The difference of the degradation process between tool individuals was demonstrated by experimental data.Based on the above analysis method of Gamma process reliability modeling,a method of Gamma process tool reliability modeling considering individual differences was proposed.The difference is described with by different scale parameters,and the Markov Chain Monte Carlo method is also used to update the model parameters based on Bayesian theory,and the tool reliability function is finally calculated.(4)Effects of cutting parameters,vibration and cutting force on tool wear.The effects of cutting parameters,vibration and cutting force on tool wear were analyzed.The results show that the increase of spindle speed and feed speed will aggravate the tool wear.According to the regression analysis of the grinding length of diamond grains and the tool wear ratio at different rotating speeds,it is obvious that the tool wear and the grinding length are nonlinear.The mean cutting force and vibration amplitude have a certain correlation withtool wear,and the increase of cutting force and vibration amplitude will aggravate tool wear.The reliability curve calculated based on the cumulative model of tool degradation can only be fitted according to the reliability at a fixed time,and there are some defects in the fitting curve.The tool reliability model without considering the individual differences can calculate the tool reliability at any time,but it is only applicable to a single tool.The tool degradation incremental model with considering the individual differences of tools is adopted Fully considering the differences between individual tools,and can meet certain accuracy requirements,the modeling effect is better,and has a wide range of applicability.