Reliability Evaluation Of 315T Isothermal Forming Hydraulic Press Based On Bayes Theory

The technology of reliability evaluation is the actual reliability index that the tested products under various test conditions through the reliability test and the statistical analysis of the test results.At present,the reliability evaluation method of CNC machine tools based on a large number of samples has been very mature.Because of the small sample and lack of test data,the traditional evaluation method based on the large number law can't effectively evaluate its reliability.In this thesis,a Bayes reliability evaluation method that modify prior information by expert experience is proposed.The method make full use of large fault data of similar machine tool as the prior information and fusion to correct amends it by the multi-source expert information.The method is used to solve the problem of assess difficult as there is only one prototype of the 315 T equal temperature forming hydraulic machine with fewer faults data.(1)According to the characteristics of the structure,design and material of the 315 T isothermal forming hydraulic press,the 180 T isothermal forming hydraulic press is selected as the similar machine tool,and the sufficient historical fault data of this type of machine is obtained by data collection.(2)First,the fault data of similar machine are processed as the Bayes a priori information of 315 T isothermal forming hydraulic press,then analysis the differences between similar machine tools and the existing machine tools.The traditional expert judgment gives a priori distribution directly,and there is subjective error.This paper propose two methods of indirectly extracted expert experience,and two kinds of expert information are fused according to the weight of the credibility of information sources;the effective integration of subjective and objective prior information is realized by amend the quantitative expert experience on similar machine tool failure information.(3)The modified prior information is resampled by Monte Carlo method,and the distribution model of Bayes prior distribution parameters is obtained.The likelihood function of Bayes theory is calculated by using the fault data of field test.According to the Bayes formula,the prior distribution and the likelihood function are fused to obtain the probability density function of MTBF for 315 T equal temperature thermo-forming hydraulic press.(4)Based on Markoff Montecarlo principle(MCMC),the parameter estimation value of MTBF distribution model and MTBF estimation value of 315 T equal temperature thermo-forming hydraulic press are obtained by Win BUGS software.According to the MTBF evaluation value,the reliability level of 315 T equal temperature thermo-forming hydraulic press is evaluated.(5)FMECA analysis of machine tools is carried out to find out the weak links and related parts of the whole machine system,and some suggestions for improvement or compensation are put forward.