Application Research On Reliability Improvement Technique Of CNC Lathes

Based on the subject of national high-tech research development plan topic "Numerical control Equipment And System Reliability, Key technologies Development And Application", By analyzing the history and actuality home and abroad,due to the current widespread applications of the CNC lathe,which is the fundamental equipment of the modern manufactural technology,its quality and the reliability has an immediate influence to the national development level of the advanced manufactured technology,along with the development of the advanced manufactured technology,it requests the lathe not only to have the superior performance and the highly automated function,to have the credibility in the performance and the function aspects,The author has proposed this topic research,according to the CNC development plan and the demand to the increasing reliability of factories and developing trend of CNC made in China,The application research of the CNC reliability growth technology,it is part of the CNC product credibility project,mainly focus on the existing problems in the Reliability research in our country,By using the reliability project elementary theory and the mathematical statistic method,and profiting from the method in the reliability research in the other field,The author has carried on the detailed analysis and the discussions to the lathe's reliability. And has established initially the elementary theory of the CNC reliability growth technology,Also has carried on the related reliability test,the reorganization,the induction and the analysis to the field data,has studied the research of the reliability growth technology, but also has analyzed the CNC lathe subsystem fault mode and the reasons,Advices and suggestions on how to improve and increase reliability are proposed.Based on the experiment and the inspection research in recent one year,the present paper has conducted the research to the each performance criterion of the CNC machine,the failure interval time model and the CNC machine experimental sampling scheme.First,reliability analysis relys on the massive reliable data,because in the product entire life cycle,regardless of being the product development,the design,the manufacturing stage,usages and the maintenance stage,the reliability data analysis issues can be involved all the time. Therefore,the reliability test technology and the data collection analysis is very important , they are the important components in the failure report, the analysis and the correction system (Failure Reporting , Analysis and Corrective Action Systems - FRACAS),the product reliability test,the failure analysis,the reliability design and the usage,they all rely on the reliability information. In order to process and preserve the formerly tentative data properly,and to be getting more convenient and more practical reliable parameters,we need to establish a set of statistical analysis system to adapt to the CNC machine's development request,in view of the fact that the above reasons,according to the research results of the reliability theory and the mathematical statistic knowledge,the current CNC machine Reliability theory research results and the related mathematical statistic aspect knowledge,the author has compiled the CNC machine statistical data analysis system software,and has established the developed product reliability database. Second,the data analysis is the foundation to establish the mathematical model , in order to adapt the computation informationization request,this paper will determine the failure time interval model parameter , establishes two parameter Weibull mathematical model directly through the failure data fitting straight line,this method has enriched the CNC machine failure time analysis mathematical model theory.Third,based on the failure data statistical result of the CNC machine,according to the machine's actual situation,based on simple and practical requests,the author has proved that the sampling process is the continual random process by designating the simple random sampling method,arranging the sampling scheme and examining sampling data randomness.Fourth,because the product structure is infinitely varied,the failure mode are also varied,we must study its incipient failure reasons and propose the improved solutions according to the product's incipient failure pattern. This article has indicated that the CNC lathe's incipient failure has often happened in the customer's products and had the high and frequent failure rate characteristic through the CNCl lathe reliability foundational condition inspection and the failure distribution rule research,this is one of the important attributes that currently influence the domestic product's prestige. In order to discover and eliminate the earlier stage latent failure and the lathe user can enter directly to the stable accidentally failure stage,the incipient failure experiment,analysis and the research to the CNC lathe have the vital practical significance. Above the current research basis,this research had determined the failure Weibull probability chart,according to the collected CNC lathe's failure data,the usage of the software,the author has carried on the reliability analysis to the failure data,has calculated the reliability evaluation criterion and has established the failure time interval distribution model,the basis failure time interval distribution model and has given the average trouble-free operating time spot estimate and the range estimate.Fifth,the author has adopted the theory and the statistics in the failure distribution pattern's judgment rules. When the CNC lathe's failure data is processed,Most of them obey the Weibull distribution,the exponent distribution and the logarithm distribution. Because this batch of data gathered underwent the incipient failure experiment in the factory,the machine user had already used one-and-a-half years,the machine has already passed the incipient failure time,the failure tends to be steady basically,and is very possible to enter the accidentally failure time,and also the theory of probability,logarithm distribution's probability density function curve presents the single peak shape,the Weibull distribution probability density function curve presents the single peak shape or the monotonous degressive shape differently according to its shape parameter,but exponent distribution's probability density function curve presents the monotonous degressive shape,and the single parameter exponent distribution is in the reliability project application is one kind of simple and popular distribution,and the failure rate is a constant,based on above reasons,we can use the exponent distribution to describe the failure time interval distribution model first,then obtains this type of machine's reliability criterion.Finally based on the failure probability density function curve,the failure rate distribution function curve and the maintenance function curve,the article interprets this CNC machine failure time interval and the maintenance time distributed characteristic and the tendency by computation.The present paper's ultimate objective is to apply the reliability growth technology of the CNC machine into the same domestic product by doing the related technical research,and to improve the MTBF value (the mean time between failure) to make it close to the international advanced level by the development. At present,the reliability growth has become one of the extremely important constituents in the reliability projects. In the decisive product life stages such as the product development,production and so on,the only way of linking all kinds of reliability actions together and passes through the product entire life process is to carry on the analysis management and achieve the project revision by using the reliability growth technology.The practice has proved that the experiment,the analysis and the management of using the reliability growth technology is the effective way to enhance the product reliability,saves the development funds and reduces the development cycle. Moreover, regarding the products need to do the reliability assessment or the evaluation,if these products has applied the reliability growth technology successfully in the development or the production and has obtained the complete failure data,then they can be used in the evaluation or the product reliability confirmation.The research has analyzed failure mode,effect and criticality analysis to some CNC lathe;the research has found out the reasons for causing the internal failure and discovered the weak link ; the dissertation also has proposed some reliability improvement suggestions to the machine parts or the subsystems.