| Machining center is an important equipment of modern machinery manufacturing industry,which is the representative of the development level of national manufacturing industry.With the growth of market demand and rapid development of science and technology,the degree of automation,accuracy,efficiency,speed and reliability of machining centers are constantly improving.As a landmark key functional component of machining center,tool magazine system has the characteristics of high failure rate and difficult maintenance,etc.Improving its reliability level is an important way to realize the effective growth of the reliability level of the whole machining center.Reliability growth improvement design is the key technology to improve product reliability.By establishing the reliability growth model and formulating reasonable and accurate reliability target and reliability growth improvement design scheme,certain failures will not occur anymore and the reliability of tool magazine system will be improved.Through the reliability calculation of the improved design of the tool magazine system,the growth target and improvement design measures can also be adjusted in time.However,since the tool magazine system is not fully repaired during actual operation and the repair degree is not a constant value,this paper improves on the basis of Duane model,establishes a new reliability growth correction model and carries out reliability improvement design of the tool magazine system based on this correction model to realize a significant increase in the inherent reliability of the tool magazine system.The main research work of this paper is as follows:(1)Taking the YP40-24 disc type tool magazine system equipped with machining center as the research object,the type,main structure and working process of the tool magazine system are analyzed.According to the field tracking test data,the main failure modes and causes of the tool magazine were analyzed,and the Weibull life distribution model of the tool magazine failure data and the model test were fitted and calculated,which provided the basis for the subsequent reliability growth model research and reliability improvement design.(2)The reliability growth model and its influencing factors were studied.The classical Duane model and the AMSAA model were compared in terms of model description,parameter calculation,applicability,advantages and disadvantages,etc.Three factors affecting the accuracy of the model were derived: sample size,maintenance time and maintenance degree,and their respective influences were analyzed.(3)A new reliability growth correction model was established considering incomplete maintenance.The total time to failure rule was first introduced to solve the problem of inaccurate reliability caused by small samples and multiple truncated tails.And then the time-varying failure repair rate function and failure introduction rate function are introduced.Based on this,the classical Duane model is improved,and a three-parameter reliability growth correction model is established,and the parameters are solved,as well as the hypothesis test and goodness-of-fit test of the model are carried out.(4)The reliability improvement design based on the reliability growth model and its reliability calculation were carried out.Under the application of the modified model,specific improvement design measures were formulated for each mode type of failure of the tool magazine system,and the reliability growth effect of the improved tool magazine was evaluated,and it was concluded that the improvement of damage type,disorder type or function type failure can make the reliability level of the tool magazine reach the growth target,so that the inherent reliability of the tool magazine at the design stage can be significantly improved.The software "Reliability growth model fitting and calculation of machining center tool magazine",which can be installed and run independently,is designed as a tool for further study of tool magazine system reliability evaluation and improvement design. |
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