Research On Reliability Analysis Technology Of Typical Meta-action Units Of NC Machine Tools

CNC maching centers are one of the highest technical contents basic equipments in the NC machine tools.At present,market demands for middle and ordinary machine tools are increasing.The fierce competition of the current markets also put forward new demands for machining centers.Intense market competition requires that not only maching centers be able to realize multiple species and small batch manufacturing with high reliability,but centerprises shorten development cycles,reduce development costs and provide highly cost-effective products.Thus,enterprises keep its predominance in the fierece markets.According to situation above,the paper carrys out research on reliability analysis technology of typical Meta-action Units of NC machine tools.The research content is mainly as follows.First,Failure Mode and Effect Analysis method toward Meta-action Units?MU-FMEA?is established.The“Function-Motion-Action”?FMA?structured decomposition method,the definition of Meta-action and Meta-action Unit are further enriched and improved.The concept and definition of Meta-action Chain are proposed.According to characteristics of Meta-action Units,the research on failure modes classifications are studied,and the Failure Mode and Effect Analysis method toward Meta-action Units is constructed.The Meta-action and Meta-action Chains are obtained by the“FMA”structured decomposition method.The paper carrys out Failure Mode and Effect Analysis toward Meta-action Units with the example of Meta-action Chain A₂?A₃?A₄.Second,the Meta-action failure modes risk analysis method is constructed based on fuzzy theory and the multiple multi-objective Optimization by ratio analysis?MULTIMOORA?by incorporating time,cost,profit,severity,occurrence and detection into the risk analysis.The weights of time,cost,profit,severity,occurrence and detection are obtained by fuzzy analytic hierarchy process?FAHP?approach.The weight of each Meta-action failure mode is obtained by fuzzy MULTIMOORA.The final comprehensive risk priority number for each failure mode is caiculated by considering all risk factors and their weights.The risk of each Meta-action failure mode is computed with MATLAB programming for the Meta-action Chain A₂?A₃?A₄ of NC rotary table,and the key Meta-action failure modes are determined.Then,the fuzzy probability fault tree analysis of Meta-action Unit?MU-FFTA?is proposed.The characteristics of fault tree analysis of Meta-action Unit?MU-FTA?are described.According to results of above risk analysis,the key Meta-action failure mode abnormal vibration of worm fault tree analysis is conducted.In order to solve the lack of reliability data,MU-FFTA method is built based on fuzzy theory,the top event failure probability computing method is determined,and top event confidence intervals under different confidence levels are calculated.Finally,fuzzy probability importance analysis is implemented for basic events of fault tree of abnormal vibration of worm.The results indicate that improving the reliability of lining is capable of significantly improving the reliability of worm rotation Meta-action Unit.Reliability improvement measures for basic events of abnormal vibration of worm are presented from perspectives of design,processing and assembling.In this way,the reliability of the worm rotation Meta-action Unit is improved.