Research On The Reliability Of The Spindle Syetem Of A Heavy-Duty CNC Milling Machine

The spindle system of heavy-duty CNC machine tool is one of the core functional subsystems of the machine tool,the reliability of the spindle system directly affects the reliability of heavy-duty CNC machine tool,so the reliability analysis of the spindle system of heavy-duty CNC machine tool is an important content to improve the reliability of heavyduty CNC machine tool.Through the reliability analysis and research of the heavy-duty CNC machine tool spindle system,the weak links of the system can be found out.In view of easy failure,effective improvement measures are put forward,at the same time,in the optimization and improvement design stage of the system,a reasonable reliability distribution scheme can be provided.This paper takes THP6513 heavy-duty CNC machine tool as the object,aiming at the reliability analysis of heavy-duty CNC machine tool spindle system,the main research contents are as follows:(1)Based on the analysis of system components and working principle,the subsystem of the spindle system is divided,which lays a foundation for the subsequent reliability research.By analyzing the maintenance data of THP6513 machine tool,the common failure modes of spindle system and the subsystems with frequent failures have been obtained.(2)The failure mode and influence analysis of each subsystem of the spindle system have been completed.The qualitative analysis of the hazard of each fault mode of spindle system based on fuzzy comprehensive evaluation has been established.The fault modes and influences of each subsystem of the spindle system,including automatic tool changing system,cooling system,lubrication system,support system and drive system,have been analyzed,and the severity grade of each fault mode has been determined.Thus,the compensation measures for each fault mode are put forward.The fuzzy comprehensive evaluation method was used to qualitatively analyze the hazard degree of each fault mode.And the ranking of the harmfulness of the fault mode was obtained.Combined with the compensation measures,it provides a reference basis for eliminating the fault and improving the system reliability.(3)The fault tree analysis has been carried out for the spindle system of heavy CNC machine tool.The fault tree was qualitatively analyzed by the uplink method,and the minimum cut set of the top event fault was obtained.Through quantitative calculation of the fault tree,the probability of occurrence of top event,system reliability and mean fault-free time were obtained.Finally,the failure rate of each intermediate event and the probability importance degree of the basic event were calculated based on the failure rate of the basic event,and the quantitative analysis of the fault tree was completed.(4)In order to allocate the reliability index reasonably to the basic events,a reliability assignment method of spindle system based on fault tree was proposed,and the failure rate was taken as the reliability assignment index.Firstly,the failure rate of the top event was assigned to the first level event by the distribution method of probability importance degree.Secondly,reliability redistribution method was used to assign the failure rate of first-level events to second-level events.Finally,the second-level events that need to adjust the failure rate were allocated to the basic events by the distribution method of analytic hierarchy process.In a word,the reliability index was reasonably allocated to each basic event layer by layer according to the structure of the fault tree.