| CNC equipment is a high-tech machine tool and is a key equipment for the modernization of manufacturing.Its technological level represents the development level of a country's manufacturing industry.In recent years,the manufacturing industry in China has entered rapid developed period,and CNC equipment has been constantly moving towards multiple functionality,flexible equipment,high precision,high speed and high reliability.Spindle system as a key component of CNC equipment,its performance is of critical importance to the processing efficiency and processing precision of CNC equipment.It is the core component to ensure the precision of CNC equipment machining.In this paper,the reliability of the spindle system of a precision CNC lathe is studied.The concentrates drawn from the study can be summarized as follows:(1)The reliability of the spindle system is analyzed by Failure Modes,Effects and Criticality Analysis(FMECA)and Fault Tree Analysis(FTA).First of all,based on the collected field fault data and fault data of the lathe spindle system with similar structure,combined with the structural characteristics and working principle of the spindle system,the Failure Modes,Effects Analysis of the spindle system are analyzed through reasonable logic inference.Then the criticality analysis of each failure mode of the spindle system is performed by the method which based on Analytic Hierarchy Process,fuzzy theory,weighted Euclidean distance and centroid defuzzification method.At last,Based on the results of FMECA,FTA is applied to the failure modes with high fuzzy risk priority numbers,the fault tree is established and the week parts of the spindle system is obtained by qualitative analysis and quantitative analysis.The results shows the week part of the spindle system is bearing wear.(2)Time-variable clearance of the spindle bearing and time-variable radial runout of the spindle models are estiblished to comprehensively study the bearings wear.Firstly,the contact model of the spindle bearing is established based on the Hertz contact theory,and the parameters such as the maximum contact stress,contact load and contact area of the bearing are calculated Then,the time-variable wear model of spindle bearing is estiblished based on the Archard fatigue wear theory.Finally,the model of time-variable clearance of the spindle bearing is developed,and the model of time-variable radial runout of the spindle is estiblished by considering the relation between the bearing clearance and radial runout of the spindle.In this paper,the radial runout of the spindle with a pair of angular contact balls is analyzed.(3)The calculation method of time-varying reliability for spindle system considering precision degradation is studied.Firstly,based on the time-varying radial runout model of the spindle,the reliability function of spindle is developed by the stress-intensity interference theory.For the purpose of reducing computation,combined the important sampling method and Kriging simulation technology,a dynamic wear process model of the bearing is presented for time-varying reliability calculating on spindle.The presented method has high computational efficiency and accuracy by comparing the calculated results among the improved first-order moment method and the Monte Carlo simulation analysis method.In addition,the reliability sensitivity of the spindle system is also analyzed based on important sampling methods. |
PDF Full Text Request