| It’s a key factor to develop the CNC machine tools that it is hard to improve its reliability.The spindle is a core part of the CNC machine tool.Therefore,it’s important to research the reliability of the CNC machine tool’s spindle to improve the quality of the machine tools.This paper researched the spindle system of HTC2050i CNC machine tool.The unreliable part of spindle system was founded by the failure mode,effects and criticality analysis(FMECA).The thermal property of the spindle system was analyzed by using the ANSYS Workbench.The distribution of temperature field,stress and deformation of the spindle system was researched.Harmonic response analysis of spindle bearing was made,that researched the variation of the mode,displacement response and stiffness of the spindle bearing.The main findings were as follows:(1)The spindle system was carried on the failure mode effect and criticality analyzes.According to the functional relationship,the spindle system was divided into four subsystems:transmission system,bearing system,sealing system and detection system.The results show that the highest frequency failure part was bearing system(52.83%),followed by the detection system(30.19%);The highest frequency failure mode was the noise is too large(43.40%),followed by spindle speed disorders(24.53%);the main cause of failure was the bearing injury(33.33%)and the component damage(27.08%);The criticality of bearing system was the most harmful,which degree was 43.2,followed by detection system,which degree was 23.93.(2)The thermal and structural coupling analysis of the spindle system is carried.According to the relationship among the spindle speed,bearing load and heat flux density,the variation rule of temperature field,stress and deformation of the spindle system with the speed and the pre-tightening force is obtained.The results show that the maximum temperature of the spindle system appears between two of front bearings.The highest temperature was 79.3 ℃ when n=4000r/min.The temperature of rear rolling bearing was much lower than the temperature of the front bearing.Changing of the temperature was more uniform in the spindle body,and it rose with the rising of the speed and pre tightening force.When the speed is lower,the maximum stress of the spindle system occurs at the edge of the shaft.When the speed is higher,the maximum stress of the spindle system occurs at the rolling body of the rear rolling bearing,maximum 596Mpa.The stress distribution of other parts was even,and it rose with the increase of temperature and the pre tightening force.The maximum deformation of the spindle system occurs at the edge of the shaft when n=500r/min,which was 0.0056mm.The maximum deformation of the spindle system occurs at the top of spindle box when n=3500r/min,which was 0.2366mm.(3)The spindle bearings were carried on modal analysis and harmonic response analysis,it was calculated the first six order natural frequency of spindle bearings,and obtained the change regulation of radial and axial dynamic stiffness of spindle bearings with the change of speed according to the empirical formula.The results show that the frequency of exciting force was far lower than the natural frequency of the bearing in the range of spindle speed.So it can avoid the resonance region effectively and assure the working accuracy.It is more obvious that the radial displacement of front and rear rolling bearings was raise when the spindle speed rose from 3500r/min to 4000r/min,which the minimal radial dynamic stiffness was 1.09×106N/mm and 2.07×106N/mm respectively.The minimal axial dynamic stiffness of the spindle ball bearing was 3.40×107N/mm,and its dynamic stiffness can assure the working accuracy. |
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