| Face grinding is a commonly used method for manufacturing the precise plane parts.The face grinding spindle is core component of the machine tool.It is of great significance to develop a high-rigidity face grinding spindle for improving the manufacturing quality of products.By far,the bearings for the face grinding spindle can be categorized into two types:rolling bearings and liquid-lubricated bearings.However,to increase the axial load-carrying capacity of the spindle fully supported by rolling bearings,large diameter rolling bearings have to be used,resulting in a large vibration at the spindle nose and high friction power loss.Moreover,the large diameter rolling bearings are dependent on imports and costly.For the face grinding spindle fully supported by liquid-lubricated bearings,the inherent defects include high manufacturing accuracy requirement and large power consumption.To overcome the above-mentioned defects and integrate high rigidity,low cost and low power consumption,this paper presents a face grinding spindle with water-lubricated hydrostatic thrust bearing and rolling bearings,taking advantages of large axial load-carrying capacity of the(large diameter)water-lubricated hydrostatic thrust bearing and low cost and low power consumption of the(small diameter)rolling bearing.As the structure of the proposed face grinding spindle is quite different from the traditional spindles with rolling bearings or liquid-lubricated bearings,it is necessary to establish the design theory and method for this kind of spindle.A systematic study on structural innovation and dynamic design of the proposed spindle is carried out.The main research contents of this paper are as follows:(1)The innovative design of face grinding spindle and design strategy analysisA face grinding spindle with water-lubricated hydrostatic thrust bearing,self-aligning ball bearing(as the front support)and the duplex angular contact ball bearing(as the rear support with an elastic housing)is presented.According to the structural characteristics of the face grinding spindle with hydrostatic bearing and rolling bearingss,the design strategy of calculating the rigid rotor dynamics and the flexible rotor dynamics of the spindle in parallel is presented.(2)Rigid rotor dynamic analysis of spindle with hydrostatic bearing and rolling bearingsBased on Newton's second law and law of the fixed-axis rotation,a 5-DOF rigid rotor dynamic model for the face grinding spindle with hydrostatic bearing and rolling bearings is established.The dynamic coefficients of the self-aligning ball bearing and the water-lubricated hydrostatic thrust bearing are derived.The equivalent stiffness of the rear support is measured by using loading method.A test device for measuring the dynamic characteristic parameters of the face grinding spindle with hydrostatic beairng and rolling bearings is developed,and the axial vibration at the spindle nose is measured.The rigid rotor dynamics of the spindle under cutting forces are analyzed.Base on a sensitivity analysis,the effects of main parameters on the rigid rotor dynamics of the spindle are revealed.(3)Flexible rotor dynamic analysis of spindle with hydrostatic bearing and rolling bearingsTaking into account the tilting effect of the water-lubricated hydrostatic thrust bearing,the modified transfer matrix is derived,and the flexible rotor dynamic model for the face grinding spindle with hysrostatic bearing and rolling beairngs is established.The unbalance response at the spindle nose is measured.The flexible rotor dynamics of the spindle are analyzed,and the effects of main parameters on the flexible rotor dynamics of the spindle are revealed.The rationality of the proposed spindle and its dynamic performance are assessed.(4)Dynamic analysis of the motorized spindle with duplex angular contact ball bearingsBased on Hertz contact theory and raceway control assumption,a 5-DOF quasi-static model for the duplex angular contact ball bearing is presented considering the bearing configuration,preload mechanism,centrifugal force and gyroscopic moment of the ball.Besides,the modified matrix including the cross-coupling stiffness coefficients of the duplex bearing is derived and the dynamic model for the motorized spindle with duplex angular contact ball bearings is established.A test study is conducted to validate the proposed model.The stiffness of the duplex angular contact ball bearing under different configuration and preload mechanism is analyzed.The influence of the cross-coupling stiffness of the tandem duplex angular contact ball bearing on the dynamic characteristics of the motorized spindle is revealed.The results show that,the proposed face grinding spindle has advantages of large axial load-carrying capacity,high precision,low power consumption and long service life,overcomes the inherent defects of the traditional spindle fully supported by rolling bearings or liquid-lubricated bearings.The presented strategy of calculating the rigid rotor dynamics and the flexible rotor dynamics of the spindle in parallel is valid for the proposed spindle.The established dynamic model of the face grinding spindle with hydrostatic bearing and rolling bearings can be used to describe its dynamic behaviors accurately,which lays a good foundation for the spindle design.For the spindle studied in this paper,the diameter of the wheel is 100mm,by introducing the water-lubricated hydrostatic thrust bearing with a diameter of 70mm,small rolling bearings can be used.In details,the diameters of the self-aligning ball bearing and the duplex angular contact ball bearing are 15mm and 12mm respectively.The axial stiffness of the spindle is 228N/?m and the first critical speed is 12565rpm.At a speed of 6000rpm,the friction power loss of the water-lubricated hydrostatic thrust bearing,self-aligning ball bearing and duplex angular contact ball bearing are 60.36W,4.13W and 2.12W respectively.The research results of this paper also have a good application prospect in the machine tool rotary table. |
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