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Factors affecting the rotation accuracy of machine tool spindle

Article source:CNC machiningResponsible editor:adminauthor:Kang Ding hardwarePopularity: Publication time:2017-04-20 17:48 font size:【 large middle Small
Factors affecting the rotation accuracy of machine tool spindle

  The spindle of the machine tool is used to install the workpiece or tool. The rotary precision of the machine tool directly affects the precision, position precision and surface roughness of the workpiece. Therefore, the processing of the workpiece will always have some errors. Combined with my practical work experience, the main factors affecting the accuracy of the spindle are analyzed as follows:

  1 spindle rotation accuracy spindle rotation accuracy refers to the machine tool spindle in the rotation of the actual axis of rotation relative to the ideal axis of rotation. The amount of change between the two is the spindle rotation error. The smaller the change is, the higher the spindle rotation accuracy is. The rotation error of spindle is affected by three factors, such as axial, radial and angular oscillation, which is more complicated.

  2 influencing factors analysis

  Because of the spindle by its shaft neck, inner and disassembly effect such as chuck manufacturing accuracy is very high, it is necessary to strictly control the size and shape of the error itself, the corresponding accuracy make it higher than the accuracy of fitting. In addition spindle rotation accuracy is also affected by the following factors.

  2.1 bearing error

  The bearing error mainly refers to the roundness error of the journal and the bearing bore.

  First, 2.1.1 is analyzed in detail by using a single oil wedge hydrodynamic sliding bearing as an example

  The use of outer circle lathe, the lathe spindle drives the workpiece rotate quickly, turning the linear motion along the guide rail, the effect of cutting force on the workpiece stable direction in this direction, the cutting force is fixed, the spindle neck will come into contact with different diameter parts and bearing a fixed the same site. If the main axis of the neck is elliptical, the spindle rotates a circle, the main axis of rotation on the axis of the two radial runout; if the main surface of the neck there is wave, then the axis of the spindle axis to produce high frequency radial runout. Therefore, the roundness error of the main shaft is the main factor, and the roundness error of the inner diameter of the bearing is a minor factor. Spindle with rolling bearings and the use of sliding bearings similar to the situation, just to the outer ring raceway equivalent to the bearing hole, the inner raceway equal to the shaft diameter can be.

  2.1. Countermeasures

  (1) change the multi oil wedge dynamic pressure bearing: because of the multi oil wedge dynamic pressure bearing spindle rotation around the production of a number of oil wedges, the journal in this case is pushed to the center, so the spindle rotation accuracy is higher.

  (2) the change of high precision rolling bearing for rolling bearing raceway has certain waviness, rolling dimension error will cause the radial runout of spindle, so to minimize the raceway waviness, reducing the rolling surface error body diameter difference and shape error, strict control of raceway.

  (3) the change of high precision hydrostatic bearing for hydrostatic bearing oil film pressure on the hydraulic pump supply is not affected by the rotational speed of the main shaft, so the error caused by the change of oil film thickness is much lower than the dynamic pressure bearing, spindle rotation can be obtained with high accuracy.

  2.2 fitting if the bearing inner ring or bearing deformation will make the shaft neck and body supporting hole roundness; if the spindle shaft, bearing cover, gasket surface and the spindle rotation axis is not perpendicular to the bearing assembly due to uneven stress caused by raceway tilt, resulting in radial and axial error. Countermeasures: (1) to improve the machining accuracy of the parts: that is, to improve the processing accuracy of the bearing surface of the box body, bearing end cover, etc.. (2) to improve the assembly quality: the transfer error method or the error compensation method for multiple adjustments, if necessary, the local processing method to improve the assembly quality.

  2.3 bearing clearance

  If the bearing clearance is too large, if the load or speed is changed, the error will increase rapidly. The bearing clearance not only causes the spindle to have a certain static displacement, but also makes the axis of the spindle to be very complicated. Response: the amount of rolling bearing preload can eliminate the gap is very good, because the inner and outer rings of bearing and roller elastic deformation affect each other, do not increase the bearing stiffness, and error, so as to improve the accuracy of.

  2.4 stiffness and thermal deformation

  The stiffness is not equal in different positions. When the direction of the external load changes rapidly with the high speed rotation of the main shaft, the main shaft will produce errors due to the inconsistent deformation. So it is necessary to improve the stiffness of the weak link. Under the influence of cutting heat and friction heat, the axial expansion and radial displacement of the spindle should occur. Because of the radial thermal deformation of the bearing and the thermal deformation of the bearings, the precision of the spindle will be affected. Therefore, it is necessary to try to reduce heat or forced cooling.

  2.5 spindle speed

  Affected by the spindle itself quality is not balanced, machine tools, random vibration, displacement when the spindle speed increases the axis of spindle the spindle speed increases rapidly, so the best within the optimal speed range, but also to avoid the resonance region of the machine tool, so as to improve the machining accuracy.

  3 conclusion

  In the actual production, we should analyze the concrete problems, find out the main factors, take the right measures to reduce the errors and improve the efficiency.

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