Application of Linear Bearings in High Speed and Precision Spindle Unit Support

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Application of Linear Bearings in High Speed and Precision Spindle Unit Support

With the rapid development of modern mechanical manufacturing industry towards high precision, high speed, and high efficiency, high-speed precision spindle units have become the preferred solution for machine tool spindles due to their significant advantages such as compact structure, light weight, small inertia, low vibration, low noise, and fast response. Due to the high working speed of this type of spindle, its structural design and manufacturing requirements are very strict, which brings a series of technical difficulties such as controlling thermal deformation of the spindle and selecting supports. We have established a vibration analysis model for the spindle unit, solved the critical speed and main vibration mode of the system, and studied the influence of linear bearings on the radial vibration characteristics of the spindle. We have obtained several practical research results.

At present, most high-speed and precision spindles at home and abroad use rolling bearing support. This type of spindle has high requirements for rolling bearings, and generally improves the stiffness of the bearings and the vibration performance of the spindle by applying preloading force. However, using this structure during high-speed operation can cause axial elongation and thermal deformation of the spindle due to heating, which can seriously affect the bearing preload, affect the stiffness of the bearing, cause excessive temperature rise of the bearing, and thus affect the bearing life, and even cause the bearing to burn out, resulting in the failure of the spindle unit. To address this phenomenon, linear bearing support can be added to the design of high-speed spindle structures to suppress the negative effects caused by heating. But the addition of linear bearings will reduce the radial support stiffness of the spindle, further affecting the vibration characteristics of the spindle.

1. After adding linear bearings, the first critical speed of the system decreases, indicating that the stiffness of the linear bearings has a significant impact on the stiffness of the spindle system. The essence of this effect is that the addition of linear bearings reduces the support stiffness of the spindle, which is the main factor affecting the critical speed of the spindle system. Therefore, although the addition of linear bearings can effectively suppress the influence of thermal deformation of the spindle on the preloading force of the rolling bearings, the influence of the stiffness of the linear bearings themselves on the vibration characteristics of the system cannot be ignored.

2. Adding linear bearings in the structural design of the spindle can effectively suppress the adverse effects of thermal deformation of the spindle. Although vibration analysis shows that the use of linear bearings will reduce the critical speed of the system, reasonable design can still ensure that it meets the design requirements.

For example, the Z-high speed of the high-speed spindle system is 24000r/min. After adding linear bearings, the first critical speed of the system is 32760r/min. It can be seen that the Z-high speed of the system is far lower than the first critical speed of the system. It can be seen that for the analyzed system, although the use of linear bearings reduces the first critical speed of the system, overall, the vibration characteristics of the system still meet the requirements.

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