The bearing accuracy on the spindle of machine tool should be ISOP5 or above, and for the spindle support of CNC machine tools, machining centers and other high-speed and high-precision machine tools, ISOP4 or above accuracy should be selected; Spindle bearings include angular contact ball bearings, tapered roller bearings, and cylindrical roller bearings. The following Hui Pu bearing to tell you about the three configuration forms of CNC machine tool spindle bearing:
- Double row cylindrical roller bearings and double-row 60o angular contact ball bearings are used for the front support, and diagonal contact ball bearings are used for the back support. This configuration form makes the comprehensive stiffness of the spindle greatly improved, can meet the requirements of strong cutting, so it is widely used in all kinds of CNC machine tool spindle.
Adopt high-precision double row angular contact ball bearings . Angular contact ball bearing has good high-speed performance, the spindle speed can reach 4000r/min, but its bearing capacity is small, so it is suitable for high-speed, light load and precision CNC machine tool spindle. In the spindle of machining center, in order to improve the bearing capacity, sometimes the front support of 3 or 4 angular contact ball bearings combination is used, and the sleeve is used to achieve pre-tightening.
Double-row and single-row tapered bearings are adopted . The bearing has high radial and axial stiffness, can bear heavy loads, especially strong dynamic loads, and has good installation and adjustment performance. However, this bearing configuration limits the spindle speed and accuracy, so it is suitable for medium precision, low speed and heavy load CNC machine tool spindles.
With the development of material industry, there is a tendency to use ceramic ball bearings in CNC machine spindles. The points of this bearing are: light ball weight, small centrifugal force, small dynamic friction torque; The thermal expansion caused by temperature rise is small, so that the preload of the spindle is stable; Small elastic deformation, high stiffness, long life. The disadvantage is the high cost.
In the structure of the spindle, to deal with chuck or tool clamping, spindle unloading, spindle bearing positioning and clearance adjustment, spindle assembly lubrication and sealing and a series of problems on the process. In order to minimize the influence of thermal deformation caused by the temperature rise of the spindle assembly on the working accuracy of the machine tool, the heat of the spindle assembly is usually taken away by the circulating system of lubricating oil, so that the spindle assembly and the box can maintain a constant temperature. In some CNC milling and boring machines, the cooling device is used to achieve the ideal temperature control. In recent years, the spindle bearings of some CNC machine tools are lubricated with grease, which can be used for 7~10 years per grease addition, simplifying the structure, reducing the cost and simple maintenance. However, it is necessary to prevent the mixing of lubricating oil and grease, usually using the labyrinth seal.
For the spindle of CNC lathe, because the power chuck and the clamping hydraulic cylinder are installed on the two sides of it, the spindle stiffness must be improved, and a reasonable connection should be designed to improve the connection stiffness between the power chuck and the spindle.