What Kind Of Bearings Are Used In CNC Machine Tools?

​​In the field of industrial processing, the most commonly used and convenient machine is the CNC machine tool. Bearings are one of the most indispensable parts of CNC machine tools, and are particularly important in the main transmission movement of CNC machine tools.

The main transmission movement of CNC machine tools refers to the transmission movement of production and chip cutting. For example, the spindle on the CNC lathe drives the rotation movement of the workpiece, and the spindle on the vertical machining center drives the rotation movement of the milling cutter, boring cutter, and grinding wheel. The main transmission movement of the CNC machine tool is driven by the main transmission motor and is one of the forming movements of the machine tool.

As a key component of the CNC machine tool, the performance of the spindle will directly affect the machine tool’s rotation accuracy, speed, rigidity, temperature rise, noise and other parameters, and then affect the processing quality of the workpiece, such as the dimensional accuracy of the parts, surface roughness and other indicators. Therefore, in order to maintain the excellent processing capability of the machine tool, high-performance bearings must be used. The precision requirement for bearings used on CNC machine tool spindles is ISO P5 or above (P5 or P4 is the ISO precision level, usually P0, P6, P5, P4, P2 from low to high). The spindle bearings of high-speed, high-precision machine tools such as CNC machine tools and machining centers should use ISO P4 and above precision.

Angular contact ball bearings
Angular contact ball bearings are mostly suitable for high-speed, light-load, and precision CNC lathes. The rolling element of angular contact ball bearings is a ball; because it is point contact (unlike the line contact of roller bearings), it can provide higher speed, less heat generation, and higher rotation accuracy. In some ultra-high-speed spindle applications, hybrid bearings with ceramic balls (usually Si3N4 or Al2O3) are also used. Compared with traditional fully hardened steel balls, the characteristics of ceramic ball materials give ceramic ball bearings high rigidity, high speed, high temperature resistance, and long life to meet the requirements of high-end customers for machine tool bearing products.

As for the contact angle of angular contact ball bearings, the more popular ones are 15° and 25° contact angles; generally, the contact angle of 15° has higher speed performance, while the contact angle of 25° has higher axial load capacity. Because the choice of preload has a great influence on the application of precision angular contact ball bearings, for example, in high-load and high-rigidity occasions, medium or heavy bearing preload is generally selected;

For some high-speed and high-precision applications, in the early selection of bearings, it is necessary to pay attention to the selection of appropriate preload, and light preload is generally more common. Preload is generally divided into three types: light, medium and heavy; in order to facilitate customer use, several major bearing manufacturers in the world and we generally provide bearings with pre-ground bearing end faces and preloaded bearings, which is what we usually call universal paired precision angular contact ball bearings. This type of bearing eliminates the customer’s preload adjustment, thereby saving installation time.

Tapered roller bearings

Tapered roller bearings have high radial and axial stiffness, can withstand heavy loads, especially strong dynamic loads, and have good installation and adjustment performance. In some CNC machine tool applications with heavy loads and certain speed requirements, such as waste grinding of forgings, threading machines for oil pipelines, heavy lathes and milling machines, choosing tapered roller bearings is an ideal solution. Since the rollers of tapered roller bearings adopt a line contact design, they can provide high rigidity and load for the spindle; in addition, tapered roller bearings are pure rolling bearings, which can well reduce the operating torque and heat of the bearings, thereby ensuring the speed and accuracy of the spindle.

Cylindrical roller bearings

Double-row cylindrical roller bearings are also used in machine tool spindle applications, usually in combination with angular contact ball bearings or thrust bearings. The front support adopts a combination of double-row short cylindrical roller bearings and 60° angular contact double-row radial thrust ball bearings, and the rear support adopts paired radial thrust ball bearings. This configuration can greatly improve the overall stiffness of the spindle and meet the requirements of strong chipping, so it is widely used in various CNC machine tools.

Deep groove ball bearings

Deep groove ball bearings are generally only used to bear radial loads. Since the clearance is not adjustable, it is often used in situations where precision requirements are not high and pre-tightening is not required, such as the spindle of an ordinary drilling machine.