Reasonable selection of rotary table bearings

The rotary table commonly used in CNC machine tools has an indexing table and a CNC rotary table. When machining certain parts of CNC machine tools, in addition to the linear feed motion of the three coordinate axes X, Y and Z, there are sometimes circular motions around the three coordinate axes X, Y and Z. A, B, C axis.

The CNC rotary table can be used to achieve the circumferential feed motion, in addition to the indexing movement. The function of the indexing table is only to transfer the workpiece to the surface, and the automatic tool changing device is used together to realize the multiple installations of several surfaces in one installation of the workpiece, thereby greatly improving the working efficiency. The shape of the CNC turntable and the indexing table are not much different, but the structure has a series of features. Since the CNC rotary table can realize the feed motion, it has many similarities in structure to the feed drive mechanism of the CNC machine tool. The difference is that the drive mechanism realizes the linear feed motion, and the CNC rotary table realizes the circular feed motion.

The rotary table is widely used in various CNC milling machines, boring machines, various vertical vehicles and vertical milling machines. In addition to requiring the rotary table to withstand the weight of the workpiece well, it is also necessary to ensure its rotation accuracy under load. The rotary table bearing, as the core component of the turntable, not only has a high load carrying capacity during the operation of the turntable, but also needs to have high rotation precision, high anti-overturning capability, and high rotational speed capability.

Thrust ball bearing + cylindrical roller bearing

Thrust ball bearings can withstand certain axial forces, so the bearings are mainly used to bear the weight of the workpiece; cylindrical roller bearings are mainly used for radial positioning and external radial forces (such as cutting force, milling force, etc.) . This type of design is widely used and relatively inexpensive. Since the thrust ball is a point contact bearing, its axial bearing capacity is relatively limited, and it is mainly used for small or medium-sized machine tool rotary table. In addition, the lubrication of the thrust ball is also difficult.

2. Static pressure bearing + precision cylindrical roller bearing

A hydrostatic bearing is a plain bearing that supplies pressure oil externally and establishes a static pressure bearing oil film in the bearing to achieve liquid lubrication. Hydrostatic bearing always works under liquid lubrication from start to stop, so there is no wear, long service life and low starting power. In addition, this bearing also has the advantages of high rotation precision, large oil film stiffness, and can suppress oil film oscillation. Precision cylindrical roller bearings have good radial bearing capacity, and thanks to the use of precision bearings, the rotary table’s rotation accuracy is also guaranteed. Rotary tables designed with this type can withstand high axial forces. Some workpieces weigh more than 200t and turntables exceed 10m. However, this type of design also has some shortcomings. Because the hydrostatic bearing must be equipped with a special oil supply system to supply the pressure oil, the maintenance is complicated and the cost is relatively high.

3. Crossed roller bearings

Cross roller bearings (Fig. 3) are commonly used on turntables. Crossed roller bearings are characterized by two raceways in the bearing and two rows of rollers arranged in a row. Compared to conventional thrust bearing + radial centering bearing combinations (Fig. 4), the cross roller bearing is compact and compact, and simplifies the table design, thereby reducing the cost of the turntable.

In addition, due to the use of optimized preload, this type of bearing has a high stiffness, so the rigidity and accuracy of the turntable are also guaranteed. Thanks to the design of the two-row cross-roller, the effective span of the bearing can be significantly improved, so this type of bearing has a high anti-overturning moment. In the cross roller bearing, there are two types: the first is a cylindrical cross roller bearing, and the second is a tapered cross roller bearing. In general, cylindrical cross-roller bearings are less expensive than conical crossed roller bearings and are suitable for use in turntable applications where the rotational speed is relatively low. Conical crossed roller bearings use a purely rolling design of tapered rollers for high running accuracy and speed capability. Strong, reducing the advantages of shaft length and processing cost. Crossed roller bearings are suitable for all types of vertical or horizontal boring machines, as well as applications such as vertical mills, vertical stands and large gear milling machines.

All in all, the bearing, as the core component of the machine tool spindle and turntable, plays a decisive role in the performance of the machine tool. In order to be able to choose the right size and type of bearing, we need to consider a variety of working conditions, such as operating speed, lubrication, installation type, spindle stiffness, accuracy and other requirements. As far as the bearing itself is concerned, only by fully understanding its design features and the advantages and disadvantages brought about by it, can the best performance of the bearing be achieved.

Hongyuan Bearing Technology Co., Ltd. ranks first in China in terms of quality and output of YRT rotary table bearings and precision cross roller bearings. It is a leading manufacturer of special bearings in China; its products are sold all over the world, occupying 70% of YRT rotary bearing market in China. 40% of the products are exported to Germany and Italy, and the United States, Japan, South Korea, Taiwan, etc. all have Hongyuan Bearings, which have won unanimous praise from domestic and foreign customers.