008618266359149
Abstract: This article briefly introduces the cross roller bearing and highlights its application in the design of the spindle structure of large CNC vertical lathes through comparison with conventional structural examples.
Keywords: Cross roller bearings; Vertical lathe; principal axis
1. Introduction
Nowadays, the spindle structure of most large CNC vertical lathes is a conventional form, which is a combination of double row cylindrical roller bearings and flat bearings. By selecting a set of cross roller bearings with appropriate specifications, the above requirements can be met, greatly simplifying the mechanical structure of the main shaft. It is easy to install hydraulic chucks and rotary cylinders on it, achieving automatic positioning and clamping to improve processing efficiency. The performance of the workpiece remains stable even under high overturning torque. This article only takes two types of vertical lathes as examples to introduce the application of cross roller bearings in the design of machine tool spindle structures.
2. Characteristics of cross roller bearings
The inner rollers of the cross roller bearing are in line contact with the raceway, and are arranged in a 90 ° vertical cross spacing on the raceway section. Therefore, a set of bearings can bear both radial and axial loads simultaneously, and the rigidity is 3-4 times that of traditional models; The installation operation is also very simple. Due to the cross arrangement of the rollers and the fact that the inner or outer ring of the cross roller bearing is a two part structure, the bearing clearance can be adjusted, allowing for high-precision rotational motion even when preloaded. Mainly used for high-precision work turntables, machine tools, industrial robot arms, medical machinery joints, etc.
Figure 1
3. Basic structure of CNC vertical lathe spindle with conventional bearing arrangement
The spindle structure of CK51125 CNC vertical lathe is shown in Figure 2. In this conventional vertical lathe spindle structure design, the main load-bearing method is to use double row cylindrical roller bearings and flat bearings, as shown in Figure 2. The main motor transmits motion to the spindle through the large gear 7 through the transmission chain. The double row cylindrical roller bearing 5 bears radial load, and the radial load of the main shaft is relatively small, while the axial load is relatively large, mainly from cutting force and the imbalance force of the workbench and workpiece; The large flat bearing 6 mainly bears axial loads, which mainly come from the weight and cutting force of worktable 12, flange 10, large gear 7, workpiece, etc. These are very important factors when selecting bearings. When this type of bearing combination is used, the main shaft structure has a large load-bearing capacity and is relatively cheap, but the structure is complex, making it difficult to manufacture and install parts.
Figure 2
1. Base 2. Synchronous pulley 3. Main shaft 4. Equipped with grinding pad 5. Double
Column cylindrical roller bearing 6. Large flat bearing 7. Large gear 8.
Spacer 9. Synchronous shaft 10. flange 11. Small flat bearing 12.
Workbench
4. Basic mechanism for installing cross roller bearings on CNC vertical lathe spindles
The spindle structure of CK51125A CNC vertical lathe is shown in Figure 3. In the vertical lathe spindle structure equipped with cross roller bearings, all the precision and working load of the main movement of the machine tool are carried by the cross roller bearings. Compared with conventional spindle structures, the transmission mode of motion is the same, and the load source is basically the same. However, the spindle structure equipped with cross roller bearings is very simple (as shown in Figure 3). Cross roller bearings also have a feature of saving space and making it very convenient to install hydraulic chucks, as shown in Figure 4. The main shaft (actually a fake main shaft, mainly used to connect encoders and rotary cylinders) is easily modified into a set of main shaft structures with hydraulic chucks by adding a slightly modified mounting seat 3 at the lower end, connecting rotary cylinder 2, and connecting it to hydraulic chuck 11 through a pull rod 5 in the middle. The conventional arrangement of bearings in the spindle structure (as shown in Figure 2) is quite difficult.
Figure 3
1. Base 2. Installation seat 3. Magnetic encoder 4. Main shaft 5. Main bearing seat 6. Lower bearing cover 7. Cross roller bearing 8. Large gear 9. Upper bearing cover 10. Waterproof flange 11. Workbench
For the cross roller bearing XR766051, if domestically produced, the cost is generally slightly higher than that of equivalent specifications of double row cylindrical roller bearings with flat bearings; If imported products are selected, such as FAG from Germany, TIMKEN from the United States, and IKO from Japan, the price will be 7-10 times higher than domestic products.
Figure 4
1. Base 2. Rotary cylinder 3. Installation seat 4. Magnetic encoder 5. Rod 6. Spindle 7. Main bearing seat 8. Lower bearing cover 9. Cross roller bearing 10. Large gear 11. Upper bearing cover 12. Waterproof flange 13. Hydraulic chuck
5. Conclusion
This article introduces the application of two forms of combination, cross roller bearings and ordinary bearings, in the vertical lathe spindle system. Designers can choose the structural form of the spindle system according to the different fields of their products.
2024 March 2nd Week KYOCM Product Recommendation:
Thrust ball bearings are designed to take axial (thrust) loads at high speeds, but they cannot take any radial loads. These bearings feature bearing washers with raceway grooves in which the balls move.
Thrust ball bearings are classified into “flat seat” and “aligning seat” types, based on the shape of the housing washer (outer ring seat), and as single-direction or double-direction. Spherical and aligning seat washers help to provide tolerance for mounting errors.
2024-03-08