1. Introduction
With the rapid development of my country's national economy and the needs of national defense construction, there is an urgent and large demand for the processing of (CNC) heavy-duty machine tools and ultra-large tonnage parts. In (CNC) heavy-duty horizontal lathes, the tailstock mainly plays the role of clamping and supporting the workpiece, and the tailstock system moves according to the length of the workpiece being processed to achieve the clamping capacity of the workpiece. The traditional tailstock structure is: a worm gear driven by a geared motor, which meshes with the rack on the machine bed to achieve the longitudinal feed motion of the tailstock on the machine bed. In order to prevent the tailstock from moving backward under the action of turning force, a pin anti-reverse device is installed on the tailstock. However, this mechanism is widely used in ordinary and CNC horizontal lathes. For heavy-duty horizontal lathes, since the weight of the workpiece being turned is over 100t, and the weight of the upper and lower parts of the tailstock is also around 30t, the torque transmitted by the worm gear and rack transmission is insufficient, the gears may break, and creeping may occur, which affects the movement of the tailstock on the machine bed. Therefore, a tailstock moving device for a (CNC) heavy-duty horizontal lathe was developed, replacing the gear and rack transmission with a worm gear and rack transmission. This primarily overcomes the problems of insufficient torque transmission, vibration, and creeping during tailstock movement. This mechanism features simple structure, convenient adjustment, easy and flexible operation, and smooth and reliable tailstock movement, thus ensuring the machining accuracy of the workpiece.
2. Introduction to the tailstock moving device of a heavy-duty horizontal lathe (CNC)
This tailstock moving device for CNC heavy-duty horizontal lathes is based on our company's over ten years of production experience with CNC heavy-duty horizontal lathes and an analysis of tailstock moving methods in domestic and international CNC heavy-duty horizontal lathes. It provides a device where the tailstock on a CNC heavy-duty horizontal lathe is driven by a geared motor to reduce speed, and a worm gear meshes with a worm wheel, enabling the tailstock system to move longitudinally on the workpiece bed. This improves the transmission torque and rigidity of the heavy-duty tailstock, thereby improving the machining accuracy of the workpiece. Our technical solution involves analyzing the impact of the tailstock moving method on the machining accuracy of the machine tool, primarily focusing on how to overcome the axial torque and creeping phenomenon generated during the movement of the heavy-duty tailstock, and achieving corresponding motion efficiency without increasing motor power. This tailstock moving device for CNC heavy-duty horizontal lathes mainly overcomes problems such as low axial traction force, unstable movement, and large reverse impact force. Compared to gear and rack drives, worm gear drives are easier to achieve reciprocating motion at lower speeds, offer better transmission rigidity, have a compact structure with low inertia, simple structure, convenient adjustment, easy and flexible operation, high motion sensitivity, and good stability, which are beneficial for improving transmission accuracy and stability. Worm gear drives are mainly used in the table feed mechanisms of machine tools such as gantry milling machines and horizontal boring machines. Their application in the tailstock movement of (CNC) heavy-duty horizontal lathes represents a new attempt and technological expansion.
3. Design principle of the tailstock moving device of a (CNC) heavy-duty horizontal lathe
3.1 Structural Principle of the Tailstock Moving Device of a Heavy-Duty Horizontal Lathe (CNC)
In the attached diagram: 1. Cylindrical roller bearing; 2. Worm gear; 3. Angular contact ball bearing; 4. Round nut; 5. Spacer; 6. Flange; 7. Connecting sleeve; 8. Expansion sleeve; 9. Gear motor; 10. Expansion flange; 11. Gasket; 12. Y-shaped rubber seal; 13. Round nut; 14. Adjusting shim; 15. Worm gear; 16. Oil retainer ring; 17. Tapered roller bearing; 18. Gear shaft; 19. Tailstock; 20. Rack; 21. Bed.
Figure 1. Schematic diagram of the original (CNC) heavy-duty horizontal lathe tailstock moving device.
In the attached diagram: 1. Tailstock; 2. Worm gear; 3. Pressure plate; 4. Nut; 5. Bed; 6. Shaft spring retainer; 7. Cylindrical roller bearing; 8. Hole spring retainer; 9. Gear I shaft; 10. Gear; 11. Flat key; 12. Deep groove ball bearing; 13. Gearbox; 14. Deep groove ball bearing; 15. Spacer; 16. Bolt; 17. Shaft II; 18. Adjusting shim; 19. Cylindrical roller bearing; 20. Flange; 21. Screw; 22. Washer; 23. Thrust cylindrical roller bearing; 24. Gear; 25. Flat key; 26. Worm; 27. Stud.
Figure 2 (CNC) Schematic diagram of the tailstock moving device of a heavy-duty horizontal lathe.
As shown in Figure 2, in the tailstock moving device of the (CNC) heavy-duty horizontal lathe, firstly, gear shaft 9 of type I is installed in the body hole of tailstock 1 and fixed by cylindrical roller bearing 7, deep groove ball bearing 12, bore spring retainer 8, and shaft spring retainer 6. Then, shaft 17 of type II is installed in the shaft hole of tailstock 1, and gear 10 is installed and fixed on shaft 17 by deep groove ball bearing 14 and spacer 15, so that gear 10 meshes with gear shaft 9 of type I, and the meshing rotation is flexible. Then, the worm 26 is installed in the shaft hole of the tailstock 1, and its left end is positioned by the thrust cylindrical roller bearing 23, the washer 22, and the cylindrical roller bearing 19. The gear 24 is installed on the shaft of the worm 26 and meshes with the gear 10 on the II shaft 17. The worm 26 is driven to rotate by connecting the key 25. Then, the thrust cylindrical roller bearing 23, the washer 22, the cylindrical roller bearing 19, the flange 20, the adjusting shim 18, and the screw 21 on the right end are installed, adjusted, and positioned. After the shafts on the tailstock 1 are installed, the tailstock 1 is fixed to the bed 5 by the pressure plate 3, the stud 27, and the nut 4. The worm 3 is then installed on the bed 5, ensuring that the center of the worm 3 and the worm 26 are aligned on the same horizontal plane. Finally, the geared motor 13 is installed in the inner hole of the I gear shaft 9 of the tailstock 1, positioned and connected by the key 11, and then installed on the tailstock 1 by the bolt 16.
3.2 Usage of the tailstock moving device of a (CNC) heavy-duty horizontal lathe
When the workpiece needs to be clamped, the geared motor 13 drives the gear shaft 9 of the first gear, which in turn drives the gear 10 on the second shaft 17 to rotate. This, in turn, drives the gear 24 on the worm 26 to rotate. The gear 24 is connected to the worm 26 via a double flat key, thus driving the worm 26 to rotate and mesh with the worm rack 2 mounted on the bed 5, causing the tailstock 1 to make longitudinal feed movements on the bed 5. After moving to a certain position, it is locked by the pressure plate 3. This device changes the gear and rack transmission to a worm gear transmission, which improves the axial traction force of the machine tool, reduces the axial backlash of the tailstock, reduces the crawling phenomenon during tailstock movement, greatly improves the transmission rigidity, and makes the transmission components compact with low inertia. In addition, the worm gear has an anti-backlash function.
The mechanism features a simple structure, convenient adjustment, easy and flexible operation, high motion sensitivity, and good stability, which helps to improve transmission accuracy and stability.
3.3 Advantages of the tailstock moving device in a heavy-duty horizontal lathe (CNC)
1) The impact of the tailstock's movement method on the machining accuracy of the machine tool mainly concerns how to overcome the axial torque and creep phenomenon generated when the heavy tailstock moves, and how to make the tailstock movement produce corresponding motion efficiency without increasing the motor power.
2) The use of worm gear transmission improves the axial traction force of the machine tool, reduces the clearance of axial movement of the tailstock, reduces the crawling phenomenon when the tailstock moves, greatly improves the transmission rigidity, and makes the transmission components compact with low inertia. In addition, the worm gear has a backlash prevention function.
3) The mechanism is simple in structure, easy to adjust, easy and flexible to operate, highly sensitive to movement, and has good stability, which helps to improve transmission accuracy and stability.
4. Conclusion
The tailstock moving device of a CNC heavy-duty horizontal lathe mainly overcomes the problems of low axial traction force, unstable movement, and large reverse impact force. Compared with gear and rack transmission, it is easier to obtain reciprocating motion at lower speeds, has good transmission rigidity, compact transmission components with low inertia, simple structure, convenient adjustment, easy and flexible operation, high motion sensitivity, and good stability, which is conducive to improving transmission accuracy and stability. Worm gear transmission is mainly used in the table feed mechanism of machine tools such as gantry milling machines and horizontal boring machines. Its application in the tailstock moving mechanism of a CNC heavy-duty horizontal lathe is also a new attempt and technological expansion.
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