As the core transmission element in CNC tool machinery, ball screws play a vital role in providing accurate positioning, high speed and repeatability. However, in practical applications, the problem of decreased accuracy of ball screws often troubles operators and maintenance engineers. In order to ensure that the ball screw can continue to perform high-precision performance stably, this article will discuss how to effectively avoid the accuracy of the ball screw from declining again from multiple perspectives such as installation, maintenance, and design optimization.
1. Ensure correct installation
1. Coaxiality adjustment: When installing the ball screw, ensure its coaxiality with the motor, coupling and other related components. Use a high-precision dial indicator to detect and adjust to control the coaxiality error within the allowable range, usually less than 0.05mm. Poor coaxiality will cause the screw to generate additional radial forces during rotation, accelerating wear of the balls and raceways.
2. Horizontal and vertical adjustment: For high-precision machine tool applications, ensure that the horizontal and vertical errors of the screw are controlled within a small range, such as not exceeding 0.02mm per meter of length. Use tools such as a level to assist in adjustment to ensure that the screw is in the correct installation position.
2. Use appropriate installation methods
For long-stroke ball screws, it is recommended to install them with both ends fixed. This installation method can effectively reduce the axial movement of the screw and improve the axial rigidity of the screw, thereby better withstanding cutting forces and ensuring machining accuracy.
3. Regular inspection and maintenance
1. Component status inspection: Regularly check the component status of the ball screw, including the wear of the balls, the surface quality of the raceways, and the looseness of the nuts. If the ball is found to be severely worn or the raceway has obvious scratches, peeling, etc., the corresponding parts should be replaced in time.
2. Cleaning and Lubrication: Keep the ball screw clean to avoid accumulation of impurities and dust. At the same time, select the appropriate lubricant according to the use speed and load of the ball screw to reduce friction torque and wear.
4. Optimized design and manufacturing
1. Ball groove design: Adopt Goethe-style arched ball groove design. This design has a deep V-shaped cross-section with good circulation, which helps reduce torque and vibration caused by extrusion.
2. Preload Adjustment: When two ball screw nuts are used together, the preload can be adjusted to optimize performance. Using disc springs instead of solid washers can reduce ball screw torque because disc springs allow axial deformation to reduce extrusion.
3. Use of isolation balls: In order to reduce the friction between adjacent balls, isolation balls can be used. The isolating balls are slightly smaller in diameter than the load-bearing balls, and they rotate in the opposite direction to the load-bearing balls, thereby reducing contact friction. It should be noted, however, that the use of isolation balls may reduce the ball screw's load-bearing capacity, so this needs to be compensated by reducing the operating load or increasing the ball screw size.
5. Thermal expansion compensation and cooling
1. Preload application: Compensates for thermal expansion by applying preload to the ball screw. This can be accomplished by machining the screw shaft to negative tolerance dimensions, subjecting the ball screw nut to compression during assembly.
2. Cooling system application: In the case of extremely high temperatures, you can consider installing a separate cooling system into the ball screw and spraying air or oil mist on the screw shaft. Typically, air cooling is more effective. In addition, cooling can also be performed by passing pressurized water through the hollow shaft ball screw to reduce the temperature of the ball screw.
To sum up, by ensuring correct installation, adopting appropriate installation methods, regular inspection and maintenance, optimizing design and manufacturing, and thermal expansion compensation and cooling, the accuracy of the ball screw can be effectively avoided from declining again.
Source: Mechanical Design Alliance
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