What is the difference between modern CNC machine tools and traditional machine tools?

Modern CNC machine tool screw and traditional machine tool screw

There are three differences between the screw of modern CNC machine tools and the screw of traditional machine tools: structure, precision and precision guarantee mechanism.

Ball screws are mainly used for screws of CNC machine tools. In terms of structure, unlike other screws, there are many balls rolling between the screw shaft and the screw nut of the ball screw pair. Generally speaking, the ball screw has a complex structure, high precision, and high motion efficiency, but it has poor seismic performance and high maintenance costs. Traditional machine tool screws are mostly trapezoidal screws. The sliding movement of the trapezoidal screw often leads to inaccurate pitch. Within a certain accuracy range, the rotation angle and linear movement distance of the nut will be non-linear. Therefore, the trapezoidal screw has a simple structure, poor accuracy, low movement efficiency, good seismic performance, and maintenance costs lower than that of a ball screw.

In terms of accuracy, the gap between the ball screw and the nut used in modern CNC machine tools is very small, and the pitch accuracy is very high. The screw speed has a linear relationship with the moving distance of the nut, and the machining accuracy is high. The common screw and nut used in traditional machine tools have a large gap and an inaccurate pitch. Within a certain accuracy range, the rotation angle and the linear movement distance of the nut are nonlinear, and the overall machining accuracy is poor.

From the point of view of accuracy guarantee mechanism, modern numerical control equipment mostly uses servo motor + ball screw + grating to ensure accuracy. Traditional machine tools rely on mechanical transmission to control accuracy.

Advantages of ball screws

The application of ball screws is becoming more and more extensive, not only because of the popularity of CNC machine tools, but also because of its own advantages. Compared with ordinary screws, ball screws have the following advantages.

1. Shorter driving torque

Because there are more balls rolling between the screw shaft of the ball screw pair and the screw nut of the screw pair, higher motion efficiency can be obtained.

2. High precision

The particularity of the structure of the ball screw, the movement mode and the accuracy guarantee mechanism make it more accurate than the ordinary screw.

three. Possibility of micro-feed

The ball screw pair is a kind of ball motion, so the starting torque is very small, and there will be no sliding motion phenomenon like crawling, which can ensure the realization of accurate micro feed.

4. No backlash, high rigidity

The ball screw pair can be pressurized, because the pressure can make the axial gap reach a negative value, and then obtain a higher rigidity (the ball screw applies pressure to the ball. In the actual mechanical device, the repulsive force of the ball can make the wire mother Increased stiffness of the part).

5. Possibility of high-speed feeding

The ball screw can realize high-speed feeding (movement) due to its high efficiency and low heat generation.

Although the ball screw has obvious advantages, due to its poor seismic performance, corresponding shock absorption measures should be taken during installation to extend the service life of the screw and reduce maintenance costs.