Basic requirements for the feed drive of CNC machine tools

June 13, 2023

CNC machine tools can be divided into two major blocks: the CNC system and the machine tool. The CNC system mainly completes the control of the position of the table, the start and stop of the spindle, the commutation, the shift, the selection of the tool, the replacement, the hydraulic system, the cooling system, and the lubrication system according to the input program. In order to complete the processing of parts, the machine tool must perform two major movements: main movement and feed movement. In addition to being controlled by the CNC, the main movements and feed movements of CNC machine tools should be characterized by fast response, high precision, and high stability in the mechanical structure.

This lecture focuses on the mechanical structure characteristics of the feed system.

1, high transmission stiffness

The high transmission stiffness of the feed drive system mainly depends on the stiffness of the screw nut pair (linear motion) or the worm gear (rotary motion) and its supporting parts. Insufficient stiffness together with frictional resistance can cause the table to crawl and cause reverse dead zones, affecting transmission accuracy. Shortening the transmission chain, selecting the screw size, and pre-tightening the screw nut pair and supporting components are effective ways to improve the transmission stiffness.

2. High resonance

In order to improve the anti-vibration performance of the feed system, the mechanical components should have a high natural frequency and appropriate damping. Generally, the natural frequency of the mechanical transmission system should be 2 to 3 times higher than the natural frequency of the servo drive system.

3. Low friction

The feed transmission system requires smooth movement, accurate positioning and good quick response characteristics. It is necessary to reduce the frictional resistance of the moving parts and the difference between the dynamic and static friction coefficients. Ball screw nut pairs are commonly used in feed transmission systems.

4. Low inertia

Because the feed system often needs to start, stop, shift or reverse, if the inertia of the mechanical transmission is large, it will increase the load and degrade the dynamic performance of the system. Therefore, under the premise of meeting the strength and rigidity, the weight of the moving parts and the size of each transmission element should be reduced as much as possible so as to improve the ability of the transmission parts to respond quickly to commands.

5. No gap

Mechanical clearance is another major cause of the reverse dead zone of the feed system. Therefore, all links of the drive chain, including gear pairs, screw nut pairs, couplings and their supporting components, etc., should be eliminated. Structural measures.

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Author:

Ms. SU LAN RONG

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susu@cn-tianhui.com

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