Typical failures and maintenance strategies of CNC machine tools

With the development of electronic technology and active technology, the application of numerical control technology has become more and more extensive. When a CNC machine tool fails, we must first understand the failure phenomenon, how it occurs, and how it happened. If the failure can be reproduced, the course of the failure should be observed. Only by grasping the first-hand situation can the fault be eliminated.

Typical failures and maintenance countermeasures of CNC machine tools

Compared with traditional machine tools, CNC machine tools based on computer control technology are less likely to fail, but it does not mean that there will be no failures. Generally speaking, the failure of CNC machine tools can be divided into the following aspects:

2.1 Feed drive chain failure

The feed transmission chain belongs to the inner transmission chain, and the two ends are the main shaft and the tool post. Its function is to realize the longitudinal or lateral movement of the tool. The guide rails of CNC machine tools are generally realized by rolling friction pairs. In other words, the failure of the feed transmission chain is mainly due to the decline in the quality of motion. If the mechanical parts do not move to the specified position, the operation is suddenly interrupted, the positioning is inaccurate, and the bearing noise is loud. At this time, feed transmission will occur. The chain is faulty. For this type of failure, repairs need to be made from the following aspects: one is to improve the transmission accuracy, realize the adjustment of each pair of movement preload, adjust the loose connecting rod, and eliminate the transmission gap; the second is to improve the transmission efficiency of the transmission system. Transmission stiffness, for the pre-tightening force of the screw nut pair and support, the size of the screw itself should be adjusted and improved to achieve the ideal transmission stiffness. The third is to pay attention to the adjustment of motion accuracy. On the basis of ensuring the intensity and accuracy of the motion, reduce the mass of the moving parts, thereby reducing the diameter and mass of the rotating parts.

2.2 Spindle component failure

The failure of the spindle rotation system of the CNC machine tool is caused by the abnormal operation of the spindle components. Generally speaking, it is mainly manifested in the following aspects: First, the spindle heats up, which may be caused by bearing damage, excessive pre-tightening force, poor quality of lubricating oil, and excessive or excessive lubricating oil. At this time, the following work should be done less: to repair and replace the bearings; adjust the preload; to clean the spindle box, replace the lubricating oil, and regularly check the lubrication status; the second is the excessive noise of the spindle, which may be due to the poor dynamic balance of the spindle components , The gear is worn out, and the bearing falls off. Factors such as damage, lubrication not reaching the ideal level, poor machining parts, improper selection of fixtures, etc., should also be analyzed in detail: realizing dynamic balance rework; repair or replacement of gears; replacement of bearings; adjustment or replacement of adjustment transmission belts; adjustment of lubrication The amount of oil to meet the requirements of the processor. Correct the parts and adjust the gap between the ball screws.

2.3 Automatic tool change failure

Practice has proved that in machining centers equipped with automatic tool changers, more than 50% of machine tool failures are related to automatic tool changers, which are mainly manifested as tool magazine movement failures, excessive positioning errors, and unstable grip. In order to solve this problem, we should do the following: First, in the process of automatically switching to equipment settings, we should choose components with high reliability as much as possible, whether it is sensing components, pneumatic components or H hydraulic components. Reasonable choice. If the parts are not working properly, they should be replaced to avoid the continuous spread of faults; secondly, avoid integrating overweight and overlong tools into the tool library to avoid interference with other parts of the manipulator during replacement. NG tools, do a good job of usual management, limit operating procedures, establish a sense of standardization and safety; third, check the installation line to ensure the reliability of the installation plan, adopt the sequential tool change method, and change the tool sequentially. Arrange the knives reasonably to avoid inconsistencies between the two.

2.4 Compression failure of travel switch at shaft working position

In order to ensure the reliability of the automation of CNC machine tools, a large number of travel switches are often used to detect the movement position of the machine tool. However, after long-term operation, the movement characteristics of the moving parts change slowly, and the reliability of the press decreases.