The faults caused by ball screws are diverse and have no fixed mode. Some faults are gradual and require a development process, which becomes more and more severe with the increase of usage time; Sometimes it is a sudden failure, usually without obvious symptoms, but suddenly occurs. This type of failure is caused by various adverse factors and the combined action of the outside world. So determining the true cause of the malfunction through correct detection is a prerequisite for fast and accurate maintenance.

1、 Inspection and Repair of Clearance between Ball Screw Nut Pair and Support System

When a CNC machine tool experiences large reverse errors, unstable positioning accuracy, or tool marks beyond the quadrant, the first step is to check for gaps in the screw system. The detection methods include: using a dial gauge in conjunction with a steel ball to place it in the center hole at one end of the lead screw, measuring the axial movement of the lead screw, and using another dial gauge to measure the movement of the workbench. Rotate the lead screw forward and backward, observe the values reflected on the two dial indicators, and confirm the fault location based on different changes in the values.

1. Detection and repair of clearance between screw support bearings

If the dial indicator for measuring the lead screw does not swing when the lead screw rotates in both directions, it indicates that the lead screw is not moving. If the pointer of the dial gauge swings, it indicates that the lead screw is moving. The difference between the maximum and minimum measurement values of the dial indicator is the distance of the axial movement of the lead screw. At this point, we need to check whether the back cap of the support bearing is locked, whether the support bearing has worn out, and whether the pre loaded bearing washer is suitable. If there are no problems with the bearings, just replace them with pre loaded washers. If the bearing is damaged, it needs to be replaced, equipped with pre loaded washers, and the back cap tightened. The axial displacement of the lead screw mainly depends on the accuracy of the preloaded washer on the supporting bearing. The most ideal state for the installation accuracy of the screw is that there is no positive or negative clearance, and the support bearing also has an interference of about 0.02mm.

2. Detection and maintenance of gaps generated by ball screw and double nut pairs

Through testing, if it is confirmed that the fault is not caused by the movement of the lead screw. Then it is necessary to consider whether there is a gap between the screw and nut pairs, and the detection method for this situation is basically the same as detecting the movement of the screw. Use a dial gauge to measure the maximum gap between the screw and the nut on the workbench connected to the nut. Rotate the screw in both directions and adjust it accordingly.

3. Inspection and maintenance of single nut pairs

For single nut ball screws, the gap between the screw and nut pairs cannot be adjusted. If there is a gap detected in the screw nut pair. Firstly, check whether the thread arcs of the lead screw and nut have been worn. If the wear is severe, the complete set of lead screw nuts must be replaced.

If there is slight wear during inspection, a larger diameter ball can be replaced for repair. Firstly, detect the maximum clearance of the screw nut pair, convert it into an increase in ball diameter, and then select a suitable ball for reassembly. This type of maintenance is relatively complex, requires a long time, and requires a high level of technical proficiency.

4. Gap caused by loose connection between nut flange and workbench

This problem is generally overlooked by people. Due to the long-term reciprocating movement of the machine tool, the screws that fix the faraday plate become loose and create gaps. When checking the clearance of the screw and nut, it is best to eliminate this fault factor first to avoid taking a detour during repair.

5. Repair faults such as uneven movement and excessive noise of the ball screw nut pair.

The uneven movement and excessive noise of the ball screw nut pair are mostly caused by poor lubrication, but sometimes it may also be caused by the servo motor driving parameters not being adjusted properly.

2、 Poor lubrication of bearings and screw nut pairs

If a machine tool generates noise and vibration during operation, after checking that the mechanical transmission part is not faulty, the first consideration should be given to the problem of poor lubrication. After many years of operation, the automatic lubrication system for the screw and nut of many machine tools is often blocked and cannot automatically lubricate. Adding high-temperature and high-speed resistant lubricating grease to bearings and nuts can solve the problem. Lubricating grease can ensure the normal operation of bearings and nuts for several years.

3、 Servo motor drive problem

Some machine tools generate vibration and crawling during movement, and the mechanical parts are often inspected without any problems. No matter how adjusted, vibration and crawling cannot be eliminated. After careful inspection, it was found that the servo motor drive gain parameter is not suitable for actual operating conditions. After adjusting the gain parameters, vibration and crawling can be eliminated.