Top Ten Troubleshooting Maintenance of CNC Machine Tools

Simple CNC lathes are also called economical CNC lathes. Because of their economical price and high degree of automation, they are generally recognized and widely used in the machining industry. Simple CNC lathes are developed on the basis of ordinary lathes, but their degree of automation has been greatly improved. Its automatic control system is mainly composed of a single-chip microcomputer. Through the control program, it controls the longitudinal and horizontal feed devices and tool change devices of the machine tool to automatically complete the processing of parts. Therefore, the simple CNC lathe is a more complex mechanical-electrical integration equipment, so when a failure occurs, it must be comprehensively analyzed from the two aspects of the mechanical structure and electrical control of the machine tool.
Now, combined with my own experience in actual maintenance work, I will make some analysis of its common faults

1. After the program is started, the stepper motor vibrates and does not rotate. This phenomenon is generally caused by the phase failure of the stepper motor or its control system. It may be the failure of the stepper motor itself or the failure of its drive circuit. First check whether the connecting plug of the stepping motor is in good contact. If the connecting plug is in good contact, you can replace the one-phase motor that is not faulty. If it still can’t work normally, it means that its control part is abnormal. You can focus on checking the high-power triode on the driver board and the release diode of the protection component. Under normal circumstances, the probability of damage to these two components is relatively high.

2. During the operation of the processing program, the workbench suddenly stops running, and the stepping motor shakes and does not turn. This phenomenon is generally caused by mechanical failure, but it may also be caused by a failure of the control system. At this time, the workbench can be returned to the original point first, and the processing program can be restarted. If the workbench always runs to a certain position and stops running, it should be caused by a certain part of the transmission system being damaged, deformed or stuck by foreign objects. . First cut off the power of the control system, and then turn the lead screw by hand. If the resistance at a certain part is extremely large or even cannot be turned at all, it proves that this position is faulty. Check the gap between the screw nut and the screw or whether the slide plate is too tight, whether there is any foreign matter in the ball guide groove of the ball screw, whether the screw is bent and deformed, whether the flexible gear in the stepper motor reducer is loose or whether there is any foreign matter Stuck etc. If there is no abnormality in the manual cranking, it means that the control system is faulty and should be checked according to step 1.

3. The stepper motor runs normally at low speed, but loses steps at high speed. This phenomenon may be caused by the reduction of the drive power supply voltage, which reduces the output torque of the stepper motor. Therefore, we should focus on checking the drive power supply part. When the high-voltage starter transistor is damaged, the high-voltage power supply cannot be connected, which reduces the output torque of the stepping motor at high speed, resulting in lost steps. It could also be caused by a mechanical failure. Therefore, in the case of failing to check the above components, the screw, screw nut, slide plate, stepper motor reducer and other parts should also be checked. When some parts are bent, deformed, or foreign objects are stuck, the running resistance will increase. When running at low speed, the phenomenon is not obvious, but when running at high speed, it cannot completely overcome the running resistance and cause step loss.

4. After the program runs, the tool does not return to the zero point. This phenomenon is generally caused by the failure of the control system. The tool requires low-speed operation during feeding or processing. At this time, the stepping motor runs at a low speed, and a low-voltage power supply is used for power supply. When the program returns to zero, it is required to return quickly. At this time, the stepping motor is required to run at high speed, and a high-voltage drive power supply is used. , to increase the output torque and ensure normal return to zero. There is a switching triode that controls the output of the high-voltage drive power supply. When the switching triode is damaged and returns to zero at high speed, the high-voltage power supply cannot be turned on, and the output torque of the stepping motor is not enough, resulting in loss of steps in returning to zero, resulting in cutting tools Cannot return to the origin. This failure can be eliminated by replacing the switching transistor.

5. At the end of the program running, the tool is offside when it returns to the origin. This phenomenon is generally caused by too much running resistance of the mechanical transmission system. When cutting feed, the tool holder runs at low speed, driven by low voltage, and the stepping motor has a small operating torque, which is not enough to overcome the resistance and cause step loss. When returning to zero, the stepping motor is driven by high voltage, the running speed is high, the torque is large, and there is no strenuous resistance. The stepping motor operates normally without losing steps. In this way, if you lose your steps when you go and return normally, it will cause the above phenomenon. At this time, you can check whether there are iron filings and foreign objects on the transmission gear in the stepping motor reducer or the transmission gear between the stepping motor and the lead screw, or whether the slide plate is too tight to increase the running resistance.

6. Everything is normal during empty cutting, but the size error is very large when processing workpieces. One possibility of this phenomenon is that the screw or screw nut is loosely connected to the lathe. There is no knife resistance during empty walking, and the slide plate operates normally. When machining workpieces, due to the increase of knife resistance, the connection between the screw or screw nut and the lathe is loose, resulting in the drift of the workpiece size. The connection part is strong, and the failure can be eliminated. Another possibility is caused by the electric knife holder. If the tool holder cannot be automatically locked after the tool is changed, so that the tool deviates from the processing point when eating the knife, the above phenomenon will also be caused. At this time, check the tool holder locking device and the tool holder control box.

7. The local size error of the workpiece is large, which is mainly caused by the gap between the nut and the screw. Since the screw nut and the lead screw have been running in a certain section for a long time, the gap in this section increases. At the beginning of the program, the measured screw gap is compensated in the program, but when the worn section cannot be compensated, the local size of the workpiece is out of tolerance . The solution is to repair or replace the lead screw. ( copyright)

8. The electric tool post rotates continuously when changing the tool, and cannot be positioned. This is because when the program requires a certain number of tools, the electric tool post rotates forward to select the tool. When it rotates to this number of tools, there is no response signal, so that The tool holder does not stop rotating and cannot be positioned. At this time, the Hall element on the electric tool post should be checked. When the Hall element is damaged, there will be no detection signal output when the desired tool is in place, resulting in the above phenomenon. At this time, just replace the Hall element of the knife. .

9. During the execution of the program, the computer returns to the monitoring state, and all work cannot be carried out.This phenomenon is generally caused by the failure of the monitoring program, and it may also be caused by strong magnetic interference. For strong magnetic interference, it can be solved by grounding or shielding. If the program is not executed according to the instructions or the program is not executed according to the instructions when the program is started, it will return to the monitoring state immediately. Generally, the monitoring program or computer hardware is faulty, and the suspicious chip can be replaced, such as an off-chip program memory chip, a programmable interface chip or the single-chip microcomputer itself. Sometimes the off-chip data memory failure may also cause this phenomenon. If it can’t be solved, you can find the manufacturer to debug again.

10. The processing program is often lost. In serious cases, the control system cannot work normally. If the processing program is lost after the control system is powered off, and the machine tool is powered on and the processing program is re-entered, the machine tool can process normally. It may be the backup battery voltage. Reduced or disconnected, causing the processing program in the data memory to be lost after the machine tool is powered off. At this time, just replace the backup battery. If the processing program is often partially or completely lost during processing, it is most likely caused by a data memory failure. At this time, the off-chip data memory or the single-chip microcomputer itself can be replaced. In short, the simple CNC lathe is composed of two parts: mechanical and electrical. After a fault occurs, it must be analyzed from both mechanical and electrical aspects to determine whether it is a mechanical fault or an electrical fault. Then analyze in depth to find out the fault point and deal with the fault accurately and quickly. , Improve the efficiency of machine tool maintenance.

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