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In order to give full play to the functions that CNC machining centers should have, the normal operation of CNC machine tools is very critical. When problems occur with CNC equipment, it is particularly important to eliminate faults in a timely manner. But for maintenance personnel who have little contact with machining centers, when a machine tool breaks down, they often don’t know where to start, which delays the repair time. If we can make use of the self-diagnosis function of the CNC system itself, it will be of great help to our maintenance. At the same time, as maintenance personnel, when a CNC machine tool fails, they must first learn from the operator about the symptoms of the failure, which program and time it occurred, and whether the operation method is appropriate, so that the problem can be discovered in time to avoid excessive hidden dangers and losses. Secondly, check the buttons, fuses, terminal blocks and other components, whether the screws are tightened during wiring, whether the aviation plugs and sockets are tightened, whether the plugs on the circuit board are tightened, whether each dial switch is operated correctly, etc. And according to the easy-to-detect characteristics of mechanical faults, when a machine tool overload or overheat alarm occurs, you should first check whether the inserts of the slide plate are too tight. The friction between the slide plate and the bed guide rail increases, making the motor difficult to operate. There is also whether the ball screw and the bracket are concentric. If the ball in the screw is worn and the screw is too tight, it can also overload and overheat the motor, causing electrical failure. Therefore, during the normal maintenance of CNC machine tools, we carefully do the work in the above aspects and cooperate together to avoid detours, troubleshoot problems faster, reduce the downtime of CNC machine tools, increase the utilization rate of CNC machine tools, and enable the company's production to proceed smoothly and complete the production schedule. Below, combined with my own maintenance methods and experience in CNC machine tools, I will introduce several representative fault examples for your reference. Our company currently has two JCS-018 vertical machining centers produced by the Beijing Machine Tool Research Institute. The system adopts the Japanese FANVC-BESk7M system full-featured CNC machine tool. The 7M system is controlled by a 16-bit microprocessor. The servo drive unit is a large inertia DC servo motor. The main motor It is driven by a three-phase full-wave thyristor non-circulating circuit, with the rotary transformer as the position detection element and the tachometer generator forming the speed feedback. The machine tool has experienced many abnormal alarms and abnormal phenomena during operation. We quickly eliminated the fault based on the alarm response number displayed by the CRT to ensure the normal operation of the machine tool. Example 1: Fault phenomenon, CRT displays 05#07# alarm fault inspection and analysis: Check the FANVC-BESK7M system maintenance manual. 05# is the emergency stop signal, and 07# is the speed control unit alarm. From the maintenance manual, the 05# alarm is caused by the emergency stop, so it is easier to troubleshoot the fault, such as whether the emergency stop switch is pressed, and whether the overtravel limits of the After analysis, it is believed that the 07# alarm is the key. After it is abnormal, emergency stop is used to protect it, so that the 05# and 07# alarms appear at the same time. For 07# alarm, it is stated in the maintenance manual: The speed control unit of any axis is in an alarm condition, or the contactor of the motor power line is open. When this alarm occurs, the following reasons may be considered:: ①The motor is overloaded. ②The speed control power transformer is overheated. ③The power fuse of the speed control power transformer is blown. ④The speed control unit fuse is blown. ⑤On the power input bracket of the control part, the contact between ZMGIN of the terminal block and point 2 is open. ⑥On the control part power input bracket, the AC 100V fuse (F5) is broken. ⑦The signal cable connecting the speed control unit to the control section is disconnected or has come out of the plug. ⑧The contactor (MCC) on the motor power line opened due to some other servo alarm. analyze: Check them one by one, easy first and then difficult. Item A: Use a table to check that the thermal element element is abnormal, and after turning on the NC, the X-axis, Y-axis, Z-axis, and tool magazine axes did not move and alarms 05# and 07# were generated, so item A is no. Item B: Touch the transformer with your hands to see if it is not overheated. Use a multimeter to check that OH1 and OH2 are normal. Check that the fuses in C, D and F are not broken. Item E: Use a multimeter to check the contact between ZMGIN and 2 in the wiring adjustment, and the result is normal. Therefore, the contradiction was concentrated on G and H. I used a multimeter to check the electrical resistance and found that there was an abnormality in the Y-axis speed control unit board. Because the motor has an overheating protection, the axes are connected in series with each other in this electrical wiring, and the voltage should be 24V. The process is 24V → X-axis overheat protection is normally closed → Speed control unit → Y-axis overheat protection is normally closed → Speed control unit → Z-axis overheat protection is normally closed → Z-axis speed control control unit → Tool holder overheat protection is normally closed → Tool magazine speed control unit → NC is positive Normally, when it is checked that the Y-axis overheat protection is normally closed → Y-axis speed control unit → Z-axis overheat protection is normally closed, there is no connection and an open circuit. Therefore, check the Y-axis speed control board and search the wires. It is found that a short-circuit rod is open, which is caused by being greasy and dirty. After cleaning, plug it in and start it normally. Example 2. Fault phenomenon: the spindle cannot be oriented, and the load indicates the red zone 08# alarm. Fault inspection and analysis: Check the machine tool maintenance manual, and the 08# alarm is spindle positioning fault. According to the manual requirements, we open the machine tool power cabinet and find 7 light-emitting diodes (6 green and 1 red) on the AC spindle control circuit board. These 7 indicators (from left to right) respectively represent ① directional command ② low speed gear ③ track peak detection ④ Deceleration command ⑤ fine positioning ③ positioning completed ⑤ test mode (①-③ is green, ① red) When the machine tool is oriented, observe the situation of these 7 command lights as follows. 1# light is on, 3# and 5# lights are flashing, which indicates that the positioning command has been issued, the track peak has been detected, and the positioning signal has been detected, but the system cannot complete Positioning, the spindle is still running at low speed, so the 3# and 5# lights keep flashing. From the above analysis, we suspect that it is the amplifier problem on the spindle box. We open the spindle protective cover and check the magnification at the same time. We find that the tool clamping cylinder hose on the spindle is twisted into a twisted shape and wrapped around the spindle. Analyzing this abnormal phenomenon, I We judged that the hose was coiled, causing the spindle positioning to deviate and not be able to be positioned accurately, causing the D8# alarm. We removed the hose and straightened it and installed it. We also re-adjusted the adjustment potentiometer RV11 (locating point offset) in the spindle controller. The fault was eliminated, the alarm disappeared, and the machine returned to normal operation. Example 3. Fault phenomenon: After turning on the power and turning on the NC power, each axis returns to zero, and when the axis master executes M03 to start, a 01# alarm occurs. Fault inspection and analysis: Check the service manual. 01# alarm is a fault in the spindle system, which can be indicated by the indicator light in the spindle servo device. Check that the indicator light in the AC spindle servo device is No. 4 in the 8421. The No. 4 light indicates that F1, F2, and F3 of the AC coupling circuit are fused. The No. 4 fault is divided into the following four situations: 1. The impedance of the AC power supply is too high. 2. The power transistor is burned out. 3. The diode or thyristor component is burned out. 4. The surge absorber and capacitor are damaged. Based on this analysis, check each item in turn. Only the fuse breaks two phases, and there are no other problems. Therefore, replace the fuse, turn on the power switch of the machine tool, test that the AC voltage is normal, turn on the NC power supply, and operate normally. When the program executes M03, the spindle just starts, and an 01# alarm is generated. Check F1, F2, and F. 3. The original two phases are broken again, so we make a comprehensive analysis, ignore the contents of the maintenance manual, and detect the periphery. When the busbar junction box is detected, it is found that one of the phase wires is broken, so the fault phenomenon is that the other two phases are broken. Repair the junction box, and turn on the power supply. When M03 is executed, it is normal, and the fault is solved. Example 4. Fault phenomenon: Normal processing execution program, when the tool change action M06 is executed, the tool holder is down, the spindle is not oriented, and the tool is not changed. The spindle presses the tool program again to continue processing without alarm. Fault inspection and analysis: The sequence of actions to execute the tool change command M06 is: spindle orientation, lower the tool holder, turn out 75 degrees, lower the arm, turn back 180 degrees to convert the tool, put the arm up, turn back 75 degrees, put the tool holder up, reset the cylinder 180 degrees, then issue the FIN command, and then execute the next program. Combined with the fault analysis, the PC output board and the components that perform the tool change action were checked. When G3 was checked, an abnormality was found. Normally, when G3 is changing tools, its tube corner 2 is high level, 3 is high level, 24V cannot be sent out, and the tool change action is performed. When the tool change is completed, tube corner 2 becomes low level, and the 24V voltage is sent out, and FIN is sent out, that is, the MT signal is completed. Tube corner 2 is now high level or low level, and the FN signal is sent out, there is 24V output, and the MT signal is sent out after the execution is completed, so that the NC executes the next program. The cutting tools have not been exchanged yet, so collisions may easily occur. Based on this, we removed the G3 chip, which is a reed electrical appliance. We went to the market to buy this chip, but we didn't find it. Based on its performance, we replaced it with Panasonic DSZY-S-DC5C. The fault was solved. Similar faults have not occurred for more than a year since the replacement, ensuring the normal production of the workshop. The above examples of electrical faults of CNC machine tools were selected and summarized in our maintenance examples. They reflect some problems in the electrical maintenance of CNC machine tools. To improve the electrical maintenance skills of CNC machine tools, the key is to be familiar with the performance characteristics and working principles of the CNC machine tool being repaired, and master the correct methods, such as checking the CRT alarm and display content of the CNC machine tool, and checking the maintenance manual. When a fault occurs, according to the fault phenomenon, check the electrical manual to troubleshoot the fault, continue to practice during the maintenance process, constantly explore and accumulate experience, so as to achieve the purpose of flexibly using maintenance technology to eliminate electrical faults of CNC machine tools, give full play to the utilization of CNC machine tools, and create more benefits.