Introduction to the experience of diagnosis and maintenance of CNC machine tools X Abstract: Through the maintenance of imported CNC equipment in recent years, this paper gradually understands and grasps some fault rules and rapid diagnosis methods of CNC system. The purpose is to provide reference for the use and maintenance of CNC equipment. Keywords: CNC machine tools; Diagnosis and maintenance; Methods With the continuous introduction of advanced technology and equipment from developed countries, it is an undeniable fact that the maintenance of equipment maintenance personnel in China is becoming more and more difficult. But how to adapt and master it as soon as possible is a subject that we should seriously discuss and urgently need to solve. Here, I will talk about my personal maintenance experience for many years. In recent years, the author introduced two kinds of machining centers, VA-65 and HC-800, which not only have the functions of AC servo drive and four-axis linkage, but also are equipped with full closed-loop position feedback, automatic measurement and automatic cutting monitoring system of magnetic grating. Its numerical control system was the first FANUC- 1 1M system in the world at that time. After the operation of 1 1 year, although with the increase of service life, the aging of some parts, the arrival of fault period, especially the increase of processing tasks, the equipment runs 24 hours without interruption, and there is a phenomenon of fault alarm almost every week. However, in order to ensure that the task is completed on schedule, we have carefully analyzed the failure law, accumulated relevant data, gradually mastered the maintenance essentials, tried to find out the failure point in the shortest time and completed the repair and adjustment at the fastest speed in countless maintenance tests without training at home and abroad and incomplete drawings. The following discusses the methods of rapid diagnosis and maintenance of CNC equipment from several aspects: 1 first observe the query, then deal with it, and then look at the alarm information, because most CNC systems now have relatively perfect self-diagnosis function, and the fault area can be immediately known through the prompt information, thus narrowing the detection range. For example, when an HC-800 horizontal machining center is running, the 50 10 # spindle drive unit gives an alarm. According to the prompt information, we immediately checked the spindle motor, its executive components and the spindle control board in turn, and found out the overcurrent breakpoint and then returned to normal. It took only 20 minutes to complete. But from our experience, there are also examples of being misled by alarm information, which can be relied on but not relied on. If there is no alarm information after the fault occurs, it is necessary to further use the sensor to understand the state of the equipment, and the most important thing is to ask the operator about the cause and effect of the fault. The same equipment, once its APC system suddenly rotated and scratched the shield without opening it, which has never happened before. After careful on-site inquiry and operation, we found out the fault process: the original operator first entered M60 instruction to make the _bPm_ APC system program run (changed to rotary workbench), and then entered the single-step instruction operation in manual state after the actuator stopped halfway out of control. At that time, M60 was not deleted, and the original program continued to run after its actuator returned to normal. After careful understanding and analysis, we immediately cleared all the original instructions, detected and replaced the out-of-control components, and avoided further failures. According to the alarm information and the state of the equipment before the failure, the fault area is judged to strive for maintenance time. 2 Follow the principle of maintenance from the outside to the inside, from the shallow to the deep. According to the author's maintenance experience in machining center for many years, most of the faults are caused by external components, which are greatly influenced by external factors, such as mechanical collision and wear, coolant corrosion, excessive dust accumulation, poor lubrication and so on. These disrepair parts are in an imperfect and unreliable state, which has become the biggest hidden danger of equipment failure. Overtravel alarm, zero reset error and no feedback of position signal often occur in each shaft, all of which are caused by some magnetic or mechanical switch failures. Other faults also occur in solenoid valves, motors and cables that often expand and contract. Like HC-800, the B axis does not rotate properly or sometimes does not rotate at all. The alarm prompt is: feed shaft failure (APC com2 mand), which seems to be related to the command. However, according to the fault phenomenon, we still checked the travel limit of axis B decisively, and sure enough, there was a bump with poor contact with the switch, which was normal after adjustment. This can avoid spending a lot of energy to check the whole CNC system without goals, and focus on the external links first. This is actually an empirical diagnosis. If you have the principle wiring diagram in your hand, you should compare the drawings, find out the potentials and waveforms in order, conduct targeted tests, and learn some theoretical things from them. It is precisely because we do not have such conditions that we follow the principles of from the outside to the inside, from man-made to system, and from shallow to deep in maintenance, which greatly shortens the downtime of equipment maintenance. It is also a convenient method to make full use of the PC diagram to find the fault point and call up the relevant PC diagram for analysis and verification according to the alarm information. Once the VA-65 automatic tool changer manipulator is in place, it does not execute the command to grab the tool. We immediately call up the PC diagram and check the corresponding signals from the command switch signal to the action signals of advance, retreat, loosening and tightening one by one. Finally, it is found that the signal is not sent out when the manipulator rotates. The reason is that a magnetic proximity switch is loose and doesn't work, which makes the next tool grasping action impossible, and it returns to normal after adjustment. It seems convenient and intuitive to check the fault point through PC diagram, but if you don't understand its internal action principle and working procedure, it can be said that it is also a needle in a haystack and there is no way to start. Especially without electrical schematic diagram, it is even more difficult to judge. Every output action can be filled with dozens of switching conditions, and it really takes a lot of effort to gradually understand and master it. We are constantly understanding and using it by the accumulation of usual maintenance. 4. Detection, analysis and quick treatment of difficult faults. Some parts in these two machining centers have been aging for many years, which makes their parameters extremely unstable with the change of temperature or current, resulting in the phenomenon of instant recovery of good and bad after failure, which is our most scratching fault. Everyone engaged in maintenance knows that it is easy to detect the damage of components, but it is difficult to judge whether the abnormal on-off situation is the damage of components or poor line contact, because normal signal detection cannot be carried out. Such as the transposition of B-axis worktable; The knife inlet of the tool magazine automatically opens; Clamping failure and looseness of B-axis bedplate, etc. The actuators are all solid-state relays, which drive the solenoid valve to act after receiving the command signal. There may be no abnormality during testing, and everything may be normal after starting. After several consecutive actions, stop the machine and call the police. According to the failure phenomenon and repeated cycle, we judge that it should be caused by the performance degradation of the actuator. Because the drawings are unknown and the marks are unclear, only a group of related actuators can be tested under normal and abnormal conditions respectively. After repeated tests, the components with degraded performance were finally found out from more than 30 relay components and replaced. The origin of HC-800 B axis was once out of control, and it kept rotating after the instruction was issued, and there was no alarm information. Through on-the-spot understanding and analysis, it was firstly determined that the fault of the B-axis zero detection system was caused, and the system was controlled by a magnetic proximity switch to send out a signal and then slowed down and stopped. We immediately tested the line of this signal, and no signal was sent out. If an in-place signal is set artificially, the car will stop accurately and confirm that there is a fault between the detection switch and the set signal point. However, if you want to directly detect the proximity switch, you must disassemble the B-axis and its associated adjustment axis, because this switch is installed in the B-axis workbench. Such a large structure has never been dismantled and repaired before, so it will take half a month to calculate the workload. Moreover, dozens of control cables and dozens of oil pipes must be dismantled and restored very carefully, and it is difficult to ensure the accuracy of each part after dismantling. However, in order to solve this problem, this switch must be exposed for testing and maintenance. Whether there is a simple method that can not only save the disassembly workload but also take out the detection switch, after repeated argumentation, we finally came up with a method that can take out the switch only by disassembling the B-axis end cover and adjusting the shaft magnetic ruler bracket. Although it is very difficult for electrical maintenance personnel to disassemble and detect, it ensures that the countertop does not disintegrate and minimizes the impact of future troubles. After the actual test of the switch and the in-situ installation of the handling disconnection point, the B-axis reset function was restored, and the axis adjustment position error and B-axis positioning fault affected by disassembly and assembly were compensated and adjusted. After everything was normal, it was delivered in only three days, which ensured the completion of the trial-manufacture task. Conclusion In a word, how to open your mind, enter the state as soon as possible, narrow the detection range, and directly attack the root cause of the fault is the key to the level of maintenance technicians. The seemingly simple truth is full of all aspects, and it is also the crystallization of the efforts of maintenance personnel for many years. Under the pressure of this high-frequency fault, we overcame many difficulties, tried to solve the problem in a short time, reduced the downtime of equipment, and made our due contribution to the trial production of vehicles. 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