Quick diagnosis and maintenance of the hottest CNC

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With the continuous introduction of advanced technology and equipment in developed countries, the maintenance of our equipment maintenance personnel is becoming more and more difficult, which is an undeniable fact. However, how to adapt and master it as soon as possible is a topic that we should seriously discuss and urgently need to solve. Here is some personal experience about our years of maintenance experience

the two machining centers of Hitachi precision machine va-65 and hc-800 introduced by our institute in 1987 not only have the functions of AC servo drive and four-axis linkage, but also are equipped with magnetic grid full closed-loop position feedback and automatic measurement, automatic cutting monitoring system. Its CNC was the most advanced fanuc-11m system in the world at that time. After 11 years of operation, although with the growth of service life, some components are aging and the failure period is coming. In particular, with the increase of the trial production and processing tasks of the models in the Institute and the 24-hour non-stop operation of the equipment every day, there is a phenomenon of failure alarm almost every week. However, in order to ensure the completion of the task of model trial production on schedule, we carefully analyzed the fault law, continuously accumulated relevant data, gradually mastered the maintenance essentials, tried to find out the fault point in the shortest time, and repaired and adjusted it with the fastest speed in countless maintenance tests without domestic and foreign training and incomplete drawings

the following is a brief introduction to the methods of rapid diagnosis and maintenance of CNC equipment:

1. Observe and inquire first, and then deal with it.

first look at the alarm information, because most CNC systems now have a relatively perfect self diagnosis function. Through the prompt information, you can immediately know the fault area and narrow the detection range. For example, a 5010 spin drive unit alarm alarm occurred in the operation of hc-8oo horizontal machining center. According to the prompt information, we immediately checked the spindle motor, its actuator and the spindle control board in sequence, and found out the overcurrent and open circuit point and then returned to normal, which took only 20 minutes to complete. However, from our experience, there are also examples of being misled by alarm information, so we can rely on it, but we cannot rely on it

if there is no alarm information after the fault occurs, you need to further use your senses to understand the equipment status, and the most important thing is to ask the operator about the cause and effect of the fault. Like this equipment, once its APC system suddenly rotated and scratched the shield when the shield was not opened. This phenomenon has never occurred before. After careful inquiry about the operation process on site, we made clear the fault process: the original operator first input the M60 command to make the APC system program run (replace the rotating workbench). When the actuator was out of control and stopped halfway, we carried out the single step command operation under the manual state. At that time, M60 was not deleted, and the original program action continued after its actuator returned to normal. After careful understanding and analysis, we immediately cleared all the original set instructions, detected and replaced the out of control components, and avoided the occurrence of larger faults

therefore, we should first judge the fault area according to the alarm information and the equipment state before the fault, so as to strive for maintenance time

2. Follow the maintenance principle of "from the outside to the inside, from the shallow to the deep"

according to my years of maintenance experience of the machining center, most of the fault roots come from external components, which are greatly affected by external factors., Such as mechanical collision and wear, excessive liquid corrosion, excessive dust accumulation, poor lubrication when hitting the high tonnage 3.4 product mark, which makes this long-standing components in an incomplete and unreliable state, and becomes the biggest hidden danger of equipment failure. Some magnetic or mechanical switches fail to work, such as overtravel feedback, zero reset error, and position signal non feedback that often occur on each axis. Other faults also appear on the solenoid valve, motor and often telescopic cable. For example, the b-axis rotation of hc-800 is not in place or sometimes does not rotate at all. The alarm prompt is: feed axis fault (APC command), which seems to be related to the command. However, we decisively checked the travel limits of axis B according to the fault phenomenon. Sure enough, there was a bump that did not contact the switch well, and it was normal after adjustment. This will avoid consuming a lot of energy to check the whole CNC system, and focus on the external links first

this is actually an empirical diagnosis. If we have the principle wiring diagram in hand, we should compare it according to the drawing formally, search in sequence and test the potential and waveform pertinently, and we can also understand some theoretical things from it. It is precisely because there is no such condition that we follow the principle of from external to internal, from human to system, from shallow to deep, which greatly shortens the downtime of the equipment

3. Make full use of PC diagram to find the fault point

call out the relevant PC diagram according to the alarm information for analysis and verification, which is also a convenient way of diagnosis. Once the va-65 automatic tool changing manipulator did not execute the knife grasping command after it was in place. We immediately called up the PC diagram to check the corresponding signals one by one from each command switch signal to each forward, backward, loose and tight action signal. Finally, it was found that the manipulator rotated until the signal was not sent. The reason was that a magnetic proximity switch was loose and did not work after it moved, so the next knife grasping action could not be carried out, and it returned to normal after adjustment

it is more convenient and intuitive to assist users to complete performance, installation and debugging in the shortest time from the perspective of PC diagram. However, if you do not understand its internal action principle and working procedure, you can say that you are looking for a needle in a haystack and have no way to start. In particular, it is more difficult to judge without the electrical schematic diagram. Each output action can only meet dozens of switching conditions. It really takes a lot of effort to gradually understand and master it. We are constantly understanding and using it based on the accumulation of daily maintenance

4. Detection, analysis and quick treatment of difficult faults

some components of these two machining centers are aged for a long time, making their parameters extremely unstable with the change of temperature or current, resulting in the automatic recovery of instant good and bad phenomena after faults, which is the most troublesome fault we have. Because those engaged in maintenance know that it is easy to detect if the component is broken, and it is difficult to judge whether the component is broken or the line is in poor contact under abnormal on-off conditions, because normal signal detection cannot be carried out. Such as b-axis workbench transposition; The feed port of the magazine opens automatically; In case of failure of clamping and loosening of b-axis bedplate, its actuator is a solid-state relay, which drives the solenoid valve to act after receiving the command signal. When detecting, there may be no abnormality, and everything may be normal after starting. After continuous action for several times, it will stop and alarm. According to the fault phenomenon and repeated cycle, we determined that it should be caused by the performance degradation of the actuator. Due to the unclear drawing and unclear identification, we can only test the associated group of actuator under normal and abnormal conditions. After repeated testing, we finally found and replaced the components with degraded performance from more than 30 relay components

once hc-800 b axis zero point reset is out of control, the rotation does not stop after the command is issued, and there is no alarm message. After on-site understanding and analysis, it was first determined that it was the fault of the b-axis zero point detection system, and the system controlled the actuator to slow down and stop after a magnetic proximity switch sent a signal in place. We immediately carried out a line test on this signal, and the result was that no signal was sent. If an artificial in place signal was set, the parking was accurately reset, and it was confirmed that there was a fault in the section from the detection switch to the set signal point. However, if you want to directly detect the proximity switch, you must disassemble the b-axis and its associated adjusting axis, because this switch is installed in the b-axis workbench. The dismantling and repair of such a large structure has never been done before. It takes half a month to calculate the workload, and more than a dozen control cables and dozens of oil pipes must be dismantled and restored with special care, which makes it difficult to ensure the accuracy of each part after disassembly and assembly, but in order to solve the problem, this switch must be exposed for detection and maintenance. Can we use a simple method that can save the workload of disassembly and assembly and take out this detection switch? After repeated demonstration, we finally come up with a method that only remove the b-axis end cover and the shaft adjusting magnetic ruler bracket to take out this switch. Although it is very difficult for electrical maintenance personnel to disassemble and test, it ensures that the table top does not disassemble and minimizes the future impact. After actually testing the switch and processing the breaking point, the b-axis reset function was restored after the in-situ installation, and the axis adjustment position error and b-axis positioning fault affected by the disassembly and assembly were compensated and adjusted. After everything was normal, it took only three days to deliver it for use, ensuring the completion of the trial production and processing tasks to display the required values in the computer interface

in addition, in recent years, these two devices have experienced four failures of power board, servo control board and CRT motherboard, three of which are repaired in the shortest time by our own ability

in a word, how to open the mind and enter the state as soon as possible in the process of dealing with the fault, narrow the detection range, and directly touch 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 years of hard work of maintenance personnel. Under the pressure of such high-frequency faults, we overcame many difficulties, tried our best to solve the problems in a short time, reduced the number of equipment downtime, and made our due contribution to the model trial production. (end)

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