As a new industry, the direct purpose and final result of CNC machine tool maintenance technology is to make CNC machine tool return to normal operation, so as to ensure the smooth use of equipment. CNC machine tool is an efficient automatic machine tool, which integrates new technical achievements in various fields such as computer technology, automation technology, servo drive, precision measurement and precision machinery, It is a new mechanical control technology. Because of its good economic performance and high production efficiency, it is more and more important in production. However, due to the advanced nature of CNC machine tools and the instability of faults, most of the faults are in the form of comprehensive failure. Therefore, the maintenance of NC machine tools is very difficult, and the maintenance of NC machine tools is not standardized, which makes NC maintenance work in a state of chaos. In order to improve the use of CNC machine tools, combined with the maintenance principle of CNC machine tools, This paper discusses the general maintenance methods for CNC machine tools.
Observation
When the CNC machine tool breaks down, first of all, it is necessary to find out the fault phenomenon, how to happen and the process. If the fault can be reproduced, the process of fault occurrence should be observed. Only when the first-hand situation is known can the fault be eliminated.
At the same time, observe whether there is mechanical damage; whether there is burning trace, whether the resistance and wire have changed color; whether there are abnormal conditions in the operation and sealing parts, such as splash, falling off, spillage, oil, smoke, Mars, etc.; whether the circuit breaker and relay trip, whether the fuse is fused; whether the machine tool power supply is lack of phase, whether the three-phase is seriously uneven, and whether the machine tool voltage is normal; Whether the parts on the electrical components are falling off, broken, stuck, loose joints, etc.; whether the switch is suitable; whether the processing procedure of the operator is correct, etc. This step is the most intuitive for the maintenance and detection of CNC machine tools, and it is also the step that tests the familiarity of maintenance personnel with the hardware structure of machine tools.
Smell
Identify odors. When the moving parts of the machine tool have severe friction, the electrical insulation layer will be burned, and the smell of oil, smoke, gas and insulating materials will be produced; when the machine tool is discharged, the smell of ozone will be produced, and the sound of discharge will be heard.
Inquiry
Ask what happened when the machine failed. It is better to formulate strict management measures during NC machining, and stipulate that operators can make detailed records in case of faults. In this way, it can avoid that the maintenance personnel are not around and can accurately reflect the specific situation of the fault. When the CNC machine tool breaks down, first stop the machine tool, protect the site, and the operator shall record the fault in detail as much as possible, in which important information shall be observed and recorded in detail, such as: the phenomenon when the fault occurs, the location where the fault occurs, the state of the bed when the fault occurs and the situation of the control system, etc. If the fault occurs in the automatic processing mode, the processing program number when the fault occurs, the program segment number when the fault occurs, the tool number used in processing and other specific information shall be recorded. If the machining accuracy is out of tolerance or the contour error is too large, the number of the workpiece to be processed shall be recorded, and the unqualified workpiece shall be retained for specific analysis. In case of failure, if the system has alarm display, the alarm display and alarm code of the system shall be recorded. If it is a failure occurred during machining of parts, the probability of failure during machining of similar parts shall be recorded.
Accuracy
That is to diagnose and repair the fault, which is also the most important step in the maintenance of CNC machine tools.
It can be divided into the following specific steps to complete.
4.1 system parameter inspection method
At present, the operation system of CNC machine has more and more strong self diagnosis function. Most faults of CNC machine can be diagnosed and corresponding measures can be taken. When the CNC machine tool breaks down, sometimes the alarm information will be displayed on the display, sometimes there will be alarm devices on the CNC device, PLC device and drive device, for example, the alarm light will flash, beep, etc. At this time, first check the maintenance manual and check the corresponding parameter settings. The loss and incorrect setting of system parameters will cause the change or failure of machine performance. For example, in the automatic machining of FANUC system machine tool, the tool holder stops moving and the screen displays 500501 alarm. After querying the parameter manual, it is known that the corresponding parameter is that the positive and negative limit values of the stored stroke limit are beyond. At this time, the machine tool can be changed to the manual state to shake the tool holder to the correct stroke range and correct the parameter, and the alarm can be released.
4.2 reset machine tool method
In the process of processing, the system alarm caused by instantaneous fault can be cleared by hardware reset or turn on and off the system power in turn. If the system is confused due to power failure, unplugging circuit board or under voltage of battery in the working storage area of the system, the system must be initially cleared. Before clearing, it is necessary to copy and record the important data, If the fault cannot be eliminated after initialization, perform hardware diagnosis.
4.3 measurement and diagnosis
Measurement is the basic method to diagnose equipment fault. We can use multimeter, oscilloscope, logic tester and other instruments to measure the electronic circuit. For example, when determining the phase sequence of the three-phase power supply in the CNC system, the phase sequence table can be used to measure, that is, the three-phase power supply line is connected to the phase sequence table. When the phase sequence is correct, the phase sequence table rotates clockwise, and vice versa. Double channel oscilloscope can also be used for measurement. If the phase sequence is correct, the phase difference of each two phases is 120 °.
4.4 principle analysis method
When other maintenance methods are difficult to solve the fault, we can start from the working principle of the machine tool to check step by step, and finally find out the cause of the fault. For example, the author once met a machine tool with fanuc0itd system, when processing thread, the phenomenon of disordered teeth appeared. According to the basic principle of position control of CNC system, it can be basically determined that the fault is on the rotary encoder, and it is likely that the feedback signal is lost, Once the numerical control device gives the command position of the feed, the actual position fed back will always be incorrect, and the position error will never be eliminated, resulting in the problem of thread interpolation. When the pulse encoder is removed for inspection, it is found that the filament inside the encoder is broken, resulting in no feedback input signal, which is consistent with the phenomenon of principle analysis. After replacing the encoder, the fault is eliminated.
4.5 device exchange method
For some faults related to the control system, it is sometimes not easy to confirm which part has a problem. In the case of ensuring no further damage, the parts or components suspected to have a fault can be replaced with the same spare parts or the same parts or components on the same model machine tool or other parts of the machine tool to determine whether there is a fault. If the fault is removed after the replacement of the device, it can be determined that it is caused by the damage of the device. If the fault is still the same, it can be proved that the device is in good condition and can be detected by other methods.
As a new industry, the direct purpose and final result of CNC machine tool maintenance technology is to make CNC machine tool return to normal operation, so as to ensure the smooth use of equipment. The development of numerical control technology is changing with each passing day. New equipment and new systems emerge in endlessly. As the relevant personnel engaged in the maintenance technology of numerical control system, they should constantly learn and master new knowledge and technology, summarize and summarize them, make them available and sustainable, and provide reference for the rest of the industry.
