In order to improve the utilization of CNC machine tools, combined with the maintenance principle of CNC machine tools, this article briefly talks about the general methods of CNC machine maintenance. The author summarizes it into the four methods of "look, smell, ask, and cut".

 

1. Hope

 

That is to use human sense organs such as hands, eyes, ears, nose, etc. to find the cause of the fault. This is one of the simplest and most direct methods.

 

When a CNC machine tool fails, we must first understand the failure phenomenon, how it happened and how it happened. If the fault can be reproduced, the process of the fault 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 are burn marks, whether the resistance and wires have changed color; whether there are abnormal conditions in the running and sealing parts, such as splashes, falling materials, spills, oil, smoke, sparks, etc.; , Whether the relay is tripped, whether the fuse is blown; Whether the machine tool power supply lacks phase, whether the three-phase is severely uneven, whether the machine voltage is normal; Whether the parts on the electrical components are off, disconnected, jammed, loosened, etc.; switch Whether it is appropriate; whether the processing procedure of the operator is correct, etc. This step is the most intuitive for the maintenance and inspection of CNC machine tools, and it is also the step that most tests the familiarity of the maintenance personnel with the hardware structure of the machine tool.

2. Smell

 

Identify whether there is a peculiar smell. When the moving parts of the machine tool are violently rubbed, the electrical insulation layer will be burnt, and at the same time it will produce oil, smoke, gas, and the burnt smell of insulating materials; when the machine tool is discharged, it will produce ozone smell and the sound of discharge will be heard.

 

3. Ask

 

That is, inquire about the situation when the machine fails. It is best to formulate strict management measures during CNC machining, and require operators to make detailed records when encountering failures. In this way, it can avoid that the maintenance personnel are not around when the failure occurs and can accurately reflect the specific situation of the failure. When a CNC machine tool fails, the machine must first be stopped to protect the site. The operator should record the fault as detailed as possible, and important information must be observed and recorded in detail.

 

For example: the phenomenon when the failure occurred, the location where the failure occurred, and the state of the machine tool and the control system when the failure occurred. If the fault occurs in the automatic processing mode, the specific information such as the processing program number when the fault occurred, the program segment number where the fault occurred, and the tool number used during processing should be recorded. In the event of faults such as excessive machining accuracy or excessive contour error, the number of the workpiece to be processed should be recorded, and the unqualified workpiece should be retained for specific analysis. In the event of a failure, if the system has an alarm display, the system's alarm display and alarm code should be recorded. If it is a failure that occurs when processing parts, the probability of failure when processing similar workpieces should be recorded.

4. Cut

 

That is, to diagnose the failure phenomenon and repair it. This step is also the most important step for CNC machine tool repair.

 

Which can be divided into the following specific steps to complete.

 

4.1 System parameter inspection method

 

Now the self-diagnosis function of the operating system of CNC machine tools is getting stronger and stronger, most of the faults of CNC machine tools can be diagnosed and corresponding measures can be taken. When a CNC machine tool fails, sometimes an alarm message is displayed on the display, and sometimes there are alarm devices on the CNC device, PLC device, and drive device, such as flashing and buzzing alarm lights. At this time, first check the maintenance manual and check the corresponding parameter settings. Loss of system parameters and incorrect settings will cause changes in machine tool performance or malfunctions. For example, in FANUC system machine tool automatic processing, the machine tool holder stops moving and the screen displays 500, 501 alarms, query the parameter manual to find that the corresponding parameter is that the positive and negative limits of the storage stroke limit are exceeded. At this time, the machine can be changed to manual state and shake After the tool post reaches the correct stroke range and correct the parameters, the alarm can be released.

 

4.2 Reset machine method

 

During processing, the system alarms caused by transient faults can be reset by hardware or turn on and off the system power in order to clear the faults. If the system working storage area is caused by power failure, unplugging the circuit board or battery undervoltage, the system is chaotic. The system must be initialized and cleared. Before clearing, you should make a copy of important data. If the fault cannot be eliminated after initialization, perform hardware diagnosis.

 

4.3 Measurement diagnosis method

 

The measurement method is the basic method for diagnosing equipment failures. We can use multimeters, oscilloscopes, logic testers and other instruments to measure electronic circuits. For example, the phase sequence table can be used to determine the phase sequence of the three-phase power supply of the numerical control system, that is, connect the three-phase power cord to the phase sequence table. When the phase sequence is correct, the phase sequence table rotates clockwise, and vice versa. You can also use a dual-channel oscilloscope to measure. If the phase sequence is correct, the phase difference of each two-phase waveform is 120°.

 

4.4 Principle analysis method

 

When other maintenance methods are difficult to solve the fault, you can check the working principle of the machine step by step, and finally find out the cause of the fault. For example, the author once encountered a machine tool using FANUC 0iTD system, which appeared chaotic teeth during thread processing. According to the basic principle of CNC system position control, it can basically be determined that the fault lies in the rotary encoder, and it is likely to be feedback The signal is lost. In this way, once the numerical control device gives the command position of the feed amount, the actual position feedback will always be incorrect, and the position error can never be eliminated, causing problems with thread interpolation. When the pulse encoder was removed for inspection, it was found that the filament inside the encoder was broken, resulting in no feedback input signal, which was consistent with the principle analysis. After the encoder was replaced, the fault was eliminated.

 

4.5 Device Exchange Method

 

For some faults related to the control system, it is sometimes not easy to confirm which part is faulty. In the case of ensuring that there is no further damage, you can use the same spare parts or the same type of machine tool for the suspected faulty parts or components. Replace the same parts or components on other parts of the machine to determine whether a failure occurs. If the fault is resolved after replacing the device, it can be determined that the device is damaged. If the fault persists, the device is proved to be intact, and other methods can be used to continue testing.

 

The above are just some of the author's simple knowledge, and there are still many immature places. As a new industry of CNC machine tool repair technology, its direct purpose and final result is to restore the CNC machine tool to normal operation, thereby ensuring the smooth use of the equipment. The development of CNC technology can be said to be changing with each passing day. New equipment and new systems are emerging in endlessly. As the relevant personnel engaged in CNC system maintenance technology, they should continuously learn and master new knowledge and technology, and summarize and summarize them so that they can be used. It can provide a reference for the rest of the industry so that everyone can make progress together.