Maintenance of the CNC system

Extend the life of components and the wear cycle of parts, prevent various failures, and improve the average trouble-free working time and service life of CNC machine tools.
Note on usage
1. The use environment of CNC machine tools: It is best to place CNC machine tools in a constant temperature environment and away from equipment with large vibrations (such as punches) and equipment with electromagnetic interference;
2. Power requirements;
3. CNC machine tools should have operating procedures: perform regular maintenance and upkeep, and record and protect the site in case of failure;
4. CNC machine tools should not be stored for a long time. Long-term storage system failure and data loss may occur;
5. Pay attention to training and equipping operators, maintenance personnel and programmers.
Maintenance Charter
Maintenance of CNC system
1. Strictly abide by operating procedures and daily maintenance systems.
2. Prevent dust from entering the CNC device: Floating dust and metal powder can easily cause the insulation resistance between components to decrease, resulting in malfunction or even damage to the components.
3. Clean the cooling and ventilation system of the CNC cabinet regularly.
4. Frequently monitor the grid voltage of the CNC system: the grid voltage ranges from 85% to 110% of the rated value.
5. Replace the memory battery regularly.
6. Maintenance of the CNC system when it is not in use for a long time: frequently power on the CNC system or run the CNC machine tool through the warm-up program.
7. Maintenance of spare circuit boards and maintenance of mechanical components.
Maintenance of mechanical components
1. Maintenance of tool magazine and tool changing robot
1) When manually loading a knife into the tool magazine, make sure it is installed in place and check whether the locking on the tool holder is reliable;
2) It is strictly prohibited to load overweight and overlong tools into the tool magazine to prevent the tool from falling or the tool from colliding with the workpiece, fixture, etc. when the manipulator changes the tool;
3) When using the sequential tool selection method, you must pay attention to whether the order of placing the tools on the tool magazine is correct. In other tool selection methods, you should also pay attention to whether the tool number you change is consistent with the required tool to prevent accidents caused by changing the wrong tool;
4) Pay attention to keeping the tool handle and knife sleeve clean;
5) Always check whether the zero return position of the tool magazine is correct, check whether the position of the machine tool spindle returning to the tool change point is in place, and adjust it in time, otherwise the tool change action cannot be completed;
6) When starting up, the tool magazine and manipulator should be run dry first, and check whether all parts are working normally, especially whether the travel switches and solenoid valves can operate normally.
2. Maintenance of ball screw pair
1) Regularly check and adjust the axial clearance of the screw nut pair to ensure reverse transmission accuracy and axial stiffness;
2) Regularly check whether the connection between the screw support and the machine bed is loose and whether the support bearing is damaged. If there are any of the above problems, tighten the loose parts in time and replace the support bearings;
3) For ball screws that use grease, clean the old grease on the screw once every six months and replace it with new grease. The ball screw lubricated with lubricating oil should be refueled once a day before machine tool operation;
4) Pay attention to avoid hard dust or chips from entering the screw guard and hitting the guard during work. If the protective device is damaged, it must be replaced in time.
3. Maintenance of main transmission chain
1) Regularly adjust the tightness of the spindle drive belt;
2) Prevent various impurities from entering the fuel tank. Change lubricating oil once a year;
3) Keep the connection between the spindle and the tool holder clean. The displacement of the hydraulic cylinder and piston needs to be adjusted in time;
4) Adjust the counterweight in time.
4. Hydraulic system maintenance
1) Filter or replace the oil regularly;
2) Control the temperature of the oil in the hydraulic system;
3) Prevent hydraulic system leakage;
4) Regularly check and clean the fuel tank and pipelines;
5) Implement daily point inspection system.
5. Pneumatic system maintenance
1) Remove impurities and moisture from compressed air;
2) Check the oil supply amount of the lubricator in the system;
3) Maintain the sealing of the system;
4) Pay attention to regulating work pressure;
5) Clean or replace pneumatic components and filter elements.
Troubleshooting
In CNC machine tools, most faults can be checked, but there are also some faults where the alarm information provided is vague or even no alarm at all, or the occurrence period is long, irregular, and irregular, which brings difficulties to the search and analysis. Many difficulties. For this type of machine tool failure, it is necessary to analyze the specific situation and conduct a patient search, and the inspection particularly requires comprehensive knowledge of mechanics, electrical, hydraulics, etc., otherwise it will be difficult to quickly and correctly find the real cause of the failure.
Abnormal machining accuracy failure: changes or modifications in system parameters, mechanical failure, unoptimized electrical parameters of the machine tool, abnormal motor operation, abnormal machine tool position loop or improper control logic are common causes of abnormal machining accuracy failure of CNC machine tools in production. Find out the relevant Identify the fault point and deal with it, and the machine tool can return to normal. In production, faults with abnormal machining accuracy of CNC machine tools are often encountered. Such faults are highly concealed and difficult to diagnose.
There are five main reasons for this type of failure:
1. The machine tool feed unit is modified or changed;
2. The zero offset (NULLOFFSET) of each axis of the machine tool is abnormal;
3. The axial backlash (BACKLASH) is abnormal;
4. The motor is running abnormally, that is, the electrical and control parts are faulty;
5. Mechanical failure, such as screws, bearings, couplings and other components.
In addition, the preparation of processing programs, tool selection and human factors may also lead to abnormal processing accuracy.
If the machining accuracy is abnormal due to mechanical failure, the following aspects should be checked one by one.
1. Check the machining program segment that is running when the machine tool accuracy is abnormal, especially the tool length compensation and the calibration and calculation of the machining coordinate system (G54~G59).
2. In the jog mode, the Z-axis is repeatedly moved, and the motion status is diagnosed through sight, touch, and listening. It is found that the Z-direction movement sound is abnormal, especially the rapid jog, and the noise is more obvious. Judging from this, there may be hidden dangers in mechanical aspects [1].
troubleshooting
1. Initialization reset method: Under normal circumstances, when a system alarm is caused by a transient fault, the fault can be cleared by hardware reset or switching the system power on and off in sequence. If the system working storage area is in chaos due to power outage, unplugging and plugging circuit boards or battery undervoltage , the system must be initialized and cleared. Before clearing, attention should be paid to data copy records. If the fault still cannot be eliminated after initialization, perform hardware diagnosis.
2. Parameter change and program correction method: System parameters are the basis for determining system functions. Wrong parameter settings may cause system failure or certain functions to be invalid. Sometimes user program errors can cause downtime. You can use the system's block search function to check and correct all errors to ensure normal operation.
3. Adjustment, optimal adjustment method: Adjustment is the simplest and easiest method. Correct system faults by adjusting the potentiometer. For example, during maintenance at a factory, the system display screen was chaotic, but it became normal after adjustment. For example, in a certain factory, the spindle belt slipped during starting and braking. The reason was that the load torque of the spindle was large, and the ramp time of the driving device was set too small, but it was normal after adjustment.
Optimization adjustment is a comprehensive adjustment method that systematically achieves the best match between the servo drive system and the dragged mechanical system. The method is very simple. Use a multi-line recorder or a dual-trace oscilloscope with storage function. Observe the response relationship between the command and speed feedback or current feedback. By adjusting the proportional coefficient and integral time of the speed regulator, the servo system can achieve the best working state with high dynamic response characteristics without oscillation. When there is no oscilloscope or recorder on site, according to experience, adjust to make the motor start to vibrate, and then slowly adjust it in the reverse direction until the oscillation is eliminated.
4. Spare parts replacement method: Use good spare parts to replace the diagnosed bad circuit board, and perform corresponding initialization startup to put the machine tool into normal operation quickly, and then repair or return the bad board. This is the most common troubleshooting method.
5. Method to improve power quality: Generally, a regulated power supply is used to improve power fluctuations. For high-frequency interference, capacitor filtering can be used to reduce power board failures through these preventive measures.
6. Maintenance information tracking method: Some large manufacturing companies continuously modify and improve system software or hardware based on accidental failures caused by design defects in actual work. These modifications are continuously provided to maintenance personnel in the form of maintenance information. Use this as a basis for troubleshooting to troubleshoot correctly and thoroughly.
diagnosis method
The electrical fault diagnosis of CNC machine tools has three stages: fault detection, fault judgment and isolation, and fault location. The first stage of fault detection is to test the CNC machine tool to determine whether there is a fault; the second stage is to determine the nature of the fault and isolate the faulty component or module; the third stage is to locate the fault to a replaceable module or printed circuit board circuit boards to shorten repair time. In order to detect system faults in time, quickly determine the location of the fault and eliminate it in time, fault diagnosis should be as few and simple as possible, and the time required for fault diagnosis should be as short as possible. For this purpose, the following diagnostic methods can be used:
1. Intuitive method
Use your sense organs to pay attention to various phenomena when a malfunction occurs, such as whether there are sparks or bright lights during the malfunction, whether there are abnormal sounds, whether there is abnormal heat, and whether there is a burnt smell, etc. Carefully observe the surface condition of each printed circuit board that may fail to see whether there are signs of burns and damage to further narrow the scope of inspection. This is the most basic and commonly used method.
2. Self-diagnosis function of CNC system
Relying on the CNC system's ability to quickly process data, multi-channel and rapid signal collection and processing are performed on the error location, and then the diagnostic program performs logical analysis and judgment to determine whether there is a fault in the system and locate the fault in a timely manner. The self-diagnostic functions of modern CNC systems can be divided into the following two categories:
1) Power-on self-diagnosis Power-on self-diagnosis means that from each time power is turned on until it enters the normal operating preparation state, the system's internal diagnostic program automatically executes the CPU, memory, bus, I/O unit and other modules, printed circuit boards, Functional testing of CRT units, photoelectric readers, floppy disk drives and other equipment before operation to confirm whether the main hardware of the system can work normally.
2) Fault information prompts: When a fault occurs during machine tool operation, the number and content will be displayed on the CRT display. According to the prompts, consult the relevant maintenance manual to confirm the cause of the failure and the troubleshooting method. Generally speaking, the richer the fault information prompted by the CNC machine tool diagnostic function, the more convenient it is for fault diagnosis. However, it should be noted that for some faults, the cause of the fault can be directly confirmed based on the fault content prompts and consulting the manual; while for some faults, the real cause does not match the fault content prompts, or one fault shows multiple fault causes, which requires maintenance personnel to Find out the inner connection between them and indirectly confirm the cause of the failure.
3. Data and status check
The self-diagnosis of the CNC system can not only display fault alarm information on the CRT display, but also provide machine tool parameters and status information in the form of multi-page "diagnostic addresses" and "diagnostic data". Common data and status checks include parameter checks and There are two types of interface checks.
1) Parameter check The machine tool data of CNC machine tools are important parameters obtained through a series of tests and adjustments, and are the guarantee for the normal operation of the machine tool. These data include gain, acceleration, profile monitoring tolerance, backlash compensation value, screw pitch compensation value, etc. When subjected to external interference, data will be lost or confused, and the machine tool will not work properly.
2) Interface check The input/output interface signals between the CNC system and the machine tool include the interface input/output signals between the CNC system and the PLC, and the PLC and the machine tool. The input/output interface diagnosis of the CNC system can display the status of all switching signals on the CRT display, using "1" or "0" to indicate the presence or absence of the signal. The status display can be used to check whether the CNC system has output the signal to the machine tool. Whether signals such as switch values on the machine tool side and the machine tool side have been input to the CNC system, so that the fault can be located on the machine tool side or in the CNC system.
4. Alarm indicator light shows fault
Within the CNC system of modern CNC machine tools, in addition to the above-mentioned "software" alarms such as self-diagnosis functions and status displays, there are also many "hardware" alarm indicators, which are distributed on power supplies, servo drives, input/output and other devices. According to The indications of these warning lights can determine the cause of the malfunction.
5. Spare board replacement method
Using a spare circuit board to replace a template with suspected faults is a quick and easy way to determine the cause of the fault. It is often used in functional modules of CNC systems, such as CRT modules, memory modules, etc. It should be noted that before replacing the spare board, the relevant circuits should be checked to avoid damage to the good board due to short circuit. At the same time, you should also check whether the selector switch and jumper on the test board are consistent with the original template. For some templates, you should also pay attention to the template. Adjustment of upper potentiometer. After replacing the memory board, the memory should be initialized according to the system requirements, otherwise the system will still not work properly.
6. Exchange method
In CNC machine tools, there are often modules or units with the same functions. By exchanging the same modules or units with each other and observing the failure transfer situation, the location of the fault can be quickly determined. This method is often used for fault detection of servo feed drive devices, and can also be used for the interchange of identical modules in the CNC system.
7. Tapping method
The CNC system is composed of various circuit boards. Each circuit board will have many solder joints. Any weak soldering or poor contact may cause failure. When gently tapping circuit boards, connectors or electrical components with suspected faults with an insulator, if a fault occurs, the fault is likely to be at the location where the fault was struck.
8. Measurement comparison method
For the convenience of detection, the module or unit is equipped with detection terminals. Using instruments such as multimeters and oscilloscopes, the levels or waveforms detected through these terminals can be compared with the normal values ​​and the values during the fault to analyze the cause and condition of the fault. The location of the fault. Due to the comprehensive and complex characteristics of CNC machine tools, there are many factors causing failures. Sometimes several of the above fault diagnosis methods need to be applied at the same time to comprehensively analyze the fault and quickly diagnose the fault location to eliminate the fault. At the same time, some fault phenomena are electrical, but the cause is mechanical; conversely, the fault phenomenon may be mechanical, but the cause is electrical; or both. Therefore, its fault diagnosis often cannot be simply attributed to electrical or mechanical aspects, but must be comprehensively considered.