For any CNC machine tool to work continuously and reliably for a long time, in addition to the quality factor of the machine tool itself, it is closely related to the correct maintenance, timely troubleshooting and timely maintenance during use. From the point of view of improving the effectiveness of CNC machine tools, maintenance should include two aspects: one is daily maintenance (preventive maintenance), which is to extend the MTBF of the machine’s mean time between failures; on the other hand, it is fault repair. The aim is to minimize the mean time to repair MTTR. Doing these two tasks is the basic guarantee for fully utilizing the equipment’s effectiveness.
In order to give full play to the benefits of CNC machine tools, it is important to do preventive maintenance, make the CNC system less faulty, and improve the average trouble-free working time of the system. In addition, you should always be prepared for maintenance, and repair it in time when the system fails, in order to minimize downtime. This requires that you must be familiar with the structure and performance of the equipment, familiar with the structure and basic operation of the CNC system, understand the inspection points available for maintenance on the printed circuit board used in the system, and master the normal level and waveform for comparison and analysis during maintenance failure. . In addition, the technical data and original setting parameters of the CNC system and programmable controller (PLC) should be properly preserved, and the typical part programs commonly used. Depending on the actual use, some vulnerable parts such as fuses, brushes, and easily defective transistor modules and printed circuit boards can be provided. For the standby circuit board, it should be installed on the CNC system on a regular basis to avoid malfunction due to long-term use.
The key to preventive maintenance is to strengthen daily maintenance and maintenance. The following should usually be done:
1. The CNC system programming, operation and maintenance personnel equipped for CNC machine tools should be familiar with the mechanical structure, numerical control device, high-voltage equipment, hydraulic system, gas circuit and other parts of the equipment used, as well as the specified use environment and processing conditions. Wait. And strictly follow the requirements of the machine tool and numerical control device instruction manual to use the machine tool correctly and reasonably, try to avoid malfunction caused by improper operation.
2. Many systems use a paper tape reader as the input device of the program. The paper tape information such as system parameters and part processing programs must be input into the CNC system through the tape reader. If the tape reading portion of the tape reader (that is, the light-emitting and light-receiving portions of the reading head) is dirty, the read tape information may be erroneous, so that the surface of the reading head, the paper tape pressing plate, and the paper tape channel surface Always check and remove dirt in time. The moving parts of the tape reader, such as the driving roller, the guiding roller pressing roller, the tensioning arm roller, etc., should be cleaned frequently and ensure good lubrication.
3. Clean the air filter regularly. When the air filter installed on the numerical control cabinet and the electrical cabinet door has a lot of dust, the cooling air in the cabinet will not flow smoothly. If this is the case for a long time, the temperature inside the cabinet will rise and the system will not work reliably. Therefore, it should be checked regularly according to the use environment, and at least once every six months. The specific method is as follows: first remove the fastening screw, take out the inner core of the air filter, and use compressed air to blow off the dust on the filter element from the inside out. If the filter is dirty, you can also gently vibrate the filter at the same time. If the above method does not work, you can use a neutral detergent (5% detergent ratio) to rinse, but do not rub, then put the filter in a cool, ventilated place to dry Just do it. 4. Regular battery maintenance. For numerical control devices that use CMOS memory to store system parameters, in order to avoid loss of parameters during shutdown and power failure, battery power is used to maintain. When the battery voltage is lower than the CMOS hold voltage, the battery can be automatically charged when the machine is turned on. Under normal circumstances, the battery can ensure that the information is saved for more than 1000h after the power is cut off. When the machine is shut down for a long time, it should be powered on regularly according to the requirements of the manual to make the battery replenish power. If such a numerical control device displays a battery failure alarm on the CRT or with an indicator light, it indicates that the voltage is too low, the battery has failed, and a new battery needs to be replaced. In order to save the original data, the battery should be replaced with the power on, and the polarity of the battery should not be reversed.
5. The DC servo motor should be inspected and cleaned regularly. The DC servo motor is equipped with a brush, which wears and wears in contact with the commutator during operation. Excessive wear of the brush will affect the working performance of the motor and even damage the motor, so it must be checked and replaced regularly. For general machine tools such as CNC lathes, CNC milling machines and machining center machines, they can be inspected once a year. For machines that frequently perform acceleration and deceleration, such as punching machines, they should be inspected every two months. When checking, disconnect the CNC system power supply and the motor is completely cooled. First remove the brush cover, take out the brush, and measure the length. Under normal circumstances. When the brush wears to half of the original length, it should not be used any more, and the new brush of the same model must be replaced. The second step should carefully check whether the curved contact surface of the brush and the commutator has deep grooves or cracks, and whether the brush spring has any ignition marks. If the above phenomenon occurs, the surface of the commutator must be carefully checked. If the commutator is normal, replace the new brush and check again after one month; if the above phenomenon occurs, consider whether the motor’s working conditions are excessively bad and the motor itself is faulty. Before installing a new brush, clean the brush hole with clean compressed air that does not contain metal powder and moisture. Be sure to blow the brush powder that sticks to the hole wall. If it is difficult to blow, use a screwdriver or other tools to assist in cleaning until the walls of the holes are all clean. However, care should be taken to avoid damage to the commutator surface and the hole wall. Finally, the new brush is loaded, the brush cover is tightened, and the servo motor runs dry for a while, so that the new brush surface matches the commutator. 6, pay attention to the closed CNC cabinet door. Under normal circumstances, it should be avoided to open the CNC cabinet door at will, especially for long-term open door operation. The air filter should be cleaned in time. And you can never use the method of opening the door to dissipate heat, otherwise it will not be worth the candle. Because a lot of dust, oil mist and metal powder float in the air in the workshop, these impurities fall on the printed circuit board and electronic components, which easily cause the insulation resistance of the components to drop and cause malfunctions, even the components and printing. The board is damaged and scrapped. Especially for the CNC machine tools that install the spindle control system in the power cabinet, if the power cabinet door is not closed or the seal is poor, it is easy to cause damage to the electrical components and the spindle control is out of order.
7. Regularly clean the cooling device to enhance the heat dissipation effect. Some servo motors or spindle motors have forced cooling devices on the casing. If the protection net or heat sink of the cooling device is dirty, affecting the circulation of air, the cooling capacity will be reduced, and the heat loss will cause malfunction. Therefore, these cooling devices should be cleaned regularly. If the protective net is too dusty to interfere with ventilation, it can be removed for cleaning. When the heat sink has a lot of dust, it can be blown off with compressed air or with a thin rod. Drain the dust in the middle of the heat sink. However, care should be taken during operation. Do not crush and dissipate the heat sinks, so as not to affect the heat dissipation effect. The above-mentioned cleaning cycle is generally once every six months, and may be appropriately shortened according to specific circumstances.
8. For CNC machine tools that are not used for a long time, the CNC system should be energized frequently, and it can be run empty when the machine is locked. In the southern plum rain season where the air humidity becomes larger, it should be energized every day, and the heat emitted by the electrical components itself is used to drive out the moisture in the numerical control cabinet. To ensure the stability and reliability of the circuit performance. Practice has proved that the machine tools that are not used after passing through Huangmeitian are often prone to various types of failures. If the CNC machine tool is idle for more than half a year, the brush of the DC servo motor should be taken out to avoid corrosion of the commutator surface due to chemical action, the commutation performance is deteriorated, and even the motor is damaged.
9. For parts that frequently move on the machine, whether it is mechanical or control, it should be checked regularly. For example, in CNC machine tools, in order to ensure the reliability of the machine work, a number of travel switches that limit the position of the motion are used. The reliability of these travel switches directly affects the operational reliability of the whole machine. In addition, the mechanical and electrical structure of the automatic tool changer on the machine tool is relatively complicated, and it is a place where it is prone to failure. Therefore, the electrical system that controls the selection and positioning of the tool magazine and the operation status of the travel switch that detects the running position of the robot should be checked frequently. To ensure that the machine works properly.
Any CNC machine tool will inevitably experience wear and failure after long-term operation, but extend the working life of components, prolong the wear cycle of machine components, prevent accidental malignant accidents, and strive for reliable operation of machine tools for a long time. The purpose of preventive maintenance and maintenance of machine tools. General machine tool manuals have specific requirements for maintenance inspection, and should be operated in strict accordance with the regulations.
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