How to carry out preventive maintenance of CNC mac

2022-07-25
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How to carry out preventive maintenance of CNC machine tools

for any CNC machine tool to work continuously and reliably for a long time, in addition to its own quality factors, it is also closely related to the correct maintenance, timely troubleshooting and timely maintenance during use. From the perspective of improving the effectiveness of CNC machine tools, maintenance should include two meanings: one is daily maintenance (preventive maintenance), which is to extend the MTBF of the machine tools; The other is fault maintenance, which aims to minimize the mean time to repair (MTTR). Doing these two tasks well is the basic guarantee to give full play to the equipment efficiency

in order to give full play to the benefits of CNC machine tools, it is important to do a good job in the preventive maintenance of the province's new material industry sales revenue of 78billion yuan in 2013, so as to reduce the number of failures of the CNC system and improve the average trouble free working time of the system. In addition, preparations for maintenance shall be made at any time to repair the system in time in case of failure, so as to minimize the downtime for repair. This requires that you be familiar with the structure and performance of the equipment, the composition and basic operation of the CNC system, the inspection points available for maintenance on the printed circuit board used by the system, and master its normal level and waveform for comparison and analysis in case of maintenance faults. In addition, the technical data, original setting parameters and commonly used typical part programs of CNC system and programmable controller (PLC) shall be properly saved. According to the actual use, some vulnerable spare parts can be properly equipped, such as fuse, brush, transistor module and printed circuit board that are easy to fail. As for the spare circuit board, it shall be installed on the CNC system regularly for power on operation to avoid failure due to long-term use

the key to preventive maintenance is to strengthen the daily maintenance. Generally, the following points should be achieved:

1. The programming, operation and maintenance personnel of the numerical control system digital display impact height system equipped for the numerical control machine tool should be familiar with the characteristics of the mechanical structure, numerical control device, strong current equipment, hydraulic system, air circuit and other parts of the equipment used, as well as the specified use environment, processing conditions, etc. In addition, the machine tool shall be used correctly and reasonably in strict accordance with the requirements of the operation manual of the machine tool and numerical control device, and the failure caused by improper operation shall be avoided as far as possible

2. Many systems use a paper tape reader as the program input device. The system parameters, part processing programs and other paper tape information must be input into the CNC system through the paper tape reader. If there is dirt on the tape reading part of the tape reader (i.e. the light emitting and light receiving parts of the reading head), the read tape information will be wrong. Therefore, the surface of the reading head, the paper tape pressing plate and the surface of the paper tape channel should be checked frequently to remove the dirt in time. The moving parts of the paper tape reader, such as the driving wheel roller, guide roller, compression roller, tension arm roller, etc., shall be cleaned frequently and well lubricated

3. Clean the air filter regularly. When the air filter installed on the door of the numerical control cabinet and the electrical cabinet is dusty, the cooling air in the cabinet will not circulate smoothly. If this happens for a long time, the temperature in the cabinet will rise, so that the system can not work reliably. Therefore, it should be checked regularly according to the service environment, and removed and cleaned at least once every six months. The specific method is as follows: first remove the fastening screws, take out the inner core of the air filter, and use compressed air to blow 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 fails to work, you can use neutral detergent (detergent proportion: 5%), but do not rub it. Then put the filter element in a cool and ventilated place to dry

4. Regularly maintain the battery. For numerical control devices that use CMOS memory to store system parameters, in order to avoid parameter loss during shutdown and power failure, battery power supply is used to maintain. When the battery voltage is lower than the CMOS holding voltage, the battery can be automatically charged when the machine is started. Generally, the battery can ensure that the information can be stored for more than 1000h after power failure. When the machine tool is shut down for a long time, it should also be powered on regularly according to the requirements of the manual to make the battery supplement power. If this kind of numerical control device displays battery fault alarm on CRT or with indicator light, it indicates that the voltage is too low, the battery has failed, and it needs to be replaced with a new battery. In order to save the original data, the battery shall be replaced when the power is turned on, and the polarity of the battery shall not be reversed

5. The DC servo motor shall be inspected and cleaned regularly. The DC servo motor is equipped with an electric brush, which is gradually worn due to contact and friction with the commutator during operation. Excessive wear of the brush will affect the working performance of the motor and even cause damage to 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 machine tools that frequently perform acceleration and deceleration work, such as punch presses, they should be checked every two months. The inspection shall be carried out when the power supply of the CNC system is disconnected and the motor has been completely cooled. First, remove the brush cover, take out the brush, and measure its length. Generally, the brush cover shall be removed. When the brush is worn to half of the original length, it should not be used any more, and a new brush of the same model must be replaced. The second step is to carefully check whether there are deep grooves or cracks on the arc contact surface between the brush and the commutator, and whether the brush spring has spark marks. If there are any of the above phenomena, carefully check the surface of the commutator. If the commutator is normal, replace it with a new brush and check it again after one month; If the above phenomena still occur, it is necessary to consider whether the working conditions of the motor are too bad to cause the motor fault. Before installing a new brush, clean the brush hole with clean compressed air that does not contain metal powder and moisture, and be sure to blow out the brush powder adhered to the hole wall. If it is difficult to purge, tools such as screwdriver can be used to assist in cleaning until the hole wall is completely clean. However, pay attention to avoid damage to the commutator surface and hole wall by the screwdriver tip. Finally, install a new brush, tighten the brush cover, and make the servo motor run in for a period of time, so that the surface of the new brush is consistent with the commutator

6. Pay attention to sealing the CNC cabinet door. In general, it shall be avoided to open the CNC cabinet door at will, especially for long-term open door operation. Clean the air filter in time. And must not use the method of opening the cabinet door to dissipate heat, otherwise the gain is not worth the loss. Because there is a large amount of dust, oil mist and metal powder floating in the air of the workshop, these sundries fall on the printed circuit board and electronic components, which is easy to cause the insulation resistance of components and parts to drop and failure, and even make the components and parts and printed circuit board a kind of damage and scrap produced in batch by our laboratory machine manufacturer. Especially for the CNC machine tool with the spindle control system installed in the strong current cabinet, if the door of the strong current cabinet is not closed tightly or poorly sealed, it is also easy to cause damage to the electrical components and make the spindle control failure

7. Regularly clean the cooling device to enhance the heat dissipation effect. Some servo motors or spindle motors are equipped with forced cooling devices on the casing. If the protection of the cooling device or the heat sink is very dirty, which will affect the air circulation, the cooling capacity will inevitably be reduced, and failures will occur due to heat loss. Therefore, these cooling devices should be cleaned regularly. The specific methods are as follows: if the ventilation is hindered due to too much protective dust, they can be removed for cleaning; When there is a lot of dust on the heat sink, you can use compressed air to blow it away, or use a thin rod to go deep into the middle of the heat sink to remove the dust. However, be careful not to squeeze and deform the heat sink, or overlap it, so as not to affect the heat dissipation effect. The cleaning cycle of the above electronic tensile testing machine is generally once every half a year except for the power interface, which can also be appropriately shortened according to specific conditions

8. For CNC machine tools that are not used for a long time, the CNC system should be powered on frequently to make it run idle when the machine tool is locked. In the southern plum rain season when the air is wet, the power should be turned on every day, and the heat emitted by the electrical components should be used to drive away the moisture in the numerical control cabinet. To ensure the stability and reliability of circuit performance. Practice has proved that machine tools that are not in use are prone to various failures after Huangmei day. If the numerical control machine tool is idle for more than half a year, the brush of the DC servo motor shall be taken out to avoid corrosion of the commutator surface due to chemical action, deterioration of commutation performance, or even damage to the motor

9. For the frequently moving parts on the machine tool, whether from the mechanical or control drive, they should be inspected regularly as a key point. For example, in order to ensure the reliability of the CNC machine tool, many travel switches are used to limit the movement position. The reliability of these travel switches directly affects the working reliability of the whole machine. In addition, the mechanical and electrical structures of the automatic tool change device on the machine tool are complex, which is prone to failure. Therefore, the electrical system that controls the tool selection and positioning of the tool magazine and the working conditions of the travel switch that detects the operating position of the manipulator should be frequently checked to ensure the normal operation of the machine tool

any CNC machine tool will inevitably suffer from wear and failure after long-term operation. However, the purpose of daily preventive maintenance is to prolong the working life of components, prolong the wear cycle of machine parts, prevent the occurrence of unexpected and malignant accidents, and strive for the machine tool to work reliably for a long time. Generally, the operation manual of the machine tool has specific requirements for maintenance and inspection, which should be operated in strict accordance with the regulations

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