Preventive maintenance of CNC equipment

Preventive maintenance is to pay attention to removing factors that may cause equipment failures and difficult to solve after failures before the failure occurs. Generally speaking, it should include: equipment selection, correct use of equipment and roving inspections during operation.
①From the perspective of maintenance, the selection of CNC equipment

In the selection and investigation of equipment, in addition to equipment availability parameters, its maintainability parameters should include: equipment advancement, reliability, maintainability technical indicators. Advancement means that the equipment must have the technical content of the development level of the times; reliability means the mean time between failures and the mean failure rate of the equipment, especially whether the control system has passed the quality inspection assessment of the national authority; maintainability means its Whether it is easy to repair, whether there is a good market to buy spare parts, whether the technical information for various repairs is complete, whether there is good after-sales service, whether the repair technical ability is available, and whether the equipment performance and price ratio is reasonable.

Special attention should be paid to the integrity of the drawings and data, the backup system disk, the PLC program software, the system transmission software, the transmission means, and the operation password, etc., all of which are indispensable. The technical training for the user cannot go through the scene, these must be indicated in the order contract and implemented carefully, otherwise it will bring troubles to future work. In addition, if it is not a special case, try to use the same series of CNC systems from the same company, so that spare parts, drawings, and data are used. Programming and operation are good, but also conducive to equipment management and maintenance.

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②Insist on the correct use of equipment

The correct use of numerical control equipment is the key to reducing equipment failures and prolonging its service life. It occupies a very important position in preventive maintenance. According to statistics, one third of the failures are caused by man-made, and general maintenance (such as oil injection, cleaning, inspection, etc.) is carried out by the operator. The solution is to emphasize equipment management, use and maintenance awareness, and strengthen Business and technical training, improve the quality of operators, enable them to master machine tool performance as soon as possible, strictly implement equipment operating procedures and maintenance procedures to ensure that the equipment is running in a reasonable working state.

③Persist in roving inspections during equipment operation

According to the advanced nature, complexity and high intelligence of CNC equipment, its maintenance and maintenance work is much more complicated and demanding than ordinary equipment. Maintenance personnel should go through regular inspections, such as the operation of the exhaust fan of the CNC system, whether the cabinet or motor is hot, whether there is abnormal sound or smell, whether the pressure gauge is normal, whether the pipeline and joints are leaking, and whether the lubrication status is Good, etc., actively prevent failures and accidents. If abnormalities are found, they should be resolved in time. Only by doing so can the failure be eliminated in the state of eruption, which can reduce all avoidable losses.

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CNC equipment maintenance example

1. Fault diagnosis of CNC system

①System self-diagnosis

General CNC systems have a relatively complete self-diagnosis system, whether it is a FANUC system or a Siemens system, it can make limited self-diagnosis for itself or its interface during power-on initialization or during operation. The maintenance personnel should be familiar with various alarm information of the system self-diagnosis. Analyze according to the specification to determine the scope of the fault. To locate the faulty components, the imported CNC system can only be located at the board level.

②Soft fault of CNC system

The soft fault of the numerical control system refers to the system software and PLC program of the control system. Some systems write them in EPROM and insert them on the motherboard, and some reside on the hard disk. Once there is a problem with these software, the system will cause total or partial chaos. When it is determined that the software is faulty, the spare software or spare EPROM should be used to replace it, and the operation steps should be strictly followed after initialization and trial operation. This type of failure is generally not difficult to recover as long as there is a backup file. The difficulty lies in the fact that the backup software is not complete, the dedicated transmission equipment is not available, or the manufacturer’s operating methods set password confidentiality and other factors that cannot be restored.

③Using the PLC program to locate the interface failure between the machine tool and the CNC system

Now general CNC control systems are equipped with PLC controllers, most of which are built-in PLC control. The maintenance personnel should analyze the control electronics of the machine tool according to the ladder diagram, and visually see the status of the CNC system I/O on the CRT. Through the logic analysis of the PLC program, it is convenient to check the location of the problem. Such as the self-diagnosis page in FANUC-OT system, T command in FANUC-7M system, etc.

2. Troubleshooting steps

① Ask the operator the reason for the failure

When a failure occurs, the maintenance personnel generally do not rush to do it. They should carefully ask what the working state of the machine tool was when the failure occurred, its manifestation, the consequences, and whether it was a misoperation. Can the fault be reproduced?

②Surface and basic power supply inspection

It is mainly to observe whether the equipment is abnormal, such as mechanical jam, motor burnout, fuse blown, etc. First check whether the AC/DC power supply is normal, and minimize the fault range as much as possible.

③Analyze the drawings and determine the fault location

Analyze the PLC ladder diagram according to the drawings to determine whether the fault is mechanical, electrical, hydraulic or pneumatic.

④Expand ideas and analyze based on experience

Based on empirical analysis, we must expand our thinking, not limited to the scope of the maintenance manual, the maintenance information only provides an idea, and sometimes it is very limited. For example, for a FANUC-OT CNC lathe in our factory, the CRT has no screen after it is turned on, and the power module alarm indicator is on. According to the maintenance manual, it is found that the 24EDC power supply shared by the CRT and the I/O interface is only between the positive terminal and the DC ground.

There are 1-2Ω resistors, and similar devices use 155Ω resistors. According to the data, this type of fault is generally on the motherboard and can only be sent to the manufacturer for repair. But we expand our thinking and first unplug the Ml8 cable plug. The fault is still there. Unplug the C-Sl4 plug and there is a short-circuit phenomenon. After removing it, the machine tool returns to normal.