The value of CNC machine tools ranges from several hundred thousand yuan to ten million yuan. It is generally the key equipment for key processes in key products of enterprises. Once the machine is shut down, its impact and losses are often great. However, people tend to pay more attention to such equipment, not only paying less attention to rational use, but also paying too little attention to their maintenance and repair work. It mainly studies the maintenance and preventive measures for common faults of CNC machine tools. Common maintenance methods for CNC machine tools CNC equipment maintenance is a very complicated and high-tech work. CNC equipment is quite different from ordinary equipment. Using the self-diagnosis function of the numerical control system, the general CNC system has a relatively complete self-diagnosis system. Whether it is a FANUC system or a Siemens system, the CNC system can make a certain range of self or interface to itself or during operation. diagnosis. Maintenance personnel should be familiar with the system self-diagnosis of various alarm information. According to the specification, the fault range is determined to locate the faulty components. For the imported CNC system, the board level can only be positioned to the board level. The chip level maintenance can generally rely on the after-sales maintenance department of each CNC system. Logical search using the plc program Now the general CNC control system has a PLC controller, mostly built-in PLC control. The maintenance personnel should analyze the machine control electric appliance according to the ladder diagram, and visually see the state of the CNC system I/O on the CRT. Through the logic analysis of the PLC program, it is convenient to check the existence of the problem, such as the self-diagnosis page in the FANUC-OT system. According to the drawing PLC ladder diagram, the interface between the machine tool and the CNC system is faulty to determine whether the fault location is mechanical, electrical, hydraulic or pneumatic. Full communication with the operators on the spot The on-site operator is the closest partner of CNC machine tools, and the operator is also the first discoverer of various faults. Therefore, when the fault occurs, the maintenance personnel should generally not rush to start the operation. First, they should fully communicate with the operator. They should carefully inquire about the working state, the form of the machine, the consequences, and whether the fault occurred during the fault. Reproduction, etc., which helps maintenance personnel to quickly analyze and determine the cause of the malfunction. Anti-jamming measures for CNC machine tools The CNC system of the machine tool contains both high-voltage and high-current high-power equipment, as well as low-voltage, low-current control and signal processing equipment, that is, weak current equipment. The strong electromagnetic interference generated by strong electrical equipment poses a great threat to the normal operation of weak electrical equipment. In addition, the electromagnetic environment at the production site where the system is located is relatively harsh. The interference of various power loads outside the system, the interference of the power supply system, and the interference of electromagnetic waves in the atmosphere can seriously affect the weak electrical equipment in the system, because the weak electrical equipment is strong. Electrical equipment, so once the weak electrical equipment is disturbed, it will eventually lead to paralysis of the entire system.
Generally, measures are taken from the following aspects to improve the disturbance interference capability of the numerical control system. To reduce the interference of power supply lines and signal lines, the following measures can be taken: (1) CNC machine tools are far away from equipment with medium and high frequency power supplies.
(2) CNC machine tools should not be powered by the same power supply line with high-power and frequent start-stop devices.
(3) Install an AC voltage regulator for the undervoltage, overvoltage and voltage fluctuations of the grid voltage for a long time.
(4) Use a power supply filter. The role of the line filter is two-way. It not only prevents noise in the grid from entering the device, but also suppresses noise generated by the device from contaminating the grid.
(5) Use an isolation transformer with a shield. The isolation transformer is a widely used power supply anti-interference device. Its most basic function is to achieve electrical isolation between the circuit and the circuit to solve the interference between the device and the device.
(6) The wiring of the analog signal transmission line should be as short as possible and shielded lines should be used.
(7) The output signals of the photoelectric encoder, the manual pulse generator, the grating scale, etc. are connected in parallel at the receiving circuit to suppress high-frequency interference. The shield of the photoelectric encoder cable is grounded at both ends.
(8) The motor drive cable shield is grounded at both ends.
(9) The power line and the signal line are separately routed.
(10) The control signal line is shielded twisted pair. To reduce the interference in the machine's electrical control system, the following measures can be taken: (1) In the power input part, the varistor protection (surge absorber) suppresses noise such as transients and sharp bees in the line.
(2) The inductive load is equipped with an absorbing circuit to suppress transient noise. Inductive loads in the system, such as relays, contactors, electromagnetic cymbals, motors, etc., generate strong impulse noise when turned off, affecting the normal operation of other circuits, and must add an absorbing circuit at the inductive load to suppress transient noise. The DC inductive component (DC relay coil) is connected in parallel with the two-way tube. AC contactor, solenoid valve, relay coil parallel RC RC absorber. A RC RC absorber is connected in parallel between the armature windings of the three-phase AC motor.
(3) Guarantee a good "grounding". “Grounding†is a key anti-jamming technology in the installation of CNC machine tools. The control equipment in the numerical control system and the electrical cabinet must be “grounded†according to the requirements of the instruction manual. Otherwise, many interference factors in the power grid will interfere with the operation of the machine through the “groundâ€. CNC machine tool inspection Because CNC machine tools integrate machine, electricity, liquid, gas and other technologies, it must have scientific management of its maintenance, and purposefully develop corresponding rules and regulations. The hidden troubles discovered during the maintenance process should be cleared in time to avoid downtime and repair, thus prolonging the average time between failures of equipment and increasing the utilization rate of the machine. Carrying out inspections is an effective way to maintain CNC machine tools.
The maintenance of equipment based on inspections is an inspection management system developed on the basis of the introduction of the preventive maintenance system in the United States. The inspection is to perform fixed-point, regular inspection and maintenance of the equipment in accordance with the provisions of the relevant maintenance documents. The advantage is that the occurrence of faults and performance degradation can be eliminated in the bud, (information source: http://) to prevent over-repair or under-repair, the disadvantage is that the regular inspection work is large. This modern maintenance management system with the inspection as the core in the operation phase of the equipment can achieve the purpose of reducing the failure rate and maintenance cost and improving the maintenance efficiency.
The inspection of CNC machine tools is the basis for the development of condition monitoring and fault diagnosis, and mainly includes the following contents:
(1) Fixed point: First, determine how many maintenance points a CNC machine tool has, scientifically analyze the equipment, and identify the parts that may be faulty. As long as you look at these maintenance points, you will find them in time.
(2) Calibration: Each maintenance point should be standardized one by one, such as clearance, temperature, pressure, flow, tightness, etc., must have a clear quantity standard, as long as it does not exceed the specified standard, it is not a failure.
(3) Regular: How often to check, to set the inspection cycle. Some points may be checked several times per shift, and some points may be checked once or several months, depending on the circumstances.
(4) Fixed items: Each maintenance point should check which items are also clearly defined. Each point may check one item or several items.
(5) Personification: Who should carry out the inspection, whether it is the operator, maintenance personnel or technical personnel, should be implemented according to the inspection site and technical accuracy requirements.
(6) Fixed method: How to check if there is a rule, whether it is manual observation or instrumental measurement, whether it is ordinary instrument or precision instrument.
(7) Inspection: The environment and steps to be inspected shall be specified, whether it is checked during production or stopped, whether it is disintegrated or not disintegrated.
(8) Record: The inspection should be recorded in detail and clearly filled out in the prescribed format. To fill in the inspection data and its difference with the specified standards, judgment impressions, and handling opinions, the inspector should sign and indicate the inspection time.
(9) Processing: Check that the intermediate processing and adjustment should be processed and adjusted in time, and record the processing results. If there is no ability or no condition to deal with, it is necessary to promptly report the relevant personnel and arrange for handling. However, any person, at any time, must fill in the processing record.
(10) Analysis: The inspection records and processing records should be systematically analyzed regularly to find weak “maintenance pointsâ€, that is, points with high failure rate or large loss points, and put forward opinions and design designers to improve the design.
The inspection of CNC machine tools can be divided into two levels: daily inspection and full-time inspection. The daily inspection is responsible for checking the general parts of the machine, and processing and checking the faults that occur during the operation of the machine, which are carried out by the machine operator. The full-time inspection is responsible for the key inspection of the key parts and important parts of the machine tool, the monitoring of the equipment status and the diagnosis of the equipment, the development of the inspection plan, and the diagnosis record. Analyze the maintenance results and propose suggestions for improving equipment maintenance management, which will be carried out by full-time maintenance personnel. As a work system, the inspection of CNC machine tools must be carried out carefully and held in order to ensure the normal operation of the machine.
From the requirements and contents of the inspection, the inspection can be divided into three levels: full-time inspection, daily inspection and production inspection, and the schematic diagram of the CNC machine inspection and maintenance process. 1 Full-time inspection is responsible for the key inspection and preparation of state monitoring and fault diagnosis and fixed point inspection plan for key parts and important parts of the machine tool, making diagnostic records, analyzing maintenance results, and proposing suggestions for improving equipment maintenance management. 2 Daily inspection is responsible for checking the general parts of the machine, handling and checking the faults that occur during the operation of the machine. 3 Production inspection is responsible for the inspection of CNC machine tools in production operation, and is responsible for lubrication, fastening and other work. As a work system, the inspection must be carried out carefully and persevered in order to ensure the normal operation of the CNC machine.
Detailed records from the occurrence of faults, analysis and judgment to the elimination of various problems in the whole process, various measures taken, related circuit diagrams, related parameters and related software involved, and error analysis and troubleshooting methods should also be recorded and recorded. The reason for its invalidity. Summarize the various types of drawings and texts required in the troubleshooting process. If there are any deficiencies, you should find ways to fill them up later, and study them in the following days for future needs.
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