When maintaining CNC machine tools, it is often found that there is power failure, and the power control line of some systems is more complicated than that of direct power supply system. The following is the analysis paper of CNC machine tool fault and maintenance that I collected for you, hoping to help you.
This paper first summarizes the common faults of modern CNC machine tools, then introduces the basic methods of fault diagnosis, and then puts forward the maintenance principles and specific methods for the diagnosed faults, hoping to provide effective suggestions for the diagnosis and maintenance of CNC machine tools.
Keywords: alarm fault of CNC machine tool, reset of CNC PLC
CNC machine tool is a high-tech intensive electromechanical equipment integrating mechanical, electronic and electrical, hydraulic, pneumatic, optical and computer technologies. Therefore, the efficiency is high and the cost is high. When a fault occurs, it is also difficult to diagnose and may even lead to downtime. These devices are often in the key processes of key positions, and once they fail, they will cause huge losses to enterprises. Although the reliability of numerical control system is getting higher and higher now, due to the changes of operation and external environment, failures will inevitably occur. In order to strengthen the use management and maintenance of numerical control equipment, reduce the failure rate, summarize common failures, adopt correct fault diagnosis methods, repair and eliminate failures in time, shorten the fault maintenance time, and make the machine tool resume work as soon as possible, which is an important problem for mechanical workers.
First, the common faults of modern CNC machine tools
(1) Power failure
When maintaining CNC machine tools, it is often found that there is power failure, and the power control line of some systems is more complicated than that of direct power supply system. Maintenance according to the schematic diagram is the most effective and reliable method. On some machine tools, due to the need of machine tool interlocking, external power-off signals are used. At this time, the fault causes should be comprehensively analyzed according to the electrical schematic diagram of the machine tool, and the external power failure factors can be eliminated before starting.
(2) The system has an alarm display fault.
Software alarm display failure: the alarm number and alarm information displayed on the display of CNC system are software alarm display. Because the numerical control system has self-diagnosis function, once a fault is detected, it will be handled according to the fault level, and the alarm information and alarm number will be displayed on the display. Software alarm can be divided into PLC alarm and NC alarm. The alarm information of the former comes from the alarm text compiled by the machine tool manufacturer, and most of them belong to the fault alarm of the machine tool side. When this kind of fault occurs, it can be diagnosed according to the alarm information or PLC user program. The latter is the fault alarm of the numerical control part. The cause and treatment of this alarm can be found in the maintenance manual of CNC system through the alarm number, so as to determine the possible cause of the fault.
B. Hardware alarm display failure: Hardware alarm display usually refers to the alarm indication of indicator lights on each unit equipment. In the numerical control system, there are many indicator lights used to indicate faulty components, such as control system operation panel, servo control unit, CPU motherboard and other components. Once these indicators indicate the fault state in the CNC system, the location and nature of the fault can be roughly judged according to the alarm meaning of the indicators on the corresponding parts, which will bring great benefits to fault analysis and diagnosis. Therefore, maintenance personnel should pay attention to check whether the status of these indicators is normal during daily maintenance and fault maintenance.
(3) Fault-free alarm display of the system
This kind of fault occurs without any software and hardware alarm display, which brings difficulties to analysis and diagnosis. Generally speaking, the failure without alarm display is mostly caused by hardware failure, except for public power supply, which is generally caused by poor connection. Therefore, it is necessary to check the connecting cable between the system and the monitor and the monitor itself. Display confusion or abnormal display is usually caused by software errors in the system; However, the specific problems still need to be analyzed in detail, and the diagnosis must be analyzed according to the specific fault phenomenon, machine tool working principle, CNC system working principle, PLC ladder diagram and maintenance experience.
(4) CNC device failure
A, CNC device software failure: some machine tool failures are due to problems in processing programs, and some failures are due to improper data setting of machine tools. Such a fault belongs to a software fault. As long as the cause of the fault is found and modified accordingly, the fault will be eliminated.
B. Hardware failure of numerical control device: Some machine tool failures are caused by hardware problems of control system, and such failures can only be eliminated after replacement or maintenance. For example, the display screen of a CNC lathe does not show the failure of this mechanism, but checks that the input power of the power module of the machine tool control system is normal, but there is no 5V voltage on the power module, indicating that the power module is damaged, and it can work normally as long as the machine tool is repaired.
(5) partial failure of PLC
Due to the programming problem of PLC users, the fault occurred when the CNC machine tool was running. In addition, if PLC user programming is unscientific, it will also cause some machine side faults not to alarm, so PLC user programming is very important.
Because there is something wrong with the PLC input and output module, it is a hardware failure that cannot work normally. When individual input/output ports fail, the PLC program can be modified for maintenance, or the failed interface can be replaced with a standby interface to achieve the purpose of troubleshooting.
Second, the basic method of fault diagnosis of CNC machine tools
Fault diagnosis is the first step of CNC machine tool maintenance. It can not only quickly find out the cause of the fault, eliminate the fault, but also prevent the occurrence and expansion of the fault. Generally speaking, the fault diagnosis methods of CNC machine tools mainly include the following:
(A) conventional diagnostic methods
Routine inspection of mechanical, electrical and hydraulic parts of CNC machine tools usually includes:
First, check the specifications of the power supply (including voltage, frequency, phase sequence, capacity, etc.). ) meets the requirements; Secondly, check whether the connection of CNC, servo drive, spindle drive, motor and input/output signal is correct and reliable; Thirdly, check whether the printed circuit board in CNC, servo drive and other equipment is firmly installed and whether the plug-in is loose; Fourth, check whether the settings and adjustments of CNC, servo drive, spindle drive and potentiometer are correct; Fifth, whether the oil pressure and air pressure of hydraulic, pneumatic and lubricating parts meet the requirements of machine tools; Sixth, whether the electrical components and mechanical parts are obviously damaged.
(2) state diagnosis method
The cause of the failure is determined by monitoring the working state of the actuator. In modern CNC system, the dynamic and static detection of main parameters of servo feed system, spindle drive system, power supply module and all input and output signals of CNC system, including internal relays and timers, can also be checked by diagnostic parameters of CNC system.
(3) Action diagnosis method
By observing and monitoring the actual movement of the machine tool, the bad parts of the movement can be judged and the fault source can be traced.
(D) System self-diagnosis method
This is a diagnostic method that uses self-diagnostic program or special diagnostic software to self-diagnose and test the key hardware and control software in the system. It mainly includes three aspects: starting self-diagnosis, online monitoring and offline testing.
Three, the basic principles of CNC machine tool maintenance
Generally speaking, the maintenance of CNC machine tools must first follow some basic principles, which will often lead to clear thinking and get twice the result with half the effort. (1) Think before you do it.
For CNC machine tools with faults, we should not rush to start work, but should first understand the process and phenomenon of faults. For unfamiliar equipment, we should also be familiar with the circuit principle and structural characteristics and abide by the corresponding rules. Before disassembly, you should be fully familiar with the function, location, connection mode of each component and its relationship with other surrounding equipment. In the absence of an assembly drawing, you should draw a sketch and mark it when disassembling.
(2) First external, then internal
Check the equipment for obvious cracks and defects, understand its maintenance history and service life, and then check the inside of the machine. Before disassembly, the peripheral fault factors should be eliminated, and the disassembly can only be carried out after the internal fault is determined, otherwise the fault will be enlarged, the machine tool will lose precision and the performance will be reduced.
(3) machinery precedes electricity
After confirming that the mechanical parts are trouble-free, electrical inspection should be carried out. When checking the circuit fault, it is necessary to find the fault position with testing instruments. After confirming that there is no poor contact fault, it is necessary to check the operation relationship between the circuit and the machinery in a targeted manner to avoid misjudgment.
(d) Static before dynamic.
Firstly, check whether the cable plug-in is installed according to the interface specification, and whether the cable and module connector are firm and consistent for the CNC machine tool in the debugging stage or just after maintenance under the static state of machine tool power failure; Whether the circuit board is connected correctly; Whether the devices on all integrated circuits are normal without deformation, etc. Old equipment that has been idle for a long time or lacks maintenance will cause obvious faults such as signal transmission interruption due to cable fatigue damage and oxidation corrosion of connection points.
(5) Cleaning before maintenance
For seriously polluted CNC equipment, first clean its buttons, connection points and contacts. Check whether the external control key is faulty. Many faults are caused by dirt and conductive dust. Once cleaned, faults are often eliminated.
(6) Power supply in front of equipment
The failure rate of power supply is very high in the whole faulty equipment, so it is often twice the result with half the effort to repair the power supply first.
(seven) after the replacement of the first row of patients.
Don't rush to replace damaged electrical components. After confirming that the peripheral circuit is normal, consider replacing the damaged electrical components.
(8) Simple before complex
When a variety of faults are intertwined and hidden, and cannot be started for a while, the easy problem should be solved first, and then the difficult problem should be solved. Often after simple problems are solved, difficult problems may become easier.
Fourth, the maintenance method
In the maintenance of CNC machine tools, the choice of maintenance methods is not in place, which directly affects the quality of machine tool maintenance. Maintenance methods often used in the maintenance process are as follows:
(A) the initial reset method
When the instantaneous fault causes the system alarm, the fault can be cleared by hardware reset or switching the system power supply in turn. If the working storage area of the system is chaotic due to power failure, unplugging the circuit board or battery undervoltage, the system must be initialized and cleared, and the data copy record should be made before clearing. If the fault cannot be eliminated after initialization, hardware diagnosis should be carried out.
(B) parameters change, the program is more correct
System parameters are the basis of determining system functions. Wrong parameter setting may cause system failure or a function is invalid. Sometimes user program errors can also cause downtime, and all errors can be checked and corrected through the system search function to ensure its normal operation.
(3) Adjust and optimize the adjustment method
Adjustment is the simplest way to correct system failure by adjusting potentiometer.
(4) Replacement method of spare parts
Replacing the diagnosed bad circuit board with good spare parts, and carrying out corresponding initialization and startup, so that the machine tool can be put into normal operation quickly, and then repairing or repairing the bad circuit board is the most commonly used troubleshooting method at present.
(E) Improve the power quality laws.
At present, regulated power supply is generally used to improve power supply fluctuation. Capacitance filtering method can be used for high frequency interference, and these preventive measures can reduce the failure of power board.
refer to
Ren Jianping. Fault diagnosis and maintenance of modern CNC machine tools [M]. Beijing: National Defense Industry Press, 200 1.
Han Hongluan, Rong. Structure and maintenance of CNC machine tools [M]. Beijing: Machinery Industry Press, 2004.
Wang. Troubleshooting methods and examples of CNC machine tools [J]. Heavy Machinery Technology, 2006, (4): 40-4 1.
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