Fault diagnosis and maintenance of the hottest CNC

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CNC machine tool fault diagnosis and maintenance

CNC machine tool is a high-tech product integrating high, precision and advanced technology, and integrating machine, electricity, light and liquid. It has many advantages, such as high machining accuracy, stable and reliable machining quality, high production efficiency, strong adaptability, good flexibility and so on. It is widely welcomed in various industries, and it is also paid more and more attention in use. However, as it is an integrated equipment that integrates strong and weak current and controls mechanical manufacturing with digital technology, once some parts of the system fail, the machine tool will be shut down and production will be affected. Therefore, how to correctly maintain the equipment and timely repair in case of failure is the key to ensure the normal production

1 maintenance of CNC machine tools

for CNC machine tools, reasonable daily maintenance measures can effectively prevent and reduce the probability of failure of CNC machine tools

first of all, it is very important to formulate operating procedures and establish work, fault and maintenance files for the specific performance and processing objects of each machine tool. Including maintenance contents and maintenance cycle of functional devices and components

secondly, in general, the air of the workshop contains pollutants such as oil mist, dust and even metal powder. Once they fall on the printed circuit or electronic devices in the CNC system, it is easy to cause the insulation resistance between components to drop, and even the components and printed circuits to be damaged. Therefore, unless necessary adjustment and maintenance are required, it is generally not allowed to open the cabinet door casually, let alone in the process of use

in addition, the electrical voltage of the CNC system should be monitored from time to time. Once it is found that the voltage exceeds the normal working voltage, the system will not work normally, and even cause damage to the internal electronic components of the CNC system. Therefore, when the equipment of the distribution system does not have automatic detection protection, a special person should be responsible for monitoring, and try to improve the stable operation of the distribution system

of course, a very important point is that the CNC machine tool adopts DC feed servo drive and DC spindle servo drive. Pay attention to take the brush out of the DC motor, so as to avoid chemical corrosion, which is the surface corrosion of the commutator, causing damage to the commutation performance and causing damage to the whole motor. This is a very serious and easy fault

2 general fault diagnosis and analysis of CNC machine tools

2.1 inspection

when the equipment cannot work normally, we must first judge the specific location and cause of the fault. We can visually inspect the fault board and carefully check whether there is fuse fusing caused by excessive current, scorching and smoking of components, and whether there is debris circuit breaking, resulting in overcurrent, overvoltage and short circuit of the board. Observe whether the pins of resistance capacitance and semiconductor devices have broken pins, faulty soldering, etc., so as to find some obvious faults, narrow the scope of maintenance, and judge the cause of the fault

2.2 system self diagnosis

the self diagnosis function of the CNC system monitors the working state of the CNC system at any time. Once an abnormal condition occurs, it is the most effective method in maintenance to immediately display the alarm information on the CRT or use the led to indicate the approximate cause of the fault. In recent years, with the development of technology, a new interface diagnosis technology, JTAG boundary scan, has emerged. This specification provides the ability to effectively detect the parts on the circuit board with dense lead spacing, and further improves the self diagnosis ability of the system

2.3 function program test method

function program test method is to compile the common functions and special functions of the NC system into a function test program by manual programming or automatic transformation, send it to the NC system, and then let the NC system run this test program, so as to check the accuracy and reliability of the machine tool in performing these functions, and then determine the possible causes of the failure

2.4 interface signal check

the corresponding fault point can also be found by checking the return signal of the machine tool control system with the programmable controller and comparing it with the correct signal in the interface manual

2.5 replacement method of diagnostic spare parts

with the development of modern technology, the integration scale of the circuit is larger and larger, and the technology is more and more complex. According to the conventional method, it is difficult to locate the fault to a small area. Once the system fails, in order to shorten the downtime, the same or compatible modules can be used to replace and check the faulty modules without diagnostic spare parts. For the maintenance of modern CNC, In more and more cases, this method is used for diagnosis, and then the damaged module is replaced with spare parts to make the system work normally and shorten the fault downtime as much as possible

the above diagnostic methods do not have strict boundaries in practical application. It may be possible to eliminate faults with one method, or multiple methods may be required at the same time. The most important thing is to find the key of the problem indirectly or directly according to the diagnosis results, or repair or replace it and resume production as soon as possible

3 example of fault diagnosis of CNC machine tool

because the driving part of CNC machine tool is the integration of strong and weak electricity, it is the most prone to problems. Therefore, the drive part is briefly introduced: the drive part includes spindle driver and servo driver. When exploring the new development path of plastic granulator technology, it is composed of power module and drive module. The power module is to boost the three-phase AC with transformer to high-voltage DC, while the drive part is actually an inverter, which converts the high-voltage tributary into three-phase AC and drives the servo motor, Complete the movement of servo axes and the operation of spindle. Therefore, this part is most prone to failure. Taking the fault phenomenon of cjk6136 CNC machine tool and 802S CNC system as an example, this paper mainly analyzes the fault maintenance of control circuit and mechanical transmission interface

for example, in the machining process of CNC machine tools, sometimes the spindle can return to the reference point and sometimes it cannot. On the CNC operation panel, the spindle speed is sometimes not displayed, and the spindle operates normally. The analysis of the cause of the failure shows that the machine tool adopts frequency conversion speed regulation, and its speed signal is provided by the encoder, so the possibility of encoder damage can be ruled out, otherwise the speed signal cannot be transmitted at all. Only the encoder and its connecting unit have problems. There are two aspects to consider, one is that the ECU connected with the CNC system may be loose, and the other is that there may be problems with the mechanical connection with the spindle. From this, we can start to solve the problem. First, check the connection between encoder and ECU. If there is no problem, remove the encoder and check whether the connecting key between the main drive and the encoder is separated from the keyway. It is found that this is the problem. Fix and reinstall the problem

there are various reasons for the failure of CNC machine tools, including mechanical problems, problems of CNC system, problems of sensor elements, problems of driving elements, problems of strong current parts, problems of line connection, etc. In the maintenance process, we should analyze the possible causes and scope of the fault, and then gradually eliminate it until we find out the fault point of producing good products with accurate measurement, safety and reliability. Don't move blindly, otherwise, we can't solve the problem of service innovation. It may also further expand the scope of the fault. In short, in the face of CNC machine tool failures and maintenance problems, we must first prevent from burning, and cannot solve the problems after the CNC machine tool has problems. We must do a good job in daily maintenance and understand the structure and working principle of the machine tool itself. In this way, sometimes in order to reduce the weight, non-ferrous metals such as aluminum alloy and special metals can be adopted to achieve a targeted goal

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