CNC machine tool is the abbreviation of Computer numerical co ntrol machine tools, which is an automatic machine tool with program control system. The control system is capable of logically processing a program having control code or other symbolic instruction specifications, decodes it, and uses a coded digital representation to input the numerical control device through the information carrier. Through the arithmetic processing, various control signals are issued by the numerical control device to control the movement of the machine tool, and the parts are automatically processed according to the shape and size required by the drawings.
Detailed explanation of electrical fault analysis and maintenance techniques of CNC machine tools
1. Diagnosis of electrical faults of CNC machine tools
Usually, the machine tool manufacturer provides a PLC program list or ladder diagram of the CNC machine tool. The maintenance personnel often analyze the cause of the fault according to the PLC program, which puts forward the requirements for the maintenance personnel skill of the machine tool. If the maintenance personnel do not understand the PLC language of the CNC system, the diagnosis will be very difficult. With the development of CNC machine tool manufacturing technology, the diagnostic function of CNC machine tools has become a technical indicator to measure the performance of CNC machine tools. The CNC system can provide hardware, drive, programming, operation and other related diagnostic functions, including alarm information with clear text description, or provide online help function, or provide an alarm manual. The diagnosis of machine tool electrical faults is also receiving more and more attention from machine tool manufacturers.
2. Causes and diagnostic analysis of electrical faults of CNC machine tools
The main causes of electrical faults in CNC machine tools are power failure, CNC system position loop fault, accidental shutdown fault, and abnormal spindle speed of the spindle servo system. As shown in Figure 1. Talking about the Electrical Fault Analysis and Maintenance Technology of CNC Machine Tools
2.1 power failure
In the components that maintain the normal operation of the CNC machine system, the power supply has a greater impact on the CNC machine. It can directly cause the shutdown of the CNC machine system or system damage. Due to the high quality of science and technology in western developed countries, the power supply design of machine tools is not considered. Relative to Western countries, China's power supply network has large fluctuations and high harmonics, coupled with the influence of human factors, power supply failures of machine tools have occurred.
2.2 CNC system position loop failure
(1) When there is no command, the coordinate axis generates motion. This situation may occur because the CNC machine system coordinate axis drift is too large, the speed or position loop is not properly connected, the feedback wiring is open, and the system measurement components are damaged.
(2) The coordinates of the CNC machine cannot find the zero point. The occurrence of such a situation is related to the open wiring or encoder damage, the failure of the optical zero return deceleration switch, the shift of the grid zero mark, and the zero direction away from the zero point. (3) Position loop alarm. This situation may be caused by the fact that the measuring components of the system have been damaged, there is no established control interface signal, and the position measuring circuit is open.
(4) The quality of the workpiece processed by the machine tool is degraded, which deteriorates in dynamics, and even when it is possible to reach certain speed values. Insufficient lubrication of the guide rails or wear or excessive mechanical transmission system clearance, or even severe wear, may be the biggest cause of this situation. Check and adjust the speed and position loop of the electrical control of the system and the matching status of related parameters after the mechanical fault is eliminated.
2.3 sporadic shutdown failure
The occurrence of this situation is related to two reasons: if the fault is eliminated after the power is turned off after the machine is powered off, it is the combination of certain operation and function operation of the machine tool, which causes the BUG of the related software in the design. resulting in. The other is that the machine is too humid. In some parts of China, machine tools are often placed near the gate of the factory. When the machine is running, the door of the machine power cabinet is opened for a long time. A large amount of dust, metal debris or water mist in the nearby air enters it, thus affecting the power equipment. normal work.
2.4 spindle servo system spindle speed is abnormal
There are many reasons for the abnormal spindle speed of the machine tool spindle servo system. First, the shifting system of the mechanical transmission part of the CNC machine tool may be abnormal and must be re-adjusted. Secondly, the cable connection of the spindle drive is interrupted or the status indicator of the drive is damaged. The cable must be reconnected or replaced. Again, it is caused by the deterioration of the stability of the output signal of the position control board in the machine control cabinet. If the above problems can be ruled out, the control board can be further reviewed.
3. Elimination and maintenance technology of electrical faults of CNC machine tools
3.1 Strictly follow the operating procedures
The CNC system programming, operation and maintenance personnel must strictly abide by the operating procedures and operate in strict accordance with the machine tool and system instruction manual. Try to avoid electrical failure of the CNC machine tool due to improper operation.
3.2 Regular maintenance of tape readers or disk readers
The operator of the CNC machine tool should regularly clean the moving part of the tape reader. Once a week, the guide roller and the tension arm roller should be filled with lubricating oil once every six months. In addition, the heads in the disk drive in the disk reader should be specially cleaned, and the special cleaning disk should be used for regular cleaning.
3.3 Monitoring the grid voltage of the CNC system
For CNC systems, the safety range of the grid voltage rating is between 85% and 110%. Outside of this range, the operation of the CNC system can be unstable and even damage important electronic components. This requires CNC machine operators to always pay attention to the voltage fluctuations of the CNC system. In some areas where the quality of the power grid is not high, a special AC stabilized power supply device should be installed on the numerical control system to reduce the incidence of failure.
3.4 Regular inspection and replacement of DC motor brushes
Annual inspections of CNC lathes, CNC milling machines, and machining centers are required. For frequently accelerated machine tools, such as the punching process, a two-month inspection is required.
4, summary
In summary, the CNC machine operator should regularly check the hardware and software of the CNC system to ensure that the CNC machine tool can safely and stably work, and eliminate the possible faults of the CNC machine tool in the bud. CNC machine operators must learn to analyze the faults in the CNC system, know how to repair and maintain the CNC system, and ensure that the CNC machine can work normally.
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