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Discussion On Several Methods Of CNC Machine Tool Maintenance

Discussion On Several Methods Of CNC Machine Tool MaintenanceDiscussion On Several Methods Of CNC Machine Tool Maintenance

CNC machine tools are complex mechatronic products. Its maintenance is different from that of ordinary machine tools. It is not simply a fault of mechanical, electrical, hydraulic, or numerical control systems. During the maintenance process, these aspects must be comprehensively analyzed to determine the problem The cause and deal with it. In these aspects, the CNC system can play a leading role. For the maintenance of large imported machine tools, the understanding of the PLC program cannot be completely based on the structure of the PLC statement and the logic control. It is more about the mechanical structure of the machine tool and the full understanding of the machining process. Can do more with less, this article briefly introduces several methods often used in the maintenance process of CNC machine tools, and give examples to illustrate.
Keywords: CNC machine tools: Maintenance

1.Intuitive method

Example 1: A five-axis linkage CNC boring and milling machine produced by German MAHO company. The CNC system is a Philips system. During a JJII process program transmission, the transmission interface of the CPU board was burned due to improper handling. Remove the CPU board and observe carefully, it is found that there are obvious burn marks on the RS232 interface. Carefully observe under the magnifying glass, and re-jump the broken line: and replace an 8255 chip, reinstall it on the machine, enter the machine parameters, and the machine returns to normal. The CPU board has been running so far and is in good condition.

2. Self-diagnostic function analysis method

Example 2: A 16-meter large vertical car produced by Wuhan Heavy Machine Tool Factory suddenly reported No. 43 alarm (PLC is not ready to work) during a process. Read the fault code 34 in the ISTACK and consult the Siemens 840C diagnostic manual, which reads: Interface-DMP module startup error. Check all the DMP modules including the handheld unit, and find that the base plate of the DMP module connected to the ground console is not powered on. Consult the electrical drawing and find that an air switch supplying the voltage tripped, closed it and the fault disappeared.

3. System reset method

Example 3: A CNC boring and milling machine of Czech SKODA company, the CNC system is Siemens 840C system. An alarm No. 43 (PLC is not ready to work) appears during a processing. Check the Siemens diagnostic manual. The cause of the failure is a hardware or software failure of the general data interface connection, or an error in the PLC machine data or inconsistent with the user program. After power-on and reset, the fault phenomenon changed. The power LED on the CSB board (central service board) of the CNC system is green and the out-put err LED is red. Alarm No. 43 still appears, and the X, Y, Z, U, and W axes of the machine tool are blocked, hydraulic and static pressure systems cannot be established, and alarm conditions have occurred in the 611D series of servo drive systems. According to the analysis of the cause of the failure, X, Y, Z, The blocked U and W axes are related to the output error of the CSB board. Enter the system reset interface to reset the PLC and run NCK POWERON. At this time, the ANW-PLG file originally stored under the USER / PLC menu is loaded. The output err LED on the board is still red, and the remaining alarms are not cleared. Analysis of the cause of the failure may be due to the confusion of the machine tool data during the power-on process, or the failure of the CSB board hardware itself. Remove the CSB board for inspection after power failure. No burnout was found. After cleaning, the alarm is still installed. According to the general reset method provided by Siemens, set the CSB board segment switch to the “l” position and power on again, set the system time / period, and load the machine data backed up on the MMC hard disk in the MDD (Machine Data Dialogue) folder. The system returns to normal. The red LED on the CSB board’s ouLputerr goes out, all alarms are eliminated, and the hydraulic system returns to normal. But X, Y, Z, U. The W axis still can’t move. Check the information and find that a subroutine SPF793 compiled by SKODA company is not running. SPF793 is transferred to NCK to run the program. All faults are eliminated. The fault handling process is a comprehensive system installation. As for SPF793 may be an installation subroutine compiled by SKODA, it must be run to unlock the interpolation axes of the machine tool.

4.PLC program analysis method

There are the most CNC machine tools, and the most frequent failure is that some logic functions of the machine tools cannot be realized. At this time, it is necessary to analyze the electrical schematic diagram, PLC program, hydraulic schematic diagram and other materials to find out the cause of the failure, repair or replace its components, and restore the CNC machine to normal work.
Example 4: The 16-meter large vertical car produced by the Wuhan Heavy Machine Tool Plant mentioned above, suddenly found that the X-axis and the oil tank spilled a lot of oil during use. Checking the same oil circuit did not find any clogging. Looking at the electrical schematics, it was found that only the X-axis regular lubrication and fixed-range lubrication were supplied. The program PG720 is used for real-time monitoring in the field, and the output point Q11.4 of the relay 9KY50 is asked in the PB10 towel control. The procedure is as follows:
PB1O segment 5
A T40: Load T40
L KT030.3; set T40 time to 300 seconds
SE T41; load to T41
AN T41; load T41
L KT002.2: Set the time of T41 to 2 seconds
SE T40; load to T40
C DB32; call DB32 block
A (0 DO.10; X-axis positive motion signal 0 DO.11; X-axis negative motion signal)
A T40; flip control
0 T38; power-on control oiling and lubrication = Q11.4; control 9KY50 relay
The meaning of the PLC control here is that when the X axis is moved, the control of the output Q11.4 has been used to control the output Q11.4 when the T40 and T41 are not placed. Monitoring the PLC status found that the logic was operating normally, monitoring 9KY50 found that the output was completely controlled according to the PLC program, and then the hydraulic solenoid valve was checked to find that the solenoid valve was always on regardless of whether the PLC had an output or not. Remove the 9KY50, measure with a multimeter, find that the normally open contacts are stuck, replace with a new intermediate relay, and troubleshoot.

5. Replacement method

Example 5: A 500-ton program-controlled punch produced by the German company Wingaden is equipped with an electronic cam controller. During one use, the electronic cam controller alarms, the content of which is a system failure, which paralyzes the entire machine tool. The electronic cam was removed, and it was found that it has two identical circuit boards, and one of the circuit board’s alarm red LED lights up, and the other is completely normal. After the adjustment, the fault transfers, and it proves that one of the hardware is faulty. The board was removed at the same time and a total of 8 pluggable chips were found. Four of them were swapped and compared again. The fault phenomenon did not transfer. Then the remaining two chips were swapped. The fault phenomenon shifted. So far, find out the problematic ones. chip. However, because this chip is an EPROM chip, the program in a good EPROM chip is written into the purchased EPROM chip of the same type by a writer. After installation, the failure phenomenon disappears. This time the fault is completely eliminated using the replacement method, gradually narrowing down the scope of the fault, find out the cause of the fault and eliminate it.

6. Conclusion

In short, during the service period of CNC machine tools, it is necessary to pay attention to maintenance and the backup of technical data. At the same time, it is necessary to learn and analyze the relationships between the internal systems of CNC machine tools and understand the relationship between them in order to facilitate the analysis of hard or soft faults during maintenance. Ability to judge and repair CNC machine tools.

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