CNC machine tools are complex mechatronic products. Their maintenance is different from that of ordinary machine tools. They are not simply mechanical, electrical, hydraulic, or numerical control systems. They must be comprehensively analyzed in the maintenance process to determine the problem. Cause and handle it. In these aspects the CNC system can play a leading role. For the maintenance of large-scale imported machine tools, the understanding of the PLC program can not be completely established in the PLC statement structure and logic control, more is a full understanding of the machine's mechanical structure, as well as the processing process, master these analysis of the PLC program Can play a multiplier role, this article briefly introduced several methods commonly used in the maintenance of CNC machine tools, and give examples.

1 Intuitive Example 1: A 5-axis CNC boring and milling machine produced by a German MAHO company. The numerical control system is a Philips system. In a transmission NC program, due to improper handling, the transmission interface of the CPU board was burned out. The CPU board was removed and carefully observed, and it was found that there were noticeable burn marks at the RS232 interface. Observe carefully under the magnifying glass, and reconnect the disconnected part: replace a 8255 chip, install it on the machine, input the machine parameters, and the machine will return to normal. The CPU board has been running so far and is in good condition.

2 Analysis of self-diagnosis function Law 2: A 16-meter large-scale vertical lathe produced by a heavy-duty machine tool plant in Wuhan suddenly appeared No. 43 alarm in one processing (the PLC was not ready to work). Read fault code 34 in ISTACK and consult the Siemens 840C Diagnostic Manual, which reads: Interface-DMP Module Startup Error. Check all DMP modules, including the handheld unit, and find that the DMP module backplane connected to the ground control console is not powered. Check the electrical drawing for an air switch trip that provides the voltage and close the fault and disappear.

3 System resets Act 3: A CNC boring and milling machine of the Czech company SKODA, the CNC system is a Siemens 840C system. No. 43 alarm occurred during a machining process (the PLC was not ready to work). Check the Siemens Diagnostics Manual. The cause of the fault is the hardware or software failure of the general data interface connection or the PLC machine data error or inconsistency with the user program. After the power-on reset, the fault phenomenon has changed. The Power LED on the CNC board (Central Service Board) is green and the out-puterrLED is red. The No. 43 alarm still appeared, and the X, Y, Z, U, and W axes of the machine tool were all blocked, the hydraulic and static pressure systems could not be established, and the servo drive system 611D series had alarm conditions. The reason for the failure was considered to be X, Y, Z, U, W axis is blocked and CSB board output error, enter the system reset interface to reset the PLC, run NCKPOWERON at this time the original stored in the USER / PLC menu ANW-PLG file is loaded, No. 43 alarm eliminated, but the CSB board The outputerrLED is still displayed in red and the remaining alarms are not cleared. Analysis of the cause of the failure may be due to the chaos of the machine data during the power-on process and the possibility that the CSB board hardware itself is faulty. When the power supply was removed and the CSB board was removed for inspection, no burn was found. After the cleaning process, the reinstallation of the alarm still exists. According to the total reset method provided by Siemens, the CSB board setting switch is set to “I” position to re-power on, set the system time/date, and load the machine data backed up on the MMC hard disk in MDD (Machine Data Dialog). The system is back to normal. CSB board out-outerrLED red light is off, the alarm is completely eliminated, and the hydraulic system returns to normal. But X, Y, Z, U. The W axis still can't move. Check the information diagnosis and found that a subroutine SPF793 compiled by SKODA company is not running. Put the SPF793 into the NCK to run the program and all the faults are eliminated. The fault handling process is a full-scale system installation. As for the SPF793, it may be a subroutine for SKODA's own installation. This program must be run to unlock the interpolation axes of the machine tool.

4 PLC program analysis method CNC machine tool is the most, the most frequent trouble is that some logic functions of the machine tool can't be realized. At this point, it is necessary to combine electrical schematics, PLC programs, hydraulic schematics, and other data for analysis, to find out the cause of the fault, and to repair or replace its components so that the CNC machine tool can return to normal operation.

Example 4: The 16-meter-long vertical lathe produced by the Wuhan Heavy Machine Tool Plant mentioned above was suddenly found to have spilled oil in the X-axis and oil sump in large quantities during use. Check the oil line and did not find the blockage phenomenon, check the electrical schematic diagram to find the oil supply only the X-axis timing lubrication and fixed-speed lubrication. With the real-time monitoring of the programmer PG720, the output point Q11.4 of the control relay 9KY50 found in PB10 is as follows:

PB1O paragraph 5

AT40: Loading T40

LKT030.3; set T40 time to SET41 for 300 seconds; load to T41

ANT41; Loading T41

LKT002.2: Set T41 to 2 seconds for SET40; load to T40

CDB32; Call DB32 Block A (0D0.10; X-axis forward motion signal 0D0.11; X-axis negative motion signal)

AT40; flip control 0T38; power control lubrication lubrication = Q11.4; control 9KY50 relay PLC control here is enough in the X axis movement, the use of T40 and T41 not set flip time to output Q11.4 The control has reached the effect of regular lubrication. Monitor PLC status discovery logic is running normally, monitor 9KY50 found out completely according to PLC program control output, and then check the hydraulic solenoid valve whether or not the PLC output solenoid valve is always in the state, it is enough to say that at any time. Remove the 9KY50, measure it with a multimeter, and find that the normally open contacts are stuck, replace the new intermediate relay, and troubleshoot.

5 Replacement of Act No. 5: A 500-ton programmable press produced by the Wyndham, Germany, equipped with an electronic cam controller. In the course of one use, the electronic cam controller alarms, the content is the system breakdown, causes the entire machine tool to rake. The electronic cam device was removed and it was found that it had two identical circuit boards, and the alarm red LED indicator on one circuit board was on, and the other one was completely normal. After the transfer, the fault occurred and it was proved that one of the hardware was faulty. When the board was removed, a total of eight pluggable chips were found. Four of the chips were swapped and compared again. The fault phenomenon did not shift. Then the remaining two chips were swapped and the faulty phenomenon was transferred. So far, the problem has been identified. chip. However, since this chip is an EPROM chip, a program in a good EPROM chip is written into the EPROM chip of the same type that is purchased using a write tablet, and after installation, the failure phenomenon disappears. The elimination of this failure is completely replaced by the replacement method, gradually narrowing down the scope of the failure, identifying the cause of the failure and eliminating it.

6 Conclusion In conclusion, during the service life of CNC machine tools, attention should be paid to maintenance, and the backup of technical data should be emphasized. At the same time, the correlation between the internal systems of CNC machine tools should be studied and analyzed to understand the relationship between them so as to facilitate the analysis when the maintenance is a hard fault or a soft fault. , Improve the judgment and maintenance capabilities of CNC machine tools.