Fault diagnosis, processing and after-care analysis of CNC machine tools

CNC machine tools are high-efficiency and complex automatic machine tools with high technical content, machine and electricity. When the machine tool is running, parts and components will inevitably have different degrees and different types of faults. Therefore, familiar with machinery The characteristics of faults, mastering the common methods and means of mechanical fault diagnosis of CNC machine tools, have a significant effect on determining the cause and elimination of faults.

First, the principle and basic requirements of CNC machine tool fault diagnosis

1.1 Troubleshooting principle.

It mainly includes the following aspects: 1) Fully investigate the phenomenon of failure, firstly investigate the operator, and inquire in detail about the whole process of the failure, what phenomena have occurred, and what measures have been taken. Then do a detailed survey on the site; 2) When looking for the cause of the fault, the idea should be broad, whether it is integrated electrical appliances, or mechanical and hydraulic, as long as there is a possibility of causing the fault, it should be listed as comprehensively as possible. Then carry out comprehensive judgment and optimization selection to determine the most likely cause of the failure; 3) first mechanical and then electrical, first static and dynamic principle. Before troubleshooting, you should first take care to eliminate mechanical failures. In the running state, dynamic observation, inspection and testing are performed to find faults. If a destructive fault occurs after power-on, the danger must be removed before powering up.

1.2 Troubleshooting requirements.

In addition to a wealth of professional knowledge, personnel who perform CNC fault diagnosis operations need to have certain hands-on ability and practical operation experience. They require the staff to combine practical experience, be good at analysis and thinking, and analyze the cause of the fault by the actual operation of the faulty machine tool. It should be changed invariably to achieve the effect of one. Complete maintenance tools and diagnostic instruments are essential. Common tools such as screwdrivers, pliers, wrenches, electric soldering irons, etc., commonly used measuring instruments such as multimeters, oscilloscopes, signal generators, etc. In addition, the staff also needs to prepare the necessary technical materials, such as CNC machine tool electrical principle drawings, structural layout drawings, CNC system parameter specifications, maintenance instructions, installation, operation, and operating instructions.

Second, the idea of ​​troubleshooting

The design ideas of different CNC systems vary widely, but regardless of the system, their basic principles and composition are very similar. Therefore, in the event of a machine tool failure, the maintenance personnel must have a clear idea of ​​fault handling: investigate the fault site, confirm the fault phenomenon, the nature of the fault, and fully grasp the fault information, so as to achieve "multiple brains, be careful" to avoid the expansion of faults. . Identify the complexity of the fault based on the fault information you have and list all the suspects of the fault location. Prepare the necessary technical materials, such as machine tool specifications, electrical control schematics, etc., based on which to analyze the cause of the fault, develop a solution to troubleshoot, require an open mind, and should not limit the fault to a certain part of the machine tool.

After determining the troubleshooting scheme, use a measuring instrument such as a multimeter or an oscilloscope to verify and detect the fault by the test method, locate the fault location step by step, and confirm whether the fault belongs to an electrical fault or a mechanical fault, whether it is systematic or random. Is it a fault or an external fault? Troubleshooting. Usually the problem will be solved immediately after finding the cause of the failure.

Third, the fault handling method and fault examples

The numerical control system of CNC machine tools is the core of CNC machine tools. Its reliable operation is directly related to the normal operation of the entire equipment. The following summarizes some methods for judging and eliminating CNC machine faults.

3.1 intuitive method

Example 1: A five-axis CNC boring and milling machine produced by a German company MAHO, the CNC system is a Philips system. In a transmission NC program, the transmission interface of the CPU board is burned out due to improper processing. Remove the CPU board and observe it carefully. It is found that there are obvious burn marks on the RS232 interface. Carefully observe under the magnifying glass, re-jump the broken wire: and replace a piece of 8255 chip, the latest installation on the machine, input the machine parameters, the machine returns to normal. The CPU board has been running until now and is in good condition.

3.2 Self-diagnosis function analysis

Example 2: A 16-meter large vertical car produced by a heavy-duty machine tool factory in Wuhan suddenly has an alarm No. 43 in a process (PLC is not ready for work). Read the fault code 34 in ISTACK and consult the Siemens 840C diagnostic manual. The content is: Interface - DMP module startup error. Check all DMP modules, including the handheld unit, and find that the DMP module backplane connected to the ground console is not powered. Look at the electrical drawing and find an air switch trip that supplies the voltage, and turn it off and the fault disappears.

3.3PLC program analysis method

CNC machine tools have the most, the most frequent failure is that some logic functions of the machine tool cannot be realized. At this point, it is necessary to analyze the electrical schematic, PLC program, hydraulic schematic and other data to find out the cause of the fault, repair or replace its components, so that the CNC machine can resume normal work.

Example 3: It is also said that the 16-meter large vertical car produced by Wuhan Heavy-duty Machine Tool Plant mentioned above suddenly found that the X-axis and the oil tank overflowed a lot. Check the same oil line and found no blockage. Check the electrical schematic diagram and find that only the X-axis timing lubrication and the fixed-range lubrication are available for oil supply. Using the PG720 on-site real-time monitoring, the output point Q11.4 of the control intermediate relay 9KY50 is found in PB10 as follows:

PB1O segment 5

AT40: Load T40

LKT030.3; set the T40 time to 300 seconds

SET41; loaded to T41

ANT41; loading T41

LKT002.2: Set the time of T41 to 2 seconds

SET40; loaded 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-on control lubrication lubrication = Q11.4; control 9KY50 relay

The meaning of the PLC control here is enough to control the output Q11.4 with the turning time that is not set by T40 and T41 when the X axis is moving. The effect of timing lubrication has been achieved. Monitoring PLC status found that the logic is running normally, monitoring 9KY50 found that the output is completely in accordance with the PLC program control, and then check the hydraulic solenoid valve to find that whether the PLC has an output solenoid valve is in the normal state, it is enough to say that oil is always used. Remove the 9KY50, measure with a multimeter, find the normally open contact sticking, replace the new intermediate relay, and troubleshoot.

3.4 replacement method

Example 4: A 500-ton program-controlled punch press produced by the German company Wengaden is equipped with an electronic cam controller. The electronic cam controller alarms during a single use, and the content is a system failure, causing the entire machine to smash. The electronic cam gear was removed and found to have 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 adjustment, the fault occurred and it was proved that one of the hardware was faulty. At the same time, the board was removed and found to have a total of 8 pluggable chips. Four of them were adjusted, and the faults were not transferred. Then the remaining two chips were reversed, and the fault phenomenon was transferred. chip. However, since the chip is an EPROM chip, the program in the good EPROM slice is written into the purchased EPROM chip of the same type by the writer, and the fault phenomenon disappears after installation. The elimination of this fault completely uses the replacement method, gradually narrowing the scope of the fault, finding out the cause of the fault and eliminating it.

Fourth, the confirmation of troubleshooting and aftercare work

After the troubleshooting, the maintenance work can not be completed. It is necessary to analyze the deep-seated causes of the fault from the technical and management aspects, and take appropriate measures to prevent the fault from happening again. If necessary, the equipment can be modified and improved according to the site conditions using mature technology.

After a period of time, ask about the operating conditions of the operator's machine tool and perform a full inspection of the point of failure again. Finally, make a maintenance record, detailing the entire process of maintenance, including repair time, replacement part model specifications and failure cause analysis. Find out what you lack from the process of troubleshooting, develop a learning plan, and finally enrich yourself.