1X axis does not perform automatic reference point return The machine is a JCS-018 vertical machining center produced by a research institute and the CNC system is FANUC-BESK7M. After a fault occurs, check that there are no alarms on the CRT and there are no alarm indications on all parts of the machine tool. However, the manual X-axis can be moved, and after the X-axis is manually moved to the reference point, the machine tool can perform normal machining and repeat the above phenomenon after the machining is completed. According to the above situation, we judge: NC system and servo system have no fault. Considering that the fault occurs on the X axis back to the reference point, it is suspected that the fault is related to the change of the parameters of the X axis reference point. However, when we are in TE mode, we adjust the parameters related to the X axis reference point at address F. Examined, but found that these parameters are normal. From the working principle of CNC machine tools, the axis reference point is related to the origin and reference point of the axis, in addition to the parameters. Check the limit switch on the X-axis reference point on the machine and find that it has malfunctioned due to oil contamination, ie it is always on. Therefore, when the machining program is completed, the system assumes that it has returned to the reference point. Therefore, the X axis does not return to the reference point. After the trip switch is cleaned and repaired, troubleshooting is performed.

2 During the automatic processing, the A and B tables have no exchange action. The machine is a MKC-500 horizontal machining center produced in Hungary and the CNC system is SIEMENS 820M. When a fault occurs, the machine tool program has completed the M06 function in the L60 subroutine, the curtain has been opened, but there is no exchange action on the A, B table, the program is in a stopped state, and there is no alarm display on the CNC system. From the machine tool table exchange flow chart can be seen: When the A, B table exchange, there are two conditions must be met: First, the curtain must be opened; Second, the table should be in a relaxed state and rise. Check the above two conditions:

(1) The curtain is open and the conditions are met.

(2) The workbench is not raised and the conditions are not met, ie the workbench is still clamped. According to the instruction manual of the machine tool, the clamping and loosening of the rotary table are all related to the SP03 pressure relay, and the corresponding PLC input point of the SP03 pressure relay is E9.0. When the machine is in the normal machining state, the rotary table is clamped, E9.0=1; when the machine is in the exchange state, the rotary table is relaxed, E9.0=0, and the A and B table exchanges are prepared. According to its working principle, to make the workbench exchange, it is necessary to make E9.0=0 and the workbench relax even if the SP03 pressure relay is disconnected. We found that the SP03 pressure relay failed due to oil contamination. After cleaning and repairing, when adjusting to the workbench exchange, E9.0=0; when the workbench is processed, E9.0=1. Troubleshooting.

3 The robot does not change the tool during automatic machining. The machine is a KT1400 vertical machining center produced by a certain research institute, and the CNC system is a FANUC0 system. It was found that the manipulator did not change the knife in the automatic control mode and there was no alarm. In the manual mode, the tool can be changed and the automatic machining can be continued after the tool change. Based on the above checks, we judged that the CNC system and the servo system had no failure. Considering that the motion of the magazine motor and robot is controlled by Fuji inverter alone, the inspection will focus on the inverter. When observing the manual status, the magazine and tool change are accurate. Observe the automatic status, the magazine rotation is normal, and the tool change is abnormal. Check that the NC control signal has been issued and that the control contactor has also been engaged, indicating that the tool change signal has been fed to the frequency converter. Check the working condition of the frequency converter and find that when the manual tool change is performed, the operating frequency is 35 Hz, and the operating frequency is only 2 Hz when the automatic tool change is performed. At such low frequencies, the manipulator certainly cannot perform normal tool change operations. The reason for the failure is that when the manipulator is changing the tool, the substation suddenly loses power, causing the manipulator to jam when the tool is changed. After the power is restored, the above failure occurs. After resetting its frequency to 35Hz, the trouble was removed and the robot returned to normal.

4 Rotary table In the process of lifting or rotating, the odd number positioning is correct, and the even number positioning is not allowed for the machine and system as described in fault 2. After the failure, the machine tool does not have any alarm. When the positioning is inaccurate, the machine tool cannot work, but after the table is lifted again and again, the positioning is correct, and the machine tool can continue to work. According to this fault phenomenon, we suspect that the rotary encoder on the rotary table motor is loose or misaligned. However, failures cannot be ruled out by repeatedly adjusting the rotary encoder and modifying the parameters related to the rotary encoder. The drive system is the same as the magazine motor drive system. We use the replacement method for exchange. When the magazine drive system is changed to the rotary table, the fault is eliminated. After changing the rotary table drive system to the magazine, the magazine could not find the correct tool number. Through this inspection, we determined that the workbench drive system has failed. The drive system is the SIMODRIVE 611-A feed drive. By consulting the manual of the drive system and the analysis of the fault of the drive system, it is agreed that the drive device has no hardware failure. The above-mentioned failures are mainly caused by the wear of mechanical moving parts after long-term operation, the changes in the performance of electrical components, and the like, which cause the servo system and the dragged mechanical system to fail to achieve the best match. It can be known from the technical data that this situation can be achieved by adjusting the proportional coefficient KP and the integral time TN of the speed controller so that the servo system achieves a high dynamic response characteristic without an oscillating optimal operating state. After we fine-tune the rotary table drive system with reference to the KP scale on the tool magazine motor drive and the TN scale, the fault can be eliminated. No alarm fault occupies a large proportion in the breakdown of CNC machine tools. Failures are usually caused by external conditions such as power supply voltage, hydraulic pressure, pneumatic pressure, oil pollution, and ambient temperature. As described in Faults 1, 2, and 3 in this article. In addition, after the NC machine tool is used for a long time, due to the aging of components and the wear of mechanical parts, it will also cause problems in the matching of the system and the mechanical part, resulting in the occurrence of no alarm failure, as described in Fault 4 of this paper. Therefore, paying attention to the use environment of CNC machine tools and strengthening the maintenance of CNC machine tools is the fundamental way to reduce the probability of no alarm failure and is an important means to ensure the normal operation of CNC machine tools.