CNC machine tool common fault diagnosis and maintenance - Database & Sql Blog Articles

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The faults of CNC machine tools are mainly concentrated on the spindle part and the feed servo system. Some problems such as faults of auxiliary control devices and open circuit of control loops are also common. The following describes the troubleshooting of common faults in CNC machine tools.
1. Detection method for common faults in the spindle section The CNC machine spindle drive system is mainly used for the spindle rotary motion of the machine tool. Generally, the spindle drive system should have a wide constant power range, short acceleration and deceleration time, wide speed range, strong overload capability, low motor temperature and low noise. The common faults of the main shaft are mainly concentrated on the failure of the spindle drive system and the failure of the spindle hydraulic pressure and the spindle flow detection.
2. Common fault examples of the spindle system [Example 1] A German 13-meter CNC gantry milling machine spindle can not be loosened! Check plc found that the input and output signals are available, indicating that the 24V power supply has been output, check the solenoid valve and find that the valve is not connected after the power is turned on, to determine the damage of the valve body! Even worse after the solenoid valve is normal.
[Example 2] A domestic 6-meter-three CNC vertical car main shaft flow pressure detection point alarm. The inspection found that the spindle flow detection unit consists of four pressure flow detection points. The PLC program displays one of the detection points and alarms. The multimeters are all connected at each detection point. Therefore, it is judged that the oil pipeline is not smooth, and the oil pipeline is cleared. Clearing returns to normal.
[Example 3] A domestically produced CNC ten-meter vertical car spindle does not rotate. No alarm was found after inspection. The vertical feed axis consists of two left and right tool holders. The left tool holder can continue to be driven by the CNC axis. However, the right tool holder is not a normal digital display axis. The PLC program is found to find that the right handheld unit selection button cannot be selected. Therefore, check that the handheld unit finds that the button 24V power line is open. Because the handheld unit stops in series with the spindle stop in the PLC program, the spindle cannot be started. After the 24V power line of the handheld unit is restored, everything returns to normal.
[Example 4] The screen of a domestically produced CNC ten-meter vertical car spindle did not move. After inspection, it was found that the line connecting the spindle encoder and the driver did not damage the open circuit. The spindle encoder was removed and the encoder was found to be damaged, and the new code was replaced. The digital display returns to normal.
3. Detection method for common faults in the feed servo section The feed servo system is not only an important part of the CNC machine tool, but also a special part of the general machine tool that distinguishes the CNC machine tool. Its positioning accuracy is high, and the tracking response signal response is fast and stable. Well, ensuring the normal operation of the feed servo system is essential to fully utilize the role of the CNC machine. The feed servo system controls the displacement of the moving parts of the machine tool, mainly in linear motion. The common faults mainly focus on the faults of the servo control unit, the faults in the position feedback part and the faults of the servo motor. The general detection process is to first see if it has a servo enable signal, that is, whether the enable condition is satisfied according to the PLC program. Then look at whether the screen axis value changes, whether the servo axis has moved, and whether there is a command voltage on the servo unit, so that it can be determined that the position feedback problem or the servo motor or mechanical problem.
4. Common fault examples of the feed servo system [Example 1] A domestic CNC 200-bed Y-axis starts when flying. Initially, the feedback is not normal. Upon inspection, it was found that the full-closed feedback of the grating ruler was not working, and the system had become semi-closed and caused the speed. The Y-axis returns to normal after replacing the scale ruler head.
[Example 2] A domestic 17-meter CNC gantry milling machine Y-axis servo system alarm display Y-axis drive overload. After inspection, it was found that there was no problem in the mechanical load, and further inspection revealed that the machine oil leakage into the motor caused the motor to be damaged. The servo system returns to normal after replacing the Y-axis servo motor.
[Example 3] A domestic 1680 CNC sleeper Z-axis can not return to the reference point. After checking, the axis is set to the forward reference point, but when the reference point is returned, the Z axis goes in the negative direction, so it is judged that the system has pressed the reference point block by default. Further inspection revealed that the zero operating line was connected to 24V, and the normally open point became a normally closed point. After replacing the reference point operation line with the spare line, it returns to normal.
5. Inspection of other common faults The failure of the common AC three-phase asynchronous motor due to phase loss or grounding is the most common fault of CNC machine tools. Grounding the motor will cause an instantaneous increase in current to disconnect the circuit breaker. Open circuits at the input and output points of the auxiliary circuit are also common. The following describes several common faults.
[Example 1] The main oil pump of a CNC 1680 horizontal lathe could not be started. The inspection found that the circuit breaker was disconnected. The motor winding is grounded with a multimeter motor, so it is judged that the motor is damaged and normal after replacing the motor.
[Example 2] A CNC 260 boring machine turntable did not retreat. After checking, it was found to be normal forward, but the back is not and the input indicator is not lit at the same time. Further check that the PLC input point is not there. Check the button station and find that the 24V power supply of the button is normal. The button is not damaged by the multimeter. Therefore, it is determined that the button operation line is broken, and the operation line is replaced with a spare line.