CNC milling machine common failures

CNC milling machine common failures

CNC milling machine common failures:

1. Overtravel, when the feed movement exceeds the soft limit set by the software, the ultra-remote alarm content will occur. The fault can be eliminated and the alarm can be removed according to the CNC system manual.

2. Overload, when the load of the feed movement is too large, frequent forward and reverse movement and the feed transmission chain are in poor lubrication state, it will cause an overload fault. Generally, alarm information such as servo motor overload, overheating or overcurrent will be displayed on the CRT. At the same time, the feed drive unit overload and overcurrent information in the strong electric cabinet will be displayed.

3. Motion, the reasons for the motion phenomenon during feeding are:
The speed measurement signal is unstable, such as the fault of the speed measurement device and the interference of the speed measurement feedback signal.
The position control signal is bad or unstable or interfered.
Poor contact of the terminals, such as loose screws.
When the movement occurs at the moment of moving from the forward movement to the reverse movement, it is generally caused by the backlash of the feed transmission chain or the servo system gain is too large.

4. Creeping is generally caused by poor lubrication of the feed drive chain, low servo system gain, and excessive external load. In particular, pay attention to the defects of the servo motor and the ball screw coupling itself, such as cracks, etc., which can cause the ball screw rotation and the rotation of the servo motor to be out of sync, which makes the feed movement fluctuate quickly and slowly, resulting in a crawling phenomenon.

5. Machine tool vibration, analyze whether the machine tool vibration period is related to the feed rate:
If it is related to the feed rate, the vibration is generally related to that the speed loop gain of the axis is too high or the speed feedback is faulty.
If it has nothing to do with the feed speed, the vibration is generally related to the position gain being too high or the speed feedback fault.
If vibration occurs during acceleration and deceleration, it is often caused by too small acceleration and deceleration time.

6. The servo motor does not rotate, and the CNC system can process the speed control signal at the time of the feed drive, which is generally +24V DC relay coil voltage.
Check whether the CNC system has a quick control signal output
Check whether the enable signal is connected. Observe the I/O status through the CRT, analyze the PLC trapezoid (or flow chart) to determine whether the starting conditions of the feed axis, such as lubrication and cooling, are met.
For servo motors with electromagnetic brakes, check whether the electromagnetic brakes are released.
The feed drive unit is malfunctioning.
The servo motor is malfunctioning.

7. Position following error alarm. When the servo axis movement exceeds the position tolerance range, the CNC system will generate an alarm of excessive position error, including following error, contour error and positioning error. The main reasons are: mechanical transmission system failure, The speed control power supply fails, the servo system gain is set incorrectly or the position deviation value is set incorrectly, the cumulative error of the feed transmission chain is too large, the servo is overloaded or malfunctions.

8. Drift, when the command value is zero, the coordinate axis is still moving, causing position error. Elimination by drift compensation method and zero speed on the drive unit.

9. Reference point return faults. Reference point return faults are generally divided into two types: the reference point cannot be found and the reference point cannot be found. The first type of fault is generally the signal of the reference point deceleration switch or the zero mark of the zero pulse encoder or Whether there is a fault in the zero mark of the light barrier; the latter type of fault is caused by the improper setting of the current block position of the reference point switch, and the current block position needs to be readjusted.

10. The servo motor automatically rotates after it is turned on. The main reason: the polarity of the position feedback is wrong, the position of the coordinate axis is shifted due to external force, the driver, the tachogenerator servo motor or the system position measurement loop is bad, and the motor or driver is faulty.


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