Common Fault handling of CNC Machining centers

The common faults of CNC machining centers can be classified by core systems. The following are the corresponding fault phenomena, causes and standardized handling plans, covering more than 90% of the high-frequency problems in daily operations.

Ⅰ. Faults related to handwheel operation

Fault phenomenon ‌ : the handwheel operating shaft has no response, the rate switching fails, and the movement is stuck

The cause of the fault is ‌ : poor contact of the shaft selection/rate switch, damage to the pulse generation disk, and breakage of the internal connection wire

Solution ‌ : Enter the system diagnostic interface to check the contact signal. Replace the switch if damaged. Check the power supply and resistance value of the pulse disk. If any are abnormal, replace it. Measure the continuity of each connecting wire section by section. If a wire breaks, replace it

Ⅱ. Faults of the XYZ axes and the main shaft housing

Fault phenomena ‌ : abnormal noise during shaft operation, excessive vibration, deviation in positioning accuracy, and spindle movement

The cause of the fault is ‌ : deformation of the protective cover, damage to the transmission bearing, mismatch between the servo parameters and mechanical characteristics, and deviation in the parallelism of the pulley

Solution ‌ : Repair the deformed protective cover; Inspect and position the bearings. Replace them if damaged. Readjust the servo gain and resonance suppression parameters; Correct the parallelism of the pulleys and replace the severely worn main shaft belts directly

Ⅲ. Oil pump lubrication faults

Fault phenomenon ‌ : insufficient lubrication of the guide rail, failure to start the cutting oil pump, oil pressure alarm

Cause of failure ‌ : insufficient oil level, damaged oil pressure valve, blocked oil passage, short circuit of motor coil, opposite rotation direction

Solution ‌ : Replenish qualified guide rail oil; Check the oil pressure valve. Replace it if the pressure is insufficient. Clean the oil pump filter screen; Correct the motor rotation direction. If the coil is short-circuited, replace the motor

Ⅳ. Faults of abnormal processing accuracy

Fault phenomenon ‌ : workpiece size out of tolerance, surface roughness not up to standard, large backlash

Cause of failure ‌ : improper backlash compensation, loose insert, wear of lead screw and nut, spindle movement, incorrect programming process

Solution ‌ : Use a dial indicator to correct the backlash; Adjust the tightness of the inserts on each axis. Check the wear of the lead screw and nut. Replace them if they exceed the tolerance. Repair the clearance of the main shaft bearing; Optimize the cutting path process

Ⅴ. Machine tool return-to-zero Faults

Fault phenomenon ‌ : abnormal zeroing action, inability to find the origin, large coordinate deviation after zeroing

The cause of the fault is ‌ : the origin switch contact is stuck, the position of the stop block is offset, water enters the switch and rusts it, the line is disconnected, and the PLC input point is burned out

Solution ‌ : Clean the stuck limit switch, or replace it directly; Adjust the installation position of the stop block to ensure that the switch contacts can be pressed together. Replace the switch and ensure proper waterproofing. Check the continuity of the circuit and replace the burned-out I/O input points

Ⅵ. Faults related to loose or replaced tools

Fault phenomenon ‌ : the spindle cannot release the tool, the tool magazine keeps rotating and cannot complete the tool change

The cause of the fault is ‌ : damage to the loose knife solenoid valve, insufficient air source pressure, wear of the pull claw, detachment of the proximity switch, and deviation of the main shaft accurate stop position

Solution ‌ : detect the action of the solenoid valve. Replace it if damaged. Check the air source pressure and replenish the air pressure. Replace the worn main shaft pull claws; Re-fix the tool magazine counting proximity switch; Adjust the accurate stop parameters of the main shaft to ensure that the end face key is parallel to the X-axis

Ⅶ. Hard limit alarm type faults

Fault phenomenon ‌ : The machine tool triggers positive and negative hard limit alarms, and the shaft cannot continue to move

The cause of the fault is ‌ : the contact of the travel switch is pressed and stuck, the switch is damaged, the circuit is open, and the position of the limit stop block is offset

Solution ‌ : manually reverse the shaft out of the limit area; Clear the stuck limit switch and replace it if it is damaged. Check the connection of the circuit and adjust the installation position of the limit stop block