It is found that there is abnormal sound in the spindle and gearbox when the spindle speed is below 500r / min. observing the power meter of the motor, it is found that the output power of the motor is unstable and the pointer swings greatly. However, the abnormal sound disappeared when it was used above 1201r / min. After startup, the power meter of the motor will swing automatically without rotation command, and the motor will drift and rotate automatically. After normal operation, the braking time is too long, and the machine tool has no alarm.
According to the phenomenon observed, the main shaft controller may be out of control, and the mechanical transmission or motor can not be eliminated. Due to the heavy workload of dismantling the mechanical part, the spindle controller of the electrical part is checked first. The controller is Siemens 6sc-6502. First, check the preset parameters in the controller, and then check the control board, all of which are normal. After checking that the circuit board is dirty, clean the circuit board according to the requirements, but after it is installed, the machine fails as usual. Therefore, the fault causes in the controller can be eliminated temporarily. In order to determine whether the fault is in the motor or in the mechanical transmission part, it is necessary to separate the motor from the machinery. After the separation, it is found that when the motor speed command is close to 450R / min, the abnormal sound starts to appear continuously, but when the instruction of 1201r / Min is given, the abnormal sound disappears again. For this reason, we analyzed the spindle part. The original 450 R / min command given at low speed and 4500r / min command at high speed are the same to the motor at the highest speed, but the gear decelerates at low speed, so the fault can be basically determined in the motor part. After analysis, the abnormal sound may be caused by poor bearing.
When the motor was disassembled for inspection, it was found that the bearing was damaged. When the bearing was stuck at high speed, the load was increased, which made the power meter swing and deflect. But after stopping, the motor drifted and the brake was too slow. After checking, the encoder disc was scratched. After replacing the bearing and encoder, all the faults were eliminated. This fault is mainly due to the abnormal sound when the spindle rotates. Therefore, it is necessary to find out the sound source before checking. Abnormal sound is common for mechanical rubbing, jamming and bearing damage.
CNC machining center spindle orientation usually adopts three ways: magnetic sensor, encoder and mechanical orientation. When using magnetic sensor and encoder, in addition to adjusting the position of components, it can also adjust the machine parameters. There is no alarm when the orientation error occurs, and it can only be detected when there is an interruption in the process of tool change.
Once in a refitted CNC machining center, there was a fault of inaccurate orientation. At the beginning, the machine tool was often interrupted in the work, but the frequency was not many. The machine could work again after restarting, and the fault occurred repeatedly. After careful observation of the machine tool after the fault occurred, it was found that the real cause of the fault was the position deviation of the spindle after orientation. It is strange that if the spindle is touched by hand after orientation (similar to the situation when the tool is inserted into the spindle during tool change), the spindle will drift in the opposite direction. Check the electrical part without any alarm, and the mechanical part is very simple.
The orientation of the machine tool uses encoder, so from the fault phenomenon and possible parts, the possibility of electrical part is relatively small, the most important mechanical connection. Therefore, it was decided to check the mechanical connection part. When checking the connection of the encoder, it was found that the set screw of the coupling sleeve on the encoder was loose, which caused the coupling sleeve to retreat, resulting in excessive clearance between the coupling part and the spindle, and the rotation was not synchronous. The failure was eliminated after the set screw was fixed as required. In case of spindle orientation failure, the analysis and treatment shall be carried out according to the specific structure of the machine tool. The electrical part shall be checked first, and then the mechanical part shall be considered if it is confirmed to be normal.
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