Machining center spindle maintenance and common failure analysis

Because electric vehicles are so prevalent, hub motors are frequently used in the power systems of these vehicles. High-speed brushless gear hub motors are used in many sectors because of their advantages in torque and load.

The machining center spindle usually uses servo motor adjust speed, and its structure is relatively simple, but the machining center has automatic tool clamping, and chip automatic removal device, and a spindle quasi-stop device, due to these devices have more accessories, common spindle failure also occurs in these parts, the following specific analysis of its.

Spindle heating and degradation of rotational accuracy

Failure of the phenomenon: processing out of the workpiece hole precision is low, the cylindricity is very poor, the spindle heats up quickly, processing noise is very large.

Failure cause analysis: After a long period of observation of the machine tool spindle can be determined, that the machine tool spindle centering taper hole in the process of multiple tool change damage, the main cause of damage is the use of the process of tool change in the plucking, insertion to the error, damage to the spindle centering hole taper, carefully analyzed and found that the spindle components of the failure of the cause of four points:

 

1. The grease of the spindle bearings is not by the requirements, mixed with dust impurities and water, these impurities mainly come from the compressed air used in the machining center which is not distilled and dried, and during the pneumatic chip clearing, the dust and moisture enter into the grease of the spindle bearings, resulting in poor lubrication of the spindle bearings, which generates heat and noise;
2. Damage on the positioning surface of the tapered hole in the spindle used to locate the tool, resulting in the tapered surface of the spindle and the tapered surface of the tool shank not being a perfect match, and the machined holes showing a trace of eccentricity;
3. The front bearing preload of the spindle is reduced, resulting in a larger bearing clearance;
4. The spring of the automatic clamping device inside the spindle failed due to fatigue, and the tool could not be fully tensioned and deviated from its original position.

Solutions

In response to the above reasons, there are some measures we can take to counter these problems.

1. Replace the front bearing of the spindle, use qualified grease, and adjust the bearing clearance;
2. Grind the positioning surface of the tapered hole inside the spindle to pass the test, and use the coloring method to ensure that the contact surface with the tool shank is not less than 90%;
3. Replace the spring of the clamping device and adjust the preload of the bearing.

In addition, in the process of operation should always check the spindle bore, shank clean and fit condition, to increase the air fine filter and drying device, to reasonably arrange the machining process, do not make the machine overload work.

Damage to tie rod balls of spindle parts of machining centers

The phenomenon of failure: The steel ball of the tie rod of the automatic tool clamping mechanism in the spindle is often damaged, and the taper of the end of the tool shank of the tool is also often damaged.

Failure cause analysis: It was found that the spindle loosening action and the manipulator pulling action are not coordinated, the specific reason is that the limit switch is installed at the end of the booster cylinder, in the cylinder's piston action in place, the piston of the booster cylinder can not be in place on time, leading to a violent pulling of the knife in the clamping structure of the manipulator is not yet fully loosened, serious damage to the tie rod steel ball and the tensioning screws.

Troubleshooting measures: clean the cylinder, replace the sealing ring, adjust the pressure, so that the two actions are coordinated, while regularly checking the gas-liquid booster cylinder, and eliminate potential safety hazards on time.

Problems with damaged locating keys on spindle components

Failure to occur phenomenon: tool change sound is large, the front of the spindle toggle tool shank rotation of the positioning key local deformation.

Failure cause analysis: After research, it was found that the loud sound during tool change occurred in the stage of robotic tool insertion, due to the spindle quasi-parking position error problem and the spindle tool change reference point drift problem. Machining centers usually use Hall elements for directional detection, Hall elements of the set screw after a long time after the use of loosening, resulting in the robot inserting the tool shank keyway not aligned with the positioning key on the spindle, so it will crash the positioning key; while the spindle tool change reference point drift may be the CNC system circuit board contact failure, electrical parameters change, proximity switches are fixed loosening, etc., the drift of reference points The drift of reference point may be caused by poor contact of CNC system circuit board, change of electrical parameter, loose fixing of proximity switch, etc. The drift of the reference point causes the taper surface of the tool shank to hit the centering taper hole directly when it is inserted into the taper hole of the spindle motor, which will cause abnormal noise.

Troubleshooting measures: adjust the installation position of the Hall element and add anti-loosening glue fastening, while adjusting the tool change the reference point, and replace the positioning key at the front of the spindle. In addition, in the process of machining centers to regularly check the spindle quasi-stopping position and spindle tool change reference point position changes, the occurrence of anomalies should be checked on time.

In addition, the machining center will cause some other faults, in the maintenance, in line with the first periphery after the internal, first software after hardware, first mechanical after the principle of electrical, according to the machining center of the relevant information and machining process, the failure to carefully check, gradually narrow the scope of the failure, and finally determine the cause of the failure, within the feasible range of treatment measures and recorded for future maintenance.

Conclusion

The machining center spindle is the core component of the machining center, in the use of the process should be carefully maintenance and care it, for some common mechanical failures to be found and dealt with on time through daily inspections, to reduce the number of machining center failures downtime and maintenance time, to ensure that the daily operation of the machining center to extend the service life of machining centers, to save costs for your production.