The spindle of a CNC tool grinder is the core component for achieving high-precision grinding of cutting tools. Its abnormal noise faults not only affect the machining accuracy of the tool (such as excessive roundness of the cutting edge and decreased surface roughness), but also may exacerbate the wear of the spindle components and cause more serious equipment damage. It is necessary to combine the sound characteristics of abnormal sounds (such as high-frequency harsh sounds and periodic muffled sounds), accurately investigate from three dimensions: spindle bearings, transmission structure, and lubrication system, and develop targeted treatment strategies.
1、 Locate the root cause of the fault based on the characteristics of abnormal noise
Different types of abnormal noises correspond to different faults: if there is a "high-frequency piercing friction sound" when the spindle starts, and the sound intensifies with the increase of speed, it is mostly a bearing fault (such as ball wear, raceway pitting); If there is a "periodic muffled noise" during operation and it is synchronized with the spindle rotation frequency, it may be due to loose or eccentric transmission components (such as belts, couplings); If the abnormal noise is mixed with "oil flow noise", the lubrication system needs to be checked first (such as oil blockage or insufficient oil volume). When troubleshooting, it is necessary to first shut down the machine and cut off the power supply. By manually rotating the spindle to feel the change in resistance, and combining auditory and tactile senses to comprehensively determine the scope of the fault, blind disassembly can be avoided.
2、 Layered investigation and processing strategy
（1） Main shaft bearing failure: the core cause of high-frequency abnormal noise
Bearings are the most common cause of spindle abnormal noise, and long-term high-speed operation can easily lead to ball fatigue, cage deformation, or abnormal preload force. When processing, it is necessary to first disassemble the spindle end cover, remove the bearing, and observe: if there are obvious scratches, pitting corrosion on the surface of the ball, or concave grooves on the raceway, it is necessary to replace it with a high-precision angular contact ball bearing of the same model (CNC tool grinding machine spindles often use this type of bearing, and attention should be paid to the accuracy level of the bearing being consistent with the original model); If there is no obvious damage to the bearing but uneven rotational resistance, it may be due to improper preload force. The preload force needs to be reset by adjusting the nut to ensure smooth rotation of the spindle without jamming. After replacing the bearing, it is necessary to apply special high-temperature lubricating grease (avoid using ordinary butter to prevent high-temperature deterioration), and then reset it in the original order to ensure that the coaxiality error of the bearing installation is controlled within 0.005mm.
（2） Abnormal transmission structure: key cause of periodic abnormal noise
The main shaft transmission relies heavily on belts or couplings. If the belt tension is insufficient, it can cause the transmission to slip and produce "periodic jumping noise"; If the coupling bolts are loose or the end faces are worn, it will cause an "eccentric impact sound". When dealing with belt problems, it is necessary to first loosen the fixing bolts of the motor, adjust the position of the motor to make the belt tension moderate (press the belt with your fingers, and control the sinking amount within 5-8mm), and at the same time check whether there are cracks or aging on the surface of the belt. If there are, it needs to be replaced as a whole; For the coupling failure, it is necessary to disassemble the coupling, clean the impurities on the end face, replace the worn elastic pad, and calibrate the coaxiality of the coupling with a dial gauge to ensure that the radial runout error is ≤ 0.01mm and avoid vibration during transmission.
（3） Lubrication system failure: an important factor accompanied by noise
Insufficient lubrication can cause dry friction in the spindle components, resulting in "rough friction noise". When troubleshooting, it is necessary to first check the level of the lubricating oil tank. If it is lower than the minimum scale line, special spindle lubricating oil should be supplemented (choose the viscosity grade according to the equipment manual, and do not mix different types of oil); If the oil level is sufficient but abnormal noise still exists, it is necessary to disassemble the lubrication pipeline, clean the internal oil and impurities, check whether the fuel injector is blocked, and ensure that the lubricating oil can be accurately sprayed onto the bearings and transmission parts. At the same time, check the pressure of the lubrication system. If the pressure is too low (below the specified value of the equipment), the oil pump needs to be repaired or the filter element needs to be replaced to ensure stable lubrication pressure.
3、 Verification and prevention after repair
After troubleshooting, a no-load test run is required: first run the spindle at low speed for 10-15 minutes and observe for any residual abnormal noise; Gradually increase to the rated speed, use a dial gauge to detect the radial runout and end face runout of the spindle, and confirm that the accuracy has returned to the standard range of the equipment. In daily maintenance, it is necessary to establish a mechanism of "weekly inspection of lubrication status, monthly detection of spindle accuracy, and quarterly inspection of transmission components" to prevent abnormal noise faults in advance and ensure the long-term stable operation of CNC tool grinders.