The author believes that compared with general machine tools, CNC machine tools have a simple mechanical structure, so the correct rate of fault diagnosis for CNC machine tools is high. This paper takes numerical control lathe and CNC grinding machine as the object, and briefly introduces the methods of detection, analysis and diagnosis. The CNC lathe is based on the HZ-07 model manufactured by Shanghai No. 2 Machine Tool Plant. The spindle drive system is shown as 1. Using the PCM300D fault diagnosis instrument, the analysis software Labstar is used.
For each test, the air speed is set to 1200 rpm, and the acceleration sensor is placed at the same position on the outer wall of the headstock. The larger the dB value, the larger the vibration energy and the more serious the fault. On the contrary, the smaller the dB value, the slight or no fault. dB value and corresponding countermeasures.
When analyzing the spectrum, the power spectrum is mainly analyzed. Firstly, the distribution of vibration energy is firstly known in the high spectrum. Most of the common vibration energy is distributed in the frequency range of O-50Hz, and the fault is mainly concentrated on the rolling bearing. After finding and calculating the shaft frequency of the spindle bearing, the fault characteristic frequency is IHz and ZoHz respectively. In the table, F., F, FI, F, and Fb respectively represent the cage of the rolling bearing, the inner raceway when the outer raceway is not pre-tensioned, and the fault characteristic frequency of the inner raceway and the roller when pre-tightening, which will be on the spectrum. The main peak is compared with the values ​​of the internal shaft frequency (Fr) of 20 Hz. As long as the partial coincidence, the bearing can be initially diagnosed to be faulty.
The detection side dB>30 fault is obviously faulty and not serious. According to the processing precision requirements, it is decided to continue to use or repair the fractal spectrum to find the fault source for no reason. “Repair or adjustment, if there is obvious fault frequency of a certain bearing in multiple frames, The bearing can be diagnosed as faulty, and the peak size of F., F., etc. can be used to determine where the fault mainly exists in the bearing, and whether the need for updating depends on the accuracy of the workpiece.
The spectrum and diagnostic methods of common fault characteristics are as follows: When the axial frequency and its multi-step multiplication are apparent in the spectrum, the spindle system parts should be suspected to be loose. At this time, the random frequency is often also numerous. When there is a significant 1/2 frequency multiplication of the axial frequency and its multi-order frequency multiplication, it should be suspected that there is looseness of the shaft hole between the pulley and the shaft and the key, and the key and the groove are loose.
When the peak frequency of the axial frequency of the frequency spectrum is significantly larger than the peak value of the axial frequency, it should be suspected that the spindle is unbalanced when rotating, and this imbalance is often not caused by the spindle system itself, but by the dynamic balance of the tooling installed at the front end of the spindle. Bad. From the many faults that have been discovered, this kind of dynamic balance is poor. As the machine tool is used for a long time, the front and rear bearings of the machine tool will be damaged.
In comparison, the damage of the rear bearing is more obvious. The above spectrum appears when the shaft is bent. The author believes that the spindle of the CNC lathe is rigid. The installation accuracy is high and the possibility of such a failure is small. Compared with CNC lathes, CNC grinding machines have higher precision. Because of the high price, managers and repairers often have the fear of dismantling and fear of repair.
Once the accuracy of the workpiece is low, it is often necessary to adjust the grinding wheel first and then adjust the fixture. If the spindle bearings are not valid, but the update will sometimes appear to be unhelpful. Therefore, it is more valuable to use the vibration method for the grinding spindle bearing. However, the specific diagnostic method is not the same as the CNC lathe. Partially arranged in the batch grinding process after heat treatment of the workpiece, the first piece processed every day must be checked by the full-time inspectors according to the process requirements, such as roundness, taper, etc., only after the various indicators are qualified, can be processed continuously.
For each CNC grinding machine, each of the workpiece machining accuracy error reports is an important reference for analyzing the bearing failure of the grinding machine spindle. The following is an example of how to analyze and diagnose the imported CNC M12T internal and external cylindrical grinding machine. The CNC M12T CNC grinding machine has automatic functions such as automatic clamping of workpieces, automatic feeding, automatic inspection of workpiece machining dimensions, automatic grinding of grinding wheels, and automatic maintenance of the constant linear speed of the grinding wheel.
Caution The sensor must be placed close to the part to be tested. The wire of the sensor should be as short as possible. The measured spindle shaft frequency should not be 50, 25 or 16. When sampling, the fasteners must be tightened, especially the motor frame and the fastening parts at the base of the oil pump. Any moving parts that are not related to sampling should be stopped as much as possible. If there is a device that generates strong vibration near the machine to be tested, the equipment should be suspended as much as possible. If there is any difficulty, the machine to be tested can be sampled in the non-operating state (ie, at rest) and then sampled in the running state. In the analysis, the signals appearing in the non-operating state are identified and eliminated.
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