CNC milling machine use in the process of spindle noise failure analysis

First, spindle noise failure analysis

In many CNC milling machine, due to the main spindle speed change system is still using a number of transmission shafts, gears and bearings, so it is inevitable to produce vibration noise friction noise and impact noise in the work. And CNC milling machine main drive system speed change is in the state of the machine does not stop working, completed by the computer control, so it is more continuous than ordinary machine tools produce noise, more representative.

CNC milling machine, in the initial use of the noise is larger, and the source of noise mainly from the main drive system, with the prolongation of the use of time noise is getting bigger and bigger, with a sound level meter in the spindle 2000r/min under the speed of the noise was measured as 85.2dB.

Failure check and analysis

Mechanical system is subject to any external excitation force, the system will respond to this excitation force and vibration. This vibration energy is propagated throughout the system, when propagated to the radiation surface, this energy is converted into pressure waves, through the air and then out, that is, acoustic radiation. Therefore, the three steps of excitation response, system internal transmission and sound radiation are the formation process of vibration noise, friction noise and impact noise.

Shanghai machining center manufacturers CNC milling machine main drive system soil work, it is due to gears, bearings and other parts after the excitation response, and in the internal transmission and radiation of the system and the noise, and these parts and due to the emergence of abnormalities, so that the excitation force to increase and thus increase the noise.

(1) Gear noise analysis. CNC milling machine's main drive system mainly relies on gears to complete the speed change and transmission, therefore, the gear mesh transmission is one of the main noise sources.

The main transmission system of the machine tool gears in the operation of the noise generated mainly:

① gears in mesh, teeth and teeth between the continuous impact of the gears in the mesh frequency generated by forced vibration and impact noise.

② because the gear is subject to the role of external excitation force and generate the gear intrinsic frequency of transient free vibration and noise.

③ Due to the gear and drive shaft and bearing assembly eccentricity caused by rotational imbalance inertia force, which produces a low-frequency vibration consistent with the rotational speed. As the shaft rotates, a resonant noise is emitted once per revolution.

(4) Self-excited vibration of gears due to friction between teeth and teeth and friction noise. If the tooth surface is uneven, it will cause rapid periodic impact noise.

(2) Bearing noise analysis. The spindle speed change system of this CNC milling machine has a total of 38 rolling bearings. The assembly, preload, concentricity, lubrication conditions and the size of the load acting on the bearings, radial clearance, etc. of the bearings and the journal and support holes have a great influence on the noise. And the manufacturing deviation of the bearing itself determines the noise of the bearing to a large extent. The parts of rolling bearings that are more prone to deformation are their inner and outer rings. Under the influence of external factors and its own precision, the inner and outer rings may produce rocking vibration, axial vibration, radial vibration, radial vibration of the bearing ring itself and axial bending vibration.

With the gear, the same reason, the higher the speed of the bearing, the greater the rotary fundamental frequency, the noise also increases the bearing rolling body within and outside the ring of the respective precision if not high, will become the main factor affecting the bearing noise rolling body or bearing on the inner and outer ring of the depression point is a lot of, in the spectrum of the high harmonics of the frequency of the performance of these frequencies, caused by the higher the noise is also higher.