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Maintenance method of spindle noise malfunction of CNC milling machine

2018/6/26 11:34:10 Viewers:
In many CNC milling machines, a number of transmission shafts, gears and bearings are still used in the gearshift system of the spindle, so it is inevitable to produce vibration noise, friction noise and impact noise in the work. And the transmission of the main transmission system of the CNC milling machine is completed by the computer control in the state of the machine tool without stopping work, so it is more continuous and representative than the noise produced by the ordinary machine tool.
One, analysis of main shaft noise fault
In many CNC milling machines, a number of transmission shafts, gears and bearings are still used in the gearshift system of the spindle, so it is inevitable to produce vibration noise, friction noise and impact noise in the work. And the transmission of the main transmission system of the CNC milling machine is completed by the computer control in the state of the machine tool without stopping work, so it is more continuous and representative than the noise produced by the ordinary machine tool.
The noise of a numerical control milling machine is larger in the first use, and the noise source is mainly from the main transmission system. With the longer use time, the noise is getting bigger and bigger. The noise is measured with the sound level at the speed of the spindle 2000r/min, and the noise is 85.2dB.
Fault inspection and analysis
Mechanical system is subjected to any external excitation force, and the system will vibrate in response to the excitation force. This vibrational energy propagates throughout the system, and when transmitted to the radiation surface, the energy is converted into a pressure wave, which is transmitted again through the air, 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.
When the main transmission system of the CNC milling machine is made, it is due to the excitation response of the gear, bearing and other parts, and the noise appears in the transmission and radiation of the system, and these parts increase the exciting force and make the noise increase because of the abnormal situation.
(1) analysis of gear noise. The main transmission system of CNC milling machine is mainly based on gear to complete the transmission and transmission. Therefore, the meshing transmission of gears is one of the main sources of noise.
The noise generated by gears in the main drive system of machine tools mainly includes:
(1) in gear meshing, a continuous impact between teeth and teeth causes the gear to generate forced vibration and impact noise at the meshing frequency.
(2) because the gear is subjected to external excitation force, the natural frequency of the gear is generated by transient free vibration and noise.
3. Because of the eccentric assembly of gears and transmission shafts and bearings, the inertia force of rotation is not balanced, resulting in low frequency vibration consistent with the speed. With the rotation of the shaft, a resonance noise is emitted at each turn.
Because of the friction between teeth and teeth, the self-excited vibration of gear and friction noise are generated. If the tooth surface is uneven, it will cause rapid periodic impact noise.
(2) analysis of bearing noise. The spindle speed changing system of the CNC milling machine has 38 rolling bearings. The assembly, pretightening force, concentricity, lubrication conditions and the size of the load on the bearing and the radial clearance have a great influence on the noise of the bearing and the shaft neck and supporting holes. Moreover, the manufacturing error of the bearing itself determines the noise of the bearing to a large extent. The most easily deformed part of rolling bearing is its inner and outer rings. Under the influence of external factors and its own precision, the inner and outer ring may produce the vibration of swaying vibration, axial vibration, radial vibration, radial vibration and axial bending vibration of the bearing ring itself.
With the same gear, the higher the speed of the bearing, the greater the frequency of the rotary base, and the noise will increase the accuracy of the inner ring of the bearing rolling, if it is not high, it will become the main factor affecting the noise of the bearing, and the inner and outer rings of the roller or bearing are many, and the high harmonic waves of these frequencies are shown on the spectrum. The higher the noise is.
Two, the malfunction of the spindle noise
1. gear noise control
Because the noise of the gear is caused by many factors, some of them are the characteristics of the gear noise in the spindle motion system, which is determined by the parameters of the gear design. On the basis of the original design, it is repaired and improved on the original gear to reduce the noise.
(1) tooth top repair edge. Due to the influence of tooth shape error and pitch, elastic deformation of the gear tooth load causes instantaneous collision and impact. Therefore, in order to reduce the meshing impact caused by the concave and convex tooth crown, the gear top can be trimming. The purpose of margin modification is to correct the bending deformation of gears and compensate for gear errors, so as to reduce gear noise. The trim margin depends on the pitch error and the bending deformation of the rear gear, and the bending direction. The trim margin is mainly aimed at the gear pairs with the highest engaging frequency of the machine tool and the different trim margins adopted by these gears when the modulus is 3, 4, and 5mm. In order to repair the edge, we must pay attention to the control of the repair edge, and take the method of repeated test, so as to avoid the excessive repair of the working tooth profile, or when the margin is too small to repair the edge of the tooth, it can only repair the tooth top or only repair the tooth root according to the specific conditions of these pairs of gears, only repair the tooth top or repair the tooth alone. When the roots fail to achieve good results, the radial and axial values of the margins of the teeth and the roots can be allocated to a gear.