First, Spindle Noise Failure Analysis
In many CNC milling machines, the spindle's shifting system still relies on multiple transmission shafts, gears, and bearings. As a result, vibration noise, friction noise, and impact noise are commonly generated during operation. Unlike traditional machine tools, the shifting of the main drive system in CNC milling machines is controlled by a computer while the machine is running, making the noise more continuous and representative.
When a CNC milling machine is first used, the noise level is relatively high, primarily due to the main drive system. Over time, as the machine is used more frequently, the noise tends to increase. At a spindle speed of 2000r/min, the measured noise level is approximately 85.2dB. This indicates that noise is a significant issue that needs to be addressed for better performance and user comfort.
Fault Checking and Analysis
Vibration and noise in mechanical systems occur when external forces excite the system, causing it to respond with vibrations. These vibrations travel through the system and eventually radiate into the air as sound waves. Therefore, the formation of noise involves three key stages: excitation response, internal vibration transmission, and acoustic radiation. In the case of CNC milling machines, the main drive system is particularly susceptible to these phenomena, especially when components like gears or bearings begin to show signs of wear or misalignment.
When the main drive system is operating, the interaction between gears, bearings, and other components can generate noise. If any of these components experience abnormal conditions—such as misalignment, wear, or lack of lubrication—the resulting vibrations become more pronounced, leading to increased noise levels.
Gear Noise Analysis
The main drive system of a CNC milling machine depends heavily on gears for shifting and power transmission. As such, gear meshing is one of the primary sources of noise. Several factors contribute to gear noise, including:
- Continuous impact between gear teeth during meshing, which causes forced vibration at the meshing frequency and results in impact noise.
- Transient free vibration caused by external forces acting on the gear, generating additional noise.
- Unbalanced inertia forces from eccentricity in the gear or shaft, leading to low-frequency vibrations that produce resonance noise per rotation.
- Self-excited vibrations due to tooth-to-tooth friction, which can cause frictional noise, especially if the tooth surfaces are uneven.
Bearing Noise Analysis
The spindle shifting system in a CNC milling machine contains 38 rolling bearings. The noise generated by these bearings is influenced by several factors, including their assembly, pre-tightening force, concentricity, lubrication condition, load, and radial clearance. Additionally, manufacturing deviations in the bearing itself play a significant role in determining the noise level. Rolling bearings are prone to various types of vibration, such as rocking, axial, and radial vibrations, which can lead to increased noise levels.
Higher rotational speeds generally result in higher fundamental frequencies and increased noise. Poorly manufactured inner and outer rings can also contribute to noise, especially when they have imperfections like dents or uneven surfaces. These irregularities can create higher harmonics in the noise spectrum, further increasing the overall noise level.
Second, Spindle Noise Troubleshooting
Gear Noise Control
Since gear noise arises from multiple factors, addressing it often involves modifying the existing design without altering its core structure. Here are some effective strategies:
- Tooth Tip Trimming: Adjusting the top of the gear teeth can reduce meshing impact caused by unevenness. The trimming amount should be carefully controlled to avoid damaging the working profile or failing to correct the issue.
- Controlling Tooth Profile Error: Gear tooth shape errors, often caused by machining or long-term use, can significantly affect noise levels. Correcting these errors by shaping the teeth appropriately can help reduce noise.
- Controlling Center Distance: Changes in the center distance between meshing gears can alter the pressure angle, leading to periodic noise increases. Ensuring proper alignment and minimizing deformation helps control this.
- Lubrication Optimization: Proper lubrication not only reduces friction but also dampens vibrations. Using oil with appropriate viscosity and ensuring even distribution across the gear teeth can significantly lower noise levels.
Bearing Noise Control
- Improving Inner and Outer Ring Quality: High-precision bearings with minimal waviness and surface flaws produce less noise. Ensuring proper fit and alignment during installation is crucial for reducing vibration and noise.
- Optimizing Bearing Fit: The radial clearance between the bearing and the shaft must be carefully controlled. A proper fit allows the oil film to dampen vibrations effectively, reducing noise. Both over-tight and loose fits can negatively impact noise levels.
By focusing on these areas, it's possible to significantly reduce noise in the spindle system of a CNC milling machine, improving both performance and operator comfort. Regular maintenance and attention to detail in component selection and installation are essential for long-term noise control.
Check Valves,Check Valve ,Double Check Valve,Wafer Check Valve
WENZHOU DIYE VALVE&FITTINGS CO.,LTD , https://www.diye-valve.com