Vibration of the knife in the CNC turning process is very common, and it is generally manifested as: uneven and rough surface of the part, accompanied by harsh sounds, unstable dimensions, etc…
In order to better solve these common problems, we have to understand the source of this problem: resonance point
On Wikipedia, it is explained like this:
The resonance point (acoustics is called resonance) refers to the situation when a physical system vibrates with a greater amplitude than other frequencies at a specific frequency; these specific frequencies are called resonance frequencies, which are very small. Periodic driving force can CNC machining huge vibrations because the system stores vibration energy as damping. There is a very small chance that the resonance frequency is approximately equal to the natural frequency or natural frequency of the system, which is the frequency during free oscillation.
In a normal cutting environment, the rotation speed of the spindle remains stable, and the frequency and amplitude of vibration are also maintained within an acceptable range.
As the vibration frequency increases, the vibration amplitude will increase accordingly.
The most obvious example is:
In some intermittent CNC turning processing environments, as the spindle speed increases, not only will it not increase the surface roughness of the workpiece, but on the contrary, it will make the surface rougher.
For example, increasing the speed is equivalent to increasing the frequency of vibration; a rough surface means that when the tool touches the workpiece, the contact point on the circumference has a slight change, and it also shows that the amplitude of the vibration has been amplified.
This does not mean that increasing the frequency of the vibration will definitely increase the amplitude of the vibration. Only this result will be more obvious when the resonance is excited.
Essentially, in order to ensure the parts have a stable roughness, it is necessary to maintain a stable vibration amplitude. Keep the generated vibration away from the resonance frequency and no longer increase the amplitude of the vibration.
If forced to shorten the time for resonance to occur, it will also have a positive effect on controlling the amplitude of vibration. The unique function of Haas lathe, SSV (Spindle Speed Floating), uses the changing speed to shorten the time of resonance, thereby achieving the purpose of improving roughness.
