Shaking cutter is very common during turning, which is generally shown as: uneven and rough surface of parts, accompanied by harsh sound, unstable dimensions, etc
In order to better solve these common problems, we have to understand the root cause of this problem: resonance point
On Wikipedia, it is explained as follows:
Resonance point (acoustics is called resonance) refers to the situation when a physical system vibrates with greater amplitude than other frequencies at a specific frequency; These specific frequencies are called resonance frequencies. Under the resonance frequency, a small periodic driving force can produce huge vibration, 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 of the system, or called natural frequency, which is the frequency of free oscillation.
In the previous video, we used tuning forks and table tennis balls to show the effect of resonance on vibration amplitude.
In a normal cutting environment, the spindle speed remains stable, and the frequency and amplitude of vibration are also maintained within an acceptable range.
With the increase of vibration frequency, the vibration amplitude will also increase accordingly.
The most obvious examples are:
In some intermittent turning environments, with the increase of spindle speed, the workpiece surface roughness will not be improved, on the contrary, the surface will be rougher.
In this case, increasing the speed is equivalent to increasing the frequency of vibration; The rough surface means that when the tool contacts the workpiece, the contact point on the circumference has slightly changed, which also indicates that the amplitude of vibration has been amplified.
This does not mean that increasing the frequency of vibration will definitely increase the amplitude of vibration. Only when resonance is excited can this result be more obvious.
In essence, to ensure the stable roughness of parts, it is necessary to maintain a stable vibration amplitude. Keep the generated vibration away from the resonant frequency, and no longer increase the amplitude of vibration.
If forced, shortening the time of resonance will also have a positive impact on the control of vibration amplitude. The special function SSV (spindle speed floating) of Haas lathe makes use of the changing speed to shorten the time when resonance occurs, so as to improve the roughness.
