Damping

Let’s talk about damping. We can think of damping as energy that escapes a mechanical system without causing vibration. More damping means that the vibration magnitude is smaller (with all other conditions remaining the same).

This video shows the results from impact (or tap) testing with two different damping values. The top panel shows the hammer force input (black). The middle panel displays the vibration response for one damping value (blue) and twice that value (red).

We see that the impact causes the structure to vibrate at its natural frequency and that the vibration decays over time. The red decay rate is faster (more damping) than the blue.The bottom panel shows the magnitude of the frequency response function, or FRF, which is the frequency domain ratio of the response to the force. We observe a peak at the natural frequency of 50.3 Hz with a taller blue peak (less damping).Every tool-holder-spindle has an associated FRF that can be measured using the impact test.

Any opportunity we have to increase damping will reduce the FRF magnitude and increase the associated material removal rate for machining. Let’s get damp!