Milling Force & Vibration Part 2

Let’s talk more about milling force and vibration. In my previous post, I included a movie that showed the force (top panel) and tool displacement (bottom) for a stable down milling operation, where the moving dots enabled you to correlate the dynamic force to the displacement. I’ve repeated that exercise here, but now for an unstable cut (chatter).

For this simulation, a 20 mm diameter endmill with four teeth and 30 deg helix angle is machining 6061-T6 aluminum. The cutting conditions remain the same: the axial depth is 4 mm, the radial depth is 5 mm (25% radial immersion), and the feed per tooth is 0.1 mm, but the spindle speed is now 5500 rpm (it was 5000 rpm on the previous post).

We see that the process now does not repeat from one tooth to the next so the cut is unstable. The results in the video are for the y direction, where x is the feed direction. If we look through the tool to the workpiece, the y direction is perpendicular to x in this plane. The tool axis is the z direction.

Milling dynamics are fun! I’ll follow soon with other examples, including other bifurcations.