Calibrating the Material Properties

Categories: Using MillMax

Tap-testing very accurately predicts stable spindle speeds. There are, however, tens of thousands of different tool geometry and material property combinations for which we can only make assumptions. Therefore, our depth and width of cut predictions may be conservative. Where you will see this is when you tap-test an existing tool and the Dashboard shows chatter where they are currently running stable, such as this example:

By quickly lowering the depth of cut, you can see that their current speed of 7000 RPM shows that it is in the conditionally stable (yellow) zone.

This is important information. The customer has done a bunch of tool testing for you. We must adjust the material properties to match the known stable cut of 7000 RPM, 0.2500" Ae and 0.3750" Ap. Here is how we do it.

Go back to Setup > Project

Change the Material Database from Generic Database to Generic Database-1. With each Generic Database 1 through 4, we have incrementally adjusted the Process Damping Wavelength and the Material Stiffness or Cutting Force Coefficient. 

This next step is important or it won't work. You must click on the Material Group or Name and RESELECT the same material, in this case N2 for the changes to take effect.

Click NO.

Now, generate a new Dashboard using the DCC button. In this case the change from Generic Database-1 was not enough, so move on to Generic Database-2, generate another Dashboards and if necessary 3 and 4.

In this case, Generic Database-3, calibrated the Dashboard to match the known stable parameters. In most instances, the known stable cut is in yellow or conditionally stable. When users use trial and error they are typically right at the edge (yellow) of stable zones.

To see what is going on we produced two stability lobe diagrams for this tool. The first was at the Generic Database material properties. The users parameters are marked with the blue dot.

Here is the stability lobe using the Generic Database-3 parameters. Note that the locations of the good speeds did not change, but the maximum depth of cut increased.