Hi everybody,
So i have 3 Blue Elephant 6090 Router machines and i have been working with those machines for 2 years.
My machines got 2.2 KW spindle and 600x900 (mm) grid and im using air cooling for the parts and water cooling for the spindles.

A new problem comes up.

I have made some GCodes for aluminum 6061 milling and its work fine until some point that it doesnt.
I have a few part that im working on for the past 3 days, after 6 parts or so, the machines was working fine and the end mills keeps running great, and suddenly they start breaking.
I didnt changed anything, same end mills, same feeds and speeds, same machines.

What could cause this problem?