I am an undergraduate student in electromagnetics. I am analyzing and researching Kollmorgen TBMS series motors. What I am curious about is why its motors are wrapped with a "shell" around the stator and what is its main purpose? In addition, I found that its rotor core does not seem to be in the form of laminations, but as a whole, so what I want to know is what materials they use, like the positions of 1 and 2 in my picture .
Those are called flux rings. They're standard on pretty much all motors. They close the magnetic loops in the core so the flux doesn't need to escape into the air to find its way back to the other end of the coil.