Stator lamination stack losses to to secondary operations

[Clyde38]

I have a customer that would like to increase the ID of their stator for an outside rotor PM Brushless motor. They only want to remove about 0.001" of material with a dremel tool. The motor is operated at about 1.5 W at 2000 r/min. They asked if this would be a problem due to the smear that will occur from the dremel shorting out the lamination stack. I told them no, this should not be a problem. First, does anyone disagree with my reply (I do not know how many slots or poles the motor has)? This motor is basically a fan motor.

Now I am asking if anyone knows of any studies or reports that they may have seen or actually done themselves that address this scenario. Specifically for the above situation as well as the effect (if any) of interlocking laminations, machining the OD of a stator to improve the thermal interface to an aluminum housing, etc. I have seen in the past an outside stator lamination stack that had very thick welds on the OD and this created additional cogging and losses for the motor (compared to a bonded stack of the same lamination).

 

[electricpete]

In the squirrel cage inducation motors that I work with, it is very common for the lamination stack to be shorted together at the O.D. by the welded structural ribs.

Since all flux is contained within the core, shorts at the OD alone cannot form any loop path enclosing net non-zero flux. But when/if a short forms somewhere further into the core or at the bore, then the short at the OD can become part of the loop.

So (at least in the case of the motors I work with), the od shorts are part of the design. We protect the core condition and temperature to minimize shorts at other locations. Grinding on core od would not be a problem even if it created smearing / shorting. Grinding on bore would be a big problem if smeared.


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(2B)+(2B)' ?