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FOR some years now, it has been a common practice to die cast the squirrel cages of induction motor rotors. The die cast rotor has many advantages of simplicity, ruggedness, and durability as well as low cost. One feature of die castings is the tendency for all castings to have a perfect outside surface even though the interior may contain voids, blow holes, or porosity. This feature is an advantage when the appearance of the die cast article is of primary importance. However, in an electric rotor, it is a disadvantage as no visual inspection methods will disclose a faulty interior which may affect the electrical performance.