To improve circularity and inner/outer diameter accuracy of a yoke by eliminating bending inclination defect of a steel plate which is rounded into a cylindrical shape.
By the following steps, the motor yoke made of a steel which is shaped into a cylinder is manufactured. First, a steel plate is rounded to form a cylindrical semimanufactured product 10. Then, a core metal 11 is inserted into an inner circumferential side of the product 10. The product 10 is inserted into a serration mold 12 with the metal 11 held on the inside and a plurality of stripe grooves 2 extending in the axial direction are simultaneously formed on the outer circumferential surface of the product 10 by serration processing. In the yoke, distortion generated at a rounding work is released by the grooves 2 while following to the metal 11, and a bending inclination defect is eliminated and the yoke is improved in the circularity and inner/outer diameter accuracy.
FUSEGAWA SHUICHI
YAMAGAMI GENSAKU
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