| 摘要 |
PROBLEM TO BE SOLVED: To provide a method by which an aluminum motor frame having a low internal gradient can be manufactured with high productivity. SOLUTION: In a forming die in which fixing jigs 11 which can be moved in crossing directions are arranged in the form of a cross on a fixed plate 10 and a mandrel 9 which is rotationally moved in the vertical direction and has a large-diameter front end section 9a is positioned in the middle of the inner peripheral sections 11a of the front ends of the jigs 11, and then, a plurality of freely rotatable spinning rollers 9b are arranged in the peripheral direction on the side face of the front end section 9a, the barrel section 1a of an aluminum frame having an inner peripheral surface inclined in the axial direction is positioned among the inner peripheral sections 11a with the larger inside- diameter side of the section 1a upward. Then the internal surface of the barrel section 1a is formed by plastically deforming the internal surface by pressing the internal surface with the spinning rollers 9b by feeding the mandrel 9 at a fixed speed toward the smaller inside diameter side of the section 1a from the larger inside diameter side of the section 1b by rotating the mandrel 9 at a fixed rotating speed while the external surface of the barrel section 9a is held by means of the inner peripheral sections 11a.
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