| 摘要 |
PROBLEM TO BE SOLVED: To improve a fatigue life in a rotational bending durability test and to reduce weight by setting a plate thickness of a decorative hole to be equal to a material original plate thickness and setting a plate thickness of a flange part to be thinner than those of a hat middle side part and a hat top part. SOLUTION: A disc 2 is formed by setting a plate thickness of a hub mounting part 3 equal to or thinner than a material original plate thickness, a plate thickness of a hat middle side part 4 and a plate thickness of a hat top part 5 to be thinner than that of the hub mounting part 3, a plate thickness of a decorative hole part 6 to the material original plate thickness, and a plate thickness of a flange part 7 to be thinner than those of the hat middle side part 4 and the hat top part 5, that is, to be the thinnest thickness. Actually, when a plate thickness ratio to the disc material original thickness is set 1, a ratio of a plate thickness t1 of the hub mounting part 3 is set to be 0.8-1.0, a ratio of a plate thickness t2 of the hat middle side part 4 and a ratio of a plate thickness t3 of the hat top part 5 are set to be 0.75-0.90, a ratio of a plate thickness t4 of the decorative hole part 6 is set to be 1.0, and a ratio of plate thickness t5 of the flange part 7 close to the welding part is set to be 0.55-0.75 in the best way for formation of the disc 2.
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