| 摘要 |
PROBLEM TO BE SOLVED: To injection-mold a disclike synthetic resin molding having a plurality of ribs radially molded integrally with a lightened disc connecting a boss and a rim, with high dimensional precision. SOLUTION: By cyclically changing the radial wall thickness of the rim along the circumferential direction, a portion of the rim to which the ends of the ribs are connected is formed to be the thinnest.
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