| 摘要 |
PROBLEM TO BE SOLVED: To form a product having outer diameter range which is unformable by executing O press forming by using a die for O press forming in which radiuses and radius center positions of upper/lower dies are different. SOLUTION: O press forming is executed with an upper die 1 and lower die 2 for O press forming. The upper die 1 is a UO steel tube O press forming die for existing inch size. The lower die 2 is a die to be newly produced for millimeter size. A radius R/radius center A of the upper die 1 and radius R'/ radius center A' of the lower die 2 are different in value/position. The upper/ lower dies 1, 2 have a liner part B cut off from true round state. An offset quantityαof the radius centers A, A' of the upper/lower dies, an expanding rateβafter forming and an outer diameter Z of product steel tube are in conformance with the equation I and equation II. Roundness of the steel tube after O press forming is taken into account, an offset quantity and radius R' are decided and then a steel tube of an outer diameter Z is formed. The lower die 2 only is required to newly produce and the die production cost is made low.
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