| 摘要 |
PROBLEM TO BE SOLVED: To avoid a crack due to thinning of a bulged part and to precisely form a bulged part by applying an internal pressure and a axial compression load in the flow direction of a tube stock having a round cross section and forming a roughly flat part to a die face to the part changing from the axial direction of the tube stock to the bulging direction. SOLUTION: A forming die 1 is formed with upper/lower dies 2, 3 split in the axial direction, the upper die 2 is subjected to parting/clamping in the A-B direction. Semicircle shaped die holes 4, 5 are formed in the upper/lower dies 2, 3, a cylindrical hole 7 having the diameter roughly equal to an outer diameter of a tube stock 6 is formed by working with alignment of both die holes 4, 5. A bulged part forming die hole 8 is formed as branched in the direction orthogonal to the axial center of the cylindrical die hole 7. A pressurized fluid is pressure supplied to the cylindrical die hole 7 from pressurized fluid nozzles 11, 12. A roughly flat part 13 is formed at the part where a flow direction of the tube stock 6 is changed from the axial direction to the direction of the bulged part forming die hole 8. The roughly flat part 13 is a roughly triangular, its bottom side is a straight line parallel to the tube stock 6 and its apex is positioned at a face of the bulged part forming die hole 8.
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