| 摘要 |
<p>PURPOSE:To provide a plate with excellent flatability from an extruded material where the whole or a part of the section is formed in the U-shape. CONSTITUTION:In a stretch opening method in which a thin-walled extruded mateiral 1 where the whole or a part of the section is formed in the U-shape having linear parts 3, 3 on each end of a curved part 2 in a semi-circular shape is stretched at the linear parts 3, 3 and opened at the curved part 2 to be worked into the plate, the extruded material 1 is formed to be thin-walled of the constant thickness at the curved part 2, and the thickness t1 is regulated to meet the inequality 0.7t<=t1<=0.98t for the thickness (t) of the linear part 3. It is preferable that the thickness changing position of the extrusion 1 from the thickness (t) of the linear part 3 to the thickness t1 of the curved part 3 be present between the boundaries 4, 4 between the curved part 2 and the linear parts 3, 3 and the position deviated from these boundaries 4, 4 to the linear parts 3, 3 side by the thickness (t), and that a tapered part 5 be formed in the thickness changing position.</p> |
