| 摘要 |
<p>A box-like frame member (16) is formed by compressing an internally-pressurized tubular blank (15) within a die (11,13) having a cavity (35,41) conforming to the final box-like cross section desired for the product (16), and increasing the pressure to exceed the yield limit of the wall of the blank (15) to expand the blank (15) into conformity with the die cavity (35,41). The blank (15) is selected so that the final product (16) and the die cavity (35,41) have a circumference preferably no more than about 5% larger than the circumference of the blank, to avoid weakening or cracking of the blank through excessive circumferential expansion. The internal pressure forces the blank (15) evenly into the corners of the die (35,41) on closing and allows the blank (15) to be confined within the die (11,13) without sections (47) of the die pinching the blank (15,45) on closing of the die (11,13).</p> |
