| 摘要 |
<p>A box section frame member is formed by deforming the opposing sides of a tubular blank inwardly to provide curved concave portions (19b, 21b, 26b, 27b, 32b, 33b,) in areas corresponding to opposing flat surfaces of the product. The deformed blank is expanded, under internally applied fluid pressure within a sectioned die, sections (18b, 24b, 31b) becoming trapezoidal, square and rectangular respectively. The concave portions of the deformed blank allow the blank to be confined within the die without pinching of the blank occurring upon closure of the die; permit substantially uniform expansion of the blank within the die; and allow the blank and final product to be formed with a smooth, continuous cross-section. This avoids stress concentration in the deformed blank and final product which can impair the mechanical strength of the product. To avoid weakening, cracking or yielding through excessive circumferential expansion the final product should have a circumference no more than 5% larger than the circumference of the tubular blank. The tubular blank may be bent into complex configurations, preferably before deformation.</p> |
