Research on Two-Step Hydro-Bulge Forming of Ellipsoidal Shell with Larger Axis Length Ratio

Shi-Jian Yuan¹, Lan Hu^1,2, Zhu-Bin He¹, Bu-Gang Teng¹, Zhong-Ren Wang¹ª¤

(1.National Key Laboratory of Precision Hot Processing of Metals, Harbin Institute of Technology, Harbin 150001, China;ª¤2. Shanghai Aerospace Equipments Manufacturer, Shanghai 200245, China)ª¤ª¤ª¤



Abstract:

The two-step hydro-bulge forming technique was proposed to manufacture the ellipsoidal shell with the length ratio of the long axis to the short axis larger than 1.4. A central tube was introduced into the first step of the hydro-bulge forming process to constrain the over growth of the short axis during bulging, and then the central tube was replaced with two polar plates in the second step of the hydro-bulge forming process to manufacture an integral ellipsoidal shell. It is shown that the central tube restricts the growth of the short axis and simultaneously reduces the shrunk tendency of the long axis. The wrinkling occurs due to the latitudinal compressive stress at the equator at the early stage of hydro-bulge forming. However, with the increase of internal pressure, the compressive stress areas gradually decrease and finally the tensile latitudinal stress occupies approximately the whole shell, thus the wrinkles are eliminated. A sound ellipsoidal shell with the axis length ratio of 1.8 is obtained after two-step hydro bulging.ª¤

Key words:  hydro-bulge forming  ellipsoidal shell  latitudinal stress  wrinkling  axis length ratioª¤

DOI£º10.11916/j.issn.1005-9113.2013.03.015

Clc Number:TG39

Fund: