Radial envelope forming mechanism and process design method for cylindrical rings with thin wall and high web ribs

Cylindrical rings with thin wall and high web ribs (CRTWHWR) are widely used as the key load bearing structures such as rocket body and space station cabin in aerospace field. However, it is still difficult to efficiently manufacture CRTWHWR with high performance because of their extreme geometry with thin-walled skins, high web ribs and large size. In this paper, a novel radial envelope forming process is put forward to efficiently achieve the plastic forming of CRTWHWR with high performance. Firstly, the principle of radial envelope forming process is clarified. Then, an efficient design method for the tool motion and geometry is proposed based on the reverse envelope principle, i.e., CRTWHWR is adopted to reversely envelope the tool and thus the tool which does not interfere with CRTWHWR can be efficiently obtained in a single operation. Finally, a reasonable 3D FE model of the radial envelope forming process of CRTWHWR is established and the radial envelope forming mechanism of CRTWHWR is comprehensively revealed. Through the FE simulation and experiments with material of plastic mud, a typical CRTWHWR with diameter of 300 mm, axial height of 192 mm, the maximum rib height of 25 mm, the minimum rib thickness of 3 mm and skin thickness of 5 mm is radial envelope formed, i.e., the ratio of the maximum rib height to the minimum rib thickness reaches 8.33, the ratio of the maximum rib height to skin thickness reaches 5 and the ratio of diameter to the minimum rib thickness reaches 100. The above results verify that the proposed radial envelope forming process has great potentials in efficiently manufacturing CRTWHWR with extreme geometry.