Evaluation of the sinking processes for high-pressure-gas cylinders

Abstract

High-pressure-gas cylinders are used in broad applications. Cracks on the open end would occur during the riveting stage. Such forming defects are caused by excessive hardening, although the open end has been annealed with induction heating prior to the sinking operation. Therefore, a proper design for the sinking dies is essential to the forming production of the HPG cylinders. In this paper, two die-design concepts were examined which included the conventional design for six-stage sinking with fixed die radius, and the economic design for five-stage sinking with incremental die radii. Finite element software DEFORM 2D was used to investigate the two sinking schemes. The effect of the sinking schemes on the sinking load, strain distribution, and lip thickness were analysed. The results show that the economic five-stage sinking with a large increment of die radii can provide less strain hardening as compared to other sinking schemes. Although the forming load level is acceptable and the change of lip thickness is insignificant, the production cost of the five-stage scheme is still high. A more economic measure by sinking with one-stage rotary swaging can provide an alternative scheme with advantages of simple die design and saving the lead for annealing.