Prediction and control of bending quality of double-layered gap tube

Thin-walled double-layered gap tube (DLGT) has a promising potential to be widely used in making aerospace pipeline systems and the complicated structures in many industrial clusters. However, it presents a challenge to achieve precisely forming of the needed tube structure. During the rotary draw bending (RDB) of DLGT, the diversities of materials and geometries to be made lead to the difficulties in accurate prediction and efficient control of the forming quality. For an accurate prediction, the anisotropic characterization of the thin-walled tube was realized by designing a novel ring hoop specimen and the viscoplastic self-consistent model simulation. Three yield criteria were employed, and it is found that Yld2000-2D criterion has the best prediction accuracy. For efficient control, the rigid constraints of forming dies and flexible constraints of filling medium were employed. For rigid constraints, it is proven that the traction force provided by the inner clamp die is decisive in preventing the wrinkling and slip of tube and the fully constrained die structure has the best controllability of forming quality. For flexible constraints, the solid structure of filling medium provides more uniform constraints to tubes and is the most ideal structure. When a special channel structure is required, the outer channel structure plays a more significant role in the deformation of the inner tube, resulting in a better controllability of forming quality than the inner channel structure.