The evolution of cross-sectional dimension for double wall brazed tube in the multi-pass roll forming

The manufacturing process of double wall brazed tube (DWBT) consists of the multi-pass roll forming from the flat strip to double wall structure and brazing process. And the poor roundness of cross section for DWBT in the multi-pass roll forming not only affects the forming accuracy and quality, but also restricts the subsequent brazing process of DWBT. Thus, the parameters of Hill’48 yield criterion for the steel strip were firstly determined in this paper, and the reliable 3D finite element model of the multi-pass roll forming of DWBT was established based on ABAQUS/Explicit platform. Then the cross-sectional dimension of DWBT after each roll forming was analyzed. The results show that the multi-pass roll forming of DWBT requires the cooperation of the forming roller, horizontal roller and vertical roller, and the radius of the horizontal roller profile becomes larger with the increasing roll pass. The evolution of cross section is accompanied by the accumulation of equivalent strain, following the forming sequence of two arms on both sides, inner wall, outer wall and sizing process. An expression representing roundness is proposed, and it is concluded that the roundness of the outer tube is better than that of inner tube. Moreover, the cross-sectional distribution of the outer tube is more uniform along the circumferential direction.