Core rod deformation principle of rolled coaxial composite bar

The cross-section profile and dimensional accuracy of core rod was hard to control because of no direct contact between the core rod and the forming tools while coaxial composite bar was rolled. The core rod roundness severely deviated from tolerance limits after hot rolled in square-oval grooves. Based on establishment of the deformation resistance models of the clad and core materials, the deformation of coaxial composite bar in hot rolling process was numerically simulated by three dimensional thermal-mechanical coupled elastic-plastic finite element method. The effects of rolling pass design, clad and core contour on deformation and shape of the core material after rolling were studied respectively. The numerical calculation results were verified by industrial rolling experiments. The results show that the influence of rolling groove design on the core ellipticity is remarkable, but the clad and core contours are the secondary factors. It is because that square-oval groove system leads to an asymmetrical accumulative equivalent strain distribution on the cross section of the workpiece and the severe elliptic core after rolling. Deceasing reduction of K4 groove and increasing reduction of K3 groove can improve the core symmetry deformation of the workpiece and reduce its out-of-roundness.