FE modeling of warm flanging process of large T-pipe from thick-wall cylinder

The large T-branch pipe made from the thick-wall cylinder is an important part in power, petroleum, and chemical equipment. The warm flanging process is used to manufacture the high-performance large T-branch pipe from thick-wall cylinder. The warm flanging process has a bulk-forming characteristic with heterogeneous temperature field and represents very different from the sheet flanging process. The finite element method is adopted to study the warm flanging process of large T-branch pipe due to complex local heating and local deformation. A viscoplastic FE model was built to simulate the whole process in the same process, including heating, forming, cooling, and relevant elastic springback. Only one set of mesh was used to ensure the connection of heating and forming, which was never proposed in the warm flanging process before. The experiment was conducted to verify the proposed model by comparing the geometry and defects. Accordingly, two kinds of typical defects, buckling and wrinkling, were found in both of the simulation and experiment results. And, the reasons of defects were investigated with the stress and metal flow analysis. The short lower die leads to the buckling. Due to the ellipse outer edge, the uneven rebound makes wrinkling at the ends of the process. Three relevant improved methods, lengthening the lower die, increasing the fillet of the upper die, and increasing the radius of the upper die, were proposed and studied to decline the defects.