Control strategy of over-bending setting round for pipe-end of large pipes by mould press type method

The setting round process is one of the most important processes to ensure the quality of large pipe products. The setting round for pipe-end is a local elasto-plasticity deformation process, so it is difficult to quantificationally analyze the springback law because of the influence of rigidity. The physical experiments were used to study the equivalence relation between the setting round process for pipe-end and the circle-to-oval process for pipe-end, and the similarity relation between the circle-to-oval process for pipe-end and the circle-to-oval process for short pipes. The results indicate that the reductions are equal both in the setting round process and the circle-to-oval process for pipe-end; the relationship between the ovality after unloading and the relative reduction is linear in the circle-to-oval process both for pipe-end and the whole pipe, and the horizontal axis intercepts of the two lines are equal. Based on the relation above, the two-step control strategy of over-bending setting round for pipe-end was built, which can control the residual ovality of pipe within 0.5%.