Stress and springback analyses of API X70 pipeline steel under 3-roller bending via finite element method

Abstract

3-Roller bending is a widely applied manufacturing process, particularly in structural steel pipe industry. However, due to the difficulty and high cost of measuring stress distribution inside sheet material via traditional method, internal stress/strain response during forming is largely unexplored. The focuses of this study are two: (1) to map the radii of curvature as well as the stress inside the work piece during forming by utilizing the meshing mechanism of finite element method, and (2) to further provide some numeric guidelines for the configuration of the rolling system in order to improve production efficiency and product quality. The results of this study indicate that: (1) it is crucial to properly choose forming parameter in order to produce product with desired radii; (2) much like a gradual springback process, the radii of curvature gradually increase from the top roller to the exit-side bottom roller; (3) under the assumptions made in this study, to produce pipes with a specified diameter with varying configurations of the 3-roller system will not significantly change the final residual stress; and (4) finally, shifting of the neutral axis up to 2.0% of the thickness toward the compressing side during the forming process is observed.