Springback and longitudinal bow in chain-die forming U and hat channels

Zhenye Liang,Shichao Ding,Tianxia Zou,Yang Liu,Yinghong Peng,Hua Xiao,Dayong Li,Lei Shi

doi:10.1007/s00170-021-07374-y

Abstract

Springback and longitudinal bow are two major shape defects in gradual forming processes like chain-die forming and roll forming. In this study, the springback and longitudinal bow of AHSS in chain-die forming of hat and U profiles are investigated through experiment and finite element simulation. The disparity of springback along the longitudinal direction and longitudinal bow signifies complex deformation during chain-die forming. Based on finite element simulation of the chain-die forming, the gradual forming process realized by sequential die blocks causes bending and reverse-bending in the web area and redundant deformation of the sheet metal, which leads to nonuniform bending moment and accumulated stresses along the longitudinal direction. At the same time, the redundant deformation will also result in the longitudinal strain on the edge, while the downhill characteristic of chain-die forming reduces the maximum longitudinal strain on the edge and introduces longitudinal strain on the web. The nonuniform longitudinal strain distribution along the transversal direction causes disparate downward and upward bowing longitudinal bow for chain-die formed AHSS hat and U profiles. By the established model, the disparate springback and longitudinal bow behavior can be quantitatively evaluated, which is helpful to chain-die forming process design.

Highlights

Advanced high-strength steels (AHSS) have been found more extensive usage in automotive manufacturing for weight reduction and crash safety [1]
Gradual forming techniques have become attractive to AHSS product manufacturing due to their incremental deformation nature that enables the forming of small radius [3]
In this study, shape errors in chain-die forming of AHSS channels are numerically and experimentally studied

Summary

Introduction

Advanced high-strength steels (AHSS) have been found more extensive usage in automotive manufacturing for weight reduction and crash safety [1]. The development of high-strength steels posed great challenges to stamping, i.e., shear fracture when being draw-bended through a tight radius [2]. Gradual forming techniques have become attractive to AHSS product manufacturing due to their incremental deformation nature that enables the forming of small radius [3]. Alloy sheets are gradually formed through incremental bending, and a small bend radius could be realized [6]. Chain-die forming was recently proposed to fabricate AHSS products and falls into gradual forming techniques of sheet metals [7]. In contrast with roll forming, chain-die forming increases the forming length by enlarging the radii of the rolls to tens of meters, which is realized by discrete die blocks attached to a rotational track board, as shown in Fig. 1 [8,9]

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