Analytical and numerical analyses of the longitudinal plastic strain and web-warping in Chain-die-formed AHSS sections with variable widths

Abstract

Chain-die forming is a new sheet metal forming technology proposed which has the capability to fabricate advanced high-strength steel (AHSS) variable cross-section profiles. The existing research reveals that the control of longitudinal plastic strain and web-warping are two significant issues which determine the success of the fabrication of AHSS variable cross-section profiles. In this paper, both analytical and numerical methods are employed to analyse the longitudinal plastic strain and web-warping in Chain-die-formed AHSS sections with variable widths. By contrast to the existing analytical modelling in regards to flexible roll forming of irregular profiles, in this study, as Chain-die forming can be considered a continuous stamping process, the analytical models are purely established on the basis of geometric relationships between the pre-cut sheet and forming tools. In theory, no longitudinal plastic strain, id est maximum web-warping, could occur. No web-warping, id est maximum longitudinal plastic strain, could also arise. The real situation is included between such two extremes, and they are strongly dependent on some critical geometric parameters of the pre-cut sheet and forming tools. This is seen to be consistent with the simulation and experimental results. Subsequently, due to different forming mechanisms and loading processes, the severity and characteristics of the longitudinal plastic strain and web-warping of chain-die-formed AHSS sections with variable widths show distinct differences compared with those of flexible-rolled-formed profiles. Finally, Chain-die forming has been further proved to maximally reserve the material’s elongation as the redundant deformation is almost avoided during the forming process. This study provides an effective mathematical expression to analyse and predict longitudinal plastic strain and web-warping of chain-die-formed AHSS variable cross-section profiles. It is expected to be useful to tooling designers to quickly assess the severity of a Chain-die forming process in the tooling design stage in order to shorten the tooling development time.