Revisiting the wrinkling limits in flexible roll forming

Abstract

This article presents a new understanding on the deformation mechanics of flexible roll forming and is focused on the occurrence of flange wrinkling. The presentation draws from the experimental and numerical simulation of flexible roll forming to the determination of the wrinkling limits by means of a new theoretical and experimental methodology based on the utilization of rectangular test specimens loaded in axial compression. This research work is performed in mild steel sheets and the results show that the combined evolution of the effective strain with stress triaxiality obtained from finite element modelling of flexible roll forming and from the rectangular test specimens loaded in axial compression can be successfully utilized to predict the occurrence of flange wrinkling in variable cross-sectional profiles produced by flexible roll forming. The proposed methodology can, therefore, be considered an alternative to existing approaches based on simplified analytical and numerical procedures.

Formability limits by wrinkling in sheet metal forming

“…As a consequence, it is necessary to introduce a quantity designated as the 'initial effective width' w e 0 to adjust the experimental settings and observations to the finite element simulative conditions, as follows (Figure 3 where F exp cr and F fem cr are the experimental and finite element predicted critical forces at the onset of plastic instability. 16 The second procedure utilizes the finite element evolution of the principal strains with the ratio h=l of the amplitude h to the length l of the deformed test specimens (hereafter designated as the 'normalized amplitude of plastic instability waves') to determine the critical strain pairs (" crit 1 , " crit 2 ) at the instant of time when the critical force F cr is attained and wrinkling starts (h 4 0mm, Figure 3(c)). The critical strain pairs for test specimens with different initial lengths l 0 are then employed to construct the WLC in the principal strain space (Figure 3(d)).…”

“…The horizontal movement of the holders (H) produces the compression loads that are applied on both clamped sides w 0 of the test specimens. The self-centring clamping system is a simplified version of that used by Kasaei et al 16 and consists of two clamping shoes (S) and two clamping elements (C). The clamping shoes (S) serve to attach the clamping elements (C) to the holders (H).…”

“…This paper is focused on a new testing methodology to determine the onset of wrinkling in sheet metal forming that circumvents the aforementioned problems related to the occurrence of cracking prior to wrinkling. The development has its origins in the work of Kasaei et al 16 to determine the process window of flexible roll forming and makes use of a rectangular sheet clamped at two opposite edges and compressed in a double-action tool frame along its longitudinal direction.…”

Flexibility in metal forming

“…Products from this process are shown in Fig. 14 Flange wrinkling and web warping are two major failure modes in flexible roll forming [77,78]. They are caused by longitudinal compressive and tensile stresses in the inlet and outlet zones of the change in section [56] Larrañaga and Galdos [105] investigated the enhancement of the accuracy for the flexible roll forming.…”

Effect of Roll Gap Setup on Shape Defects during a Flexible Roll Forming Process

“…Kasaei et al investigated wrinkling limits in the flexible roll forming process using the experimental and numerical simulation. 17) They predicted the occurrence of flange wrinkling in variable cross-sectional profiles via the combined evolution of the effective strain and stress triaxiality. Groche et al developed an analytical one-step model to produce wrinkling-free parts with flexible roll forming.…”