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abstract3D finite element analysis is employed to simulate a cold roll-forming process. Numericalresults of longitudinal strains and displacement trajectories are compared with experimen-tal results available in the literature. Through a parametrical study, significant impacts of theyield limit and the work-hardening exponent on the product quality are observed, whereasforming speed and friction at roll-sheet interface appear to play a minor role.© 2007 Elsevier B.V. All rights reserved. 1. IntroductionCold roll-forming process is an industrial process for manu-facturing long sheet metal products with constant sections.In this process, an originally plane sheet is transformed into adesired profile without a considerable change of sheet thick-ness through the action of a series of pairs of forming rolls.This kind of high-speed production process is well suited forthe manufacturing of long sheets to close tolerances withoutmuch handling.Hence, roll-forming is mainly characterised by a bending-type deformation, which is continuously changing as thematerial moves through the rolls. The deformation mayinclude longitudinal stretching and bending, transverse bend-ing and shear. More importantly, the process of deformationis quite complex, since it varies across the section. Thus thereare often undesirable strains generated in the sheet, and it israther difficult to control their magnitude so that the qualityof the section is not significantly affected both in cross-sectiongeometry and in longitudinal curvature. If a large number ofrolls are used in the tool design, the applied bending is verygradual and unwanted strains are reduced. However, due toeconomical constraints, the number of rolls must be min-imised in order to reduce the overall cost.51241
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One must thereforetry to reduce tooling costs without compromising the sectionquality.Industrial practice largely relies on empiricismand heuris-tic rules for the design of roll-forming.Unfortunately, there arefewdesign rules that are universally accepted, since thewholedesign process of roll-forming is rather subjective. Workshoptests using a trial-and-error method is the common practicebut it inevitably requires a large amount ofmaterial and time.Under such circumstances, numerical simulation appears tobe an attractive alternative, since it allows reducing the timenecessary for roll pass design of new products.Different approaches have been proposed for the mod-elling of the forming process. Based on a hypotheticaldeformed sheet surface; i.e. a predefined geometry, simplifiedapproaches, which do not require an important effort of com-putation, can be developed. For example, Kiuchi (1973) have suggested a sinusoidal “shape function” to describe themiddlesheet surface between the roll stands for the formation of a cir-cular section. Alternatively, Nefussi and Gilormini (1993) havepreferred a Coons patch technique for the middle deformedsheet surface. Towards a more practical solution, which canbe applied for complex sections, the finite element methodhas recently obtained increasing attention in the simulationof cold roll-forming process. From the assumption on contin-uously moving rigid surfaces between two stations, Brunet etal. (1996) have proposed an elastic–plastic finite element tech-nique,where a 2D plane stress analysiswithmoving boundaryconditions is combined with a 3D shell analysis. On the otherhand, a combined 2D and 3D analysis has also been employedby Hong et al. (2001), where the assumption of a uniform ofstrain-rate over the cross section was adopted. For a morerealistic prediction and at the expense of increasing computa-tional effort, a 3D analysis has been attempted by (Heislitz etal., 1996) in the prediction of strain distributions, sheet geom-etry during and after the forming process. Besides the finiteelementmethod, the finite stripmethod has also been appliedfor the study of roll-forming process (Han et al., 2002).In this study, based on an in-house software namedMetafor (Ponthot, 1995), 3D-finite element simulation will beused to analyse the cold forming process. Our attention ismainly paid to the development of strains, which is likely ameasure of forming severity and potential forming problems.Indeed, if the legs of a profile are bent step-by-step from onestand to another, the edges travel a longerway than theweb ofthe profile. This leads to higher values of strains and stressesin the edges.