Analytic model for multi-point large-radius bending of steel sheets

While the majority of industrial sheet bending processes consist of conventional air bending, more complex bending processes such as multi-point bending are also utilized. Multi-point bending involves forming several bends simultaneously with changing contact conditions. Of the various models that may be employed to simulate such processes, analytic models are most attractive for industrial applications as they are time-efficient, strongly theoretically supported and easily extended to a wide range of dies layouts without the need of additional experimental data. In this paper a new analytic model is presented to predict the forming forces, the deformation of the sheet and the springback. The model is based on the literature around large-radius air bending. The geometry of the sheet is determined at each moment as a function of the tool’s positions. The reaction forces are calculated based on the equilibrium of forces and moments and the springback is calculated based on the elastic unloading of the internal bending forces. The model has been compared with a more time consuming finite element (FE) model and the geometry of the sheet has been experimentally verified by means of digital processing of video images. The proposed analytic model shows good agreement with the computational FE model and it is demonstrated to be a robust tool for calculation of the bending characteristics

Multiscale modelling of asymmetric rolling with an anisotropic constitutive law

A parametric study is presented which employs a new anisotropic constitutive law in order to study the influence of anisotropic plasticity on the deformation field of the ASymmetric Rolling (ASR) process. A version of the FACET method is presented where an analytical yield function is restricted to the subspace of the stress and strain rate space relevant for 2D FEA, but can still accurately reproduce the plastic anisotropy of an underlying Crystal Plasticity (CP) model. The influence of anisotropy on the deformation field and corresponding texture evolution is examined in terms of the changes in texture component volume fractions and formation of texture gradients. It is found that a material with the anisotropy of a sharp cold rolled aluminium alloy is more beneficial than that of a recrystallised hot rolled aluminium alloy, and this influence of anisotropy suggests that ASR may be best carried out in the latest stages of cold rolling.status: publishe

Prediction of deformation textures in asymmetric rolling of aluminium alloys

Asymmetric cold rolling (ASR) has been shown to have potential to improve the formability of aluminium sheet alloys in deep drawing by increasing the normal plastic anisotropy, mainly as a result of the additional shear strains it imposes and the consequent alteration of the crystallographic texture. It is generally found that the process produces shear strains that vary across the sheet thickness, resulting in heterogeneity of the texture and related properties. While it may be a typical design goal of conventional rolling processes to maximise product homogeneity, it is not yet understood to what degree, in the context of the unique texture control possible with ASR, homogeneity and formability are conflicting objectives. Research describing the influence of process parameters on these phenomena has been reported for particular experimental ASR configurations, but a more broad exploration of the process window by parametric study has yet to be presented, in particular in the context of anisotropic plasticity and control of texture evolution. The work presented here addresses this need via a parametric study employing anisotropic FE and multi-scale material modelling to provide insight into the link between the process parameters and the final texture. It is demonstrated that a range of textures and degrees of homogeneity are achievable for aluminium with this innovative process, with potential for improving the formability in deep drawing. The results of this work are used in a subsequent analysis (presented separately) of the texture change during annealing, and an assessment of the resulting forming properties and impact of texture gradients via simulations of tensile tests.status: publishe

Process parameter influence on texture heterogeneity in asymmetric rolling of aluminium sheet alloys

Experimental investigations of asymmetric rolling of sheet alloys demonstrate that this process may be used to alter the crystallographic texture by the introduction of shear components. Such texture components are desirable for their potential to improve the formability of aluminium alloys in deep drawing, because they do not transform to the detrimental cube component after recrystallisation. It is however not precisely known how the process parameters affect the texture evolution and the formation of texture gradients. The results of a parametric finite element study of the deformation field and the texture evolution arising during a single pass of asymmetric cold rolling are presented together with an assessment of the impact of texture gradients on the macroscopic anisotropy determined by multi-scale modelling. The modelling approach is validated with textures measured for a single pass of asymmetric rolling of an aluminium sheet alloy. The study targets an industrially feasible process window and presents the relationships found between shear texture volume fractions, texture heterogeneity, plastic anisotropy and several types of process parameters (geometric, contact and material).status: publishe

Validation of a multi-scale model for shear deformation of an aluminium sheet alloy

Aluminium is a potential light weight alternative to steel for deep drawn sheet components, but generally does not compare well to steels in terms of formability. Research in polycrystalline plasticity indicates applying shear to rolled fcc alloys improves their deep drawability by favourably modifying their crystallographic texture. Such processing could be realised industrially by cold asymmetric rolling (ASR), but in order to gain detailed understanding of the influence of process parameters on the evolution and through thickness homogeneity of the texture a validated full field multi-scale model of the process is required. This study examines the ability of a hierarchical multi-scale approach to predict evolved textures for aluminium sheet subjected to a mechanical test exhibiting a deformation mode relevant for ASR, namely simple shear. The homogeneity of the deformation field is assessed with full field strain measurement by digital image correlation, and macrotexture is measured by x-ray diffraction. The discrepancies are discussed and further work to validate the modelling approach for simulation of texture evolution in the ASR process is briefly outlined.status: publishe