Tribologie du laminage à froid de tôles = Tribology in metal forming

Free access articleInternational audienceLe laminage dépend de manière critique du frottement et de la lubrification, tant pour le contrôle du procédé que pour la qualité du produit fini. Pechiney et Usinor ont donc entrepris en 1995, en partenariat avec le CNRS, un ambitieux projet regroupant sept laboratoires publics autour de l'Irsid et du Centre de Recherches de Voreppe, sur les deux grands domaines de la lubrification : mécanique de la formation du film lubrifiant entre surfaces rugueuses déformables, et formation des films limites (tribochimie), en vue de construire un modèle de laminage incluant un modèle de frottement prédictif et local. Ce sont les efforts et les résultats de ce CPR (Contrat de Programme de Recherches) « Mise en Forme des Matériaux : contact métal-outil-lubrifiant qui sont décrits dans ce numéro et un numéro ultérieur de Science et Génie des Matériaux = Strip rolling processes depend critically on friction and lubrication for process control as well as for strip quality. Pechiney and Usinor companies have therefore joined with CNRS (National Scientific Research Centre of France) to build an ambitious project gathering seven French public laboratories and their own research centres, Irsid and Centre de Recherches de Voreppe. The two major fields of lubrication were addressed: the formation of fluid lubricant films between rough deformable surfaces, and the formation of boundary films (tribochemistry). The final purpose was to derive a model of rolling processes including a predictive, local friction model. This issue and a future issue of Science et Génie des Matériaux present the efforts and the results of this Research Programme Contract "Materials forming: metal - tools - lubricant contact"

From steady-state to cyclic metal forming processes

Reprinted with permission from AIP Conf. Proc. May 17, 2007 Volume 908, pp. 209-214 MATERIALS PROCESSING AND DESIGN; Modeling, Simulation and Applications; NUMIFORM '07; Proceedings of the 9th International Conference on Numerical Methods in Industrial Forming Processes; doi:10.1063/1.2740813. Copyright 2007 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of PhysicsInternational audienceContinuous processes often exhibit a high proportion of steady state, and have been modeled with steady-state formulations for thirty years, resulting in very CPU-time efficient computations. On the other hand, incremental forming processes generally remain a challenge for FEM software, because of the local nature of deformation compared with the size of the part to be formed, and of the large number of deformation steps needed. Among them however, certain semi-continuous metal forming processes can be characterized as periodic, or cyclic. In this case, an efficient computational strategy can be derived from the ideas behind the steady-state models. This will be illustrated with the example of pilgering, a seamless tube cold rolling process

Frottement et lubrification en mise en forme = Numerical modelling of lubricated foil rolling

Free access articleInternational audienceUn modèle de lubrification en laminage à froid de tôle a été adapté au laminage en très faible épaisseur. Il prend en compte l'évolution de la géométrie des aspérités et de la pression du lubrifiant le long de l'emprise. Le frottement entre le cylindre et la rugosité de la tôle est représenté au choix par les modèles de Coulomb ou de Tresca. Dans le premier cas, la contrainte de cisaillement est limitée par la contrainte d'écoulement en cisaillement de la tôle. On introduit une nouvelle modification à ces lois standard pour simuler le frottement glissant dans les zones de réduction et le frottement collant dans la zone neutre centrale. On examine les variations de force de laminage, d'épaisseur de film lubrifiant et d'aire réelle de contact avec la vitesse de laminage, pour des conditions typiques du laminage d'aluminium en feuille mince, de 50 à 25 μm. = A model of lubricated cold strip rolling is extended to the thin foil case. The model considers the evolution of asperity geometry and lubricant pressure through the bite. Friction between the roll and the asperities on the strip is modelled using the Coulomb and Tresca friction factor approaches. The shear stress in the Coulomb friction model is limited to the shear yield stress of the strip. A novel modification to these standard friction laws is used to mimic slipping friction in the reduction regions and sticking friction in a central neutral zone. The variation of rolling load, lubricant film thickness and asperity contact area with rolling speed is examined, for conditions typical of rolling aluminium foil from a thickness of 50 to 25 $\mu$m

Une méthode multimaillages multiphysiques pour accélérer la simulation numérique des procédés incrémentaux continus: Application au laminage à pas de pèlerin

National audienceDans cet article, nous proposons une méthode multimaillages multiphysiques pour accélérer la simulation numérique des procédés incrémentaux continus. Dans cette approche, un maillage localement raffiné uniquement dans la zone de déformation est utilisé pour résoudre les équations de la mécanique alors qu'un maillage uniformément raffiné sert à stocker les variables d'état et à effectuer les calculs thermiques. Un transport précis et efficace des champs entre les différents maillages permet de préserver la précision des résultats. Dans ce travail, nous proposons une extension de la méthode multimaillages à des procédés de forgeage continus mettant en jeux des matériaux élasto plastiques, en utilisant des opérateurs de transport de champs basés sur des techniques de recouvrement de type SPR (Superconvergent Patch Recovery). La simulation numérique du laminage à pas de pèlerin est présentée comme cas d'applicatio

Application of the arbitrary lagrangian eulerian formulation to the numerical simulation of stationary forming processes with dominant tangential material motion

International audienceIn this paper, an Arbitrary Lagrangian Eulerian (ALE) formulation has been developed for 3D FEM simulations of quasi-stationary metal forming processes (such as drawing, rolling, extrusion ...). In such a formulation, the mesh is updated independently from the material motion, allowing the mesh to be continuously optimized. It is however difficult in 3D to relocate mesh nodes such that the movement of the material domain boundaries can be followed. In general, it is achieved by setting the normal component of the mesh velocity equal to the normal component of the material velocity for each boundary node. This initial choice was found unsatisfactory for processes with dominant tangential velocity. For such cases, a new procedure has been implemented in the FORGE3 (R) software [1]. The surface nodes are projected onto the intermediate surface computed at the end of the Lagrangian virtual updating stage. Different strategies are developed to project the nodes, according to the topological entities they belong to (vertices, edges, plane or curved surfaces). A comparison for wire and bar drawing processes is provided between a standard Updated Lagrangian formulation [1] and the present ALE formulation, showing very similar results (geometry shape, drawing stress, strain rates ...)

Tribological study of a press-fit assembling process

International audienceA particular case of press-fitting of two metal parts is studied, with high fit interference inducing high contact pressures and plastic deformation of the bushing and collar. Furthermore, the female piece is polymer-coated by cataphoresis, and the coating evolution by damage and wear during sliding promotes significant changes of friction with sliding length. These particular frictional properties impact the structural mechanics behaviour of the system during assembling

Méthode multi-échelle pour la modélisation du flambage des tôles minces sous contraintes résiduelles - Application au laminage

National audienceDans le laminage à froid, l'apparition d'une distribution hétérogène de contraintes résiduelles peut engendrer le flambage de la tôle laminée, entraînant un " défaut de planéité ". L'objectif est de définir un modèle macroscopique simple décrivant les modes et amplitudes de flambage d'une tôle sous l'effet des contraintes résiduelles issues du laminage. Le présent article présente une nouvelle méthode bi-échelle [1,2] comme une alternative du modèle de flambage développé dans [10-13]. Elle utilise un développement en séries de Fourier, pour résoudre les équations de Von Karman (flambage des tôles minces). Couplé avec le modèle de laminage Lam3/Tec3, cette technique a le potentiel de détecter la charge critique et le mode de flambage, puis de décrire l'état post-flambé de la tôle (amplitude des défauts, redistribution des contraintes)

Coupled rolling and buckling model for friction-sensitive setting of flatness actuators

International audienceFlatness defects in thin strip cold rolling are a consequence of buckling due to roll thermo-elastic deformation and the resulting heterogeneous strip plastic deformation. A coupled rolling - buckling model has been developed [Abdelkhalek et al. 2011]. It has shown that (i) taking buckling into account results in completely different stress fields and fits correctly the measured on-line residual stresses under tension ("stress-meter rolls"); (ii) coupling buckling in the post-bite area and the rolling model, whatever the technique, changes little the in-bite fields. The model is applied here to the effect of friction on optimal setting of a flatness actuator, Work Roll Bending

Flatness Defect in Thin Strip Cold Rolling and the Friction Impact on it

International audienceFlatness defects are one of the major problems in strip rolling. They are manifested by a wavy shape on the edge, in the center or in between. Waves are most of the time transverse, but all directions can be observed. These defects come from the heterogeneity of the stress field and the resulting buckling of the compressive areas out of the roll bite. This paper is based on the approach proposed by [1-3] and [4], and programmed previously [5-7] in the FEM software LAM3/TEC3 [8]. In the present paper, the latter is enhanced and applied to the impact of friction and strip tension on flatness of a rolled thin strip. The study shows how the optimal setting of Work Roll Bending force (WRB) should be changed when friction varies

Identification methodology and comparison of phenomenological ductile damage models for complex loading paths

National audienceUnderstanding and modeling of ductile damage mechanisms remains a major issue for many industrial cold forming processes. The ability of numerical modeling to predict the ductile fracture is indeed crucial. However, this modeling is limited because of the complexity to take into account the influence of the complex loading paths (multi-axial and non-monotonic, nonproportional, shear effects, etc.) on damage mechanisms