The Effect of the Initial Stress and Strain State in Sheet Metals on the Roller Levelling Process

Due to increasing requirements regarding the flatness of sheet metals, the process of roller levelling is of particular importance. The process itself is influenced by a high number of parameters such as machine design, sheet dimension, and material properties. Therefore, it is desirable to provide an online process control to react on changes of those process parameters. One possible approach for the layout of a process control and the identification of reference values is the use of the Finite Element Method (FEM). Considering the alternate bending a sheet metal undergoes when passing through a roller leveller, kinematic hardening of the sheet material must be taken into account. Additionally, the initial stress and strain distribution of the sheet metal – e.g. induced by coiling – has an influence on the material behaviour and consequently on the process parameters. With respect to these effects, a coupled FE model, which accounts for the initial state of the sheet metal, is introduced. An inverse calculation of material parameters describing the behaviour under cyclic load conditions has been done for an aluminium alloy AA5005 and a mild steel DC01. Based on this numerical setup, the influence of the initial stress state in the pre-levelled sheet metal on the roller levelling process has been deduced. Accompanying experiments on a down-sized roller leveller were carried out for a validation of the numerical setup.

[1]  John A. Nelder,et al.  A Simplex Method for Function Minimization , 1965, Comput. J..

[2]  E. Doege,et al.  Analysis of the levelling process based upon an analytic forming model , 2002 .

[3]  Gerhard Hirt,et al.  Adjusting of Roller Levellers by Finite Element Simulations Including a Closed-Loop Control , 2014 .

[4]  B. Scholtes,et al.  Residual stress states as a result of bending and straightening processes of steels in different heat treatment conditions , 2012 .

[5]  O. Benevolenski,et al.  MATERIAL CHARACTERIZATION FOR SIMULATION OF SHEET METAL FORMING , 2005 .

[6]  Wilhelm Guericke.  Material Model Describing Cyclic Elastic-Plastic Deformation of Roller Levelling and Straightening Processes , 2009 .

[7]  A. W. Lees,et al.  Formation of residual stresses owing to tension levelling of cold rolled strip , 2001 .

[8]  Z. T. Zhang,et al.  Stress and residual stress distributions in plane strain bending , 1998 .

[9]  Joseba Mendiguren,et al.  Testing and Modeling of Roll Levelling Process , 2014 .

[10]  Tomáš Návrat,et al.  A New Model for Fast Analysis of Leveling Process , 2012 .

[11]  Mattias Widmark,et al.  Low cycle constant amplitude fully reversed strain controlled testing of low carbon and stainless sheet steels for simulation of straightening operations , 2000 .

[12]  Zdeněk P. Bažant,et al.  Mechanics of solid materials , 1992 .

[13]  Fusahito Yoshida,et al.  Inverse approach to identification of material parameters of cyclic elasto-plasticity for component layers of a bimetallic sheet , 2003 .

[14]  J. Chaboche.  Constitutive equations for cyclic plasticity and cyclic viscoplasticity , 1989 .