A strategy for the controlled setting of flatness and residual stress distribution in sheet metals via roller levelling

Abstract

Abstract High-efficient, fully-automated strip processing lines rely on homogeneous conditions of the incoming metal strip. Roller levelling machines are therefore placed in the initial stage of sheet processing lines to ensure both the strip flatness and a desired residual stress distribution. Even though a sheet metal appears perfectly flat, the residual stress distribution may be disadvantageous and lead to flatness defects in the downstream production. Furthermore, the material properties of the metal strip may change along its length and make an adaption of the leveller’s setting necessary. To link both target values of sheet flatness and residual stress distribution, a numerical model of a seven-roll leveller is used to determine roll positions resulting in a flat sheet and a defined residual stress distribution. Thus, correlations between the initial sheet properties, the machine settings and the final sheet properties can be derived. Additionally, the influence of changing material parameters is shown. All results will finally be used to provide a reference for a feed-forward process control based on a force measurement in the first load triangle of a roller leveller. In order to validate the numerical results, experiments on a down-sized roller leveller are conducted which show that the changes of the forces in each load triangle correspond to the numerical results when changing both the initial sheet state and the intermesh. Thus, the general potential of changing the residual stress distribution via roller levelling can be investigated using numerical calculations.