Numerical Investigation of a Process Control for the Roller Levelling Process Based on a Force Measurement

Markus Grüber,Gerhard Hirt

doi:10.4028/www.scientific.net/msf.854.249

Abstract

When processing conventional semi-finished metal strips, distinctive changes in the material properties along the strip length are unavoidable. The roller levelling process is sensitive to changes of those strip characteristics. Thus, a process control allowing for an online adaption of the roller levelling machine according to the actual strip characteristics is highly desirable. In order to enable a precise process layout, the calculation by the Finite Element Method (FEM) provides a suited strategy. Furthermore, the coupling of user-subroutines to an FE code offers the possibility to implement and test respective control strategies. This work proposes a control strategy that is based on a force measurement in the first load triangle of a levelling machine. A first FE model including a feedback control is used to calculate the dependence between the force in the first load triangle and the roll intermesh in the last load triangle leading to a flat sheet. The results are transferred to meta models – so called control curves – that give a direct relationship between the measured force and the roll intermesh. Within a second FE setup a feed-forward control based on these control curves is implemented and the proposed control strategy is investigated for varying yield strengths along the strip length. Thus, the time consuming FE simulations that are necessary to obtain the control curves are decoupled from the actual levelling process. According to the obtained results, the introduced approach is able to improve the sheet flatness for thin sheets when a change in the material properties occurs.

Highlights

When feeding sheet metals through conventional sheet processing lines, a crucial step is to pitch the decoiled strip into the first step of the processing line
Within this work a feed-forward process control for the roller levelling process is proposed that is capable of adjusting the leveller machine if changes of the flow stress occur along the sheet length
In order to obtain the necessary control curves that correlate the force in the first load triangle of a five roll leveller and the intermesh leading to a flat sheet in the last load triangle, an FE setup including a feedback control is used

Summary

Introduction

When feeding sheet metals through conventional sheet processing lines, a crucial step is to pitch the decoiled strip into the first step of the processing line. Roller levelling machines are used to ensure a certain flatness and thereby a stable guidance of the strip to the actual processing line [1]. The roller levelling process is basically a reversed bending operation the metal strip undergoes when passing through the machine. Each single bending is defined by the positions of the rolls with respect to each other. These roll positions are defined by the so called roll intermesh. The intermesh refers to the roll position relative to the pitches of the lower rolls. A small value of the roll intermesh leads to greater bending, that is a greater curvature, of the sheet metal (Fig. 1)

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Conclusion