Defined adjustment of the residual stress distribution in strip and sheet material via roller levelling

• Applicant: Professor Dr.-Ing. Gerhard Hirt
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: from 2017 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 322638998

Due to the ongoing trend for automation in strip and sheet production lines, it is necessary to ensure steady conditions in the material when looking for a disturbance-free production process. Essential characteristics of strips and sheets are both flatness and the distribution of residual stresses within the material. Despite the flatness of strips and sheets the distribution of the residual stresses might be disadvantageous and could lead to flatness defects after cutting of the material.In order to provide the desired flatness as well as a beneficial residual stress distribution roller levelling machines are used at the initial stage of the production process. Such levelling machines are able to target both on flatness and the residual stress distribution. The optimum adjustment of these levelling machines depends on various parameters. Up to now it is not possible to measure the residual stress distribution during the process and it is thereby not possible to use the stress distribution as a reference value for a process control. Therefore, this research proposal aims on the development of a numerical model that enables for a process layout respecting both flatness and residual stress distribution. In collaboration with an industrial partner an existing numerical model from a previous DFG-project is to be enhanced regarding the consideration of the residual stress distribution. At first, the dependence between the adjustment of the levelling machine and the residual stress distribution will be investigated using the numerical model. A comparison to calculations from process models developed by the industrial partner allows particularly for a consistency check regarding the used material data describing the behaviour under reversed cyclic bending load. Furthermore, the industrial partner provides optimisation criteria for the residual stress distribution based on relevant applications. These optimisation criteria will be transferred to numerical model which includes a virtual feedback-control.This numerical model including a feedback-control can calculate the adjustment of the levelling machine leading to simultaneously optimised flatness and residual stress distribution. An experimental measurement of the residual stress distribution via diffractometric methods enables for a validation and optimisation of the numerical model. Thus, a numerical model is available capable of determining the adjustment of roller levelling machines that lead both to flatness and an optimised residual stress distribution. Additionally, this model provides information about the possibility to influence the residual stress distribution through bending processes.

• DFG Programme: Research Grants (Transfer Project)
• Application Partner: SMS group GmbH