Feedback control of surface properties of cold-rolled semi-finished products by development of a novel control concept based on online-roughness measurements of the strip surface

• Applicants: Dr.-Ing. David Bailly, since 7/2024; Dr.-Ing. Sebastian Stemmler
• Subject Area: Automation, Mechatronics, Control Systems, Intelligent Technical Systems, Robotics ; Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 424333859

This research project aims to develop a property control system for the re-rolling process based on roughness-measurements of the outgoing strip surface. The surface topology imprinted during rerolling significantly influences functional properties of metallic semi-finished products such as paintability (paint adhesion), surface gloss or tribological properties (friction coefficient). Today, the re-rolling process is controlled by specifying a rolling force. The latter is calculated in advance using models which describe the imprinting of the structured roll. However, there is no active control of the strip properties. Moreover, deviations due to inaccurate modeling or process disturbances (e.g. roll wear, inhomogeneous friction conditions in the roll gap) are neither monitored nor fed back to the process, such that the functional properties vary across the rolled strip. In this context, a cascaded control loop for tracking strip properties was developed in the previous funding periods of the priority program 2183. Based on model predictive control (MPR), a roughness controller was designed that enables low-level tracking of a given roughness average Ra independently of the required strip geometry (strip thickness). For this purpose, a fast metamodel for describing the roll’s imprinting was derived in the first funding period based on an offline multiscale simulation. Model deviations are identified at runtime using the integrated roughness sensor. The data is then used to adapt the controller models. In order to decouple the strip’s surface topography and geometry, the strip tension was investigated as an additional actuator apart from using a secondary roll stand. The results indicate that the strip tension does indeed influence the imprinting of the work roll, which is especially true for asymmetric strip tensions. During the second funding period, the control topology was extended by models relating the strip’s surface roughness and functional properties. On top level, the control loop was then closed by means of a new soft sensor integrating the said models for online prediction of the strip properties. In addition to an analysis of the feasible process window, the roughness controller was furthermore reformulated to explicitly account for uncertainties in the process modeling. In the third funding period, validation of the property controller under industry-like process conditions is planned. Here, an additional rolling material, the roll wear, higher rolling speeds, and the use of lubricants will be considered. Furthermore, the effect of the property controller on strip characteristics such as yield strength or two-dimensional roughness characteristics will be investigated. Concluding rolling tests aim to quantify the improvement in strip property by comparing the property controller to a conventional process control. Finally, design principles for the property-controlled forming process will be derived.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2183: Property-controlled metal forming processes
• International Connection: Netherlands
• Co-Investigators: Professor Dr.-Ing. Dirk Abel; Professorin Dr.-Ing. Heike Vallery
• Ehemaliger Antragsteller: Professor Dr.-Ing. Gerhard Hirt, until 6/2024