Simulation of Fluid-Structure-Contact Interaction in Metal Forming Using the Example of Skin-Pass Rolling

• Applicants: Professor Dr.-Ing. Gerhard Hirt; Dr.-Ing. Norbert Hosters
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing ; Coating and Surface Technology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 523163077

Flat-rolled aluminum semi-finished products are increasingly being used in automotive body sheet applications to meet the global demand for energy efficiency and the resulting lightweight construction trend. Compared with steel, the challenges in production lie in ensuring high-quality properties of the surface finish. Examples include the application of lubrication pockets for subsequent forming processes and the influence of optical properties, especially after painting. Understanding all the influencing variables and mechanisms in production is thus highly relevant to achieving the desired surface profile. A defined surface is set in the so-called skin-pass rolling process by imprinting textured rolls onto the strip. However, findings from the skin-pass rolling of steel can only be transferred to the skin-pass rolling of aluminum to a limited extent due to three key differences: (1) the softer base material, (2) the use of lubricant, and (3) the more significant height reductions. The result of these differences is that lubricant inclusions in the cavities of both surfaces actively participate in the forming process. Hydrostatic and hydrodynamic effects of the entrapped fluid thus significantly influence which surface features of the work roll are in contact with the softer strip and, therefore, on the strip’s final roughness profile. A fully comprehensive process design and the prediction of the final surface properties with experimental methods are only possible at great expense (laboratory tests and production trials in the rolling mill). Numerical methods, on the other hand, face the challenges of linking the different scales (process observation on the millimeter scale and roughness on the micrometer scale) as well as mapping the topology change in the flow problem of the lubricant on the other. A simulative process design of the skin-pass rolling of aluminum is currently not state of the art. However, this gap can only be closed based on a profound understanding of the process and a multi-layered fundamental knowledge of numerical methods. To this end, the interdisciplinary group of applicants intends to pool their expertise in the proposed project. This includes the already achieved scale linkage in skin-pass rolling, experience in experimental investigations of forming processes and surface imprinting (IBF), as well as expertise in method development for mapping fluid-structure-contact interactions (CATS). The intended methodology could shorten downtimes in case of process changes and reduce scrap due to insufficient surface quality via a targeted design of the skin-pass rolling process. This can reduce production costs and increase the attractiveness of the use of aluminum in automotive bodies.

• DFG Programme: Research Grants