Abstract
Friction influences the formability in sheet metal forming processes. It depends on the local contact condition between tool and sheet metal. Therefore, precise estimation of real area of contact is the first step for an accurate prediction of friction. In this study, a multi-scale contact model is developed to predict deformation of asperities on a rough uncoated and coated surfaces under normal load. The model accounts for the coating thickness and material behavior of coating and substrate. Finite element simulations are performed to determine the contact pressure of single asperities of different sizes. These are used to determine the real area of contact. The model is validated relative to the experiments performed on uncoated and zinc coated steel sheets.
Highlights
The real area of contact between two surfaces is determined by the persistence of the highest asperities to deformation mainly at the softer surface
The real contact area is influenced by local contact pressure, surface topographies of the sheet metal as well as the forming tool, their material behavior, lubri cant condition and temperature in the sheet metal-tool contact [1,2,3] the first step to have a reliable prediction of friction coefficient is to accurately estimate real area of contact at sheet metal-tool interface
The results show that model is able to predict the real area of contact for the nominal contact pressure range upto 60 MPa very well
Summary
The real area of contact between two surfaces is determined by the persistence of the highest asperities to deformation mainly at the softer surface. It is generally assumed that real area of contact is solely controlled by plastic deformation of the asperities while a perfectly-plastic material model is utilized. Reliable modeling of friction in sheet metal forming simulations is vital for the accuracy of the formability analyses [1]. Friction in sheet metal forming is a local phenomenon which depends on continuously evolving contact conditions during the forming process. The real contact area is influenced by local contact pressure, surface topographies of the sheet metal as well as the forming tool, their material behavior, lubri cant condition and temperature in the sheet metal-tool contact [1,2,3] the first step to have a reliable prediction of friction coefficient is to accurately estimate real area of contact at sheet metal-tool interface
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