Abstract
In deep drawing processes, mixed lubrication friction regime is common in which the friction condition is governed by solid–solid asperity contacts and lubricant pressure. In this study, a friction model in the mixed lubrication regime is developed that accounts for the effect of the surface topographies of sheet and tool on the lubricant pressure distribution. The overall friction due to solid–solid asperity contacts and lubricant pressure is determined using a coupled hydrodynamic and boundary friction models. The model is utilized in an in-house FE code (DiekA) for deep drawing simulations. In the FE simulations, the lubricant pressure is determined by solving the average Reynolds equation. The flow factors required in the average Reynolds equation are determined separately using measured tool and sheet surface topographies. Cross-die experiments are performed at different lubricant amounts to validate the friction model at a component level. The results show that punch force vs. displacement and strain field from experiments and FE simulations (using the new friction model) correlate very well.
Highlights
Accurate description of friction in forming simulations is necessary for reliable formability analyses
In sheet metal forming, friction behavior at the tool–sheet contact depends on the local contact condi tions at asperity level such as the topographies of the contacting sur faces, contact loads and material
The FE simulations are performed in which friction behavior is modeled using the mixed lubrication friction model
Summary
Accurate description of friction in forming simulations is necessary for reliable formability analyses. In sheet metal forming, friction behavior at the tool–sheet contact depends on the local contact condi tions at asperity level such as the topographies of the contacting sur faces, contact loads and material. Two predominant lubrication regimes exist in sheet metal forming applications are: boundary and mixed lubrication regimes. In the boundary lubrication regime, the overall friction is determined solely by solid-solid contact forces. In the mixed lubrication regime, the total contact load at the tool–sheet metal is shared by the solid–solid asperity contacts (boundary lubrica tion) and lubricant pressure. The lubricant pressure distribution is estimated by solving the Reynolds equation In this regime, the influence of roughness or surface texture on the fluid flow is significant which must be considered to determine the lubricant pressure distribution using the Reynolds equation
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