FE forming analysis with nonlinear friction coefficient model considering contact pressure, sliding velocity and sliding length

• A nonlinear friction coefficient model was developed based on the friction tests.
• Effects of sliding length was estimated by new friction tests with a long bar tool.
• The present model improves the prediction accuracy of press load–stroke properties.
• The present model is effective for predicting formability of large drawing panels.
• Effects of press motion control with servo press on formability can be estimated.

A nonlinear friction coefficient model which considers contact pressure, sliding velocity and sliding length was developed to improve the accuracy of predictions of the formability of steel sheets. The effects of contact pressure and sliding velocity under mixed lubrication were estimated based on a friction test in which a long steel sheet was drawn between two dies. The effect of the sliding length under the condition of lack of lubricants was estimated in another friction test, in which a long tool bar was placed between steel sheets and drawn continuously at the same position on the sheets. The results of cup drawing experiments and a finite element (FE) forming analysis using the developed friction model demonstrated that the model improves the accuracy of predictions of the formability of steel sheets. Finally, the effect of press motion control with a servo press on formability improvement was estimated by using the nonlinear model.