Abstract
When the sheet metal stamping processes are simulated, different values of the friction coefficient need to be defined in different regions, considering the nature of the deformation process. Thus, the regression and analytical models to determine the friction coefficient under the blankholder and on the die drawing edge by the strip drawing test are presented in the article. These models were verified by experimental strip drawing test under the same contact conditions. Zn coated high strength low alloyed steel sheet H220PD+Z100 was used at experiments and friction tests were done against the tool steel and TiCN MP coated tool steel. The results indicate, that values of friction coefficients evaluated by linear regression are lower than evaluated from analytical models. The positive effect of coating TiCN MP when applied on the contact surfaces was found, thus, decreases the friction coefficient and the drawing force scattering during the strip drawing test.
Highlights
There are many parameters influencing the sheet metal formability from the view of stamping, such as material properties, the die and the punch geometry, the contact surfaces’ microgeometry, lubrication, etc. [1,2,3,4,5] Their accurate determination is ambiguous because these are changed from one case of the stamping process to another
When friction coefficient evaluated under the blank holder according to Eq (3.), it varied from 0.320 to 0.353, i.e. 0.334 ± 0.017 for friction pair tool steel / Zn surface; and from 0.304 to 0.318, i.e. 0.310 ± 0.007 for friction pair TiCN coating / Zn surface
When friction coefficient evaluated on the drawing edge according to Eq (4.), it varied from 0.314 to 0.343. i.e. 0.326 ± 0.013 for friction pair tool steel / Zn surface; and from 0.307 to 0.326, i.e. 0.317 ± 0.008
Summary
There are many parameters influencing the sheet metal formability from the view of stamping, such as material properties, the die and the punch geometry, the contact surfaces’ microgeometry, lubrication, etc. [1,2,3,4,5] Their accurate determination is ambiguous because these are changed from one case of the stamping process to another. In the case the roller is fixed we model the loading of curved contact areas on the die drawing edge (Fig. 1-B). Exchangeable grips were used and this allowed modelling friction conditions tool steel/Zn surface and TiCN MP coating/Zn surface.
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