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The study concerns the analysis of significant contact friction changes by changing the size of crystal grains in the processes of free axisymmetric work pieces upsetting, initial height of 2 mm. The friction changes result with significant changes in forming force. This phenomenon usually characterizes micro forming processes. Using hard experimental data in the creation of numerical FE (finite element) model, a dependence of the changes of contact friction in correlation to the change of the work piece crystal grain size for three different grain sizes: 39, 47 and 76 μm is presented. It is shown that the friction factor is increased by reducing the size of crystal grains. Physical interpretation of the results is given by theory of Bowden and Tabor.

FEM Analyses of Friction Coefficient in Open Die Coining Process of Different Grain Sizes