Identification of coulomb and constant shear frictions in hot aluminum forming by using warm and hot upsetting sliding test

This study aims to identify the Coulomb friction coefficient and shear friction factor in aluminum forming processes at high temperatures by using the warm and hot upsetting sliding test (WHUST). The presence of pile-up material in front of the contactor when performing the WHUST on aluminum alloys at elevated temperatures modified the contact geometry. Thus, in this study, the pile-up material was derived as a parameter in the analytical equations. It was found that the analytical equation allows to identify the Coulomb friction coefficient directly from the experimental data, while the analytical equation for the shear friction factor requires the yield stress at the contact surface in addition to the experimental data. For the experiment, the WHUST was performed on AA6082-T6 aluminum alloy against AISI H13 hot work tool steel under dry contact conditions at 400 °C. To precisely control the testing temperature, the WHUST apparatus was installed into the heating chamber of the Bruker UMT TriboLab. Finite Element Analysis (FEA) was used to determine the yield stress at the contact surface. In this study, three commercial FEA software, ABAQUS, DEFORM, and FORGE NxT, with two different sets of material data based on Hansel-Spittel material behavior law were carried out to demonstrate the variations in the computational results of the yield stress and its impact on the identification result of the shear friction factor. Finally, the Coulomb friction coefficient was 0.57, and the shear friction factor ranged between 0.76 and 0.90, depending on the yield stress obtained from the FEA software.