The effect of strain-hardening on frictional behavior in tip test

In previous investigation of the tip test using aluminum alloy AL6061-O, it was found that the distance of radial tip from the external side surface of the workpiece deformed has a linear relationship with the maximum forming load measured at a certain punch stroke. In this study, further experiments with aluminum alloys AL2024-O, AL5083-O, AL6061-O, AL7075-O, annealed carbon steel AISI 1010 and pure copper C12100 were carried out to investigate the effect of material properties on frictional behavior by the tip test for the materials commonly used in bulk metal forming. To characterize the relationships among radial tip distance, maximum forming load and shear friction factor, finite element analyses were employed. It was observed that the linear relationships among these three were maintained for the various tested materials. Also, it was found that the friction condition at the punch was always higher than that at the lower die interface such that the ratio of shear friction factors at the die and punch interfaces should be less than one. By examining the material properties currently tested, it was determined that this ratio could be estimated from a logarithmic equation from the value of strain-hardening exponent, depending on the material used.