The Effect of Surface Finish on Aluminum Sheet Friction Behavior

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The Effect of Surface Finish on Aluminum Sheet Friction Behavior

Cohen, Donald / sanchez PhD, L. Rafael / Brattstrom, Lars-Erik / Hartfield-Wunsch, Susan E.

Aluminum sheet is commercially available in three surface finishes, mill finish (MF), electric discharge texture (EDT), and dull finish (DF). This surface finish impacts the friction behavior during sheet metal forming. A study was done to compare ten commercially available sheet samples from several suppliers. The friction behavior was characterized in the longitudinal and transverse directions using a Draw Bead Simulator (DBS) test, resulting in a coefficient of friction (COF) value for each material. Characterization of the friction behavior in each direction provides useful data for formability analysis. To quantitatively characterize the surface finish, three-dimensional MicroTexture measurements were done with a WYKO NT8000 instrument. In general, the MF samples have the smoothest surface, with Sa values of 0.20-0.30 μm and the lowest COF values. The EDT samples have the roughest surface, with Sa values of 0.60-1.00 μm, and the highest COF values. The DF sample falls between the MF and EDT with Sa = 0.60 μm. Also, the EDT and DF samples have a more isotropic surface, as indicated by Stylus X Ra/Stylus Y Ra = 0.97-1.01, and the COF values are approximately the same in the transverse and longitudinal directions for these samples. The MF samples are less isotropic, with Stylus X Ra/Stylus Y Ra = 1.79-4.87, and the COF values are lower in the transverse direction than in the longitudinal direction for the MF samples.