Determination of Friction Coefficient in Structural Forming Analysis Considering Anisotropic Yield Function

This paper discusses a method to determine the friction coefficient between molds and a sheet material during metal-forming processes. A deep-drawing process with a hemispherical punch was performed with a 99.9% pure copper ultra-thin sheet material (0.15 mm thick). Tensile tests were conducted along three specimen orientations to determine the material properties for use in finite element (FE) simulations. Different calibration methods for an anisotropic yield function (Hill48) were examined to describe the yield and r-value behaviors. FE simulations with different friction coefficients and constitutive equations were performed to confirm the variation in force vs. displacement response and major/minor strain fields. To determine the friction coefficient, an optimization process was conducted to minimize the differences between the FE and experimental results, which showed good agreement when the optimized friction coefficient was applied. The proposed method would be useful for generating precise FE models for sheet-metal-forming processes.