Modeling of the friction caused by lubrication and surface roughness in sheet metal forming

In order to find the effect of material property and lubricant viscosity on the frictional characteristics of both coated and uncoated metals, a sheet metal friction tester was designed and tensile test, surface roughness test, and friction test were performed with several kinds of drawing oils. Test results showed that as the lubricant viscosity becomes lower, the friction coefficient is higher. When surface roughness is extremely low or high, friction coefficient is high. Electric galvanized sheet metals have relatively high friction coefficients. Based on experimental measurements, the friction model considering lubricant viscosity and surface roughness is developed for using in the finite element analysis of sheet metal forming processes. The validity and accuracy of the friction model are shown comparing the punch loads among FEM analysis results employing current friction model and conventional friction model and experimental measurement.