Friction modeling in computer simulation of sheet metal forming processes

A hydrodynamic lubrication model was coupled to a finite element model of sheet deformation to study the formation of the lubricant film in axisymmetric stretch forming. When sheet bending effects were included, the combined model showed good agreement with interferometric film thickness measurements previously reported by Hector. An essentially closed form method of predicting the initial film thickness was developed based on these findings.; A realistic friction model for sheet metal forming which combines internal variables such as lubricant film thickness and workpiece roughness with traditional external variables like pressure and surface velocity was developed and implemented. The model utilized the new film thickness calculation methodology. The model was coupled with a membrane finite element code and applied to an axisymmetric stretch forming operation. The influence of the thermal and the roughness effect on lubrication has been discussed. The transition from the mixed film regime to the boundary regime was modeled by considering the load sharing process between the asperity contact and the lubricant film.; The results of the computer simulation were compared with the experimentally measured strain distributions in axisymmetric stretch forming experiments with a variety of different lubrication conditions. The simulation results show good agreement with the experimental measurements. The total time penalty for using the realistic friction model is less than 15% of the total computational time.