An enhanced boundary lubrication friction model for sheet metal forming

A new micromechanics-based friction model a under boundary lubrication is proposed to enhance an existing surface asperity-based friction model. The study presents a formulation of equilibrium between the plastically deformable workpiece and contact tool, and the newly proposed geometrical modeling of the tool surface to implement the plowing effect. Under this scheme, the contact tool is modeled based on the primary summits in the tool height distribution identified by a measured wavelength, which avoids the dependency on the accurate measurement of summit profiles. Also, the model can consider the micro-scale interaction between metal workpiece and tool surface. The developed micromechanics-based friction model is validated by comparing the calculated nominal friction coefficients of advanced high-strength steels (AHSS) at different contact pressures with those of experiment. Finally, the friction model is implemented in finite element (FE) software to simulate two forming processes: U-draw/bending and an in-line incremental die forming. The predicted forming force and springback in the sheet metal forming agree well with the experimentally measured ones, which verifies the accuracy and numerical efficiency of the proposed friction model and its numerical implantation.