Investigation of local tribological conditions in the secondary shear zone for dry and wet machining using a microscale simulation model

Abstract This study presents a microscale tribological simulation model to investigate local friction conditions in the secondary shear zone during both dry and wet machining. The precise characterization of tool-chip interactions, particularly the influence of plastic deformation and metalworking fluids on friction, remains a challenge in machining research. To address this, a combined experimental and numerical approach was employed. Chip root surfaces were analyzed using laser scanning microscopy, while friction tests quantified the coefficient of friction of thermally formed reaction layers. The results show that these layer drastically influence the frictional behavior. The simulation model was developed in two stages. First, a solid contact model based on the Johnson-Cook plasticity model was used to represent plastic deformation under dry conditions. It was found that the coefficient of friction decreases with increasing contact pressure and temperature. Second, a coupled simulation approach was introduced to investigate the influence of metalworking fluids, demonstrating a transition from dry conditions to mixed lubrication at lower pressures. Below a pressure of 200 MPa, friction was substantially reduced, whereas above 600 MPa, the lubricant film failed, resulting in dry contact conditions. These findings emphasize the importance of considering both mechanical and thermal interactions when modeling friction in metal cutting. The simulation framework provides a basis for future research on thermal integration and multi-scale simulation of chip formation.