Multiphysics coupled modeling and mechanism analyzing of magnetorheological finishing for stainless-steel capillary inner surfaces

High-quality capillary inner surfaces are essential for advanced medical devices, yet their millimeter-scale confined geometry makes precision finishing difficult. To investigate the material removal mechanism in magnetorheological finishing (MRF), a coupled magnetic–flow-field model was developed to evaluate the effects of inlet velocity and magnetic flux density. Finishing experiments were conducted to assess the consistency between the simulated and experimental parameter-dependent trends and to examine the proposed synergistic removal mechanism. A material removal model incorporating magnetically induced pressure and near-wall abrasive velocity was further established to quantitatively describe the removal behavior. The simulations showed that wall shear stress increased with inlet velocity, with a reduced incremental increase at higher velocities, while increasing magnetic flux density enhanced both near-wall shear and abrasive confinement. The experimental material removal exhibited similar trends, supporting the combined contributions of hydrodynamic shear and magnetic confinement. After finishing, surface protrusions, grooves, and asperity peaks were significantly reduced, and the areal roughness (Sa) decreased from 1.3 μm to 59 nm. The material removal model showed reasonable agreement with the experimental measurements, with a mean relative error of 7.53%. These results provide a basis for understanding the removal mechanism and quantitatively describing material removal in MRF of capillary inner surfaces.