Rotational magnetorheological finishing of the interior surface of a small 316L stainless steel tube

316L stainless steel small tubes with a sufficiently smooth inner surface are needed for the service performance of equipment. To address the challenges of poor surface quality and limited machining space on the inner walls of them, a magnetorheological finishing technique, which employs a rotational magnetic field combined with reciprocating motion, is introduced for polishing narrow inside walls. Based on finite element analysis, the effect of various permanent magnet layouts on the polishing zone is examined, revealing that the N–S layout of strip magnets is more suitable as an optimized magnetic field generator. The interior surface polishing process of tubes applying this method was studied through multi-physics field coupled simulation, which analyzed the applied force and confirmed the benefit of a rotary magnetic field. Developing specialized equipment is followed by polishing experiments on the internal walls of small tubes. The feasibility of the proposed technique and simulation results is verified. These experiments also examine how diverse process parameters affect surface roughness, such as the types of abrasive, combinations of carbonyl iron powder and abrasive sizes, processing time, and the velocity of the magnetic field's rotation. With the optimal process parameters, the internal surface roughness is diminished from Sa 312 nm to Sa 28 nm, and the fine texture of the original surface is removed.