High-precision ceramic extrusion dies are essential for micro-tube manufacturing, where internal bores are critical to minimizing extrusion friction, reducing material adhesion, and extending die life. Conventional polishing methods are ineffective due to limited tool access, risk of micro-cracking, and inability to achieve nanometric surface finishes within enclosed geometries. This study explores the application of magnetorheological finishing (MRF) for deterministic, damage-free polishing of internal bores in zirconia/alumina ceramic die with diameters of 5 mm. A custom-designed internal MRF tool, optimized MR fluid formulation with sub-micron diamond abrasives, and controlled magnetic field parameters were employed to achieve uniform surface improvement without compromising bore geometry. Experimental results demonstrate a reduction in average surface roughness (Ra) from 0.42 µm to 0.025 µm, representing a 94.0% improvement, alongside a 15% increase in surface microhardness and significant reduction in friction coefficient during simulated extrusion tests. Experimental validation of finishing performance and micro-extrusion relevance was based on internal bore surface roughness measurements using replica-based optical profilometry, microhardness testing, and tribological evaluation under simulated sliding conditions, rather than direct micro-extrusion trials.
Manpreet Singh (Mon,) studied this question.