Magnetorheological finishing of AISI 304 stainless steel for precision optical mold applications

Nano-finishing of metallic injection molds is crucial to achieve high surface integrity of the polymer-based optical molded products. The exceptional hardness, shrinkage capacity and thermal resistance of AISI 304 stainless steel, make it ideal for mold material. Various metallic mold industries demand nano-scale surface smoothness with exceptional dimensional accuracy. To meet these requirements, magnetorheological (MR) finishing has been conducted over mold surface. Further, to enhance the effectiveness of the MR finishing, a disk-shaped mild steel part was strategically placed beneath the non-magnetic workpiece. After incorporating mild steel part, the magnetic flux density rises from 0.22 to 0.4 Tesla in working region. To achieve optimal finishing performance, response surface methodology (RSM) was employed to optimize the finishing parameters. The optimized regression model was validated using artificial neural network predicted model. Consequently, the surface area roughness (Sa) was measured using optical profilometer. Its result showed substantial improvement in Sa value from an initial 3.60 µm to 0.091 µm after lapping, and further reduced to 0.009 µm following 80 min of MR finishing. Moreover, a marked improvement in the waviness profile, surface morphology, and reflectivity confirmed that MR finishing meets high-quality finishing standards, yielding superior surface quality and enhanced productivity of optically molded products.