Abstract:

：Shear-thickening polishing (STP) technology is used on ultraprecision machining of Si₃N₄ ceramics cylindrical workpiece. The STP slurry with diamond abrasives is prepared for STP process and its rheological property is studied. The polishing performance of Si₃N₄ ceramics with STP is analyzed. The machining efficiency, surface quality and roundness error of Si₃N₄ ceramic cylindrical workpiece are studied. Results show that STP slurry with diamond abrasives exhibits non-Newtonian power-law fluid characteristics with shear-thickening effect. When the shear rate () increases, the storage modulus (G′) and loss modulus (G″) show a growth trend. In addition, the dissipation factor (n′) decreases continuously. The STP removal characteristic of Si₃N₄ ceramics is a continuous micro cutting process of “flexible polishing”. As using STP slurry with abrasive particle size of 0.2 μm, the difference of material removal rate (MRR) between theoretical and experimental results is 6.12%, and the validation of MRR model is verified. The MRR decreases from 4.20 μm/h to 4.00 μm/h after 60 mins′ polishing and the average surface roughnessR_a reduces from 107.2 nm to 26.5 nm; and after 120 mins′ polishing, the MRR decreases to 3.85 μm/h andR_a can be reduced to 6.5 nm; under the same conditions, the STP with diamond abrasives slurry can obtain the Si₃N₄ ceramics cylindrical workpiece with roundness error reduced from RONt 1.418 μm to RONt 0.360 μm, which indicates that STP process achieves the ultraprecision polishing of Si₃N₄ ceramics cylindrical workpiece.

Key words: diamond abrasive, high-efficiency machining, rheology, roundness error, shear-thickening polishing(STP), silicon nitride, surface roughness, polishing