Optimization of a Three-section Arc-shaped Flow Channel in a Magnetohydrodynamic Polishing Disc

WANG Zhaopei; FENG Ming; CHEN Zhixiang; FANG Zheng; JIANG Min; LI Min

doi:10.16490/j.cnki.issn.1001-3660.2026.15.004

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Surface Technology ›› 2026, Vol. 55 ›› Issue (15) : 40-52. DOI: 10.16490/j.cnki.issn.1001-3660.2026.15.004

Precision and Ultra-precision Machining

Optimization of a Three-section Arc-shaped Flow Channel in a Magnetohydrodynamic Polishing Disc

WANG Zhaopei¹, FENG Ming^1a,1b,2,3, CHEN Zhixiang^1a,1b,*, FANG Zheng², JIANG Min², LI Min³

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Abstract

Lithium niobate (LiNbO₃) crystals, renowned for their exceptional electro-optical and acousto-optical properties, are indispensable substrate materials for high-frequency filters and optical waveguides. However, their intrinsic characteristics such as high hardness, brittleness, and strong anisotropy pose significant challenges to ultra-precision machining. Conventional contact polishing techniques often result in low material removal rates, surface scratches, and subsurface damage. To overcome these limitations and achieve high-efficiency, damage-free planarization, the work aims to propose an integrated optimization strategy based on hydrodynamic lubrication theory. The strategy combines flow-channel geometry design, Python-based machine-learning parametric modeling and optimization, and validation through 3D transient numerical simulations with ANSYS Fluent. The objective is to significantly enhance the hydrodynamic effect and load-carrying capacity while improving the uniformity of the pressure distribution by scientifically reconstructing the flow-field characteristics, thereby enabling efficient, stable, and low-damage ultra-precision polishing of hard and brittle materials. Firstly, a parametric model of the arc-shaped flow channel was established, identifying key geometric variables (X₁, X₂, X₃). Through Python programming, Latin Hypercube Sampling (LHS) was employed to generate a representative dataset. This dataset was then fitted to a nonlinear polynomial regression model via the Scikit-learn library to accurately map the complex relationship between the channel parameters (X₁, X₂, X₃) and the maximum dynamic pressure P_max_. Subsequently, the Sequential Least Squares Quadratic Programming (SLSQP) algorithm was applied to solve the constrained optimization problem, determining the optimal geometric-parameter combination that maximizes hydrodynamic pressure. To validate the design and explore the effects of process parameters, a three-dimensional transient flow-field model was developed with Ansys Fluent. The simulation results indicated that the optimized arc-shaped channel significantly outperformed the traditional trapezoidal design, increasing the average dynamic pressure on the workpiece surface by approximately 35%, thereby demonstrating the effectiveness of the optimization strategy. Furthermore, the effects of key process parameters on the magnitude and uniformity of dynamic pressure were systematically analyzed. The results revealed that the speed ratio $|i|$was a key factor controlling flow-field behavior. At low-speed ratios ($|i|\leqslant1$), the pressure distribution was asymmetric and unstable. However, at high-speed ratios ($|i|\geqslant2$), particularly at a ratio of 10∶1, the dynamic pressure exhibited a highly stable, axisymmetric concentric-haoring distribution. Under these conditions, the dynamic-pressure non-uniformity coefficient (M_p) reached a minimum value of 56.93%, indicating optimal uniformity. The working gap had a differentiated impact on polishing-performance parameters. While the average dynamic pressure was relatively insensitive to variations in the gap, the load-carrying capacity F_c showed a distinct peak at a gap of 100 μm, identifying this as the ideal value for stable machining. In addition, increasing the solid volume fraction of silica nanoparticles in the polishing fluid was shown to effectively enhance dynamic-pressure performance. Higher solid content significantly increased fluid viscosity, resulting in substantial improvements in both dynamic pressure and load-carrying capacity. In conclusion, this work demonstrates that the MA-HDP method, supported by an optimized arc-shaped flow channel and appropriate process parameters, can generate a robust and uniform hydrodynamic pressure film. These findings provide a solid theoretical foundation and valuable technical reference for optimizing ultra-precision polishing processes for LiNbO₃ and other hard, brittle materials, ensuring a balance between high processing efficiency and excellent surface integrity.

Key words

magnetohydrodynamic polishing / arc-shaped flow channel / Fluent / speed ratio / uniformity / low damage

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WANG Zhaopei, FENG Ming, CHEN Zhixiang, FANG Zheng, JIANG Min, LI Min. Optimization of a Three-section Arc-shaped Flow Channel in a Magnetohydrodynamic Polishing Disc[J]. Surface Technology. 2026, 55(15): 40-52

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Funding

Natural Science Foundation of Zhejiang Province (LQ23E050003); National Natural Science Foundation of China (General Program 52475446, Overseas 2023); Anhui Provincial Natural Science Foundation (General Program 2308085ME170); Major Key Project of Anhui Provincial Science and Technology Innovation Action Plan (202423i08050035); Wenzhou Major Science and Technology Innovation Project (ZG2022029)