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<p>Polymethyl methacrylate (PMMA) is widely used in optical systems due to its high transparency and stable refractive properties. However, achieving deterministic nanometer-scale finishing on complex three-dimensional geometries, particularly hemispherical components, remains a major challenge. Conventional magnetorheological finishing (MRF) systems are primarily designed for planar or simple curved surfaces and lack effective magnetic field concentration and uniformity within confined hemispherical cavities, resulting in limited polishing stability and controllability. To address this limitation, a mechanism-driven hemispherical Halbach-array-based MRF system is proposed, in which magnetic field topology is engineered to regulate the rheological behavior of the polishing fluid and the associated material removal mechanism. By optimizing magnet geometry and spatial arrangement while keeping magnet material and quantity constant, a spherical Halbach configuration was developed, achieving a peak magnetic flux density of 1.97 T with enhanced inward field concentration and gradient stability. This strengthened magnetic confinement improves polishing ribbon stiffness and removal uniformity. A coupled magnetic-rheological-mechanical framework was established to clarify the relationship between magnetic field intensity, shear stress evolution, and material removal modes under varying inlet pressure, fluid velocity, rotational speed, and cutting depth. Finite element simulations and experimental measurements show good agreement in magnetic field distribution and removal behavior. The optimized system achieved uniform material removal and a consistent nanometer-scale surface finish (Ra = 1&#xa0;nm) across the hemispherical PMMA surface. This field-engineered Halbach-MRF strategy extends deterministic magnetorheological polishing to complex three-dimensional polymer optics and provides a new approach for precision manufacturing of advanced optical components.</p>

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Novel hemispherical Halbach array configuration and material removal mechanisms for magnetorheological polishing of polymethyl methacrylate

  • 期刊论文

  • 发表日期：

    2026年5月6日

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  • Quach Vu Hieu,
  • Nguyen Tien Tung,
  • Le Thi Phuong Thanh,
  • Nguyen Chi Tam,
  • Dao Ngoc Hoanh,
  • Le Dang Ha,
  • Nguyen Minh Quang,
  • Nguyen Duy Trinh

摘要

Polymethyl methacrylate (PMMA) is widely used in optical systems due to its high transparency and stable refractive properties. However, achieving deterministic nanometer-scale finishing on complex three-dimensional geometries, particularly hemispherical components, remains a major challenge. Conventional magnetorheological finishing (MRF) systems are primarily designed for planar or simple curved surfaces and lack effective magnetic field concentration and uniformity within confined hemispherical cavities, resulting in limited polishing stability and controllability. To address this limitation, a mechanism-driven hemispherical Halbach-array-based MRF system is proposed, in which magnetic field topology is engineered to regulate the rheological behavior of the polishing fluid and the associated material removal mechanism. By optimizing magnet geometry and spatial arrangement while keeping magnet material and quantity constant, a spherical Halbach configuration was developed, achieving a peak magnetic flux density of 1.97 T with enhanced inward field concentration and gradient stability. This strengthened magnetic confinement improves polishing ribbon stiffness and removal uniformity. A coupled magnetic-rheological-mechanical framework was established to clarify the relationship between magnetic field intensity, shear stress evolution, and material removal modes under varying inlet pressure, fluid velocity, rotational speed, and cutting depth. Finite element simulations and experimental measurements show good agreement in magnetic field distribution and removal behavior. The optimized system achieved uniform material removal and a consistent nanometer-scale surface finish (Ra = 1 nm) across the hemispherical PMMA surface. This field-engineered Halbach-MRF strategy extends deterministic magnetorheological polishing to complex three-dimensional polymer optics and provides a new approach for precision manufacturing of advanced optical components.