Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Industrial and Systems Engineering | en_US |
| dc.contributor.advisor | Cheung, C. F. Benny (ISE) | en_US |
| dc.contributor.advisor | Wang, Chunjin (ISE) | en_US |
| dc.creator | Zhang, Zili | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/13649 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | Novel shape-adaptive multi-jet polishing system for precision manufacturing of freeform surfaces | en_US |
| dcterms.abstract | Fluid jet polishing (FJP) is widely used in ultra-precision manufacturing of freeform surfaces, such as molds and optical components, to achieve high surface quality and form accuracy. Key indices for high-end freeform components include high spatial frequency (HSF) error, low spatial frequency (LSF) error, and middle spatial frequency (MSF) error, which relate to surface roughness, form accuracy, and surface ripple, respectively. Research on these parameters in FJP is incomplete, necessitating a novel polishing system to enhance performance. The micro-scale evolution of surface morphology during FJP is not well understood, complicating predictions of surface roughness under varying conditions and often requiring costly trial-and-error methods. Additionally, material removal characteristics vary across freeform surfaces due to geometry and edge effects, making it challenging to achieve high form accuracy. To improve accuracy, the nozzle's feed rate is adjusted in the polishing process. However, challenges remain instability from high acceleration speeds. Besides, the material removal rate at the workpiece edge is significantly higher than at the interior, exacerbating edge effects. Furthermore, controlling MSF error from regular tool paths is crucial, as it negatively impacts optical component performance by causing small-angle scattering and reducing imaging contrast. To address these problems, this thesis presents a systematic theoretical and experimental investigation of the material removal characteristics of FJP at a multi-scale and establishes a novel shape-adaptive multi-jet polishing (MJP) method and hence system. The form accuracy of the freeform surfaces, along with surface quality and polishing efficiency, was enhanced. The work can be divided into five parts. | en_US |
| dcterms.abstract | In Part I, a physical model was developed to predict surface morphology and roughness after fluid jet polishing (FJP) by integrating computational fluid dynamics (CFD) simulation with kinetic analysis of abrasives. The erosion process of a single abrasive was analyzed, and the overlap of erosion pits was modeled to simulate surface evolution and determine roughness. Various polishing parameters, such as jet pressure, angle, and abrasive size, were considered. Experiments validated the model, showing good agreement between simulation and experimental results, enhancing understanding of microscale material removal in FJP. | en_US |
| dcterms.abstract | In Part II, the tool influence function (TIF) variation during freeform surface polishing was modeled using CFD to improve form accuracy. Spot polishing experiments on surfaces with different curvatures and slopes confirmed the simulation results, demonstrating the effectiveness of the CFD model. The study revealed how surface curvature and slope affect material erosion distribution, contributing to a database of TIFs for ultra-precision form control in FJP. | en_US |
| dcterms.abstract | Part III established a mathematical model for material removal rate through force analysis and CFD simulation, finding it proportional to jet pressure with a constant k determined by the workpiece and abrasive properties. Experiments validated the model, showing that controlling jet pressure rather than dwell time can achieve deterministic material removal, reducing motion system instability. | en_US |
| dcterms.abstract | In Part IV, a modified jet polishing (MJP) method was introduced to reduce middle spatial frequency (MSF) error, featuring a more complex and adjustable TIF. Results indicated that nozzle orientation and path spacing significantly influence MSF error, leading to optimized parameters for high surface quality. | en_US |
| dcterms.abstract | Based on the results in Part II, and Part III, Part V presented a novel pressure-dependent shape-adaptive MJP (PDSAMJP) system designed to compensate for material removal differences across positions. The edge effect was modeled and mitigated by optimizing jet pressure. The nozzle moved at a constant feed rate, controlling jet pressure offline with a pre-set code to accurately manage material removal distribution. Effectiveness was validated through force sensor measurements and comparisons of form accuracy with traditional methods, demonstrating uniform MJP performance on freeform surfaces. | en_US |
| dcterms.abstract | The originality and significance of this thesis lie in the development of a novel pressure-dependent shape-adaptive polishing system for freeform surfaces, based on comprehensive theoretical models. This research elucidates multi-scale material removal characteristics and multi-parameter control, effectively addressing HSF, LSF, and MSF errors in the FJP process. The development of predictive models, along with strategies for edge effect mitigation and nozzle optimization, facilitates parameter optimization and leads to substantial enhancements in surface quality and form accuracy. Additionally, the PDSAMJP system enhances efficiency in the ultra-precision manufacturing of freeform surfaces. | en_US |
| dcterms.extent | xxxviii, 238 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2025 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.accessRights | open access | en_US |
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