Papers by Author: Chi Fai Cheung

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Authors: Chi Fai Cheung, Wing Bun Lee, Sandy To, H.F. Li, Su Juan Wang
Abstract: The fabrication of high-quality optical microstructural surfaces is based on fast tool servo (FTS) machining. It makes use of auxiliary piezo-electric driven servos to rapidly actuate the diamond tool with a fine resolution and a sufficiently high bandwidth for machining optical microstructures with submicrometer form accuracy and a nanometric surface finish without the need for any subsequent post processing. However, the achievement of a superior mirror finish and form accuracy still depends largely on the experience and skills of the machine operators, acquired through an expensive trial-and-error approach to using new materials, new mircostructural surface designs, or new machine tools. As a result, this paper, a model-based simulation system is presented for the optimization of surface quality in the FTS machining of optical microstructures. Preliminary experimental work and the results are also presented.
Authors: Dong Gao, Ying Xue Yao, Wing Bun Lee, Chi Fai Cheung
Abstract: Virtual manufacturing (VM) is an emerging technology that provides a digital tool for the optimization of the production efficiency through simulations prior to the start of actual production. A NC program translator is one of the crucial components for virtual machining which allows the simulation and verification of NC tool path before actual machining. In this paper, a framework of a NC program translator for diamond turning of precision optics is presented.
Authors: Tsz Chun Kwok, Chi Fai Cheung, Suet To, Wing Bun Lee
Abstract: In this paper, a framework of surface generation model in the fast tool servo (FTS) machining of optical microstructures will be described. The integrated model is totally composed of a tool path generator (TPG), a surface topography model (STM) and an optimization model (OM). To develop the tool path generator, two parts should be involved. The first part is the tool path generated based on cutting conditions such as the feed rate and spindle speed, the geometry of optical microstructures, and diamond tool geometry. Another part is the synchronized motion generated by the tool actuation of the FTS at a bandwidth higher than the rotational frequency of the spindle. The surface topography model will be generated based on the TPG and used to predict the technological aspects of FTS machining. It takes into the account the kinematic and dynamic characteristics of the cutting process. The former includes the tool path generated by the tool path generator. The later includes the relative vibration between the tool and the workpiece caused by the axial error motion of the spindle as well as the synchronized motion of the FTS system. The optimization model will be undertaken by an iterative algorithm, which will be developed based on the TPG and STM. The OM will be expected to output the verified tool path, the suggested optimum cutting conditions, and the diagrams with predicted cutting performance characteristic and process parameters being investigated. Eventually, the successful development of this surface generation model can contribute for the knowledge of ultra-precision machining with FTS and the further development of the performance of the machining system.
Authors: Ling Bao Kong, Chi Fai Cheung, Wing Bun Lee, Sandy To
Abstract: This paper presents an integrated platform for modelling and measurement of freeform surface generation in ultra-precision raster milling. It is composed of several components which are optics design component, tool path generator, modelling system, measurement system, evaluation component, compensation component and optimization component, respectively. The research emphasizes on modelling and simulation of freeform surface generation, the prediction of the cutting performance and hence the optimization of cutting strategy in the ultra-precision raster milling of freeform surfaces. A measurement system is also proposed to carry out a fast and efficient measurement plan of freeform surfaces. Non-uniform Rational B-Spline (NURBS) will be employed for the development of the integrated platform which will meet Standard for the Exchange of Product model data (STEP).
Authors: Ka Fu Chu, Chi Fai Cheung
Abstract: Effective inventory management strategies and their efficient implementation are recognized as important elements in a manufacturer’s business model. The targets are reduction of the level and value of inventory maintained, high speed in transforming them to orders delivered to customers and flexibility in dealing with demand changes. This paper proposes a business model for inventory management in a Hong Kong plastic products manufacturing company with production facilities located in the mainland. It shows how E-business technology applications have opened up the horizon for realization of such a business model. A supply chain strategy based on mutual trust and inventory information visibility is essential in the implementation of such a business model. The model has been found to be valid and feasible. The benefits attainable to parties in the supply chain are evaluated. It is proposed that the model can also be applied successfully for similar benefits in other companies.
Authors: K.C. Chan, M.V. Ramesh, Wing Bun Lee, Chi Fai Cheung
Authors: Suet To, Er Qi Wang, Wing Bun Lee, Chi Fai Cheung
Abstract: An investigation into a Digital Manufacturing and Testing Procedure (DMTP) for freeform optics is presented in this paper. The paper studies the characteristics of the DMTP which are of special use in ultra-precision machining (UPM) of freeform optics, i.e. the construction of a model of DMTP, the construction of a digital prototype of an optical system, a Digital Testing (DT) system for image quality, digital testing and simulation of the optical image quality.
Authors: M.N. Cheng, Chi Fai Cheung, Wing Bun Lee, Sandy To
Abstract: Ultra-precision raster milling is an emerging manufacturing technology for the fabrication of high precision and high quality components with a surface roughness of less than 10 nm and a form error of less than 0.2 μm without the need for any subsequent post polishing. Surface quality of a raster milled surface is affected by process factors and material factors, respectively. The process factors involve cutting conditions, cutting strategies, and relative vibration between the tool and the workpiece which are related to the cutting geometry and the dynamic characteristics of the cutting process. The material factors considered are material property and swelling of the work materials. Due to different cutting mechanics, the process factors affecting the surface quality are more complicated, as compared with ultra-precision diamond turning, such as swing distance and step distance. This paper presents an experimental investigation of the distinctive process factors affecting the surface roughness in ultra-precision multi-axis raster milling. Experimental results indicate that the influence due to the process factors can be minimized through a proper selection of operational settings and better control of dynamic characteristics of the machine.
Authors: H.F. Li, Chi Fai Cheung, Ling Bao Kong, Wing Bun Lee, Sandy To
Abstract: Ultra-precision freeform surfaces have become widely used in advanced optics manufacture. Although these surfaces can be fabricated by ultra-precision freeform machining technology with sub-micrometer form accuracy and surface finish in nanometer range, our current understanding on the evaluation of surface quality of these surfaces is still far from perfect. In this paper, a study of measurement technology for ultra-precision freeform surfaces is presented.
Authors: Sandy To, Chi Fai Cheung, Su Juan Wang, Wing Bun Lee
Abstract: Optical communication is gaining popularity in telecommunications; most obviously evident is the increase in demand for a large variety of fiber optic components. V-groove structure quality is critical to the functionality of the fiber connector as it governs the position of the optic fibers. The main parameters, which determine the V-groove quality, include core pitch, surface roughness and the position of centerline. In this paper, a series of cutting conditions were applied to investigate the effect of different machining parameters on the V-groove quality. In the experiment, the V-groove structure is machined by a 40° single crystal diamond tool on aluminium alloy with different cutting conditions. Based on the findings, the relationship between the cutting conditions on the surface roughness was explored. The implications of these findings on the improvement of the surface finish of V-groove profile are discussed.
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