Papers by Author: Suet To

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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: Guo Qing Zhang, Suet To
Abstract: Tool wear measurement has drawn a significant of attention in the past decades. However, no research has been found on the investigation of tool wear measurement in ultra-precision raster milling (UPRM) process since it is a relative complex cutting process. In the present study, tool wear characteristics were identified by using cutting chip morphologies and a groove cutting. Tool wear investigation using cutting chips is effective because diamond tool wear characteristics can be directly imprinted on the cutting chip surface. Through the inspection of chip surfaces, the profile and location of the tool fracture can be identified. Also, through the groove cutting, the cutting edge retreat due to the tool flank wear can be identified. In this research, a mathematical model was established to calculate the tool retreat. The experimental result shows that the proposed tool wear investigation method is an effective method.
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: Su Juan Wang, Suet To, Chi Fai Cheung, Wing Bun Lee
Abstract: Ultra-precision raster milling (UPRM) can directly achieve the fabrication of threedimensional non-axisymmetric freeform components with nanometeric surface finish and submicrometric form accuracy. During the past few years, a lot of research on computerized numerical control (CNC) machining technologies has been conducted; however, little of this research makes any contribution to UPRM. This paper studies the mechanism of scallop height generation for UPRM. Through analyzing the cutting edge locus and the scallop height generation mechanism, a model for feed-intervals and for raster-interval scallop height generation, are presented. Parameters such as selection of feed direction (vertical cutting and horizontal cutting), feed rate, spindle speed, tool nose radius, swing distance, feed length and raster distance have been taken into consideration in the scallop generation models.
Authors: Chi Fai Cheung, Wing Bun Lee, P. Charlton, Suet To
Abstract: Ultra-precision polishing is an emerging technology for producing superfinishing surfaces with sub-micrometer form accuracy and surface finish in nanometer range. It has been applied in superpolishing the freeform bearing surfaces of orthopaedic implants. It is believe that the superfinished surfaces are capable of prolonging the life of the implants. In this paper, an experimental investigation of ultra-precision polishing of orthopaedic implants and the study of the wear characteristics of the superfinished surfaces using a multi-directional pin-on-plate wear test simulator are implemented. Tests were carried out over 3 million cycles using Zeeko IRP200 superfinished cobalt chrome pins articulating against cross-linked UHMWPE plates. The results were compared to that of manually polished pins articulated against the same UHMWPE material. The results show that the Zeeko IRP200 polished pins produced better wear performance that that of the manually polished pins.
Authors: Suet To, Hao Wang, Bing Li, Chi Fai Cheung
Abstract: Ultra-precision raster milling is one of the most significant techniques for the fabrication of high precision components with the surface roughness less than 10nm and form errors less than 0.2 um, without the need for any subsequent polishing. However, no matter how well a machine may be designed, there is a limit to the accuracy that can be achieved. This paper studies the machining errors caused by the diamond tool and the axis motions using Freeform 705G. With an empirical approach, the error sources are separated based on their effects on the surface finish. The main source leading to poor surface finish is identified. This establishes a basis for subsequent error compensation and equipment maintenance.
Authors: Ming Chu Kong, Wing Bun Lee, Chi Fai Cheung, Suet To
Abstract: The formation of tool marks in single-point diamond turning is a fundamental study of the effect of materials swelling and recovery on surface roughness on a machined surface. A series of orthogonal face cutting tests has been conducted among plate aluminum alloy, oxygen-free high conductivity copper and electroless nickel phosphorus under the same cutting conditions by the use of facet tools with different front clearance angles. The results show that the regular width of the undulating pattern in tool marks could be explained by side swelling and the micro-waviness within a tool mark is caused by burnishing and recovery.
Authors: Tsz Chun Kwok, Suet To, Chi Fai Cheung, Su Juan Wang, Wing Bun Lee
Abstract: Microlens arrays are widely used as critical components in a large number of photonics and telecommunication products. The increasing demand for high-tech products provides an expanding room for the development of the micro-fabrication technology. This study presents a tool compensation for correcting the form error of fabricated microlenses in ultra-precision machining with fast-tool-servo (FTS) system. After presentation of optimal cutting conditions deduced on the basis of cutting experiments of microlens arrays, a tool radius compensation method will be proposed and evaluated in this paper. This methodology makes use of form measurement data from a Form Talysurf system to modify the C program employed in the software of ultra-precision machining FTS system – SOP. The form error was successfully reduced after implementation of tool compensation.
Authors: Suet To, Bing Yan Jiang, Can Weng, Wing Bun Lee
Abstract: The aspheric VCD lens is hard to fabricate by injection moulding due to its small volume and high precision requirement. The processing conditions have critical effects on the quality of the moulded lenses. An optic lens needs precisely controlled surface contours, so determination of the processing conditions for lens moulding becomes very complicated. This study’s purpose is to investigate experimentally some effects of the moulding conditions on the form errors of injection moulded lens. An aspheric VCD lens was moulded using polymethyl methacrylate. Different combinations of moulding conditions were used focusing on moulding process parameters of the ram speed, the mould temperature, the melt temperature and the packing pressure, The predicted model of form errors was formulated by orthogonal and regression analysis. Finally, the predicted model is proven to be valid based on the residual diagnostic plots.
Authors: Chi Fai Cheung, K.C. Chan, Wing Bun Lee, M.V. Ramesh, Suet To
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