Papers by Author: H.Y. Tam

Abstract: This paper reports on an investigation of the relationship between the polishing force and the contact characteristics as the polishing tool approaches the boundary of a part surface during polishing. It was previous established that, for fixed abrasives, when the polishing tool is on the inner surface, the relationship between the polishing force and the pressure at the contact is approximately Hertzian and the contact is a full ellipse. The contact cannot be a full ellipse as the tool touches the boundary. The same polishing force could yield rather different pressure distribution, and thus rate of material removal, within the contact region. A model is proposed to relate the force and the pressure distribution as the tool is close to the edge of a part surface. The model takes into account changes of the contact near the edge. Experimental results are also presented to validate the proposed method.

Abstract: This paper reports a study of a micro-EDM process to fabricate micro-through holes in 30 micron thick copper sheets. Circular holes in various micro-sizes were produced by a micro-EDM machine and with tungsten electrodes. Scanning electron microscopy (SEM) and energy dispersion spectroscopy (EDX) were used to identify the influence of electric sparks on the quality of the fabricated features by careful study of resulted cavitation, adhesion of debris, and re-solidification of molten materials, etc. Such analyses allow the generalization of the relevant fabrication mechanisms. In addition, measurements of overcut of the holes facilitate a working model to be developed for predicting the overcut as a function of process parameters including the discharge capacitance and the working voltage of the circuitry. Results of this study enable the derivation of proper settings for fabricating holes of good quality and permit the precision fabrication of the range of micro-throughholes.

Abstract: This paper reports on an investigation of the relationship between the polishing force and the contact characteristics as the polishing tool approaches the boundary of a part surface during polishing. It was previous established that, for fixed abrasives, when the polishing tool is on the inner surface, the relationship between the polishing force and the pressure at the contact is approximately Hertzian and the contact is a full ellipse. The contact cannot be a full ellipse as the tool touches the boundary. The same polishing force could yield rather different pressure distribution, and thus rate of material removal, within the contact region. A model is proposed to relate the force and the pressure distribution as the tool is close to the edge of a part surface. The model takes into account changes of the contact near the edge. Experimental results are also presented to validate the proposed method.

Abstract: This paper proposes a sub-aperture grinding tool for loose abrasive computer controlled surfacing, which is designed to perform epicyclic motion and rotate around its centre at a rapid rate, whilst the entire mechanism revolves around a secondary centre at a slower rate. In actual process, the wear of the tool could affect the material removal function, and make the process unstable, thus in fact, it is difficult to make a deterministic manufacturing. The focus of the present paper is on wearing characteristics of sub-aperture tools and the wear evenness as the main objectives. To make a further study, material removal function of the tool is firstly established through theoretically modelling, next, a correlative function with weighted factors is built, which is suitable for specifying the wearing degree of the tool. Finally, to discover the relationship between the material removal rate and the tool wearing characteristics, and to optimize the grinding process, analysis and experiments are then carried out on a K9 glass specimen by means of three kinds of tool materials, i.e., polyurethane pad, aluminum plate and pitch based on the proposed technique and model. The results indicated that the required high efficiency and precision could be achieved by choosing proper processes.