Browsing by Author "Hong, SY"

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Lubrication mechanisms of LN2 in ecological cryogenic machining
(2006)
Hong, SY
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機械工程學系
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Department of Mechanical Engineering
Cryogenic machining is considered an environmentally safe alternative to conventional machining where cutting fluid is used. In cryogenic machining, liquid nitrogen (LN2) is well recognized as an effective coolant due to its low temperature, however, its lubrication effect is less well known. Our previous studies of the change in cutting forces, tool wear, chip microstructure, and friction coefficient indicate a possible lubrication effect of LN2. This paper proposes two mechanisms on how LN2 can provide lubrication in the cutting process. To verify these proposed LN2 mechanisms and distinguish them, idealized disk-flat contact tests were performed. A low temperature can alter the material properties and change the friction coefficient between the specimens. However, from the test results, this lubrication mechanism was dependent on the material pairs. An uncoated carbide insert with a low carbon steel or titanium alloy disk test showed reduction of friction under LN2 cooling, but a coated insert increased the friction force. LN2 injection to form a physical barrier or hydrodynamic effect between two bodies is always effective in reducing the friction force.
Theories and algorithms for 3-D root canal model construction
(2005-09-15)
Dong, J
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Hong, SY
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Hasselgren, G
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機械工程學系
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Department of Mechanical Engineering
This paper presents theories and algorithms for 3-D root canal model construction from 2-D X-ray images in a clinically practical way: (1) the geometrical rectification algorithm for correcting distorted 2-D X-ray images, (2) the transformation algorithms from 2-D X-ray image coordinate system to unified 3-D reference coordinate system, (3) the merging algorithms and theory for obtaining spatial root canal centerline by intersecting two surfaces with assumed parallel projection, and (4) the elliptical theory for exploring the root canal cross-sectional geometry. Using those theories and algorithms, three 3-D computer models constructed from teeth samples are presented to show the feasibility. The internal geometrical structure provided by 3-D computer graphics enables the clinician and the patient to comprehend root canal morphology efficiently, and the destructive access preparation before a clinician's inspection may be avoided during clinic practice. (c) 2005 Elsevier Ltd. All rights reserved.