Browsing by Author "Tsai, Yu-Chung"

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Glass material model for the forming stage of the glass molding process
(2008-05-26)
Tsai, Yu-Chung
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Hung, Chinghua
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Hung, Jung-Chung
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機械工程學系
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Department of Mechanical Engineering
The aim of this research is to obtain an accurate material model for glass that can be used in finite element (FE) analysis of the glass molding process. A thorough understanding of the deformation behavior of the glass specimens was acquired by performing uniaxial compression tests. The elasto-viscoplastic model was utilized for the glass material at the molding temperature to construct the FE model, and a suitable set of parameters for this material model was verified by comparing the simulation results to the experimental data. As a result, the feasibility of the elasto-viscoplastic model for glass at the molding temperature was confirmed; this material model can be used in FE analysis of the prediction and modification of properties of the final lens products. (C) 2008 Published by Elsevier B.V.
Investigation of the effects of ultrasonic vibration-assisted micro-upsetting on brass
(2013-09-15)
Hung, Jung-Chung
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Tsai, Yu-Chung
;
機械工程學系
;
Department of Mechanical Engineering
Ultrasonic vibration is widely applied in traditional metal forming to soften material and to increase formability. However, the effects of ultrasonic vibration on miniaturized workpieces must be studied before applying its benefits to metallic micro-forming. This study investigates the effects of applying ultrasonic vibration to micro-forming, along with two other factors: specimen size and grain size. Conventional (without ultrasonic vibration) and ultrasonic vibration micro-upsetting experiments were conducted using brass (C2600). Specimens of three different dimensions (phi 3 x 4.5 mm, phi 2 x 3 mm, and phi 1 x 1.5 mm) and of three grain sizes (12 mu m, 44 mu m, and 90 mu m) were used. The conventional micro-upsetting (CMU) experiment revealed the size-effect in which flow stress decreased with the miniaturizing of the specimen. Flow stress also decreased as the grain size increased, but at a smaller magnitude than that of the size-effect. Results show that ultrasonic vibration-assisted micro-upsetting (UMU) decreased the flow stress effectively, especially in miniaturized specimens. The amount of decrease was related more to the dimension than to the grain size of the specimen. (C) 2013 Elsevier B.V. All rights reserved.
The effect of ultrasonic-vibration on upsetting
(2006)
Hung, Jung-Chung
;
Tsai, Yu-Chung
;
Hung, Chinghua
;
機械工程學系
;
Department of Mechanical Engineering
Ultrasonic-vibration upsetting is a process in which a cylindrical specimen is compressed by an axial force while the ultrasonic vibration is simultaneously applied to the die. Homogenous deformation is difficult to achieve during this process because of the friction at the interface between the specimen and the die. An extrapolated compression test was performed in this study on aluminum alloy specimens to explore the effect of superimposing ultrasonic-vibration during upsetting. Experimental results indicate that ultrasonic-vibration reduced the compressive force when the friction was eliminated by the extrapolated compression test. The specimen size also influences the force-reducing effects of ultrasonic-vibration. The decrease in the compressive force is smaller for a larger specimen. The barreling profile of the specimen after test indicates that the interface friction will increase during ultrasonic-vibration compression. Additionally, the raised material temperatures are caused by ultrasonic-vibration. Experimental results of the hot extrapolated compression test and the hot ring compression test indicate that the drop in the flow stress and the increase in the interface friction are caused by the increase in the temperature of the material under ultrasonic vibration.