Browsing by Author "Lin, Chih-Chia"

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Fabricating High-Aspect Ratio Microchannels on Metallic Sheets Using Hydroforming
(2012)
Lin, Chih-Chia
;
Yan, Jhen-Jie
;
Hung, Chinghua
;
Hung, Jung-Chung
;
交大名義發表
High-aspect ratio microchannels on bipolar plates have the advantage of improving fuel cell performance. This study formed high-aspect ratio microchannels by increasing the forming pressure, and predicted excellent aspect ratio of micro-flow channels by optimization analysis during the hydroforming process. This study used an experimental high-pressure hydroforming apparatus that provides various pressures to form microchannels on 304 stainless steel sheets with 0.1 mm thickness. Simultaneously, finite element analysis software was used to analyze the hydroforming process. First, the precision of the finite element model was verified by comparing simulations with experiments. Subsequently, the optimization software was connected to the finite element software to determine the optimal aspect ratio of microchannels by changing the dimension of micro-flow channels and pressures. Furthermore, the results of the simulations, hydroforming experiments, and related literature were discussed. The result indicated that the high-pressure hydroforming technique was feasibility, which formed high aspect ratio microchannels with 200 MPa, and the optimization predicted aspect ratio could reach 0.478 when changing geometries of channels and pressures. This research proposed a design process through hydroforming experiments, finite element analysis, and optimization analysis when predicting and designing the dimensions of micro-flow channels on metallic bipolar plates.
Fabrication of micro-flow channels for metallic bipolar plates by a high-pressure hydroforming apparatus
(2012-05-15)
Hung, Jung-Chung
;
Lin, Chih-Chia
;
機械工程學系
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Department of Mechanical Engineering
High aspect-ratio micro-flow channels on bipolar plates have the advantage of improving fuel cell performance. This study forms micro-flow channels with a high aspect ratio by increasing the forming pressure during the hydroforming process. This study designs and constructs a mechanical apparatus to enable a two-stage pressure increase in the hydroforming process. A high-pressure container is designed with three-layered tapered cylinders to sustain 1230.17 MPa working pressures, and a special seal component is designed to seal the high-pressure fluid and maintain high pressure. The feasibility of this high-pressure hydroforming technique is verified in preliminary tests. The investigation indicates that the aspect ratio of micro-flow channels can reach 0.468 when a hydrostatic pressure of 250 MPa is applied. Compared with the maximum aspect ratio of 0.31 formed using the traditional hydroforming process, the aspect ratio of micro-flow channels in this study was 51% higher, which enables the fuel cells with metallic bipolar plates to meet both performance and manufacturing requirements. (C) 2012 Elsevier B.V. All rights reserved.
Investigations on the material property changes of ultrasonic-vibration assisted aluminum alloy upsetting
(2013-03-01)
Hung, Jung-Chung
;
Lin, Chih-Chia
;
機械工程學系
;
Department of Mechanical Engineering
Numerous studies have shown the benefit of ultrasonic-vibration assisted metal forming. This benefit include a reduction in forming forces, which might be attributed to the superposition of stress, increased temperatures, the effects of interface friction, and energy absorption of dislocation. This study conducts a series of experiments and analyses to investigate the main mechanisms of a reduction in forming forces during ultrasonic-vibration assisted A6061-T6 aluminum alloy upsetting. The findings of this research confirm that, under frictionless conditions, ultrasonic vibration still reduced forming forces, and ultrasonic vibration can increase the temperature of specimens and soften specimen surface during upsetting. From metallographic analyses and micro-hardness tests, the results reveal that energy absorption of dislocation was occurred during upsetting, which also contribute to the reduction of forming force. This research concludes that the mechanisms of increased temperatures and energy absorption of dislocation can affect the material property and make a reduction in forming forces; however, the interface friction effect has nothing to do with a reduction in forming forces. (C) 2012 Published by Elsevier Ltd.