Papers by Author: Yu Ming Lee

Abstract: In this study, the parametric effects of the EMM process were studied by both numerical simulation and experimental tests. The numerical simulation was performed using commercial software, FEMLAB, to establish a multi-physics model which consists of electrical field, convection and diffusion phenomena to simulate the parametric effects of pulse rate, pulse duty, electrode gap and inflow velocity. From the simulated results, the relationship between parameters and the distribution of metal removal could be established. Proper process variables were also chosen to conduct the EMM experiments. After the experiments, the profile of the processed rectangular slot was measured by a Keyence digital microscope. Comparing profile of the processed rectangular slot with the profile of the cathode, the machining accuracy of EMM process could be determined. It could also verify the efficacy of the multi-physics model for predicting machining accuracy. From this study, the effects of parameters such as pulse rate, pulse duty, electrode gap and inflow velocity are better understood. The simulation model could be employed as a predictive tool to provide optimal parameters for better machining accuracy and process stability of the EMM process.

Abstract: Due to lack of desirable mechanical properties of silicon substrate; the current trend of micro-fabrication technology is towards metallic materials. In this study, the electrochemical micromachining (EMM) technology is developed to fabricate micro-scale flow channels on thin metallic 316L stainless steel plate. The cathode electrode, the tool, is the mirror image of flow channels. It was produced by the MEMS and UV-LIGA technology and the size is 200μm in width and 500μm in height for the intension to fabricate a serpentine flow channel of 200μm in both depth and width. Because of the electrode size, the process control parameters and geometrical features surpassed conventional and CMOS methods. The flow channels on 0.6mm thick SS 316L plates were fabricated by EMM process within 30 seconds with effective area of 625mm2. The dimensions of flow channel were varying from 1504m to 5004m in width and about 2004m in depth. The results demonstrate the EMM technology produces good quality metallic flow channels efficiently.

Abstract: The fuel cell has the potential to become an indispensable source of electric power. However, some problems have not yet been resolved. Measuring the temperature and humidity inside the fuel cells is currently difficult. Accordingly, in this study, micro sensors were fabricated within the fuel cell, in which the temperature and humidity distributions were measured. The substrate of the fuel cell was made of stainless steel (SS-304) and etching was employed to fabricate the channel on the stainless steel substrate. Then micro-electro-mechanical-systems (MEMS) technology was used to fabricate the array micro temperature and humidity sensors on the rib of channel of stainless steel. The advantages of array micro temperature sensors are their small volume, their high accuracy, their short response time, the simplicity of their fabrication, their mass production and their ability to measure the temperature at a precise location more effectively than the traditional thermocouple. The micro humidity sensors were made from gold and titanium as down and up electrodes in the channel. The performance curve of the single cell was operating at 41.54 °C and gas flow rates of H2/O2 at 200/200ml/min. The max power density of the bipolar with micro sensor was 56 mW/cm2.

Abstract: In this study, the parametric effects of the EMM process were studied by both numerical simulation and experimental tests. The numerical simulation was performed using commercial software, FEMLAB, to establish a multi-physics model which consists of electrical field, convection and diffusion phenomena to simulate the parametric effects of pulse rate, pulse duty, electrode gap and inflow velocity. From the simulated results, the relationship between parameters and the distribution of metal removal could be established. Proper process variables were also chosen to conduct the EMM experiments. After the experiments, the profile of the processed rectangular slot was measured by a Keyence digital microscope. Comparing profile of the processed rectangular slot with the profile of the cathode, the machining accuracy of EMM process could be determined. It could also verify the goodness of the multi-physics model for predicting machining accuracy. From this study, the effects of parameters such as pulse rate, pulse duty, electrode gap and inflow velocity are better understood. The simulation model could be employed as a predictive tool to provide optimal parameters for better machining accuracy and process stability of the EMM process.

Abstract: Passive film of stainless steels possesses good corrosion resistant property. However, the passive film formed in nature is not uniform and the quality is not consistent. It is the major causes for local corrosion. The pitting potential test is a traditional method to test local corrosion of stainless steels. The local corrosion is usually induced by the break-down of the passive film. Therefore, it can be utilized to evaluate the quality of the passive film. Also, because the pitting test is quick and inexpensive, many tests can be performed to evaluate the uniformity of the passive film. This study focuses on SS316 stainless steel. The specimens were treated with electropolishing processes. The original and the processed specimens were tested by pitting potential tests. From these results, the distribution and the uniformity of passive film could be evaluated. An efficient and inexpensive index of the uniformity of the passive film is proposed.