Papers by Author: Yao Yang Tsai

Abstract: Two-phase heat transfer devices such as heat pipes and vapor chambers are composed of an evaporator, an adiabatic section and a condenser. For the dry-out prevention and capillary purpose, adiabatic sections and evaporators are covered by wick structures. Common wick structures are grooves, mesh, sintered powder and their combination. Combining with the wick structures, the major phase change effects on evaporators are thin-film evaporation. For the research between parameters of wick structure and evaporator performance, we developed a facility to measure the heat transfer on evaporators. To ensure the least heat losing, the path of heat flux and test condition were designed with several thermal guards. A pressure control system was established with balance mechanisms to maintain a stable condition of low pressure. Since temperature differences are very fast while the major phase change effect is thin-film evaporation, a high speed data acquisition system was used. Based on this test platform, the performance of evaporators can be determined at specific conditions.

Abstract: In the past half century, EDM (electrical discharge machining) is one of the most popular methods for manufacturing casting and plastic injection molds. Unlike other traditional mechanical cutting methods, EDM removes materials away by sparks, which leads to high temperature and pressure. As a result, it has no restriction to hardness because of its non-contact property. However, there will be recast layers on the surface of work-pieces and thus the surface need improved. In order to decrease the surface roughness, we added different powders into dielectric to become ERF (electrorheological fluid). By rotating spindle, the chain structures of ERF can improve surface of SKD11. The result shows that, when the gap is 100μm and electrode φ2, starch has 61% improvement rate and Al2O3 has 14.97%.

Abstract: Dry Electrical discharge machining (Dry EDM), using gas as dielectric, has been developed to solve problems against environment. It has both advantages of high material removal ratio (MRR) and low relative electrode wear ratio (REWR). We investigated the effect of duty factor, peak current, and reference ratio of gap voltage on MRR and REWR of Dry EDM, respectively. Moreover, trying to prove the attachment on electrode surface could decline REWR. It is considered that melting material of work-piece was sputtered and stuck onto electrode surface, and to become a protection layer as result in low REWR. However, the attachment will be removed under the condition of high peak current and high discharge frequency. But the amount of attachment just has little change when discharge number and arc discharge ratio are both decrease.

Abstract: Suspending powder in dielectric fluid of EDM (electrical discharge machining) has been developed to improve the quality of machined surface recently. The used powders are usually Al, Cu, Cr and so on metal powder because conductive particle can increase the spark gap and improve surface roughness of machined surface. Semi-conductive powder, Si is also utilized for the sake of increasing machining speed. This paper presents a new tryout to suspend polymer particles in the dielectric fluid of EDM. Experimental results show that the EDM process with suspending polymer particles still can be carried out but its surface roughness is not so good in conventional EDM oil. However the conventional EDM oil was taken the replace of silicone oil, suspending polyaniline (PANI-emer) of high molecular weight (Mw~65000) has finer improvement even better than using Si powder. Its surface roughness achieves less than Ra 0.2μm at low concentration and will be decreased gradually with increasing the concentration of PANI-emer (Mw~65000). The surface roughness is Ra 0.14μm when the powders concentration is 10g/l. Even for different type of polyaniline shows different machining characteristics. The surfaces roughness becomes worse when the concentration of low molecular weight PANI-emer (Mw~20000) is higher. An electric-conductive PANI-salt powder has a rapid decrease of surface roughness with increasing its concentration than other materials.

Abstract: A new cutting force model of micro-milling was developed based on calculating the instantaneously projected area of cutting in this study. According to the rotation trajectory of cutting edge, the instantaneous cutting area projected to xy-plane was first divided into several portions and determined with rectangular integral. After the cutting coefficients were experimentally investigated, the cutting force of micro-milling with different cutting conditions can be determined. Because the developed cutting force was function of cutting parameters, such as spindle speed, feed rate, depth of cut, with taking the cutter deflection into account it was further used to the determine of optimal cutting parameters for obtaining better cutting efficiency and machining accuracy. To verify the proposed cutting force model and the way to determine the optimal cutting parameters, micro-milling experiments were conducted. The results have shown the feasibility of the proposed model and method.

Abstract: Electrical discharge machining (EDM) is an excellent technology to machining die and mold, but it is uneasy to obtain mirror-like surface. Powder-Mixed dielectric electrical discharge machining (PMD-EDM) is the innovative technology of EDM process, which can improve the quality of machined surface and applied in EDM finish machining now. The powder is usually hard particles, such as Al, Cu, Cr and Si in PMD-EDM. This paper presents a new research of PMD-EDM with suspending soft particles and abrasive grits in the dielectric fluid, especially focus on surface roughness. Experimental result shows the EDM process with polymer particles and abrasive grits can be carried out in silicone oil and the surface roughness has the finer improvement when increasing the rotation speed. Also, the effect of hard particles suspending in dielectric fluid are also discussed and compared. The surface roughness using polymer particles and abrasive in specific condition was better than only hard particles in silicone oil. Moreover, mixing abrasive and polymer in EDM can perform the polishing process.