Papers by Author: Zi Long Peng

Abstract: Based on the analysis of electrical discharge process characteristics, the principle of achieving deposition process and removal process using micro EDM is proposed. By controlling the tool electrode wear in one micro EDM system, it is easy to achieve the different machining type of deposition or removal process. Centering on the problem of tool electrode wear, the process conditions of the deposition and removal including machining polarity, machining dielectric medium, discharge parameters and the tool electrode rotation are researched detailedly. Results show that under the discharge phenomena between electrodes, metal material can be deposited to form micro structures, and the transfer strategy from deposition to removal process can be controlled easily. The machining procedure for fabrication of micro structures based on depostion and removal process are put forward. And finally, some examles with well shape and dimension accuracy are given to validate the processing ability for micro machining.

Abstract: Dissolving action of Ag and P during weld brazing of thick copper plates without preheating was investigated and the mechanical performance of the weld of copper was analyzed. The difference of dissolving action between Ag and P is that Ag-Cu binary alloys dissolve base metals in form of body dissolution, while P diffuse into grain boundary first and reach the limit solid solubility gradually then the surface layer of base metal begins to dissolving. The stirring function of arc is important for dissolving action of P but has little effect on dissolving action of Ag. P in form of rigid and brittle Cu3P increases the micro-hardness of welds.

Abstract: Based on the analysis of micro electrical discharge machining (micro EDM) principle, the process conditions of micro EDM deposition has been obtained. Micro EDM deposition is a new EDM method, in which the process conditions includes selecting air as working medium, short pulse duration, long pulse interval, low discharge current and setting the tool electrode as anode. In micro EDM deposition experiments, two types pulse generators of transistor type and RC type are applied respectively. The characteristics of discharge waveforms using each type pulse generator are researched. Results show that both two types pulse generators can be applied in the micro EDM deposition process. The transistor type is easy to obtain the same single discharge energy, but short circuit will damage the deposited material. While RC type can adjust discharge energy according to the discharge gap state, which is well used in micro EDM deposition process with the high deposition rate.

Abstract: The micro growth process and characteristics of deposited material in micro EDM deposition are researched in this paper. In the initial stage of the deposition the deposited material is not an even layer in the diameter direction of tool electrode. The emergence of deposited material will affect the next pulse discharge distribution between tool electrode and workpiece. A micro cylinder with the diameter of 85µm, height of 255µm formed successfully with the fine surface quality using the tool electrode diameter of 200µm. It has shown that micro EDM deposition process has the ability to fabrication more finer micro structures with thinner electrode. The characteristics of deposited material including bonding behavior between deposited material and workpiece, energy spectrum analysis, hardness test and resist compression test of the deposited material have been tested. Results show that the deposited material has compact microstructure and bonds close to the workpiece, which can be used in the occasion of withstanding compress.

Abstract: . The purpose of this paper is to study the application of electrochemical machining (ECM) technology for the fabrication of micro structures. The stray current corrosion, i.e. machining localization is a critical obstacle to micro fabrication for ECM. To machine micro structures by electrochemical machining ultra short voltage pulse is used. The effects of electrochemical machining parameters such as voltage, pulse duration, pulse frequency, and electrolyte composition on the machining accuracy were studied. In experiments, a micro hole was machined on stainless steel with cylindrical and square electrodes to investigate these effects.

Abstract: A reversible machining method using micro electrical discharge machining (EDM) was developed. This new method can achieve depositing or selective removing of metal material for the fabrication of micro structures. It is easy to transform the machining process from deposition to removal in one EDM machining system. In micro EDM deposition process, brass, tungsten and steel material can be deposited successfully. The deposited material has compact fine texture and combines close to workpiece. Then, micro complex structures by series deposition strategy and sub-deposition strategy were deposited. In the selective removal process, the machining effects of different working mediums were researched. Results show that the machining effect in liquid medium is better than that of in air. Finally, using the micro reversible EDM process, a micro square column with 0.070mm in side length, 0.750mm in height and a micro cylinder with 0.140mm in diameter, 1.180mm in height were fabricated.

Abstract: The designing of a micro turbine for micro gas turbine engine is presented in this paper. Micro power system is becoming more and more important for micro- and nano-scale system. The fast development of MEMS (Micro Electromechanical Systems) has strongly enhanced the application of new harder work materials. The fabrication of metallic 3D microstructures has been one of the most attractive topics of micro machining. Currently the basic materials of Micro-turbine Engineering were nonmetal materials such as SiC, most of them are 2D or quasi-3D structures. As a low cost, flexible, good repeatable machining process with negligible process forces, micro-EDM milling is well suited for freeform metallic micro structures. A three-dimensional micro turbine was fabricated by micro-EDM milling. A major problem in micro-EDM milling of complex 3D structure by using micro-electrode is the electrode wear. For reducing the impact of electrode wear, A new CAM system based on the UG software platform is developed in order to get good accuracy 2and higher efficiency. A simple tool path generation by CAD/CAM software and a general electrode wear compensation strategy is presented. The wear compensation can be apart from the design of CAD/CAM systems, so existing common CAD/CAM systems can be used to generate milling tool path with an unequal thickness lamination. And then post process for wear compensation and EDM milling can be done to modify tool path by adding wear compensation. The micro turbine blades of which the material is nickel alloy (GH4169) were successfully fabricated by using this strategy. The diameters of turbine are 2.8mm, and the height of each blade is 0.4mm.

Abstract: The purpose of this paper is to study electrochemical micro machining (ECM) technology on stainless steel. The micro machining of stainless steel is difficult by electrochemical machining, especially in machining deep micro holes, because of an oxide layer formed on the surface. To machining stainless steel, HF is usually used in electrolyte to destabilize the oxide layer. In this paper, ECM of stainless steel by applying short pulses in less toxic and corrosive electrolyte is research. The influence of electrochemical machining parameters such as voltage, current, electrolyte composition to machine stainless steel was investigated. The results showed that the oxide layer can be reduced by adding chloride and complex.

Abstract: Based on the principle of micro electrical discharge machining (EDM), a reversible machining method is proposed, which can achieve depositing or removing selectively metal material for the fabrication of micro structures. It is easy to transform the machining process from deposition to removal in one machining system. The characteristics of the deposited material show that the components of deposited material are almost the same as those of the tool electrode, and the metallurgical bonding has formed on the interface between the deposited material and the base. Moreover, the deposited material has well machinability in different micro EDM selective removal process, including micro EDM die-sinking and micro EDM milling. As a result, a micro square column with 0.1mm in side length, 0.88mm in height and a micro cylinder with 0.14mm in diameter, 1.18mm in height were fabricated by using the micro reversible EDM process.

Abstract: Based on analysis of the mechanism of Electrical Discharge Machining (EDM) and the characteristics of deposition processing, the processing conditions of micro EDM Deposition (micro EDD) are determined. Micro EDD is a new EDM method taking air as machining medium, using narrow pulse width, long pulse interval, low discharge current and connecting the tool electrode with the anode of pulse generator. Using EDM shaping machine and brass, tungsten and steel as tool electrode respectively, micro cylinders are deposited on high-speed steel surface. And then the microstructure of deposit is analyzed detailedly. Results show that elements of the deposited material distribute uniformly, whose components depend on the tool electrode material. As the high cooling rate of the solidification process, the deposit grain size refines obviously, which leads to the hardness of tungsten or steel deposit increasing. Moreover, the Metallurgical bonding has occurred on the interface between deposit and high-speed steel base, whose thickness is about 5μm.