Papers by Author: Wan Sheng Zhao

Abstract: In this paper electrochemical machining of micro slots using a shaped electrode instead of the traditional cylindrical electrode is presented. By applying shaped electrode the flow state of processing can be improved. An electrochemical machining (ECM system for meeting the requirements of the ECM process was established and a shaped electrode was fabricated by BEDG (Block Electrical Discharge Grinding). A set of experiments were carried out to investigate the influence of shaped electrode on machining efficiency and shape precision. The results show that the side gap and frontal gap of the micro slots can be reduced and machining speed will be improved when the shaped electrode was used compare with cylindrical electrode.

Abstract: This paper aims to introduce the performance of bunched-electrode for die-sinking EDM. Bunched-electrode was formed by bunching numerous hollow cell-electrodes together to generate an electrode in which end surface matches the final surface of the mould cavity. FEM analysis and experiments were conducted to demonstrate the feasibility and effectiveness of bunched electrode in ED machining. Experiments show that while machining with bunched-electrode, it is feasible to apply a much higher peak current to achieve higher MRR. Meanwhile, a special phenomenon called shallow radial craters in machining with bunched-electrodes was observed and analyzed. One possible reason may be that the plasma columns in the gap are distorted outwards by strong inner pressure flushing.

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: 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: A multi-axis micro-EDM machine tool for small hole is developed. It mainly includes marble base, precision servo and linear-motor platforms, RC pulse power supply, CCD microscope and so on. Superiority of linear motor used on the Z axis is analyzed. Primary experiments, in which small electrodes with different materials are used to machine 3mm thickness TC4, are carried out. Histograms of open-circuit voltage and capacitance to machining efficiency and electrode relative wear and small-hole samples are given. Influence rules of open-circuit voltage and capacitance to machining efficiency and electrode relative wear are analyzed according to experimental results.

Abstract: A micro-EDM equipment which can fabricate three-dimensional micro-structures is developed. A method of electrode wear compensation on-line which is very important to micro 3D structures machined by micro-EDM is presented. In this method, the wear of electrode can be predicted by the statistics law of open rate of discharge status, therefore, its precise model which is very difficult to build as well as the special CAD/CAM system is hardly necessary. At the same time, the micro-EDM CAD/CAM technology which applies the universal CAD/CAM software for milling is also researched and experienced on Unigraphics (UG). At last, micro 3D structures, a micro hemisphere with diameter ∅150+m and a micro 3D beam which is very popular in MEMS, are machined on silicon wafer by this way, which proves the wide useful of this method and the promising application in MEMS.

Abstract: The performance and stability of output of electrical discharge machining (EDM) are determined by the output of EDM pulse power supply. In order to resolve disadvantages of conventional pulse power supply, such as undesirable efficiency and low power factor, the prototype design of energy-saving EDM pulse power supply is developed. It is composed of such three stages as a single-phase active power factor correction (PFC) pre-regulator, a full-bridge phase shift zero voltage switching (FB-PS-ZVS) converter based on complex control paralleled of machining current closed-loop and voltage closed-loop at period of spark gap insulation, and a pulse generator based on machining sequence control. The PFC pre-regulator contributes to a great increase to about 0.95 in its power factor. The efficiency of the new system is considerably increased to about 70% due to design of ZVS. The pulse generator contributes to the pulse machining current without a tail. Experiment results demonstrates that the prototype is capable of low electrode wear, high speed, stable machining.

Abstract: Experiments of combining micro EDM with USM are carried out to enhance the machining ability and flexibility of the micro EDM, improve the machining state, and increase the productivity and aspect ratio of the micro holes. Basing on RC pulse power supply and workpiece vibration, the micro holes are drilled. The results of comparing experiments indicate that in the processes of both micro EDM without USM and micro EDM with USM, the machining velocity and the wear of the electrode increase with the increase of open voltage and loop capacitance. The experiment results of amplitude influencing on the machining process indicate that with the increase of ultrasonic amplitude, the machining velocity heightens and the aspect ratio of the micro holes augments; at the same time, however, the wear of the electrode and the extensive magnitude of the holes increase. Micro holes with some cross-section and accurate profile are drilled steadily.

Abstract: Two kinds of specimen made of a kind of Ta-W alloy material with high melting point about 3000°C were processed by a traditional EDM (TEDM) and a powder mixed EDM (PMEDM) separately, and its surface characteristics were tested. After processing, their surfaces had the roughness of Ra 0.542μm and Ra 0.174μm, respectively. Moreover, their surface wear-resistance was studied on a CJS111A friction and wear tester. The micro-appearances on the wear surfaces were observed and analyzed by using a SEM. The test results indicated that the better wear-resisting ability the specimen, the higher wear rate displayed during the test the grinding balls. The wear rates of grinding balls corresponding to the two processed surfaces are 2.4×10-5 mm3/m for the TEDM and 1.4×10-4 mm3/m for the PMEDM, and the latter is 5.8 times of the former. The results show that the PMEDM is better at improving the wear-resistance, roughness and hardness than the TEDM, which means that the technique of PMEDM has a great potential in processing the special material.