Wan Sheng Zhao

Study on Block Electrode Discharge Grinding of Micro Rods

Block electrode discharge grinding is an effective approach to produce micro rods. However, it is difficult to fabricate the rods into desired miniature and precision. To solve this problem, the tangential feeding method is proposed to control the finish size of micro rods. With this method, the micro rod is first fed in its radial direction, and then in the tangential direction for an enough distance. The wear of the block electrode decreases gradually from the start to the end, and the wear in the end can be neglected. Experiments indicate that the large capacitance or voltage can obtain high machining speed, while the small ones can gain thin micro rods. Based on this result, the policy of delaminating grinding is adopted to gain enough thin micro rods at a high machining speed. The Φ5µm micro rods can be ground with this method. SEM results show that the relative error of the size control is less than 10%.

Research on Multifunctional Micro Machining Equipment

To perform several micro-machining on same machine tool, a micro machining equipment was researched and developed. The equipment adopts some high and new technologies. It is equipped with high precision XYZ stage, a spindle with high rotation accuracy and variable rotation speed, a granite worktable, a block electro discharge grinding unit for machining micro rod, a ultrasonic vibration unit for workpiece vibrating, a high frequency pulse power supply for micro-ECM and a video microscopic system with high enlargement factor. The equipment can perform micro electro discharge machining (EDM), micro electrochemical machining (ECM), micro ultrasonic machining (USM) as well as their combination. It can also machine 3D microstructures. A series of experiments were carried out. Using micro-EDM, micro rods with the diameter of less than 5µm were ground on block electrode, micro holes and 3D microstructures were obtained. Shaped holes were machined by using combination of micro-EDM and micro-USM. A micro hole with the diameter of 100µm was machined via micro-ECM.

Research on a Micro EDM Equipment and Its Application

A micro electro discharge machining (EDM) equipment is developed in this paper. It includes granite basement which can decrease stray capacitance, precise servo mechanism, precise high speed rotary spindle, a RC-pulse generator used by micro EDM, machining states detecting system and machining process control system. In addition to these, a new type of wire electro discharge grinding (WEDG) unit is designed and set up in this equipment. The CNC interpolation for the 3 axes linkage movement can be realized easily on this equipment. Therefore, micro shaft, micro hole, and 3D microstructure can be machined easily by using this equipment. The relationship between rotating speed of spindle or dielectric and the machining efficiency or the relative electrode wear rate is researched through machining experiments. Experiments show that the microelectrode diameter as small as 12 μm and the micro hole with minimum size of 25 μm could be obtained steadily, and the maximum aspect ratios of microelectrode and micro hole are over 25 and 10 respectively. At last, a complicated 3D microstructure is machined by using this equipment and micro-EDM technology. Introduction Miniaturization of instrument and device has changed the world greatly. Miniaturized products become more popular for their small volume, light weight, stable performance and portability. The development and application of MEMS promote the developing progress of miniaturized products. At the same time, the miniaturized products accelerate the development of micro-machining technology. As an important branch of micro-machining technology, micro-EDM has found widely application in industry because of its machining without contact, machining surface with high aspect ratio easily and high capability to machine micro 3D structure. Compared with normal EDM, due to the diminish of the machining size, micro-EDM needs higher precision and sensitivity of mechanical structure, advanced process and method of fabricating the micro-electrode on-line, a micro-energy pulse generator and a better electric discharge gap control system. Researchers at home and aboard have been doing much work and achieved surprisingly progress [1-5]. Most of those equipments chose piezoelectric ceramics as driven part. The reason is that piezoelectric ceramics has very high displacement sensitivity and high frequency response. However, because of its limited stroke, people had to design a special mechanism to increase its driving force or enlarge its stroke. Thus, the system becomes much complex. After analyzing the characteristic of machining process of micro-EDM, a micro-EDM equipment is developed in this paper. It includes a granite basement which can decrease stray capacitance, a precise servo mechanism, a precise high speed rotary spindle, a RC-pulse generator, a discharge states detecting system and a machining process control system. In addition to these, a new type of wire electro discharge grinding (WEDG) unit is designed and set up in this equipment. The CNC interpolation for the 3 axes linkage movement can be realized easily on this equipment. Therefore, micro shaft, micro hole and 3D microstructure can be machined easily by using this equipment. The Design of the Micro-EDM Equipment The equipment photograph a and the schematic diagram b are shown as Fig.1. The basement is made Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 567-571 doi:10.4028/www.scientific.net/KEM.259-260.567

A Surface Modification Method by EDM and Its Application to Cutting Tools

This paper describes a new surface modification method by Electrical Discharge Machining (EDM) to create a hard ceramic layer on the workpiece. When a kind of metallic material that makes hard carbide is used as an electrode of EDM, hard ceramic layer can be deposited in a certain condition in the process of EDM. In this paper, characteristics of the layer and the application of this method to cutting tools are discussed. First, the principle of this surface modification method is shown. Secondly, the characteristics of the layer are studied in detail. Through the discuss of wear characteristics of the electrode and formation characteristics of the layer, it can be found that there are some distinct differences between the traditional EDM technology and this new EDM surface modification method. Thirdly, the micro-hardness test of the layer at the different distance from the base metal is carried out. It shows that there is a hard area also under the surface of base metal. At last, as an application of EDM surface modification method, cutting test of cutting tools is done, and it confirms that the life of the cutting tool by EDM surface modification is much longer than that of without layer.

Surface Properties of 3000°C High Melting Point Material by Powder Mixed EDM

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.

A micro-deposition method by using EDM

A new micro EDM method is described. First, the basic principles of micro EDD are analyzed and realized conditions are predicted. Then with an ordinary EDM shaping machine and electrode brass, steel and tungsten, a large number of experiments are carried out in air to obtain the effects of different processing parameters on micro EDD. A micro cylinder with 0.19mm in diameter and 7.35mm in height is formed on high-speed steel surface. By exchanging the polarities of electrode and workpiece the deposited material can be removed selectively, thus the reversible machining is realized. In the end, measurements show that the deposited material is compact and hardened, whose components depend on the tool electrode material although Zn in brass electrode is oxidized to ZnO.

Electrochemical Machining of Micro Slots Using Shaped Electrode

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.

Performance of Bunched-Electrode in EDM

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.

Study to Enhance the Precision of Micro-EDM

Considering the key technologies to enhance the accuracy of micro-EDM, a micro-EDM system and some techniques are researched. In this system, a micro-energy pulse power supply whose open voltage and capacitance can be adjusted is developed. The detection and control subsystem of the machining process is designed and applied. A simple method of machining high precision microelectrodes is adopted. The forming mechanism of the gap in EDM process is analyzed theoretically. The processing experiments are carried out on the system, and the results basically coincide with the theoretical analysis. The experimental results of machining microelectrodes and micro holes show that the Ø4.5±0.5μm microelectrodes can be ground, and the Ø6±2.0μm micro holes can be drilled.

Study on Technology of Micro-EDM with Lower Working Voltage

This paper presents new machining technology of micro-EDM with lower working voltage in RC pulse power source. How to control the discharging energy of one pulse supplied by RC power is crucial to the technology of micro-EDM. The process of discharging has been studied, then the feasibility of machining with lower working voltage has been put forward, in order to reduce the discharge energy of one pulse effectively. On the basis of a great deal of experiments, the effect of working voltage on surface quality is studied, also the effect of working voltage on machining efficiency has been found out and been analyzed theoretically. The result shows that lower working voltage can reduce the working energy observably, and then improve the machining surface quality attended by reducing of machining efficiency. However, there is a good machining effect when the working voltage is about 15~20V. Considering working efficiency, a new technology of block electro-discharge grinding (BEDG) with lower working voltage has been applied. As shown by the experimental result with the technology, the minimum diameter of micro-shaft reaches 32m. Moreover, the micro-shaft has very high surface quality of Ra 0.1252m and its coaxial diameter error is controlled within 0.152m.