Zhen Long Wang

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%.

Discussion of electrical discharge machining in gas

Summary form only given. For the microcosmical understanding of electrical discharge machining (EDM) in gas (dry EDM), the influences of such parameters as polarity and gas pressure on EDM in gas were discussed based on theory of gas discharge and experiments; meanwhile, the influencing factors of material remove rate (MRR) in dry EDM and reasons for the low relative wear ratio (RWR) are analyzed mainly according to the gas medium characteristics. Positive polarity was recommended in dry EDM because electrodes play main roles in collision and ionization; the notable feature of dry EDM is very low RWR and the reasons for low RWR are analyzed as follows: (1) the passage developing to anode is stronger than the passage toward cathode, which can be used to explain that the energy absorbed by anode is larger than the energy absorbed by cathode, and that is main reason for lower RWR. (2) Tool electrode was protected by the debris adheres on the tool. Additionally, discharge passage extends rapidly in gas medium although it is limited by liquid in conventional EDM, which leads to weaker workpiece cool effect and low MRR in dry EDM; Finally, to ensure machining process stable at the sparkle discharge state, a certain gas pressure is necessary to strengthen deionization in dry EDM and to keep discharge points disperse in gap.

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

Experimental Study of Microelectrode Array and Micro-Hole Array Fabricated by Ultrasonic Enhanced Micro-EDM

Micro electrical discharge machining (EDM), enhanced with ultrasonic vibration, is explored and assessed as a method for developing microelectrode array, for microelectrode array fabricated by LIGA has shortcomings such as complex technology and high price. Based on the mechanism of micro-EDM, micro-hole array discharges to fabricate microelectrode array by reverse copying. In the process of reverse copying, the thicker rod electrode can not rotate, resulting in electric arc and short-circuit occurring easily, so it is necessary to add ultrasonic vibration on the plane plate electrode, in order to exclude debris as soon as possible and stabilize machining process. In the process of machining, four parameters, such as working voltage, working capacity, ultrasonic amplitude and holes spacing, are important to machining efficiency, each parameter has four typical values. In order to reduce experiment times, a scheme of orthogonal experiment was designed with different parameters combination. With result of experiments, the ratio of mean square deviation to error mean square deviation of each parameter was calculated and significance of each parameter was obtained, and the best parameters combination was asserted through theoretical calculation. Also, experimental study of using microelectrode array to machine micro-hole array by Micro- EDM was made and influence curve of each parameter was drawn. Finally, 5×5 arrays of microelectrode were obtained, the diameter of single electrode is less than about 30.m and heightto- width aspect ratios is more than 8, moreover, these microelectrode arrays have good coaxiality and surface quality.

Experimental Research on Machining Performance of Electrode Materials in Dry EDM

Electrode materials are important factors affecting machining performances (MP) of electrical discharge machining (EDM). Experiments using different electrode materials were carried out in compressed air aim to realize MP of electrical discharge machining in gas (dry EDM). Experimental results show that a minimum pulse interval exists for given parameters and tool material. Calorific performances of tool materials are main influencing factors of MP on the condition of thorough deionization. Copper achieves the best MP in the experimental tool materials. Experimental results of different workpiece materials depict that material remove rate (MRR) and surface roughness (SR) value increase with increases of discharge energy. SKD61 steel achieves the highest MRR and SR value in the experimental materials. Material holding better performance of heat resistant, such as titanium alloy (TC4), achieves the lowest MRR.

Micro-Forming Process and Microstructure of Deposit by Using Micro EDM Deposition in Air

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.

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.

Micro-Hole Drilled by EDM-ECM Combined Processing

A new method for drilling micro-hole called EDM-ECM combined processing is proposed in this paper. This method consists of EDM shaping and ECM finishing, and they are carried out in sequence on the same machine tool with the same electrode but different dielectric medium. Micro-hole drilling experiment was done by micro-EDM, micro-ECM and EDM-ECM combined processing. The results show that the machining efficiency is improved by 9.2 times compared to conventional micro-ECM, and machining precision and shape accuracy of micro-hole are much better. The surface quality and mechanical property of the workpiece are improved, since the recast layer and surface defects generated by EDM are removed completely by ECM finishing. It proves that this combined machining method is possible and useful in the field of micro-hole drilling.

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.