Papers by Author: Fu Qiang Hu

Abstract: This paper researches the material erosion mechanisms of high silicon- aluminum (Si-Al) alloy in micro electrical discharge machining (Micro-EDM). By using Quanta 200F environment scanning electron microscope, the microstructure of Al-50wt%Si alloy by spray forming was observed. And a simplified model of high Si-Al alloy was set up. The Al-50wt%Si alloy was machined by using copper electrode and tungsten electrode respectively. And the differences of surface morphologies and element energy spectrum were compared. The process and the material erosion mechanisms of high Si-Al alloy in Micro-EDM were analyzed in detail. The results may provide theoretical basis for Micro-EDM of high Si-Al alloy.

Abstract: Because of the high content of Si, traditional machining can hardly machine micro and small structures. While there is almost no microscopic force in the process of micro-electrical discharge milling (MEDM), so it has great advantages. In the process of MEDM for high silicon aluminum (Si-Al) alloy, the impacts of electrical parameters on processing time, the trend and degree of electrode wear are researched. The Al-50wt%Si alloy made by spray forming (SF) and casting forming (CF) and electrode of copper and tungsten are adopted to do the research. Related processing laws are summarized. A micro-3D structure was made by using appropriate parameters based on the experiment and research.

Abstract: The powder mixed electro-discharge machining (PMEDM) technologies of silicon carbide particle reinforced aluminium matrix composites (SiCp/Al) are researched in this article. SiCp/Al is widely acknowledged as one of the most competitive varieties of metal matrix composites, firstly applied in the aviation, aerospace and military fields, and gradually extended. Because of the hard and brittle SiC particles contained in this material, mechanical machining is difficult, but EDM does have some advantages. To the same kind of moderate volume fraction (45%) SiCp/Al material, a comparative test was conducted using two kinds of processing methods, traditional EDM (the former) and PMEDM (the latter). Effects of the electrical parameters of both processing methods on the material removal rate (MRR) were analyzed and compared. After processing, the surface roughness value of the former is Ra1.386μm while the latter is Ra0.406μm which is only 29.3% of the former. The surface hardness was also tested by the MTS nano indenter: the former is about 1.7GPa, and the latter is about 2.2GPa which is 1.3 times of the former. Finally, to the machined surface, the micro-topography and the component of ‘white point’ were observed and analyzed by using scanning electron microscope (SEM) and energy spectrum respectively. Experiments and investigation results show that the PMEDM has a better performance compared with traditional EDM in improving the roughness, hardness and so on. So PMEDM will have a great potential in the processing of aluminium matrix composites.

Abstract: In this paper a kind of architecture for an energy-saving EDM supply composed of three serial stages in the topology and its practical design are discussed. Various special controllers and its assisted circuits are introduced in the each of the three serial stages. The PFC controller UC3854 placed on the front stage provides satisfactory input power factor of the system. The PWM controller UC3875 mounted on the middle stage realize the closed control of the current of the inductance limiting machining current. An embedded controller PIC16F877 on the final stage is chosen to setting such machining variables as peak current, discharge duration and pulse interval. The communication with host PC is also realized by the same embedded controller. The architecture based on model of multi-controller parallel working guarantees capacity of the system real-time process. The prototype of the energy-saving EDM pulse supply using MOSFET power device is developed. A lot of experiments have demonstrated the feasibility and stability of the practical design.

Abstract: The silicon carbide particle reinforced aluminium matrix composite (SiCp/Al) which is acknowledged as one of the most competitive metal matrix composites is now widely applied in aviation, aerospace and military fields, and its application is extending gradually. As a result of the hard and brittle SiC particles contained, mechanical machining of the material is difficult, but the method of electric discharge machining (EDM) has certain prominent advantages. In this paper, SiCp/Al was machined using micro-EDM. First, a Ф40μm × 4.1mm micro tool electrode of which the aspect ratio is up to 100 was made; and then, through experiment, the impact of open-circuit voltage and electrode material on processing speed and electrode wear was analyzed; finally, 28μm wide micro slits, micro square platform of 34μm long on each side and other micro three-dimensional structure were machined. Research and experimental results show that the use of appropriate micro-machining parameters and reasonable processing methods can improve processing performance to better achieve the micro-EDM of SiCp /Al.

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.

Abstract: This research work aims to explore the feasibility of applying electrochemical machining (ECM) to micromachining. An experimental setup for micro-ECM has been developed. Lower machining voltage, lower concentration of passivity electrolyte, high-frequency short-pulse power supply and micro tool electrode rotating at high speed have been synthetically adopted to localize the dissolution area in micro-ECM, so the machining gap can be kept at about 10 μm and the better resolution of machined shape is achieved. A micro-hole with 45μm diameter is drilled on the stainless steel foil with 100μm thickness. A new approach of fabricating microstructure by micro-ECM milling with a simple micro electrode is proposed, and the micro beam with width of about 50μm which has high precision is fabricated by micro-EC milling on the stainless steel foil (1Cr18Ni9Ti) with 300μm thickness. A mathematics model has been established, which can be used to simulate the process of shaping workpieces in the process of micro-ECM.

Abstract: 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.

Abstract: 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%.

Abstract: 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.