| In micro and nanometer machining field, two material machining modes are popularly taken. One is reducing material top down, the other is increasing material bottom up. If the reversible machining of reducing and increasing material can be easily achieved by changing control strategy in the same machining system, it is significant to rich material machining technologies and to provide new machining methods. Because electrical discharge machining (EDM) has no macro resistance, and removes hard material using soft material, it is one of effective ways to solve manufacturing questions of complex parts and hard-to-cut material. The new micro electrical discharge deposition (EDD) technology proposed in this paper is able to not only grow or modify material on defective parts, but also obtain micro three-dimensional structures with concave and convex characters.Micro EDD is based on the basic principles of ordinary EDM. So the basic principles of micro EDD are analyzed, and the realized conditions are predicted. Then a heat conduction model of micro EDD machining in the air is built through selecting a proper heat-source model, thermal boundary conditions and discharge channel diameters etc. With the finite element analysis method of Ansys, the transient thermal field of the tool electrode and workpiece is analyzed under single pulse, and the processing parameters range of micro EDD in the air is predicted.Then with an ordinary EDM shaping machine DP30, and 45# steel, tungsten and brass as electrodes, micro EDD machining can be realized in the air. By only exchanging the polarities of electrode and workpiece, the deposited material can be removed selectively, thus the reversible material machining is realized. A large number of experiments are carried out to obtain the effects of different processing parameters on micro EDD. In order to search the intrinsic essence of micro EDD, the deposition experiments are also carried out against the gravity, in argon and in magnetic field.To fabricate further two and three-dimensional structure, two deposition strategies are brought forward in this paper, which are the continuous deposition strategy of single cylinder and the delamination scanning deposition strategy. Through planning electrodes'path, the shapes of HIT character type array, reciprocating straight, arc and quadrilateral are deposited. In addition, only using the feed in Z axis without X, Y axis or NC function, a micro three-dimensional spiral structure can be obtained with brass electrode using special parameters. The process rules of micro spiral deposition are generalized experimentally. It is found that micro spirals can be deposited stably against the gravity and under the random angle between the electrode and workpiece.The materials by micro EDD are detected performance. The measurements show that the components of the deposited material depend on those of the tool electrode material. The deposited material features obvious delaminating structures, and the combining of the deposited material and the base is compact. The hardness of 45# steel and tungsten both increase obviously after EDD. The micro spiral is corrosion resistant. In addition, the deposition in argon can avoid oxidation, that in magnetic field can make structure more compact.The micro EDD method in the air has some features, such as more simple facilities, better operability, wider material adaptability, easily controlling energy and facing on workshops. Therefore, is has wide application foreground.
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