Key Technologies Of Micro Reversible EDM Method Based On Micro EDM Deposition And Removal Process

The level of Advanced Manufacturing Technology (AMT) is one of the most important factors to influence economic development and modernization. With the development of manufacturing technology, materials processing is no longer confined to traditional removal process. As an important branch of AMT, micro machining technology has been much accounted of all over the world. With the unique advantages such as non-contact process, small removal unit, energy easy to be controlled and so on, micro electrical discharge machining (EDM) process has become one of the research focuses in the field of micro-machining.In the past, the researches of micro EDM mainly focus on how to improve the machining accuracy, the machining efficiency, and the micro-level of removal. But the principle of EDM determines the phenomena of tool electrode wear and polarity effect are inevitable. In this paper, the tool electrode wear and the polarity effect in micro EDM process are researched firstly based on analyzing the mechanism and process characteristics of micro EDM. On this basis, a reversible machining method is put forward, in which metal material can be deposited or removed in one EDM machining system. From analyzing the polarity effect, the working medium, the processing parameters, the processing conditions of the micro reversible EDM and the transformation strategy from deposition machining to removal machining are researched.The major factors influence the tool electrode removal in micro EDM deposition are analyzed, and the temperature field simulation of tool electrode under the condition of single discharge with time-varying discharge channel radius is developed. Through analyzing the micro-process of the tool electrode removal, the law of different tool electrode removal form with different discharge energy density in discharge channel is obtained. In addition, the discharge waveform characteristics of transistor pulse source and RC pulse source in micro EDM deposition are analyzed, the formation process of the deposited material with the discharge characteristics are researched.The characteristics of the deposited material have been analyzed detailed, the results show that the deposited material has compact fine texture and bonds close to the base material, the components of the deposited material are almost the same as those of the tool electrode and micro oxidation occurs using air working medium. Hardness test results show that when using 45 steel and tungsten as tool electrode, the hardness of deposited materials increase obviously compare with the tool electrode. Moreover, the deposited material has a better ability to withstand compression loads. Brass deposited material can withstand the maximum pressure of about 490Mpa and 45 steel deposited material of about 1764Mpa, which show that micro EDM deposition process can be applied to fabrication of micro supporting structures.The deposition strategies of fabricating micro structures by using micro EDM deposition process are researched. In this paper, two kinds of deposition strategies are put forward, which are multi-deposition based on the stability of single cylinder deposition and scanning layer by layer deposition based on discharge gap servo. The deposition strategy combines the tool electrode real-time servo along Z axis with the X-Y plane single layer scanning path planning is built. The tool electrode wear compensation model and the consistency law of deposition layer are analyzed. In this research, a scanning path planning method of arbitrary shape in X-Y plan is built too, and the samples from deposition experiments have satisfied results.On the basis of above researches, the machining system of micro reversible EDM is built and the micro reversible EDM method is put forward. The micro reversible EDM method can be divided into three continuous processes, which are micro tool electrode on-line machining, micro EDM deposition process, and micro EDM selective removal process. In step of selective removal process, several removal strategies including direct removing along Z-axis, axial direction array-holes and radial direction micro holes drilling on the deposited micro cylinder and micro EDM milling were carried out respectively, micro 3D structures of metal material with high shape accuracy and high dimensional precision are fabricated successfully. In micro EDM milling process, a present length method of tool electrode is applied to compensate the axial wear, which improve the machining efficiency and machining precision and easy to achieve the better results of clearing rootAll above, the reversible EDM method is a breakthrough of traditional EDM, which provides the ability of depositing or removing metal material for fabrication of micro structures in one machining system. The new reversible EDM process has the advantages such as the low-cost equipment requirements, a wide adaptability of materials and the energy easy to be controlled and so on, which provides a new technique method for micro machining technology.