| Recently, micro electric discharge machining (micro EDM) has been promising on micro-dimension manufacturing due to its non-contact process without macro cutting force, relatively low requirements for the strength and the stiffness of the tools and good applicability to machine allotype cavity mode. Thus, micro EDM is a crucial technique for micro structure manufacturing and has been widely used in applications of aerospace, aviation, national defense, energy, transportation and medical equipment. However, micro EDM generally releases extremely low energy in one single impulse accompanying with high electric impulse frequency and short discharging duration, and finally brings a difficulty in achieving precise and effective control to the manufacturing process, which leads to instability and low efficiency and thus limit the development of micro EDM technique. To expand the application range of micro EDM and improve the overall processing level of micro machining area, it is such a necessary way to improve the processing efficiency of micro EDM and ensure high efficiency and quality of micro EDM process. In this dissertation, in order to break through the bottle necks of micro EDM and to solve the key technologies on increasing its processing efficiency, a series of research activities were done based on a thorough analysis to the mechanism and the features of micro EDM technique, which includes3-D high-precision micro EDM system establishment, multi-objective optimization for processing parameters, intelligent control for the manufacturing process, discharge state prediction, servo motion on-line prediction and control and electrode compensation. In addition, the above solutions were applied to conduct high-efficiency micro groove array EDM on difficult-to-cut alloys. The detailed contents in this dissertation are as follows:A high-precision3-D micro EDM system was established under the requirement of high precision and high sensitivity. The system contains a Z axle micro-electrode ultra precision stage which is driven by a linear motor while the work piece on X/Y axles ultra precision stage is activated by AC servo motors. IPC industrial controller and the PMC multi-axis motion controller with PCI1714digital signal acquisition card are employed to compose an open digital system in upper-lower computer mode. An intelligent-software-controlled system offers many characteristics such as servo motion control, interval digital signal acquisition, impulse power setting etc. This system runs stably when it conduct actual machining and has provided a favorable platform for the study on key technology of high-efficiency micro EDM.A non-dominated based multi-objective genetic algorithm was proposed to solve the difficulty on optimizing the parameters of processing for micro EDM. The processing time and electrode wear were taken into account to optimize the parameters applied in processing. A processing relationship model was built to provide fitness function to the multi-objective genetic algorithm when imported the theory of supported vector machine under the micro and deep hole orthogonal machining experiments. The experimental evidence showed that the optimized parameter significantly decreased processing time and made the amount of the electrode wear within an accepted range.In order to solve such problems of manufacturing induced uncertainty in micro EDM process as high discharging frequency, severely distorted discharging signal and too much noise, the traditional fuzzy membership function was expanded to the Type-2mode to improve the ability of system describing uncertain information. Also, a two-step control method to the micro EDM was proposed based on the interval Type-2fuzzy set. The first step involved the sampling point discharge state inspection system while the servo motion control system was included in the second step. It was verified by experiments that the proposed control method could significantly increase the efficiency of processing compared to the average voltage and traditional fuzzy control method, and a good processing quality could be obtained, especially these advantages would become more significant in a worse machining environment.To avoid the hysteretic nature in traditional control, investigations on discharge state prediction and on-line servo motion prediction were performed. A predicted approach in discharge state using micro EDM was developed combining with the empirical mode decomposition principle and the linear predict method, which gave an accurately predicted result and was validated to be well suitable for the non-linear time-varying signal prediction. Besides, an on-line servo motion prediction and control method was proposed based on the grey catastrophic predicting principle. While inspecting the current discharge state, the servo motion in future cycles could be synchronously predicted, resulting in a comprehensive control strategy of the servo system. It was shown under the tests that the proposed feeding speed on-line prediction and control method had significantly diminished the rollback phenomena of the micro electrode and dramatically improved the processing efficiency.A deep sawing micro EDM slicing milling method was proposed with respect to the problem of the micro electrode wear during micro3-D part machining and low efficiency, and based on this method the fixed length compensation concept for the micro electrode was defined. The wear law of micro electrode was explained by observing the configuration variation of micro electrode processed as different length, and micro electrode compensation model for single-layer deep cutting was thus established. The experiments indicated that a relatively high precision of dimension was obtained and the processing efficiency was significantly improved when processed a micro groove of200μm depth one-time. According to the requirement for processing micro grooves on difficult-to-cut alloys, a particular processing law for difficult-to-cut alloys micro EDM was studied referred to orthogonal machining technique. The experiments using micro grooves EDM on difficult-to-cut alloys were also performed based on the proposed micro EDM processing approaches discussed previously. The experimental results showed micro EDM technique presented in this paper helped to bring a high processing quality for micro slots with high processing efficiency. Therefore, micro EDM technique developed by this dissertation was found to have an important influence on providing a high processing efficiency, solving the difficulty in processing difficult-to-cut material for micro parts, extending the industrial application and improving the capability of manufacturing in micro-precise area. |
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