| In recent years, with the enhancement of overall national strength, the aviation industry has been rapid developed, as the heart of a aircraft- engines, its performance will be a key to keep the rapid development of the aviation industry, in order to be able to manufacture the engine with a big thrust to weight ratio, the material of engine blades requires a high temperature performance, at the same time, the development of cooling technology has become extremely important, and film cooling holes on a turbine blade play an extremely important role for the cooling efficiency. Currently, machining film cooling holes on a blade, the most common approach is to use EDM. When using EDM, the formation of taper will be happened because of the loss of the electrode and the "second discharge" phenomenon. When a hole just punches through, the shape of the hole is conical. For machining through-holes on an open workpiece, the common approach is to feed the electrode over a certain distance to accomplish taper compensation, and to eliminate taper caused by the electrode. But for the semi-closed structure of the blade, the electrode can not be allowed to feed unrestricted downward, otherwise it will cause mistaken machining on the rear wall of the blade. Therefore, the feed rate of the electrode must be controlled.In this paper, aiming at the problem of machining air-film cooling holes on a blade in EDM, the current status of the research on the electrode wear compensation technology of film holes on a blade in EDM in the domestic and foreign has been summarized; The hardware design of a discharge state detection device has been carried out; The design of discharge rate statistics-communication program based on FPGA and the design of upper computer monitoring platform has been carried out; The experimental study on the taper compensation control of the film hole machining based on the discharge state detecting device has been carried out.Through the discharge state detecting device, the discharge waveforms can be distinguished. Through the FPGA-based statistic module, the discharge rate can be calculated, and the proportion of each discharge waveform can be send to the PC interface and the LED display plate. Based on the feature, the discharge state will change suddenly as the completion of taper compensation, through the strategy of judgment, identification of the time of the end can be achieved, as well as the PC interface and the LED display plate can output the signal for the end, so the feed rate of the electrode can be controlled in taper compensation process.Ultimately, through orthogonal experiment, the Optimal parameters have been found to make the projecting amount of the electrode be shortest. The projecting amounts of the electrode have been controlled in the range of 2mm~2.5mm, and the taper angles of holes have been controlled in the range of 1~1.4 degrees. While eliminating taper, it can ensure a safe distance between the rear wall of the blade and the tip of the electrode, thereby solving the problem of taper compensation on machining through-holes on a blade in EDM. |
