Key Technologies For ECDM Machining Of Non-conductive Hard And Brittle Materials

Non-conductive materials, such as pyrex and ceramics, are widely used in the areas of aeronautics and astronautics, biomedical, chemical industry, and metallurgy because of their properties of excellent insulating performance, corrosion resistance, high-temperature resistance and high hardness. However their super hard and brittle characteristics make it difficult to produce micro structures by traditional cutting process. Electrochemical discharge machining(ECDM) is regarded as a good choice to machine these materials. In this dissertation, some key techniques for ECDM were studied.The machining principle of ECDM was discussed. This phenomenon of decreased geometric accuracy and machining speed with the increase of machining depth in conventional ECDM hole drilling was analyzed. As the hole becomes deeper, the electrolyte around the tool electrode is hard to update, so the gas film is difficult to form. In this area, electro-discharge decreases, and more discharge is transferred to the inlet of the hole. As a result, the inlet diameter becomes bigger, and the machining velocity and quality decreases. To solve these problems, a reverse-configurated ECDM method was proposed, in which the workpiece is fixed on the spindle and the tool electrode is assembled at the bottom of the electrolyte tank. The reversed tool-workpiece configuration makes the bubbles rising and gathering under the workpiece to form gas film easily. Thus, the discharges can continue. Besides, the rotating of tool electrode is beneficial to electrolyte update and debris exhaustion.The reverse-configurated ECDM platform was established. A series of ECDM experiments, including the comparison experiments with conventional ECDM, were conducted. Current signal acquired during the machining process was analyzed to understand the material removal principle and machining characteristics. Several parameters including machining voltage, electrolyte concentration, feeding velocity and rotating speed were studied to achieve their effects on the hole inlet diameter and machining reproducibility. The results showed that reverse-configurated ECDM could make gas film more stable, decrease the discharges near the inlet of the hole, As a result, the machining velocity, quality and reproducibility of the reverse-configurated ECDM are accordingly improved.A reasonable machining process was designed to produce Laval nozzle on a microcrystalline-mica-ceramics(MCMC) sample with a throat diameter of 0.4mm, which is an ECDM machined micro hole followed by ultrasonic machining from both sides of the sample. The use of spiral tool electrode in ECDM greatly improved the ECDM performance. Then a ultrasonic machining equipment was set up, and the Laval nozzle was accomplished.The results showed the reverse-configurated ECDM method is of great potential in the micro machining of hard and brittle non-conductive materials and is worthy to be further studied.