Abstract : The experimental study and model analysis of the EDM workability of commonly used structural ceramic materials are carried out. It provides a new analytical method for predicting the EDM workability of structural ceramic materials under specific conditions. Abstract:The present paper experiments with and models the machinability of structural ceramics by EDM,providing a new method of analysing the machinability of stuctural ceramics by EDM.on certain conditions.▲ 1 Introduction EDM technology has been applied to the processing of structural ceramic materials and has been rapidly developed in the past 20 years. The inherent characteristics of structural ceramic materials make the process characteristics exhibited by EDM different from metals. Since the 1980s, many scholars have been devoted to the study of the external characteristics of EDM in structural ceramics. Different scholars have used different materials, obtained different process data under different conditions, and analyzed and summarized the same or similar technological rules. The dispersion of process laws is large and it is difficult to predict the feasibility of using EDM for certain structural ceramics. In this paper, experimental research and theoretical analysis are carried out around this issue, and a more scientific analytical method for predicting EDM workability of structural ceramics is obtained. 2 Material Selection in Experimental Design In structural ceramics, oxides, nitrides, and carbides are the three major series. Alumina is a typical representative of a meltable structural ceramic material and is the most mature of the oxide series structural ceramics. Its storage in the earth's crust is rich, accounting for about 25% of the total weight of the earth's crust, and its low price and excellent performance. According to historical records, only Boshan District, Zibo City, Shandong Province, contains billions of tons of high-quality bauxite. The development of inexpensive and quite mature research has made the use of alumina-based composite ceramic materials a wide range of applications involving various fields such as metallurgy, chemical industry, electromechanics, shipbuilding, aerospace, and light industry. Can be used to manufacture turning tools, milling cutters, calipers, various seals, drawing dies, drawing tower wheels, sliding plates, valves for chemical equipment, pumps, bearings for astronauts, rocket nose cones, etc. 3 Predictive analysis of machinability The processing efficiency and electrode loss satisfying the surface integrity are the decisive indicators to measure the feasibility of EDM for certain structural ceramic materials. For structural ceramic materials, the duration of the peak current is the key factor affecting the processing efficiency and electrode loss [1 ~3〕. As can be seen from the figure above, the maximum melting volume peaks at ts<40 ns, and the melting volume is small at 200 ns. Compared with the Vm-ts curve of the processed material, the value of ts of the processed material approaching and the positive value of the tool material away from the maximum value of the melt is optimal. Table 1 Changes in electrode loss at different pulse widths (%) Table 2 Changes in electrode losses at different peak currents (%) Table 3 Study parameters in Table 1 0.12 Table 4 Study parameters in Table 2 0.12 Table 5 Correction results of electrode losses at different pulse widths (%) Table 6 Correction results of electrode losses at different peak currents (%) 4 Summary The curve of the maximum melting volume with the pulse width obtained by modeling analysis can be used to predict the possibility of EDM for certain structural ceramic materials. In-depth and extensive research should be conducted to compile such curves under various specific conditions into an atlas or database software, so that EDM can become an effective and convenient processing method for structural ceramics.
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Keywords: Structural ceramics EDM Machinability
Silicon nitride is a typical representative of a class of structural ceramic materials with lower temperature decomposition, lower thermal conductivity (low temperature), and more glassy phase in the grain boundary, and is the most active and the most advanced in the structural ceramics of the nitride series. One. With excellent thermal shock resistance, low friction coefficient and strong self-lubricating ability, its application range exceeds that of alumina. In the U.S. ceramic gas turbine plan, silicon nitride is used to make rotors, stators, and scrolls. In anhydrous cold ceramic engines, hot-pressed silicon nitride is used as the piston top. In the gas turbine of the Federal Republic of Germany, Si3N4 is used as a rotor and a stator, and a reaction-fired Si3N4 is used as a burner. In Japan, piston sleeves, cylinder liners, and sub-combustion chambers in a single-cylinder diesel engine are manufactured using pressureless sintered Si3N4. Japan's Isuzu Motor Company's all-ceramic engine also uses mainly Si3N4-based structural ceramic materials. The high-temperature valves, bearings, rolling bearings and other ceramic parts developed in China are also the best performance of Si3N4-based materials.
Silicon carbide (commonly known as "carborundum") is a typical representative of a type of structural ceramic material that has no melting point, good thermal conductivity, and less glass in grain boundaries, and is the most widely used type of carbide in structural ceramics. The hardness of silicon carbide is second only to alumina, and its thermal conductivity is very good. The theoretical thermal conductivity is 400Wm*°C, which is much larger than that of alumina and silicon nitride. Its application in the tool industry has long been known. In recent years, it has been widely used in the manufacture of high-temperature components (rocket engine nozzles, magneto-electric generator electrodes, etc.), wear-resistant parts (all kinds of mechanical seal rings, wire drawing dies, etc.), corrosion-resistant parts (chemical pumps, Valves, nozzles, etc.) are the most promising high temperature materials and their normal temperature strength can be maintained up to 1200°C without significant reduction.
3.1. Determination of the optimal pulse width The key to determining whether a certain structural ceramic material can be processed on a specific EDM machine is whether the optimum pulse width can be obtained. By comprehensively analyzing the variation curve of the melting volume with the peak current duration ts of various materials, the optimal ts value corresponding to high efficiency and low loss can be predicted. If brass is used as a tool electrode and modeled brass is used as the anode, the maximum melting volume vs. ts curve is shown in the figure below. 
For example, comparing the Vm-ts curves [3] of the Al2O3, SiC, and Si3N4 with the above figure, the optimized pulse width of the three materials is in the range of 0.5 to 2 [mu]s. The optimal pulse width of Al2O3 is 0.5μs, and the optimal pulse width of SiC and Si3N4 is 1μs.
3.2 Prediction of Tool Electrode Loss Using the curve of the maximum melting volume with ts can predict the tool electrode loss, as shown in Table 1, Table 2 experimental and analytical results. The study parameters in Table 1 are shown in Table 3, and the study parameters in Table 2 are shown in Table 4.
1.5mm brass rod Al2O3 160 0.5 1:6 