RESUMEN
There are two main ways of carrying out the electrical discharge machining of the insulating ceramics: changing the electrical and chemical properties of ceramics due to additives in producing composites/nanocomposites and changing the electrical and chemical properties in the interelectrode gap. This review summarizes and analyzes the current data on the machinability in water suspension and hydrocarbons depending on the electrical properties of the ceramic composites and assisting means such as coating and powder. There are provided the existing approaches and original methods for solving the global problem of the electrical discharge machining of insulating ceramics, suggesting further development of the existing methods since, up to now, the experimental research is non-systemic. The dependencies of the machinability on the electrical properties of conductive ceramic composites, the specific electrical resistance of the assisting coating, and the assisting powder's band gap and concentration for machining insulating ceramics are revealed. The higher the electrical conductivity, the higher the machinability of ceramic composites, and the lower the band gap, the higher the machinability for insulating ceramics. Two technological gaps were revealed in the powder's concentration that can be a particular case of logarithmic decrement of attenuation. The proposed approach suggests using assisting powder with the lower band gap.
RESUMEN
The mechanism of the material destruction under discharge pulses and material removal mechanism based on the thermochemical nature of the electrical erosion during electrical discharge machining of conductive materials were researched. The experiments were conducted for two structural materials used in the aerospace industry, namely austenite anticorrosion X10CrNiTi18-10 (12kH18N10T) steel and 2024 (D16) duralumin, machined by a brass tool of 0.25 mm in diameter in a deionized water medium. The optimized wire electrical discharge machining factors, measured discharge gaps (recommended offset is 170-175 µm and 195-199 µm, respectively), X-ray photoelectron spectroscopy for both types of materials are reported. Elemental analysis showed the presence of metallic Zn, CuO, iron oxides, chromium oxides, and 58.07% carbides (precipitation and normal atmospheric contamination) for steel and the presence of metallic Zn, CuO, ZnO, aluminum oxide, and 40.37% carbides (contamination) for duralumin. For the first time, calculating the thermochemistry parameters for reactions of Zn(OH)2, ZnO, and NiO formation was produced. The ability of Ni of chrome-nickel steel to interact with Zn of brass electrode was thermochemically proved. The standard enthalpy of the Ni5Zn21 intermetallic compound formation (erosion dust) ΔH0298 is -225.96 kJ/mol; the entropy of the crystalline phase Scint is 424.64 J/(mol·K).
RESUMEN
The productivity of electrical discharge machining (EDM) is relatively low owing to the natural laws of electrical erosion. Precise EDM demands uninterrupted control of the discharge gap and adjustment of process parameters. It is particularly critical for processing large workpieces with complex linear surfaces and for materials with threshold conductivities such as the new advanced ceramic nanocomposites Al2O3+TiC and Al2O3+SiCw+TiC(30-40%). In these cases, adequate flushing of erosion products is hampered by the geometry of the working space or by the small value of the required discharge gap, which does not exceed 2.2-2.5 µm. The methods of adaptive control in modern computer numerical control systems of EDM equipment based on measuring the electrical parameters in the working zone have been shown to be ineffective in the cases described above. This study aims to investigate the natural phenomena of material sublimation under discharge pulses for conductive ceramics and nanocomposites. The measured conductivities of the samples are higher than the percolation threshold. However, the question of machinability remains open owing to detected processing interruptions and poor quality of machined surfaces. New knowledge on EDM of conductive ceramics and nanocomposites can improve the final quality of the machined surfaces and productivity of the method by the introduction of advanced monitoring and control methods based on acoustic emissions. The manuscript presents an up-to-date overview and current state of the research on the subject area. The obtained morphology of the samples and discussion of the findings complete the experimental part of the study. The scientific basis for a new type of adaptive control system is provided. This can improve the effectiveness of parameter control for machining conductive ceramics and nanocomposites and contribute to an increase in the EDM performance for the most critical cases.