Electrical discharge machining of ceramic nanocomposites: sublimation phenomena and adaptive control

Abstract

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.

Wire Tool Electrode Behavior and Wear under Discharge Pulses

“…The occurred conditions are close to the conditions of lightning formation [20]. The temperature in the interelectrode gap achieves high value in a microsecond [21][22][23].…”

“…The vibroacoustic monitoring was provided by piezoelectric accelerometers mounted on the elastic system of the machine [23,[25][26][27]51,52] (Figure 2). The data received by the accelerometers signals were forwarded to preamplifiers, amplifiers VShV003 (JSC Izmeritel, Taganrog, Russia), and an analog-to-digital converter E440 (L-card, Saint-Petersburg, Russia), and recorded with a personal computer (PC).…”

“…The vibroacoustic signal reflects the changes in the weight and structure of the workpiece, the main discharging factors that correlated with the force diagram in the working zone [27,55] that influence the amplitude of the signal in the wide range of spectra [23,25,26,51,52].…”

Electrical Discharge Machining of Oxide Nanocomposite: Nanomodification of Surface and Subsurface Layers

“…Two electrodes are placed on the distance that correlates to the conductivity of the material to be processed and there is dielectric permittivity of the medium between two electrodes. The material with higher conductivity requires a larger space between electrodes [21][22][23]. The material with lower conductivity is normally called the workpiece electrode, while material of high conductivity is a tool electrode-the destruction of the workpiece should occur more intensively that the destruction of the tool, otherwise the technology has no sense.…”

Dynamic Model of Electrical Discharge Machining and Algorithm of Extreme Control Through Acoustic Signal

“…Electrical discharge machining (EDM) is one of the most high-precision types of machining. Modern CNC machines allow obtaining products with an accuracy of 1 micron at the positioning step of the linear guides being as small as 80-100 nm [1][2][3][4][5][6][7][8]. The field of application of this technology significantly expands in the case, when 4 to 6 independent coordinates are used [9,10].…”