On Electrical Discharge Machining of Non-Conductive Ceramics: A Review

Abstract

The inability of ceramic and nanoceramic processing without expensive diamond tools and with a high-material-removal rate hampers the scope of its potential applications and does not allow humanity to make a full shift to the sixth technological paradigm associated with Kuhn scientific revolutions and Kondratieff's waves and restrains the growth of the economy. The authors completed a review on the research state of ceramic and nanoceramic processing by electrical discharge machining, which is possibly solved by two principal approaches associated with the usage of standard commercially available machine tools. The first approach is related to the introduction of expensive secondary phase; the second approach proposes initiate processing by adding auxiliary electrodes in the form of coating, suspension, aerosol, or 3D-printed layer based on the components of silver, copper, or graphite in combination with an improved dielectric oil environment by introducing graphite or carbon nanoparticles, which is hugely relevant today.Technologies 2019, 7, 55 2 of 16 of cutting tools limits the resulting geometry of the product. Other machining methods such as vibroacoustic machining, laser and electron beam scribing, selective laser sintering with a binder, find their specific place in the processing of ceramics. However, they do not allow the receiving of all geometrically possible shapes of the product without losses on the operational parameters of ceramics [16][17][18].One of the most popular methods for the production of parts, regardless of their hardness, is electrical discharge machining (EDM). However, it requires the material to be conductive [19][20][21]. The process of electrical erosion of the material consists of initiating electric pulses in the interelectrode gap, in the breakdown of the dielectric medium in the gap, in establishing a discharge channel, where the temperature reaches more than 10,000 • C (low-temperature plasma). Due to such temperatures, the material is ablated, the drops of cooled material as eroded debris are washed away by the flow of the dielectric medium, and the electrodes again approach to resume the cycle. Thus, a unique crater-like topology on the surface of the workpiece is created [22][23][24][25].The inability of ceramics and nanoceramics to conduct current hampers the scope of its potential applications and restrains the growth of the progress and the switch to the next technological paradigm that most of the scientists associate with the term "nano" [26][27][28][29][30][31][32].Thus, it can be concluded that the study and development of a method for electrical discharge machining of non-conductive ceramics and nanoceramics are incredibly relevant today.The authors propose to apply the dialectical approach of cognition as a scientific approach to solve the formulated scientific problem. The dialectical approach includes the systematization and updating of existing knowledge and new data about the object of research.

Understanding Material Removal Mechanism and Effects of Machining Parameters during EDM of Zirconia-Toughened Alumina Ceramic

“…Although electrical conductivity of the non-conductor ceramics can be enhanced to the required minimum level by doping with conductor materials, it has its downside of reduced mechanical properties as well. Therefore, one of the modified EDM approaches known as Assistive Electrode Method allows for the machining of nonconductive ceramics with the help of some metallic conductive layer on the workpiece [ 29 , 30 , 31 ]. In this assistive electrode approach, the conductive layer initiates EDM process, and then pyrolytic carbon molecules generated from dielectric attach themselves with the nonconductive workpiece and continue the EDM process by providing the necessary electrical conductivity [ 32 , 33 ].…”

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

“…Other parameters of the process can be varied in a similar way, including the value of the discharge, by maintaining the constancy of the ratio of useful energy to consumed energy [36,82,83]. It can be seen that, in the latter case, the signal becomes more complex during electrical discharge machining of the nanocomposites compared with other processing methods [7,23]. Quite weighty components appear around the spectral maximum at the frequency of the impulse action, indicating the presence of discharges between the electrodes and non-periodic short-circuits, which contribute to the energy of signals.…”

“…Powders were preliminarily mixed in a multidirectional Turbula shaker mixer (Eskens B.V., Alphen aan den Rijn, The Netherlands) in ethanol at 150 rpm for 24 h. Lyophilizer FreeZone2.5 (LabConco, Kansas, MO, USA) was used for drying of the slurries to avoid TiC agglomerates in the ceramic matrix and additional sieving [7,8]. The collector temperature was of 50 ± 2 • C, the shell temperature was of +23 ± 2 • C; the chamber pressure was of 0.02 ± 0.01 mbar.…”

“…Electrical discharge machining is a well-known technology used for processing conductive materials [1][2][3][4], while there are always developed techniques to subject the non-conductive material to electroerosive wear [5][6][7][8]. However, these techniques do not show any outstanding results due to small volumetric performance and expensive assisting materials-nanoparticles of precious or rare materials, labor-intensive techniques of conductive layers applications, etc.…”

Editorial for the Special Issue “Reviews and Advances in Materials Processing”

“…Among the three review papers, two of the articles address electro-discharge machining of non-conductive ceramics and a combination of materials written by Volosova et al [1,2]. The critical issues and the way forward in each case is intelligently described by authors.…”