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Magnetic Field Assistance in the EDM Process
Published in Basil Kuriachen, Jose Mathew, Uday Shanker Dixit, Electric Discharge Hybrid-Machining Processes, 2022
Mahavir Singh, Vyom Sharma, Janakarajan Ramkumar
The confinement of the plasma channel refers to the reduction in radius of the heat source incident on the workpiece electrode. A higher energy density is achievable with the plasma channel compressed to a smaller area, as plasma is the primary heat source in the EDM process. Due to the application of an external electric field, an electric force acts on the charged particles in the plasma channel. In MFAEDM, as the magnetic field is applied (static or pulsating), the magnetic force acts in the transverse direction to the electric field. This force acts radially inward (towards the center of plasma) in the plasma channel to confine it to a smaller radius. The combined effect of electric force and magnetic force, in other words, Lorentz force, minimizes the plasma channel, and thus a smaller diameter crater is formed on the surface [23]. A self-induced Lorentz force also acts on the plasma channel, but it gets nullified as it is present in both the conditions whether or not the magnetic field is functional. Figure 10.6 depicts a representation of the plasma column, the crater formed on the workpiece in traditional EDM (no magnetic field), and MFAEDM. It has also been established that the pulsed magnetic field reduces the losses in magnetic flux associated with a permanent magnet, and is thus found to be more effective in augmenting machining rate, producing better surface integrity and causing insignificant tool wear in the EDM [24].
Micromachining
Published in Chander Prakash, Sunpreet Singh, J. Paulo Davim, Advanced Manufacturing and Processing Technology, 2020
Venkatasreenivasula Reddy Perla, K.J. Rathanraj
When pulsed DC power is supplied to two electrodes, and as the distance between electrodes reaches IEG, a strong electrical field is generated. As the pulse begins, the applied voltage attains breakdown voltage value, and the workpiece surface temperature will increase. Hence, the dielectric fluid present between the gap gets vaporized, and the plasma channel will be generated. Now, the plasma channel produces an instantaneous temperature range of more than 10,000°C. The sudden increase in temperature causes local heating of electrodes (more on the anode), and the workpiece material will easily melt and evaporate because the melting point of the workpiece is very much less than spark temperature. This creates a crater on the workpiece and leaves some debris on the surface [51]. These particles are flushed away by dielectric fluid flow during pulse off time. Now the pulse duration ends, a new pulse will start to create new local erosion, and the cycle continues till the required machining shape is produced. The trends of voltage and current during the machining phase for one complete pulse are related to various phases such as ignition, plasma formation, discharge phase, and ejection phase as shown in the figure 4.16.
Generation of Plasma in Liquid
Published in Yong Yang, Young I. Cho, Alexander Fridman, Plasma Discharge in Liquid, 2017
Yong Yang, Young I. Cho, Alexander Fridman
When a plasma discharge is initiated between two electrodes, the medium between the two electrodes is ionized, creating a plasma channel. The plasma discharge generates UV radiation and converts surrounding water molecules into active radical species due to the high energy level produced by the discharge. The microorganisms could be effectively inactivated, while the organic contaminants could be oxidized through the contact with active radicals. The chemical kinetics of these reactions remains an area of significant research. Various active species can be considered the by-products of plasma discharge in water. The production of these species by plasma discharge is affected by a number of parameters, such as applied voltage, rise time, pulse duration, total energy, polarity, the electric conductivity of water, and so on. Among the active species, hydroxyl radical, atomic oxygen, ozone, and hydrogen peroxide are the most important ones for the sterilization and removal of unwanted organic compounds in water. Table 2.2 summarizes the oxidation potentials of various active species produced by plasma in water, which ranges from 1.78 V (hydrogen peroxide) to 2.8 V (hydroxyl radical). Note that fluorine has the highest oxidation potential of 3.03 V, whereas chlorine, which is one of the most commonly used chemicals for water decontamination, has an oxidation potential of only 1.36 V.
Review on tools and tool wear in EDM
Published in Machining Science and Technology, 2021
Deepak Sharma, Somashekhar S. Hiremath
The EDM process involves the removal of material by a sequence of rapid reoccurring discharges among the conductive tool and workpiece. The basic principle of EDM is, when the voltage reached to some predetermined value, the electrons break loose from the tool and accelerates toward the workpiece. During their travel within in the spark gap, the electrons collide with the neutral dielectric fluid molecules and cause ionization. Then, these electrons and ions together form the plasma channel. This plasma channel enables the spark discharge to take place through the dielectric fluid. As a result of spark, a very high temperature of the order of 10,000 °C − 12,000 °C is produced, which instantaneously melts and vaporizes the workpiece material and leaving behind a tiny crater. A small amount of the vaporized material in the form of debris is dispersed into the space surrounding the electrodes. Some portion of these dispersed debris is removed by the dielectric fluid and the remaining are solidified. The detailed mechanism of material removal in EDM is available in various textbooks (Gosh and Malik, 2010; Koc and Ozel, 2019).
Hydrodynamic arc moving mechanism in EDM of polycrystalline diamond
Published in Materials and Manufacturing Processes, 2022
Xiangzhi Wang, Hun Guo, Ge Wu, Songlin Ding
Plasma is actually a conductive gas, which can be regarded as transparent to slow-moving electrons.[26] However, high-speed moving charged particles inevitably collide, there is a specific resistance in the process of particles’ movement. When current passes through the plasma, this resistance causes electrical energy to be converted into heat. When conducting electrons transfer energy to conductor atoms through collisions, they generate heat on a tiny scale. The plasma channel also participates in conduction while flowing, producing strong ohmic heating and heat radiation effects. During the movement of the plasma channel, the electromagnetic force will be generated, affecting the plasma’s motion. Fig. 3 shows the plasma channel movement behaviors within one single-pulse discharge cycle when flushing at a speed of 1 m/s. It can be seen from the figure that the plasma channel forms before 6 μs after discharge begins Fig. 3(a). The plasma channel gradually deforms under the action of hydrodynamic force, which increases the erosion range. Deformation occurs first at 1/4 of the length of the sparking gap from the surface of the workpiece (Fig. 3(b‒c)) due to the fastest external liquid flow rate. The first moving part of the channel drags the arc and makes it move on the workpiece surface (Fig. 3(d‒j)). The temperature of a large part of the plasma channel is 7000–8000 k, and the core part near the cathode can be as high as 14000 k (red region). The core high-temperature area gradually decreases as the arc moves, which indicates that the plasma must adjust its temperature to adapt to changes in shapes due to the elongation of the arc.
Role of stabilizers on agglomeration of debris during micro-electrical discharge machining
Published in Machining Science and Technology, 2019
Ranjeet K. Sahu, Somashekhar S. Hiremath
Colloidal aluminium nanoparticles are generated using an in-house developed µ-EDM experimental setup. In this setup, aluminium nanoparticles are directly generated in dielectric fluid (DI water) or suspension media (DI water + stabilizers). μ-EDM is a non-contact machining process which is basically based on the thermo-electric energy created between the two electrodes: tool and the workpiece surrounded by a dielectric fluid. In this process, a plasma channel is generated by the breakdown of the dielectric fluid caused by the electric potential between the electrodes. This channel enables the spark discharge to take place through the dielectric and thus, material is removed from both the electrodes through melting and evaporation.