26
Remanufacturing and Advanced Machining
(Palanikumar and Davim, 2013). It should be noted, however, that the workpiece (2)
should be connected to the electrode where more heat is released, so that the material removal is to be maximized on the workpiece while the tool wear is minimal
(Schulze, 2017). In particular, negative electrode polarity with a high MRR is recommended for high-precision machining, and in the wire EDM process, the electrode
“wire” usually has a negative polarity to keep the machining rate high with a reduced
tool wear rate (Qudeiri et al., 2020). Other major electrical parameters of the EDM
process are as follows: discharge voltage, peak current, pulse duration and interval,
and pulse wave form.
The entire process takes place in a liquid dielectric environment, such as kerosene, oil, or distilled water. Usually, two main types of fluids are distinguished,
namely deionized water and the so-called dielectric oils based on hydrocarbon compounds (Uhlmann et al., 2010). The former is considered an ecofriendly substance
since it does not release harmful gases, such as CO or CH 4 , and yields a higher MRR
and lower electrode wear (Rahman et al., 2014).
The dielectric fluid performs several main functions (Uhlmann et al., 2010):
• Isolation of the tool electrode from the workpiece electrode to achieve a
high current density in the plasma channel
• Cooling down the heated surfaces of the electrodes and exerting a counter
pressure against the expanding plasma channel
• Removal of particles after the discharge process preventing the particles
from developing linkages between the electrodes that would cause process
interruptions by short-circuiting or damage to the electrode surfaces
To perform these tasks, the dielectric liquid should display low viscosity, chemical neutrality toward tool and workpiece materials, intoxicity, safety, and low cost.
Discharge erosion is determined by the chemical composition of the electrodes (tool
and workpiece), dielectric liquid and energetic characteristics of electrical pulses,
as well as by the process conditions. Thermophysical properties of a material, especially the melting and boiling temperatures, play a decisive role in the EDM and
determine its machinability (Weingärtner et al., 2012). Generally, materials with
lower melting temperatures can be eroded faster so that higher MRRs are achieved.
If the machinability of a normalized steel is taken as a unit, then heat-resistant steels
would have machinability of 1.3–1.4, while refractory metals and hard alloys would
reach merely 0.4–0.5. Since hardened steels have thermal conductivity reduced,
their machinability in the EDM process is 25–30% higher.
There are three main types of the EDM, depending on the electrode used
(Palanikumar and Davim, 2013):
1. Die-sinking EDM consists of an electrode made according to a required
shape and a workpiece submerged in an insulating liquid. During erosion,
the shape of the electrode forms its inverse shape in the workpiece. This
is an important accurate process normally used for making mold cavities.
The machining speed depends upon the type of material, the area of the
Remanufacturing and Advanced Machining
(Palanikumar and Davim, 2013). It should be noted, however, that the workpiece (2)
should be connected to the electrode where more heat is released, so that the material removal is to be maximized on the workpiece while the tool wear is minimal
(Schulze, 2017). In particular, negative electrode polarity with a high MRR is recommended for high-precision machining, and in the wire EDM process, the electrode
“wire” usually has a negative polarity to keep the machining rate high with a reduced
tool wear rate (Qudeiri et al., 2020). Other major electrical parameters of the EDM
process are as follows: discharge voltage, peak current, pulse duration and interval,
and pulse wave form.
The entire process takes place in a liquid dielectric environment, such as kerosene, oil, or distilled water. Usually, two main types of fluids are distinguished,
namely deionized water and the so-called dielectric oils based on hydrocarbon compounds (Uhlmann et al., 2010). The former is considered an ecofriendly substance
since it does not release harmful gases, such as CO or CH 4 , and yields a higher MRR
and lower electrode wear (Rahman et al., 2014).
The dielectric fluid performs several main functions (Uhlmann et al., 2010):
• Isolation of the tool electrode from the workpiece electrode to achieve a
high current density in the plasma channel
• Cooling down the heated surfaces of the electrodes and exerting a counter
pressure against the expanding plasma channel
• Removal of particles after the discharge process preventing the particles
from developing linkages between the electrodes that would cause process
interruptions by short-circuiting or damage to the electrode surfaces
To perform these tasks, the dielectric liquid should display low viscosity, chemical neutrality toward tool and workpiece materials, intoxicity, safety, and low cost.
Discharge erosion is determined by the chemical composition of the electrodes (tool
and workpiece), dielectric liquid and energetic characteristics of electrical pulses,
as well as by the process conditions. Thermophysical properties of a material, especially the melting and boiling temperatures, play a decisive role in the EDM and
determine its machinability (Weingärtner et al., 2012). Generally, materials with
lower melting temperatures can be eroded faster so that higher MRRs are achieved.
If the machinability of a normalized steel is taken as a unit, then heat-resistant steels
would have machinability of 1.3–1.4, while refractory metals and hard alloys would
reach merely 0.4–0.5. Since hardened steels have thermal conductivity reduced,
their machinability in the EDM process is 25–30% higher.
There are three main types of the EDM, depending on the electrode used
(Palanikumar and Davim, 2013):
1. Die-sinking EDM consists of an electrode made according to a required
shape and a workpiece submerged in an insulating liquid. During erosion,
the shape of the electrode forms its inverse shape in the workpiece. This
is an important accurate process normally used for making mold cavities.
The machining speed depends upon the type of material, the area of the