EML6323 Nontraditional Manufacturing (Spring, 2023) 03/26/2023
An Overview of Electrical Discharge Machining (EDM)
Aidan Vega, Yikai Yang, Shiru Wei, Andre Tomlinson (University of Florida)
Abstract
Electrical Discharge Machining, or EDM is a metal fabrication technique which relies on electrical discharge erosion,
which is caused by intense voltage pulses between the tool and the workpiece, which serve as the electrodes. With a
liquid dielectric between them, this process results in material removal in both electrodes. This process is
advantageous because it ignores the hardness of the workpiece and is able to machine complex geometry and
extremely thin features. This paper will discuss the types, applications, and restrictions of using EDM, as well as the
underlying process and required equipment.
1. Introduction and hole drilling methods. Die-sinking involves creating
In traditional machine techniques, the cutting tools are a specialized tool in the shape of the desired feature
made of high-speed steel or carbide based material to instead of using a traditional milling process, allowing for
cut the workpiece. For instance, milling and drilling more complex shapes and sharper turns to be made.
provide high stress to the target material, which results Wire EDM uses a wire electrode which removes
in deformation and separation of the workpiece. material as it is fed through a predetermined path
Nevertheless, there are materials that can not be through the workpiece. Hole drilling is similar to die
machined by conventional techniques such as tungsten casting in working principle but is used to machine holes
carbide(WC), Titanium(Ti), and hardened steel[1]. These of extremely small sizes, through or blind, which require
materials will prevent deformation and separation from little to no deburring or finishing. One goal of this paper
high stress acting on them due to their hardness. In is to distinguish between the differences in these
addition, the prolonged and high force on the cutting tool methods and determine the applications each is best
will lead to intense tool wear and high cost in suited for when compared to each other and other
maintenance. Conversely, Electrical Discharge machining processes.
Machining will not have physical contact with the
workpiece [2]. EDM can machine conductive materials EDM’s wide-ranging applications have secured its heavy
and ignore their mechanical resistance to deformation use across many industries such as automotive,
and fracture. The electric spark will be generated by the medical, electronics manufacturing, defense, and
electrode to erode the workpiece(Fig.1), and this makes aerospace. Its extreme usefulness derives from its
EDM an effective method to machine hard-to-machine ability to machine many materials once proved difficult
materials. such as heat-resistant alloys, carbides, and ceramics.
Additionally, its ability to fabricate features of extremely
small size has made it useful for high precision
applications such as ultra-small compressors and
turbine blades. Restrictions include thermal effects to
the workpiece, tool wear, and the requirement of
electrically conductive materials.
2. Electrical Discharge Machining
2.1 History and development of process
Electrical discharge machining was first discovered by
Joseph Priestly in the late 18th century. Nevertheless, it
wasn't until the 1940s that the modern EDM process
was developed by Soviet researchers B.R. and N.I.
Lazarenko. In the following years, EDM technology was
refined and became a viable industrial process in the
1960s.[4].
In 1967, the Soviet Union introduced the first
Figure 1. Basic component of EDM[3] commercially available EDM machine that used wire as
an electrode. Subsequently, Andrew Engineering
There are primarily three distinct types of electrical developed wire EDM machines with the ability to follow
discharge machining. These include die sinking, wire, lines from drawings. The same company also pioneered
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the development of the first Computer Numerical Control
(CNC) wire EDM machine in 1976[5]. Wire EDM is a
widely adopted metal cutting technology that is
commonly employed to cut complex and hard materials.
It finds extensive usage in mold and tool manufacturing.
Additionally, it has emerged as a prevalent technique for
producing prototypes of parts, particularly in the low
production volume industries[6].
The wire EDM technology is distinctly different from
other metal cutting machines in the market, and people
mainly understand it because of its wire-based features.
However, there are several other methods in the EDM
that do not use wire cutting, one of which is die sinking
EDM. The origins of die-sinking EDM can be traced
back to the end of World War II in 1943 when two Soviet
researchers B.R. and N.I. Lazarenko were
commissioned to study methods to prevent erosion of
Figure.2 Die-sinking EDM[3]
tungsten electrical contacts caused by sparking effects.
Although they were unable to complete their research,
their efforts greatly contributed to the development of
2.2.2 Wire
this technology. They discovered that it was possible to
Wire EDM is a specialized machining process that uses
control erosion more precisely under specific conditions,
an electrically charged wire to cut through conductive
inspiring them to invent the EDM machine tool for
materials with high precision. In this process, a thin wire
processing hard material like tungsten. Lazarenkos’
is used as the electrode and is guided through the
machine, named the R-C-type machine. was charged
workpiece in a controlled manner(Fig.3), creating the
using a resistor-capacitor circuit and became the
desired shape or cut. The wire is held between two
precursor to modern die-sinking EDM machine[6].
spools and passes through the workpiece, while an
In addition to Wire and die-sinking EDM, hole drilling
electric current is applied to it, creating sparks that
EDM which is also known as hole popper, fast hole
erode the material. Wire EDM is often used to create
EDM[7]. This process is a dependable method for
complex shapes and contours in hard materials such as
achieving exceptional precision and can be used with
titanium, tungsten, and steel, and is particularly useful in
any conductive material. Its flexibility in creating cavities
the manufacturing of molds and dies used in various
of varying shapes meets the demanding specifications
industries. The process provides high accuracy,
of the market. Hole drilling EDM’s precise and
excellent surface finish, and can produce parts with
concentrated action is particularly well-suited for
intricate details and sharp corners that would be difficult
intricate work on robust components. This attribute
or impossible to achieve using other machining
makes it ideal for industries such as aviation and power
methods.
generation turbines that require extreme accuracy under
high-stress conditions[8].
2.2 Material Removal Mechanism
2.2.1 Die-sinking
Die sinking, also known as EDM (electrical discharge
machining) or spark erosion, is a machining process
used to create complex shapes and cavities in hard
materials such as metals, using electrical sparks. In die
sinking, a specially designed electrode is used to create
the desired shape or cavity in the workpiece, by
repeatedly discharging electrical sparks between the
electrode and the workpiece(Fig.2). These electrical
discharges remove small amounts of material from the Figure.3 Wire EDM[9]
workpiece, gradually creating the desired shape or
cavity. Die sinking is widely used in various industries, 2.2.3 Hole Drilling
including aerospace, automotive, and medical device Hole Drilling EDM is a specialized machining process
manufacturing, for creating precision components with used to create deep, precise holes in hard materials
high accuracy and surface finish. The process is using electrical discharge. In this process, a small
particularly useful for creating intricate designs or diameter electrode is used to drill a hole through the
shapes that are difficult to achieve using other workpiece by repeatedly discharging electrical sparks
machining methods. between the electrode and the workpiece(Fig.4). The
process is highly precise and can create holes with very
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small diameters and depths, as well as complex shapes example of the scale of holes made with micro-drilling
and contours. Hole Drilling EDM is widely used in EDM is shown below (Fig.5).
various industries, including aerospace, medical device
manufacturing, and automotive, for creating small,
precise holes in materials such as stainless steel,
titanium, and carbide. The process is particularly useful
for creating cooling holes in turbine blades, fuel injection
nozzles, and other high-performance components, as
well as for creating holes with high aspect ratios or in
difficult-to-machine materials. The process provides high
accuracy, excellent surface finish, and can produce
parts with intricate details and sharp corners that would
be difficult or impossible to achieve using other
machining methods.
Figure.5 Microdrilling Example [13]
3.2 Wire EDM
Wire EDM is used widely in the automotive, medical,
and aerospace industry. While those industries all have
of some commonalities, wire EDM is used in all of these
industries for various technical reasons.
The automotive industry favors wire EDMs due to its
ability to produce parts that are typically stronger than
the wire electrode. Some examples of the automotive
Figure.4 Hole Drilling EDM[10]
components made by wire EDM are bumpers, dashes,
3. Applications and Restrictions car doors, and seat brackets [5].
3.1 Micro-EDM
Micro-EDM is the designation for EDM technology The medical industry uses wire EDM in order to make
applied in extremely small scale products. The same small complex parts that demand high accuracy. The
working principle applies, but Electrical Discharge main benefit of wire EDM in the medical industry is that
Machining lends itself extremely well to these the varying wire diameter determines the size of the cut.
micro-applications. Using a motion drive of high This allows for both larger, less-accurate parts to be
precision and taking advantage of the most advanced made but also allows for small features to be added
CNC technology allows for features to be manufactured without sacrificing structural integrity [5]. Components
on both a small scale and with three-dimensional control like dental implants, syringes, and specialized needles
[11]. are all examples of
According to [11], the output of micro-EDM results in Lastly, the aerospace industry uses wire EDM in order to
features with tolerances of less than 1 micron. Some make parts that can not be exposed to high
products include micro-compressors and miniature gas temperatures that other traditional machining processes
turbines, both of which require high precision to perform would expose the part too. [5] One of the most common
their respective functions to a satisfactory degree. parts made by wire EDM is landing gear. Landing gear
is often made with tough, heat-treated metal. The
Micro-drilling is a facet of micro-EDM which employs the temperatures involved with wire EDM allow for the
hole-drilling function of EDM on a small scale. Drilling landing gear to remain at the desired rockwell hardness.
holes with diameters on the micron-scale (125 microns
as used in [8]) can be achieved with high-aspect ratios. 3.3 Ceramics
Additionally, one study [12] shows that micro-EDM can Ceramics often have extremely high hardness
be used to fabricate tapered and reverse-tapered holes. properties, good wear resistance, can be biocompatible,
The tapered holes produced featured a difference of and retain their properties at extreme temperatures
about 60 microns (100 to 160 microns), and reverse when compared to most metals and polymers. This
tapered holes were produced with a variation of 3 makes them suitable for industries such as medical and
microns [12]. This shows the level of high precision and aerospace [14]. EDM is a highly advantageous method
variation of features possible with micro-EDM. An of manufacturing ceramics due to it ignoring their high
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hardness. However, many ceramics have poor electrical
conductivity, making it difficult for EDM’s material
removal to occur. This issue can be resolved in some
different ways, but one advanced method is the
‘Assisting Electrode Method’ [14]. This consists of a
conductive layer being placed on the surface of the
ceramic workpiece. The heat generated due to the spark
between the tool electrode and conductive layer carries
enough energy to form cracks in the workpiece and
allow the hydrocarbons in the dielectric fluid to bond into
parts of the ceramic workpiece [14]. These compounds
are conductive and result in the ceramic containing a
surface layer which has high enough conductivity for
EDM to occur. This method has allowed for hole
machining on the micrometer scale on ceramics that are
non-conductive in nature [14].
Figure.7 micro-cavities with surfaces inclined [17]
3.4 Restriction of Thermal Effect
While Electrical Discharge Machining has many 4. Conclusion
advantages and applications, the immense heat While the EDM process may seem common now, the
produced leaves thermal effects on the workpiece. EDM process is relatively new. Before the late 1960s, the
leaves three types of layers on the surface: the recast manufacturing industry was primarily driven by
layer, the heat affected zone, and the converted layer conventional machining processes. These machining
[15]. The recast layer is formed from molten particles of processes which had been used for centuries in one
the workpiece solidifying back onto the surface, and form or the other had one major restriction. Traditional
occurs if not properly flushed away. It has been manufacturing techniques were not equipped for
observed as being anywhere from 2.5-50 microns [15] hard-to-machine materials. It quickly became clear that
and is hard, brittle, porous, and often contains cracks. the invention of EDM would revolutionize machining
The heat affected zone is produced due to the quick completely.
alterations of heating and quenching from electrical
discharge and cooling effects of the dielectric, EDM utilized spark erosion to remove material of
respectively. It can be about 25 microns thick and electrically conductive workpieces. The spark is created
contains grain boundary defects, cracks, and residual using the tool as one electrode and the workpiece as the
stresses[15]. Lastly, the converted layer is beneath the other, with a dielectric fluid submerging the workpiece.
heat affected zone and has a small change in its grain The fluid also acts as a coolant which improves the
structure. These restrictions can be minimized by quality of machined parts. Electrical Discharge
altering EDM process parameters such as the pulse-on Machining has three main variations. These include
time [16] and removal of the recast layer. die-sinking EDM, wire EDM, and hole-drilling EDM.
3.5 Other Miscellaneous Applications Once EDM was proven a viable industry process, the
Other examples of parts and products produced by EDM application list grew. EDM is used in the automotive,
technology include blisks, ceramics bearing for medical, electronics manufacturing, defense, and
aerospace applications (Fig.6), micro-scale punching aerospace industries. The many advantages of the EDM
molds, micro-cavities with surfaces inclined (Fig.7), process allowed for all of these industries to utilize the
micro-gears, and more. process to save billions of dollars and countless hours.
EDM has its restrictions, including thermal effects to the
workpiece, tool wear, and the requirement of electrically
conductive materials. However, the advantages heavily
outweigh the cons/restrictions and in some cases these
restrictions can be overcome (as seen in the machining
of ceramics).
In conclusion, Electrical Discharge Machining is an
exceptional manufacturing technique. Its erosion
material removal which ignores workpiece hardness has
made it indispensable in many fields and industries. Like
any process, EDM has its disadvantages and
Figure.6 Bearing [17] restrictions, but its ability to machine materials and
features that other processes are incapable of has
secured its spot in industry since it was introduced.
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