2. Fundamentals of EDM
• The process dates back to WW I & II when work as well
as substantial tool material was removed due to manual
feeding of electrode.
• Later vibratory electrodes were used to control inter
electrode gap.
• Two Russian scientists developed R-C circuit and servo
controller.
• The Die sinking version of EDM was developed
sometime in 1940s.
• The process modeling involves understanding of
complex hydrodynamic and thermodynamic behavior of
the fluid.
4. Fundamentals of EDM
Voltage –Current curves (Free, Normal, Stationary
located, and Short circuit discharges)
General observations
Difficult to start the process with very clean
dielectric
Firing of high current discharges at same voltage is
easy in contaminated dielectric
New ignition opt to ignite in prior discharge regions
Greater ignition preferences in more contaminated
regions
5. Fundamentals of EDM
• DC pulses of appropriate shape, frequency and duty cycle
are used. This is used even for motor control now-a-days.
Frequency is ~ 100,000 Hz.
• Spark is initiated at the peak between the contacting surfaces
and exists only momentarily. Spark temp is 12,000 C. Metal
as well as dielectric will evaporate at this intense localized
heat. A crater is caused by both due to the local evaporation
as well as the vapor action.
• Vapor quenches and next spark it at another narrow place.
Thus, spark wanders throughout the surface making uniform
metal removal for the desired finish.
6. Fundamentals of EDM
• Material removal in EDM is based on erosion effect.
• Several theories have been proposed:
– Electro-mechanical theory: electric field force exceeds the
cohesive force of lattice.
– Thermo-mechanical theory: Melting of material by ‘flame-jets’.
– Thermo-electric theory: Generation of extremely high
temperature due to high intensity discharge current.
7. Fundamentals of EDM
Debris and Bubble particles generated
by single spark
Debris gathering at Bubble boundary
8. Fundamentals of EDM
Large number of Spherical particles with few non-
spherical particles
Spherical particles are rich in workpiece material
and non-spherical particles are rich in tool material
Understanding of Erosion Mechanism and Oxide
free power production
Important parameters affecting Debris morphology
are
Current
Voltage Input Energy
Pulse On-time
Capacitance
9. Fundamentals of EDM
Micro analysis reveals that there is movement of
material from workpiece to cathode and vice-versa
Normal distribution of particle size (Stochastic nature)
Structures of Debris-
Large Size & Small Size
Hollow & Solid Debris
Satellite structure
Hollow Spheres
Dents
Burnt Cores
10. Fundamentals of EDM
Microanalysis of Debris – Low Energy
Densely populated,
Small diameter, solid
particles
a)Dendrite structure; b)Solid
sphere; c)Satellite formation;
d) Non-spherical particles
11. Fundamentals of EDM
Larger population of
hollow satellites with
dents, surface cracks, and
burnt core
a)Debris structure, b)Hollow sphere,
c)Dendrite structure, d)Satellite with
dent formation, e)Dent formation
12. Fundamentals of EDM
Effect of Tool Rotation.
Results in fine debris particles and improved process
stability.
Effect of Ultrasonic Vibrations.
Larger particles
Large number of particles with spherical geometry
More uniformity of spherical and non-spherical
particles
Uniform mixing of materials
More collision between debris particles
14. Fundamentals of EDM
A series of voltage
pulses of magnitude
about 20 to 120 V and
frequency on the order
of 5 kHz is applied
between the two
electrodes, which are
separated by a small
gap, typically 0.01 to
0.5 mm.
When using RC
generators, the voltage
pulses are responsible
for material removal.
15. Breakdown of dielectric during one cycle
Temperatures
of about 8000
to 12,000 C
and heat fluxes
up to 1017
W/m2 are
attained during
process
16. Breakdown of dielectric during one cycle
Explosion and
implosion action of
dielectric
EDM performance
measures such as
material removal
rate, electrode tool
wear, and surface
finish, for the same
energy, depends
on the shape of the
current pulses.
17. Voltage and Current characteristics
Types of pulses
Effect of pulses
Pulse classification systems
Data acquisition and classification
22. Flushing
The main functions of the dielectric fluid are to
1. Flush the eroded particles from the machining gap
2. Provide insulation between the electrode and the workpiece
3. Cool the section that was heated by the discharging effect
The main requirements of the EDM dielectric fluids are adequate
viscosity, high flash point, good oxidation stability, minimum odor,
low cost, and good electrical discharge efficiency
27. Process Stability
Indication of constantly moving spark
Importance of Debris content in inter-electrode
gap
Discharge conduction through debris chain
Effect on surface cracks
Process stability primarily depends on discharge
transitivity rather than breakdown strength
Absence of Debris can be one of the causes of
arching
28. Processing and Response
parameters
• Electrode material
• Accuracy and finish of electrode manufacture
• Current/ voltage
• Frequency
• Pulse width
29. Operating parameters
• Current and voltage: As
the voltage drops from A to
B, the current increases
because of the negative
voltage-current
relationship. At C, current
is interrupted, and voltage
goes to zero and reverses
to D; but since there is no
break down in opposite
direction, no current
reversal takes place. The
voltage now returns to
zero and waits for the next
pulse.
30. Operating parameters
• The energy dissipated in the
system is voltage times current
times time, it remains fairly
constant.
• At ‘A’ energy is zero.
• ‘B’ represents the power going to
the work.
• ‘C’, ‘D’, ‘E’ and ‘F’ represent traces
at where there are either voltage or
current is zero, hence no power.
• In section ‘B’ voltage times current
is nearly constant, indicates a
constant input of power during a
current pulse.
31. Operating parameters
• In the inter electrode gap, there is
a mixture of electrons, ions, and
neutral atoms in the gaseous
form.
• Cathode supplies electrons for the
flow of current so should be
enough to emit the electrons, also
positive ions in front of cathode
provide a pulling force.
• Cathode material also matters –
Cu is a low melting point alloy so it
melts (at 1083 C) and emits
electrons by heat and electric
field.
• Graphite, W, Mo emit electrons at
the temperatures below there
melting points hence are more
stable as cathode.
32. Operating parameters
• Resistance to the flow of current is higher near the electrodes.
• The voltage drop near cathode is smaller as compared to that
of anode. It helps electrons in achieving high speed to ionize
the gases near cathode.
• Cathode voltage drop ranges from 12V for Cu to 25V for
graphite.
• The plasma generated is at 6000 to 10,0000 C.
• (+) ions and electrons (-), due to the mass difference ions move
slowly therefore, 95% of the current is carried by electrons.
• The electrons and ions provide major power input to the
cathode and anode surfaces.
• When the current is high, evaporation of material from anode
occurs, the stream of atoms coming out of anode surface
interferes with the electrons going to the anode.
• Some ions get ionized at the near anode drop but the electrons
get additional energy to cause more vaporization of anode.
33. Operating parameters
• Straight polarity: in which
electrode is usually a
cathode (-). Here, work
surface energy can be
controlled by controlling the
current so that anode drop
energy provides proper wear
and desired surface finish.
• Reverse polarity: in which
electrode anode (+) and
work (-), in which rough cut
higher cutting rates can be
obtained with virtually no
electrode wear.
34. Operating parameters
• Electrode rotating:
Improves flushing
difficulties with speed of
about 200 rpm max. It
provides better surface
finish.
• Electrode orbiting:
Electrode does not rotate
but revolve in an orbit.
Orbiting need not be
restricted to round shape.
• Both actions reduce
electrode wear as it gets
distributed uniformly.
35. Operating parameters
• No Wear EDM: It is defined as the condition when the electrode
to work wear ratio is 1% or less.
• Effect of arc duration: Melting depth is a function of arc duration
for a circular non expanding heat source.
• The maximum melting depth occurs at different durations for
different materials subjected to same energy. The melting depth
reaches a peak value with an increase in arc duration, it reduces
with further increase in the arc duration.
• Thus, it should be possible to choose an arc duration which
maximizes the work erosion while holding the electrode to some
lesser value.
• In Cu and steel system, at the arc duration suitable for maximum
melting of steel, the melting of Cu is at the minimum.
36. Operating parameters
• Electrode polarity: The energy distribution between anode
and cathode is a function of –
– ratio of electron current to ion current at cathode
– Physical constant (work function) of the cathode material.
– In Cu as cathode current density decreases, the electron to ion
current ratio also decreases. As the arc duration increases, the energy
delivered to the gap concentrates at the cathode. Therefore, the
electrode must be of positive duration if long arc durations are used
to achieve the no-wear condition.
• Electrode coating is observed in Cu-steel system.
– Coating of electrodes with thin black film of carbon which has erosion
resistance and tend to reduce electrode wear.
37. Processing and Response parameters
Effect of Current
As current increases, the depth and width of the crater becomes
larger. So also the MRR. But this may result in rough surface.
However, this can be used to our advantages to obtain matty
surface.
38. Processing and Response parameters
Effect of Frequency
As frequency increases, the depth and width of the crater becomes smaller
although the MRR may not be affected as there will be more craters per unit
time. However, frequency has a limit since initiation of spark requires certain
minimum time required for the breakdown of the dielectric. Similarly the
spark needs some time to quench. In principle, one should operate as high a
freq as possible.
39. Processing and Response parameters
Effect of Voltage
Gap ↓ Voltage ↓
Voltage ↓ Current ↓
Current ↓ MRR ↓
Current ↓ Accuracy & finish ↑
Gap ↓ Poor flow of dielectric.
40. Processing and Response parameters
Effect on fatigue Life
A layer of resolidified metal of 0.002
– 0.050 mm thick remains on the
surface. This may flake off during
cyclic loading. When high fatigue life
is required, this layer must be
removed on a subsequent operation
such as chemical etching.
42. EDM process Variations
50
Content Percentage
40
30
20
10
0
1 2 3
Group Number Normal Discharge
Open Circuit
Abnormal Discharge
Group Number Group 1 Group 2 Group 3
Planetary Motion Yes No No
Debris Layer Yes Yes No
Input Voltage 15mV 15mV 15mV
43. EDM process Variations
Modern controllers uses gap controlling strategy to
control debris
Dielectric flushing (injection, suction, & electrode
jump)
Jet sweeping
Rotary Electrode/workpiece method.
Without With
Rotation Rotation
44. EDM process Variations
Magnetic Assistance
Use of Magnetic field 1(05A,20µs), 2( 20A,350µs)
Magnetic force used to change path of debris motion.
Magnets attached on plates rotating under machining
zone
Magnetic force is useful not only at low energy but also at
high energy inputs
45. EDM process Variations
Vibration Assistance
Condition of Adhesion Debris removal and Sparking
The combined process of EDM with USM had the potential to prevent
debris accumulation, improve machining efficiency, and modify the
machined surface.
46. Dielectric Fluid – Desirable properties
• Break down characteristic: Non-conducting until breakdown
and very high conduction through rapid ionization just after
breakdown.
• High latent heat
– to minimize evaporation
– to contain the spark in a narrow region for localized
sparking
• Low viscosity for ease of flow
• Efficiency as coolant. It is kerosene or water.
47. Dielectric Fluid
• Functions of Dielectric Fluid
It acts as an insulator until sufficiently high potential is
reached .
Acts as a coolant medium and reduces the extremely high
temp. in the arc gap.
More importantly, the dielectric fluid is pumped through
the arc gap to flush away the eroded particles between
the work piece and the electrode which is critical to high
metal removal rates and good machining conditions.
48. Dielectric Fluid
Work Material Fluid Medium Application
Aluminum
Brass
Mild Steel Hydrocarbon oil
Stainless or glycerin-water Submerged
steel (90:10)
Tool steel
Tungsten
Carbide Mineral oil
49. Dielectric Fluid
• Dielectric fluids: should have very high flash point and very
low viscosity.
– Petroleum based hydrocarbons
– Silicon fluids mixture with petroleum oils for machining of titanium,
high MRR and good SF.
– Kerosene, water-in oil emulsion, distilled water.
• Cooling of dielectric is required sometimes while cutting with
high amperage can be done by using heat exchangers.
• Filtering of dielectric is necessary to filter out 2 – 5 µm
particles.
50. Dielectric Fluid
• Insulation and conduction: Insulating characteristic is
measured by the maximum voltage that can be applied
before ionization.
• Cooling: ability to resolidify vaporized material into chips ,
thermal transfer capability.
• Flushing: Sufficiently viscous to pass through a small gap
&remove debris.
• Methods of fluid
application
– Normal flow
– Reverse flow
– Jet flushing
– Immersion flushing
51. Workpiece and Tool Material
Electrode Materials Applications
Brass High Accuracy for most metals
Copper Smooth finish
Low accuracy for holes
Zinc Alloys Commonly used for steel, forging
cavities
Copper-Graphite General Purpose work
Steel Used for nonferrous metals
Copper Tungsten High accuracy for detail work
Graphite Large volume/fine details
Low wear
Excellent machinability
52. Workpiece and Tool Material
• Tool electrodes transport current to the work surface.
• Graphite
– Coarse (for large volume) or fine (for fine finish).
– Normally used for steel provides large MRR/A as compared to
other metallic electrodes.
– When used for WC, deposits of carbon on work leads to flow of
current without ionization of dielectric and hence arcing. High
density, fine particles preferred.
– Average surface finish using graphite electrodes:0.5 µm Ra.
• Copper Graphite
– For rough and finish machining of WC.
53. Workpiece and Tool Material
• Copper
– When smoothest surface finish is required.
– In no-wear mode, copper works best under low ampere and long
spark times.
– Tellurium increases the machinability of copper.
– Free machining brass is used for making complex shaped
electrodes.
– Copper tungsten (70% W) for fine detail and high-precision EDM.
High density, strength, thermal and electrical conductivity.
• Tungsten
– Tungsten carbide is used for cutting steel and WC.
– Small holes of deeper dimensions.
54. Workpiece and Tool Material
• Electrical conductivity Tool W/P rw
• Less wear due to the spark Brass Brass 0.5
(Low rw) Brass Hard C.S. 1.0
• Good machinability Brass WC 3.0
• Good surface finish on w/p
Loss of material from the tool
Wear ratio rw =
Loss of material from the work piece
rw increases with material hardness and decreases with the
increase in melting point of the tool material.
55. Advantages
Any material that is electrically conductive can be cut
Hardened work pieces can be machined eliminating the
deformation caused by heat treatment.
Complex dies sections and molds can be produced
accurately, faster, and at lower costs.
The EDM process is burr-free.
Thin fragile sections such as webs or fins can be easily
machined without deforming the part.
56. Disadvantages
High specific energy consumption (about 50 times that in
conventional machining)
When force circulation of dielectric is not possible,
removal rate is quite low
Surface tends to be rough for larger removal rates
EDM process is not applicable to non-conducting
materials
57. Applications
• Mold and die making, slowly becoming a production
process.
• Machining of ‘difficult-to-machine’ materials.
• Miniature and fragile parts that can not withstand the force
of conventional cutting. Holes of 0.05 mm, slots of 0.3 mm
• As EDM is a very slow process, it can be justified only
where the hardness is too high or the features cannot be
realized by other means.
• Tool making: sharp corners, small features, deep features
etc. With the advent of hard cutting tools, full sinking is out
of fashion.
• Removal of broken drills or fasteners
• Deep hole drilling of small holes. Eg.: turbine blades, fuel
injection nozzles, inkjet printer head etc.
59. Wire EDM
• This process is similar to contour cutting with a band saw.
• Slow moving wire travels along a prescribed path, cutting the
work piece with discharge sparks.
• Wire should have sufficient tensile strength and fracture
toughness.
• Wire is made of brass, copper or tungsten. (about 0.25mm in
diameter).
60. Wire EDM
Process
• Thin wire of as low as 0.03mm
dia is used as the tool.
• For through features dies for
punching, blanking and piercing;
templates and profile gauges;
extruder screws etc.
• Taper also possible
• Upto 4 axes available.
• Water is the common di-electric
62. WEDM Process
• Machining of hard and complex shapes with Sharp
corners.
• Risk of wire breakage and bending has undermined the
full potential of the process drastically reducing the
efficiency and accuracy of the WEDM operation
• WEDM utilizes a continuously travelling wire electrode
made of thin copper, brass or tungsten of diameter 0.05–
0.3 mm, which is capable of achieving very small corner
radii
• The material is eroded ahead of the wire and there is no
direct contact between the workpiece and the wire,
eliminating the mechanical stresses during machining
• Machining of EXOTIC and HSTR alloys
63. WEDM Process
• The material removal mechanism of WEDM is very similar
to the conventional EDM process involving the erosion
effect produced by the electrical discharges (sparks)
• The WEDM process makes use of electrical energy
generating a channel of plasma between the cathode and
anode, and turns it into thermal energy at a temperature in
the range of 8000–12,000 C or as high as 20,000 C
• A varying degree of taper ranging from15 degree for a
100 mm thick to 30 degree for a 400 mm thick workpiece
can also be obtained on the cut surface.
• The microprocessor also constantly maintains the gap
between the wire and the workpiece, which varies
from0.025 to 0.05 mm
64. WEDM Process
• Number of passes are required to achieve the required
degree of accuracy and surface finish
• Dry WEDM (in gas) to achieve the high degree of surface
finish
• The typical WEDM cutting rates (CRs) are 300 mm2/min for
a 50 mm thick D2 tool steel and 750 mm2/min for a 150 mm
thick aluminium , and SF quality is as fine as 0.04–0.25
µRa
• The deionised water is not suitable for conventional EDM
as it causes rapid electrode wear, but its low viscosity and
rapid cooling rate make it ideal for WEDM
65. Hybrid WEDM Process
• WEDG – machining of fine rods used in electronic circuits;
machining of electrodes as small as 5 micron in diameter
advantages of WEDG include the ability to machine a rod
with a large aspect ratio, maintaining the concentricity of
the rod and providing a wider choice of complex shapes
such as tapered and stepped shapes at various sections.
• Ultrasonic Vibrations to wire to improve surface finish and
cutting ratios
• Wire electrochemical grinding
66. WEDM Applications
• Modern tooling applications - wafering of silicon and machining
of compacting dies made of sintered carbide
• For dressing a rotating metal bond diamond wheel used for the
precision form grinding of ceramics
• Advanced ceramic materials – other common machining
processes for machining ceramics are diamond grinding and
lapping.
• Machining of boron carbide and silicon carbide
• MRR and surface roughness depends on processing parameters
as well as workpiece material
• Machining of naturally non-conductor by doping with
conducting material
• Machining of modern composite materials
• MMC and carbon fiber polymers
67. Major Research issues
• WEDM process optimization
Factors affecting performance measures – pulse duration, discharge
frequency and discharge current intensity
Cutting ratio – Factors affecting CR are properties of the workpiece
material and dielectric fluid, machine characteristics, adjustable
machining parameters, and component geometry. Use of DOE, ANN.
It was found that the machining parameters such as the pulse on/off
duration, peak current, open circuit voltage, servo reference voltage,
electrical capacitance and table speed are the critical parameters for the
estimation of the CR and SF.
MRR - discharge current, pulse duration and pulse frequency are the
significant control factors affecting the MRR and SF, while the wire
speed, wire tension and dielectric flow rate have the least effect
Surface finish – all the electrical parameters have a significant effect on
the surface finish
68. Major research issues
• Wire EDM process monitoring and control
Fuzzy control system - proportional controls were used traditionally
control the gap. Conventional control algorithms based on explicit
mathematical and statistical models have been developed for EDM or
WEDM operations
Pulse discrimination system
Knowledge system
Ignition delay based system
Wire breakage - rapid rise in frequency is observed before wire
breaks; control strategy to switch off the generator at high frequency,
localized high temperature causes wire breakage, excessive thermal
force
Wire material breakage and fracture
Wire lag and wire vibrations- plasma and material erosion forces,
hydraulic forces due to dielectric flow
69. Applications
The common applications of WEDM include the fabrication of the
stamping and extrusion tools and dies, fixtures and gauges,
prototypes, aircraft and medical parts, and grinding wheel form
tools.
72. Outline
Principle of EDM process
Characteristics of EDM process
Control of Discharge location
Micro-manufacturing
Scope of micromachining
Classification of micromachining processes
Role of micro-EDM in micromachining
Micro-reverse EDM
Research issues in micro-EDM related processes
Experiments I micro-reverse EDM
Future of micromachining
72
73. Electrode gap monitoring and control
10 MHz
• Mathematical adaptive control theory
• Advances in computer technology and advanced algorithms for machine control
(Artificial intelligence, ANN)
73
74. Micro-Manufacturing - What is it?
Manufacture of products with the following features:
about 100 µm to about 10 mm in size
contain very complex 3-D (free-form) surfaces
70 µm - Human Hair
employ a wide range of engineering materials 25 µm - Characters
possess extremely high relative accuracies in the 10-3 to 10-5 range
Micro-milling
Fanuc - Japan
Zeiss - Germany
Micro-parts
Micro-structures manufactured by micro-SLA Micro-EDM
Klocke Nanotechnik
Japan NTU - Taiwan
Micro-Motor
74
75. Why Miniaturization?
• Minimizing energy and materials used for the
manufacture of devices
• Integration with electronics; simplifying systems
• Cost/performance advantages
• Faster devices
• Increased selectivity and sensitivity
• Drawback-Size effect in mechanical micromachining
75
76. Scope of micromachining processes
MICRO MACHINING
Micro Machining
Removal of material at micro level
Macro components but material removal is at micro/nano level
Micro/nano components and material removal is at micro/nano level
Unfortunately, the
Definition
present day notion is
Material removal is micro/nano level
with no constraint on the size of the
component
Machining of highly miniature
components with miniature
features – NOT CORRECT
76
77. Classification of micromachining processes
FABRICATION
Macro-fabrication Micro-fabrication
Hybrid Micro-machining µ-nano finishing
Processes
Mechanical - µ Beam energy based Chem. & EC -µ
machining - µ machining machining
USM EBM PCMM
AJM LBM ECMM
AWJM EDM
WJM IBM
PBM
78. Micromachining processes
Energy Used Principle Processes and Features
Mechanical Material removal via highly Cutting, grinding, sandblasting.
Force concentrated force UR ~ 100 nm, edge radius<1 µm
Melting and Material removal via melting EDM, LBM, EBM. Small UR by
vaporization and/or vaporization and reduced the pulse energy,
debris by high pressure gas concentration of energy via ultra
short pulse duration and/or sharply
focused beam by optics
Ablation Decomposition of atoms Excimer/Femto second laser. High
using incident photon energy dimensional accuracy, less HAZ but
or direct vaporization of low machining speed and high cost
material via high energy of equipment
pulses
Solidification Liquid or paste is solidified in Injection molding, die casting, etc.
a mold and shape of the mold curing may be required after molding
is replicated and porosity
78
79. Micromachining processes
Energy Used Principle Processes and Features
Dissolution Chemical or electrochemical Chemical, PCM and ECM. Small UR,
reaction based ionic negligible force. Inter-electrode gap,
dissolution flow of electrolyte influences
accuracy
Plastic Shape of the product Micro-punching, extrusion, etc.
Deformation specified by die/punch/mold No UR is involved, high speed,
spring-back and difficulties in die or
mold making
Lamination Material in solid powder or Stereolithography, internal as well as
liquid form is solidified layer- external profiles can be formed
by-layer. easily.
79
80. Role of EDM in micromachining
Non-contact machining
3D machining
Physical characteristics such as hardness, brittleness
dose not affect the process
Use of deionized water as dielectric
Absence of Size Effect
80
81. Comparison of EDM and micro-EDM
The Resistance Capacitance Relaxation (RC-
relaxation) circuit used in EDM is replaced by the RC-
pulse circuit in micro-EDM.
In the RC-relaxation circuit, current and gap voltage
are controlled at a pre-defined level throughout the
pulse on-time but in modeling attempts in micro-
EDM based on RC pulse circuits, the current and
voltage are frequently assumed to be constant.
On the other hand, in a single discharge of RC-pulse
generator, the voltage and current are not
maintained to any pre-defined level but depend
upon the capacitor charge state at any instant.
E = V I Duty cycle
E = ½ CV^2
81
82. Comparison of EDM and micro-EDM
EDM Micro-EDM
Circuitry Elements
• RC relaxation type • RC single pulse discharge
• Single spark process • Single spark process
• Forced process for constant voltage • Single capacitance discharge, no
and current const V and I
• User defined pulse on time • No control – gap characteristics
Scaling Effects
• Interelectrode gap is 10’s of µm • Interelectrode gap is 1-5 µm
• Low efficiency • High efficiency
Typical single spark crater
82
83. Micro-analysis of Debris
Large number of Spherical particles with few non-
spherical particles
Spherical particles are rich in workpiece material and
non-spherical particles are rich in tool material
Understanding of Erosion Mechanism and Oxide free
power production
Important parameters affecting Debris morphology are
Current
Voltage
Pulse On-time Input Energy
Capacitance
84. Micro-analysis of Debris
Micro analysis reveals that there is movement of material from
workpiece to cathode and vice-versa
Normal distribution of particle size (Stochastic nature)
Structures of Debris
Low Energy
Large Size & Small Size
Hollow & Solid Debris
Satellite structure
Hollow Spheres
Dents
Burnt Cores
High Energy
85. EDM process stability How will you measure?
Ignition delay time
Effect of Tool Rotation
Effect of Ultrasonic Vibrations
Effect of workpiece-tool material
combination
Effect of polarity
PMEDM
Effect of dielectric
Group Number Group 1 Group 2 Group 3
Planetary Motion Yes No No
External material layer Yes Yes No
86. Micro-EDM process stability
Indication of constantly moving spark
Importance of eroded material in inter-electrode gap
Discharge conduction through debris chain
Effect on surface cracks
Process stability primarily depends on discharge transitivity
rather than breakdown strength – Yo et al.
Absence of metallic particles can be one of the causes of arching
1 –Low energy
2 – High Energy
87. Variants of micro-EDM
Figure : Micro rods machining processes
Process Capability Limitation
BEDG Min. 3 µm diameter electrode, maximum 10 Only single electrodes can be machined
aspect ratio, 0.6 µRa surface finish
Micro-WEDG Min. 5 µm diameter electrode, maximum 10 Cylindrical electrodes as well as arrayed
aspect ratio, 0.8 µRa surface finish electrodes can’t be machined
Micro-WEDM Best results obtained are 10x10 square array (23 Cylindrical arrayed structures can’t be
µm width, 700 µm height), minimum machining machined
size achievable is 20 µm, surface finish 0.07-0.35
µm Ra, and maximum aspect ratio 100
Diamond milling micro tower of 1 mm in height and 25 μm square Mechanical process involves machining
stresses 87
87
88. Research issues in micro-EDM
Micro-EDM Research Areas
Handling Electrode and Machining
Measurement
workpiece Process
preparation
Surface
Electrode Off-machine electrode Process Sources of
quality
preparation Parameters Errors
Parts Dimensions
Mfg. Micro 3D Machine
Drilling,
electrode
threading Electrode
holes (WEDM)
Jigs and
Fixture
On-machine electrode
Electrode
Stationery Guided wear and
Rotating Disk
block running wire machining
strategies
Uniform wear Multi Wear
Z-compensation
method electrode monitoring
system
88
89. Applications
Machining of mould and die in high strength materials (Carbides,
die steel, conducting ceramics) – Recently replaced by high speed
milling process
Chemical aspects of EDM
– Production of fine particle powders
– RESA (for ultrafine powders)- Reactive Electrode Submerged Arc EDM
– Diamond like carbon and nano-tubes (solidification of evaporated
material)
– Large amount of energy is consumed in the chemical action during EDM
– Supplying oxygen can enhance the MRR during the process
89
90. Machining of arrayed micro-structures by REDM
Reverse replication of
arrayed hole on the
plate electrode to the
bulk material by change
aa) Normal EDM
in the polarity
Bulk Rod Machined structures
have a dimensions
ab) Reverse EDM Micro-rods equal to the original
Figure : Working of micro and reverse micro EDM processes dimension of pocket
minus interelectrode
gap
Important operating
parameters are voltage ,
capacitance, threshold,
and the feed
Figure : a) array of 4 microrod machined, b) plate used as 90
a tool during machining
91. Machining of arrayed micro-structures by REDM
Problem Statement : Machining of high aspect ratio arrayed
microstructures by micro reverse EDM process.
91
Figure : set up of the micro-REDM process
92. Applications of micro-REDM
Applications
Mechanical MEMS Biomedical
Micromachining Arrayed holes for passing As a interface device for
As a electrode in wires in MEMS devices capturing neural signals
arrayed hole/cavity Thin wall structures as a Brain neural activity
machining cooling devices in MEMS recording
Mask preparation system Arrayed microholes as a
As a tool for generating Shaft for micro robots spray nozzels in the
stable plasma micro actuator biotechnology applications
Microneedels- syringe
Heat Exchanging Holding sights for the
Hexagonal and thin wall testing reagents
structures
Automobile
Micronozzels
92
95. Experiments in micro-REDM
Workpiece geometry :
Machining of 400 µm square
and 200 µm cylindrical
electrodes, machined length 1
mm
Images of the micro rods machined in
each run of experiment 95
96. Surface Morphology Surface near tip exhibits number
of craters , whereas the surface at
Root Surface the root is relatively smooth.
Smooth surface with almost no
pits is observed near the root in
the magnified image of fabricated
structure
Tip Surface
A
Sample 3
A
96
