edm and varinats-presentation.pdf

7/25/2019 EDM and varinats-presentation.pdf

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The process dates back to WW I & II when work as well

as substantial tool material was removed due to manualfeeding of electrode.

Later vibratory electrodes were used to control inter

electrode gap.

Two Russian scientists developed R-C circuit and servocontroller.

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.

Fundamentals of EDM


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Fundamentals of EDM

Preparation Phase

Phase of Discharge

Interval Phase


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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 contaminatedregions


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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 localizedheat. 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 uniformmetal removal for the desired finish.

Fundamentals of EDM


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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.

Fundamentals of EDM


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Debris gathering at Bubble boundary

Debris and Bubble particles generated

by single spark

Fundamentals of EDM


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Large number of Spherical particles with few non-spherical particles

Spherical particles are rich in workpiece materialand non-spherical particles are rich in tool material

Understanding of Erosion Mechanism and Oxidefree power production

Important parameters affecting Debris morphologyare

Current Voltage

Pulse On-time

Capacitance

Input Energy

Fundamentals of EDM


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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

Fundamentals of EDM


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a)Dendrite structure; b)Solid

sphere; c)Satellite formation;

d) Non-spherical particles

Microanalysis of Debris Low EnergyDensely populated,

Small diameter, solid

particles

Fundamentals of EDM


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a)Debris structure, b)Hollow sphere,

c)Dendrite structure, d)Satellite with

dent formation, e)Dent formation

Larger population of

hollow satellites with

dents, surface cracks, and

burnt core

Fundamentals of EDM


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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

Fundamentals of EDM


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Fundamentals of EDM


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A series of voltage

pulses of magnitudeabout 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 RCgenerators, the voltage

pulses are responsible

for material removal.

Fundamentals of EDM


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Breakdown of dielectric during one cycle

Temperatures

of about 8000

to 12,000 C

and heat fluxes

up to 1017

W/m2 areattained during

process


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Breakdown of dielectric during one cycle

Explosion and

implosion action of

dielectric

EDM performancemeasures such as

material removal

rate, electrode tool

wear, and surface

finish, for the same

energy, depends

on the shape of the

current pulses.


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Voltage and Current characteristics

Types of pulses Effect of pulses

Pulse classification systems

Data acquisition and classification


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EDM Schematics


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Components of EDM


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Tool Wear and Tool Materials

Graphite is

suitable materialwith good

electrical

conductivity and

machinability

Copper

WCu and WAg

Brass


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Corner wear ratio


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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


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Parameters affecting EDM performance


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Erosion Rate and Surface Finish


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Effect of Pulse Current and Pulse on time


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EDM hazards


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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

Process Stability

P i d R


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Processing and Response

parameters

Electrode material Accuracy and finish of electrode manufacture

Current/ voltage

Frequency Pulse width


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Current and voltage: As

the voltage drops from A toB, the current increases

because of the negative

voltage-current

relationship. At C, current

is interrupted, and voltagegoes to zero and reverses

to D; but since there is no

break down in opposite

direction, no currentreversal takes place. The

voltage now returns to

zero and waits for the next

pulse.

Operating parameters


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The energy dissipated in the

system is voltage times currenttimes 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 aconstant input of power during a

current pulse.



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In the inter electrode gap, there is

a mixture of electrons, ions, andneutral atoms in the gaseousform.

Cathode supplies electrons for theflow of current so should beenough to emit the electrons, also

positive ions in front of cathodeprovide a pulling force.

Cathode material also matters Cu is a low melting point alloy so itmelts (at 1083 C) and emitselectrons by heat and electricfield.

Graphite, W, Mo emit electrons atthe temperatures below theremelting points hence are morestable as cathode.



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Resistance to the flow of current is higher near the electrodes.

The voltage drop near cathode is smaller as compared to thatof 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 electronset additional ener to cause more va orization of anode.



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Straight polarity: in which

electrode is usually acathode (-). Here, work

surface energy can be

controlled by controlling the

current so that anode dropenergy 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.



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Electrode rotating:Improves flushingdifficulties with speed ofabout 200 rpm max. Itprovides better surface

finish. Electrode orbiting:

Electrode does not rotatebut revolve in an orbit.Orbiting need not be

restricted to round shape. Both actions reduce

electrode wear as it getsdistributed uniformly.



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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 depthreaches 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 somelesser value.

In Cu and steel system, at the arc duration suitable for maximum

melting of steel, the melting of Cu is at the minimum.



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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 ioncurrent ratio also decreases. As the arc duration increases, the energy

delivered to the gap concentrates at the cathode. Therefore, theelectrode must be of positive duration if long arc durations are usedto 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.



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As current increases, the depth and width of the crater becomeslarger. So also the MRR. But this may result in rough surface.

However, this can be used to our advantages to obtain matty

surface.

Processing and Response parameters

Effect of Current


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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 thespark needs some time to quench. In principle, one should operate as high a

freq as possible.

Processing and Response parameters

Effect of Frequency


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Gap Voltage

Voltage Current

Current MRR

Current

Accuracy & finish Gap Poor flow of dielectric.

Processing and Response parametersEffect of Voltage


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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.

Processing and Response parametersEffect on fatigue Life


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Machine Construction


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EDM process Variations

0

10

20

30

40

50

1 2 3

Group Number

C

ontentPercentage

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


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Modern controllers uses gap controlling strategy to

control debris

Dielectric flushing (injection, suction, & electrode

jump)

Jet sweeping

Rotary Electrode/workpiece method.

Without

Rotation

With

Rotation




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Use of Magnetic field

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

1(05A,20s), 2( 20A,350s)

Magnetic Assistance



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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.

Vibration Assistance



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Break down characteristic: Non-conducting until breakdown

and very high conduction through rapid ionization just afterbreakdown.

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.

Dielectric Fluid Desirable properties


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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.

Dielectric Fluid


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Dielectric Fluid

Work Material Fluid Medium Application

Aluminum

Hydrocarbon oil

or glycerin-water

(90:10)Submerged

BrassMild Steel

Stainless

steel

Tool steel

Tungsten

Carbide Mineral oil


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Dielectric fluids: should have very high flash point and verylow 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 mparticles.

Dielectric Fluid


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Insulation and conduction: Insulating characteristic is

measured by the maximum voltage that can be appliedbefore 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

Dielectric Fluid


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Workpiece and Tool Material

Electrode Materials Applications

Brass High Accuracy for most metalsCopper 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


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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 ofcurrent without ionization of dielectric and hence arcing. High

density, fine particles preferred.

Average surface finish using graphite electrodes:0.5 m Ra.

Copper Graphite For rough and finish machining of WC.



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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 shapedelectrodes.

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.


k d l l


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Electrical conductivity

Less wear due to the spark

(Low rw)

Good machinability

Good surface finish on w/p

Loss of material from the toolWear ratio

Loss of material from the work piecewr =

Tool W/P rw

Brass Brass 0.5

Brass Hard C.S. 1.0

Brass WC 3.0

rw

increases with material hardness and decreases with the

increase in melting point of the tool material.


d


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Any material that is electrically conductive can be cut

Hardened work pieces can be machined eliminating thedeformation caused by heat treatment.

Complex dies sections and molds can be producedaccurately, faster, and at lower costs.

The EDM process is burr-free.

Thin fragile sections such as webs or fins can be easilymachined without deforming the part.

Advantages

Di d


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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

Disadvantages

A li i


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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 forceof 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 berealized 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.

Wi EDM


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Wire-EDM

Wire EDM


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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).

Wire EDM


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Wire EDM

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

Process

WEDM hi l ifi ti


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WEDM machine classification

WEDM P


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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 nodirect contact between the workpiece and the wire,

eliminating the mechanical stresses during machining

Machining of EXOTIC and HSTR alloys

WEDM Process

WEDM P


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The material removal mechanism of WEDM is very similar

to the conventional EDM process involving the erosioneffect 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 inthe range of 800012,000 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

WEDM Process

WEDM Process


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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 mmthick aluminium , and SF quality is as fine as 0.040.25

Ra

The deionised water is not suitable for conventional EDM

as it causes rapid electrode wear, but its low viscosity andrapid cooling rate make it ideal for WEDM

WEDM Process

Hybrid WEDM Process


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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

Hybrid WEDM Process

WEDM Applications


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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 withconducting material

Machining of modern composite materials

MMC and carbon fiber polymers

WEDM Applications

Major Research issues


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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/offduration, 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 wirespeed, wire tension and dielectric flow rate have the least effect

Surface finish all the electrical parameters have a significant effect on

the surface finish

Major Research issues

Major research issues


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Wire EDM process monitoring and control

Fuzzy control system - proportional controls were used traditionallycontrol 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

Major research issues

Applications


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Applications

The common applications of WEDM include the fabrication of thestamping and extrusion tools and dies, fixtures and gauges,

prototypes, aircraft and medical parts, and grinding wheel form

tools.


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END


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Micro-EDM processes

71

Outline


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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

Electrode gap monitoring and control


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Electrode gap monitoring and control

73

10 MHz

Mathematical adaptive control theory

Advances in computer technology and advanced algorithms for machine control

(Artificial intelligence, ANN)

Micro-Manufacturing - What is it?


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Micro-Manufacturing - What is i t?

74

Micro-structures manufactured by micro-SLA

JapanKlocke Nanotechnik

Micro-Motor

Zeiss - Germany

Micro-parts

Micro-EDM

NTU - Taiwan

Micro-milling

Fanuc - Japan

70 m - Human Hair

25 m - Characters

Manufacture of products with the following features:

about 100 m to about 10 mm in size contain very complex 3-D (free-form) surfaces

employ a wide range of engineering materials

possess extremely high relative accuracies in the 10-3 to 10-5 range

Why Miniaturization?


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75

Minimizing energy and materials used for themanufacture of devices

Integration with electronics; simplifying systems

Cost/performance advantages

Faster devices

Increased selectivity and sensitivity

Drawback-Size effect in mechanical micromachining

y

Scope of micromachining processes


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76

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

present day notion is

Machining of highly miniature

components with miniature

features NOT CORRECT

Definition

Material removal is micro/nano level

with no constraint on the size of the

component

p f g p

Classification of micromachining processes


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FABRICATION

Macro-fabrication

Mechanical -

machining

Micro-machining

Beam energy based

- machining

Chem. & EC -

machining

-nano finishing

USM

AJM

AWJM

WJM

EBM

LBM

EDM

IBM

PBM

PCMM

ECMM

Micro-fabrication

f f g p

Hybrid

Processes

Micromachining processes


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78

Energy Used Principle Processes and Features

Mechanical

Force

Material removal via highly

concentrated force

Cutting, grinding, sandblasting.

UR ~ 100 nm, edge radius


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79

Energy Used Principle Processes and Features

Dissolution Chemical or electrochemical

reaction based ionicdissolution

Chemical, PCM and ECM. Small UR,

negligible force. Inter-electrode gap,flow of electrolyte influences

accuracy

Plastic

Deformation

Shape of the product

specified by die/punch/mold

Micro-punching, extrusion, etc.

No UR is involved, high speed,

spring-back and difficulties in die ormold making

Lamination Material in solid powder or

liquid form is solidified layer-

by-layer.

Stereolithography, internal as well as

external profiles can be formed

easily.

Role of EDM in micromachining


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Non-contact machining

3D machining Physical characteristics such as hardness, brittleness

dose not affect the process

Use of deionized water as dielectric

Absence ofSize Effect

80

Comparison of EDM and micro-EDM


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81

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 = CV^2

Comparison of EDM and micro-EDM


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82

EDM Micro-EDM

Circuitry Elements

RC relaxation type

Single spark process

Forced process for constant voltage

and current

User defined pulse on time

RC single pulse discharge

Single spark process

Single capacitance discharge, no

const V and I

No control gap characteristics

Scaling Effects

Interelectrode gap is 10s of m

Low efficiency

Interelectrode gap is 1-5 m

High efficiency

Typical single spark crater

Micro-analysis of Debris


83/98

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

Capacitance

Input Energy

Micro-analysis of Debris


84/98

Structures of Debris

Large Size & Small Size

Hollow & Solid Debris

Satellite structure

Hollow Spheres

Dents

Burnt Cores

Micro analysis reveals that there is movement of material from

workpiece to cathode and vice-versa

Normal distribution of particle size (Stochastic nature)

Low Energy

High Energy

EDM process stability How will you measure? I iti d l ti


85/98

Effect of Tool Rotation

Effect of Ultrasonic Vibrations

Effect of workpiece-tool materialcombination

Effect of polarity

PMEDM

Effect of dielectric

Ignition delay time

Group Number Group 1 Group 2 Group 3

Planetary Motion Yes No No

External material layer Yes Yes No

Micro-EDM process stability


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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 energy2 High Energy

Variants of micro-EDM


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8787

Figure : Micro rods machining processes

Process Capability Limitation

BEDG Min. 3 m diameter electrode, maximum 10

aspect ratio, 0.6 Ra surface finish

Only single electrodes can be machined

Micro-WEDG Min. 5 m diameter electrode, maximum 10

aspect ratio, 0.8 Ra surface finish

Cylindrical electrodes as well as arrayed

electrodes cant be machined

Micro-WEDM Best results obtained are 10x10 square array (23

m width, 700 m height), minimum machining

size achievable is 20 m, surface finish 0.07-0.35

m Ra, and maximum aspect ratio 100

Cylindrical arrayed structures cant be

machined

Diamond milling micro tower of 1 mm in height and 25 m square Mechanical process involves machining

stresses

Research issues in micro-EDM


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88

Micro-EDM Research Areas

Handling Electrode and

workpiecepreparation

Off-machine electrode

preparation

Drilling,

threading

holes (WEDM)

Mfg. Micro 3D

electrode

On-machine electrode

Stationery

blockRotating DiskGuided

running wire

Machining

Process

Process

Parameters

Sources of

Errors

Machine

Electrode

Jigs and

Fixture

Electrode

wear and

machining

strategies

Multi

electrodeZ-compensation

Wear

monitoring

system

Uniform wear

method

Measurement

Surface

quality

Dimensions

Electrode

Parts

Applications


89/98

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 evaporatedmaterial)

Large amount of energy is consumed in the chemical action during EDM

Supplying oxygen can enhance the MRR during the process

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Machining of arrayed micro-structures by REDM


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Reverse replication of

arrayed hole on the

plate electrode to thebulk material by change

in the polarity

Machined structures

have a dimensions

equal to the originaldimension of pocket

minus interelectrode

gap

Important operating

parameters are voltage ,capacitance, threshold,

and the feed

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Figure : Working of micro and reverse micro EDM processes

aa) Normal EDM

ab) Reverse EDM

Figure : a) array of 4 microrod machined, b) plate used as

a tool during machining

Bulk Rod

Micro-rods

Machining of arrayed micro-structures by REDM


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Problem Statement : Machining of high aspect ratio arrayed

microstructures by micro reverse EDM process.

91Figure : set up of the micro-REDM process

Applications of micro-REDM


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Mechanical

Micromachining

As a electrode inarrayed hole/cavity

machiningMask preparation

As a tool for generating

stable plasma

Heat Exchanging

Hexagonal and thin wallstructures

Automobile

Micronozzels

Biomedical

As a interface device for

capturing neural signals

Brain neural activity

recordingArrayed microholes as a

spray nozzels in the

biotechnology applications

Microneedels- syringe

Holding sights for the

testing reagents

MEMS

Arrayed holes for passing

wires in MEMS devices

Thin wall structures as a

cooling devices in MEMSsystem

Shaft for micro robots

micro actuator

Applications

Components fabricated by micro-REDM


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Reverse-micro Wire EDM


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Workpiece geometry :

Experiments in micro-REDM


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Images of the micro rods machined in

each run of experiment

Workpiece geometry :

Machining of 400 m square

and 200 m cylindrical

electrodes, machined length 1mm

Surface Morphology Surface near tip exhibits numberof craters , whereas the surface at


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the root is relatively smooth.

Smooth surface with almost no

pits is observed near the root in

the magnified image of fabricated

structure

Root Surface

Tip Surface

A

A

Sample 3

Arrayed structures machined at MTL IIT Bombay


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edm and varinats-presentation.pdf

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