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    Micro-EDM processesand Application of micro-reverse

    EDM processfor microscale fabrication

    1

    Presented bySachin A. Mastud

    VJTI, Mumbai

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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

    2

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    Principle of EDM

    3

    Preparation Phase

    Phase of Discharge

    Interval Phase

    10 MHz

    Elecro-mechanical Theory

    Thermo-mechanical Theory

    Thermo-electric Theory

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    Electrode gap monitoring and control

    4

    10 MHz

    Mathematical adaptive control theory Advances in computer technology and advanced algorithms for machine control

    (Artificial intelligence, ANN)

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    5

    Electrode gap monitoring and control

    Debris gathering at Bubble boundary

    Debris and Bubble particles generated

    by single spark Difficult to understand the EDM gapphenomena Even in steady state

    conditions

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    Arc Machining and Spark Machining Any difference? Criteria of selection of dielectric

    Air as a dielectric Dry EDM

    Flushing Suction, pressurized, interrupted, two-way,

    internal, oxidized dielectric

    Forces during EDM

    Expansion, dissociation, and contraction of the bubbles

    formed during process

    Variation from maximum positive to minimum negative,

    negligible in case of sinking EDM however quantifiable in W-

    EDM and Micro-EDM

    6

    Characteristicsof EDM

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    Measurement of discharge location Factors affecting the discharge position

    Discharge location Nano-powders (Mirror surface finish)

    One voltage pulse for bundle of electrode

    Multi-spark EDM process

    7

    Control ofdischargelocation

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    Pulse conditions

    Pulses with longer peak current and

    duration achieves high MRR and

    less tool wear Formation of

    carbon layer Rough conditions

    Low current and low pulse

    duration brings high surface finish,

    less tool wear and low MRR

    High current and low pulse on time

    results in higher MRR, and EDMefficiency; however high tool wear

    8

    Interaction of parameters

    Removal

    Rate

    SurfaceRoughness

    Tool Wear

    D

    ischarge

    C

    urrent

    Time

    No waveform which can satisfy allthe constraints

    Factorsinfluencingthe tool wear Influence of polarity normal EDM tool-positive

    micro-EDM Workpiece positive

    Influence of thermal properties to tool and workpiece material

    - Thermal conductivity

    - Higher melting or boiling point

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    MicroMicro--ManufacturingManufacturing - What is it?

    9

    Micro-structures manufactured by micro-SLA Japan

    Klocke NanotechnikMicro-Motor

    Zeiss- GermanyMicro-parts

    Micro-EDMNTU - Taiwan

    Micro-millingFanuc- Japan

    70 m - Human Hair

    25 m - Characters

    Manufacture of productswith the followingfeatures:

    about 100100 m to about 10 mm in sizem to about 10 mm in size

    contain very complex 33--DD (free(free--form) surfacesform) surfaces

    employ a wide range of engineeringmaterialswide range of engineeringmaterials

    possess extremely high relative accuraciesextremely high relative accuraciesin the 10-3 to 10-5 range

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    10

    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

    Why Miniaturization?

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    11

    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 NOTCORRECT

    DefinitionMaterial removal is micro/nano level

    with no constraint on the size of the

    component

    Scope 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

    Classification of micromachining processes

    HybridProcesses

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    Micromachiningprocesses

    13

    Energy Used Principle Processesand Features

    Mechanical

    Force

    Material removal via highly

    concentrated force

    Cutting, grinding, sandblasting.

    UR ~ 100 nm, edge radius

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    Micromachiningprocesses

    14

    Energy Used Principle Processesand Features

    Dissolution Chemical or electrochemicalreaction based ionic

    dissolution

    Chemical, PCM and ECM. Small UR,negligible force. Inter-electrode gap,

    flow of electrolyte influences

    accuracy

    PlasticDeformation

    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 or

    mold making

    Lamination Material in solid powder orliquid form is solidified layer-

    by-layer.

    Stereolithography, internal as well as

    external profiles can be formed

    easily.

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    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 ofSize Effect

    15

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    16

    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= CV 2

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    17

    EDM Micro-EDM

    Circuitry Elements

    RC relaxation type Single spark process Forced process for constant voltageand current

    User defined pulse on time

    RC single pulse discharge Single spark process Single capacitance discharge, noconst 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

    Comparison of EDM and micro-EDM

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    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-analysisof Debris

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    Structures of Debris

    Large Size & Small Size

    Hollow & Solid Debris

    Satellite structure

    Hollow Spheres

    Dents

    Burnt Cores

    Micro-analysisof Debris

    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

    HighEnergy

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    Effect of Tool Rotation

    Effect of Ultrasonic Vibrations

    Effect of workpiece-tool material

    combination

    Effect of polarity

    PMEDM

    Effect of dielectric

    EDM processstability How will you measure? Ignition delay time

    GroupNumber Group1 Group2 Group3

    PlanetaryMotion Yes No NoExternal material layer Yes Yes No

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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

    Micro-EDM processstability

    1 Low energy2 High Energy

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    22

    Variants of micro-EDM

    22

    Figure : Micro rods machining processes

    Process Capability Limitation

    BEDG Min. 3 m diameter electrode, maximum10aspect ratio, 0.6 Ra surface finish

    Only single electrodescanbe machined

    Micro-WEDG Min. 5 mdiameter electrode, maximum10aspect ratio, 0.8 Ra surface finish

    Cylindrical electrodesaswell asarrayedelectrodescant be machined

    Micro-WEDM Best resultsobtainedare 10x10square array (23m width, 700 m height), minimum machiningsize achievable is20 m, surface finish 0.07-0.35m Ra, and maximumaspect ratio 100

    Cylindrical arrayed structurescant bemachined

    Diamond milling microtower of 1 mm in height and 25 m square Mechanicalprocessinvolvesmachiningstresses

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    23

    Research issuesin micro-EDMMicro-EDM Research Areas

    Handling Electrode andworkpiece

    preparation

    Off-machine electrodepreparation

    Drilling,threading

    holes(WEDM)

    Mfg. Micro 3Delectrode

    On-machine electrode

    Stationery

    blockRotating Disk

    Guided

    running wire

    MachiningProcess

    ProcessParameters

    SourcesofErrors

    Machine

    Electrode

    Jigsand

    Fixture

    Electrodewear and

    machiningstrategies

    Multi

    electrode Z-compensation

    Wear

    monitoringsystem

    Uniform wear

    method

    Measurement

    Surfacequality

    Dimensions

    Electrode

    Parts

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    Machining of mould and die in high strength materials (Carbides,

    die steel, conducting ceramics) Recently replaced by high speedmilling 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

    24

    Applications

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    Reverse replication of

    arrayed hole on theplate electrode to the

    bulk material by change

    in the polarity

    Machined structures

    have a dimensions

    equal to the original

    dimension of pocket

    minus interelectrode

    gap

    Important operating

    parameters are voltage ,

    capacitance, threshold,

    and the feed

    25

    Machining of arrayed micro-structuresby REDM

    Figure : Working of micro and reverse micro EDM processes

    aa) Normal EDM

    ab) ReverseEDM

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

    a tool during machining

    Bulk Rod

    Micro-rods

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    Problem Statement : Machining of high aspect ratio arrayedmicrostructures by micro reverse EDM process.

    26Figure : set up of the micro-REDM process

    Machining of arrayed micro-structuresby REDM

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    27

    Applicationsof micro-REDM

    Process is capable of achieving

    Machining ofarrayed structureswith varying shapes(Replication of initial geometry)

    High aspect ratio structures

    (aspect ratio of 33 has been achieved)

    Reduced errors due to tool position and tool wear

    (Less error due to no need of positioning)

    Increase in productivity Thin and long wall structures

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    28

    Applicationsof micro-REDM

    Mechanical

    Micromachining

    As a electrode inarrayed hole/cavity

    machining

    Mask preparation

    As a tool for generatingstable plasma

    Heat ExchangingHexagonal and thin wall

    structures

    Automobile

    Micronozzels

    Biomedical

    As a interface device for

    capturing neural signals

    Brain neural activity

    recording

    Arrayed microholes as a

    spray nozzels in thebiotechnology 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 MEMS

    system

    Shaft for micro robotsmicro actuator

    Applications

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    29

    Authors ResultsAchieved Methodology

    Kim et. al.

    (2006)

    V and C as parameters, array of 3 microrods each

    of 35 m in diameter and 1.5 mm in length formed

    on WC bulk rod

    micro-EDM to fabricate the microholes

    on a plate and then plate was used as a

    tool

    Yi et. al.

    (2007)

    3X3 and 4X4 array of 80m square, height 600 m,

    wall thickness was 15 m.

    Single electrode machined by micro-

    WEDM, arrayed holes are machined on SS

    plate by micro-EDM

    Zeng et. al.

    (2008)

    AgW 5X5 electrode array, average diameter 35

    m, length 250 m, 100 m hole spacing.

    Use of ultrasonic vibrations at 20 KHz frequency.

    Block micro-WEDG to fabricate single rod,

    machining arrayed holes on plate by

    machining individual hole

    Review of work done in micro-REDM

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    Cu plate thickness = 200 m

    Bulk WC rod of 300 m initialdiameter

    Operating parameters were 80 and

    100 V voltage and 50, 650, 5000 pF

    capacitance

    30

    Figure : Fabricated arrayed microrods (30 m

    dia., 1.5 mm height) [2].

    Figure : Effect of voltage at the constant

    capacitance on machining time [2]

    Figure : Effect of capacitance on

    machining time [2]

    Review of work done in micro-REDM

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    31

    Componentsfabricated by micro-REDM

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    32

    0

    50

    100

    150

    200

    250

    300

    60 80 100 150

    MachiningTime(Min)

    Voltage

    Effect of Voltage

    0

    200

    400

    600

    800

    1000

    1200

    1 2 3 4

    MachiningTime(Min)

    CapacitanceL evel

    Effect of Cpacitance

    0

    10

    20

    30

    40

    50

    60

    70

    80

    0.2 0.4 0.6 0.8

    MachiningTime(Min)

    Amplitude

    Eff ect of Amplitudeof vibration

    a)

    b) c)

    Figure : 5x5 arrayed electrode

    (35 m diameter, 8 aspect ratio) [13]

    Figure : Effect of a) voltage, b) amplitude of vibration , and c) capacitanceon machining rate . [13]

    V= 100 V C =4700 pF

    Amplitude = 0.4 m

    Review of work done in micro-REDM

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    Machining of 3x3 and 4x4

    microarrayed structure with

    each square rod of 80 m

    Micro-REDM is done at 100V

    and 500 pF capacitance

    No characterization of micro-

    REDM process

    33

    Figure : a) hole array on plate prior to machining,

    b) after the machining

    Figure : a) machined electrode array , b) used electrode

    array for micro-EDM of holes

    Review of work done in micro-REDM

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    34

    Review of work in Reverse-micro Wire EDM

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    No detailed study which characterize the micro-REDM process indicating

    the process capability is done

    Process responses like surface finish, erosion rate and the geometricalaccuracies are not quantified

    No data on the process mechanicsdifference between the micro-EDM andthe micro-REDM process is reported

    Only plausible reasons are given in the literature for process instability in

    micro REDM process

    No mathematical model is available which can predict the processresponses in arrayed structure machining via reverse EDM

    35

    Review of work done in micro-REDM

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    36

    Issuesin micro-REDM

    Issuesin micro-REDM process

    Issuesrelated to processstabilityand accuracy

    Formation of short bridge

    Less positional accuracy

    compared with number of

    pulses

    Spark formation on singlerod even though it is

    simultaneous processing

    No tool rotation

    Less MRR

    Issuesrelated totool electrode

    Tool wear

    Thin plates, more

    pocket enlargement

    Accurate machining

    of pockets on plate

    Issuesrelated tofabricatedstructures

    Tapered surface

    Surface burning

    Non uniform surface

    morphology

    High surface roughnessDelicate structures

    Deflection of microrods

    Redeposit layer

    Gas entrapment

    Deformation of electrode

    due to power of arc

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    37

    Experimentsin micro-REDM

    Level Voltage(V) Capacitance(nF) Threshold(%) Feed(m/ sec)

    1 80 1 25 5

    2 100 10 50 15

    ColumnA B C D

    Expt. run Voltage Capacitance Threshold Feed

    1 1 1 1 1

    2 1 1 2 2

    3 1 2 1 2

    4 1 2 2 1

    5 2 1 1 2

    6 2 1 2 1

    7 2 2 1 1

    8 2 2 2 2

    Measured Response

    Geometrical accuracySurface roughness

    Zero error length

    Erosion rate

    Surface finish

    Surface morphology

    Operating parameters and selected levels

    Scheme of experimentation

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    38

    Imagesof the micro rods machined ineach run of experiment

    Workpiece geometry :Machining of 400 m square

    and 200 m cylindricalelectrodes, machined length 1

    mm

    Experimentsin micro-REDM

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    39

    Machining Time

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    Main effect plot for dimensional accuracy- cylindrical rod

    40

    Meanof%ErrorinDiameter

    100V080V

    -30

    -40

    -50

    -60

    10nF01nF

    50%25%

    -30

    -40

    -50

    -60

    15micron/s05micron/s

    GapVoltage Capacitance

    Threshold Feed

    MainEffectsPlot (data means) for%Error inDiameter CylindriacalRodat 0%L

    OperatingParameter Voltage Capacitance Threshold Feed

    Parameter Setting 80-100 V 1-10 nF 25-50 % 5-15 m/sec

    Change in Response (at 0% L) 48% 16%

    Change in Response (at 25% L) 36% 27%

    Change in Response (at 50% L) 33% 30%

    Change in Response (at 75% L) 48% 25%

    Changein Response (at 100% L) Not Significant 110%

    Meanof%ErrorinDiameter

    100V080V

    8

    6

    4

    2

    0

    10nF01nF

    50%25%

    8

    6

    4

    2

    0

    15micron/s05micron/s

    GapVoltage Capacitance

    Threshold Feed

    MainEffectsPlot (data means) for%Error inDiameter at 100%L

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    Preliminary experiments- Geometrical accuracy

    41

    Figure : % Error in diameter of Cylindrical Rod at varying a)

    voltage, b) capacitance, c) threshold , and d) feed

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    Main effect plot for geometrical accuracy- Square rod

    42

    OperatingParameter Voltage Capacitance Threshold Feed

    Parameter Setting 80-100 V 1-10 nF 25-50 % 5-15 m/sec

    Change in Response (at 0% L) 64% Not Significant -73% Not Significant

    Change in Response (at 25% L) 28% 29% Not Significant Not Significant

    Change in Response (at 50% L) 46% 31% Not Significant -25%

    Change in Response (at 75% L) 49% 28% -40% -42%

    Changein Response (at 100% L) Not Significant Not Significant Not Significant Not Significant

    Meanof%ErrorinSideofRod

    100V080V

    -15

    -20

    -25

    -30

    10nF01nF

    50%25%

    -15

    -20

    -25

    -30

    15micron/s05micron/s

    GapVoltage Capacitance

    Threshold Feed

    MainEffectsPlot (data means) for%Error inSideofRodat 0%L

    Meanof%ErrorinSideofRod

    100V080V

    1

    0

    -1

    -2

    -3

    10nF01nF

    50%25%

    1

    0

    -1

    -2

    -3

    15micron/s05micron/s

    GapVoltage Capacitance

    Threshold Feed

    MainEffectsPlot (data means) for%Error inSideofRodat 100%L

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    43

    %Error in the side of square rod

    Figure : % Error in diameter of Square Rod at varying a) voltage,b) capacitance, c) threshold , and d) feed

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    Main effect plot for Erosion Rate

    Increase in the capacitance and voltage increases the pulse energy and

    flushing strength

    Increasing the energy content per pulse increases the crater size and thesurface roughness

    44

    OperatingParameter Voltage Capacitance Threshold Feed

    Parameter Setting 80-100 V 1-10 nF 25-50 % 5-15 m/sec

    Change in Response (Erosion rate) 300% 250% Not Significant Not Significant

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    Main effect plot for Zero Error Length- Cylindrical rod

    45

    OperatingParameter Voltage Capacitance Threshold Feed

    Parameter Setting 80-100 V 1-10 nF 25-50 % 5-15 m/sec

    Change in Response (Zero error

    length)

    Not Significant -11% Not Significant 10%

    None of the processingparameter isfound significant for zero error length of square rod

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    Main effect plot for surface roughness

    Value of surface roughness varies from 1.6 m Ra to as high as 6.3 m Ra

    under different experimental conditions.

    Voltage and machining time affects the surface roughness, at 80V

    machining time is more and at the 100V pulse energy is more

    46

    Sample 3

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    Main effect plot for surface roughness-cylindrical rod

    47

    OperatingParameter Voltage Capacitance Threshold Feed

    Parameter Setting 80-100 V 1-10 nF 25-50 % 5-15 m/sec

    Change in Response

    (Surface Roughness)

    Not Significant -28% 38% -20%

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    Main effect plot for surface roughness- square rod

    48

    OperatingParameter Voltage Capacitance Threshold Feed

    Parameter Setting 80-100 V 1-10 nF 25-50 % 5-15 m/sec

    Change in Response (Surface Roughness) -50% -85% Not significant Not significant

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    Surface Morphology

    49

    Surface near tip exhibits number

    of craters , whereas the surface at

    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

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    0

    5

    10

    15

    20

    25

    1 2 3 4

    Oxygen

    Percenatge

    SampleNumber

    SqaureRodAtTip

    AtRoot

    0

    5

    10

    15

    20

    25

    30

    1 2 3 4

    Oxygen

    Percentage

    SampleNumber

    CylindricalRodAtTip

    AtRoot

    0

    5

    10

    15

    20

    25

    30

    35

    40

    45

    1 2 3 4

    CarbonPercentage

    SampleNumber

    SquareRodAtTip

    AtRoot

    0

    5

    10

    15

    20

    25

    30

    35

    40

    45

    1 2 3 4

    CarbonPercentage

    Sample Number

    CylindricalRodAtTip

    AtRoot

    (a) (b)

    (c) (d)

    EDSanalysis Oand Ccontent

    50

    Element Carbon Oxygen Copper Zinc

    Percentage 12.55 4.40 54.30 23.68

    Element Oxygen Carbon

    Square Cylinder Square Cylinder

    At Tip At Root At Tip At Root At Tip At Root At Tip At Root

    Maximum 18% 7% 27% 12% 42% 22% 41% 15%

    Minimum 4% 4% 5% 3% 17% 0% 0% 0%

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    0

    10

    20

    3040

    50

    60

    70

    1 2 3 4

    CopperPercentage

    SampleNumber

    SquareRodAtTip

    AtRoot

    0

    10

    20

    30

    4050

    60

    70

    80

    90

    1 2 3 4

    CopperPercentage

    Sample Number

    Cylindrical RodAt Tip

    At Root

    0

    5

    10

    15

    20

    25

    30

    35

    40

    1 2 3 4

    ZincPercentage

    Sample Number

    SquareRodAt Tip

    At Root

    0

    5

    10

    15

    20

    25

    30

    35

    40

    1 2 3 4

    ZincPercentage

    SampleNumber

    CylindricalRodAt Tip

    At Root

    (a) (b)

    (c) (d)

    EDSanalysis Cuand Zncontent

    51

    Element Carbon Oxygen Copper Zinc

    Percentage 12.55 4.40 54.30 23.68

    Element Copper Zinc

    Square Cylindrical Square Cylindrical

    At Tip At Root At Tip At Root At Tip At Root At Tip At Root

    Maximum 58% 65% 62% 82% 30% 34% 22% 34%

    Minimum 25% 45% 18% 50% 5% 22% 0% 0%

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    Experiment Results

    52

    Maximum % error in dimensions are more at 80V compared with

    100 V; 60%(max) error in the diameterof machined rod observed

    at the tip

    With change in voltage from 80 V to 100 V erosion rate

    increases 3 times while increasing capacitance from 1 nF to

    10 nF, erosion rate increases by 2.5 times.

    Increasing the capacitance and decreasing the feed rate

    achieves improvement in zero error length

    Surface roughness (Ra ) varies between 1.6-6.3 mIn general less variation in the response parameters are

    observed with the change in threshold and feed values

    Maximum oxygen content (27%) is observed at the tip of

    cylindrical rod, while maximum carbon (42%) is observed at the tip

    of square rod.

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    53

    Conclusion

    Understanding of micro-EDM machining characteristics are

    important to achieve important response variables

    Voltage and capacitance emerges as a most influential process

    parameters in micro REDM

    Quantification of the roles played by debris during the micro-

    EDM/micro-REDM process are not reported widely

    Tool (plate) wear and frequent arcing are the main causes for

    tapered surface

    Need to model the process for predicting geometrical accuracies and

    bridge formation mechanism

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    Arrayed structures machined at MTLIIT Bombay

    54

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    55

    Future of micromachining

    From Photonics Spectra, 1998

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    56

    Assembly

    Machine

    Robot

    Punching

    Machine

    Electrical

    Discharge

    Machine

    MillingMachine

    Future of micromachining

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    57