Kamla Karr a Jurk Ar

7/27/2019 Kamla Karr a Jurk Ar

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K. P. Rajurkar

Distinguished Professor of Engineering,Center for Nontraditional Manufacturing Research,

University of Nebraska-Lincoln.

US-Korea Workshop on Miniaturization Technologies

September 9, 2004

Complex Shapes by Micro-EDM, Micro-ECM &

Micro-USM


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Presentation Outline

Introduction

Micromachining Technology

Micro EDM

1. 3D Micro Cavity Machining2. Application Planetary Movement

Micro ECM

1. Gap Modeling2. Experimental Results

Micro USM

Summary


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1. IC Packages with Micro Devices

2. Fuel Injection Nozzle for Automobiles

3. Biotechnology

4. Medical Applications

5. Multifunctional Compact Devices (CD/DVD players)

Micromachining Applications


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Micro-EDM


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Material Removal Mechanism of EDM

workpiece+anode

-cathode

(a) Tool and workpiece immersed in

dielectric liquid.

(b) A spark is generated between tool and

workpiece.

(c) The high temperature causes the melting

and vaporization of electrodes.

(d) At the end of the pulse, the molten

material is ejected from surface, leaving a

shallow crater.

electrode

Basics of Micro EDM


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Macro Vs. Micro EDM

Macro Micro

Principle Thermal Material Removal Similar (?)

Equipment

Pulse Generator Switch circuit RC circuit

Dielectric Mineral oil, Deionized water Mineral oil

Flushing External and Internal No flushing

Electrode Material Copper / Graphite Tungsten

Process Parameters

Current 0.5 400A 0.1 10mA

Voltage 40 400V 60 120V

Pulse Duration 0.5s 8ms ns s

Electrode Wear Ratio 1 5% 1.5 100%

Surface Roughness 0.8 3.1m 0.07 1m


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Micro EDM Equipment


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1. Discharge Voltage (60V to 110V)

2. Capacitance (usually up to 3300pF)

3. Tool Material (Tungsten, other conductive materials)

4. Tool Size (4m to 1mm)

5. Dielectric (Mineral oil or deionized water)

Machining Parameters


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1. Machine any conductivematerials.

2. Single or medium size production.

3. Holes (Aspect ratio, 5:1 in oil, 10:1 in deionized water,

18:1 using special method, 100m in diameter, stainless

steel).

4. Slots and Arbitrary 3D micro molds.

Capabilities of Micro EDM


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The electrode wear ratio in micro EDM is larger than that of

conventional EDM.

The fabrication of complex shaped electrodes itself is a kind

of micromachining.

No CAD/CAM system is available to generate tool paths

when simple shaped electrodes are used to generate complex

cavities because the electrode wear cannot be easily taken intoaccount.

3D Micro Cavities Machining


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(a) Conventional Wear. (b) Uniform Wear.

Simple Shaped Electrode Wear


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The uniform wear concept is based on the fact that undercertain conditions, the shape of the electrode is regained due to

the electrode wear after machining one layer.

Rules of the tool path design:(a) Layer-by-layer machining.

(b) To-and-from Scanning.

(c) Tool paths overlapping.

(d) Machining the central part and the boundary of the

machined surface alternately.

Concept of Uniform Wear Method


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CAD Module CAM Module

Part Modeling

Feature

Data

Slicing the

machined features

and calculating area

of each sliced

surface

Area ofsliced

surfaces

Generating tool

paths for machined

featuresTool

paths

data

Re-generating tool

paths and

compensating

electrode wear length

based on the uniform

wear method

Post processor

NC codes

Transferring NC

codes to micro-EDM

Tool paths data

generation by

the new

approach

Integration of Uniform Wear Method with

CAD/CAM


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Open circuit voltage 80V

Capacitor 100pF

Workpiece material SUS304

Electrode material Tungsten

Machining Conditions


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CAD design of a complex cavity (Dimension: m).

CAD Drawing using Pro-Engineer


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(a) Top View. (b) Oblique View.

Geometry Machined


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CAD design of a complex cavity (Dimension: m).

Design


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(a) Top View. (b) Oblique View.

Machining Results


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Electrodes after machining.

Tool Electrode


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Planetary movement of electrode provides an extra space foreasier removal of debris from the discharge gap.

Reduces the debris concentration.

Reduces the occurrence of abnormal discharges.Reduces the electrode wear.

Improves the machining efficiency.

Planetary Movement in Micro EDM


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Capacitance 100pF, 220pF

Workpiece material Stainless Steel AISI 304


Tool path Point-to-point, Continuous moving

Shapes of machined

features

Triangular, Square, Hexagonal

Electrode feed 100m, 200m

Electrode size 60m to 80m

Machining Conditions


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Square holes without planetary movement

Square holes with planetary movement

Influence on Edge and Corner


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0

500

1000

1500

2000

2500

0 50 100 150 200 250 300

Electrode Feed Depth (m)

Time(Second)

Feed rate (0.6m/sec), Without planetary movementFeed rate (3m/sec), Without planetary movement

Feed rate (0.6m/sec), With planetary movement

Electrode feed Vs. Machining time


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0

500

1000

15002000

2500

3000

3500

4000

4500

5000

Feed rate

(0.6m/sec),

Without planetarymovement

Feed rate(3m/sec),

Without planetarymovement

Feed rate(0.6m/sec),

With planetarymovement

MaterialRemovalRate(m3/sec

Material Removal Rate


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0

1

2

3

45

6

7

8

Triangle Square Hexagon

Hole Shape

ElectrodeWearRatio(%)

Without Planetary Movement With Planetary Movement

Electrode Wear Ratio


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Micro EDM

Controller

Planetary

Movement

Controller

Water Reservoir

Valve

Water

Pump

WaterDeionizing

Resin

Conductivity

Meter

Probe

Horizontal

Electrode

Feed

Mechanism

Electrode

WorkpieceY-Z Stage

Computer

Horizontal Machining Setup for Micro Holes of

High Aspect Ratio


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Capacitance 220pF, 1000pF

Dielectric medium Deionized water, mineral oil

Workpiece material Stainless Steel AISI 304L


Electrode size 60m to 80m

Conductivity 0.3 to 0.4 S/cm

Machining Conditions for Deep Hole Drilling


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Micro hole through 2.5mm plate.

Hole entrance (D=145m).Hole exit (D=120m).

When the plate is drilled through, besides the normal tool wear, the reduction of

subsequent discharges (because the debris is ejected out from the hole exit easily)

result in a small exit diameter.

A Micro Hole with Aspect Ratio of 18


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Electrode before cleaning after hole drilling.

Electrode after cleaning after hole drilling.

Electrode After Machining


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0

500

1000

15002000

2500

3000

3500

0 100 200 300

Time (minutes)

Electrodefeed(m)

Deionized water Mineral oil

Effect of Dielectric on Machining time


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Surface Roughness Measurement

o Atomic Force Microscope

o Stylus based Profilometer

o Optical Interferometer


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Surface Roughness Calculation

Raw Data

Waviness (Freq = 100mm-1)

Roughness


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Experiment Results

Voltage = 80V

0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

0 500 1000 1500 2000 2500 3000 3500

Capacitance (pF)

SurfaceRoughne

ss(Ra,nm)

25 50 75Hole Depth (x0.1m)


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Discharge Energy Vs Crater Size

100pF

3300pF

220pF

1000pF

80V, 5m deep


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Micro-ECM


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Anodic dissolution process in an electrolyte cell

The amount of material dissolved is directly proportional to the amountof charge passing through the electrodes

ECM Cell

Workpiece Tool

electrode

Electro Chemical Machining (ECM)


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Side Gap

along Width

Sx

Side Gap

along Length

SyFrontal Gap

from the Face

of the tool

Sf

ECMM

PROCESS

Duty Cycle

Voltage

Initial Inter

electrode Gap

Electrolyte

Concentration

Tool electrode Feed

Rate

Frequency

ECMM Factors


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Cylindrical electrode with flatface

Linear potential distribution

No changes in electrolyte

properties

Gas generation effect isnegligible

Homogeneous work piecematerial

Surface of anode isuniformly covered by theelectrolyte

ECMM Process Modeling


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1. Drive System

2. Microscope

3. Electrolyte jet nozzle

6. Light Source regulator

4. Power supply

5. Oscilloscope

1.2 Vertical Slide

Designed Setup


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Coefficient of multiple determination = 95%.

Voltage, feed rate, and duty factors have been foundsignificant on all performance measures.

Frequency does not affect the frontal gap.

The interaction of voltage with duty factor in case of sidegap along width has been found significant.

Duty factor gives better results at lower level (0.3).

Frequency gives better results at 1000 KHz.

Statistical Analysis Results


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Feed rate (Vf) = 42 mm/min

Pulse frequency = 1MHz,

Duty Factor = 0.3

Voltage Vs Side & Frontal Gap

0

20

40

60

80

100

120

140

160

180

0 5 10 15

Voltage (Volt)

Gapin

micrometer

Side Gap

Frontal gap

Experimental Investigation: Effect of Voltage


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Voltage (U) = 5 V, Duty factor = 0.3

Pulse Frequency = 1MHz,

0

20

40

60

0 20 40 60 80 100

Vf mm/min

gapin

micrometer

Side gap

Frontal gap

Experimental Investigation: Effect of Feed Rate


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Feed rate (Vf) = 42 mm/minPulse frequency = 1MHz,

Duty Factor = 0.3

0.00

0.50

1.00

1.50

2.00

2.50

0.00 0.50 1.00 1.50 2.00 2.50

Ratio of voltage to the base

level

RatioofFrontalgap

tothe

baselevel

Theoratical

Experimental

Linear (Theoratical)

Linear

(Experimental)

Theoretical

Experimental

Linear Theoretical

Linear experimental

Verification of Theoretical Model


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Feed rate (Vf) = 42 mm/minPulse frequency = 1MHz,

Duty Factor = 0.3

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0.00 0.50 1.00 1.50 2.00 2.50

ratio of Voltage to the base level

Ratioo

fSidegap

tothebaselevel

Theoratical

Experimental

Linear (Experimental)

Linear (Theorati cal)

Theoretical

Experimental

Linear

Theoretical

Linear

experimental

Verification of Theoretical Model Cont


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160 m

0.6

mm

2.18mm

Workpiece material SS 440

Tool electrode material Tungsten

Tool electrode diameter 100 m

Voltage 6 volt

Pulse frequency 1MHz

Duty cycle 0.3

Initial interelectrode gap 20 m

Feed rate 42 mm/min

Electrolyte concentration 10%

ECMM Generated Micro Cavities


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Micro-USM


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WorkpieceMicro Tool

Mandrel

Abrasive Slurry

TransducerUltrasonicGenerator

Micro Ultrasonic Machining (USM)


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Equipment Setup

2

Load Sensor

PC

Transformer

Ultrasonic

Generator

V-ShapedBearing

Transducer

Workpiece

Motor

Mandrel

RS232

DB25 connector

Carriage

Micro Tool

XYZ Stages


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Ultrasonic generator Weighing Balance Transducer

Stages

Carriage

Micro Tool

V-Shaped Bearing Mandrel

Setup - Pictures


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Machining Conditions for 3D Cavity Generation

FACTORS LEVEL

Static load control (g) 0.45

Amplitude (m) 3

Wear ratio 0.12Side gap (m) 6

Tool material Tungsten

Work material Silicon

Front gap (m) 0Abrasive size (m) 0.5-1

Tool diameter (m) 57.9


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SEM Pictures of Machined Tool and Square Micro

Cavity

Wear length (m) 143.5

Machining time (hours) 10.2

Tool after machining

Square cavity with 1/8thof sphere


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(A) Micro EDM

1. Micro EDM can be used to fabricate arbitrary 3D

micro structures, micro parts and micro molds.

2. To machine 3D micro shapes correctly, it is necessary

to maintain the shape of electrode tip and compensatethe electrode wear. The experimental results show that

the uniform wear method can solve the problem of

electrode wear.

3. An approach of integrating the uniform wear method

with CAD/CAM is proposed. Some complex shaped

micro cavities have been machined successfully.

Summary


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1. A mathematical model for predicting frontal and side gap has

been developed and experimentally verified.

2. The ability of the proposed system has been demonstrated by

machining two complex cavities of 160 and 180m slotwidth with sharp edges and straight walls.

(B) Micro ECM

Summary


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1. An USM system has been successful designed and built.

2. 3D cavities were machined to show the capability of USM

process.

(C) Micro USM

Summary


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(A) Micro EDM

1. Optimization of machining parameters such as feed rate andscanning speed based on the electrode wear model and

hydrodynamic analysis of dielectric flow in the gap.

(B) Micro ECM1. Integration of the Micro EDM and Micro ECM and generation

of 3-D micro cavities.

2. Introduction of the planetary motion of the tool electrode.

(C) Micro USM

1. Application of Uniform Wear Method and its integration with

CAD/CAM to Micro Ultrasonic Machining Process to generate

3D complex arbitrary micro cavities.

Future Work


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Thank You

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Kamla Karr a Jurk Ar

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