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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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Open circuit voltage 80V
Capacitance 100pF, 220pF
Workpiece material Stainless Steel AISI 304
Electrode material Tungsten
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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Open circuit voltage 80V
Capacitance 220pF, 1000pF
Dielectric medium Deionized water, mineral oil
Workpiece material Stainless Steel AISI 304L
Electrode material Tungsten
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