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MODELING AND OPTIMIZATION OF MICRO EDM PROCESS

MuralidharaME05D036

Research Guide:Prof. M. Singaperumal

Precision Engineering and Instrumentation LaboratoryMechanical Engineering Department

Indian Institute of Technology Madras Chennai

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Introduction

Micro EDM is a non-conventional, non-contact machining process where the material is melted and removed from the work surface by the sparks produced between anode and cathode immersed inside the dielectric medium

Used for machining micro features like through, blind and tapered micro holes, straight, circular and spiral micro channels which are used in MEMS devices

Micro EDM is a better alternative to microfabricationtechniques for production of some of the 3D microstructure in silicon

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1. To develop a Micro EDM process model considering the heat generated in the Plasma

2. To develop a model for the piezoelectric actuator considering Hysteresis effect and to validate the model experimentally

3. To simulate the Micro EDM process based on the developed models

4. To develop a controller for Micro EDM process for feeding the tool considering the tool erosion and to achieve the required depth of micromachining

5. To find the optimum process parameters for a specific tool and workpiece material

Objective

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Micro EDM Model

PiezoactuatorModel

Controller

Required Depth

Total Tool Feed Reference

Optimum Gap

Actual Gap (MRR + TWR)

V

F

DC

Block diagram of simulation model

X-Y Stage

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Proposed Micro EDM Setup

Open loop gap voltage

Reference Gap

Voltage

Open loop V

Micro EDM Controller Piezo

Drive

Required Depth Actual

Depth

Tool wear length

Tool feed length

X-Y-θ Table

Piezoactuator

Amplifier

Discharge Power supply

PulseControlcircuitFilter

Dielectric Fluid Recirculation System

Gap Voltage sensor

F

Duty Cycle

Feed

back

V

+

-

+

-

V

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In-House developed Micro EDM Set-up

X-Y-θ Table

Tool feed rate Controller

Gap Voltage

Piezoelectric Microctuator

Driver

Reference Gap Voltage

Discharge Power supply

PulseControlcircuit Amplifier

Piezoactuator

Fig. 1 Micro EDM Set-up

WorkpieceTool

X

Z

FrequencyDuty Cycle

Voltage

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Silicon Micromachining using Micro EDM• Silicon Wafer Details:630µm thick, 0.1Ωcm resistivity

• Machining time: 7 minutes• Tool Diameter outer:1.57mm, Inner: 0.54mm• 2D View from Surface Profiler

F = 4.3kHz

D.C. = 33.4%

Voltage = 60V

600µm

440µm

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3D View of the Machined Structure

Surface roughness can be improved by

• dielectric fluid filtering and recirculation

•careful selection of machining parameters

• selecting proper polarity

•giving rotary motions to the tool

• roughing operations at higher voltage and finishing operations at lower voltage

•Post process treatments like etching

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The voltage across the hysteresis element is given by( ) ( )

( ) ( )

1

sgn sgn

i i

i

b bi

i ii

i b i i

n

H ii

q q q qif v

C CV

V i and q q C v i else

V V=

⎧ ⎫− −⎪ ⎪<⎪ ⎪= ⎨ ⎬⎪ ⎪

= −⎪ ⎪⎩ ⎭

=∑

T

H

q xFt

CVt

VH

•q

Vin

+

-

+

+

-

-

tq•

TVt

k bFt=TVt

m

x

+

-

+

Vin

+

VH

Vt Ft x

VtCp

Tx

q

T

Cp

Hysteresis Model for

Piezoactuator

Mechanical Model for

Piezoactuator

T

q = Tx + Cp VtVin = VH + VtVH = H(q)Ft = T Vt

tmx bx kx F+ + =&& &

Model For Piezoelectric Actuator

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1. Simulation for displacement of piezoelectric actuator using the developed model

2. Experimental determination of feed back gap voltage corresponding to a gap width which will result in sparks of required characteristics

3. Modeling of workpiece and tool removal process in Micro EDM by considering the heat generated in plasma.

• Simulation of Micro EDM process integrating Micro EDM model with the piezoelectric actuator model

• Designing a control system to control the tool feed rate considering tool wear rate and MRR

• Experimental validation of the developed Micro EDM model

Work to be Done