optimization of micro wire electro discharge machining process parameters using aerospace material

97 Pages·2013·2.25 MB·English

OPTIMIZATION OF MICRO WIRE ELECTRO DISCHARGE
MACHINING PROCESS PARAMETERS USING AEROSPACE
MATERIAL
A Thesis Submitted to
National Institute of Technology, Rourkela
In Partial fulfillment of the requirement for the degree of
Master of Technology
in
Mechanical Engineering
By
MANOJ KUMAR MOHANTA
Roll No. 211ME2351
Under the guidance and supervision of
Prof. K. P. MAITY

Department of Mechanical Engineering
National Institute of Technology
Rourkela -769 008 (India)
2013
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National Institute of Technology
Rourkela
CERTIFICATE
This is to certify that the thesis entitled “OPTIMIZATION OF MICRO WIRE ELECTRO
DISCHARGE MACHINING PROCESS PARAMETERS USING AEROSPACE
MATERIAL” submitted to the National Institute of Technology, Rourkela by MANOJ
KUMAR MOHANTA, Roll No. 211ME2351 for the award of the Degree of Master of
Technology in Mechanical Engineering with specialization in Production Engineering is a record
of bonafide research work carried out by him under my supervision and guidance. The results
presented in this thesis has not been, to the best of my knowledge, submitted to any other
University or Institute for the award of any degree or diploma. The thesis, in my opinion, has
reached the standards fulfilling the requirement for the award of the degree of Master of
technology in accordance with regulations of the Institute.

Place: NIT Rourkela Dr. K. P. Maity
Date: HOD & Professor
Department of Mechanical Engineering
National Institute of Technology, Rourkela
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ACKNOWLEDGEMENT
I would like to express my gratitude to my supervisor Prof. K.P Maity for the useful comments,
remarks and engagement through the learning process of this master thesis. I am also grateful to
Prof. Sunil Kumar Sarangi, director NIT Rourkela who took keen interest in the work. A
special thanks goes to Ritanjali Sethy, who help me to understand and gave suggestion about the
task “PCA based optimizations”. A special gratitude I give to Mr. Kanhu Charan Nayak whose
contribution in stimulating suggestions and encouragement helped me to coordinate my project
especially in writing this report.
I am obliged to all my friends of NIT, Rourkela, for the valuable information provided by them
in their respective fields. I am grateful for their cooperation during the period of my assignment.
Lastly, I thank almighty and my parents for their constant encouragement without which this
assignment would not be possible.

Date: Manoj Kumar Mohanta
Place: Roll no: 211ME2351
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Nomenclature

EDM Electrical discharge machining
µWEDM Micro Wire Electrical discharge machining
MRR Material removal rate (mm3/min)
Hi heat input to the work piece
V Voltage (V)
I Current (Amp)
Q(r) Heat flux (W/m2)
R Spark radius (µm)
K Thermal conductivity (W/mK)
T Temperature variable (K)
T0 Initial temperature (K)
Ton Spark-on time (µs)
Toff Spark-off time (µs)
x,y Cartesian coordinate of work piece
Cp Specific heat (J/kgK)
Cv Crater volume (µm3)
PCA Principal Component Analysis
GRA Grey Relational Analysis
TOPSIS Technique for Order Preference by Similarity to Ideal
Solution

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Abstract
From the last few decades there has been increasing demand of compact, integrated and small
size products by a non-traditional process for accurate and cost-effective measurement of
material properties. These are needed for machining of tools and product design, the
development of micro size components, the growing needs for micro-feature generation. Micro-
manufacturing processes have good machining performance specifications. Machining
performance specifications of concern include minimum feature size, tolerance, surface finish,
and material removal rate (MRR). These made the micro wire EDM an important manufacturing
process to meet the demands. Micro Wire electrical discharge machining (WEDM) technology
has been widely used in production, aerospace/aircraft, medical and virtually all areas of
conductive material machining. Material properties such as light weight, high strength and
corrosion resistance etc. makes the Aluminum (Al) as a demanding material in the aerospace
industry. Aluminum has high coefficient of linear expansion which should be taken in to account
at the design state to compensate differences in expansion. Hence there is a need to model for the
residual stress before machining the aluminum work piece. This project presents the machining
of the aerospace material (Al) using wire EDM with in micro size. The objective of this project
is to investigate the performance of micro wire EDM machining of Al material. WEDM is
extensively used in machining of conductive materials when accuracy and tight tolerance is
important. Simple and easily understandable model for an axisymmetric 2D model for wire
electric discharge machining (WEDM) has been developed using the finite element method
(FEM). Correctness of the present FEA modeling method has been checked by comparing the
present thermal modeling with the previously developed thermal model of INCONEL718
material. The observation have been influenced on various characteristics namely, material
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removal rate (MRR) and residual stress. Comparison was done between the theoretical MRR and
the experimental results. Design was based on L9 orthogonal array that was taken by Taguchi
design of experiment (DOE) approach with three-level, three factors Experiments have been
conducted for each experimental run. Three principal component analysis (PCA) based
optimization technique have been performed and each optimization results were discussed. It is
found that among the three PCA-based approaches i.e. weighted principal component analysis
(WPCA), Grey relational analysis (GRA) combined with PCA, and PCA based TOPSIS method.
PCA based TOPSIS method results in the best optimization performance in micro WEDM
process. Effect of different process parameters (voltage, current, pulse on time) on temperature
distribution has also been analyzed from the thermal model of Aluminum work piece.

Keywords: Aluminum, Micro WEDM, ANSYS, Modeling, MRR, Residual stress, optimization,
WPCA, TOPSIS, Grey relational analysis.

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Contents
Chapter Page
No. No.
CERTIFICATE i
ACKNOWLEDGEMENT ii
Nomenclature iii
Abstract iv
List of Figures v
List of Tables vi
1 Introduction
1.1 Introduction 1
1.2 Principle of wire electrical discharge machining 2

2 Literature review 4
3 Modeling of micro WEDM
3.1 Introduction 9
3.2 Modeling process of micro Wire EDM using ANSYS by finite element method
(FEM) 9
3.2.1 Discretize the Domain 10
3.2.2 Develop Shape Functions 10
3.3 Thermal modeling of EDM to micro Wire EDM 11
3.3.1 Assumptions 12
3.3.2 Thermal Modeling 12
3.3.3 Governing Equation 12
3.3.4 Initial condition 13
3.3.5 Boundary conditions 13
3.3.6 Heat input 14
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3.3.7 Material properties 15
3.3.8 Spark Radius 15
3.4 Finite Element Analysis Procedure 16
3.4.1 Preprocessing 17
3.4.1.1 Definition of Element type 17
3.4.1.2 Material properties 17
3.4.1.3 Finite Element Modeling of the work piece 17
3.4.2 Solution 18
3.4.2.1 Application of Thermal Loads 18
3.4.3 Post processing 18
3.5 Modeling of MRR of µ wire EDM 18
3.5.1 MRR calculation for multi- discharge 19
3.6 Measuring residual stress caused by Wire EDM 20
3.6.1 Thermo-mechanical analysis 20
3.6.2 Modeling steps for residual stress (coupled thermal –structural analysis) 20

4 Optimization Techniques 24
4.1 Multi- objective Optimization 24
4.1.1 Weighted principal component Analysis 24
4.1.2 Grey relational analysis coupled with principal component analysis 29
4.1.3 PCA-Based TOPSIS Method 30
5 Experimental work 33
5.1 Taguchi Design of experiments 36
6 Results and discussions
6.1 ANSYS model confirmation 39
6.2 Thermal modeling of micro wire EDM for single spark 43
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6.3 Modeling results of MRR for micro wire EDM 47
6.4 Modeling results of Residual Stress modeling for micro wire EDM 53
6.5 Modeling Results 58
6.6 Comparison between theoretical and experimental results 58
6.7 Effect of different process parameters 59
6.7.1 Effect of Voltage 59
6.7.2 Effect of Current 61
6.7.3 Effect of pulse duration (Ton) 63
6.8 Weighted Principal Component Analysis (WPCA) Results 65
6.9 Grey relational analysis coupled with PCA results 69
6.10 Result of PCA based TOPSIS method 72
7 Conclusions 76

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List of figure
Figure contents Page
No. No.
Figure 1.1 Types of EDM processes 2
Figure 2.2 computer numerical system 3
Figure 3.1 Discretized control volume 10
Figure 3.2 1-D linear element 10
Figure 3.3 Schematic representation of the domain considered for the numerical
model 13
Figure 3.4 Thermal modeling of EDM 14
Figure 3.5 Two-dimensional view of the meshed model with element size of 20µm
18
Figure 3.6 Calculation of crater Volume 19
Figure 3.7 Flow chart of procedure for thermal modeling and residual stress 22
Figure 3.8 over view of numerical procedure to find out residual stress 23
Figure 4.1 purpose of grey relational analysis 29
Figure 5.1 Wire EDM machine 34
Figure 5.2 Aluminum work piece is cut by WEDM 35
Figure 5.3 Images of micro cut on the work piece 36
Figure 6.1 Temperature distribution of earlier developed model for
INCONEL 718 40
Figure 6.2 our developed thermal modeling for inconel718 material 40
Figure 6.3 Temperature distribution in Aluminum (Al) work piece with V=22V,
I=1.5A and P=0.2 41
Figure 6.4 Temperature distribution in Aluminum (Al) work piece with V=22V,
I=1A and P=0.08 43
x