1. Process optimization on CNC WEDM for Al-6061 Material using
Taguchi Technique to Enhance Surface Finish and Machining Time
Rajesh.S1, Vinitesh.K.V1, Lingaraju.K.N, 1 Ramesh Babu.K2
[1] Dept. of Mechanical Engineering, Govt. Engineering College. Chamarajanagar-571313, [2] Dept. of
PG Studies, Govt. Tool Room and Training Centre, plot no. 93 & 94, K.R.S road Mysore-16.
ABSTRACT
Electro Discharge Machining (EDM) is an electro-thermal non-traditional machining
process, in which material removal takes place through the process of controlled spark
generation between a pair of electrodes which are submerged in a dielectric medium. In this
paper, wire-cut electric discharge machining (WEDM) of Al-6061 material has been consider
using WEDM with a brass wire electrode by using Taguchi technique has been reported. The
Taguchi Technique is used to formulate the experimental data by using Taguchi’s orthogonal
arrays under different parameter condition like voltage, power, voltage gap and wire tension
and analyzed the effect of each parameter on the machining characteristics to predict the
optimal choice for each and It is found that these parameters have a significant influence on
machining characteristic such as Surface finish, Electrode wear rate and Machining time.
KEYWORDS: WEDM, Taguchi method, DOE, Orthogonal array, machining time, Surface finish.
Introduction
Electrical discharge machining (EDM) is better stability and higher productivity of the
a non-traditional, thermo-electrical process, WEDM. The wire cut EDM uses a very thin
which erodes materials from the work piece wire 0.2 to 0.3 mm in diameter as an
by a series of discrete sparks between the electrode and machines a work piece with
work and tool electrode immersed in a liquid electrical discharge like a band saw by
dielectric medium. These electrical moving either the work piece or wire.
discharges melt and vaporize minute Erosion of the metal utilizing the
amounts of the work material, which are phenomenon of spark discharge that is the
then ejected and flushed away by the very same as in conventional EDM. The
dielectric. A wire EDM (WEDM) generates prominent feature of a moving wire is that a
spark discharges between a small wire complicated cutout can be easily machined
electrode and a work piece with de-ionized without using a forming electrode. Wire cut
water as the dielectric medium and erodes EDM machine basically consists of a
the work piece to produce complex two and machine proper composed of a work piece
three dimensional shapes according to a contour movement control unit (NC unit or
computer numerically controlled (CNC) copying unit), work piece mounting table
path. The main goals of WEDM and wire driven section for accurately
manufacturers and users are to achieve a moving the wire at constant tension, a

2. machining power supply which applies according to the material and height of the
electrical energy to the wire electrode and a work piece and tool material from a manual
unit which supplies a dielectric fluid provided by the WEDM manufacturer. it has
(distilled water) with constant specific several special features.
resistance. For the optimal selection of Principle of CNC WEDM:
process parameters, the Taguchi method has In wire EDM, the conductive materials
been extensively adopted in manufacturing are machined with a series of electrical
to improve processes with single discharges (sparks) that are produced
performance characteristic. between an accurately positioned moving
wire (the electrode) and the work piece.
High frequency pulses of alternating or
Experimental Process: direct current is discharged from the wire to
Figure 1 depicts schematically the the work piece with a very small spark gap
experimental set up. through an insulated dielectric fluid (water).
Many sparks can be observed at one
time. This is because actual discharges can
occur more than one hundred thousand times
per second, with discharge sparks lasting in
the range of 1/1,000,000 of a second or less.
The volume of metal removed during this
short period of spark discharge depends on
the desired cutting speed and the surface
finish required. The heat of each electrical
spark, estimated at around 15,000° to
21,000° Fahrenheit, erodes away a tiny bit
of material that is vaporized and melted
Fig: 1 Experimental set up
from the work piece. (Some of the wire
Wire EDM uses deionized water as a
material is also eroded away) These particles
dielectric fluid in this experiment. Diameter
(chips) are flushed away from the cut with
of electrode and thickness of work piece is
stream of de-ionized water through the top
measured by digimatic micrometer. (Make:
and bottom flushing nozzles. The water also
Mitutoyo, Least count: 0.001 mm). Weight
prevents heat build-up in the work piece.
of work piece is measured by Precisa-make
Without this cooling, thermal expansion of
weighing machine (Accuracy: 0.1mg).
the part would affect size and positional
The experiments were performed on
accuracy. Keep in mind that it is the ON and
FA10S MITSUBISHI high precision CNC
OFF time of the spark that is repeated over
WEDM, The basic parts of the WEDM
and over that removes material, not just the
machine consists of a wire, a work table, a
flow of electric current. Al-6061 material
servo mechanism, a power supply and
was the target material used in this
dielectric supply system. It allows the
Investigation.
operator to choose input parameters

3. Properties of Aluminium-6061: Taguchi Method:
Properties It is a quality control methodology that
Density (g/cm3 ) 2.7 combines control chart and process control
Melting Point (°C) 580 with product and process design to achieve a
Modulus of Elasticity 70-80 robust total design. It aims to produce
(GPa)
product variability with a system for
Thermal Conductivity 173
(W/m.K) developing specifications and designing
Electrical Resistivity 3.7 – 4.0 x10-6 them into a product or process. Taguchi
(Ω.cm) methods focus on design – the development
Co-Efficient of Thermal 23.5x10-6 of superior performance designs (of
Expansion (m/m.°C) products and manufacturing processes) to
deliver quality.
Design of Experiments: Two major tools used in Taguchi’s
Design of experiments (DOE) or method are one is signal(S) to noise (N)
experimental design is the design of any ratio i.e. S/N ratio to measure the quality and
information gathering exercises where the other is orthogonal arrays to
variation is present, whether under the full accommodate many factors simultaneously
control of the experimenter or not. to evaluate the machining performances.
Design process should be seen as three The ability of orthogonal arrays lies in
stages: evaluating the machining performance with
Systems design a less number of experiments when
Parameter design compared to full factorial experiments
Tolerance design. which reduces the number of trials. This
System design identifies the basic greatly reduces the time required in
elements of the design, design at the conducting the experiments and also in
conceptual level, involving creativity and evaluating the significant and insignificant
innovation. parameters.
Parameter design determines the most The general steps involved in the Taguchi
appropriate, optimizing set of parameters Method are as follows:
covering these design elements by 1. Define the process objective, or more
identifying the settings of each parameter specifically, a target value for a performance
which will minimize variation from the measure of the process.
target performance of the product. 2. Determine the design parameters affecting
Tolerance design finally identifies the the process. Parameters are variables within
components of the design which are the process that affect the performance
sensitive in affecting the quality of the measure
product and establishes tolerance limits 3. Create orthogonal arrays for the
which will give the required level of parameter design indicating the number and
variation in the design. conditions for each experiment. The
selection of orthogonal arrays is based on

4. the number of parameters and the levels of Table1: Taguchi L9 Orthogonal Array
variation for each parameter, and will be Design Matrix
expounded below.
4. Conduct the experiments indicated in the Exp. No. Factor 1 Factor 2 Factor 3 Factors 4
01 1 1 1 1
completed array to collect data on the effect 02 1 2 2 2
on the performance measure. 03 1 3 3 3
5. Complete data analysis to determine the 04 2 1 2 3
effect of the different parameters on the 05 2 2 3 1
06 2 3 1 2
performance measure.
07 3 1 3 2
08 3 2 1 3
DOE for CNC WEDM of Al-6061 09 3 3 2 1
Material: Responses measured:-
The design of experiment chosen for the 1) Machining time (MT),
WEDM of Al-6061 was a Taguchi L9 2) Surface Roughness (SR).
orthogonal array, by carrying out a total
number of 9 experiments along with 2 Table2: Level values of input factors
verification experiments (optional). Testing
L9 Orthogonal Array: Symbols Level1 Level2 Level3
parameters
In L9 (34) array 9 rows represent the 9 A Voltage (V) 7 12 16
experiment to be conducted with 3 columns B Current(I) 3 6 12
at 3 levels of the corresponding factor. The Voltage gap
C 51 59 75
matrix form of these arrays is Shown, where (Vg)
Wire tension
1, 2, 3 in the table represents the level of D 7 8 10
(WT)
each parameters.
Table 3: L9 Design Matrix
Input Factors:-
Parameter level
1) Voltage (v) Exp no.
2) Current (Ip) A B C D
3) Voltage gap (Vg) 1 7 3 51 7
4) Wire tension (WT) 2 7 6 59 8
3 7 12 75 10
4 12 3 59 10
5 12 6 75 7
6 12 12 51 8
7 16 3 75 8
8 16 6 51 10
9 16 12 59 7

5. Table4: Experimental Results and A sample calculation is shown for factor
Calculations of Various Response Factors B [current]:
based on Taguchi L9 Orthogonal Array
Exp no. MT in min SR in µm Sn1 = = 38.99
1 2 1 2
1 4.8 4.86 16.9 17.1 Sn2 = = 32.718
2 4.7 4.63 15.8 16.3
3 4.92 5 16.7 17.1
Sn3 = = 35.057
4 4.24 4.4 36.3 35.8
5 5.2 5 34.8 35.3
Δ = 38.99 – 32.718 = 6.272
6 4.83 4.72 16.7 17
7 4.62 4.58 15.8 16.32 Table 6: Response Table for Signal to
8 4.9 5.2 35.2 34.9
Noise Ratios for MT
9 4.44 4.63 35 35.1
leve A B C D
l [voltag [current] [voltag [wire
For machining time:
e]in v in amp e gap] tension
Sm1= = 46.6578 ]
1 39.823 38.99 34.806 34.272
St1 = (4.82+4.862) = 46.6596 2 32.843 32.718 33.889 39.823
3 34.102 35.057 35.073 32.672
Se1 = St1 – Sm1 = 1.8×10-3 Δ 6.9794 6.272 4.1847 7.151
rank 2 3 4 1
ve = = = 1.8×10-3
Therefore, wire tension (WT) has the
maximum effect on machining time.
S
n1 =10log [ ] = 41.126
Table 7: Calculation of Signal to Noise
Table 5: Calculation of Signal to Noise ratio for SR
ratio for MT
Exp Parameters SR in µm SN
Parameters level MT in min SN
Exp no. level
no. A B C D 1 2
A B C D 1 2
1 1 1 1 1 16.9 17.1 41.598
1 1 1 1 1 4.8 4.86 41.126
2 1 2 2 2 4.7 4.63 39.485 2 1 2 2 2 15.8 16.3 33.139
3 1 3 3 3 4.92 5 38.8578 3 1 3 3 3 16.7 17.1 35.526
4 2 1 2 3 4.24 4.4 31.63
4 2 1 2 3 36.3 35.8 40.168
5 2 2 3 1 5.2 5 31.1394
6 2 3 1 2 4.83 4.72 35.7613 5 2 2 3 1 34.8 35.3 39.924
7 3 1 3 2 4.62 4.58 44.244 6 2 3 1 2 16.7 17 37.990
8 3 2 1 3 4.9 5.2 27.5298 7 3 1 3 2 15.8 16.3 32.804
9 3 3 2 1 4.44 4.63 30.522
8 3 2 1 3 35.2 34.9 44.362
9 3 3 2 1 35 35.1 53.904

6. publishing Company Limited, New Delhi,
(1999).
Table 8: Response Table for Signal to 2. Phadke M.S, Quality Engineering Using
Noise ratios for SR Robust Design, Prentice- Hall, Englewood
Cliffs,NJ, (1989).
leve A B C D
3. Williams, R.E., Rajurkar, K.P., Study of
l [voltage [current] [voltage [wire
Wire Electrical Discharge Machining
] in v in amp gap] tension]
Surface Characteristics, Journal of
1 36.754 38.19 41.32 45.142 Materials Processing Technology, Vol. 28,
2 39.36 39.1415 42.4036 34.65 pp.486-493, (1991).
3 43.6898 42.48 36.0846 40.108 4. R.E. Williams, K.P. Rajurkar, Study of
Δ 6.9358 4.29 6.32 10.49 wire electrical discharge machined surfaced
rank 2 4 3 1 characteristics, J. Mater. Process. Technol.
28 (1991) 127–138.
5. R .Ramakrishnan, L .Karunamoorthy,
Therefore wire tension (WT) has the
“Surface roughness model for CNC wire
largest effect on surface roughness.
electro discharge machining”, J Manuf
CONCLUSION: Technol Today, 2004, Vol. 3(5), pp. 8-11.
6. Phillip J. Ross. Taguchi techniques for
The machining time (MT) mainly
affected by wire tension (WT).voltage (V) quality engineering, McGraw-Hill Book
company, New York
has less effect on it. Voltage gap (Vg) and
7. Dr. S. S. Khandare & Mitesh a. Popat,
current (I) has a least effect on MT. The
Experimental Investigations of EDM to
surface roughness (SR) is mainly influenced
optimize Material Removal Rate & Surface
by wire tension (WT). The effect of voltage
Roughness through Taguchi’s Technique of
gap (Vg) and voltage (V) is less on SR and
Design of Experiments. IEEE explore,
current (I) has least effect on it.
ICETET-09, pg 476 – 482 Print ISBN: 978-
Some portion of the material is
1-4244-5250-7, (2009).
conductive and some portion is non-
conductive wherein CNC WEDM requires 8. T.A. Spedding and Z.Q. Wang.
Parametric optimization and surface
conductive work piece. So the composite
characterization of wire electrical discharge
properties of the work piece also lead to
machining process. Precis. Eng. 20(1): pp.5-
some observations which contradict the
theoretical belief. 15, 1997.
9. R. E. Williams and K. P. Rajurkar, Study
of wire electrical discharged machine
REFERENCES surface characteristics, Journal of Materials
1.Pandey P C , Shan H S, Modern Processing Technology,28(1991) pp.
Machining Processes, Tata McGraw-Hill 127-13