This document summarizes a study that used the Taguchi method to analyze the effect of parameters like voltage, current, and pulse on time on material removal rate (MRR) and surface roughness (SR) during CNC EDM of SK-5 material. Experiments were conducted based on an L9 orthogonal array with 3 factors at 3 levels. Analysis found voltage had the largest effect on MRR while pulse on time most influenced SR. The optimized parameters were experiment 4 for MRR and experiment 7 for SR. In conclusion, the Taguchi method helped determine the best settings of CNC EDM parameters for machining SK-5.

1. IMPLEMENTATION OF TAGUCHI METHOD ON CNC EDM FOR SK5
MATERIAL
Kiran.H.G1, Raghunandan.H.S1, Lingaraju.K.N, 1 Ramesh Babu.K2
[1] Dept. of Mechanical Engineering, Govt. Engineering College. Chamarajanagar-571313, Karnataka
[2] Dept. of PG Studies, Govt. Tool Room and Training Centre, plot no. 93 & 94, K.R.S road Mysore-16.
ABSTRACT
Electrical discharge machining (EDM) is a non conventional machining process for
shaping hard metals and forming deep complex shaped holes by arc erosion in all kinds of
electro-conductive materials. EDM is a thermoelectric process in which heat energy of spark is
used to remove material from the work piece. In this paper, the cutting of Sk-5 material using
electro discharge machining (CNC EDM) with a copper electrode by using Taguchi
methodology has been reported. The Taguchi method is used to formulate the experimental
layout, to analyze the effect of each parameter on the machining characteristics, and to predict
the optimal choice for each CNC EDM parameter such as current, voltage and pulse ON time. It
is found that these parameters have a significant influence on machining characteristic such as
material removal rate (MRR) and surface roughness (SR).
KEYWORDS: CNC EDM, Taguchi method, DOE, Orthogonal array, Material removal rate,
Surface roughness.
1. INTRODUCTION:
Electrical Discharge Machining or EDM is a machining method primarily used for hard
metals or those that would be impossible to machine with traditional techniques. The non-contact
machining technique has been continuously evolving from a mere tool and dies making process
to a micro-scale application machining alternative attracting a significant amount of research
interests.CNC EDM is especially well-suited for cutting intricate contours or delicate cavities
that would be difficult to produce with other cutting tools. Metals that can be machined with
CNC EDM include hardened tool-steel, titanium and carbide etc. One critical limitation,
however, is that CNC EDM only works with materials that are electrically conductive. CNC
EDM is a thermoelectric process in which heat energy of spark is used to remove material from
the work piece. The work piece and the tool should be made of electrically conductive material.
A spark is produced between the two electrodes (tool and work piece) and its location is
determined by the narrowest gap between the two. Duration of each spark is very short. The
entire cycle time is usually few micro-seconds (μs). The frequency of sparking may be as high as
thousands of sparks per second. The area over which a spark is effective is also very small.
Temperature of the area under the spark is very high. As a result, the spark energy is capable of
partly melting and partly vaporizing material from the localized area on both the electrodes, i.e.
the work piece and tool. The material is removed in the form of craters, which spread over the
entire surface of the work piece. Finally, the cavity produced in the work piece is approximately
the replica of the tool.

2. 2. Experimental Process:
CNC EDM oil was used as a dielectric fluid in this experiment. Diameter of electrode and
thickness of work piece is measured by digimatic micrometer. (Make: Mitutoyo, Least count:
0.001 mm). Weight of work piece is measured by Precisa-make weighing machine (Accuracy:
0.1mg). Figure 1 depicts schematically the experimental set up.
Fig: 1 Experimental set up
2.1. Principle of CNC EDM:
Electric discharge machining is a controlled metal removing technique whereby an electric
spark is used to cut the work piece, which takes a shape opposite to that of the cutting tool or
electrode. The electrode is made from electrically conductive material. The electrode, made to
the shape of the cavity required, and the work pieces are both submerged in a dielectric fluid.
Dielectric fluid should be nonconductor of electricity. A servo mechanism maintains a gap of
about 0.01 to 0.02mm between the electrode & the work piece, preventing them from coming
into contact with each other. A direct current of low voltage & high amperage is delivered to the
electrode at the rate of approximately 50 KHz. These electrical energy impulses vaporize the oil
at this point. This permits the spark to jump the gap between the electrode and the work piece
through the dielectric fluid. Intense heat is created in the localized area of the spark impact, the
metal melts and a small particle of molten metal is expelled from the surface of the work piece.
The dielectric fluid which is constantly being circulated carries away the eroded particles of
metal during the off cycle of the pulse and also assists in dissipating the heat caused by the spark.
The experiments were performed on EDNC 32H MAKINO high precision CNC EDM.
Servo Mechanism:
It is important that there is no physical contact between electrode & work piece, otherwise
both electrode & work piece will be damaged. Electro discharge machines are equipped with a
servo control mechanism that automatically maintains a constant gap of 0.01mm to 0.02mm
between the electrode & work piece. If the gap is too large, ionization of the dielectric fluid does
not occur and machining cannot take place. If the gap is too small, the tool and the work piece
may weld together. Servo feed control mechanisms can be used to control the vertical movement
of the electrode fro sinking cavities.
Sk-5 material was the target material used in this Investigation. Experiments were
performed using an electric discharge machine. A copper as an electrode to erode a work piece
of Sk-5.
Alloy steel (SK-5) properties:

3. properties T (°C)
Density (×1000 kg/m3) 7.7-8.03 25
Elastic Modulus (GPa) 190-210 25
Yield Strength (Mpa) 1034 25
Hardness (HB) 335 25
Thermal Conductivity (W/m-K) 42.7 100
Melting temperature (°C) 477 1370 - 1400
Specific Heat (J/kg-K) 1370 - 1400 50-100
2.2. Design of Experiments:
Design of experiments (DOE) or experimental design is the design of any information
gathering exercises where variation is present, whether under the full control of the experimenter
or not.
Design process should be seen as three stages:
Systems design
Parameter design
Tolerance design.
Systems design identifies the basic elements of the design, which will produce the desired
output, such as the best combination of processes and materials.
Parameter design determines the most appropriate, optimizing set of parameters covering
these design elements by identifying the settings of each parameter which will minimize
variation from the target performance of the product.
Tolerance design finally identifies the components of the design which are sensitive in
affecting the quality of the product and establishes tolerance limits which will give the required
level of variation in the design.
2.3. Taguchi Method:
Taguchi methods are the most recent additions to the toolkit of design, process and
manufacturing engineers, and quality assurance experts. In contrast to statistical process control,
which attempts to control the factors that adversely affect the quality of production, Taguchi
methods focus on design – the development of superior performance designs (of products and
manufacturing processes) to deliver quality.

4. An experimental design scheme of statistical experiments that uses orthogonal arrays
however entails the following considerations and consequences:
1). Define the process objective, or more specifically, a target value for a performance measure
of the process. This may be a MRR, SR etc. The target of a process may also be a minimum or
maximum.
2). Determine the design parameters affecting the process. Parameters are variables within the
process that affect the performance measure such as MRR, SR etc. that can be easily controlled.
The number of levels that the parameters should be varied at must be specified.
3). Create orthogonal arrays for the parameter design indicating the number of and conditions for
each experiment. The selection of orthogonal arrays is based on the number of parameters and
the levels of variation for each parameter, and will be expounded below.
4). Conduct the experiments indicated in the completed array to collect data on the effect on the
performance measure.
5). Complete data analysis to determine the effect of the different parameters on the performance
measure.
3.1. Design of Experiment for CNC EDM of Sk-5 Material:
The design of experiment (D.O.E.) chosen for the electric discharge Machining of Sk-5 was
a Taguchi L9 orthogonal array, by carrying out a total number of 9 experiments along with 2
verification experiments (optional).
L9 Orthogonal Array:
In L9 (34) array 9 rows represent the 9 experiment to be conducted with 3 columns at 3
levels of the corresponding factor. The matrix form of these arrays is Shown in Table 3, where 1,
2, 3 in the table represents the level of each parameters.
Input Factors:-
1) Voltage (V).
2) Current (I),
3) Pulse – On Time (Ton),
Exp. No. Factor 1 Factor 2 Factor 3
01 1 1 1
02 1 2 2
03 1 3 3
04 2 1 2
05 2 2 3
06 2 3 1
07 3 1 3
08 3 2 1
09 3 3 2
Table1: Taguchi L9 Orthogonal Array Design Matrix

5. Responses measured:-
1) Material Removal Rate (MRR),
2) Surface Roughness (SR).
Symbols Testing parameters Level1 Level2 Level3
A Voltage (V) 20 22 25
B Current(I) 10 19 45
C Pulse ON time(Ton) 48 58 75
Table2: Level values of input factor
Exp no. Parameter level
A B C
1 20 10 48
2 20 19 58
3 20 45 75
4 22 10 58
5 22 19 75
6 22 45 48
7 25 10 75
8 25 19 48
9 25 45 58
Table 3: L9 Design Matrix
Exp no. MRR in g/min SR in µm
1 2 1 2
1 .114 .116 45 47
2 .198 .195 59 60
3 .46 .5 95 92
4 .27 .32 60 61
5 .635 .66 88 84
6 .506 .49 78 76
7 .77 .73 103 96
8 .38 .4 66 68
9 .8475 .8 109 114
Table4: Experimental Results & Calculation of Various Response Factors based on
Taguchi L9 Orthogonal Array

6. For Material Removal Rate:
Sm1= =.02645
St1 = (.114 +.1162) =.026452
2
Se1 = St1 – Sm1 = .2 ×10-6
ve = = = 2×10-6
S
n1 =10log [ ] = 38.203
Exp no. Parameters level MRR in g/min SN
A B C 1 2
1 1 1 1 .114 .116 38.2033
2 1 2 2 .198 .195 39.335
3 1 3 3 .46 .5 24.586
4 2 1 2 .27 .32 18.39
5 2 2 3 .635 .66 31.2746
6 2 3 1 .506 .49 32.871
7 3 1 3 .77 .73 28.467
8 3 2 1 .38 .4 28.808
9 3 3 2 .8475 .8 27.788
Table 5: Calculation of Signal to Noise ratio for MRR
A sample calculation is shown for factor B [current]:
Sn1 = = 28.3534
Sn2 = = 33.145
Sn3 = = 28.415
Δ = 33.6713 – 28.3534 = 4.79
level A [voltage] in v B [current] in amp C [pulse ON time]
1 34.04 28.3534 33.294
2 27.511 33.145 28.5043
3 28.3543 28.415 28.1092
Δ 6.529 4.79 5.1848
rank 1 3 2
Table 6: Response Table for Signal to Noise Ratios for MRR
Therefore, voltage (V) has the maximum effect on material removal rate.

7. Exp no. Parameters level SR in µm SN
A B C 1 2
1 1 1 1 45 47 30.24
2 1 2 2 59 60 38.500
3 1 3 3 95 92 32.88
4 2 1 2 60 61 38.645
5 2 2 3 88 84 29.656
6 2 3 1 78 76 34.718
7 3 1 3 103 96 26.059
8 3 2 1 66 68 33.510
9 3 3 2 109 114 29.97
Table 7: Calculation of Signal to Noise ratio for SR
level A [voltage] in v B [current] in amp C [pulse ON time]
1 33.87 31.648 33.822
2 34.34 33.888 35.705
3 29.85 32.522 29.532
Δ 4.49 2.241 6.173
rank 2 3 1
Table 8: Response Table for Signal to Noise Ratios for SR
Therefore pulse ON time has the largest effect on surface roughness.
4. CONCLUSION:
The material removal rate (MRR) mainly affected by Voltage (v). Pulse-on time (Ton)
has less effect on it. Current (I) has a least effect on MRR. The surface roughness (SR) is mainly
influenced by pulse-on time (Ton). The effect of voltage (V) has less on SR and current (I) has
least effect on it.
Exp no. 4 is the OPTIMIZED PARAMETER for MATERIAL REMOVAL RATE and Exp
no. 7 is the OPTIMIZED PARAMETER for SURFACE ROUGHNESS.
Some portion of the material is conductive and some portion is non-conductive wherein
CNC EDM requires conductive work piece. So the composite properties of the work piece also
lead to some observations which contradict the theoretical belief.

8. REFERENCES
1. I Puertas, C J Luis, L Alvarez, Analysis of the influence of CNC EDM parameters on surface quality,
MRR and SR of WC-Co. Public university of Navarre (Spain)
2. Yan B. H., Tsai H. C., Huang F. Y., The effect in CNC EDM of a dielectric of a urea solution in water
on modifying the surface of titanium, International Journal of Machine Tools & Manufacture 45 (2005),
p. 194 – 200.
3. Chen S. L., Yan B. H., Huang F. Y., Influence of kerosene and distilled water as dielectrics on the
electric discharge machining characteristics of Ti– 6A1–4V, Journal of Materials Processing Technology
87 (1999), p. 107 – 111.
4. C.J.Luis, I Puretas, G. Villa, Material removal rate & electrode Wear study on the CNC EDM of silicon
Carbide, Journal of Materials Processing Technology 164-164 92005) p.889-896.
5. A.A.Khan, Electrode wear & Material removal rate during CNC EDM of aluminum & mild steel using
copper and brass electrodes. Springer- verlsk-5 London Limited 2007.
6. Ranjit K.Roy, Design of Experiments Using the Tsk-5uchi Approach, John Wiley & Sons, New York,
2001.
7. P.M.George, B.K.Raghunath, L.M. Manocha, Ashish M Warrier, CNC EDM machining of Carbon
Carbon composite- a Taguchi approach.
8. Ali Ozgedik, Can Cogan, An Experimental investigations of tool wear in electric discharge machining,
Received on 07/10/2003
9. K. H. Ho, S .T .Newman, State of the art electrical discharge machining (CNC EDM), International
journal of Machine Tools & Manufacture 43 (2003) 1287- 1300