Study of EDM Parameters on Mild Steel Using Brass Electrode

International Journal of Engineering Trends and Technology (IJETT) – Volume17 Number7–Nov2014

ISSN: 2231-5381 http://www.ijettjournal.org Page 305

Study of EDM Parameters on Mild Steel Using Brass Electrode Amit Kumar#1, Abhishek Gaikwad*2, Amit Tiwari#3

# 1,3,Production Engineering (ME), SSET, Allahabad-211007, SHIATS, Allahabad, Uttar Pradesh (India)

*2 Assistant Professor, Dept of Mechanical Engineering, SSET, Allahabad-211007 (U.P)

Abstract— Optimization is one of the techniques used in manufacturing sectors to arrive for the best manufacturing conditions, which is an essential need for industries towards manufacturing of quality products at lower cost. This paper aims to study of process parameters such as current, pulse ON and OFF time in Electrical Discharge Machining (EDM) process to identify the variations in three performance characteristics such as material removal rate, electrode wear rate, for machining Mild Steel using brass electrode. Based on the experiments conducted on L9 orthogonal array, study has been carried out using Taguchi method. Response tables and graphs were used to find the optimal levels of parameters in EDM process. The confirmation experiments were carried out to validate the optimal results. Thus, the machining parameters for EDM were optimized for achieving the combined objectives of higher rate of material removal, lower wear rate on tool, on the work material considered in this work. The obtained results show that the Taguchi method study is being effective technique to find the best machining parameters for EDM process. Keywords— EDM, EWR, MRR, Taguchi Technique.

I. INTRODUCTION Electric discharge machining (EDM) has widespread applications for manufacturing dies and tools to produce plastics moldings, die casting, and sheet metal dies etc[1][2]. Implementation of EDM process will awaken manufacturing engineers, product designers, tool engineer and metallurgical engineers about unique capabilities and benefits of this process [3].where the process is based on removing material from a part by means of a series of repeated electrical discharges between tool called the electrode and the work piece in the presence of a dielectric fluid [4]. The electrode is moved toward the work piece until the gap is small enough so that the impressed voltage is great enough to ionize the dielectric [5]. Short duration discharges are generated in a liquid dielectric gap, which separates tool and work piece. The material is removed with the erosive effect of the electrical discharges from tool and work piece [6]. EDM does not make direct contact between the electrode and the work piece where it can eliminate mechanical stresses chatter and vibration problems during machining [7]. Materials of any hardness can be cut as long as the material can conduct electricity [8]. EDM techniques have developed in many areas. Trends on activities carried out by researchers depend on the interest of the researchers and the availability of the technology.

The objective of the present work is to investigate MRR and EWR on EDM of Mild Steel and to optimize these

performance characteristics with maximum MRR and minimum EWR, simultaneously.

II. MATERIAL PROPERTIES A. Workpiece properties

Mild steel is chosen as the work piece material and brass material is used as the tool electrode material. The work material properties and the photographic view of workpiece are given in Table.1and Fig.1.respectively.

TABLE 1 CHEMICAL COMPOSITION OF MILD STEEL

Fe C Ni Mn Si P S 98.977% 0.095% 10-14% 0.490% 0.251% 0.011% 0.014%

Fig 1 Mild Steel used for experiment

B. Electrode (Tool) Properties In this experiment brass is selected as a tool material. The physical properties of electrode material and the photographic view of electrode are given in Table.2 and Fig.2 respectively.

TABLE 2 PHYSICAL PROPERTIES OF ELECTRODE MATERIAL

Properties Cu-Zn (60-40)

Melting point (oC) 910

Density (g/cm3) 10.98 g / cm3

Electrical conductivity(I.A.C.S% at 20 oC) 78~85

Hardness(HRB) 93

Elastic modulus (GPa) 648



Fig 2 brass electrode used for experiment

III. EXPERIMENTAL DATA The machining parameters chosen for the present experiment are Pulse-on time (ton) is the duration of time (in µs). The discharge current, Ip (in Amp) is allowed to flow per cycle. Pulse-off time (toff) be the duration of time (in µs) between two consecutive sparks and fluid pressure (in kg/cm2)

IV. EXPERIMENTAL METHOD Control parameters selected for the present experiment .i.e. Discharge current (in Amp),Pulse-on time (in µs). Pulse-off time (in µs) and fluid pressure (in kg/cm2). Machining was carried out on EDM of Electronic Electra plus C 3822 Die Sinking Machine as shown in Fig 3. Machine is provided with fixed pulse voltage. The control parameters were selected from the range. EDM has maximum discharge current capacity of 20 Ampere. A servo mechanism maintains a gap of about 0.01 to 0.02mm between the electrode & the workpiece, 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 workpiece through the dielectric fluid. A series of experiments have been conducted by varying control parameters such as current, pulse on time, pulse off time, fluid pressure with each has 3 levels. Commercial grade kerosene is used as dielectric fluid to analyses the effects on MRR as per the Taguchi orthogonal L9 array. A brass electrode of diameter 5 mm is used as cutting tool and the work piece of Mild steel is machined for 20 minutes to record the readings. Observations are taken in the form of mass of material removed per min (gram/min) for both work piece and brass electrode. Mass lost is measured with accuracy 0.001 milligram. The data collected in MRR and EWR form is optimized and analyzed by Taguchi technique.

Fig 3 EDM machine used for experiment

V. MRR AND EWR MRR = Material Removal Rate EWR = Electrode Wear Rate The material removal rate (MRR) of the work piece can be calculated by using the following equation.

MRR = The electrode wear rate (EWR) of the electrode can be calculated by using the following equation. EWR =

VI. SIGNAL TO NOISE RATIO Taguchi's emphasis on minimizing deviation from target led him to develop measures of the process output that incorporate both the location of the output as well as the variation. These measures are called signal to noise ratios. The signal to noise ratio provides a measure of the impact of noise factors on performance. The larger the S/N, the more robust the product is against noise. Calculation of the S/N ratio depends on the experimental objective:



In Case of MRR: Bigger-the-Better

In Case of EWR: Smaller-the-Better

VII. DESIGN OF EXPERIMENT AND DATA ANALYSIS Design of experiment is the step before starting the experimental work. Design of experiments (DOE) is used to study the effect of multiple variable simultaneously, which is a powerful statistical technique introduced by R.A.Fisher in England in 1920’s.The design of experiment (D.O.E.) chosen for the electric discharge machining of Mild steel was a Taguchi L9 orthogonal array, by carrying out a total number of 9 experiments along with 4 verification experiments (optional). In L9 (34) array 9 rows represent the 9 experiment to be conducted with 4 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.

TABLE 3 LEVEL VALUES OF INPUT FACTOR

Factor Levels 1 2 3

Pulse ON time (µs)

4 8 12

Pulse OFF time (µs)

2 4 6

Discharge current (A)

4 6 8

Fluid Pressure ( kg/cm2 )

0.1 0.2 0.3

TABLE 4 DESIGN MATRIX OF L9 ORTHOGONAL ARRAY

Exp. No. Factor A Factor B Factor C Factor D 1 1 1 1 1 2 1 2 2 2 3 1 3 3 3 4 2 1 2 3 5 2 2 3 1 6 2 3 1 2 7 3 1 3 2 8 3 2 1 3 9 3 3 2 1

TABLE 5 EXPERIMANTAL MATRIX OF L9 ORTHOGONAL ARRAY

Exp. No.

Pulse on

Time (µ Sec)

Pulse off

Time (µ Sec)

Current (A)

Fluid Pressure (Kg/cm3)

M.R.R gm/min

E.W.R gm/min

1 4 2 4 0.1 0.0005 0.0065 2 4 4 6 0.2 0.003 0.003 3 4 6 8 0.3 0.007 0.0215 4 8 2 6 0.3 0.002 0.0145 5 8 4 8 0.1 0.008 0.037 6 8 6 4 0.2 0.006 0.019 7 12 2 8 0.2 0.003 0.008 8 12 4 4 0.3 0.0015 0.0005 9 12 6 6 0.1 0.01 0.0075

TABLE 6

OBSERVATION OF S/N RATIO

Exp. No.

Pulse on

Time (µ Sec)

Pulse off

Time (µ Sec)

Current (A)

Fluid Pressure (Kg/cm3

)

S/N Ratio (MRR)

S/N Ratio (EWR)

1 4 2 4 0.1 -66.0206 43.7417 2 4 4 6 0.2 -50.4576 50.4576 3 4 6 8 0.3 -43.0980 33.3512 4 8 2 6 0.3 -53.9794 36.7726 5 8 4 8 0.1 -41.9382 28.6360 6 8 6 4 0.2 -44.4370 34.4249 7 12 2 8 0.2 -50.4576 41.9382 8 12 4 4 0.3 -56.4782 66.0206 9 12 6 6 0.1 -40.0000 42.4988

TABLE 7 S/N RATIO FOR EWR

LEVEL

Pulse on

Pulse off

Current Fluid

Pressure

1 42.52 40.82 48.06 38.29 2 33.28 48.37 43.24 42.27 3 50.15 36.76 34.64 45.38

DELTA 16.88 11.61 13.42 7.09 RANK 1 3 2 4

TABLE 8 RESPONSE MEAN FOR EWR

LEVEL

Pulse on

Pulse off

Current Fluid

Pressure

1 0.010333 0.009667 0.008667 0.017000 2 0.023500 0.013500 0.008333 0.010000 3 0.005333 0.016000 0.022167 0.012167

DELTA 0.018167 0.006333 0.013833 0.007000



TABLE 9 S/N RATIO FOR MRR

LEVEL

Pulse on

Pulse off

Current Fluid

Pressure

1 -53.19 -56.82 -55.65 -49.32 2 -46.78 -49.62 -48.15 -48.45 3 -48.96 -42.51 -45.16 -51.19

DELTA 6.41 14.31 10.48 2.73 RANK 3 1 2 4

TABLE 10 RESPONSE MEAN FOR MRR

LEVEL

Pulse on

Pulse off

Current Fluid

Pressure

1 0.003500 0.001833 0.002667 0.006167 2 0.005333 0.004167 0.005000 0.004000 3 0.004833 0.007667 0.006000 0.003500

DELTA 0.001833 0.005833 0.003333 0.002667

VIII. RESULT AND ANALYSIS

1284

-42

-44

-46

-48

-50

-52

-54

-56

-58642 864 0.30.20.1

Pulse on

Mea

n of

SN

ratio

s

Pulse off Current Fluid Pressure

Main Effects Plot for SN ratiosData Means

Signal-to-noise: Larger is better

Fig 4 Mean of SN Ratio of MRR

1284

0.008

0.007

0.006

0.005

0.004

0.003

0.002

642 864 0.30.20.1

Pulse on

Mea

n of

Mea

ns


Main Effects Plot for MeansData Means

Fig 5 Mean of Means of MRR

1284

50

45

40

35

642 864 0.30.20.1

Pulse onM

ean

of S

N ra

tios

Pulse of f Current Fluid Pressure

Main Effects Plot for SN ratiosData Means

Signal-to-noise: Smaller is better

Fig 6 Mean of SN Ratio of EWR



1284

0.025

0.020

0.015

0.010

0.005

642 864 0.30.20.1

Pulse onM

ean

of M

eans


Main Effects Plot for MeansData Means

Fig 7 Mean of Means of EWR

IX. CONCLUSIONS The Die-sinker EDM is widely used machine for machining of hard material with high precision, high surface finish, complex profiles. The cost incurred for machining of hard and complex profile parts is less than the other methods of machining. From the results it is found that The Material removal rate is increased when pulse on time is increased. MRR mainly affected by current and pulse off time. MRR least affected by fluid pressure. Optimum parameters of input factors are as follows: Current: 8Amp, Pulse on time:8 µ sec, Pulse off time :6 µ sec Fluid Pressure :0.2 kg/cm2 EWR is mainly affected by current followed by pulse off time. Electrode wear rate is least affected by fluid pressure. Optimal parameters of input factors are as follows: Current: 6Amp, Pulse on time: 12 µ sec, Pulse off time: 2 µ sec, Fluid Pressure: 0.2 kg/cm2

Acknowledgment The authors are thankful to faculty members of SSET and M/s Rajat Engineers and their Technical assistance, staff for giving full support during the performance of the experiment. The authors are also extremely thankful to the Head of Department of Mechanical Engg and research advisor for their motivation during research work.

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viable alternatives for production with specific reference to electric discharge machining”, J Sci Ind Res,62(2002) 678- 682.

[3] Singh S, Maheshwari S & Pandey P C, “Some investigations into the electric discharge machining of hardened tool steel using different electrode materials”, J Mater Process Technol, 149 (2004) 272 277.

[4] C.J. Luis, I. Puertas, G. Villa, Material removal rate and electrode wear study on the EDM of silicon carbide, Journal of Materials Processing Technology 164–165 (2005) 889–896.

[5] B. Bojorquez, R.T. Marloth, O.S. Es-Said, Formation of a crater in the workpiece on an electrical discharge machine, Engineering Failure Analysis 9 (2002) 93–97.

[6] J. Marafona, J.A.G. Chousal, A finite element model of EDM based on the Joule effect, International Journal of Machine Tools & Manufacture 46 (2005) 1–8.

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Study of EDM Parameters on Mild Steel Using Brass Electrode