Comparative study on variation of process characteristics on al and die steel process

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN

0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME

170

COMPARATIVE STUDY ON VARIATION OF PROCESS

CHARACTERISTICS ON AL AND DIE STEEL COMPONENTS IN

SINK EDM PROCESS

1K.L.Uday Kiran,

2R.Rajendra,

3G.Chandramohan Reddy,

4A.M.K Prasad

1, 2, 4 University College of Engineering, Osmania University, Hyderabad, A.P, India

3Mahatma Gandhi Institute of Technology, Hyderabad, A.P, India

ABSTRACT:

Electrical Discharge Machining (EDM) process is a well established non-traditional

machining option for manufacturing geometrically complex and hard material parts that are extremely

difficult to machine by conventional machining process. In this process the material removal is

occurred electro thermally by a series of successive discrete discharges between electrode and the

work piece.

This paper presents the results of experimental studies carried out to conduct a comprehensive

investigation on the influence of EDM parameter (current) on process characteristics in sink EDM

process. The studied process characteristics included material removal rate, tool wear ratio, and

surface roughness parameters of two work pieces (Al & Die steel) by using a common tool (Cu). The

variation of process characteristics at different currents was studied. The observation revealed that the

MRR, TWR, Surface roughness parameters and machining time of work pieces were influenced by

current and thereby improves the quality of surface finishing and rate of production. The results of

this study could be utilized in the selection of optimum process parameter (current) to achieve the

desired EDM efficiency and surface roughness when machining Al and Die steel.

Keywords: EDM, Machining time, Material removal rate, Surface roughness, Tool wear ratio.

1. INTRODUCTION

Electrical Discharge Machining (EDM) is one of the important non-traditional machining

processes and it is widely accepted as a standard machining process in manufacturing industries. The

theory of the process was established by soviet scientists in the middle of 1940’s. They invented the

relaxation circuit and a simple servo controller tool that helped to maintain the gap width between the

tool and the work piece. This reduced arcing and made EDM machining more profitable and

produced first EDM machining in 1950’s. Major development of EDM was observed when computer

numerical control systems were applied for the machine tool industry. Thus, the EDM Process

became automatic and unattended machining method. The process uses thermal energy to generate

heat that melts and vaporizes the workpeice by ionization within the dielectric medium. The electrical

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discharges generate impulsive pressure by dielectric explosion to remove the melted material. Thus,

the amount of removed material can be effectively controlled to produce complex and precise

machine components. However, the melted material is flushed away incompletely and the remaining

material re-solidifies to form discharge craters. As a result, machined surface has micro cracks and

pores caused by high temperature gradient which reduces surface finish quality.

There have been published studies continuing surface finish of machined materials by EDM. It was

noticed that various machining parameters influenced the

surface roughness and by setting possible combination of

material removal rate and tool wear ratio

surface roughness parameters are pulsed current, pulse time, pulse pause time, voltage, dielectric

liquid pressure and electrode material. The present study

removal rate, tool wear ratio and

maximum height of the profile -Rz & Maximum roughness depth

Components using copper tool in EDM

2 .MECHANISM OF EDM

The working principle of EDM process is based on the thermoelectric energy.

Discharge Machining (EDM) is a controlled metal

means of electric spark erosion. In this

electrode submerged in a dielectric fluid with the passage of

electrode are separated by a specific small gap

gap filled with an insulating medium, preferably a

(de-mineralized) water as in fig.1.a [2]

work piece to produce the finished part to the desired shape. The metal

by applying a pulsating (ON/OFF) electrical charge of high

the work piece. This removes (erodes) ver

controlled rate.

Fig. 1(a). Working principle of EDM

The polarity normally used is straight (or normal polarity) in which tool is

while in reverse polarity the tool is

tool is towards the work piece is controlled by a servomechanism. The sparking takes place over the

entire surface of the work piece hence the replica of the tool is produced on the work piece. Usually, a

component made by EDM process is machined in two stages, viz

poor surface finish and finish machining at low MRR with high surface finish.


6499(Online) Volume 4, Issue 3, April (2013), © IAEME

171



owever, the melted material is flushed away incompletely and the remaining

solidifies to form discharge craters. As a result, machined surface has micro cracks and

pores caused by high temperature gradient which reduces surface finish quality.


noticed that various machining parameters influenced the material removal rate, tool wear ratio

surface roughness and by setting possible combination of these parameters optimum surface quality

ool wear ratio was obtained. The machining parameters which influence


d electrode material. The present study deals with the effect of current on

surface roughness parameters (Average roughness

Rz & Maximum roughness depth –Rzmax) of Al a

EDM process.

The working principle of EDM process is based on the thermoelectric energy.

Discharge Machining (EDM) is a controlled metal-removal process that is used to remove met

means of electric spark erosion. In this process the energy is created between a work piece and an

ctric fluid with the passage of electric current. The work piece and the

by a specific small gap called spark gap. Pulsed arc discharges occur in this

insulating medium, preferably a dielectric liquid like hydrocarbon oil or de

as in fig.1.a [2]. The electric spark is used as the cutting tool to cut (e

work piece to produce the finished part to the desired shape. The metal-removal process is performed

by applying a pulsating (ON/OFF) electrical charge of high-frequency current through the electrode to

(erodes) very tiny pieces of metal from the work

Working principle of EDM Fig. 1(b) Normal and reverse polarity in

EDM

The polarity normally used is straight (or normal polarity) in which tool is –ve and work piece is +ve,

while in reverse polarity the tool is +ve and work piece is negative shown in fig 1.b. Movement of the

he work piece is controlled by a servomechanism. The sparking takes place over the


component made by EDM process is machined in two stages, viz. rough machining at high MRR with

poor surface finish and finish machining at low MRR with high surface finish.

n Engineering and Technology (IJARET), ISSN

6499(Online) Volume 4, Issue 3, April (2013), © IAEME



owever, the melted material is flushed away incompletely and the remaining

solidifies to form discharge craters. As a result, machined surface has micro cracks and


ool wear ratio and

these parameters optimum surface quality,

machining parameters which influence


the effect of current on material

(Average roughness -Ra, Average

of Al and Die-Steel

The working principle of EDM process is based on the thermoelectric energy. Electrical

removal process that is used to remove metal by

created between a work piece and an

The work piece and the

Pulsed arc discharges occur in this

dielectric liquid like hydrocarbon oil or de-ionized

spark is used as the cutting tool to cut (erode) the

removal process is performed

frequency current through the electrode to

work piece at a

Normal and reverse polarity in

ve and work piece is +ve,

ovement of the

he work piece is controlled by a servomechanism. The sparking takes place over the


machining at high MRR with



172

3. DESCRIPTION OF EXPERIMENTAL SET-UP

3.1 Machine tool The experimental setup consists of CR-6C Creator (SYCNC PC-60) Sink type Electro Discharge

Machine, Taiwan (shown in fig. 2) available at Department of Mechanical Engineering, University

College of Engineering, Osmania University, Hyderabad-500007. It is energized by a 50 A pulse

generator. Ruslic oil dielectric fluid was used during the experiments. The surface roughness was

measured by Handy surf Surface testing analyzer

3.2 Work piece material

The work piece materials in this work were Al and Die steel, having the properties shown in

Table.1

3.3 Electrode material

Electrode material considered for analysis was copper and its properties being shown in Table.2

Table.1: Work piece material properties Material Al Die-Steel

Density(g/cm3

) 2.70 7.7-8.0

Thermal conductivity (W/m K) 237 19.9-48.3

Electrical resistivity (µΏ/cm) 26.50 72

Coefficient of thermal expansion (x 10-6 0

C-1

) 23.1 9.5-15.1

Melting point (o

C) 660 1435

Table.2: Electrode material properties (copper)

(g/cm3)

Thermal

conductivity

(W/m K)

Electrical resistivity

(µΏ/cm)

Coefficient of thermal

expansion (x 10-6 0

C-1

)

Melting

point

(o

C)

8.9 268-389 1.96 6.6 1083

3.4 Experimental Procedure The Experimental study was carried out on CR-6C Creator (SYCNC PC-60) Sink type

Electro Discharge Machine using ruslic oil as a die electric fluid. The experiments on Die steel and Al

samples which were in the form of cylindrical shapes of diameter 50mm each were carried out using

different machining setting’s with Copper electrode. Cylindrical copper tool’s with a diameter of

12mm each ware used as electrode’s for machining both Al and die steel work pieces. The copper

electrodes ware finished ground before experimental study. Three work pieces of each Aluminum and

Die Steel were used and machined on EDM using separate copper electrodes giving 1mm depth at

three different currents (i.e. 10 A, 15 A & 20 A).

Fig. 2 Sink type Electro Discharge Machine Fig 3 shows the Tool (Cu) and Work

piece (Al)



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The material removal rate of Al and die steel work pieces were determined by the following equation

MRR = (Wb-Wa ) /Tm , where Wb =Weight of the work piece before machining

Wa =Weight of the work piece after machining

Tm = Machining time in min

The tool wear rate of copper tool for machining Al and Die steel work pieces ware determined by the

following equation [3].

TWR = (Wtb-Wta ) /Tm, where Wtb =Weight of the tool before machining

Wta =Weight of the tool after machining

Tm = Machining time in min

The surface roughness parameters (Ra, Rz & Rz max) of machined surfaces of each material at

corresponding currents (10A, 15A & 20 A) were measured by Handy surf Surface testing analyzer

(made in Japan). The sampling length of machined surface was taken as 1.25mm.

Electronic weighing machine was used to find the weights of work samples before and after

machining.

The machining time were also recorded for carrying out analysis.

4. RESULTS AND DISCUSSION

4.1 Effect of current on material removal rate: When the current is increased from 10A to 20A, the

corresponding MRR shown in fig. 4 for Al increases from 6.22 to 10.87(x 10-3

gm/min) and from 9.20

to 17.99 (x 10-3 gm/min) for Die steel respectively. The MRR values for Al and Die steel are shown in

the Table. 3.

Table.3: MRR values of Al and Die steel work samples

The peak current increases the input power by which the increase of MRR is expected due to more

spark energy flowing from tool into work piece. This causes craters and pits on the sample and

machining becomes faster.

4.2 Effect of current on tool wear rate: When the current increases from 10A to 20A, the

corresponding TWR shown in fig.5 for machining Al increases from 1.70 to 7.80 (x 10-3

gm/min) and from 2.20 to 9.60 (x 10-3 gm/min) for Die steel. The TWR values are shown in the

table.4. Higher current causes a strong spark which results in more eroded material from the tool.

Current

(Amps)

Aluminum Work Sample Die Steel Work Sample

Weight(gms) Time

(min)

MRR×10-3

(gm/min)

Weight(gms) Time

(min)

MRR×10-3

(gm/min)

Before After Difference Before After Difference

10 213.40 212.08 1.32 212 6.22 589.24 586.4

6

2.78 302 9.20

15 212.40 210.90 1.50 162 9.25 587.04 583.6

4

3.40 231 14.71

20 218.30 216.50 1.74 160 10.87 575.48 571.3

6

4.12 229 17.99



174

Table.4: TWR values of copper tool for machining Al and Die steel work samples

Fig .4 Material Removal Rate vs Current for Al & Die steel samples

Fig .5 Tool Wear Rate vs Current of Copper Tool for Machining Al & Die steel samples

4.3 Effect of current on surface roughness parameters: Average roughness (Ra), average

maximum height (Rz) and maximum roughness depth (Rzmax) of the profile parameters variation on

surface of Die steel and Al work samples for variation of current parameter at 10, 15, 20 Amps for 1

mm depth erosion. When the current is increased from 10A to 20A, the corresponding average

roughness, average maximum height and maximum roughness depth values shown in fig. 6(a) for Al

increase from 1.62 to 1.97 µm, 9.03 to 10.86 µm and 10.96 to 14.54 µm respectively. Similarly for

Die steel as shown in fig. 6(b), the corresponding average roughness, average maximum height and

maximum roughness depth values increases from 1.99 to 2.55µm, 10.02 to 13.43µm and 10.90 to

15.40 µm respectively. The surface roughness parameter values for Al and Die steel are shown.

At a low current, a small quantity of heat is generated and a substantial portion of it

is absorbed by the surroundings. As a result, the amount of utilized energy in melting and vaporizing

Current

(Amps)

For Machining Aluminum Work Sample For Machining Die Steel Work Sample

Weight(gms) Time

(min)

TWR×10-3

(gm/min)

Weight(gms) Time

(min)

TWR×10-3

(gm/min)

Before After Difference Before After Difference

10 96.68 96.32 0.36 212 1.70 96.32 95.64 0.68 302 2.20

15 95.16 94.74 0.42 162 2.60 93.04 91.66 1.58 231 5.97

20 98.02 96.76 1.20 160 7.80 94.60 92.40 2.20 229 9.60



175

the electrodes is not so intense. However, with an increase in pulse current and with a constant

amount of pulse on-time, a stronger spark with higher thermal energy is produced, and a substantial

quantity of heat will be transferred into the electrodes. Furthermore, as the pulse current increases,

discharge strikes the surface of the sample more intensely, and creates an impact force on the molten

material in the crater and causes more molten material to be ejected out of the crater, so the surface

roughness of the machined surface increases [4].

Fig .6 (a) Surface Roughness Parameters (Ra, Rz & Rzmax) vs Current for Al samples

4.4 Effect of current on machining time: When the current is increased from 10A to 20A, the

corresponding machining time was decreased from 212 to 160 min for Al and 302 to 229 min for Die

steel samples as shown in fig.7. The machining time for both samples at corresponding currents as

depicted in Table.6.

Table.6: Machining Time for Al & Die steel work pieces:

.

Fig .7 Machining Time vs Current for Al & Die steel samples

Current

(Amps)

Machining Time in min

Al Die steel

10 212 302

15 162 231

20 160 229



176

5. CONCLUSIONS

Analysis from an experimental investigation on the effect of current on material removal rate,

tool wear ratio and surface roughness parameters in EDM process have been presented. The leading

conclusions are drawn as follows:

1. The increase in pulse current leads to a sharp increase in the MRR and surface roughness of

both Al and Die steel samples, low currents produce good surface finish quality.

2. At higher currents the surface finishing quality will be low, but the MRR will be high which

leads to improve the rate of production.

3. It was evident that the tool wear ratio increases by the increase in the pulse current, but was

less compared to MRR values for same currents.

4. It was experimental that for same currents the material removal rate, tool wear ratio and

surface roughness parameters of Die steel work samples were more than that of Al samples.

5. There was a high increase in material removal rate for Die steel compared to Al work pieces

for same machining time.

6. It was observed that the machining time decreases as the current increases and the machining

time of Die steel work samples were more than that of Al samples.

ACKNOWLEDGEMENTS

The authors are thankful to the managements of their respective institutions for their

encouragement during the course of this work.

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