On the Experimental Study of Electric Discharge Machining (EDM) of P20 Type Tool Steel

Samad Dadvandipour University of Miskolc/Department of Applied Information Science and Technology, Miskolc, Hungary

aitsamad@uni-miskolc.hu

Abstract Evaluating customer demands to link with

manufacturer may have the most important role in producing parts with utmost preciseness. Replacing traditional manufacturing process with modern and advanced process technology has already been an important alternative in competitive world market, which may fulfill the customer satisfaction in long term. Electric Discharge Machining (EDM) is one of the advanced process technology, which belongs to non-traditional manufacturing process. It is quite an expensive machining process, which is mostly used in producing molding dies of different kinds and smart pats as well as the wire EDM processes. We can say it is a thermo electrical process with analyzable material removal system. The aim of this paper is to test the effect of EDM parameters on P20 type tool steel. This type of tool steel is largely used in producing different kinds of molding dies in many industries. At this research work we have used different kind of tool electrode materials like graphite, copper and Brass. The effective parameters of electric discharge machining and outputs (response variables) of working material were defined as follows: Open circuit voltage (V), Peak current(Ic), Pulse on time (Ton), Tool wear ratio (TWR), Surface roughness (Ra), Material removal rate (MRR), and Electrode wear ratio (EWR).

Keywords: Advanced, Machining Process, EDM, Effective Parameters, Tool Steel, Outputs.

I. Introduction Electrical energy is the main factor in EDM process.

The supporting exceptions of EDM application are dielectric and sparking. There have been done lots of research works on various advent of electro-discharge machining [1, 7]. At this paper we got it that, it is worth doing research wok on hot working tool steel. The reason was firstly the availability of working material and the secondly extensive use of the working material in plastic molding dies, zinc die casting and various die molding manufacturing industries. Using different kind of electrodes we searched the effect of EDM parameters on the working material and the results were analyzed on Material Removal Rate (MRR), Electrode Wear Ratio (EWR) and Surface Roughness (Ra).

II. EXPERIMENTAL PROCEDURES Using Spark Eroding Machine we performed our

experimental test. Mineral dielectric fluid was used to accomplish our test. The chemical composition of working material is shown in Table 1. In Table 2 we can observe that there are three different tool electrodes,

which have important role in our research study. The tool electrodes were made of Graphite, Copper and Brass. Their behavior response during process is of importance, because the optimum tool electrode wear ratio can be considered in comparison with the wear ratio of other tool electrodes as well. As one of the aim of the paper, we used more than one tool electrode with different materials in order to compare their effects in our experimental study. They were illustrated in the paper. Concerning the experiment constraints, the process was carried out in an immersed dielectric bath with the cylindrical shaped electrodes with Ø 10.0x10.0mm dimension. Work pieces of Ø10mm×20mm dimension were used as samples. The preciseness of work pieces, electrode tools and HB (Brinell hardness test) were measured. The details of the above mentioned conditions are shown in Table 3.

Table 1.

Mechanical properties of the work piece material

Chemical composition of P20 tool steel

Elements Composition (wt.%)

C 1.05

Si 0.3

Mn 0.6

Cr 1

V –

Fe Balance

Table 2.

Electrode Material Properties Electrode material properties

Material

Graphite Copper Brass

Composition 99.9% copper

60%Copper, 40%Zink

Density (g/cm3)

1.811

8.904

40-60

Melting point (8C)

3350

1083

930

Electrical resistivity

(µΩ·cm)

1400

9

6.158

Hardness

HB10

HB100

HB91

245

SAMI 2013 • IEEE 11th International Symposium on Applied Machine Intelligence and Informatics • January 31 - February 2, 2013 • Herl’any, Slovakia

978-1-4673-5929-0/13/$31.00 ©2013 IEEE

Copper electrode & open-circuit Voltage=150(v)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

6 11 16 21 26 31 36

Ic(A)

MR

R(m

m^3

/min

)

Ton=10(µsec) Ton=20(µsec)

Ton=50(µsec) Ton=100(µsec)

Copper electrode & open-circuit Voltage=150(v)

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

3 23 43 63 83 103 123

T ontime(µsec)

MR

R(m

m^3

/min

)

Ic=24(A) Ic=16(A)

Ic=8(A) Ic=32(A)

Table 3. Experimental Condition

Condition and variables Description Generator type Iso pulse

Work piece P20 steel Ø10*20 mm Tool Graphite/Copper/Brass Ø10*10

Tool polarity positive Dielectric Total EDM 22 mineral oil

Flushing type Normal submerged Flushing rate zero Depth of cut 2.0mm

GAP 0.05 Machining mode standard

Finishing capacitor 0 Power available(A) 8,16,24,32 Pulse durations (µs) 10,20,50,100

Voltage(v) 100,150,200 Reference voltage(v) 70

mean waiting time 30% selector of secondary

parameters(T) 1

Duration of interval between two pulses (µs)

50

Machining time duration of pulsation(sec)

0.2

ARC Protection 5

III. Design of the Experiments

We deal with the design factors and outputs (response variables) and the techniques used in the experimental study in this part. The considerable factors [2, 3] in EDM process in our experimental study are as follows: The intensity current factor (I), which depends on the different power levels. These power levels are supplied by Spark Eroding Machine generator. The power levels of the generator are corresponding with values of the peak current (Ic), which is generated between the electrode and the part to be Machined by EDM process. The second factor is Pulse on-time (Ton), which presents the time duration (µsec) that allows the peak current to run per cycle. The third factor is Open-circuit voltage (v) which is amount of voltage activated between the part and the electrode before discharging process to be taken place. The last factor is the type of tool electrode material. The output (response variables) which taken into consideration at this study, were Surface roughness, Material removal rate and Electrode wears.

IV. RESULTS AND DISCUSSIONS

Because of its essential economical effects, material removal rate is one of the most important factors at this study work. Figure 1, shows the effect of peak current on the material removal rate at various pulse-on times. We can see that increasing the peak current results the growth of the material removal rate. We can observe that phenomena are going to decrease after passing 20(A). Here we can realize that the increase in peak current leads to the growth rate of the heat energy and the result has been associated with the rate of melting and evaporation [2]. Then increasing peak current more than a certain

level, induces arcing, which results decrease in discharging and efficiency in EDM process following decreases in material removing rate.

Figure1. Effect of peak current on Material Removal Rate at various pulse on times

The pulse on time effect on the material removal rate applying different peak current is shown in Figure 2. It is observed that the rate of material removing increases with the growth of the pulse on time. The process is continued up to 50 (µsec) then the material removal rate decreases with increasing pulse on time. In real state of experimental process we got it that the increase in the pulse durations causes the same heating temperature for longer time. This may result an increase in the evaporation rate and spreading gas bubbles with high ejecting force [8]. At that time the discharge ceases removal of bigger volume of the molten metal. This way the increase in material removal is continued with the increase of the ejecting force and this process is vital till reaching a situation where the ejecting force will have no more effect in increasing the material removal rate.

Figure 2.Effect of pulse on time on the Material Removal Rate at various peak current values

S. Dadvandipour • On the Experimental Study of Electric Discharge Machining (EDM) of P20 Type Tool Steel

246

Ic=24(A) & Ton=50(µsec)

Brass

Copper

Graphite

Brass

Graphite

Copper

Brass

Graphite

Copper

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

Electrode Type

MR

R(m

m^3

/min

open-circuit Voltage=100(v)

open-circuit Voltage=150(v)

open-circuit Voltage=200(v)

Copper electrode & open-circuit Voltage=150(v)

0

1

2

3

4

5

6

7

8

9

6 11 16 21 26 31 36

Ic(A)

EWR

(%)

Ton=10 (µsec) Ton=20 (µsec)

Ton=50 (µsec) Ton=100 (µsec)

Copper electrode & open-circuit Voltage=150(v)

0

1

2

3

4

5

6

7

8

9

4 24 44 64 84 104 124

Tontime (µsec)

EWR

(%)

Ic=8(A) Ic=16(A)

Ic=24(A) Ic=32(A)

Ic=24(A) & Ton=50(µsec)

Brass

CopperGraphite

0

2

4

6

8

10

12

14

16

18

Electrode Type

EWR

(%)

open-circuit Voltage=100(v)

open-circuit Voltage=150(v)

open-circuit Voltage=200(v)

Ra OF H13

0

1

2

3

4

5

6

7

8

9

10

0 5 10 15 20 25 30 35

Ic(A)

Ra(

µm)

Ton=10(µs) Ton=20(µs)

Ton=50(µs) Ton=100(µs)

The relationship among the different type of electrode removal rate compared with copper and brass. As is shown the material removal rate is growing with increasing voltage. Material type and the material removing rate at different open-circuit Voltage (v) is shown in Figure 3. We can see that the graphite electrode generates the highest material.

Figure 3. Relationship between the electrode material type and the

MRR at different open- circuit Voltage (V) The relationships between the electrodes wear ratio and peak current involving different pulse on time is presented in Figure 4. It is clear that the electrode wear ratio increases with growing the peak current value. The higher values of peak current generate heat energy with high value. Figure 5, shows the effect of the pulse on time on the wear ratio witch decrease with increase in pulse duration with all peak current settings. This phenomenon may happen by the transfer of larger positive ions as the diameter of plasma channel is getting wider and wider.

Figure 4. Effect of peak current on Electrode Wear Ratioat various

pulses on times It follows increasing the pulse on time and movement of electrons towards the tool electrodes which are decreased gradually [4]. So we have lower values of TWR. From

Figure 6, it is clear that in EDM with Graphite the relative wear ratio has lower values, but brass show the highest EWR [5]. Furthermore, this figure shows the effect of open-circuit Voltage on the wear ratio. It is clear that the electrode wear ratio normally increases with an increase in the open-circuit Voltage.

Figure 5. Effect of pulse on time on the Electrode Wear Ratio

at various peak current values

Figure 6. Relationship between the electrode material type

and the EWR at different open circuit Voltage (v)

Figure 7. Effect of peak current on surface roughness at

various pulse on time

247

SAMI 2013 • IEEE 11th International Symposium on Applied Machine Intelligence and Informatics • January 31 - February 2, 2013 • Herl’any, Slovakia

Ic=24(A) & Ton=50(µsec)

BrassCopper

Graphite

0

1

2

3

4

5

6

7

8

Electrode Type

Ra(

µm)

open-circuit Voltage=100(v)

open-circuit Voltage=150(v)

open-circuit Voltage=200(v)

Copper electrode & open-circuit Voltage=150(v)

0

1

2

3

4

5

6

7

8

9

10

0 20 40 60 80 100 120

Tontime (µsec)

Ra(

µm)

Ic=8(A) Ic=16(A)

Ic=24(A) Ic=24(A)

Figure 8. Effect of Pulse on Time the Surface Roughness at Various Peak Current Value

Figure 9. Relationship between the electrode material type and the

Surface Roughness at different open circuit voltage (V)

In Figure 7, we can observe the effect of peak current on the surface roughness with different pulse on time. From the resultant diagrams we can see that surface roughness increases along with increase of peak current as well. Of course it is obvious the increase in peak current generates an increase in discharge heat energy. Usually at the point where the discharge energy has increased, a pool of molten metal is made and is overheated. The overheated molten metal evaporates generating gas bubbles that explode when the discharge ceases, this way molten metal material is taken away [6, 8 and 9]. This process results a crater formation. From experimental viewpoints normally consistent discharges result in overlapped crater formation. Figure 8, shows the effect of pulse on time on the resultant surface roughness applying variable peak current values. We can see that the surface roughness insignificantly (slightly) increases as the pulse on time duration increase. Figure 9, shows the relationship between the electrode material type and the electrode

wear ratio applying open-circuit voltages. At this stage we can get such a conclusion that in roughing stages the copper electrode gives the better surface roughness followed by graphite and brass.

V. CONCLUSION

At this paper we studied and tested effect of Electric Discharge Machining (EDM) parameters on P20 type tool steel. This type of tool steel is largely used in producing different kinds of molding dies in many industries. At this research work we used different kind of tool electrode materials like graphite, copper and Brass. The experimental study of the Electric Discharge Machining process of P20 type tool steel provided us with important results for obtaining smart and complex products with high quality and machining efficiency.

ACKNOWLEDGMENT

This paper was prepared within the framework of the TAMOP-4.2.1.B-10/2/KONV-2010-0001 project having title “Improvement of the quality of higher education through the development of research-development-innovation-education”. Project takes place by the support of European Union, co-financed by the European Social Fund.

REFERENCES

[1] G. Kibria , B. R. Sarkar & B. B. Pradhan and B. Bhattacharyya, “Comparative study of different dielectrics for micro-EDM performance during micro hole machining of Ti-6Al-4V alloy,” Int. J. Adv Manuf Technol 48: pp. 557–570, 2010.

[2] M. Kiyak. and O. Çakir, “Examination of machining

parameters on surface roughness in EDM of tool steel”, Int. J. Mater. Process Technol 191: pp. 141–144, 2007.

[3] M.S. Hewidy. and T.A. El-Taweel. “Modeling the machining

parameters of wire electrical discharge machining of Inconel 601 using RSM”, J. Mater. Process Technol: 169. pp. 328–336, 2005.

[4] S. Singh. and S. Maheshwari, , “Some investigations into the

electric discharge machining of hardened tool steel using different electrode materials”, J. Mater. Process Technol 149: pp. 272–277, 2004.

[5] H.C. Tsai, B.H. Yan. and F.Y. Huang, “EDM performance of

Cr/Cu-based composite electrodes”, Int. J. Mach Tools Manuf: 43 (3), pp. 245– 252, 2003.

[6] F. Ghanem, C. Braham and H. Sidhom, “Influence of steel

type on electrical discharge machined surface integrity”, J. Mater Process Technol: 142 pp. 163-173, 2003.

[7] W. Koenig, D.F. Dauw, G. Levy and U. Panten, “EDM—

future steps towards the machining of ceramics”, Ann. CIRP: 37 (2), pp. 625–631, 1998.

[8] P.S. Mathews and P.K. Philip, “Effect of manufacturing

variables on EDM process stability while using pm electrodes”, J. Inst. Eng. (India)–PR: 78 pp. 39–43, 1997.

[9] J. Mercer, “EDM’s Effect on Surface Integrity”, http://www.

Mold Making Technology.com

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