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Research Article
 

Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM



R. Jothimurugan, K.S. Amirthagadeswaran and Joel Daniel
 
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ABSTRACT

Technologies to improve the material removal rate and reduce the tool removal rate, achieve the good surface finish and dimensional accuracy are very demanding in electrical discharge machining (EDM). The work focused on comparing performance of optimum silver coated copper tool electrode with conventionally used copper tool electrode using optimum proportionate kerosene-servotherm and commercial grade EDM oil in electrical discharge machining of Monel 400TM. The optimum thickness of silver coating over the copper tool electrode and optimum proportionate Kerosene-Servotherm dielectric were developed experimentally. The copper tool electrode with silver coating of five microns reported slightly more material removal rate, very low tool wear rate, better dimensional accuracy and good surface finish than copper tool electrode with Kerosene-Servotherm (75:25) dielectric.

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  How to cite this article:

R. Jothimurugan, K.S. Amirthagadeswaran and Joel Daniel, 2012. Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM. Journal of Applied Sciences, 12: 999-1005.

DOI: 10.3923/jas.2012.999.1005

URL: https://scialert.net/abstract/?doi=jas.2012.999.1005
 
Received: March 10, 2012; Accepted: April 03, 2012; Published: June 30, 2012



INTRODUCTION

Electrical discharge machining is a well developed unconventional thermal machining process which is being employed for successful machining of both conductive and insulating materials of any hardness with good dimensional accuracy and surface finish (Choudhury and El-Baradie, 1998). In this process, the energy intense rapid and repetitive spark discharge is maintained between work piece and tool electrode causing melting and evaporation work piece (Singh et al., 2004). It is recognized as a standard process in industries for making cavities in hardened die and process tool (Chen et al., 1999). Many research works had been done by using different tool electrode materials and dielectric media for obtaining best machining output (Pradhan et al., 2009). The performance of Cu tool electrode is better than Al electrode with kerosene in EDM of En-31 tool steel (Sharma et al., 2002). The performance of cu-cr alloys is better than Cu and brass with both kerosene and distilled water in EDM of OHMS die steel (Haron et al., 2008). The performance of WC-Cu composite was inferior to Cu tool (Chow et al., 2000). The enhancement in wear resistance of machined surface by using WC-Cu composite was observed. The Cr-Cu composite shows higher MRR than Cu and also improved the corrosion resistance of work piece (Hascalik and Cayday, 2007). The performance of ZnBr-Cu composite is superior to Cu tool was observed (Jilani and Pandey, 1984).

MATERIALS AND METHODS

In these investigations, the servotherm is mixed with different amounts (0, 12.5, 25, 37.5, 50, 62.5, 75 and 100 wt.%) of kerosene. The dielectric media of six different combinations were obtained. The copper tool electrode of 10 mm diameter and 6 mm length has been prepared and performance of the same was investigated in EDM of Monel 400TM with different combinations of kerosene-servotherm at 10 A current. A depth of cut of 5 mm was done on work piece for each combination and the optimum combination was obtained.

The comparison of performance of Cu tool electrode was done with kerosene-servotherm (75:25) and commercial grade EDM oil at different current settings (6, 7, 8, 9, 10, 11 and 12 A).

The Cu tool electrodes of 6 cm length and 10 mm diameter are prepared and they are coated with the kerosene commonly used dielectric medium with cu. tool in EDM whereas, commercial grade EDM oil is being used instead of kerosene due to possessing of superior machining output (Klocke et al., 2004).

Table 1: Chemical composition (wt.%) of Monel 400™
Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM

In the present investigation, comparing the performance of optimum Ag coated Cu tool electrode with Cu tool electrode using optimum proportion of Kerosene-Servotherm and Commercial grade EDM oil in EDM of Monel 400TM (Schumacher, 2004). The optimum silver coating over copper tool and also optimum combination of kerosene-servotherm were obtained experimentally. The comparison performance has been observed at different current settings (6, 7, 8, 9, 10, 11 and 12 A). The phase changes in tool and work piece during the EDM are also observed. There is no published study on performance of silver coated Cu tool electrode with kerosene-servotherm dielectric (Singh et al., 1985). The chemical composition of this work material is given in Table 1.

Silver coating of different thickness (5, 10, 15, 20 and 25 μ) were done on over the Cu tool electrode using electrolysis process EDM was done using silver coated copper tool electrodes with optimum combination of kerosene-servotherm dielectric at optimum current setting. From the best machining output the optimum Ag coating thickness was obtained.

RESULTS AND DISCUSSION

The studies on Monel 400TM with kerosene-servotherm of different combinations and Cu tool electrode are shown in Fig. 1, 2. Figure 1 shows that the kerosene-servotherm of different combinations evolved in different Metal Removal Rate (MRR) and Tool Wear Ratio (TWR) under the given conditions among them the kerosene-servotherm of combination 75:25 yields the MRR as 14.82% more than and TWR as 56.6% less than kerosene. This may be due to less formation of energy consuming carbon layer over the surface of the work piece during machining process. The servotherm of 100% was being used and found that the MRR is 46.2% more than and TWR is 78.17% less than kerosene. Inspite of that servotherm could not be employed as dielectric because of it is denser fluid which requires more pumping energy causing excessive heat generation during machining process.

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 1: Variation of MRR with different wt.% of servotherm in kerosene

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 2: Variation of TWR with different wt.% of servotherm in kerosene

It is clear that kerosene-servotherm (75:25) could be considered as best performed combination. This may be due to optimum combination of thermal, electrical conductivity and viscosity.

The machined surface using 100% kerosene and kerosene-servotherm (75:25%) are analyzed by SEM and their images are shown in Fig. 3- 4, respectively. From the images it was observed that thickness of energy consuming carbon layer has been formed on machined surface when using 100% Kerosene is more than Kerosene-Servotherm.

Here, after the K-S (75:25) would be referred as P dielectric medium i.e., optimum proportion of K-S dielectric medium whose performance has been compared with commercial grade EDM oil at different current settings.

Figure 5 depicts that the P dielectric medium offers more MRR than commercial grade EDM oil in most of all current setting (i.e., 8, 12, 14 and 16 A). Figure 6 shows that the P dielectric provides less TWR than commercial grade EDM oil in most of all current setting (6, 10, 12, 16 and 18 A).

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 3: SEM image of machined surface using 100% kerosene

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 4: SEM image of machined surface using 75% kerosene+25% servotherm

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 5: Variation of MRR with current for P dielectric medium and commercial grade EDM oil

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 6: Variation of TWR with current for P dielectric medium and commercial grade EDM oil

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 7: Variation of surface roughness with current for P dielectric medium and commercial grade EDM oil

In both dielectric media when the current is increased that the MRR found to be increased due to increase in input energy.

Considering the both machining outputs i.e., MRR and TWR the current setting at 10 A is found to be optimum, where the P dielectric offered MRR as 1.9% less than commercial grade EDM oil, inspite of that TWR is 55.24% less than the same. The higher current setting i.e., at 16 and 18 A the MRR and TWR are reported by the kerosene-servotherm (75:25) is much better than commercial grade EDM oil.

The Fig. 7-8 give the experimental results of surface roughness and diameteral overcut when using kerosene servotherm (75:25%) i.e., P dielectric medium and commercial grade EDM oil.

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 8: Variation of current for P dielectric medium and commercial grade EDM oil

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 9: MRR vs. different microns coated

It was found that kerosene-servotherm (75:25%) shows better surface finish and dimensional accuracy than commercial grade EDM oil.

From the arguments, that the 10A current is found to be more suitable so as to provides much lower T.W.R using optimum proportionate K-S than commercial grade EDM oil.

The performance of silver coated copper tool electrodes of different thickness (i.e., 5, 10, 15 and 20 μ) using P dielectric at different current settings are shown in Fig. 9 and 10 and it is observed that the M.R.R and T.W.R are found to be increased as the increase in coating thickness and it is due to increase in the mobility of electrons through Ag coating.

Figure 9 and 10 show, that the thickness of coating is increased by 5 μ, the corresponding increased in M.R.R and T.W.R are 6 and 46.01%, respectively, Further increasing 5 μ causing the increase in M.R.R and T.W.R are 16 and 62.9%. The thickness of coating increased beyond 15 μ, the machining output are found to be very unsatisfactory.

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 10: TWR vs. different microns coated

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 11: Surface finish vs. different microns coated

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 12: Diameteral overcut vs. different microns coated

Hence, Ag coating of 5 μ has considered as optimum.

Figure 11 and 12 give the experimental result of surface roughness and diameteral over cut using Cu tools of different thickness of Ag coating with P dielectric medium.

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 13: MRR vs. different current setting

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 14: TWR vs. different current setting

It was observed that both surface roughness and diameteral overcut are increasing in thickness of coating, it may be due to increasing input energy due to high mobility of electrons.

The performance of optimal silver coated Cu tool electrode is compared with Cu tool electrode at different current settings i.e., (6, 8, 10, 12, 14 and 18 A) are shown in Fig. 13 and 14.

The MRR reported by Ag coated Cu tool electrode is more than Cu tool at current settings of (10, 12, 14 A) and maximum of 0.3609 g min-1 is achieved at 10 A which is 26.8% more than Cu tool and corresponding reduced in TWR is 25%.

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 15: SEM images of machined surface for copper tool electrode

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 16: SEM image of machined surface for silver coated Cu tool electrode

The performance of Ag coated Cu tool electrode is much better than Cu tool electrode which is depicted in Fig. 13 and 14.

The Ag coated Cu tool electrode reports very low tool wear rate at all the current settings and very lowest tool wear had been achieved at 18 A which is 69.8% less than Cu tool. It is due to much reduced time of machining and less impingement of positive ions on surface of the tool.

The effect of silver coated Cu tool electrode and Cu tool electrode on surface roughness and diameteral overcut at different current settings using kerosene-servotherm dielectric are shown in Fig. 17 and 18, respectively from these graphs it was observed that silver coated Cu tool electrode yield less surface roughness and high diameteral accuracy than Cu tool electrode.

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 17: SR vs. Different current setting

Image for - Performance of Silver Coated Copper Tool with Kerosene-servotherm Dielectric in EDM of Monel 400TM
Fig. 18: Diameteral overcut vs. different current setting

The machined surface Monel 400TM using silver coated Cu tool electrode and Cu tool electron with P dielectric were analyzed by SEM and their image have been shown in Fig. 15 and 16, respectively.

CONCLUSIONS

The EDM performance of silver coated Cu tool electrode and Cu tool electrode using optimum proportionate K-S dielectric was analyzed with Monel 400TM. The important results are summarized as follows:

The experimentally observed performance of kerosene-servotherm of different proportion and found that K-S [75:25] reported better machining output in EDM of Monel 400TM
The performance of K-S [75:25] was compared with EDM oil and observed that K-S yields 1.9% decrease in MRR inspite of that it shows 55.24% decrease in TWR
The surface smoothness and diameteral accuracy reported by Kerosene-Servotherm are much better than commercial grade of EDM oil
The performance of optimum Ag coated Cu tool had been compared with Cu tool with optimal proportion K-S at different current setting and results are summarized as follows:
Ag coated Cu tool electrode reported 26.8% increase in MRR and 25% decrease in TWR than Cu tool
Ag coated Cu tool electrode shows better surface finish and diameteral accuracy at all current settings
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