int. j. engg. res. & sci. & tech. 2015 ahmed raza khan et ... · int. j. engg. res. &...

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Int. J. Engg. Res. & Sci. & Tech. 2015 Ahmed Raza Khan et al., 2015

INFLUENCE OF ELECTRODE MATERIAL ONQUALITY OF BLIND HOLES MACHINED VIA

ELECTRIC DISCHARGE MACHINE(DIE SINKER)

Ahmed Raza Khan*, Muhammad Awais Ahmad, Nauman Munir and Zubair Rashid Butt1

Electric Discharge Machining (EDM) has become a popular machining process for dies andmoulds industry. Hole making operations constitute a majority of the operations in dies andmolds industry. EDM utilizes an electrode for its principle requirements for the erosion of workpiece materials. This research paper is aimed to find the effects of different types of electrodematerials namely Copper, Graphite and Tungsten Carbide on the quality of blind holes generatedduring the operation. The quality of blind holes is evaluated in term of surface roughness, diametererror and axial error. Graphite as an electrode is found to be the most suitable for most ofperformance characteristics.

Keywords: Electrical Discharge Machining, Blind holes, Electrodes, Quality of holes

*Corresponding Author: Ahmed Raza Khan [email protected]

1 Department of Industrial & Manufacturing Engineering, Rachna College of Engineering & Technology, Gujranwala, Pakistan, (ConstituentCollege of University of Engineering & Technology, Lahore).

Int. J. Engg. Res. & Sci. & Tech. 2015

ISSN 2319-5991 www.ijerst.comVol. 4, No. 2, May 2015

© 2015 IJERST. All Rights Reserved

Research Paper

INTRODUCTIONElectrical Discharge Machining (EDM) is apopular non-conventional machining process thatis capable of machining precise and complexgeometries in electrically conductive hardmaterials (Chandramouli et al., 2014;Assarzadeh, and Ghoreishi , 2013; Chen et al.,2013)[1-3].

The working principle of EDM is essentially anelectro-thermal mechanism wherein, electricalenergy of discrete electrical discharges betweentwo electrodes (work piece and tool), immersedin a dielectric fluid is converted to thermal energy

that produces a plasma channel of very hightemperature ultimately resulting into erosion ofwork piece material. The unique benefit of EDMincludes the machining of conductive materialseither soft or hard by the application of thermalenergy which is produced in EDM process. In thisway, any hard conductive material can be cutwhich is difficult to machine in conventionalmachining processes (Kumar et al., 2009; Ho andNewmann, 2003; Pradhan and Jaiswal, 2011;Kalpakjian, 2009).

EDM is widely used in the manufacturing ofmoulds, dies, automotive, aerospace and surgical

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components but its low machining efficiency andpoor surface finish is a major hindrance to furtherapplications. A majority of the EDM operations inabove stated applications is blind hole-makingoperations. A blind hole refers to a hole that isreamed, drilled, or milled to a specified depthwithout breaking through to the other side of workpiece. The accuracy and quality of holes is veryimportant for the above stated applications; suchas the accuracy and quality of casted productsare dependent on the accuracy and quality of holesin dies and moulds. Therefore, this area ofmachining requires a lot of research to improveits performance (Ho and Newmann, 2003;Kalpakjian, 2009; Barman et al., 2013).

Barman et al. studied the size, shape andquality of high aspect ratio micro blind holes,which were machined via EDM (die sinker), takingvarious process parameters namely gap voltage,feed, discharge capacitance, polarity andthreshold in the study. The depth of the holegenerated was found smaller due to the wear ofthe tool (Barman et al., 2013). Furthermore, toolwear was found to be influenced by peak currentin EDM of Stainless Steel for micro holes. Theeffect of current on over cut was investigated forStainless Steel in the same study. Peak currentwas found to influence the value of overcut(Jahan, 2010), whereas surface roughnessincreases also with increasing the peak current(Denkena, 2006).

EDM performance is affected not only by theprocess parameters but also by the type ofelectrode. Various studies (Khan, 2006; Klockea,2013; Singh, 2012; Gopalakannan, 2012; Shankaret al., 2004) were conducted to evaluate theperformance of the electrodes. Khan (2006) foundthe copper electrodes more effective ascompared to Brass electrodes due to low tool

wear rates of Copper electrodes as compared toBrass electrodes. Klocke (2013) worked ondifferent grades of Graphite as electrode materialsin an EDM process. Graphite showed differentperformance characteristics as an electrodematerial. According to Klocke, Graphite has lowwear rate as compared to Copper. Singh et al.(2012), Gopalakannan et al. (2012) and Shankaret al. (2004) used different types of electrodesfor die steel, Stainless Steel and hardened toolsteel to evaluate the performance of electrodes.They found that electrode materials play aneffective role on performance of EDM (Singh etal., 2012, Gopalakannan et al., 2012; and Shankaret al., 2004) .

A study found was aimed to find the MaterialRemoval Rate (MRR) and Tool Wear Rate(TWR) using various process parameters namelypeak current, voltage and frequency for Brass andTungsten Carbide Electrode in a hole makingprocess using EDM (die sinker). It was found thatelectrode material influences MRR and TWR forEDM drilling process. Brass as an electrodeachieved higher MRR than Tungsten Carbide. Onthe other hand, Tungsten Carbide achieved lowerTWR as compared to Brass (Urso et al., 2012,2014).

The literature shows that material of theelectrode has an important role for the quality ofthe holes in EDM operation. A lot of research workhas been done to evaluate the effect of processparameters on the quality of electric dischargemachined holes. Copper as an electrode hasbeen mostly used for the research studieswhereas little research studies are found on theeffect of electrode material on the quality of electricdischarge machined holes. This research work


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is aimed to investigate the effect of electrodematerial on the quality of blind holes for AISI p20machined via EDM (die sinker). AISI p20 is animportant material for plastic moulds (Weng et al.,2011). Three dimensions of workpiece’s qualitynamely surface roughness, diameter error andaxial error have been taken in the research study.

MATERIALS AND METHODSWork Piece DetailsThree bars of AISI p20 are obtained from themarket. The chemical composition of the materialemployed is shown in Table 1.

Machining DetailsEDM (die sinker)1 was employed for blind holesgeneration. The machined employed for the studyis shown in Figure 1.

Three common materials namely Copper,Graphite and Tungsten Carbide were selected asthe materials for electrodes. Cylindrical rods with8mm diameter were used for the experiments.Holes are machined upto 1 mm depth.

Experimental ProcedureDischarge current is taken as variable parameteralong with electrode material. Three values ofdischarge current (5 Amp, 8 Amp and 10 Amp)are selected for experimentation for eachelectrode material whereas rest of the processparameters is kept constant. In this regard,following conditions are employed forexperimentation keeping in view the abovementioned literature; Time pulse on = 50 µ-s,Time pulse on = 30 µ-s, Fluid pressure = 4.9 x10-3 N/m2. Furthermore, Kerosene oil is used asthe dielectric medium and negative polarity of theelectrode and jet flushing method for flushing ofthe debris are used during experimentation.

Repeatability of experiments was validated bythree replications approach as is generallyadopted by others (Mohammed et al., 2012;Throne, 2008; Ikram, 2013; Saleem et al., 2015).Obtained values were within 5% of each otherindicating experimental variation was not anissue. Average values of the results are reportedherein.

Table 1: Chemical Composition of the Work Piece

C Si M n P S Cr M o Fe

0.4% 0.35% 1.45% 0.03% 0.10% 1.95% 0.20% balanced

Figure 1: Electric Discharge Machine used for the Operation

1 EDM Die Sinker: AGIE TRON 2U, AGIE, Switzerland.


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Measurement ProceduresSurface roughness is quantified by measuringsurface roughness parameter “Ra” using surfaceprofilometer (Surtronic 10 by Taylor Hobson) asshown in Figure 2. Three readings with a cut-offlength of 0.8 mm and evaluation length of 4.0 mmare taken and the average value is reported herein.

Diameter error is quantif ied herein bymeasuring the diameter of machined hole andsubtracting it from the diameter of the electrode(Aized, 2013). The difference becomes greaterthan zero due to the phenomenon of Overcut(Rao, 2009).

Coordinate Measuring Machine (CMM)2 is usedto find the actual diameter of the EDM drilled blindhole by using 3-points contact method. Threereadings are taken at different sections of the holeand average value is reported herein. Diameterof the electrode is subtracted from actualdiameter to find the diameter error.

Axial error is measured by subtracting theactual depth of blind hole from the nominal depthof blind hole, where nominal depth of hole is theplanned depth of the hole and actual depth of thehole is the actual distance covered by theelectrode as shown in Figure 3.

Figure 3: Diameter Error and Axial Error in Edm Of Blind Hole Generation

Figure 2: Surface Profilometer Used to Measure Surface Roughness (Ra)


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Coordinate Measuring Machine (CMM) is usedto find the actual depth of hole. 3 readings aretaken at different points and average is used forcalculation using Equation 2 to find axial error.CMM employed for the operation is shown inFigure 4.

RESULTS, ANALYSIS ANDDISCUSSIONSEffect of Electrode Material on SurfaceRoughness (Ra)Copper, Graphite and Tungsten Carbide aselectrodes provide the following results (Table 2)for surface roughness on various currentconditions.

The results obtained are plotted in Figure 5.Surface roughness (Ra) increases withincreasing the current (Amp). Copper is found toprovide the finest surface finish followed byGraphite with a close margin at all values of thecurrent. It can be seen that the difference betweenRa (Copper) and Ra (Graphite) widens at higher

values of the current. On the other hand, TungstenCarbide is found to provide the poorest finishamong the electrode materials.

Effect of Electrode Material on Axial Error(Ea)The results obtained for axial error (Ea) are listedin Table 3. The table shows that Graphite as anelectrode material provides the least values ofaxial error at all current values followed byTungsten Carbide whereas Copper is found toprovide the greatest values of the error.

The results of axial error are plotted in Figure6. It can be seen that the difference among thevalues widen for the higher current values.Clearly, Graphite was found the best electrodewhich provided the least amount of the error.

Effect of Electrode Material on DiameterError (Ed)Table 4 shows the results achieved for diametererror (Ed) at the stated cutting conditions. Theresults obtained are plotted in Figure 7.

Table 2: Results Table for Surface Roughness (Ra)

Current(Amp) Surface Roughness (µm)

Ra - Copper Ra - Graphite Ra - Tungsten Carbide

5 1.61 1.65 1.81

8 3.62 3.78 4.24

10 6.02 6.58 7.58

Table 3: Results Table for Axial Error (Ea)

Current(Amp) Axial Error (µm)

Ea - Copper Ea - Graphite Ea - Tungsten Carbide

5 40.8 25.1 35.2

8 83.2 48.1 69.5

10 118.6 70.2 95.8


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Table 4: Results Table for Diameter Error (Ed)

Current(Amp) Diameter Error (µm)

Ed - Copper Ed - Graphite Ed - Tungsten Carbide

5 61.6 35.1 37.2

8 93.2 53.2 59.5

10 115.2 73.2 81.8

Figure 4: Coordinate Measuring Machine (Cmm) Usedfor the Measurement of Axial and Diameter Error

Figure 5: Effect of Electrode Material on Surface Roughness (Ra)


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Graphite as an electrode is found as the bestelectrode for all values of the current. Graphite iffound to provide the least values of diameter erroramong all the electrodes closely followed byTungsten Carbide. It can also be seen that thedif ference between Ed (Graphite) and Ed(Tungsten Carbide) increases slightly at highervalues of the current. On the other hand, Copper

Figure 6: Effect of Electrode Material on Axial Error (Ea)

Figure 7: Effect of Electrode material on Diameter Error (ED)

is found to provide the greatest values of diametererror at all current conditions.

The above mentioned results can be explainedon the basis of material properties. Axial error iscaused by tool wear. The greater the tool wearthe greater will be the difference between theplanned depth of hole and actual depth and hencegreater will be the axial error (Swapan, 2014). Thetool wear depends on the melting point of the


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electrode, thus high melting point of the electrodecauses low amount of tool wear. Graphite exhibitsthe least values of axial error which can beexplained on the basis that it has the highestmelting point (3730oC) (Graham Hill, 2000). Samereason is applicable to the phenomenon ofdiameter error.

CONCLUSIONThree electrode materials namely Copper,Graphite and Tungsten Carbide are taken to studythe influence of electrode material on quality ofblind holes machined via EDM (die sinker). Threecurrent conditions, i.e., 5 amp, 8 amp and 10 ampare taken for the study on workpart AISI p20whereas surface roughness, axial error anddiameter error are taken as the dimensions ofquality. Following conclusions are drawn after theresearch work;

· Copper provides the best best surface finishfor blind holes among the electrodes closelyfollowed by Graphite.

· Graphite is found to be the best electrodematerial for dimensional accuracy. Graphiteprovides the least values of the error (diametererror, axial error)

From the results obtained, it can be deducedthat Graphite as an electrode provides the mostsuitable values overall for most of the statedperformance measures among all the electrodes.

ACKNOWLEDGMENTThis work is based on a thesis entitled ‘To studythe effects of different types of electrode materials(used in EDM) on surface Roughness anddimensional accuracy of workpart’ submitted toRachna College of Engineering and Technology,Gujranwala, Pakistan (Khan et al., 2011). The

authors acknowledge the support of Mr. AkbarMahmood, Factory Manager, Sayyed Engineers,Gujranwala, Pakistan and Department of Industrial& Manufacturing Engineering, University ofEngineering & Technology, Lahore, Pakistan, formaking this research wok possible.

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