performance of different electrode … cut 21 45 90 90 0.25 4.974333 -13.9353 18 cut 21 50 120 15...

International Journal of Application or Innovation in Engineering & Management (IJAIEM) Web Site: www.ijaiem.org Email: [email protected]

Volume 6, Issue 11, November 2017 ISSN 2319 - 4847

Volume 6, Issue 11, November 2017 Page 8

Abstract The aim of the study to investigate and optimization of electrical discharge machining for inspecting the machinability of DIN 1.2714 steel with cryogenically treated copper tool electrode (CT) and cryogenically untreated copper tool electrode (CUT) using Taguchi method. Din 1.2714 steel used for making forging dies of all types. This paper utilizes electrical discharge machining, which is thermal processing work pieces are not affected by mechanical properties of materials. This experiment utilizes the Taguchi method and L18 orthogonal table to obtain the electrode treatment (CT, CUT), current, pulse-on time, pulse-off time, voltage and flushing pressure in order to explore the material removal rate, tool wear rate and surface roughness. The influence of each variable and optimal processing parameter will be obtained through ANOVA analysis and verified through experimentation to improve process. Keywords: EDM, DIN 1.2714 steel, Performance electrode, Taguchi method.

1. INTRODUCTION Electrical discharge machining (EDM) is a machining method utilizing heat machining work pieces, controlling electric discharge spark to cause melting, erosion and vaporization to achieve the purpose of removing material. Because there is no direct contact between electrode and work piece, mechanical stress is not produced .Work pieces can under EDM as long as they are electrically conductive and are relatively free of such limitations as material type of mechanical properties. As a result, EDM is often used to machine high strength or hard materials, materials which, if machined using traditional machining methods, would be uneconomical or suffer from imprecision [1]. The Taguchi method can optimize the machining parameter of performance characteristics in EDM as a Taguchi method is the powerful method of design of experiment [2]. According to the Droza [3] any material to be used as tool electrode is required to conductive electricity. In fact, there is a wide range of materials used to manufacture electrodes, for instance, brass, tungsten carbides, electrolytic copper, copper-tungsten alloys, silver tungsten alloy, tellurium-copper alloys, copper-graphite alloys, graphite etc. copper is the best choice because of its facility to be highly polished. The copper-tungsten tool electrode gives good surface finish. It provides a high material removal rate and low electrode wear depending on the EDM parameter Settings as compared to metallic electrodes [4]. Copper-tungsten has a much higher density than copper; this makes it the best material for large electrodes. Cryogenic treatment can be characterized by its application temperature, below 123oK (-150oC) or at about liquid nitrogen temperature (-196oC). Cold treatment or sub-zero treatment includes below zero but higher temperatures than the cryogenic temperatures (down to about -80oC). [5] The process has a wide range of applications from industrial tooling to improvement of musical signal transmission. Some of the benefits of cryogenic treatment include longer part life, less failure due to cracking, improved thermal properties, better electrical properties including less electrical resistance, reduced coefficient of friction, less creep and walk, improved flatness, and easier machining. The Taguchi method was used early on in the process of the experiment, inspecting the effects of different parameters and levels in EDM on the various characteristics of EDM, including material removal rate (MRR), tool wear rate (TWR) and surface roughness (SR). The optimum machining parameter values were determined in this manner.

PERFORMANCE OF DIFFERENT ELECTRODE MATERIALS IN ELECTRO

DISCHARGE MACHINING DIN 1.2714

LAKHWINDER SINGH1, MANPREET SINGH2, S.C.VERMA3

1Department of Mechanical Engg., Sant Longowal institute of Engineering and Technology, Sangrur (Punjab), India

2Department of Mechanical Engg., Sant Longowal institute of Engineering and Technology, Sangrur (Punjab), India




2. DETAILS OF EXPERIMENTAL 2.1 Experimental equipment The primary equipment in this study was an Electric Discharge Machine ZNC (Z-axis Numerically Controlled) model S50; make: Sparkonix and a fixture and control device. Commercial kerosene was circulated as the dielectric fluid in the tank. The chemical composition of the DIN 1.2714 steel used is shown in Table 1. Material properties were as shown in Table 2.Our experiment method used the L18 orthogonal array as designed in the Taguchi method: parameters and correlated levels design were as as shown in Table 3. In this study, an electrode was attached to the Z-axis of EDM and a work piece secured to the work plat form in the tank, after which EDM parameters were set to perform the experiment.

Two type of cylindrical Copper electrodes, cryogenically treated (CT) and cryogenically untreated (CUT) copper rods of 12mm diameter was selected as the electrodes for machining the work piece. Machining time lasted for 20 min. After the completion of machining, the work piece and the electrodes were weighed, as material removal rate and electrode wear rate can be derived from comparing the weights of the work pieces and electrodes before and after machining. A surf coder was used to evaluate quantitatively the surface roughness of the EDMed surface, presented by Ra. For each work piece, the average of readings taken at three places of machining plane was chosen as the surface roughness value.

2.2 Design of experiments using the Taguchi approach

Table 1: Chemical composition of DIN 1.2714 steel

Table 2: Material properties of DIN 1.2714 steel

Properties DIN 1.2714 steel

Density (g/cm3) 7 .84

Thermal conductivity (W/m.K) 36.0

The Orthogonal Array forms the basis for the experimental analysis in the Taguchi method .first the experiment parameter factors and their corresponding levels are selected. Next, the experimental results are manipulated by the analysis of variance (ANOVA) method to determine the effect of each factor versus the objective function .The experiment procedures are described as follows:

a) on the required quality objective the parameters factors are selected. b) The parameter factors levels are determined. c) Based on the variable factor layout of the orthogonal array .the practical experiment can then proceed. d) Experimental results are obtained and then the ANOVA for Signal-to-Noise (S/N ratio) and contribution are

computed. e) Next the optimal parameters factor level combination is selected. f) Finally, the optimal parameter level combination is used to proceed with the confirmation experiment.

For the Taguchi Method parameter design the basic method converts the objective parameter to the S/N ratio which is treated as the quality characteristics evaluation index. The least variation and the optimal design are obtained by means of the S/N ratio. The final step is to actually conduct the experiment to confirm whether or not the experiment is successful. The benefits of S/N ratio include increasing the factor weighting effect, decreasing mutual action, simultaneously processing the average and variation, and improving engineering quality .The higher the S/N ratio, the more stable the achievable quality Depending on the required objective characteristics , different calculation methods can be applied as follows. The smaller-the-Better where the objective optimal value is the smaller the better Such as in the surface roughness and tool wear rate.

= —10log

Element Mn Si C Ni Cr Mo V

Wt% 0.75 0.25 0.55 1.65 1.10 0.45 0.10




The Larger-the-Better where the objective optimal value is the larger the better, Such as in the material removal rate.

= —10log yi the ith result of the experiment ,n the repeated number of the ith experiment.

Table 3: Experimental layout using L18 orthogonal array

Factors

Symbol

Levels

1

2

3

Electrode Treatment

ET

CT

--

CUT

Current (A)

Ip

12

15

21

Voltage (V)

Vg

40

45

50

Pulse ON Time (µs)

Pon

90

120

150

Pulse OFF Time (µs)

Poff

15

45

90

Flushing Pressure (Kg/cm2)

FP

0.25

0.50

0.75

3 ANALYSIS OF DATA AND RESULTS

In investigating EDM properties over the course of the experiment, a Taguchi L18 orthogonal array was used to organize the set up of EDM parameters ,which were ;electrode treatment, current, voltage, pulse-on time, pulse-off-time and flushing pressure. section A-C of the paper individually discuss the effects of each machining parameter on the machining characteristics of the material removal rate, tool wear rate and surface roughness .of the machining characteristics ,material removal rate was the larger the best quality ,while electrode wear rate and surface roughness were the smaller the best quality Major factors affecting material removal rate ,tool wear rate and surface roughness was derived by performing ANOVA and contribution analysis. 3.1 Material removal rate This study selected L18 orthogonal array to conduct experimental runs. The factors and levels are shown in Table 4. All the factors have three levels except electrode treatment. The S/N ratios are calculated and the larger the best quality characteristics applied for the MRR. The ANOVA and contribution analysis proceed according to the S/N ratio of the MRR in Table 4 and results are shown in Table 5. Among the six control parameters, the most notable is the [B] current, contribution ratio 56.40%, will dramatically affect the MRR.

The electrode treatment (contribution ratio 32.77%), voltage (contribution ratio 6.65%) and pulse-on-time (contribution ratio 3.06%) have physical and statistical influence the remaining minor parameters that is pulse-off-time and flushing pressure play slightly contribution to the evaluation of the MRR. Control parameters S/N ratio response plot by MRR effects is shown in Fig. 1. The optimal S/N ratio combination, the largest S/N ratio value for all control parameters, is denoted as A1/B3/C3/D3/E3/F2.

Table 4: Experimental values and S/N ratios of MRR

S No.

ET

IP

Vg

Pon

Poff

FP

Mean MRR

S/N ratio

1 CT 12 40 90 15 0.25 2.398667 -7.73747

2 CT 12 45 120 45 0.50 2.610667 -8.39265




3 CT 12 50 150 90 0.75 3.014667 -9.66219

4 CT 15 40 90 45 0.50 3.088667 -9.86312

5 CT 15 45 120 90 0.75 3.138333 -10.1204

6 CT 15 50 150 15 0.25 3.403 -10.6654

7 CT 21 40 120 15 0.75 4.476667 -13.0206

8 CT 21 45 150 45 0.25 4.642 -13.3356

9 CT 21 50 90 90 0.50 4.733333 -13.6494

10 CUT 12 40 150 90 0.50 2.692667 -8.9798

11 CUT 12 45 90 15 0.75 2.727167 -8.80734

12 CUT 12 50 120 45 0.25 3.063833 -9.73055

13 CUT 15 40 120 90 0.25 3.144 -10.0361

14 CUT 15 45 150 15 0.50 4.318333 -12.7153

15 CUT 15 50 90 45 0.75 3.479333 -11.0889

16 CUT 21 40 150 45 0.75 4.511 -13.1314

17 CUT 21 45 90 90 0.25 4.974333 -13.9353

18 CUT 21 50 120 15 0.50 5.682333 -15.1053

Figure 1 Parameter response plot for MRR

Table 5: Analysis of variance and contribution for MRR

Factors

DF

SS

MS

F-ratio

%Contribution

Electrode 1 44.610 44.61 186.9 32.77




Current (A) 2 76.848 38.42 160.2 56.40

Voltage (V) 2 9.053 4.527 18.94 6.65

Pulse on time

(µs) 2 4.173 2.086 8.72 3.06

Pulse off time

(µs) 2 0.715 0.358 1.486 0.52

Flushing

pressure (Kg/cm2) 2 0.717 0.359 1.585 0.52

Residual error 6 1.432 0.239

Total 17 136.11

3.2 Tool wear rate The S/N ratios are calculated and the smaller is better quality characteristic is applied for the TWR. The ANOVA and contribution analysis proceed according to the S/N ratio of the TWR in Table 6. Among the six control parameters, the most notable is the current [B], the contribution ratio 42.19% will dramatically affect the TWR. In addition, [A] electrode treatment with contribution ratio 33.50% and voltage (contribution ratio 22.36%) will significantly affect the TWR .The pulse-on time (contribution ratio 1.60%), pulse-off-time (contribution ratio 0.31%) and flushing pressure (contribution ratio 32.77%) play slightly contribution to the evaluation of the TWR. Control parameter S/N ratio response plot by TWR effect is shown in Fig.2.The optimal S/N ratio combination, the largest S/N ratio value for all control parameters, is denoted as A1/B1/C1/D1/E1/F1.

Table 6: Experimental values and S/N ratios of TWR

S No.

ET

IP

Vg

Pon

Poff

FP

Mean TWR

S/N ratio

1 CT 12 40 90 15 0.25 0.0028 50.92671

2 CT 12 45 120 45 0.50 0.003333 49.5358

3 CT 12 50 150 90 0.75 0.005663 44.19672

4 CT 15 40 90 45 0.50 0.005277 44.93137

5 CT 15 45 120 90 0.75 0.007543 42.43549

6 CT 15 50 150 15 0.25 0.012823 36.99986

7 CT 21 40 120 15 0.75 0.012027 38.05036

8 CT 21 45 150 45 0.25 0.01055 36.09159

9 CT 21 50 90 90 0.50 0.01421 35.01629

10 CUT 12 40 150 90 0.50 0.006157 43.83423

11 CUT 12 45 90 15 0.75 0.003323 49.55239




12 CUT 12 50 120 45 0.25 0.006097 43.95182

13 CUT 15 40 120 90 0.25 0.00793 41.8823

14 CUT 15 45 150 15 0.50 0.008793 41.07077

15 CUT 15 50 90 45 0.75 0.011917 35.32878

16 CUT 21 40 150 45 0.75 0.023677 30.19905

17 CUT 21 45 90 90 0.25 0.033987 28.98167

18 CUT 21 50 120 15 0.50 0.04503 25.28821

Table 7: Analysis of variance and contribution for TWR

Factors

DF

SS

MS

F-ratio

%Contribution

Electrode 1 280.624 280.624 315.05 33.50

Current (A)

2 353.378 176.689 77.52 42.19

Voltage (V)

2 187.276 93.638 205.34 22.36

Pulse on time

(µs) 2 13.439 6.720 14.73 1.60

Pulse off time

(µs) 2 2.653 1.327 2.91 0.31

Flushing pressure

(Kg/cm2) 2 0.088 0.044 0.09 0.01

Residual error

6 2.741 0.456

Total

17 837.458

Fig.2 Parameter response plot for TWR

3.3 Surface roughness The S/N ratios are calculated and the smaller is best quality characteristic is applied for the SR. The ANOVA and contribution analysis proceed according to the S/N ratio of the SR in Table 8. Among the six control parameters, the most notable is the current [B] (contribution ratio 40.49%), voltage [C] the contribution ratio 34.23% will




dramatically affect the SR. In addition, [A] the electrode treatment contribution ratio 22.71%, will significantly affect the SR .The flushing pressure (contribution ratio 1.05%), pulse-on time (contribution ratio 0.98%) and pulse-off-time (contribution ratio 0.54%) have physical and statistical influence. Control parameter S/N ratio response plot by SR effect is shown in Fig.3.The optimal S/N ratio combination; the largest S/N ratio value for all control parameters, is denoted as A1/B1/C1/D1/E2/F1.

Table 8: Experimental values and S/N ratios of SR

S No.

ET

IP

Vg

Pon

Poff

FP

Mean MRR

S/N ratio

1 CT 12 40 90 15 0.25 2.398667 -7.73747

2 CT 12 45 120 45 0.50 2.610667 -8.39265

3 CT 12 50 150 90 0.75 3.014667 -9.66219

4 CT 15 40 90 45 0.50 3.088667 -9.86312

5 CT 15 45 120 90 0.75 3.138333 -10.1204

6 CT 15 50 150 15 0.25 3.403 -10.6654

7 CT 21 40 120 15 0.75 4.476667 -13.0206

8 CT 21 45 150 45 0.25 4.642 -13.3356

9 CT 21 50 90 90 0.50 4.733333 -13.6494

10 CUT 12 40 150 90 0.50 2.692667 -8.9798

11 CUT 12 45 90 15 0.75 2.727167 -8.80734

12 CUT 12 50 120 45 0.25 3.063833 -9.73055

13 CUT 15 40 120 90 0.25 3.144 -10.0361

14 CUT 15 45 150 15 0.50 4.318333 -12.7153

15 CUT 15 50 90 45 0.75 3.479333 -11.0889

16 CUT 21 40 150 45 0.75 4.511 -13.1314

17 CUT 21 45 90 90 0.25 4.974333 -13.9353

18 CUT 21 50 120 15 0.50 5.682333 -15.1053

Table 9: Analysis of variance and contribution for SR

Factors

DF

SS

MS

F-ratio

%Contribution

Electrode 1 22.7873 22.7873 85.281 22.71

Current (A) 2 40.6223 20.3111 76.014 40.49




Voltage (V) 2 34.3450 17.1725 64.26 34.23

Pulse on time

(µs) 2 0.9840 0.4920 1.84 0.98

Pulse off time

(µs) 2 0.5437 0.2718 1.01 0.54

Flushing

pressure (Kg/cm2) 2 1.0599 0.5299 1.98 1.05

Residual error 6 1.6036 0.2672

Total 17 100.322

Fig.2 Parameter response plot for SR

4. CONCLUSIONS This work evaluates the comparison study of cryogenically treated electrode and untreated electrode of machining DIN 1.2714 steel by electrical discharge machining. Based on the results presented here in, we conclude the following:

1. The suggested optimal machining parameters for material removal rate are: ET (CT), Ip (21), Vg (50). Pon (150), Poff (90) and Fp (0.50) the parameter with the greatest effect on the material removal rate was current, cryogenic treated electrode, voltage and pulse-on-time showed the highest MRR. While pulse-off-time and flushing pressure have least effect on MRR.

2. The suggested optimal machining parameters for tool wear rate are: ET (CT), IP (12), Vg (40), Pon (90), Poff(15) and Fp (0.75). The significant parameters with the greatest effects on the tool wear rate were electrode treatment, current and voltage.

3. The suggested optimal parameters for surface roughness are: ET (CT),IP(12), Vg(40), Pon (90), Poff(45) and FP(0.25). The significant parameters with the greatest effects on the surface roughness were electrode treatment, current and voltage.

References

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performance of different electrode … cut 21 45 90 90 0.25 4.974333 -13.9353 18 cut 21 50 120 15...

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