Performance of a Copper Electroplated Plastic E lectrical ... · Electro dischar g e machining is an important unconventional machining ... machining (EDM ) system , working like

Performance of a Copper Electroplated Plastic

Electrical Discharge Machining Electrode Compared

to a Copper Electrode 1Saroj Kumar Padhi,

2S.S. Mahappatra and

3Harish Chandra Das

1Department of Mechanical Engineering,

Institute of Technical Education and Research,

Siksha ‘O’ Anusandhan University, Bhubaneswar, India.

[email protected]


National Institute of Technology, Rourkela, India.


Institute of Technical Education and Research,

Siksha ‘O’ Anusandhan University, Bhubaneswar, India.

Abstract

Electro discharge machining is an important unconventional machining

process being widely used in modern industrial applications and precession

works. Electrode is the most vital element of the electrical discharge

machining (EDM) system, working like a cutting tool, highly responsible for

the qualitative and quantitative responses. The present findings are made on

an electrode of acrylonitrile butadine sterane (ABS) plastic, fabricated through

fused deposition modeling (FDM), one of the additive manufacturing (AM)

process. A copper layer of about 1000 microns is deposited on the FDM ABS

plastic part by thick electroplating, which made it practicable in EDM

applications. Performances of the EDM operation with the copper coated

plastic and a copper electrode are studied while machining D2 steel. As a

result the copper coated plastic electrode performed well without failure and

less tool wear.

Key Words:Additive manufacturing, rapid tool, thick copper electroplating,

FDM, EDM electrode, response Surface method.

International Journal of Pure and Applied MathematicsVolume 114 No. 7 2017, 459-469ISSN: 1311-8080 (printed version); ISSN: 1314-3395 (on-line version)url: http://www.ijpam.euSpecial Issue ijpam.eu

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1. Introduction

In the existing scenario scientists, researchers and manufacturers are showing

their interest on rapid tooling as an important field due to its growing demand.

Now manufacturing is easier in complicated situations through high speed

computing, automated computerized environments. Additive manufacturing

(AM) is helpful in rapid fabrication of moulds/tools with reduced time and/or

cost to produce the finished products/parts instantly. Ding et al. (2004) [1]

prepared the rapid 3D part and tool combining AM and rapid tool (RT)

technique reducing wastages. Ho et al. made a study on dimensional accuracy of

electroformed rapid EDM electrode [2]. But the poor strength of AM material,

normally, unable to endure the high stresses and temperature of machining

causes shortened life and early failure of the RT.

In this work to execute the experiment three major activities are involved. i) To

prepare a 3D ABS plastic EDM electrode through FDM, ii) metalizing the

plastic electrode with a thick copper layer, and iii) EDM operation of D2 Steel

with the copper coated plastic electrode.

Generally in FDM, ABS Plastic is extruded using a stereo lithography (STL)

file using the data from the computer aided design (CAD) file [3]. Metallization

is a process to add few microns of metal layer on the plastic surface to enhance

the mechanical, electrical and physical properties i.e. strength, hardness,

corrosion resistance, electrical conductivity, surface quality and esthetic look.

Factors concerned to metallization are part type, material, metal to be plated,

environmental conditions and processes i.e. chemically reduced metal, vapor

deposition, sintering, electroplating, electro-less plating etc. Several researches

have been made on metallization of plastics [4]. EDM is preferred for difficult

to machining metals, alloys, components of complex shapes and making tools,

dies and moulds [5]. For making dies, tools and in various industrial

applications, hard-to-machine metals/alloys (i.e. D2 steel) are preferred for its

excellent anti-oxidant properties and higher resistance to stress, wear,

temperature and corrosion [6]. Traditionally machining D2 steel is very difficult

due to its toughness and work hardening quality under elevated temperatures

and also leads earlier tool failure [7].

Literature studies include quantifying the influence of EDM input parameters

and their selective combinations on machined characteristics, i.e. material-

removal rate (MRR), tool-wear rate (TWR) and surface roughness (SR) [6].

Ghewade et al. (2011) used an orthogonal-array of Taguchi method [8], to

analyze the effects of inputs on machining along with predicting and selecting

the optimized EDM input parameters. To optimize the input parameters, multi-

objective optimization techniques are also used [9]. From the results, it is

confirmed that the current intensity on MRR and pulse-on-time on TWR are

most dominating factors. EDM electrodes should possess properties like better

electrical and thermal conductivity, highly resistant to temperature and wear,

International Journal of Pure and Applied Mathematics Special Issue

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lower thermal expansion and rate of deformation while machining. Mostly

graphite and copper electrodes are used for better and stable EDM operation.

Numbers of research have been made on studying EDM performances [6, 8].

TWR is minimized to obtain better machining accuracy [10]. Out of these

reviews, it is confirmed that electrode is responsible to optimize the EDM

output responses [11].

Conventionally, processing an electrode of complex shape from the concept to

finishing level are complicated, extremely difficult, time consuming, require

special operations, techniques and high skill. As a substitute, electroformed RP

metalized parts are used as an EDM electrode. Arthur et al. (1995) [12] have

carried out experiments and stated that 175 microns thick electroplated copper

on the non conductive AM part surface can prevent the prototype from damage

during the EDM process. Finally it is also noticed that no research work has

been made on extruded FDM ABS plastic metalized part used as an EDM

electrode. Consequently, the research objectives are made to fabricate a rapid

tool EDM electrode of thick copper electroplated FDM extruded ABS plastic

part, for machining D2 steel and examine its performance by comparing with a

standard copper electrode of same geometry.

2. Experimental Set-up

A. 3D Part of ABS Plastic

The CAD model of 10φ x 25mm and 15φ x 15mm is designed. The ABS plastic

part is fabricated by the FDM machine FORTUS 400 machine.

B. Surface Conductivity Methods and Metalizing the FDM ABS Plastic Part

Method-1: A uniform layer of thoroughly mixed conductive paint (5 to 6

microns) is coated on the ABS plastic electrode and test samples, after dried the

surface became conductive for copper electroplating. The paint (Product code -

SBCI 19) is procured from ‘Constance Indichem Pvt. Ltd., Chennai-6.

Method-2: The silver colloidal solution is painted uniformly on the surface of

the FDM ABS plastic parts and samples (with a very thin smooth brush), and

then placed inside an oven (temperature set to1000C) for about 30 minutes. It is

observed that after 20-25 minutes, the liquid turns into brown color and in

another 5-7 minutes, it becomes a fine layer of pure chemically reduced silver

coat of zero Ω resistance. The silver colloidal solution is prepared with 12.5 ml

of ammonium hydroxide and 5 grams of silver acetate, vortex mixed for

complete dilution, then 1 ml of formic acid is added drop by drop and again

vortex mixed, left for 12 hours to settle the large silver particles at the bottom.

The solution is collected in a clean vial through a 200 micron filter.

Thick copper electroplating set-up: A simple set-up is used for copper

electroplating the parts and samples. To prepare the bath solution, 90 g /L of


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copper sulphate pentahydrate (CuSO4·5H2O as the copper ion source) is added

with distilled water as per the ratio and stirred thoroughly for complete mixing.

In the mixture 40 g/L of sulphuric acid (H2SO4 as a reducing agent) is added

carefully. The bath solutions temperature is maintained at 30 0C. A low rating

DC power supply of 6 volt, 500 mA is used and the current is set to 35 mA.

C. Electroplating Results and Characteristics

All the samples electroplated for different durations of time and the plating

thickness obtained are tabulated in Table 1. Examining the scanning electron

microscope (SEM) results of the electroplated samples, it is found that the layer

thickness increases with plating time.

Table 1: Plating time and plating thickness details

The electroplating characteristic depends upon several factors and those are

directly influential temperature 300C to 32

0C, voltage, current, orientation of the

cathode/anode, quality of the anode metal, the electroplating process and the

bath solution.

D. Selection of EDM Electrode

In comparison to silver paint, copper electroplated on the reduced silver is more

columnar. Hence it is selected and electroplated for around 150 hours to attain

the thickness of about 1000 microns in specific work environment.

E. Design of Experiments (DOE) Design Expert reduces the experiment counts on the responses to some selective

input parameters without affecting the required outputs. The experiments

conducted are of greater importance to appraise the performance of the

fabricated electrode as compared to a copper electrode.

Optimization of Input Parameters Response surface methodology (RSM) is applied to optimize the output of

different influencing input parameters under control and to obtain the response

surface results. RSM is used in this design to: set and fix the experimental runs,

tabulate the results of important responses and verify it to be maximum or

minimum, frame a second order response surface model to fit most excellently

and to work-out for the best combination of parameters. Finally to plot 2/3D

graphs, relating the direct/interactive responses of the input parameters.

Planning the Box–Behnken Design In this present Box-Behnken design for three levels, total number of

experimental runs required is N = k2 + k + cp, where k is the number of factors

and cp is the central point. N = 32+3+5 =17. Thus seventeen experiments with

Plating time hours Plating thickness microns

silver paint Reduced silver

8 28 32

24 85 100

48 150 170

72 245 264

96 340 398


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three factors at three levels with five centre points assisted in guesstimate a

well-designed function of the parameters (input) and the response (output).

F. EDM of D2 Steel

This present study is made on EDM of D2 steel, MRR, TWR and SR.

Comparing the performances of the tools; significance of the RT over a solid

copper tool electrode is established. The influences of EDM input parameters

i.e. current (I), pulse-on-time (Ton) and duty-factor τ = Ton/(Ton+Toff)%, on the

output responses: MRR, TWR and SR are examined. Other factors i.e. the open-

circuit voltage (V), the flushing pressure and the tool material are kept constant.

The solid tool and the electroplating are made of copper of density 8960 kg/m3.

FDM extruded ABS plastic, surface activated with reduced silver, electroplated

for about 150 hrs of diameter 15 mm φ are used as EDM electrode. Grounded

plates of 75 mm φ × 6 mm thick D2 steel of density of 7710 kg/m3 are used as

the work piece material. LEADER-1 ZNC machine with standard die-electric

fluid and input parameters of Table 2 are employed to conduct the experiments.

Table 2: Three selected levels of Box-Behnken design variables

As per the design, seventeen machining operations are conducted for both of the

electrodes and results are tabulated in tables 3 and 5.

3. Results and Discussion

The intensity of current (the main factor controls the temperature of the spark

region) is melting and evaporating the metal. 15 mm diameter machined D2

steel work samples are displayed in Figures 1(a, b and c).

Figure 1(a): Rough cut, 1(b): Semi-finish cut, 1(c): Finishing cut samples

Surface roughness is measured with a Taylor Hobson Ameket surface roughness

profile meter with 95% accuracy. For one machined surface, at three different

locations measurements are taken and tabulated. TWR and MRR are calculated

using the experimental data tabulated for decrease in weights of the electrode

material and machined surface of the work piece material after each run,

multiplied by the corresponding density of the materials. A digital weighing

machine with 0.1+w×10−6

mg precision is used to measure the weight loss.

Time for each experiment = 6 min variable Code

Variable Symbol Low level Middle level High level

-1 0 +1

Current intensity I Amp x1 2 3 4

Pulse time B (Ton) x2 50 100 150

The duty cycle C (τ) % x3 70 75 80

Flushing pressure P bar 0.35 0.35 0.35

Open circuit voltage V 40 40 40

response1= SR, response2 = TWR, response3= MRR


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The solid copper EDM electrode and ABS plastic rapid tool copper electroplated

EDM electrode (electroplated) are shown in Figures 2a and 2b.

Figure 2(a): Copper electrode, 2(b): ABS plastic RT electrode

A. Scanning Electron Microscope (SEM) Results of Samples

The ABS plastic electrodes and samples made for the destructive and non-

destructive tests are electroplated in the same bath solution and environment.

The samples are withdrawn from the plating bath at a regular time interval for

examining the characteristics of plating. All the samples are scanned using the

SEM model JEOL-JSM 6480-LV. The scanning is made on the surface texture

and the cross cut to measure the thickness of the plating. The microscopic views

of samples are demonstrated in Figure 3a and 3b. The electroplated thickness of

copper over the conductive silver paint is about 150 microns after 48 hours as

indicated in Figure 3a and about 390 microns on the reduced silver activated

surface after 96 hours. The grain structure of the electroplated surface of the

sample is shown in Figures 3b and it is observed that the structure of the plated

copper on the annealed silver surface are more regular and continuous.

Figure 3(a): Electroplated thickness, 3(b): surface texture of plated copper

B. Experimental Data

In Table 3 and 5, the Box-Behnken design data of experiments made with a RT

and a copper tool are tabulated respectively. The ANOVA for response surface-

MRR of the RT and copper tool are mentioned in Table 4 and 6 respectively.

Table 3: Box-Behnken design table of experimental data for RT Copper plated rapid tool Operating voltage 40 V Machining time 6 minutes

Std.run Factor-I A:Ip amp Factor -II B: Ton μs Factor-III C:Tau % Response-I R1 SR Response-II R2

TWR

Response-III R3 MRR

1 2 50 10 75 4.7654 0.0186 1.61

2 4 50 10 75 6.2984 0.0372 3.47

3 2 150 10 75 4.4954 0.0186 1.84

4 4 150 10 75 5.6324 0.0425 3.06

5 2 100 9 70 3.9824 0.0186 1.97

6 4 100 9 70 5.8594 0.0372 2.98

7 2 100 11 80 3.7254 0.0272 2.11

8 4 100 11 80 6.0334 0.0423 3.79

9 3 50 9 70 5.0254 0.0275 2.51

10 3 150 9 70 5.3914 0.0372 2.11

11 3 50 11 80 5.4394 0.0271 2.81

12 3 150 11 80 4.9324 0.0372 2.21

13 3 100 10 75 4.7504 0.0276 2.55

14 3 100 10 75 4.8604 0.0372 2.34

15 3 100 10 75 4.3584 0.0275 2.63


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Table 4: The Analysis of variance table for Response Surface-rapid tool MRR data Response- I MRR Rapid Tool

* RQM, PSS Type-III

Source *SS *df *MS F Value p-value

Model 4.96 7 0.71 29.96 < 0.0001 significant

A-Discharge Current 4.16 1 4.16 175.9 < 0.0001

B-Pulse-on-time 0.17 1 0.17 7.36 0.0239

C-Duty Factor 0.23 1 0.23 9.63 0.0127

AB 0.1 1 0.1 4.33 0.0672

AC 0.11 1 0.11 4.74 0.0574

A2 0.096 1 0.096 4.07 0.0744

B2 0.097 1 0.097 4.09 0.0737

-Residual 0.21 9 0.024

Lack-of-Fit 0.17 5 0.033 2.95 0.1587 Non- significant

Pure-Error 0.045 4 0.011

Cor Total 5.17 16

* RQM =Reduced Quadratic Model, PSS = Partial sum of squares, SS = Sum of Squares

df = degrees of freedom, MS = Mean Square value, p-value = Prob > F

Table 5: Box-Behnken design table with experimental data of Cu tool Copper tool Operating voltage 40 V Machining time 6 minutes

Std. run Factor-I A:Ip amp

Factor -II B: Ton

μs

Factor-III

C:Tau %

Response-I

R1 SR

Response-II

R2 TWR

Response-III

R3 MRR

1 2 50 10 75 3.890 0.037202381 1.75

2 4 50 10 75 5.423 0.074404762 3.40

3 2 150 10 75 3.620 0.055803571 1.88

4 4 150 10 75 4.757 0.093005952 2.98

5 2 100 9 70 3.107 0.037202381 1.99

6 4 100 9 70 4.984 0.074404762 2.88

7 2 100 11 80 2.850 0.055803571 2.05

8 4 100 11 80 5.158 0.093005952 3.63

9 3 50 9 70 4.150 0.055803571 2.45

10 3 150 9 70 4.516 0.074404762 2.10

11 3 50 11 80 4.564 0.055803571 2.75

12 3 150 11 80 4.057 0.074404762 2.25

13 3 100 10 75 3.875 0.055803571 2.52

14 3 100 10 75 3.985 0.074404762 2.32

15 3 100 10 75 3.483 0.055803571 2.65

Table 6: The Analysis of variance table for Response Surface-copper tool MRR data

C. Analysis of Factors and Responses Analysis of variance (ANOVA) is an imperative method to analyze the

performances of definite response factors by decomposing the inconsistency in

the response variable between dissimilar factors. In Table 3 and 5, the results of

RT and copper tool are tabulated respectively. Responses influenced by

different input parameters are analysed critically at 0.05 significant level,

eleminating the insignificant parametrs from the ANOVA table for that

* RQM, PSS Type-III MRR C T

Source *SS *

df

*MS FValue *p-value

Model 4.09 8 0.51 29 < 0.0001 Significant

A-Discharge Current 3.41 1 3.41 193.08 < 0.0001

B-Pulse-on-time 0.16 1 0.16 9.21 0.0162

C-Duty Factor 0.2 1 0.2 11.25 0.01

AB 0.076 1 0.076 4.29 0.0722

AC 0.12 1 0.12 6.75 0.0317

BC 5.63E-03 1 5.63E-03 0.32 5.88E-02

A2 0.067 1 0.067 3.67 0.0875

B2 0.065 1 0.065 3.69 0.0909

-Residual 0.14 8 0.018

Lack-of- Fit 0.066 4 0.016 0.87 0.5522 Non- significant

Pure-Error 0.075 4 0.019

Cor Total 4.23 1

6

* RQM =Reduced Quadratic Model, PSS = Partial sum of squares, *SS = Sum of Squares

*df = degrees of freedom, *MS = Mean Square value, *p-value = Prob > F


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response. MRR, SR and TWR represents the output responses of the input

parameters i.e. discharge-current A = I, pulse on time B = Ton and duty-factor C

= τ, their square terms 1 A2, B

2, C

2 and interactive terms as A*B, A*C, B*C.

Similarly, the ANOVA for all responses (MRR, SR and TWR) are analyzed and

studied for the most significant and insignificant combinations of parameters for

the various output responses. The Rapid tool and copper tool ANOVA table for

MRR are given in Table 4 and 6 respectively after eliminating the insignificant

parameters. Similarly, the analyses for all the responses are analyzed and

ultimate equations are framed using the coded factors. After analyzing the most

influencing factors on the responses of MRR, it is observed that factors A, B, C

and the square terms A2, B

2 and interactive terms A*B are significant

parameters. For the responses of TWR from the ANOVA it is seen that A, B

and C influence more along with, A2, C

2 and BC, which are significant. AB, AC

and B2 are the insignificant parameters. The ANOVA for SR it is found that A,

B and square term A2 are the important process parameters and process

parameter C is the insignificant one. For the rapid tool, the coefficient of

determination (R2) and the adjusted R2 values are as follows: 94.79 and 91.67

% for the MRR, 98.93 and 97.56% for the TWR and 98.28 and 96.08 % for the

SR. It is observed that for all the responses lack-of-fit is insignificant.

3D Graphs: Performances of Copper Tool and Rapid Tool (RT)

The RSM Box-Behnken design/analysis graphs: input parameters influencing

output responses. 3D graphs are ploted with three mutually perpendicular axis

X, Y and Z. X and Y represents input factors and Z carries the response. For

each of the three responses SR, TWR and MRR, three input parametric

combinations of A, B and C and two electrodes, nine pairs of graphs are plotted

and analyzed. Due to similarity in the performance plots of both the tool

electrodes, one pair of graph are demonstrated here. The variation in SR (R1)

for the copper tool and rapid tool, with parameters A and B are shown in Figure

5(a, b). The surface quality machined through both the electrodes decreases by

increasing the intensity of current. Though the increased value of C influences a

little, pulse-on-time (B) is more influential in reducing the SR as studied from

the graphs. Analyzing the influences of C and A also of C and B on the

Response-I (SR) there are no remarkable changes on SR graphs with the factors,

i.e. for both the tools performances are similar. The normal-plot of residuals for

the surface responses of MRR is shown in Figure 5(c), describing the data

points scattered from the mean. Closure the data points to the mean holds good

results in the response surface plots. Influences of B and A on R1 is plotted.

Figure 5(a): Copper tool 5(b): Rapid tool 5(c): Normal plots for MRR


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The variations in results of most of all the graphs plotted for the tool types are

nearly same. Experimentally it is observed that TWR for Copper electrode is

slightly more than the rapid tool. The graph indicates that the TWR for both the

electrodes increases proportionately with A and B but it indicates a little

variation from the effects of increased C. It is marked that higher values of A

and C gives higher MRR (R3), but for the two different tools comparatively

there is a little variation. There are no significant variations in graphs for the

two tools, indicating performances, those are nearly same for the factor B and A

along with factor C and B on response-III (MRR). MRR increases by increasing

A and a slight change while increasing B, however, it decreases after the value

of B is set to low. Similarly, it is shown for A and C that the increased value of

A increases MRR but the influence of C is small. (A = Current, B =Ton (Pulse-

on-time), C = Duty factor and R1 is the response I = SR, R2 is the response II =

TWR and R3 is the response III = MRR).

4. Conclusion

It is possible to fabricate an RT electrode of FDM extrudd ABS plastic within a

short period of time. Required thickness and surface conditions can be achived

by electroplating bath solution (additives) and special arrangements. The

performances of both the EDM electrodes on machining D2 steel are executed.

It is revealed that wear of RT electrode is comparably less. MRR for both the

tools are nearly same. In case of the RT (copper electroplated plastic tool), the

deposited metal is in purest form of copper, carries more current to discharge,

enhances MRR comparing to a solid copper tool. It is seen that the RT

machined surface roughness is more due to the RT electrode surface quality,

which can be enhanced to use it for finishing operations.

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Performance of a Copper Electroplated Plastic E lectrical ... · Electro dischar g e machining is an important unconventional machining ... machining (EDM ) system , working like