experimental investigation for main cut and trim … · 2018-11-12 · figure 2 shows the wire path...

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International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 10, October 2018, pp. 1518–1528, Article ID: IJMET_09_10_156 Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=9&IType=10 ISSN Print: 0976-6340 and ISSN Online: 0976-6359

© IAEME Publication Scopus Indexed

EXPERIMENTAL INVESTIGATION FOR MAIN

CUT AND TRIM CUTS OF WIRE ELECTRICAL

DISCHARGE MACHINING ON TUNGSTEN

CARBIDE

Patittar Nakwong*

Faculty of Engineering, Thammasat University, Pathumthani Thailand 12120;

Apiwat Muttamara

Faculty of Engineering, Thammasat University, Pathumthani Thailand 12120 *corresponding author

ABSTRACT

This paper presents an experimental investigation on the influence of cutting

parameters of Wire Cut Electrical Discharge Machining (WEDM) during the machining

of tungsten carbide and optimization of machining parameters on MRR, surface

roughness, kerf width and radial overcut (ROC). The investigation was conducted by

considering the variation in a set of average machining voltage (Vo), peak current (Ip)

and wire speed (Ws) with Taguchi method. The L9 orthogonal array has been used to

determine the analysis of variance the main effect of S/N ratio, and P values for indicating

the most significant parameter affecting the machining performance. The significant

factors average machining voltage and peak current for MRR and SR. voltage, and wire

speed is obtained as insignificant parameters for ROC. Further verification of

improvements in the surface quality characteristics has been made the main cut (MC) and

trim cut (TC) through confirmation test to the chosen initial parameter setting. The

optimal combination of WEDM parameters satisfies the real requirement of surface

quality machining of tungsten carbide. Analysis of variance (ANOVA) was carried out for

identifies significant parameters for MRR, surface roughness and kerf width.

KEYWORDS: Wire-EDM, Taguchi Method, Material removal rate, Surface roughness,

Kerf width

Cite this Article Patittar Nakwong. and Apiwat Muttamara, Experimental Investigation for Main Cut and Trim Cuts of Wire Electrical Discharge Machining on Tungsten Carbide, International Journal of Mechanical Engineering and Technology, 9(10), 2018, pp. 1518–1528. http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=9&IType=10

Patittar Nakwong. and Apiwat Muttamara


1. INTRODUCTION

Wire electrical discharge machine; WEDM is processing machinery difficult to cut material. Decorative, popular, widely used in industrial and manufacturing process [1]. WEDM used to produce complex shapes with high accuracy and excellent surface finish; the researchers are developed different factors and optimize processes considering process parameters and machine responses.

The mechanism to cut of WEDM depends on wire electrical conductivity and material using in the process[2]. The electrical spark between wire electrode and materials under the influence namely “kerf width,” produces short duration discharge get melt and remove the particle from workpiece flushing by de-ionized water. Essentially the machining process precision and improve the material characteristic. Liu, Li [3] explores the process capability of W-EDM on Nitinol Ni50.8Ti49.2 by main cut (MC) and four trim cuts (TC). The experimental results show the distributions of Ra are very different between MC and finish TC. and show that finish TC can reduce the Thick white layers (0‒2 μm). However, microcracks would not propagate into the heat affected zone (HAZ) below the white layer. The white layer by TC is about 50% higher than that by MC. Arikatla, Tamil Mannan [4] determining the operation of the rough cut and trim cut to improve the surface integrity and investigate microcrack, microvoid, white layer. The experimental result shows the main effect of high pule on time and peak current are affected to the surface integrity of Titanium alloy on the WEDM process. Gaurav Kumar et al., [5] aim to study the tungsten to increase mechanical parameters for wire electrical machine. The research will try to find the best way to cut tungsten carbide by variation of parameters that are different, so the experimental focus in maximum material removal rate (MRR) which have a brass wire for cutting. More overused the DOE from Taguchi and ANOVA technic. It was found that the value of the lowest surface roughness is 2.214 micron with wire Tension (0.6 N) feed rate 10m/min flushing pressure 3 kg/cm2, current 80A test results demonstrate the potential to trim a workpiece with high-efficiency rough cutting[6],[7] a study focused on the die-sinking EDM of a ceramic material such as cobalt-bonded tungsten carbide (WC–Co) analysis on the influence of intensity, pulse time and duty cycle over technological variables such as surface roughness, electrode wear (EW) and material removal rate was performed. This was done using the technique of design of experiments (DOE) [7, 8]. Other metals such as in tungsten carbide-cobalt (WC–Co), tantalum carbide (TaC), tungsten tantalum carbide (W-TaC). In another researchers study, addition, analysis of variance was used to identify key factors for the WEDM process to reinvent publishing after the neural network (BPNN) and simulated annealing algorithm (SAA) to determine the appropriate parameter settings of the WEDM process[9]. After that A.Muniappan [10] investigation, the effect and optimization of machining parameters on the kerf width and surface roughness in wire electrical discharge machining (WEDM) operations of Al 60661 hybrid composite. The factor studies were conducted under pulse on time, pulse off time, peak current, gap set voltage, wire feed rate, and wire tension. The effect of the machining parameters on the kerf width and surface roughness (SR) was determined by using analysis of variance (ANOVA) The experiments were designed with L27 orthogonal array and confirming test by grey relational analysis. Mehdi Hourmand, Ahmed A. D. Sarhan [11] investigate the effect of voltage, peak current, pulse on-off time on MRR during micro EDM drilling of WC-16% Co and analyzed by ANOVA method, as a result, show the increased of all parameter had the most effect on MRR. Part of WEDM study, Jangra and Grover [12], study the process parameter in WEDM of WC-5.3%Co the experiment was conducted RSM, ROC, SR, CS and investigate correlation four parameters: pulse-on time, pulse off time, servo voltage and wire feed by using ANOVA. As a result, show that the CS and ROC are significant interactions and Jangra, Kumar [13] experiment investigate the four parameters on WC-Co composite, HCHCr steel alloy, Nimonic-90 and Monel-400 of the rough cut and trim cut in WEDM. The result show operation of the rough cut

Experimental Investigation for Main Cut and Trim Cuts of Wire Electrical Discharge Machining on Tungsten Carbide


and trim cut under the similar parameters were observed. The trim cut process can improve the surface characteristic with an appropriate wire offset.

Based on the above this study aims to evaluate the effect of machining process parameter such as voltage (Vo), discharge current (Ip), wire speed (Ws), pulse on-off time, are correlations with the performance characteristic of surface integrity, material removal rate and kerf width by main cut and trim cuts. Highlighting of this paper to optimize method by Taguchi technic to predict WEDM process response characteristic of materials and explore the different measurement output are correlations with the performance characteristic of surface integrity, material removal rate and kerf width (Kw).

2. MATERIAL AND METHOD

2.1 Material and equipments

In this study, the experiment was conducted on Mitsubishi FA10S wire electrical discharge machine (W-EDM) with de-ionized water based dielectric. The electrode material is a brass wire of 0.25 mm in diameter. The experimental workpiece was confirmed with Energy Dispersive X-ray Spectrometry (EDS). The workpiece is tungsten carbide (W73%C11%). Figure 1 shows the experimental set up. Table 1 shows tungsten carbide properties[8]. Table 2 shows chemical composition of the tungsten carbide workpiece.

Table 1 Tungsten carbide properties.

Density (kgm-3) 1500 Melting Point (°C) 2700

Thermal Conductivity (Wm-1K-1) 7 Co-effcient of thermal expansion (10-6 K-1) 5.0

Electrical Resistivity (10-8 Ωm) 22 Modulus of Elasticity (20°C GPa) 696

Mohs hardness 7.5 Vickers hardness (kN/mm2) 2200

Table 2 Chemical composition of tungsten carbide

Element% O C W Na K Total Weight% 14.58 11.08 72.98 0.45 0.90 100

Figure 2 shows the wire path in followed for main cut and trim cut. The thickness of sample is 2.0 mm. The main cut and trim cut operate similarities of parameter and difference on feed available (FA) 4.0, 5.8 m/min and trim cut operates with wire offset (WO) 0.130 mm, the effect of three parameters; voltage open (Vo), peak current (Ip) and wire speed (Ws) were investigated for material removal rate (MRR) (mm3/min) and surface roughness (SR).

2.2 Experimental design by Taguchi Method

Taguchi design of experiment (DOE) has been used to investigate wire electrical, and wire speed. Table 3 shows Taguchi is experimental results from L9 Orthogonal Array, ANOVA analysis the relative influence of processes parameters. The result was investigated with 95% confidence intervals through MINITAB 16.



Figure 1 Wire-EDM experimental set up

Figure 2 Wire path for main cut and trim cut

3. RESULTS AND DISCUSSION

3.1 Effect of main cut and trim cut are improvement surface roughness

First, experimental is examine the effected of parameters are influenced to the surface roughness on tungsten carbide likely occur at wire electrical discharge process can explain the thermal stress after machine cooling down term of surface stress happen and WC is obtained a carbide phase sintering as a result to boundary gain crack due to reducing the surface roughness integrity [14]. After the main cut and trim cut on tungsten were investigated in order to improve the surface integrity after the WEDM process. The comparison was confirmed by Scanning Electron Microscope SEM (JEOL700). As a result the Figure 3 shows the surface roughness and ROC measurement comparison with main cut and trim cut on machining process at the same condition voltage 10 and 15 volt and carrier out peak current at 5 and 8 A. In the case of the main cut, the WEDM process with low of FA and WO affected to a size of the crater, deep hole and the diameter of crater increase hence the surface roughness increase.



Figure 3 Effect of peak current and voltage for ROC, surface roughness

In the trim cut, the wire moved faster than that of the wire of the main cut due to the wire and operated with wire offset that was machined with the high energy. Therefore the workpiece material and machine process are melting and evaporation thus the surface roughness, and ROC can be improved by trim cut WEDM [13].

Figure 4a shows the surface by the main cut characteristic by machine parameters with the main effect on SR on voltage of 10 volts, the peak current of 5 A and wire speed of 5 mm/min it contributed 1.530 µm at the same condition by using trim cut the surface roughness was reduced to 1.148 µm as shown in Figure 4a and 4b. The SEM photograph of high value of surface roughness in the experiment on voltage of 15 volts, the peak current of 8 A at wire speed of 5 mm/min it contributed 1.857 µm at the same condition by using trim cut the surface roughness was reduced to 1.781 µm and Figure 8c to Figure 8d show the highest of surface after wire machine process and the assessment of a result show the effect of peak current, voltage are affected to the formation of the surface are reduced at 0.382 µm, 0.076 µm as result by using main cut and trim cut respectively.

Vo 10 Ip 5 main cut

Vo 10 Ip 5 trim cut



Vo 15 Ip 8 main cut

Vo 15 Ip 8 trim cut

Figure 4 SEM micrograph showing surface roughness on machine condition

a) Vo 10 Ip 5 main cut, b) Vo 10 Ip 5 trim cut, c) Vo 15 Ip 8 main cut, d) Vo 15 Ip 8 trim cut

3.2 Effect of process parameters on MRR

The effect of WEDM parameter as shown the main plot of S/N ratio “The larger is better” was focused on material removal rate. Table 4 shows the experimental result of the MRR, SR, and ROC compared with main cut and trim cuts.

Table 3 Process parameter variable and their levels

Factor Unit Level 1 Level 2 Level 3

Voltage Open (Vo) Volt 6 10 15

Peak current (Ip) Amp 5 7 8

Wire Speed (Ws) m/min 5 8 12

Table 4 Experimental result of MRR, Surface Roughness, and ROC

Exp.No. Vo Ip Ws MRR (mm3/min) SR MC (µm)

SR TC

(µm)

ROC MC

(mm)

ROC TC

(mm) 1 6 5 5 1.84 1.218 1.092 0.041 0.047 2 6 7 8 3.02 1.269 1.164 0.070 0.080 3 6 8 12 4.05 1.414 1.397 0.076 0.080 4 10 5 8 2.45 1.625 1.463 0.073 0.075 5 10 7 12 4.43 1.650 1.551 0.091 0.095 6 10 8 5 5.97 1.631 1.519 0.056 0.065 7 15 5 12 4.15 1.712 1.639 0.121 0.135 8 15 7 5 5.51 1.857 1.781 0.099 0.105 9 15 8 8 6.25 2.067 2.018 0.109 0.115

Table 5 shows the effect of process parameters on MRR from ANOVA was performed and present the result of the main effect of the parameter on MRR according to the MRR is highest at the third level of voltage open (15 volts), peak current (8 A) and wire speed (12 m/min). The material removal rate increase with voltage open, peak current and wire speed increase.



According to the MRR high level of parameter is due to high energy the discharge current lead to a high melting material and evaporation of the WC. [14],[15]

The major factor was significant parameter affected MRR, voltage and wire speed are respectively. The experimental result shown the predicted of R2 at 95.6% and R2(adj) at 92.9%. Adjust the result for determines the deviation about the mean which described by the model for MRR.

Figure 5 Main effect of the parameter on MRR

Table 5 Analysis of Variance for MRR

Source DF Adj SS Adj MS F-Value P-Value

Regression 3 18.306 6.12 36.0628 0.000

Vo 1 8.057 8.057 47.6206 0.000*

IP 1 10.194 10.194 60.2494 0.000*

WS 1 0.053 0.053 0.318 0.596

Error 5 0.8460 0.3222

Total 8 19.1520

S = 0.411345 R-Sq = 95.6% R-Sq(adj) = 92.9% *significant

3.3 Effect of process parameter on surface roughness

The analysis of surface roughness (SR) “Smaller is better” the characteristic of as a variable of surface roughness was measured by using roughness tester; TIME series TR200. Figure 6 shows main effect of main cut on surface roughness. Figure 7 shows the main effect of trim cut on surface roughness. Table 6 shows the analysis of variance for main cut on surface roughness. Table 7 shows Analysis of Variance for trim cut on surface roughness. The lowest at the third level of voltage open, peak current and second level of wire speed. It can be observed that SR increased with Voltage and peak currently increased and decrease with wire speed with the peak current increase and voltage have raised. The density of discharge current was eroded and melting materials on the surface the mechanism of voltage and peak current each pulse on time is ejected and explode the article from workpiece lead to the deep hole, crater, coral reef, micro-void, kerf width, and ROC[16].



The result of the ANOVA is analysis process parameter it is observed that 95% confidence level the significant effect of the parameters when p-value less than 0.05. Table 6-7 present the result of ANOVA; it was observed the voltage is the major factor were significant parameter affected surface roughness, peak current and wire speed are respectively. The experimental result showed the predicted effected of main cut and trim cut by the R2 at 91.7%, 94.0% and R2(adj) at 88.8%, 90.4% respectively. The result for determines the deviation which described by the model for surface finish.

Table 6 Analysis of Variance for main cut on surface roughness


Regression 3 0.541 0.180 18.476 0.003*

Vo 1 0.493 0.493 50.518 0.000*

IP 1 0.047 0.047 4.871 0.078

WS 1 0.000 0.000 0.413 0.846

Error 5 0.048872 0.009774

Total 8 0.590674

S = 0.098 R-sq = 91.7% R-sq(adj) =86.8% *significant

Table 7 Analysis of Variance for trim cut surface roughness


Regression 3 0.619 0.206 26.034 0.001

Vo 1 0.530 0.530 66.778 0.000*

IP 1 0.084 0.084 10.653 0.022*

WS 1 0.005 0.005 0.672 0.449

Error 5 0.039 0.672

Total 8 0.659

S = 0.089 R-sq = 94.0% R-sq(adj) = 90.4% *significant

3.4 Effect of process parameter on kerf width and ROC

Radial overcut (ROC) occur after machine process ROC is measure between the hole of diameter produce and wire tool. The width of the wire depends on spark occur and erosion when the wire approach across a workpiece.



As a result of main cut and trim cuts are affected to kerf and ROC. The main effect of tungsten on Kerf width was measured using the stereomicroscope. Figure 8a and Figure 8b show the effect process parameter main cut and trim cut. The result show ROC of the trim cut gives a higher value than that of using main cut.

Figure 8 ROC with (a) main cut and (b) trim cut

In trim cut wire electrode return to the main cut path with the similarity value of wire offset (WO); significant impact to SR, ROC the decrease of WO over 0.125 µm. It not affected peak current to melting and erosion material because the gap between the wire electrode and workpiece is huge[18]. Thus, the large gap generating is effective of spark to work surface is a small gap between wire periphery the trim cuts is 0.007 µm causes ROC after the trim cut is slight increased.

4. CONCLUSION WEDM parameters were optimized for MRR and surface roughness individually

1. The most significant factor for MRR and surface roughness for both main cut and trim cut is voltage.

2. The parameters for main cut (Vo = 15, Ip = 8, Ws = 8 ) provides the nominal value of MRR= 2.067 mm3/min

3. The parameters for trim cut (Vo = 6, Ip = 5, Ws = 5 ) provides the nominal value of best SR=1.092 μm.

4. The parameter for evaluated comparison surface roughness with main cut (Vo = 10, Ip =5, Ws = 5) provide value of SR = 1.530 μm and trim cut provide value of SR = 1.148 μm. At the same condition show the TC is significant to improvement the SR.

5. The relationship of process parameter; current increase it a value during pulse on time namely peak current is applied roughness operations with the large surface area, MRR, kerf width and ROC slightly increase.

6. The WEDM of trim cut can be improved the surface roughness, kerf and radial overcut on work materials.

ACKNOWLEDGEMENTS

The authors acknowledge the support from Thammasat University Research Fund, Faculty of Engineering, the Thailand Research Fund (TRF), the Commission on Higher Education of Thailand (the National Research University Project), and the National Research Council of Thailand (NRCT).

10X 1:100 millimeter

10X 1:100 millimeter

WO = 0.007



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experimental investigation for main cut and trim … · 2018-11-12 · figure 2 shows the wire path...

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