This study compares the performance of Cu, CuW and AgW electrodes for micro-electrodischarge machining (micro-EDM) of silicon nitride. Copper electrodes provided the highest material removal rate but also the highest electrode wear ratio. Silver-tungsten electrodes had the lowest material removal rate and lowest electrode wear. Copper-tungsten electrodes performed intermediate to copper and silver-tungsten for both metrics. Copper electrodes also produced the smallest and most circular micro-holes, followed by copper-tungsten then silver-tungsten electrodes which produced the largest, least circular holes. The properties of the electrode materials, such as thermal conductivity and melting point, influence the micro-

1. International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies
International Transaction Journal of Engineering, Management, & Applied Sciences & Technologies
http://www.TuEngr.com, http://go.to/Research
A Study of Micro–EDM on Silicon Nitride Using Electrode Materials
a* b c
Apiwat Muttamara , Pichai Janmanee and Yasushi Fukuzawa
a,b
Department of Industrial Engineering Faculty of Engineering, Thammasat University, THAILAND
b
Department of Industrial Engineering Rajamangala University of Technology Krungthep, THAILAND
c
Department of Mechanical Engineering Faculty of Engineering, Nagaoka University of Technology,
JAPAN
ARTICLEINFO A B S T RA C T
Article history: This research proposes Cu, CuW and AgW for electrode
Received 1 August 2010
Received in revised form materials for micro-electro-discharge machining (micro-EDM),
23 August 2010 which are produced with block electrode on insulating Si3N4. With
Accepted 27 August 2010 these electrodes, some trials were evaluated considering the EDM
Available online
10 September 2010 conditions. The machining properties were estimated by the
Keywords: removal rate and tool wear ratio. The same phenomena are applied
Electrical discharge machining at the micron level for micro machining. The conductive layer was
(EDM)
Microelectrodes
investigated on the micro-hole. This study aimed at the minimum of
Wear; electrode wear ratio (EWR) discharge energy to generate the conductive layer resulting to
Micro-EDM success micro-EDM on insulating ceramics.
2010 International Transaction Journal of Engineering, Management, & Applied
Sciences & Technologies. Some Rights Reserved.
1. Introduction
The advanced materials, such as engineering ceramics, are normally difficult to machine
with traditional techniques. In addition, a higher cost for machining these materials would be
expected. The technology of electrical discharge machining (EDM) is a non-conventional non-
mechanical contact machining technology that is widely employed for electrically conductive
materials, irrespective of their hardness. Moreover, engineering ceramics such as ZrO2,Al2O3
*Corresponding author (A.Muttamara). Tel/Fax: +66-2-5643001 Ext.3189. E-mail addresses:
mapiwat@engr.tu.ac.th 2010. International Transaction Journal of Engineering, Management, & Applied 1
Sciences & Technologies. Volume 1 No.1. eISSN: 1906-9642
Online Available at http://tuengr.com/V01-01/01-01-001-007{Itjemast}_Apiwat.pdf

2. (Muttamara et al., 2009) or Si3N4 can machined by EDM with an assisting electrode (Fukuzawa
Y. et al.,1997). In this study, a detailed experimental investigation has been carried out on the
micro-EDM of Si3N4 using RC-generator as it can produce very small amount of discharge
energy. A comparative study has been presented on the performance of Cu, CuW and AgW
electrodes for the finishing micro-EDM. The machined surface were investigated in addition to
MRR and EWR.
2. Materials and Methods
The experiments were performed by Ø 40− 50 μm of Cu, CuW and AgW electrodes on 0.4
mm depth of Si3N4. Table 1 shows physical properties of electrode materials. The EDMed
surface morphology was examined with a scanning electron microscope, an energy dispersive
spectrometer (EDS). The experimental parameters were summarized in Table 2 in the following
experiments.
Table 1: Physical properties of electrode materials.
Electrode Material Melting point Thermal conductivity Specific resistance
(K) (W/m·K) (Ω·m)
Cu 1356 398 1.682x10-4
CuW 3773 205 5x10-4
AgW 1200+ 277 3x10-4
Table 2: Machining Conditions.
Electrode polarity Negative
Discharge current :ie [A] 0.7
Open voltage :ui [V] 110
Discharge duration :t e [μs] 2
Duty Factor [%] 10
Flushing pressure[MPa] 0.1
Machining fluid Kerosene
Rotating [RPM] 1000
2 Apiwat Muttamara, Pichai Janmanee and Yasushi Fukuzawa

3. 2.1 Fabrication of electrode
The electro-discharge machining block electrode method is used, due to its low investment
cost and quick set-up. Negative polarity was selected for tool electrode or micro-electrode. EDM
conditions were divided for 3 steps. Micro-electrode could be fabricated to diameter 40-50 μm.
The micro-electrode machined by the block electrode, is easily broken and have tapered
shape of the micro-rod. This problem can be solved by making some angle on the electrode block
as shown in Figure 1 (Saito et al.,1997).
Tool electrode
CuW
block
Vise
0.1o
Figure 1: Example of the gradient angle on the electrode block.
2.2 Preparation of workpiece
This experiment was carried out on 0.4 mm of Si3N4. A workpiece was prepared by WEDM
that are shown in Figure2. Consequently, the workpiece was generated conductive layer during
WEDM process. We used the generated conductive layer as an assisting electrode. The specific
resistance of the layer was estimated about 8.1x10-2 Ω·cm (Mohri et al.,2003).
During the EDM process, both tool and workpiece undergo surface modification. It is
revealed that when EDM discharge on steel using positive for tool electrode, some carbon from
working on tool surface inhibits the wear of the tool electrode (Mohri et al.,1995). And also, in
case of ceramic machining by EDM, turbostratic carbon from working oil easily to generate to
conduct-ive layer using negative for tool electrode and positive for workpiece. Polarity is found
to be the most important parameter that affects the tool electrode wear rate. In case of micro-hole
machining of carbide by electric discharge machining, B.H.Yan claimed that the tool electrode
*Corresponding author (A.Muttamara). Tel/Fax: +66-2-5643001 Ext.3189. E-mail addresses:
mapiwat@engr.tu.ac.th 2010. International Transaction Journal of Engineering, Management, & Applied 3
Sciences & Technologies. Volume 1 No.1. eISSN: 1906-9642
Online Available at http://tuengr.com/V01-01/01-01-001-007{Itjemast}_Apiwat.pdf

4. wear in negative polarity machining is much larger than that in positive polarity machining (Yan
et al.,1999). For insulating materials, EDM cannot be achieved in a micro-hole machined with
positive polarity.
Electrical
power Control circuit
source (-)
(+)
WEDMed conductive layer
Machining
direction
Wire
TiN coating Si3N4
Figure 2: Schematic illustration of workpiece with WEDMed conductive layer.
3. Results and Discussion
In these electrode materials the high melting point of tungsten is combined with the excellent
thermal conductivity of silver and copper. Both of them were carried out on micro EDM
comparing with normal electrode (copper). Figure 3 shows relationship between machining rate,
electrode wear ratio by Cu, CuW and AgW on Si3N4.
Electrode wear ratio
Material removal rate
(%)
(µm3/sec)
Figure 3: Relationship between machining rate, electrode wear ratio by Cu, CuW and
AgW on Si3N4.
4 Apiwat Muttamara, Pichai Janmanee and Yasushi Fukuzawa

5. Figure 4 shows example of Cu, CuW and AgW microelectrode before and after machining
on Si3N4 using same EDM conditions. As EDM is an electro-thermal process the electrical and
thermal conductivity and the melting point of both the electrode and workpiece play an important
role in the EDM performance. The MRR is strongly dependent on the dielectric breakdown. For
faster MRR, the dielectric breakdown will have to initiate earlier or the breakdown voltage
should be lower. Another reason for this dependency on the electrode material is the electrical
and thermal properties of the material. It has been found that the Cu electrode provides the
highest MRR, followed by the CuW and AgW electrodes. This may be explained by the fact that
AgW has the highest breakdown voltage followed by CuW and Cu. The reason for the higher
breakdown voltage of W is its higher atomic mass and hardness (Ushakov, 2004).
For the EWR of an electrode strongly depends on the electrical and thermal properties of the
electrode materials. The evaporation point, melting point, thermal conductivity and thermal
diffusivity are the important properties that affect to the electrode wear of an electrode (Tsai et
al., 2004). From the result of Figure 3, Cu gives the highest EWR, followed by CuW and AgW
respectively. The basic requirement of an electrode material is the high melting and evaporation
point in addition to high thermal conductivity. It has been found from the study that the EWR is
almost inversely proportional to the melting point of the electrode material.
And from results of holes diameter that are shown in Figure 4. It is found that Cu gives hole
diameter 85 µm, followed by CuW gives hole diameter 92 µm and AgW gives hole diameter 145
µm. The hole diameter seems involve to characteristic of electrode. The clearance of hole is large
because the electrode is eccentric. The cause of eccentric may come from insufficient cooling. In
case of Cu electrode after machining, it gives the least eccentric. Since the copper is the highest
range of thermal conductivity compared to AgW and CuW. So, the heat from the EDM process
can spread through the electrode. It does not concentrate on any portion and not make electrode
loss the straight shape.
4. Conclusion
For the micro-EDM of Si3N4 can be achieved and concluded the following results:
- Negative polarity is suitable for electrode polarity.
- Cu electrode gives the highest MRR, followed by the CuW and AgW electrodes.
*Corresponding author (A.Muttamara). Tel/Fax: +66-2-5643001 Ext.3189. E-mail addresses:
mapiwat@engr.tu.ac.th 2010. International Transaction Journal of Engineering, Management, & Applied 5
Sciences & Technologies. Volume 1 No.1. eISSN: 1906-9642
Online Available at http://tuengr.com/V01-01/01-01-001-007{Itjemast}_Apiwat.pdf

6. Before After
47 μm
a) Cu Machining time= 38 sec
Hole Diameter = 85 μm
Before After
43 μm
b) CuW Machining time = 80 sec
Hole Diameter = 92 μm
Before After
41 μm
c) AgW Machining time = 140 sec
Hole Diameter = 145 μm
Fig.4: Examples microelectrode before and after machining by a) Cu ,
b) CuW .and c) AgW (EDMed condition: ie=0.2 A, te=2μs, to=4μs, ui=110V).
6 Apiwat Muttamara, Pichai Janmanee and Yasushi Fukuzawa

7. 5. Acknowledgements
The authors would like to express their thanks to the Thailand Research Fund (TRF), the
National Research Council of Thailand (NRCT), Office of the Higher Education Commission for
their kind support of supplying materials and equipments for analysis.
6. References
Fukuzawa, Y., Mohri, N., Tani, T. (1997). Electrical discharge machining phenomena of
insulating sialon ceramics with an assisting electrode. International Journal of Electrical
Machining 2, 25–30.
Mohri, N., Y. Fukusima, Y. Fukuzawa, T. Tani and N. Saito. (2003). Layer Generation Process
on Work-piece in Electrical Discharge Machining, Annals of the CIRP, 52(1), 161-164.
Mohri, N., M. Suzuki, M. Furuya and N. Saito. (1995). Electrode wear Process in Electrical
Discharge Machining, Annals of the CIRP, 1, 65-168.
Muttamara, A., Fukuzawa, Y., Mohri, N., Tani, T. (2009).Effect of electrode Materials on EDM
of Alumina. Journal of Materials Processing Technology, 209, 2545-2552.
Saito, N. and N. Mohri. (1997). Possibility to fabricate Micro electrode,Vol.71(4) (in Japanese).
Tsai, Y., Masuzawa, T.(2004). An index to evaluate the wear resistance of the electrode in micro-
EDM, J. Mater. Process. Technol. 149 (1–3), 304–309.
Yan, B. H., F. Y. Huang, H. M. Chow and J. Y. Tsai, Micro-hole machining of carbide by
electric discharge machining. (1999). Journal of Materials Processing Technology,
(87)(1-3), 139-145.
A. Muttamara is an Assistant Professor of Department of Industrial Engineering at Thammasat University. He
received his B.Eng. from Kasetsart University and the D.Eng. in Materials Science from Nagaoka University of
Technology, Japan. Dr. Muttamara is interested involve Electrical Discharge Machining of insulating materials.
Pichai Janmanee is working as an Assistant Professor in the Department of Industrial Engineering at
Rajamangala University of Technology Krungthep (RMUTK), Bangkok, Thailand. He received a BE in Industrial
Engineering from Rajamangala University of Technology and ME in Production Engineering from King’s
Mongkut University of Technology North Bangkok(KMUT’NB). He is also pursuing his PhD studies in
Department of Industrial Engineering at Thammasat University, Pathumtani, Thailand. His areas of research
include machining and electrical discharge machining of hard materials
Yasushi FUKUZAWA is Professor of Material Science and Engineering group in Department of Mechanical
Engineering at Nagaoka University of Technology, Japan. Prof. Dr. Fukuzawa’s fields are material processing and
treatment.
*Corresponding author (A.Muttamara). Tel/Fax: +66-2-5643001 Ext.3189. E-mail addresses:
mapiwat@engr.tu.ac.th 2010. International Transaction Journal of Engineering, Management, & Applied 7
Sciences & Technologies. Volume 1 No.1. eISSN: 1906-9642
Online Available at http://tuengr.com/V01-01/01-01-001-007{Itjemast}_Apiwat.pdf