A Study of Hole Drilling on Stainless Steel AISI 431 by EDM Using Brass Tube Electrode

2011 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 Hole Drilling on Stainless Steel AISI 431 by EDM Using
Brass Tube Electrode
a a*
Pichai Janmanee , and Apiwat Muttamara
a
Department of Industrial Engineering Faculty of Engineering, Thammasat University, THAILAND

ARTICLEINFO ABSTRACT
Article history: When a depth hole is drilled by EDM, taper is occurred
Received 23 August 2011
Received in revised form which is not desired in the process. This research was focused on
23 September 2011 influence of EDM parameters on material removal rate (MRR),
Accepted 27 September 2011 electrode wear rate (EWR) and tapered hole of martensitic
Available online
27 September 2011 stainless steel AISI 431. The considered factors consist of
Keywords: electrical current, on-time, duty factor, water pressure and servo
EDM, AISI 431, rate. The experimental results reveal that MRR increases when
Electrode, increasing of servo rate. The taper of hole increases with
Brass, increasing of electrical current and servo rate. However, it is
Taper reverse proportion to water pressure and duty factor.

2011 International Transaction Journal of Engineering, Management, &
Applied Sciences & Technologies.

1 Introduction
Nowadays, stainless steel AISI 431 is a popular material used in many industries such as
water pump, kitchenware, and fittings manufacturing industries(Jeong and Min, 2007).
Because of its durability to environment. However, as drilling a hole on stainless steel is
difficult due to its properties. Therefore, various meso or micro machining methods have been
introduced, such as machining, ultrasonic, electrochemical, laser, electrical discharge
machining. Especially an electrical discharge machining (EDM) is one of non-contact thermal
process, which has advantages such as high-precision machining of conductive materials and
*Corresponding author (A. Muttamara). Tel/Fax: +66-2-5643001 Ext.3189. E-mail addresses:
mapiwat@engr.tu.ac.th. 2011. International Transaction Journal of Engineering,
Management, & Applied Sciences & Technologies. Volume 2 No.4. ISSN 2228-9860.
471
eISSN 1906-9642. Online Available at http://TuEngr.com/V02/471-481.pdf

insulating materials regardless of material hardness, (Muttamara et al, 2009&2010). However,
the important type of defect from hole drilling during EDM process is hole taper and hole
accuracy (Ali et al.2009). Therefore, in order to improve hole quality, Sharma et al.(2002) and
Bilgi et al.(2007) investigated optimum values of the process parameters experimentally such
as voltage, feed rate, pulse on time, duty cycle, and the length of un–insulate tool.

Figure 1: Characteristic of taper on EDM

In the EDM sparking hole drilling process, the viscous resistance in the narrow discharge
gap causes difficulty in the removal of debris and bubbles from the working area, abnormal
discharges are occurred and resulting in extensive electrode wear (Yu et al. 2009). Moreover,
the debris moved by pressure flow of dielectric fluid make taper on the workpiece. The hole
taper of workpiece from EDM process, which as shows in Figure 1, can be calculated by
equation (1).

tan (1)

Where D is hole entrances,
d is hole exits, and
L is hole length.

This research focuses on influence of machining variables affecting material removal rate
(MRR), electrode wear rate (EWR), and taper on martensitic stainless steel AISI 431.

2 Experimental Procedure
The experiments were carried out on 35 mm of hole depth of martensitic stainless steel
AISI 431with ZNC-EDM model JM325DZ manufactured by Joemars company, as shown in
Figure2(a). The EDM was carried out on meso-scale machining with a brass tube electrode as

472 Pichai Janmanee, and Apiwat Muttamara

outside diameter of 1 mm, inner hole diameter of 0.3 mm for flushing by dielectric fluid to
remove wear debris and heat ventilation size as shown in Figure 2(b). Principle of tube
electrode drilling is shown in Figure 2(c). The experiments were carried out in the de-ionised,
because of the advantage of material removal rate (Diver et al. 2004). The chemical
compositions and essential physical properties are shown in Table 1 and Table 2, respectively.
Table 3 shows the physical properties of an electrode. The experiment conditions are
contained in Table 4.

(a) EDM super drill model JM325DZ (b) Brass (Cu-Zn40) tube electrode

(c) ZNC-EDM drilling process

Figure 2: Experimental EDM .

473

Table 1: Chemical compositions of stainless steel AISI 431.
Element C Si Mn Cr Ni S P
Weight (%) 0.17 0.6 1.0 17.0 2.0 0.03 0.04

Table 2: Essential physical properties of stainless steel AISI 431.

Condition Temp.
Properties Value
( oC)
Density(x1000 Kg/m3) 7.8 25
Elastic modulus(GPa) 200 25
Tensile strength (MPa) 965 -
Thermal conductivity(W/m – K) 20.2 100
Electrical resistivity(10-9 Ω – m ) 720 25

Table 3: Physical properties of brass tube electrode.
Properties Cu-Zn (60-40)
Melting point ( oC) 910
Density (g/cm3) 10.98 g / cm3
Electrical conductivity(I.A.C.S% at 20 oC) 78~85
Hardness(HRB) 93
Elastic modulus (GPa) 648

Table 4: Experimental conditions.
Parameters Values
Polarity (Electrode) +
Current (A) 1-9
On-time (μs) 10,30,50,90
Duty factor (%) 10-90
Servo rate (mm/sec) 2-10
Water pressure (Kg/cm2) 20-60
Spindle speed (rpm) 100
Dielectric fluid De-ionised water

3 Results and Discussion
As for the experiments were conducted under five process factors such as ; electrical
current, on-time, duty factor, water pressure and servo rate, the data were analyzed as follows:


3.1 Analysis of Water Pressure
The experiments were conducted by varying the water pressure 20, 30, 40, 60 kg/cm2 and
fixing parameter of current at 9 A, on-time at 10 μs, duty factor at 75 %, and servo rate at 2 mm/
sec. High water pressure has influence to cutting process makes gain of the drilling speed. It
increases electrode wearing ratio but reduces taper of drilling wall as shown in Figure3(a-c).
Because high water pressure make debris dispose out from clearance space between a
workpiece and electrode surfaces. Consequently, complete spark often occurred and thus the
material removal rate increased (Diver et al. 2004).

(a) Effect of water pressure to MRR (b) Effect of water pressure to EWR

(c) Effect of water pressure to taper

Figure 3: Variations of water pressure with meso-hole results.

3.2 Analysis of current
In this experiment, we consider of each parameter by varying current 1, 2, 3, 5, 7, 9A and
fixing of parameter of on-time at 10μs, duty factor at 75%, servo rate at 2 mm/sec, and water
pressure at 40kg/cm2. As the results in Figure 4(a), it indicates that the increase of material
removal rate resulted from the raise in current. High current increases material removal rate
ratio and electrode wear ratio as shown in Figure 4(b) (Han et al. 2004). From Figure 4(c),
475

taper of drilled hole is increased because the discharges produce thermal energy according to an
electrical current (Fukuzawa et al. 2004). As estimation of the current increasing while the
cross section is still constant, it makes gain of the density of current per cross section area (Sen
and Shan, 2005), (Guitrau,1997).

(a) Effect of current to MRR (b)Effect of current to EWR

(c) Effect of current to taper

Figure 4: Variations of current with meso-hole results.

3.3 Analysis of servo rate
In this experiment, we consider factor of servo rate 2, 4, 6, 8, 10 mm/sec and fix parameter
of current 9 A, on-time at 10 μs, duty factor at 75 %, and water pressure at 40 kg/cm2. As
shown in Figure 5(a), it was found that the increasing of servo rate lead to decreasing of MRR
because the spark requires an appropriate gap. If servo rate is set up over the required value,
narrow gap will be occurred thus the spark is incomplete or short circuit (Choi and Kim, 1998),
(Han et al. 2004). When servo rate increases, electrode wear and taper increases as shown in
Figure 5(b-c). It can be explained that EDM sparking on servo rate in the narrow discharge gap

changes the contact angle of hole’s wall and the edge of electrode, observed in Figure 5(c).


Figure 5(d) shows the phenomena of EDM drilling on shallow and deep holes (Yu et al. 2009).

3.4 Analysis of Duty Factor and OnTime
The duty factor, which means the ratio between pulse duration and pulse cycle time exerts
an important role on the performance of EDM as shown in Figure6 (a). In this experiment, we
consideration of each parameters by varying duty factor 10, 15, 20, 35, 45, 60, 75, 90 %, on
time 10, 30, 50, 90 μs, and fixing parameters of current at 9 A, servo rate at 2 mm/sec, and water
pressure at 40 kg/cm2, respectively. As can be seen in Figure6 (b-c), the results were found that
the each on-time was suitable for only a specific duty factor. MRR increases with increasing of
duty factor of each on-time. However, increasing of duty factor leads to decreasing of EWR and
taper. Moreover, if increasing of on-time less than 30 µs, it still affects to MRR increases. At 75
% of duty factor for on-time 30 and 50 µs, they give same values of MRR. However, these
parameters results in low EWR and taper.

(a) Effect of servo rate with MRR (b) Effect of servo rate with EWR

(c) Effect of servo rate with taper (d) Edge wear influence to high servo rate

Figure 5: Variations of servo rate with meso-hole results.

477

(a) Relations of duty factor and cycle time (b) Effect of duty factor to MRR

(c) Effect of duty factor to EWR

(d) Effect of duty factor to taper

Figure 6: Variations of duty factor with meso-hole results.


Figure 7 shows impressions of the result from the experiment test with current at 9A,
on-time at 10μs, duty factor at 75%, servo rate at 2 mm/sec, and water pressure at 40 kg/cm2,
respectively. It shows the feature of taper could be achieved. Diameter at electrode entry was
between 1.08 mm and 0.97 mm as shown in Figure 7(a). Figure 7(b) shows result meso-hole
machined exit. Figure 8 shows an image of a section meso-hole machined using the same
condition.

(a) Hole entrance (b) Hole exit

Figure 7: Characteristic of meso-hole and electrode results.

Figure 8: SEM image of section meso-hole.

4 Conclusion
As the results of the material removal rate, electrode wear, taper in the drill hole meso-scale
by brass tube electrode, it can conclude that:
1. The MRR is lower when increasing of servo rate.
2. The taper of hole increases with increasing of electrical current and servo rate.

479

However, it is reverse proportion to water pressure and duty factor.

5 Acknowledgement
This work was supported by the National Research University Project of Thailand Office
of Higher Education Commission and the National Research Council of Thailand (NRCT).

6 References
Ali S., Hinduja S., Atkinson J., Pandya M. (2009). Shaped tube electrochemical drilling of good
quality holes. CIRP Annals - Manufacturing Technology , 58, 185-188.

Bilgi D.S., Jain V.K., Shekhar R., Kulkarni A. (2007). Hole quality and inter-electrode gap
dynamics during pulse current electrochemical deep hole drilling. International Journal
of Advanced Manufacturing Technology, 34, 79-95.

Choi I-H.,Kim J-D. (1998). A study of the characteristics of the electrochemical deburring of a
governor-shaft cross hole. Journal of Material Processing Technology, 75, 198-203.

Diver C., Atkinson J., Helml H.J., Li L. (2004). Micro-EDM drilling of tapered hole for
industrial applications. Journal of Material Processing Technology, 149, 296-303.

Fukuzawa Y., Mohri N., Tani T. and Muttamara A. (2004). Electrical discharge machining
properties of noble crystals. Journal of Materials Processing Technology, 149(1-3), 393
-397.

Guitrau E.B. (1997). The EDM Handbook. Handser Gardner publication Cincinnati, 19-54.

Han F., Wachi S., Kunieda M. (2004). Improvement of machining characteristics of micro-
EDM using transistor type isopulse generator and servo feed control. Precision
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Jeong Y. H., Min B. K. (2007). Geometry prediction of EDM-drilled holes and tool electrode
shapes of micro-EDM process using simulation. International Journal of Machine Tool
and Manufacture , 47, 187-1826.

Muttamara A., Fukuzawa Y., Mohri N., and Tani T. (2009). Effect of electrode Materials on
EDM of Alumina. Journal of Materials Processing Technology, 209, 2545-2552.

Muttamara A., Janmanee P., and Fukuzawa Y.(2010). A Study of Micro–EDM on Silicon
Nitride Using Electrode Materials. International Transaction Journal of Engineering,
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Rajasekhar A., Madhusudhan Reddy G., Mohandas T. (2009). V.S.R. Murti. Influence of
austenitizing temperature on microstructure and mechanical properties of AISI 431
martensitic stainless steel electron beam welds. Materials and Design, 30, 1612-1624.


Sen M., Shan H.S.(2005). A review of electrochemical macro- to micro-hole drilling processes.
International Journal of Machine Tool and Manufacture,45, 137-152.

Sharma S., Jain V.K., Shekhar R. (2002). Electrochemical drilling of inconel super alloy with
acidified NaCl electrolyte. International Journal of Advanced Manufacturing
Technology, 19, 492-500.

Yu Z.Y., Zhang Y., Li J., Luan J., Zhao F., Guo D. (2009). High aspect ratio micro-hole drilling
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Pichai Janmanee is 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). His areas of research include machining
and electrical discharge machining of hard materials.9

Dr.Apiwat 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. His areas of research include machining and electrical discharge
machining of hard materials.

Peer Review: This article has been internationally peer-reviewed and accepted for publication
according to the guidelines given at the journal’s website.

481

A Study of Hole Drilling on Stainless Steel AISI 431 by EDM Using Brass Tube Electrode

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