A study of ultrasonically aided micro-electrical-discharge

Journal of Materials Processing Technology 139 (2003) 226–228

A study of ultrasonically aided micro-electrical-discharge
machining by the application of workpiece vibration

Changshui Gao∗, Zhengxun Liu

Department of Mechanical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing, PR China

Abstract

In this paper the authors present a new combined method of ultrasonic and electrical-discharge machining. The most noteworthy feature
of the method is that the ultrasonic transducer does not vibrate the tool, as in traditional ultrasonic machining, but vibrates the workpiece.
Experimental results show that the workpiece vibration induced by ultrasonic action has a significant effect on the performance of the
micro-EDM process. Experimental results show that the efficiency and the aspect ratio of the hole of the ultrasonic-aided micro-EDM are
noticeably increased.
© 2003 Published by Elsevier Science B.V.

Keywords: Micro-EDM; Ultrasonic; Workpiece vibration

1. Introduction destroys the machining stabbing, especially when the elec-
trode is very thin. As a result, higher machining efficiency
There is heavy industrial demand for micro holes in and machining accuracy are very difficult to achieve in with
various materials. Many methods have been developed to a deep micro hole by electrode vibration.
meet this requirement. Micro-EDM is an important method
for the machining of deep micro holes, especially for In order to solve the problem stated above, in this paper
difficult-to-machine materials [1–4]. In electrical-discharge the authors present a new method. The most noteworthy fea-
machining, material removal starts when a generator applies ture of the method is that the ultrasonic transducer does not
a voltage between the workpiece and the tool electrode. vibrate the tool, as in traditional ultrasonic machining, but
This voltage is high enough to produce a spark between the vibrates the workpiece. The workpiece is directly attached to
two electrodes. The spark melts a small material volume a transducer to secure the vibration. One advantage of work-
on each of the electrodes. The dielectric fluid that fills the piece vibration instead of tool vibration is that it permits a
gap between the electrodes removes part of this material. freer tool system design because it does not include the set
The principle of micro-EDM is same as for conventional of transducer, horn and cone. Another advantage is that it is
EDM, but it has some special characteristics of art. In much simple and more compact than traditional systems.
micro-EDM, the circulation of dielectric and the removal of
machine-debris are very difficult, especially when the hole 2. Experimental procedure
or the cavity becomes deep, so the machining efficiency is
low and the aspect ratio of the hole is small. To improve Fig. 1 shows the experimental apparatus of this method.
the machining performance of EDM, a combined method Experiments are performed using an micro-EDM machine
of ultrasonic and electrical-discharge machining has been with a transistor switching circuit, which includes a spindle,
developed by some researchers [5–8]. In this, ultrasonic a worktable, a DC motor, a servo control, a pulse generator,
vibration is applied to the electrode. In this method, due to an ultrasonic transducer, and an ultrasonic generator.
the sucking and vibrating, dielectric circulation and debris
removal are improved by ultrasonic vibration. However, The pulse generator uses a high power N-channel filed
in micro-EDM, ultrasonic vibration of the electrode has a effect transistor as a switch, the smallest output energy
problem in that a large vibration of the rotating electrode and pulse duration can be controlled to 10−7 J and 0.1 ␮s,
respectively.
∗ Corresponding author.
Fig. 2 shows the ultrasonic transducer. The transducer is
made of four cylindrical piezoelectric elements, which are
piled up according to the same polarity. The piezoelectric

0924-0136/03/$ – see front matter © 2003 Published by Elsevier Science B.V.
doi:10.1016/S0924-0136(03)00224-3

C. Gao, Z. Liu / Journal of Materials Processing Technology 139 (2003) 226–228 227

Table 1 Electrode (+)

Polarity 200 mA
50%
Discharge current (Ip) Tungsten
Duty factor (D.F) 43 ␮m
Electrode material Stainless steel, copper
Electrode diameter 20 kHz
Workpiece material EDM oil
Ultrasonic frequency
Machining fluid

Fig. 1. The combined apparatus of ultrasonic and micro-EDM.

Fig. 2. Ultrasonic transducer.

Fig. 4. The relationships between the removal rate and the ultrasonic
driving voltage.

Fig. 3. Principle of the ultrasonic generator. ing voltage. The displacement of the piezoelectric element
increases in direct ratio with the applied voltage within a
transducer is mounted on the worktable of a micro-EDM definite range, so the vibration amplitude of the workpiece
machine. changes with driving voltage. The vibration amplitude of
the workpiece is less than 1 ␮m, so the workpiece vibration
The ultrasonic generator was developed such as to have is not enough to destroy the machining stability. The higher
a frequency, voltage and pulse duration that can be adjusted vibration amplitude causes a large pressure change between
continuously. Fig. 3 shows the principle of the ultrasonic the electrode and the workpiece. As a result the dielectric
generator. In this system, the voltage can be modulated from circulation and machine-debris removal are enhanced.
0 to 350 V, frequency can be modulated from 2 to 50 kHz,
and the smallest value of pulse duration is 1 ␮s. Fig. 5 shows the relationships between the removal rate
and different machining method. The pulse duration is
3. Experimental results and discussion 4 ␮s, the workpiece material is stainless steel and the ul-
trasonic driving voltage is 300 V. As shown in this figure,
The experiments were conducted to investigate the ef- the removal rate decreases when the workpiece thickness
fects of ultrasonic vibration of the workpiece on the ma- increases whether or not employing ultrasonically aided
chining performance. The machining conditions are shown machining. However, the removal rate of the ultrasonically
in Table 1. The polarity of the electrode is kept positive
throughout the experiment because the removal rate is higher Fig. 5. The relationships between the removal rate and different machining
than that in the reverse case. method.

Fig. 4 shows the relationships between the removal rate
and the ultrasonic driving voltage. Here, the removal rate is
expressed as the rate of workpiece thinning to the total ma-
chining time. The initial workpiece thickness is 0.2 mm and
the pulse duration is 0.4 ␮s. The results in Fig. 4 show that
the removal rate increases with increase of ultrasonic driv-

228 C. Gao, Z. Liu / Journal of Materials Processing Technology 139 (2003) 226–228

4. Conclusions

Fig. 6. The relationships between the removal rate and different workpiece The authors have developed a new ultrasonically aided
materials. EDM method by the application of workpiece vibration. Ex-
periments using the new method and comparative experi-
aided micro-EDM is about four to eight times larger than ments between the new method and traditional micro-EDM
that of micro-EDM. When the workpiece thickness is 1 mm, also have been done. The experimental results show that
the removal rate of non-ultrasonic-aided machining is very the workpiece vibration induced by the ultrasonic action has
low and is not viable available. In micro-EDM, the cir- a significant effect on the performance of the micro-EDM
culation of dielectric and the removal of machine-debris process. It was found that the efficiency of the ultrasoni-
are very difficult, especially when the aspect ratio of cally aided micro-EDM is eight times greater than that of
the hole is higher. In this case, the ultrasonic vibration micro-EDM when the workpiece thickness is 0.5 mm, the
of the workpiece improved the dielectric circulation and material is stainless steel, and the tool diameter is 43 ␮m.
machine-debris removal and it increases the aspect ratio When material is tungsten, the results also show that the
of hole. aspect ratio of the hole is noticeably increased. Therefore,
ultrasonically aided EDM by the application of workpiece
Fig. 6 shows the relationships between the removal rate vibration is a very efficient method to use for micro-EDM.
and different workpiece materials in the micro-EDM of cop-
per and stainless steel. The pulse duration is 4 ␮s and the References
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