08-08-2012, 04:31 PM
Electrochemical Discharge Machining Process
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ABSTRACT
Electrochemical discharge machining process is evolving as a promising micromachining
process. The experimental investigations in the present work substantiate this trend. In the present
work, in situ, synchronised, transient temperature and current measurements have been carried
out. The need for the transient measurements arose due to the time-varying nature of the discharge
formation and time varying circuit current. Synchronised and transient measurements revealed
the discrete nature of the process. It also helped in formulating the basic mechanism for the
discharge formation and the material removal in the process. Temperature profile on workpiece
and in electrochemical discharge machining cell is experimentally measured using pyrometer,
and two varieties of K-type thermocouples. Surface topography of the discharge-affected zones
on the workpiece has been carried out using scanning electron microscope. Measurements and
surface topographical studies reveal the potential use of this process for machining in micron
regime. With careful experimental set-up design, suitable supply voltage and its polarity, the
process can be applied for both micromachining and micro-deposition. It can be extended for
machining and or deposition of wide range of materials.
INTRODUCTION
Electrochemical discharge machining (ECDM)
is an advanced hybrid machining process comprising
the techniques of electrochemical machining (ECM)
and electro discharge machining (EDM). The process
is also referred as electrochemical spark machining
(ECSM) process. The process is important since
it can support a variety of materials including metals,
ceramics, composites, alumina, glass, etc. The process
has possible potential usage in the following areas:
LITERATURE SURVEY
Kulkarni and Jain1 have highlighted some of
the current trends and techniques used for microfabrication
of parts using electrochemical processes
(ECM, EDM, ECDM/ECSM, etc). Micro-fabrication
of the parts can be achieved by combing
micromachining and micro-deposition processes
in various sequences. Schuster2, et al. at the Fritz
Haber Institute of the Max Planck Society, Berlin,
have developed a simple ECM procedure to fabricate
3-D micro-structures. To obtain the delicate copper
prism in the middle of the hole-cavity with a
cross section area of 5 m x 10 m x 12 m,
sitting on a pedestal 15 m x 15 m x 10 m,
the tool electrode of platinum wire (10 m dia)
was used. Machining operation was performed
using pulse voltage of 1.6 V, pulse current in the
range of 0.02 - 0.03 A, pulse-on time of 50 ns,
and frequency of 2 MHz. The complete machining
time for the structure was 30 min.
EXPERIMENTAL
As mentioned, ECDM is an extension of the
ECM process. The electrolyte cell is similar to that
used in ECM. In ECDM, anode is made up of inert
material while cathode normally is made of copper.
Dilute hydrochloric acid (HCl) is generally used
as the electrolyte. When a voltage is applied to the
cell in proper polarity, i.e., positive terminal to
anode and negative terminal to cathode, reduction
of electrolyte with liberation of hydrogen gas takes
place at the cathode tip. This is similar to the
ECM process.When the applied voltage is increased
beyond a threshold value, hydrogen gas bubbles
evolve in large number at the tip of the cathode
and grow in size. Discharge occurs at the tip of
the cathode.
RESULTS AND DISCUSSION
Figure 2 gives the photograph of the display
of the stored waveforms and shows the representative
values of current and the resulting temperature
transients for copper workpiece. The upper waveform
represents the current transient and the lower waveform
the ensuing temperature transient at the dischargeaffected
zone on the workpiece. Here, two current
pulses are seen with a temperature pulse occurring
in between. Each current pulse represents the distinct
formation of the discharge at the tip of the cathode.
With the arrival of the first current pulse of about
8 A, the temperature of the copper workpiece in
the localised region increases to 865 oC due the
bombardment of the electrons on the workpiece
due to discharge formation22. The temperature soon
reduces to 815 oC after 2.8 ms.