INGENIEUR
M
icro-EDM is a non-conventional electro-
thermal machining operation. It is a
process that depends on the eroding
effect of an electric spark between a work-piece
and an electrode. It is an electro-thermal process
in which material is removed by an electrical
discharge between an electrode cutting tool and
a conductive work-piece, in conjunction with a
flushing dielectric fluid. Micro-EDM is widely used
in mould, die and tool making industries, normally
for machining complex shapes, high surface finish,
high dimensional accuracy, high precision and
difficult to machine materials (Yu et al., 1998).
There is a thin gap between the electrode tool
and work-piece of about 0.025mm. The gap is
maintained by using a servo system. The tool and
work-piece are submerged in a dielectric fluid such
as de-ionised water, kerosene and EDM oil. (Garn
et al., 2011).
An investigation into the performance of
micro-EDM using an resistance capacitive (RC)
discharge generator and a transistor generator
was conducted. Performance measures were
taken for the MRR, relative EWR, surface and
holes quality, machining time and dimensional
accuracy (Jahan et al., 2008). The findings of
the study showed that the RC pulse generator
is able to produce finer quality micro-holes
in tungsten carbide with ideal dimensional
accuracy and good circularity and a RC-type
generator consumes comparatively less time to
produce micro-holes of the same quality. On the
other hand, for electrostatic induction feeding
methods requiring only a single discharge, the
machining speed was much higher but the heat
damage on the surface of a work-piece was
lower (Koyano & Kunieda, 2010). The methods
used to determine the effect of machining
parameters and machining performance by EDM
were studied. One of the most frequently used
methods is the Taguchi method for designing
experiments. Regression analysis was used as a
mathematical tool to establish the relationship
between machining parameters and response
characteristics (Bobbili et al., 2013).
This article explains the design and fabrication
of Portable Modular Electrical Discharge Machines
(PEDM), and testing for various micro hole sizes
and parameters as performance evaluation.
6
48
VOL
2017
VOL 70
55 APRIL-JUNE
JUNE 2013
Design and Fabrication of PEDM
A PEDM is a mechanical structure assembly for
micro electrical discharge machining to facilitate
deployment at any work site. An electrical
discharge machining mechanical structure
assembly for effecting micro electrical discharge
machining comprises the following (Figure 1):
● ●
a common machine frame structure
adapted to house an X-Y positioning
apparatus and an electrode assembly,
machine frame structure comprising a
horizontal support member and a vertical
support member;
● ●
a work-piece holding tank filled with
dielectric fluid resting on X-Y positioning
apparatus adapted to secure the work-
piece to be machined; and
● ●
a controller to control EDM machining
parameters.
An electrode assembly comprises a motorised
feeding mechanism dedicated to maintaining
the vertical positioning of the tool electrode. The
motorised feeding mechanism is a stepper/servo
motor feeding mechanism. The X-Y positioning
apparatus enables the positioning of the machine
tank adapted to secure the work-piece, with the
work piece being immersed in dielectric fluid.
The work-piece tank is further adapted to be in
fluid communication with a dielectric filtration
and recirculation system comprising a dielectric
reservoir, a dielectric fluid filter, an inlet hose
and an outlet hose. The dielectric filtration and
re-circulation system further includ es a pump to
facilitate the circulation of dielectric fluid from the
work-piece holding tank to the dielectric reservoir
and ensures continuous flushing of the dielectric
fluid contained within the work-piece holding tank.
The PEDM assembly includes a DC power supply
that provides DC voltage to a stepper motor drive
which controls the approach of the electrode
to the work-piece. It includes an RC discharge
generator that creates a series of voltage pulses
between the electrode and the work-piece to
effect electrical discharge machining. The method
of controlling the approach of the tool electrode to
the work-piece comprises:
● ●
a f ir s t s te p o f m ov ing t h e t o o l
electrode towards the work-piece until