High
precision, high speed
DS
Shrivastava explains the benefits of EDM which has found various applications
in the mould making industry
EDM (Electrical Discharge Machining) is a noncontact, force free metal
removing process which eliminates mechanical distortion and gives a
burrfree cutting of a hardened material. As there is always a physical
gap between the material being cut and the cutting material, it is very
difficult to describe such a complex process of which most parts are
invisible and are accompanied by certain physical and chemical phenomenon
such as sound, heat, light and electromagnetic radiations. Over a period
of 20 years, many innovative ideas have made the process a lot more
predictable and it is in this period that EDMs have become more productive.
Technological innovations in the field of EDM aim to enhance the EDM
process output in terms of job completion time, speed, job accuracy
and the surface finish, among other things. This is achieved by improving
the efficiency of the process of EDM, by modifying the machine configuration,
and by utilising improvements in the field of electrode material.
Traditionally, EDM has been classified into two distinct categories
because of the different ways adopted in performing the process. These
are Sink EDM or Plunge EDM or RAM EDM, and Wire EDM.
SINK
EDM
ELECTRODE
– DESIGN AND MANUFACTURING
The output performance of EDM such as surface finish, accuracy and
overall productivity mainly depends upon the electrode design and the
material selected for the electrode. Commonly, 70 per cent of the cost
of the process is labour cost and the remaining 20-30 percent is the
cost of manufacturing the electrode.
There are almost 15 types of electrode materials available for EDM
out of which copper and graphite are the most popular. The primary considerations
for choosing a suitable material for the electrode (copper or graphite)
are job size, finish requirements and multiple electrode option. Commonly,
the preference is graphite when the electrode size is bigger as graphite
can be machined faster on the machining centre.
Copper, on the other hand, is more popular in India because it is cheap
and can be machined on a simple machine like Lathe. The manufacturing
of a copper electrode on wire EDM is faster whereas usage of graphite
for the same process is very slow and troublesome, and mostly avoided.
ACHIEVABLE
JOB ACCURACY ON SINK EDM
One of the major advantages of using graphite for the EDM process
is the thermal stability of the material. This property leads to an
extremely low electrode wear compared to copper.
A high electrode wear hampers the EDM machine to produce a replica
of the electrode used and in turn affects the accuracy and finish of
the job. Various features and strategies are used to accurately achieve
the dimension and finish on the die or mould.
WIRE
EDMS (WEDM)
These machines are similar to a Sink EDM machine in all respects except
design. For example, all Wire EDM machines are CNC machines whereas
Sink EDM may or may not be a CNC machine.
WIRE
ELECTRODE MATERIAL
As in Sink EDM, the electrode material of the wire plays a very vital
role in achieving the final output in this process too. There are almost
10 different characteristic parameters of a wire that are responsible
to determine its suitability for the process. Brass, copper, molybdenum
or zinc coated brass are available in the market.
........CONTD
