25-08-2017, 09:32 PM
Trepanning of Al2O3 by electro-chemical discharge machining (ECDM)
process using abrasive electrode with pulsed DC supply
Trepanning of Al2O3 by electro-chemical discharge machining.pdf (Size: 928.99 KB / Downloads: 54)
Abstract
Electro-chemical discharge machining (ECDM) of electrically non-conductive high-strength–high-temperature-resistant ceramics such
as aluminium oxide (Al2O3) by trepanning method (i.e. orbital motion of tool) has shown the possibility of drilling large size holes by
comparatively smaller electrodes efficiently and economically. However, at greater machined depth, the conventional electrode
configurations and machining parameters show that machining performance gradually deteriorates with increase in tool depth and finally
cause micro cracks on the machined surface due to thermal shocks at high voltage. To reduce this problem and to enhance the machining
performance during trepanning operation of Al2O3, a spring fed cylindrical abrasive electrode of 1.5mm diameter has been used under
the effect of the three most influential parameters, namely, pulsed DC supply voltage, duty factor and electrolyte conductivity, each at
five different levels to assess the volume of material removed, machined depth and diameteral overcut. The results obtained from this
study revealed that pulsed DC has reduced the tendency of cracking at high supply voltage compared to smooth DC and the machining
ability of the abrasive electrode was better than copper electrode as it would enhance the cutting ability due to the presence of abrasive
grains during machining. In addition to this, trepanning provides the scope for drilling bigger holes.
Introduction
The industrial demand of electrically non-conductive
ceramic, i.e. aluminium oxide (Al2O3) for making machine
tool inserts, aerospace, electrical and electronic components
is increasing because of its high hardness, improved
strength, thermal resistance and corrosion resistance at
high temperature. But on the other hand, production of
small number of parts, for diversified applications, using
mass production methods such as casting or sintering, is
not economically viable. As a result, the field of utilization
of aluminium oxide has remained comparatively narrow
and requires an improved method of machining; especially
to machine electrically non-conductive ceramics.
Experimental design
The present experimental study was intended to machine
deeper holes in sintered Al2O3 piece of size 15157mm3
by adopting trepanning method. A spring fed diamond
embedded cylindrical abrasive tool electrode of 1.5mm
diameter was used as cathode that continuously touches
the workpiece surface with nominal force to ensure a
constant gap between the active grains of electrode and
workpiece immersed few millimeter inside the electrolytic
solution and the cathode was given rotary motion of
20 rpm.
Results and discussion
The combined effect of three significant process parameters,
namely, pulsed DC supply voltage, duty factor and
electrolyte conductivity (each at five different levels), were
assessed on the volume of material removed, maximum
machined depth and diametric overcut during trepanning
of Al2O3 by cylindrical abrasive rotary electrode. These
results are compared with another experimental study
using a gravity feed copper electrode [8] under similar
operating conditions. In both the studies, the volume of
material removed from each sample of Al2O3 was
measured by weighing the workpiece before and after the
machining for 30 min using a digital weighing machine.
Conclusion
Machining of Al2O3 by spring fed orbital motion of tool
(trepanning method) has shown the possibility of drilling
large size holes in ceramics using comparatively smaller size
electrodes efficiently and economically. The use of pulse DC
has reduced the tendency of cracking at higher supply
voltage and saved energy to produce same dimension of
holes with low power input compare to smooth DC.