30-06-2012, 05:45 PM
A study on pulse control for smallhole electrical discharge machining
A study on pulse control.pdf (Size: 1.72 MB / Downloads: 44)
Introduction
EDM processes are characterized by a high aspect
ratio and a slow drilling speed, with a higher tool wear rate (TWR)
than normal EDM. Smallhole
EDM, with a tool electrode diameter
of 100 mm, is within the scope of microEDM,
because (Masuzawa
and Tönshoff, 1997) described that microEDM
is specially devoted
to the manufacture of microcomponents
whose sizes range from
1 to 999 mm. Yu and Rajurkar (2005) presented the fact that the
difficulty of removing the debris formed during an erosion process
is a major problem in drilling smallholes,
thereby limiting the
achievable aspect ratio.
The accumulation of debris also makes the dielectric fluid easier
to break down, thus inducing arc pulses. Arc pulses prefigure
a deterioration of the gap status and the instability of the EDM
process, which lead to an inefficient EDM process and damage the
surface quality in finish machining. The extent to which arc pulses
deteriorate the stability of a drilling process is even more drastic
in smallhole
EDM processes, even though the percentage of arc
pulses is less than 5%, as Jiang et al. (2011) presented.
Development of pulse generator
A rectangle pulse generator was developed for smallhole
electrical
discharge machining. The main discharge circuit, the sweep
pulse circuit and the pulse detection and control module were
designed.
Conclusion
In this paper, a pulse generator with a sweep pulse circuit was
developed. The voltage of EDM pulses was detected by a highspeed
comparator. A FPGA chip was used as a master controller of the
control module for the determination of pulse discharge status and
the MOSFET switching. A series of experiments were carried out
to examine the machining performance when shutting off harmful
pulses and applying sweep pulses. Some of the major conclusions
are given as follows.
1. Shutting off harmful pulses is helpful in improving the machining
efficiency and decreasing the tool wear rate. The application
of sweep pulses further improves the machining efficiency,
whereas the tool wear rate is higher than that by shutting off
harmful pulses.
2. The quality of the through smallhole
drilled by shutting off
harmful pulses is better than that by using normal pulses. The
taper of the through smallhole
drilled by applying sweep pulses
is higher than that by shutting off harmful pulses. Also the edges
of the hole by shutting harmful pulses are cleaner than those by
normal pulses.