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Manufacturing industry of nowadays follows a trend towards
high precision machining. Wire electrical discharge machining
(Wire-EDM) has almost occupied an important position in some
production fields, due to its capability of machining hard
materials and intricate shapes. However, the machining accuracy,
especially at corner parts, may be destroyed because of some
phenomena such as wire deflection and vibration, etc. The
purpose of this thesis is to develop a control strategy so that
the machining accuracy at corner parts for wire-EDM can be
improved. Because of the use of low-rigidity wire electrodes, it
is essential to understand the behavior of wire electrodes in
machining process. The main causes of inaccuracies due to wire-
EDM process at corner parts are illustrated. In order to
maintain machining quality at corners, a control strategy based
on fuzzy logic is proposed. The fuzzy rules based on the wire-
EDM's physical characteristics, experimental data, and operator'
s experience are constructed, so that the reduced percentage of
sparking force can be determined by a multi-variables fuzzy
logic controller. Sparking force is modified by means of
regulating the machining coefficient, OFF-TIME. Thechange of the
OFF-TIME of the discharging pulse can not only achieve the above
aim but also have a little influence in the machining process.
The objective of the total control is to improve the machining
accuracy at corner parts, but still keep the cutting feedrate at
fair values. In this thesis, the main phenomena thought to be
predominantly related to inaccuracies at corners can be improved
by the proposed control strategy. As a result of experiments,
machining errors of corner parts, especially in rough-cutting,
can be reduced to less than 50% of those in normalmachining,
while the machining process time increases not more than 10% of
the normal value.
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