Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2002-06-13
2004-08-24
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C219S069130
Reexamination Certificate
active
06781080
ABSTRACT:
TECHNICAL FIELD
The present invention relates to improvements in a wire electric discharge machine in which a workpiece is machined by electric discharge generated between a wire electrode and the workpiece.
BACKGROUND ART
In wire electric discharge machining, a workpiece is machined by electric discharge generated when electric discharge energy is supplied between a wire electrode and the workpiece. A rate of electric discharge machining is approximately proportional to an intensity of electric discharge energy supplied between the wire electrode and the workpiece. In order to enhance the rate of electric discharge machining, it is necessary to supply electric discharge energy, the intensity of which is as high as possible, however, when the intensity of supplied energy is too high, breaking of the wire is caused, and it becomes necessary to connect the wire electrode again. As a result, the productivity of electric discharge machining is remarkably impaired.
Accordingly, in order to enhance the productivity of electric discharge machining of a wire electric discharge machine, it is necessary to input electric discharge energy, the intensity of which is as high as possible, while the intensity of electric discharge energy to be inputted is restricted in a range so that breaking the wire is not caused.
FIG. 6
is a schematic illustration showing an arrangement of a conventional wire electric discharge machine. For example, this arrangement is the same as that disclosed in Japanese Unexamined Patent Publication No. 62-19322. In
FIG. 6
, reference numeral
1
is a wire electrode, reference numeral
2
is a workpiece, reference numeral
3
is a wire bobbin, reference numerals
4
a
and
4
b
are flushing nozzles of dielectric fluid, reference numeral
5
is a capstan roller, reference numeral
6
is a pinch roller, reference numeral
7
is an X-table for driving the workpiece
2
in the horizontal direction (X-direction), reference numeral
8
is a Y-table for driving the workpiece
2
in the horizontal direction (Y-direction), reference numeral
9
is an X-axis servo amplifier for controlling a drive motor not shown for driving the X-table
7
, reference numeral
10
is a Y-axis servo amplifier for controlling a drive motor not shown for driving the Y-table
8
, reference numeral
11
is an electric power source used for electric discharge machining, reference numeral
12
is an electric discharge generation detecting means, reference numeral
13
is a pulse control means, reference numeral
14
is a calculation means, reference numeral
15
is a comparison means, and reference numeral
16
is a control means.
Next, operation will be explained below. The wire electrode
1
is held and drawn by the capstan roller
5
and pinch roller
6
so that the wire electrode
1
is made to travel. While dielectric fluid is being supplied in the working gap composed of the wire electrode
1
and the workpiece
2
from the flushing nozzles of dielectric fluid
4
a
,
4
b
, electric power for electric discharge machining, which is electric discharge energy, is supplied in the working gap from the electric power source
11
used for machining, and the wire electrode
1
and the workpiece
2
are moved relatively with each other by the X-table
7
and the Y-table
8
which are positioning means, so that the workpiece
2
can be machined by electric discharge. Positioning control for controlling the relative positions of the wire electrode
1
and the workpiece
2
conducted by the positioning means is governed by the control means
16
, and also control of electric conditions conducted by the pulse control means
13
is also governed by the control means
16
.
The electric power source
11
used for electric discharge machining applies a pulse-like voltage between the wire electrode
1
and the workpiece
2
according to control conducted by the pulse control means
13
. The electric discharge generation detecting means
12
outputs a detection signal into the pulse control means
13
when electric discharge is generated between the wire electrode
1
and the workpiece
2
. The pulse control means
13
stops supplying an electric current to the wire electrode
1
from the electric power source
11
used for machining after a predetermined period of time (pulse width) has passed from the input of a detection signal from the electric discharge generation detecting means
12
. The calculation means
14
is inputted with a signal proportional to the pulse width from the pulse control means
13
and calculates its square. The thus calculated value is made to be an average machining electric current value. The comparison means
15
compares this average machining electric current value with an electric current limit which has been previously set as the maximum electric current value in a range in which wire breakage is not caused in the wire electrode
1
. In the case where the average machining electric current value exceeds the electric current limit, the pulse control means
13
is controlled so that the average machining electric current value can not be higher than the electric current limit.
The conventional wire electric discharge machine is composed as described above, and the supply of a machining electric current is suppressed, the intensity of which is higher than that of the electric current limit which has been previously set as the maximum electric current in a range in which wire breakage is not caused. In this way, breaking of the wire is prevented in the wire electrode
1
.
However, in the prior art described above, it is a problem how to determine the electric current limit. For example, it is obvious that it is harder to break the wire in a case in which the flushing nozzles of dielectric fluid
4
a
,
4
b
are arranged close to the workpiece
2
than in a case in which the flushing nozzles of dielectric fluid
4
a
,
4
b
are arranged distant from the workpiece
2
. However, the conventional wire electric discharge machine does not distinguish a difference of the electric current limit caused by a difference in the relative position of the dielectric fluid nozzle with the workpiece described above.
Accordingly, the conventional wire electric discharge machine can not accurately control to avoid breaking the wire electrode by setting the electric current limit on the assumption that the relative position of the dielectric fluid nozzle with the workpiece is the same in the whole machining process. Therefore, in the case of machining a workpiece which is partly distant from the flushing nozzles, for example, in the case of machining across a counter bored hole which can be frequently seen in a die, if electric discharge clergy is supplied on the assumption that the dielectric fluid nozzle is arranged close to the workpiece, the breakage of the wire electrode is caused when a portion distant from the dielectric fluid nozzle is machined by electric discharge. If electric discharge energy is supplied on the assumption that the dielectric fluid nozzle is distant from the workpiece, it is impossible to obtain a sufficiently high rate of machining. The above problems may be encountered in the prior art.
When an end face or a step portion is machined by electric discharge, electric discharge is intermittently generated in many cases. Therefore, in the case of machining the end face or the step portion, it is necessary to reduce an intensity of electric discharge energy compared with a case in which machining is normally conducted. As described before, in the prior art, the electric current limit is set at a constant value which has been previously set before conducting electric discharge machining. When the electric current limit is set on the basis of the normal electric discharge machining condition, breakage of the wire electrode tends to occur in the case of conducting electric discharge machining on the end face or the step portion of the workpiece. When the electric current limit is set on the basis of conducting electric discharge machining on the end face or the step portion of the
Miyake Hidetaka
Sato Tatsushi
Satou Seiji
Ukai Yoshikazu
Evans Geoffrey S.
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
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