Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2002-06-26
2004-08-10
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
Reexamination Certificate
active
06774334
ABSTRACT:
TECHNICAL FIELD
The present invention relates to improvements in a wire discharge machining method and apparatus that machines a workpiece by supplying working electric power to an interpole space between a wire electrode and the workpiece and producing a discharge.
BACKGROUND ART
FIG. 10
is an explanatory diagram showing a conventional wire discharge machining apparatus. In
FIG. 10
, this wire discharge machining apparatus comprises a wire electrode
1
, a workpiece
2
, a wire bobbin
3
, a working fluid
4
, working fluid nozzles
5
a
and
5
b
as working fluid supplying means for supplying the working fluid
4
to an interpole space between the wire electrode
1
and the workpiece
2
, a capstan roller
6
, a pinch roller
7
, an X table
8
for driving the workpiece
2
in a horizontal direction (X direction), a Y table
9
for driving the workpiece
2
in a horizontal direction (Y direction), an X-axis servo amplifier
10
for controlling a drive motor, not shown, for driving the X table
8
, a Y-axis servo amplfier
11
for controlling a drive mrotor, not shown, for driving the Y table
9
, working power supplying means
12
, bath voltage detecting means
13
, and control means
14
.
The operation will be described below. The wire electrode
1
is carried between the capstan roller
6
and the pinch roller
7
, and dragged to be opposed against the workpiece
2
. A working electric power as discharge energy is supplied into the interpole space between the wire electrode
1
and the workpiece
2
by the working power supplying means
12
, while the working fluid
4
is supplied into the interpole space through the working fluid nozzles
5
a
and
5
b
, whereby the workpiece
2
is worked into a predetermined contour shape by moving the workpiece
2
relative to the wire electrode
1
employing the X table
8
and the Y table
9
as positioning means. The control means
14
controls the positioning means to position the workpiece
2
relative to the wire electrode
1
and makes control for the electrical machining conditions.
FIG. 11
is an explanatory view showing a machining example of a corner portion by the conventional wire discharge machining apparatus. In
FIG. 11
, reference numeral
1
denotes a wire electrode, reference numeral
2
denotes a workpiece, reference numeral
15
a
denotes an outer corner, reference numeral
15
b
denotes an Lnner corner, and the paths A to E denote machining paths of the wire electrode
1
to machine the workpiece
2
.
FIG.
11
(
a
) is a view showing a machining example in which an edge corner portion is machined, and FIG.
11
(
b
) is a view showing a machining example in which a circular arc corner portion is machined.
For instance, in a case where the edge corner portion of the workpiece
2
is worked by moving the wire electrode
1
along the path A to C to E, it is known that a round shear droop as indicated by the solid line is produced in the outer corner portion
15
a
and the inner corner portion
15
b
, as shown in FIG.
11
(
a
). Thi s shear droop may be caused by low rigidity of the wire electrode
1
. That is, the wire electrode
1
is deflected due to a discharge reaction force developed between the wire electrode
1
and the workpiece
2
, forcing the wire electrode
1
to actually take the path A to B to D to E, so that the workpiece
1
is worked excessively in the outer corner portion
15
a
, and unworked in the inner corner portion
15
b
. The size of this shear droop is increased as the discharge reaction force is larger, or the machining rate is higher, and gets to about several tens &mgr;m to several hundreds &mgr;m in the ordinary roughing.
In a case where the circular arc corner portion of FIG.
11
(
b
) is worked, the wire electrode
1
is run along the path A to B to F to D to E, but practically takes the path A to B to G to D to E, due to the same reason, so that a shear droop is produced in the outer corner portion
15
a
and the inner corner portion
15
b
in the same way as in FIG.
11
(
a
).
As described above, in working the corner portion, there was a problem that a shear droop was produced in the edge corner portion and the circular arc corner portion, resuitino in a lower precision of the machined configuration.
The techniques for preventing such shear droop from arising in the ccrner portion of the workpiece in machining the corner portionweredisclosedin JP-A-2571077, JP-A-8-39356 and JP-A-2000-84743. The conventional art involves improvements in the machining precision of the corner portion by changing the relative movement speed of the wire electrode to the workpiece before and after the corner portion, and the electrical machining conditions to reduce a deflection of the wire electrode while machining the corner portion.
In these conventional arts, however, the corner portion is worked by using a significantly smaller discharge energy than when the linear portion is worked to reduce deflection of the wire electrode in working the corner portion, resulting in quite lower machining rate. Such a significant reduction in the machining rate may be the to be a lethal problem for the wire discharge machining apparatus in the light of the present situation in which the important factors of performance required are regarded to be the machining precision and the machining productivity.
Along with the improvements in the wire discharge machining in the respects of the power control for preventing disconnection or the wire electrode, the machining rate of the wire discharge machining is increased rapidly up to about 200 to 250 mm
2
/min, or about 350 to 400 mm
2
/min at the maximum machining rate, for example. That is, the discharge energy input into the interpole space between the wire electrode and the workpiece is increased. Accordingly, the wire electrode is more deflected during the machining due to an increased discharge reaction force. In such current situation, there is a problem that when the corner portion is worked at a desired precision employing the techniques of the conventional art, the machining rate is decreased significantly in the corner portion, offsetting the effect of higher machining rate, irrespective of an increased input discharge energy.
As described above, it is very important that the machining configuration precision of the corner portion is improved in machining the corner portion of the workpiece, and the machining productivity is enhanced by recducing the machining time for the corner portion to the minimum.
As a method of suppressing the increased machining time for the corner portion, it is known to correct the machining path. However with such method, the corner portion may be worked while the wire electrode is deflected, whereby it was impossible to improve the configuration precision of the corner portion over the entire area from the upper face of the workpiece through the sublevel face to the lower face. Accordingly, it is considered that the wire electrode may be deflected as least as possible, namely, the discharge energy may be decreased down to the minimum, at the corner portion to improve the machining configuration precision of the corner portion over the entire area from the upper face of the workpiece through the sublevel face to the lower face, thereby working the corner portion at the slowest machining rate. Hence, in the conventional art, there was another problem that the machining configuration precision and the machining productivity could not be improved consistently in working the corner portion of the workpiece.
DISCLOSURE OF INVENTION
The present invention has been achieved to solve the above-menticned problems, and it is an object of the invention to provide a wire discharge machining method and apparatus in which the machining configuration precision and machining productivity for the corner portion can be improved consistently in working the corner portion.
A wire discharge machining method according to this invention for machining a workpiece by supplying a discharge energy into an interpole space between a wire electrode and the workpiece
Evans Geoffrey S.
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
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