Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2001-02-27
2003-09-16
Evans, Geoffrey S. (Department: 3729)
Electric heating
Metal heating
Cutting or disintegrating
C700S162000, C700S184000
Reexamination Certificate
active
06621032
ABSTRACT:
TECHNICAL FIELD
The present invention relates to improvements in a wire discharge machining method and apparatus that allows the shape of a machined workpiece to be predicted and displayed. Throughout the specification, by the phrase “wire discharge machining” it is meant that an electric discharge—occurring between a wire electrode and a workpiece—machines the workpiece.
BACKGROUND OF THE INVENTION
FIG. 8
shows a conventional wire discharge machining apparatus. In
FIG. 8
, this wire discharge machining apparatus comprises a workpiece
1
, a wire electrode
2
, a base board
3
, an X table
6
, a Y table
7
, an X-axis servo amplifier
8
, a Y-axis servo amplifier
9
, a working fluid nozzle
11
, a working fluid
12
, a numerical control unit
13
, a program analysis means
14
, a locus movement control means
15
, a program locus drawing means
16
, a display unit
17
, and a drawn locus
18
.
The operation will be described below. In
FIG. 8
, the machining is performed by supplying a working electric power from a working power source, not shown, to a gap between the wire electrode
2
and the workpiece
1
and producing a discharge between them. In this case, the X table
6
and the Y table
7
are driven on the basis of a program stored in the numerical control unit
13
, machining the workpiece into a desired shape. That is, the numerical control unit
13
issues a speed signal to the X-axis servo amplifier
8
and the Y-axis servo amplifier
9
to drive a servo motor, not shown, to move the X table
6
and the Y table
7
, and move the workpiece
1
fixed in the base board
3
on the X table
6
, so that the workpiece is machined.
FIG. 9
shows a positional relation between the wire electrode
2
and the workpiece
1
during the first cut (first machining), in which the center of the wire electrode
2
follows the course of the machining positions calculated by the program analysis means
14
. The wire electrode center path is separated an offset value specified from that path calculated by a given program with an offset value of zero. Also, when the workpiece is removed by discharging, a gap produced between the wire electrode and the workpiece is called a discharge gap, the amount of gap being varied depending on the machining conditions.
A second cut (second machining) method has been disclosed as a common machining technique to finish the workpiece with higher precision by performing a second machining using an offset value varied in the same program. The positional relation between the wire electrode and the workpiece in the second machining is shown in FIG.
10
. As the machining conditions for use with the second machining, the discharge gap and the offset value are set to the smaller values than with the first machining, to secure an allowance for machining in the second machining. A difference in the offset value between the nth machining and the (n−1)th machining is called an nth correction amount. If the correction amount is not selected to be a suitable value, no discharge is effected at all, or conversely a short-circuit is caused, resulting in a situation of not machining the workpiece.
Assume the distance between the surface of wire electrode and the workpiece before machining to be L, the discharge gap at this time to be G, and the minimum gap between the workpiece and the wire electrode to prevent short-circuiting to be Gmax. An instance where the machining is normally performed is shown in FIG.
11
. In
FIG. 11
, the relation among L, G and Gmax is represented in accordance with an expression that follows.
Gmax
(2)<
L<G
(2)
where the number n enclosed by parentheses indicates the nth machining.
On the other hand, an instance where the discharge can not be effected owing to too large distance L between the surface of wire electrode and the workpiece before machining is shown in FIG.
12
. In this case, the relation between L and G is represented by the following expression.
G
(2)<
L
Also, an instance where the discharge is not effected due to too small distance L between the surface of wire electrode and the workpiece before machining to cause a short-circuit is shown in FIG.
13
. In this case, the relation between L and Gmax is represented by the following expression.
L
<Gmax(2)
Herein, a method for calculating the wire electrode center path in the program analysis means
14
and displaying it on the display unit
17
before practical machining will be described below.
FIG. 14
is a flow chart showing a drawing method of a program check provided inside the numerical control unit
13
of the conventional wire discharge machining apparatus, in which the program check comprises analysis means
21
for reading a command content from the content of a specified program, discrimination means
22
for discriminating whether or not the read command content is an end command, program analysis means
23
for calculating the machining position from the program content, and drawing means
24
for drawing the position analyzed by the program analysis means
23
on the display unit.
The operation will be described below. First, a command in the program specified is read by the analysis means
21
in FIG.
14
. If it is discriminated by the discrimination means
22
that the read command is an end command, the program analysis means
23
calculates the machining position followed by the center of the wire electrode, and the drawing means
24
draws a locus with a constant thickness of line on the display unit.
An instance of drawing the locus with this method is shown in
FIGS. 15 and 16
.
FIG. 15
shows a wire electrode center path when the machining is made once, and
FIG. 16
shows the wire electrode center path when the machining is made three times.
The conventional wire discharge machining method and apparatus is configured in the above way. Since the drawing is only involved in the wire electrode center path, there was a problem that the finished surface could not be predicted. In the case where the machining is performed multiple times by varying the offset value in the same program, there was another problem that it was not possible to judge whether the sufficient discharge could be effected in each machining with the set correction amount.
DISCLOSURE OF THE INVENTION
This invention has been achieved to solve the above-mentioned problems, and it is a first object of the invention to provide a wire discharge machining method and apparatus which is enabled to discriminate whether or not the finish shape of machined workpiece is produced as specified visually every time of machining.
It is a second object of the invention to provide a wire discharge machining method and apparatus which is enabled to confirm visually the predicted discharge portion every time of machining and determine the correction amount effectively.
According to a first aspect of the invention, a wire discharge machining method includes adding a predicted discharge gap to the machining conditions and reading the amount of predicted discharge gap in doing a program check, and displaying the predicted discharge gap along with the wire electrode center path on a display unit.
According to a second aspect of the invention, a wire discharge machining apparatus comprises operation means for adding a predicted discharge gap to the machining conditions and reading the amount of predicted discharge gap in doing a program check, and drawing means for displaying the predicted discharge gap along with the wire electrode center path on a display unit.
According to a third aspect of the invention, the wire discharge machining apparatus according to the second aspect of the invention further comprises drawing means for displaying the predicted discharge gap along with the wire electrode center path on the display unit in a different color every time of machining.
According to a fourth aspect of the invention, a wire discharge machining method includes adding a predicted discharge gap to the machining conditions and reading the amount of predicted discharge gap in doing a program che
Katou Kaori
Kawai Yasuhiro
Maeda Miyuki
Naka Shigeaki
Evans Geoffrey S.
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
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