Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
1999-02-05
2001-08-21
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
Reexamination Certificate
active
06278075
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improvement in a wire electric discharge machine, and particularly to a controller of a wire electric discharge machine capable of monitoring a change in thickness of a workpiece and a change in machining current density and also improving a machining performance on a workpiece having a change in thickness.
2. Description of the Related Art
FIG. 28
shows an outline of a conventional wire electric discharge machine. A main pulse generator
1
is constituted by a direct current power source, a circuit comprising switching elements such as transistors and a circuit charging and discharging a capacitor for applying voltage to a gap between a wire electrode
4
and a workpiece
5
to carry out electric discharge machining. A detection voltage generator
2
is constituted by a circuit comprising active elements such as transistors, resistors and capacitors and a direct current power source for applying pulse voltage (voltage lower than main pulse voltage) between the wire electrode
4
and the workpiece
5
for detecting whether the gap between the wire electrode
4
and the workpiece
5
is dischargeable.
Conductive brushes
3
are for conducting electricity to the wire electrode
4
and connected to terminals of the main pulse generator
1
and the detection voltage generator
2
on one side. Further, the workpiece
5
is connected to terminals of the main pulse generator
1
and the detection voltage generator
2
on other side and pulse voltage is applied from the main pulse generator
1
or the detection voltage generator
2
between the traveling wire electrode
4
and the workpiece
5
.
A discharge gap detecting device
6
is connected to the workpiece
5
and the wire electrode
4
, determines whether discharge gap is brought into a dischargeable state based on lowering of the detection pulse voltage and outputs a signal for servo feed to a feed pulse calculating device
7
by the detected voltage changed by a change in the discharge gap. The feed pulse calculating device
7
produces a series of pulses a feed pulse interval of which is normally controlled such that gap average voltage becomes constant to optimize repetition of discharge based on the signal for servo feed and outputs the series of pulses to a feed pulse distributing device
8
. The feed pulse distributing device
8
distributes the series of pulses to the drive pulses of X-axis and Y-axis based on a machining program and outputs the drive pulses to an X-axis motor control device
9
and a Y-axis motor control device
10
for driving a table mounted with the workpiece
5
.
Further, according to a conventional wire electric discharge machine shown by
FIG. 29
, a current detecting circuit
11
detects main pulse current and outputs an average machining current value in a predetermined time period. A display device
12
displays the average machining current outputted from the current detecting circuit
11
, average machining voltage outputted from the discharge gap detecting device
6
and feed speed outputted from the feed pulse calculating device
7
, respectively, by receiving data of numeral values or levels.
First, in order to detect whether electricity can be discharged between the workpiece
5
and the wire electrode
4
, detection pulse voltage is generated from the detection voltage generator
2
and is applied to the gap between the workpiece
5
and the wire electrode
4
. When electricity conduction is caused between the workpiece
5
and the wire electrode
4
and voltage drop is caused between the workpiece
5
and the wire electrode
4
, the discharge gap detecting device
6
detects the voltage drop, determines that electricity can be discharged, transmits a main pulse applying signal to the main pulse generator
1
to thereby generate a main pulse from the main pulse generator
1
and flows main pulse current (discharge machining current) to the gap between the workpiece
5
and the wire electrode
4
. Thereafter, the discharge gap detecting device
6
applies again a detection pulse to the gap after elapse of a pertinent pause time period for cooling the gap. The discharge machining is carried out by repeatedly executing the operational cycle.
In respect of a situation of repeated discharge the feed pulse calculating device
7
produces a series of pulses the feed pulse interval of which is normally controlled such that average voltage of the gap becomes constant in order to optimize repetition of discharge at the gap by the discharge gap detecting device
6
and the feed pulse calculating device
7
. The feed pulse distributing device
8
distributes the series of pulses into drive pulses of X-axis and Y-axis based on a machining program, outputs the drive pulses respectively to the X-axis motor control device
9
and the Y-axis motor control device
10
, drives a table mounted with the workpiece
5
and carries out machining instructed by the machining program on the workpiece
5
.
Further, according to the conventional wire electric discharge machine shown by
FIG. 29
, the average machining current detected by the current detecting circuit
11
, the average machining voltage detected by the discharge gap detecting device
6
and the feed speed calculated by the feed pulse calculating device
7
, are displayed on the display device
12
to thereby indicate a state in machining.
FIG. 11
shows monitor waveforms of the average machining voltage and the average machining current when the workpiece
5
having a section shown by
FIG. 10
is sliced by a conventional controller of a wire electric discharge machine mentioned above. Further,
FIG. 23
shows monitor waveforms of the average machining voltage and the average machining current when the workpiece
5
having a section shown by
FIG. 22
is sliced by the conventional controller of a wire electric discharge machine mentioned above.
Although the plate thickness of the workpiece
5
is varied, as shown by FIG.
11
and
FIG. 23
, in respect of a change in the plate thickness, the average machining voltage remains substantially constant as a whole. Similarly, the average machining current also remains substantially constant.
Normally, when the plate thickness of the workpiece
5
is changed, disconnection of the wire electrode
4
is frequently caused immediately after machining is particularly shifted from a thick portion to a thin portion. Cause therefor seems to be that pulse current is liable to concentrate at one location at a portion having a thin plate thickness. Therefore, conventionally, in order to avoid pulse current from being concentrated on a portion having a thin plate thickness, machining is carried out by modifying a machining condition to that in conformity with the portion having a thin plate thickness from start of machining such that proper average machining current is produced. This operation gives rise to a considerable drop in the machining speed.
When a change in the plate thickness is previously known and when, for example, an operation of reducing machining current in the case of a thin plate thickness and increasing the current in the case of a thick plate thickness can be carried out, the machining time period can be shortened by that amount. Conventionally, as a method of adjusting machining current by finding a change in a plate thickness, there has been devised a method in which thickness information is read from the drawings, a machining program is fabricated by including information of increasing or decreasing machining current and the information is instructed or displayed in machining. However, the thickness information is not necessarily constituted ordinarily to directly provide from dimensions of the drawings. Therefore, in constituting a machining program, the thickness information needs to particularly calculate and the thickness information needs to instruct previously. Otherwise, in carrying out cutting as in a cut model or wire electric discharge machining after coarsely constituting a workpiece already by
Hiraga Kaoru
Kamiguchi Masao
Kurihara Masaki
Evans Geoffrey S.
Fanuc Ltd.
Staas & Halsey , LLP
LandOfFree
Controller of wire electric discharge machine does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Controller of wire electric discharge machine, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Controller of wire electric discharge machine will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2435274