Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2002-11-22
2004-10-19
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
Reexamination Certificate
active
06806434
ABSTRACT:
TECHNICAL FIELD
The present invention relates to improvements in an electric discharge machine to machine a workpiece when electric discharge is generated between an electrode and the workpiece.
BACKGROUND ART
In an electric discharge machine, electric power is supplied to between an electrode and a workpiece so as to generate electric discharge between these poles, and electric discharge machining is conducted while the electrode and workpiece are relatively moving from each other.
FIG. 14
is a schematic illustration showing a constitution of a wire electric discharge machine which is an example of the conventional electric discharge machine. In
FIG. 14
, reference numeral
1
is a wire electrode composed of a wire of copper or brass, the diameter of which is approximately 0.03 mm to 0.3 mm, reference numeral
2
is a workpiece, reference numeral
3
is an electric power unit, reference numerals
4
a
and
4
b
are feeder lines, reference numeral
5
is a feeder piece, reference numeral
6
is a feed reel, reference numeral
7
is a brake roller, reference numeral
8
is a winding roller, reference numeral
9
is a winding reel, reference numeral
10
is an XY table, reference numerals
11
and
12
are an X-axis motor and Y-axis motor to drive the XY table
10
, reference numerals
13
a
and
13
b
are motor control lines, reference numeral
14
is a control unit, reference numeral
15
is a servo circuit, reference numeral
16
is a working solution, reference numeral
17
is a working solution tank, reference numeral
18
is a pump, reference numerals
19
a
and
19
b
are working solution supply pipes, and reference numeral
20
is a wire guide.
Next, operation will be explained as follows. A working solution
16
is supplied between the wire electrode
1
and the workpiece
2
from the pump
18
via the working solution supply pipes
19
a
and
19
b
. Voltage is impressed between these poles by the electric power unit
3
via the feeder lines
4
a
and
4
b
and the feeder piece
5
. When an electric potential difference between the poles exceeds the electric discharge starting voltage, electric discharge is generated, and the workpiece
2
is machined by this electric discharge.
The workpiece
2
is fixed onto the XY table
10
. When the X-axis motor
11
and Y-axis motor
12
to drive the XY table
10
are driven being controlled, the wire electrode
1
and the workpiece
2
are relatively moved from each other, so that the workpiece
2
can be machined to a predetermined profile.
FIG. 15
is an arrangement view showing an equivalent circuit of the electric power unit and load section in the case of machining a workpiece at high speed by a conventional electric discharge machine. In the view, reference numeral
3
a
is an electric power unit used for rough machining, reference numerals
4
a
and
4
b
are feeder lines, reference numeral
21
is a load section which is shown as an equivalent circuit between the wire electrode
1
and workpiece
2
, reference numeral
22
is inductance, reference numeral
23
is capacitance, reference numeral
24
is a switch, and reference numeral
25
is electric discharge resistance.
Next, operation will be explained below. In
FIG. 15
, the start of electric discharge is represented by the switch
24
in the equivalent circuit. When voltage is not impressed upon the circuit by the electric power unit
3
a
used for rough machining, the switch
24
is turned off. When voltage is impressed by the electric power unit
3
a
used for rough machining, voltage at both ends of the capacitance
23
is raised. When the voltage at both ends of the capacitance
23
is raised to an electric discharge starting voltage, an electric conductive path is formed between the poles and electric discharge is generated. Simultaneously when electric discharge is started, the switch
24
in the equivalent circuit is turned on, and an electric current flows in the electric discharge resistance
25
. By the heat generated from this electric discharge resistance
25
, temperature of the workpiece
2
is locally raised, and machining starts and proceeds so that a portion of material can be removed from the workpiece
2
.
The electric power unit
3
a
used for rough machining is a DC electric power source and directly lets a pulse electric current flow between the poles via a resistance and transistor. Output control of the electric power unit
3
a
is conducted when ON time of the transistor is set. This electric power unit
3
a
used for rough machining can output electric current pulses of various intensities of energy.
As described above, the electric power unit
3
a
used for rough machining reduces the frequency to several tens kHz and lets a high peak electric current flow. Therefore, the workpiece
2
can be machined at high speed. However, since machining is conducted by electric pulses of various intensities of energy, a machined surface becomes rough and irregular. Therefore, the electric power unit
3
a
used for rough machining is not appropriate for highly accurate machining such as finishing of the workpiece
2
.
FIG. 16
is an arrangement view showing an equivalent circuit of an electric power source and load section in the case of highly accurately machining a workpiece by a conventional electric discharge machine. For example, this arrangement is the same as that of the JP-A-6-8049. In this case, like reference characters are used to indicate like reference parts in
FIGS. 15 and 16
. In
FIG. 16
, reference numeral
3
b
is a high frequency electric power source, the frequency of which is, for example, not less than 1 MHz, reference numeral
26
is a DC electric power source, reference numeral
27
is an oscillator, reference numeral
28
is an amplifier, and reference numeral
29
is a matching circuit. Electric power of high frequency is supplied from the high frequency electric power unit
3
b
to between the poles and made to come and off at high speed. At the same time, while electric discharge energy is being restricted by adjusting impedance with the matching circuit
29
, electric discharge is easily conducted, so that a fine portion of material of the workpiece can be removed by electric discharge.
As shown in
FIG. 16
, the high frequency electric power unit
3
b
includes a DC electric power unit
26
, oscillator
27
and amplifier
28
. The DC electric power unit
26
supplies electric power necessary for operating the oscillator
27
and amplifier
28
. The oscillator
27
provides an oscillating output by a resonance circuit in which reactance elements are respectively connected between base emitters, base collectors and collector emitters of a transistor. In order to stabilize the oscillating frequency, a quartz oscillator is used in a portion of the reactance element in many cases. The amplifier
28
amplifies an electric power output of the oscillator
27
. For example, in the case of a transformer connecting type amplifier, transformers are respectively inserted between the base and emitter and also between the collector and emitter of the transistor used for amplification. DC electric power unit is connected between the collector and emitter of the transistor used for amplification, and an output, the electric power of which has been amplified, is taken out via the transformer.
DC electric power source
26
composing the high frequency electric power unit
3
b
is usually controlled so that voltage can be kept constant.
FIG. 17
is a schematic illustration showing an operation region of the output current and output voltage of DC electric power source
26
. In order to prevent the occurrence of damage caused by over-voltage and over-current, DC electric power source
26
is provided with the maximum value Vmax and Imax to restrict the output voltage and output current. Accordingly, the operation region is a hatched portion of the graph shown in
FIG. 17
surrounded by points C, D, F and E.
In order to determine the operation point, it is necessary to set an output voltage. For example, when the output voltage is set at Vo
Hashimoto Takashi
Hayashi Hideaki
Iwata Akihiko
Suzuki Akihiro
Taneda Atsushi
Evans Geoffrey S.
Mitsubishi Denki & Kabushiki Kaisha
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