Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
2002-07-15
2004-06-01
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
Reexamination Certificate
active
06744002
ABSTRACT:
TECHNICAL FIELD
The present invention relates to improvements in a wire electric discharge machining method and a wire electric discharge machine in which an electric discharge is induced in a gap formed between a wire electrode and a workpiece so that the workpiece can be machined.
BACKGROUND ART
Electric discharge machining has acquired a steadfast position as a technique for machining metallic dies and others. Therefore, electric discharge machining has been widely used for machining metallic dies in the automobile industry, electric appliance industry and semiconductor industry.
FIGS. 4A
to
4
E are schematic illustrations for explaining a mechanism of electric discharge machining. In the drawing, reference numeral
1
is an electrode, reference numeral
2
is a workpiece, reference numeral
3
is an arc column, reference numeral
4
is a machining solution and reference numeral
5
represents chips produced in the process of electric discharge machining. While the following processes (a) to (e), which correspond to
FIGS. 4A
to
4
E, are being repeatedly conducted, removal machining is conducted on the workpiece
2
by electric discharges. Each process proceeds as follows.
(a) Formation of the arc column
3
by the generation of electric discharges
(b) Local melt of the workpiece and vaporization of the machining solution
4
by the thermal energy of electric discharges
(c) Generation of vaporizing explosive power by the machining solution
4
(d) Dispersion of the melted portion (chips
5
)
(e) Cooling, coagulation and restoration of insulation between the electrodes executed by the machining solution
The present invention relates to wire electric discharge machining used for gouging, cutting and so forth. Concerning the technique of wire electric discharge machining, there is a strong demand for higher accuracy. For example, when metallic dies used in the field of manufacturing semiconductors, the dimensional accuracy of which is high, are machined, it is necessary to conduct machining with high accuracy of 1 to 2&mgr;m.
FIGS. 5A
to
5
C are schematic illustrations showing an example of the wire electric discharge machining process. In the drawing, reference numeral
1
a
is a wire electrode, reference numeral
2
is a workpiece, reference numeral
4
a
is water which is a machining solution, and reference numeral
6
is an initial hole.
FIG. 5A
shows a first cut process which is a rough machining process,
FIG. 5B
shows a second cut process which is an intermediate finishing process to be conducted after the rough machining process, and
FIG. 5C
shows a third cut process which is a final finishing process.
An example of the first cut process shown in
FIG. 5A
shows a gouging process in which the wire electrode
1
a
is threaded into the initial hole
6
and the workpiece
2
is gouged by electric discharges. In the case of the first cut process described above, since the surface roughness and the accuracy are finished in the later process, it is unnecessary to machine the workpiece with smooth surface roughness high accuracy, and it is important to increase a rate of machining so as to enhance the productivity. In order to enhance the rate of wire electric discharge machining, water
4
a
is strongly jetted out between the electrodes so that chips can be effectively ejected from between the electrodes. In order to spray water
4
a
between the electrodes uniformly and prevent the breaking of the wire electrode
1
a
, a method is adopted in which water
4
a
is stored up in a machining tank not shown and the workpiece
2
is dipped in the water
4
a.
In the conventional wire electric discharge machining method described above, the second cut process (shown in FIG.
5
B), which is executed after the first cut process (shown in FIG.
5
A), and the third cut process (shown in FIG.
5
C), are executed in the water
4
a
which is a machining solution.
When a voltage is impressed between the wire electrode
1
a
and the workpiece
2
, an electrostatic force is generated between the positive and the negative polarity. By this electrostatic force, the wire electrode
1
a
, the rigidity of which is low, is drawn onto the workpiece
2
side, which could be a cause of vibration of the wire electrode
1
a
. Due to the vibration, it becomes difficult to conduct electric discharge machining with high accuracy.
When vaporizing explosive power is generated in the machining solution by electric discharge energy (for example, as shown in FIG.
4
C), the wire electrode
1
a
is given a strong force by the vaporizing explosive power created in the machining solution in a direction opposite to the workpiece
2
, and vibration is generated. Due to the vibration, irregularities are caused on the profile of the workpiece
2
, which impairs the dimensional accuracy.
In the industry of semiconductors in which wire electric discharge machining is utilized, the following uses are increased. For example, in the case of machining metallic dies of IC lead frames, very high accuracy and very smooth surface roughness are required when a workpiece is machined, the dimensional accuracy of which is not more than 1 &mgr;m, and the surface roughness of which is not more than 1 &mgr;m Rmax, and further it becomes necessary to enhance the productivity. Especially, in the case where high accuracy and smooth surface roughness are required as described above, remarkable problems are caused by the aforementioned vibration of the wire electrode.
As a means for solving the above problems caused in wire electric discharge machining conducted in the machining solution, there is disclosed a technique of wire electric discharge machining conducted in the atmosphere while a machining solution is not being interposed between the electrodes. This technique is disclosed by the title of “Enhancement of Accuracy of Second Cut by Electric Discharge Machining Conducted in Atmosphere” written by Adachi et al. of Tokyo University of Agriculture and Technology on page 154 of the seventh issue of the fourteenth volume of “Die Technology” published by Nikkan Kogyo Shinbunsha in 1999. According to this technique, it is disclosed that the straightness of a cut section of a workpiece can be enhanced by wire electric discharge machining conducted in the atmosphere. From the viewpoint of enhancing the accuracy, this technique has a great significance. However, it is difficult to put this technique into practical use because a short circuit tends to occur between the wire electrode and the workpiece compared with the electric discharge machining conducted in a machining solution and the machining can not be stabilized and the rate of machining can not be increased.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a wire electric discharge machining method and a wire electric discharge machine capable of realizing the high accuracy and quality of wire electric discharge machining and also capable of realizing the enhancement of productivity of wire electric discharge machining.
The present invention provides a wire electric discharge machining method in which electric discharge is generated between the electrodes of a wire electrode and a workpiece so as to machine the workpiece by the electric discharge, comprising the steps of: a first step of conducting rough machining in a machining solution; and a second step of conducting finish machining in gas, wherein a relative traveling speed of the wire electrode with the workpiece in the second step is set at a constant speed not lower than a predetermined speed at which a short circuit between the electrodes can not continue for a predetermined period of time and more which has been previously set according to a required specification.
The present invention also provides a wire electric discharge machining method in which electric discharge is generated between the electrodes of a wire electrode and a workpiece so as to machine the workpiece by the electric discharge, comprising the steps of: a first step of conducting rough machining in a machining so
Evans Geoffrey S.
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
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