U.S. patent application number 09/264863 was filed with the patent office on 2001-12-13 for electorode wire for electrical discharge machining apparatus.
Invention is credited to AOYAMA, SEIGI, KAWANO, HIDEO, KIMURA, TAKAMITSU, SATO, TAKAHIRO, SHIMOJIMA, KIYOSHI, TAMURA, KOICHI, WATABE, MASATO.
Application Number | 20010050269 09/264863 |
Document ID | / |
Family ID | 26421544 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010050269 |
Kind Code |
A1 |
SHIMOJIMA, KIYOSHI ; et
al. |
December 13, 2001 |
ELECTORODE WIRE FOR ELECTRICAL DISCHARGE MACHINING APPARATUS
Abstract
It is an object of the invention to provide an electrode wire
for an electrical discharge machining apparatus, which is
low-priced in cost of production, has sufficient conductivity and
strength at high temperature and is suited for improving the speed
of electrical discharge machining. Cu--Zn alloy covering layer is
formed around a core metallic wire formed of Cu-0.02 to 0.2 Zr
alloy or Cu-0.15 to 0.25 Sn-0.15 to 0.25 In alloy.
Inventors: |
SHIMOJIMA, KIYOSHI;
(IBARAKI, JP) ; AOYAMA, SEIGI; (IBARAKI, JP)
; KAWANO, HIDEO; (IBARAKI, JP) ; TAMURA,
KOICHI; (IBARAKI, JP) ; SATO, TAKAHIRO;
(IBARAKI, JP) ; KIMURA, TAKAMITSU; (IBARAKI,
JP) ; WATABE, MASATO; (IBARAKI, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Family ID: |
26421544 |
Appl. No.: |
09/264863 |
Filed: |
March 9, 1999 |
Current U.S.
Class: |
219/69.12 ;
219/69.11; 219/69.15 |
Current CPC
Class: |
B23H 7/08 20130101 |
Class at
Publication: |
219/69.12 ;
219/69.11; 219/69.15 |
International
Class: |
B23H 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 13, 1998 |
JP |
10-80547 |
Apr 23, 1998 |
JP |
10-131397 |
Claims
What is claimed is:
1. An electrode wire for an electrical discharge machining
apparatus comprising: a core metallic wire formed of Cu-0.02 to 0.2
WT % Zr alloy or Cu-0.15 to 0.25 WT % Sn-0.15 to 0.25 WT % In
alloy, and a covering layer formed of Cu--Zn alloy.
2. An electrode wire for an electrical discharge machining
apparatus, comprising: a core metallic wire formed of Cu-0.02 to
0.2 WT % Zr alloy or Cu-0.15 to 0.25 WT % Sn-0.15 to 0.25 WT % In
alloy, and a Cu--Zn alloy covering layer formed of a single phase
composition of only .alpha. phase.
3. An electrode wire for an electrical discharge machining
apparatus according to claim 2, wherein: said Cu--Zn alloy covering
layer contains Zn of 32 to 38 weight percent.
4. An electrode wire for an electrical discharge machining
apparatus according to claim 1, wherein: a thickness of said Cu--Zn
alloy covering layer is 30 to 40 .mu.m.
5. An electrode wire for an electrical discharge machining
apparatus, comprising: a core metallic wire formed of Cu-0.02 to
0.2 WT % Zr alloy or Cu-0.15 to 0.25 WT % Sn-0.15 to 0.25 WT % In
alloy, and a Cu--Zn alloy covering layer formed of a mixing
composition of .alpha. and .beta. phases.
6. An electrode wire for an electrical discharge machining
apparatus according to claim 5, wherein: concentration of Zn of
said Cu--Zn alloy covering layer in a shallow layer below a surface
of said Cu--Zn alloy covering layer is lower than that in an inner
portion of said Cu--Zn alloy covering layer.
Description
FIELD OF THE INVENTION
[0001] This invention relates to an electrode wire for an
electrical discharge machining apparatus, and especially to an
electrode wire for an electrical discharge machining apparatus
having a covering layer.
BACKGROUND OF THE INVENTION
[0002] As a conventional electrode wire for an electrical discharge
machining apparatus, a Cu--Zn alloy wire (a brass wire) containing
Zn of 32 to 36 weight percent is used.
[0003] Besides this, a composite wire composed of a core metallic
wire formed of a steel wire and a covering layer formed of Cu-35 Zn
alloy is known as an electrode wire for an electrical discharge
machining apparatus with height strength. Moreover, an electrode
wire for the same, which is composed of a core metallic wire formed
of Cu alloy, such as Cu-0.15Sn or Cu-0.15Ag alloy, and a covering
layer formed of Cu-35Zn alloy is known (Japanese Patent Kokai
No.6-47130).
[0004] As a method for increasing electrical discharge machining
speed and obtaining an electrode wire for the same with high
efficiency, a method, in which concentration of Zn of Cu--Zn alloy
is increased or heat-resisting property of the electrode wire is
improved by adding Al to Cu--Zn alloy, is known (Furukawa Electric
Review, No.75, March, 1985).
[0005] Recently, further elevation of electrical discharge
machining speed is demanded from a view point of improvement of
productivity. In order to meet the aforementioned demand, an
electrode wire with covering layer for an electrical discharge
machining apparatus, which is composed of a core metallic wire
formed of Cu-2.0Sn, Cu-0.3Sn, Cu-13Zn, Cu-0.6Ag or Cu-4.0Zn-0.3Sn
and a covering layer formed of a Cu--Zn alloy containing Zn of high
weight percent, is proposed (Japanese Patent Kokai
No.5-339664).
[0006] However, in the aforementioned electrode wire for the
electrical discharge machining apparatus, since the Cu--Zn alloy
layer contains Zn of 38 to 49 weight percent, the Cu--Zn alloy
layer is formed of a mixing composition of .alpha. and .beta.
phases, or a single phase composition of only .beta. phase. Since
cold working of the Cu--Zn alloy layer becomes difficult as a
composition of .beta. phase becomes dominant, the aforementioned
electrode wire for the electrical discharge machining apparatus can
be produced only by hot working (hot extrusion), hence production
cost thereof becomes high.
[0007] Moreover, in the aforementioned electrode wire for the
electrical discharge machining apparatus, since Cu alloy, such as
Cu-2.0Sn, Cu-0.3Sn, Cu-13Zn, Cu-0.6Ag or Cu-4.0Zn-0.3Sn, is adopted
as material of the core metallic wire, following disadvantages are
inevitable. This product is detective in workability in the process
of drawing in case that the core metallic wire is formed of
Cu-2.0Sn. Heat-resisting property (strength at high temperature) of
the product is low, and at the time of practical use, instability
of discharge occurs because of the breaking of a wire or the
elongation of the wire before the breaking in case that the core
metallic wire is formed of Cu-13Zn. In the product with low
electrical conductivity (in case that the core metallic wire is
formed of Cu-4.0Zn-0.35Sn) or low heat-resisting property,
improvement of electrical discharge machining speed is not
satisfactory. In case of alloy containing Ag, material cost becomes
high. Referring to the core metallic wire, since heat-resisting
property of a Cu alloy disclosed in Japanese Patent Kokai
No.6-47130 is insufficient, electrical discharge machining speed
cannot be improved (Cu-0.15Sn), and material cost of Cu alloy
containing Ag is high in general.
SUMMARY OF THE INVENTION
[0008] Accordingly, it is an object of the invention to solve the
aforementioned problems and provide an electrode wire for an
electrical discharge machining apparatus composed of a core
metallic wire formed of Cu alloy and a covering layer formed of
Cu--Zn alloy, which is low priced in material cost, has
sufficiently high electrical conductivity and heat-resisting
property and is suited for improving electrical discharge machining
speed.
[0009] It is a further object of the invention to provide an
electrode wire for an electrical discharge machining apparatus,
which is composed of a core metallic wire formed of Cu alloy and a
Cu--Zn alloy covering layer formed of a single phase composition of
only .alpha. phase.
[0010] It is a still further object of the invention to provide an
electrode wire for an electrical discharge machining apparatus,
which is composed of a core metallic wire formed of Cu alloy and a
Cu--Zn alloy covering layer formed of a mixing phase composition of
.alpha. and .beta. phases.
[0011] According to the first feature of the invention, an
electrode wire for an electrical discharge machining apparatus
comprises:
[0012] a core metallic wire formed of Cu-0.02 to 0.2Zr alloy or
Cu-0.15 to 0.25Sn-0.15 to 0.25In in alloy, and
[0013] a covering layer formed of Cu--Zn alloy.
[0014] According to the second feature of the invention, an
electrode wire for an electrical discharge machining apparatus
comprises:
[0015] a core metallic wire formed of Cu-0.02 to 0.2 Zr alloy or
Cu-0.15 to 0.25Sn-0.15 to 0.25 In alloy, and
[0016] a Cu--Zn alloy covering layer formed of a single phase
composition of only .alpha. phase.
[0017] According to the third feature of the invention, an
electrode wire for an electrical discharge machining apparatus
comprises:
[0018] a core metallic wire formed of Cu-0.02 to 0.2Zr alloy or
Cu-0.15 to 0.25Sn-0.15 to 0.25 In alloy, and
[0019] a Cu--Zn alloy covering layer formed of a mixing composition
of .alpha. and .beta. phases.
[0020] The invention pays the attention to material of a core
metallic wire of an electrode wire for an electrical discharge
machining apparatus having a covering layer formed of Cu--Zn
alloy.
[0021] The reason for limiting material of the core metallic wire
to Cu-alloy is that tensile strength and electrical conductivity at
high temperature is satisfactory. A steel wire is omitted, because
it is defective in straightness, when it comes loose. Moreover, it
is difficult to apply the steel wire to a processing machine. A Cu
wire is omitted because tensile strength thereof at high
temperature is insufficient.
[0022] The reason for selecting the aforementioned numerical values
on composition of the core metallic wire will be explained.
[0023] In Cu-0.02 to 0.2Zr alloy, when concentration of Zr is less
than 0.02 weight percent, heat-resisting property of alloy is
insufficient and instability of discharge arises, and when
concentration of Zr is more than 0.2 weight percent, it exceeds the
limit of solid solution of Cu--Zn alloy and precipitation of
Cu.sub.3Zr starts, and the breaking of a wire is apt to occur, so
that concentration of Zr is limited within a range of 0.02 to 0.2
weight percent. Since Cu-0.05 to 0.16Zr alloy, in which
concentration of Zr is 0.05 to 0.16 weight percent, is widely used
for various purposes as Cu-0.16Zr alloy, this alloy is the most
economical in Cu--Zr alloy.
[0024] Next, concentrations of Sn and In in Cu-0.15 to 0.25Sn-0.15
to 0.25 In alloy will be discussed. Sn and In are added to alloy in
order to increase the strength of alloy, but the effect of Sn on a
decrease of the electrical conductivity of alloy is more noticeable
than that of In. Since the electrical conductivity of the wire
should be kept to be high from a view point of stability of
discharge characteristic, it is desirable that concentration of In
is higher that of Sn. However, since In is high-priced,
concentration of In is kept to be less than 0.25%. Accordingly,
there is necessity to increase the amount of addition of Sn, but
the conductivity of alloy noticeably decreases in case that
concentration of Sn is more than 0.25 weight percent. The
aforementioned composition is selected on the basis of trade-off
between improvement of discharge characteristic and economical
consideration.
[0025] Moreover, concentration of Zn of Cu--Zn alloy will be
discussed. In case that concentration of Zn is 32 to 38 weight
percent, Cu--Zn alloy can be formed of a single phase composition
of .alpha. phase, and in the region of .alpha. phase, although
tensile strength and hardness increases as concentration of Zn
increases, hardness is not so high and Cu--Zn alloy can be
processed by cold working. Accordingly, manufacturing process
including drawing is easily carried out. Concentration of Zn of 32
to 36 weight percent corresponds to that of Cu-35Zn alloy (65/35
brass), which is widely used for various purposes. Cu-35Zn alloy is
formed of a single phase composition of .alpha. phase, suited for
cold working, easily obtained on the market and favorable from a
viewpoint of economy.
[0026] Furthermore, since the thickness of the covering layer
formed of Cu--Zn alloy is consumed by about 30 .mu.m in an
electrical discharge machining process of high efficiency, the
thickness of the covering layer formed of Cu--Zn alloy is selected
to be more than 30 .mu.m in order to avoid a situation that the
breaking of a wire occurs, and less than 40 .mu.m, because the
electrical conductivity of the wire becomes insufficient for
fulfilling the function of an electrode wire for an electrical
discharge machining apparatus in case that the thickness of the
covering layer is more than 40 .mu.m.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] The invention will be explained in more detail in
conjunction with appended drawings, wherein:
[0028] FIG. 1 is a cross-sectional view of an electrode wire for an
electrical discharge machining apparatus having a covering
layer,
[0029] FIG. 2A is a photograph for showing a composition of a
cross-section of an electrode wire for an electrical discharge
machining apparatus according to the fourth preferred embodiment,
and
[0030] FIG. 2B shows distribution of concentration of Zn in a
Cu--Zn alloy-covering layer of the fourth preferred embodiment.
DISCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] Thereafter, the preferred embodiments of the invention will
be explained.
[0032] FIG. 1 shows a cross-sectional view of an electrode wire for
an electrical discharge machining apparatus according to the
invention.
[0033] As shown in FIG. 1, the electrode wire 3 for the electrical
discharge machining apparatus according to the invention is
composed of a core metallic wire 1 formed of Cu-0.02 to 0.2 Zr
alloy (or Cu-0.15 to 0.25 Sn-0.15 to 0.25 In alloy) and a covering
layer 2 formed of Cu--Zn alloy, which is formed of a single phase
composition of .alpha. phase or a mixing composition of .alpha. and
.beta. phases.
[0034] According to an electrode wire for an electrical discharge
machining apparatus, which is composed a core metallic wire formed
of Cu-0.02 to 0.2 Zr alloy or Cu-0.15 to 0.25 Sn-0.15 to 0.25 In
alloy and a covering layer formed of Cu--Zn alloy being formed of a
single phase composition of .alpha. phase, according to the
invention, the electrode wire for the electrical discharge
machining apparatus with high efficiency, which can be easily
processed by cold working, can be obtained. That is to say, since
the Cu--Zn alloy covering layer according to the invention is
formed of a single phase composition of .alpha. phase, the
mechanical property of the Cu--Zn alloy covering layer according to
the invention is different from that of a conventional Cu--Zn alloy
covering layer, which is formed of a mixing composition of .alpha.
and .beta. phases or a single phase composition of only .beta.
phase. Tensile strength of the former is smaller than that of the
latter, and reduction of area of the former is larger than that of
the latter, so that deformability of the former is higher than that
of the latter. In case that Cu--Zn alloy covering layer is formed
of a single phase composition of .alpha. phase, the improvement of
electrical discharge machining speed is small as compared with case
that Cu--Zn alloy layer is formed of a mixing composition of
.alpha. and .beta. phases or only .beta. phase, because
concentration of Zn is reduced. However, in case of the electrode
wire according to the invention, depreciation of the improvement of
electrical discharge machining speed is made to be as small as
possible by adopting the electrode wire having a core metallic wire
formed Cu-0.02 to 0.2 Zr or Cu-0.15 to 0.25 Sn 0.15 to 0.25 In
alloy. Although the Cu--Zn alloy covering layer is formed of a
single phase composition of .alpha. phase, electrical discharge
machining speed of the electrode wire for the electrical discharge
machining apparatus according to the invention is far higher than
that of the conventional electrode wire for the electrical
discharge machining apparatus formed of solid Cu-35Zn alloy.
[0035] Since the electrode wire can be manufactured by cold
working, the electrode wire thus obtained is low-priced and cost of
production of the electrode wire for the electrical discharge
machining apparatus can be reduced in turn.
[0036] When Cu-35Zn alloy, which is easily obtainable on the
market, the lowest in price and widely used for various purposes,
is selected among Cu--Zn alloy products, cost of production of the
electrode wire for the electrical discharge machining apparatus can
be further reduced.
[0037] On the other hand, in case that a Cu--Zn alloy covering
layer is composed of a mixing composition of .alpha. and .beta.
phases, although the improvement of electrical discharge machining
speed is high, for concentration of Zn is high, it becomes
difficult to process the Cu--Zn alloy covering layer by cold
working, as percentage of .beta. phase composition increases. In
such a case, if concentration of Zn near the surface of the Cu--Zn
alloy covering layer is made to be low by heat treatment, the
Cu--Zn alloy covering layer can be easily processed by cold
working, though the content of Zn is high as a whole. Since it is
extremely difficult to process a Cu--Zn alloy covering layer formed
of a single phase composition of only .beta. phase by cold working,
this alloy layer is in the outside of the scope in the
invention.
[0038] (The First Preferred Embodiment)
[0039] A composite wire is formed by inserting a core metallic
wire, which is formed of Cu-0.16 Zr alloy and has an external
diameter of 7.1 mm, into a pipe, which is formed of Cu-35 Zn alloy
and has an external diameter of 10 mm and a pipe thickness of 1.2
mm. The Cu-35 Zn alloy pipe is manufactured by ordinary extrusion
process.
[0040] The composite wire is formed into that with a diameter of
0.9 mm by drawing, to which heat treatment is applied for
annealing.
[0041] Finally, the composite wire with a diameter 0.9 mm is drawn
to be formed into that with a diameter of 0.25 mm, and an electrode
wire for an electrical discharge machining apparatus, which
comprises a Cu--Zn alloy covering layer with a thickness of 31
.mu.m containing Zn of 35 weight percent, can be obtained.
[0042] Moreover, a composite wire is formed by inserting a core
metallic wire, which is formed of Cu-0.16 Zr and has an external
diameter of 7.1 mm, into a pipe, which is formed of Cu-40 Zn alloy
and has an external diameter of 10 mm and a pipe thickness of 1.2
mm. The Cu-40 Zn alloy pipe is manufactured by ordinary extrusion
process.
[0043] The composite wire is formed into that with a diameter of
7.9 mm by drawing, to which heat treatment is applied for
annealing. Next, the composite wire is formed into that with a
diameter of 1.2 mm by drawing, to which heat treatment is again
applied for annealing.
[0044] Finally, the composite wire with a diameter of 1.2 mm is
drawn to be formed into that with a diameter of 0.25 mm, and an
electrode wire for an electrical discharge machining apparatus,
which comprises a Cu--Zn alloy covering layer with a thickness of
31 .mu.m containing Zn of 40 weight percent.
[0045] (The Second Preferred Embodiment)
[0046] The manufacturing process of an electrode wire for an
electrical discharge machining apparatus according to the second
preferred embodiment is the same as that of the first preferred
embodiment except that a core metallic wire is formed of
Cu-0.19Sn-0.2In alloy and an external diameter thereof is 7.1 mm,
and electrode wires for the electrical discharge machining
apparatus of two kinds, the Cu--Zn alloy layers of which
respectively contain Zn of 35 and 40 weight percent and are
commonly 31 .mu.m thick, are manufactured.
EXAMPLES FOR COMPARISON 1
[0047] Two kinds of electrode wires for an electrical discharge
machining apparatus, an manufacturing process of which is the same
as that of the first preferred embodiment except that a core
metallic wire is formed of Cu-0.2Sn alloy and an external diameter
thereof is 7.1 mm, are manufactured as examples for comparison. The
Cu--Zn alloy layers of the aforementioned electrode wires of two
kinds respectively contain Zn of 35 and 40 weight percent and are
commonly 31 .mu.m thick. It is found that the core metallic wire
formed of Cu-2.0Sn alloy is not suited for drawing process, and the
manufacturing process of the electrode wire for the discharge
machining apparatus comprising this alloy layer is not smooth.
EXAMPLE FOR COMPARISON 2
[0048] Two kinds of electrode wires for an electrical discharge
machining apparatus, a manufacturing process of which is the same
as that of the first preferred embodiment except that a core
metallic wire is formed Cu-0.3Sn alloy and an external diameter
thereof is 7.1 mm, are manufactured as examples for comparison. The
Cu--Zn alloy layers of the aforementioned electrode wires of two
kinds respectively contain Zn of 35 and 40 weight percent and are
commonly 31 .mu.m thick.
EXAMPLES FOR COMPARISON 3
[0049] Two kinds of electrode wires for an electrical discharge
machining apparatus, a manufacturing process of which is the same
as that of the first preferred embodiment except that a core
metallic wire is formed of Cu-0.15Sn alloy and an external diameter
thereof is 7.1 mm, are manufactured as examples for comparison. The
Cu--Zn alloy layers of the aforementioned electrode wires of two
kinds respectively contain Zn of 35 and 40 weight percent and are
commonly 31 .mu.m thick.
EXAMPLES FOR COMPARISON 4
[0050] Two kinds of electrode wires for an electrical discharge
machining apparatus, a manufacturing process of which is the same
as that of the first preferred embodiment except that a core
metallic wire is formed of Cu-0.13Sn alloy and an external diameter
thereof is 7.1 mm, are manufactured as examples for comparison. The
Cu--Zn alloy layers of the aforementioned electrode wires of two
kinds respectively contain Zn of 35 and 40 weight percent and are
commonly 31 .mu.m thick.
EXAMPLES FOR COMPARISON 5
[0051] Two kinds of electrode wires for an electrical discharge
machining apparatus, a manufacturing process of which is the same
as that of the first preferred embodiment except that a core
metallic wire is formed of Cu-4.0Zn-0.3Sn alloy and an external
diameter thereof is 7.1 mm, are manufactured as examples for
comparison. The Cu--Zn alloy layers of the aforementioned electrode
wires of two kinds respectively contain Zn of 35 and 40 weight
percent and are commonly 31 .mu.m thick.
EXAMPLES FOR COMPARISON 6
[0052] Two kinds of electrode wires for an electrical discharge
machining apparatus, a manufacturing process of which is the same
as that of the first preferred embodiment except that a core
metallic wire is formed of Cu-0.6Ag alloy and an external diameter
thereof is 7.1 mm, are manufactured as examples for comparison. The
Cu--Zn alloy layers of the aforementioned electrode wires of two
kinds respectively contain Zn of 35 and 40 weight percent and are
commonly 31 .mu.m thick.
EXAMPLES FOR COMPARISON 7
[0053] Two kinds of electrode wires for an electrical discharge
machining apparatus, a manufacturing process of which is the same
as that of the first preferred embodiment except that a core
metallic wire is formed of Cu-0.15Ag alloy and an external diameter
thereof is 7.1 mm, are manufactured as examples for comparison. The
Cu--Zn alloy layers of the aforementioned electrode wires of two
kinds respectively contain Zn of 35 and 40 weight percent and are
commonly 31 .mu.m thick.
A CONVENTIONAL EXAMPLE 1
[0054] An electrode wire for an electrical discharge machining
apparatus with an external diameter of 0.25 mm formed of only
Cu-35Zn alloy is manufactured.
A CONVENTIONAL EXAMPLE 2
[0055] An electrode wire for an electrical discharge machining
apparatus with an external diameter of 0.25 mm formed of only
Cu-40Zn alloy is manufactured.
[0056] Table 1 shows the data of the core metallic wires used in
the first to second preferred embodiments, the examples for
comparison 1 to 7 and the examples of the conventional electrode
wires 1 to 2. The units of chemical compositions shown in table 1
are given by weight percent.
[0057] (Table 1)
[0058] Next, strengths at high temperature (MPa), conductivities (%
IACS) and workabilities in drawing of the core metallic wires used
in the first to second preferred embodiments, the examples for
comparison 1 to 7 and the examples of the conventional electrode
wires 1 to 2 are estimated. The results of the comparison are shown
in table 1.
[0059] Strengths of the wires at high temperature are estimated as
follow. Each core metallic wire with a diameter of 7.1 mm is
deformed into that with a diameter of a 0.2 mm by drawings, and
thereafter the temperature of the core metallic wire is kept to be
300.degree. C. for ten minutes. The temperature of 300.degree. C.
corresponds to that of the core metallic wire of the electrode wire
for the electrical discharge machining apparatus, when it is
actually used for its essential purpose. Thereafter, a tensile
strength of the core metallic wire is estimated. Electrical
conductivity of the core metallic wire is measured after drawing
process. The workability in the drawing process is estimated by
actually drawing the core metallic wire by dices. The drawings are
repeated by inserting heat treatments therebetween at need, and the
workability is estimated on the basis of occurrences of the
breaking of the wire, the degree of reduction of the
cross-sectional area of the wire per one pass and the limit of
reduction rate. A double circle, a single circle and a triangle
respectively mean that the workability is excellent, acceptable and
poor.
[0060] Next, electrical discharge machining speeds of the electrode
wires for the electrical discharge machining apparatus according to
the first to second preferred embodiments, the examples for
comparison 1 to 7 and the examples of the conventional electrode
wires 1 to 2 are estimated. The results of the estimation are shown
in table 1.
[0061] Electrical discharge machining speed is measured on a work
(a sample to be machined, JIS SKD-11) with a dimension of 60 mm by
using an electrical discharge machining tester (FX10, manufactured
by Mitsubishi Electric Co.). Electrical discharge machining speed
is normalized on the basis of that of the conventional electrode
wire 1 (2.184 mm/min.).
[0062] As shown in table 1, electrical discharge machining speeds
of the electrode wires for the electrical discharge machining
apparatus according to the first to second referred embodiments and
the examples for comparison 1 to 7 are noticeably improved as
compared with those of the conventional electrode wires 1 to 2. It
can be presumed that the aforementioned results are attributable to
the fact that the electrode wire for the electrical discharge
machining apparatus with the covering layer is adopted. That is to
say, it is useful for the advance of technology to adopt the
electrode wire for the electrical discharge machining apparatus
having a covering layer in stead of that formed of solid alloy, and
thereby the speed of electrical discharge machining is
increased.
[0063] On the electrode wires for the electrical discharge
machining apparatus according to the first to second preferred
embodiments and the examples for comparison 1 to 7, which
respectively have the different qualities of the material, the
properties of the core metallic wires and the improvements of
electrical discharge machining speeds will be collectively
discussed.
[0064] In both the cases of the electrode wires for the electrical
discharge machining apparatus according the first and second
preferred embodiments, both strength at high temperature and
electrical conductivity are satisfactory, and excellent results can
be confirmed.
[0065] On the other hand, in case of an electrode wire for an
electrical discharge machining apparatus according an example for
comparison 1, workability in drawing is defective, and it is
difficult to manufacture the electrode wire for the electrical
discharge machining apparatus.
[0066] In case of an electrode wire for an electrical discharge
machining apparatus according to an example for comparison 2,
conductivity is insufficient and the improvement of the speed of
electrical discharge machining is not satisfactory.
[0067] In case of an electrode wire for an electrical discharge
machining apparatus according to an example for comparison 3,
strength at high temperature is insufficient, and the improvement
of the electrical discharge machining speed is not
satisfactory.
[0068] In case of an electrode wire for an electrical discharge
machining apparatus according to an example for comparison 4,
strength at high temperature is extremely low, and the breaking of
a wire may occur at the time of electrical discharge machining.
[0069] In case of an electrode wire for an electrical discharge
machining apparatus according to an example for comparison 5,
electrical conductivity is low, and the improvement of electrical
discharge machining speed is insufficient.
[0070] In case of an electrode wire for an electrical discharge
machining apparatus according to an example for comparison 6 and 7,
material of the core metallic wire contains Ag, and cost of
material is high in general.
[0071] (The Third Preferred Embodiment)
[0072] A composite wire is formed by inserting a core metallic
wire, which is formed of Cu-0.16Zr alloy and has an external
diameter of 7.1 mm, into a pipe, which is formed of Cu-40Zn alloy
and has an external diameter of 10 mm and a pipe thickness of 1.2
mm.
[0073] This composite wire is formed into that with a diameter of
7.9 mm by drawing, to which heat treatment is applied at
450.degree. C. for 1 hr. Next, the composite wire with a diameter
of 7.9 mm is formed into that with a diameter of 1.2 mm by drawing,
to which heat treatment is applied at 450.degree. C. for 1 hr.
[0074] Finally, the composite wire with a diameter of 1.2 mm is
formed into that with a diameter of 0.25 mm by drawing, to which
heat treatment is applied. An electrode wire for an electrical
discharge machining apparatus having a structure mentioned as
follows can be obtained by controlling the extent of heat
treatment. Concentration of Zn in the Cu--Zn alloy covering layer
varies in the radial direction within a range of 35 to 45 weight
percent. Concentration of Zn in a shallow layer, which is about 5
.mu.m deep below the surface of the covering layer, is lower than
that in a deep layer, and the total thickness of the Cu--Zn alloy
covering layer is about 31 .mu.m.
[0075] (The Fourth Preferred Embodiment)
[0076] The manufacturing process of the fourth preferred embodiment
is the same as that of the third preferred embodiment except that a
core metallic wire is formed of Cu-0.19Sn-0.2In alloy and an
external diameter thereof is 7.1 mm. An electrode wire for an
electrical discharge machining apparatus having a structure
mentioned as follow can be obtained by controlling the extent of
heat treatment. Concentration of Zn in the Cu--Zn alloy covering
layer varies in the radial direction within a range of 35 to 45
weight percent. Concentration of Zn in a shallow layer, which is
about 5 .mu.m deep below the surface of the covering layer, is
lower that in a deep layer, and the total thickness of the Cu--Zn
alloy covering layer is about 31 .mu.m.
[0077] As shown in FIG. 2B, in each of the electrode wires for the
electrical discharge machining apparatus according to the third and
fourth preferred embodiments, since concentration of Zn in a
shallow layer, which is about 5 .mu.m deep below the surface of the
Cu--Zn alloy covering layer, is about 35 weight percent,
workability in cold working is improved and drawing process at room
temperature can be easily carried out, although there is a layer
containing Zn of high concentration in an inner portion of the
Zn--Cu alloy covering layer.
[0078] FIGS. 2A and 2B show the results obtained in case of the
electrode wire for the electrical discharge machining apparatus
according to the fourth preferred embodiment. It is a matter of
course that similar results can be obtained in case of the same
according to the third preferred embodiment.
[0079] As mentioned in the above, in case of the electrode wire for
the electrical discharge machining apparatus according to the
invention, since the Cu--Zn alloy covering layer is formed around
the core metallic wire, which is formed of Cu-0.02 to 0.2 Zr alloy
or Cu-0.15 to 0.25 Sn-0.15 to 0.25 In alloy, cost of production is
low, satisfactory electrical conductivity and strength at high
temperature can be obtained and speed and efficiency of electrical
discharge machining ca be improved as compared with the
conventional electrode wire for the electrical discharge machining
apparatus comprising the known core metallic wire.
[0080] Although the invention has been described with respect to
specific embodiment for complete and clear disclosure, the appended
claims are not to be thus limited but are to be construed as
embodying all modification and alternative constructions that may
be occurred to one skilled in the art which fairly fall within the
basic teaching here is set forth.
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