Electric heating – Metal heating – Cutting or disintegrating
Reexamination Certificate
1999-03-09
2002-03-26
Elve, M. Alexandra (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C219S069110, C219S069150
Reexamination Certificate
active
06362447
ABSTRACT:
FIELD OF THE INVENTION
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
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.
Besides this, a composite wire composed of a core metallic wire formed of a steel wire and a covering layer formed of Cu—35Zn 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 Publication No. 6-47130).
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).
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).
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 &agr; and &bgr; phases, or a single phase composition of only &bgr; phase. Since cold working of the Cu—Zn alloy layer becomes difficult as a composition of &bgr; 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.
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
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.
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 &agr; phase.
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 &agr; and &bgr; phases.
According to the first feature of the invention, an electrode wire for an electrical discharge machining apparatus comprises:
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
a covering layer formed of Cu—Zn alloy.
According to the second feature of the invention, an electrode wire for an electrical discharge machining apparatus comprises:
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
a Cu—Zn alloy covering layer formed of a single phase composition of only &agr; phase.
According to the third feature of the invention, an electrode wire for an electrical discharge machining apparatus comprises:
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
a Cu—Zn alloy covering layer formed of a mixing composition of &agr;
0
and &bgr; phases.
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.
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.
The reason for selecting the aforementioned numerical values on composition of the core metallic wire will be explained.
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
3
Zr 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.
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.
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 a phase, and in the region of &agr; 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 wor
Aoyama Seigi
Kawano Hideo
Kimura Takamitsu
Sato Takahiro
Shimojima Kiyoshi
Elve M. Alexandra
Hitachi Cable Ltd.
McDermott & Will & Emery
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