Wire electrode for wire cutting electro-discharge machining

Abstract: Disclosed herein is a wire electrode for wire cutting electro-discharge machining which can improve the processing speed as well as productivity of the wire electrode. A core (2) is made of a copper alloy containing 13 percent by weight of Zn. A coating layer (1) formed on the outer periphery of the core (2) is made of a copper alloy containing 43 percent by weight of Zn.

Description: Field of the Invention The present invention relates to a wire electrode for wire cutting electro-discharge machining, and more particularly, it relates to a wire electrode for wire cutting electro-discharge machining which comprises a core and a coating layer provided on the outer periphery of the core. Description of the Background Art Wire cutting electro-discharge machining is a method of making discharge across a workpiece and a wire-type working electrode (hereinafter referred to as "wire electrode") and relatively moving the wire electrode and the workpiece for cutting the workpiece into a desired shape, which has been carried out in general. In general, a long wire electrode of 0.05 to 0.25 mm in diameter is passed through a guide so that a new wire electrode is successively supplied to a worked portion, thereby carrying out electro-discharge machining. In such electro-discharge machining, the quality of the wire electrode as employed directly exerts remarkable influences on the processing speed, processing accuracy, surface smoothness of a worked surface and the like. Thus, strongly awaited is development of a preferable material which is suitable for such electro-discharge machining. An example of a conventional wire electrode is made of a material which is prepared by adding Al, Si and the like to a Cu-Zn alloy. Zn, Al, Si and the like are added in order to improve the processing speed. If the total amount of Zn (wt.%) + 6 x Al (wt.%) + 9 x Si (wt.%) exceeds 38 percent by weight, however, it is difficult to work the material into a wire electrode. When a current which is fed to the wire electrode is increased, the processing speed is improved. If the total amount of Zn (wt.%) + 6 x Al (wt.%) + 9 x Si (wt.%) exceeds 38 percent by weight, however, the material is so deteriorated in heat resistance that the wire electrode is disadvantageously fused when the same is supplied with a large current. Thus, the current cannot be increased and hence it is impossible to improve the processing speed. Japanese Patent Publication No. 57-5648 (1982) and Japanese Patent Laying-Open Nos. 59-129629 (1984) and 59-127921 (1984) disclose other examples of conventional wire electrodes. Each of the wire electrodes disclosed in these gazettes has a two-layer structure of a core and a coating layer which is formed on the outer periphery of the core. The core is made of a copper alloy, while the coating layer is made of a zinc alloy. The coating layer is mainly composed of zinc since the processing speed is increased in proportion to the content of zinc. Such zinc contained in the coating layer is evaporated when the wire electrode is supplied with electricity, to allow smooth discharge across the wire electrode and a workpiece. Such smooth discharge leads to improvement of the processing speed. When the coating layer is mainly composed of a zinc alloy in order to improve the processing speed, however, this coating layer is made fragile. When the wire electrode is passed through a guide, therefore, the coating layer may be scraped by friction between the guide and the coating layer. EP-A-0 381 595 discloses a wire electrode with the features of the preamble of claim 1 or 3 An object of the present invention is to provide a wire electrode for wire cutting electro-discharge machining, being provided with a coating layer which is hard to scrape, having a high processing speed. The object is achieved by a wire electrode according to claim 1 or 3. According to the present invention, a copper alloy is employed as a material for the coating layer, whereby the coating layer is hard to scrape as compared with that of a zinc alloy. The coating layer provided in the inventive wire electrode for wire cutting electro-discharge machining is made of a second copper alloy containing 38 to 49 percent by weight of Zn and a rest of Cu and unavoidable impurities or a third copper alloy containing Zn and Al in a range of at least 38 percent by weight of Zn and not more than 49 percent by weight of Zn + 6 x Al and a rest of Cu and unavoidable impurities, for the following reasons: While the processing speed can be improved as the content of Zn is increased, the Zn content is restricted as described above in consideration of productivity of the wire electrode for wire cutting electro-discharge machining. If the content of Zn is less than 38 percent by weight, extrusion is disabled due to excessive plastic deformation resistance under a high temperature, and hence the material cannot be worked into a wire electrode for wire cutting electro-discharge machining. When the content of Zn or Zn + 6 x Al exceeds 49 percent by weight, on the other hand, fragility of the material is so increased that it is difficult to work the same into a wire electrode for wire cutting electro-discharge machining. A metal layer of a Cu-Zn alloy exhibits an α phase when the content of Zn is not more than 40 percent by weight, while the same exhibits a β phase when the Zn content exceeds 40 percent by weight. The β phase is fragile as compared with the α phase. The third copper alloy contains Al, which is adapted to improve heat resistance of the third alloy. The range of 6 x Al is set by reason that Al has a Zn equivalent of 6. In order to obtain a wire electrode for wire cutting electro-discharge machining according to the present invention in excellent productivity, a Cu-Zn or Cu-Zn-Al alloy is extruded through a conformer on the outer periphery of a core in a stage having a larger wire diameter than the final one, and then worked into a desired wire diameter. This method is disclosed in Japanese Patent Laying-Open No. 55-156614 (1980), for example. As hereinabove described, the processing speed is improved as the content of Zn or Zn + Al is increased. In consideration of improvement in processing speed, therefore, the content of Zn or Zn + Al is preferably maximized. On the other hand, tensile strength under a high temperature is reduced as the amount of Zn contained in the copper alloy is increased. Each of the second and third copper alloys, containing at least 38 percent by weight of Zn, is insufficient in tensile strength under a high temperature. Therefore, the first copper alloy for forming the core preferably contains not more than 20 percent by weight of Zn or not more-than 7 percent by weight of at least either Sn or Ag. When the core is made of such a material, it is possible to increase conductivity as well as to improve tensile strength under a high temperature. If the component of the core material is out of the above range, conductivity is extremely reduced and tensile strength under a high temperature is lowered while plastic deformation is made difficult, and hence it is difficult to work the material into a wire electrode for wire cutting electro-discharge machining. The first copper alloy may alternatively contain not more than 20 percent by weight of Zn and not more than 7 percent by weight of at least either Sn or An so that the total content of these elements is not more than 27 percent by weight. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is a sectional view showing an embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1 is a sectional view showing a wire electrode for wire cutting electro-discharge machining according to an embodiment of the present invention. A coating layer 1 is formed on the outer periphery of a core 2. The thickness t of the coating layer 1 is preferably 10 to 20 % of the diameter d of the wire electrode for wire cutting electro-discharge machining. If the former exceeds 20 % of the latter, the wire electrode for wire cutting electro-discharge machining is reduced in tensile strength under a high temperature, since the coating layer 1 has lower tensile strength under a high temperature as compared with the core 2. If the former is less than 10 % of the latter, on the other hand, the processing speed may not be so high. Samples of wire electrodes for wire cutting electro-discharge machining were prepared in compositions shown in Table 1. Coating Layer Core Inventive Sample 1 Cu39%Zn Cu - 2.0%Sn 2 Cu - 40%Zn - 0.5%Al Cu - 0.3%Sn 3 Cu - 43%Zn Cu - 13%Zn 4 Cu - 41%Zn - 0.7%Al Cu - 0.6%Ag 5 Cu - 43%Zn - 1.0%Al Cu - 4.0%Zn - 0.3%Sn Comparative Sample 6 Cu - 30%Zn Cu - 13%Zn 7 Cu - 45%Zn-1.0%Al Cu - 0.3%Sn 8 Cu - 35%Zn Cu - 0.3%Sn Conventional Sample 9 Cu - 35%Zn 10 Cu - 35%Zn - 0.05%Al The inventive samples 1 to 5 were continuously extruded by a Conform ( con tinuous form ing) machine so that the wire electrodes for wire cutting electro-discharge machining had outer diameters of 8 mm with respect to cores of 5.3 mm in outer diameter. The extrusion temperature was 450°C. Drawing and intermediate softening were repeated on the as-extruded rods, to prepare wire electrodes for wire cutting electro-discharge machining having outer diameters of 0.3 mm. As to the comparative sample 6, it was impossible to prepare a wire electrode for wire cutting electro-discharge machining since this sample allowed no continuous extrusion. As to the comparative sample 7, it was impossible to prepare a wire electrode for wire cutting electro-discharge machining due to wire breaking during drawing, although this sample allowed continuous extrusion. As to the comparative sample 8, a wire electrode for wire cutting electro-discharge machining was prepared by pipe engagement, since this sample allowed no continuous extrusion. On the other hand, the conventional samples 9 and 10 had single layer structures. These wire electrodes for wire cutting electro-discharge machining were subjected to measurement of conductivity values and processing speeds. Table 2 shows the results. Conductivity (%IACS) Processing Speed Inventive Sample 1 30 130 2 40 140 3 33 135 4 43 165 5 40 160 Comparative Sample 6 unmeasurable unmeasurable 7 unmeasurable unmeasurable 8 unmeasurable unmeasurable Conventional Sample 9 18 100 10 18.5 105 Referring to Table 2, the processing speeds are relatively expressed on the basis of the conventional sample 9 exhibiting a value of 100. As understood from Table 2, the inventive samples were superior in conductivity and processing speed to the conventional samples. The comparative sample 8, which was close to the inventive samples in both conductivity and processing speed, was inferior in productivity to the inventive samples which were prepared through a Conform machine, since this sample was prepared by pipe engagement. According to the inventive wire electrode for wire cutting electro-discharge machining, as hereinabove described, it is possible to improve the processing speed, while it is also possible to improve productivity of the wire electrode for wire cutting electro-discharge machining.

Claims: A wire electrode for wire cutting electro-discharge machining, comprising: a core containing a first copper alloy; and a coating layer, being formed on the outer periphery of said core, containing a second copper alloy containing Zn and Al characterized in that said second copper alloy containing Zn and Al in a range of at least 38 percent by weight of Zn and not more than 49 percent by weight of Zn + 6 x Al and a rest of Cu and unavoidable impurities, wherein said first copper alloy contains not more than 20 percent by weight of Zn, and the thickness of said coating layer is 10 to 20 % of a sectional diameter of said wire electrode for wire cutting electro-discharge machining. A wire electrode for wire cutting electro-discharge machining in accordance with claim 1, wherein said first copper alloy contains not more than 7 percent by weight of at least either Sn or Ag. A wire electrode for wire cutting electro-discharge machining, comprising: a core containing a first copper alloy; and a coating layer, being formed on the outer periphery of said core, containing a second copper alloy containing Zn and Al characterized in that said second copper alloy containing Zn and Al in a range of at least 38 percent by weight of Zn and not more than 49 percent by weight of Zn + 6 x Al and a rest of Cu and unavoidable impurities, wherein said first copper alloy contains not more than 7 percent by weight of at least either Sn or Ag, and the thickness of said coating layer is 10 to 20 % of a sectional diameter of said wire electrode for wire cutting electro-discharge machining.

Inventors: EZAKI SHIGEO, MIYAZAKI KENJI, OHKUBO NAOYUKI, EZAKI, SHIGEO, MIYAZAKI, KENJI, OHKUBO, NAOYUKI, EZAKI, SHIGEO, C/O OSAKA WORKS OF SUMITOMO, MIYAZAKI, KENJI, C/O OSAKA WORKS OF SUMITOMO, OHKUBO, NAOYUKI, C/O OSAKA WORKS OF SUMITOMO
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LIMITED
Application year: 1993
Main classification: B23H7
IPC codes: C22C9, B23H7, C22F1