KR100345958B1 - Zr-contained electrode wire for electrical discharge machining and its method - Google Patents

Abstract

The present invention relates to a wire discharge machining electrode wire coated with a copper plating layer on the surface of a steel wire having a tensile strength of a predetermined level or more at room temperature, and then coated a brass plating layer containing zirconium (Zr) on the copper plating layer.

In the electrode wire for electrical discharge machining of the present invention to coat the plating layer on the surface of the steel wire, the copper plating layer as the intermediate layer is coated to 20 to 50% of the electrode wire cross-sectional area, the outermost brass plating layer to be 3 to 10% of the electrode wire cross-sectional area, wherein The brass plating layer has technical characteristics in controlling the components to be 60 to 65 wt% of copper, 35 to 40 wt% of zinc and 0.03 to 0.8 wt% of zirconium.

In the electrode wire of the present invention, since the decrease in tensile strength due to heat generated during electrical discharge machining is inevitable in view of metal properties, a wire wire having a tensile strength of a certain level or more is selected at room temperature to maintain high tensile strength even at high temperatures, and zirconium is added to the brass layer. Thus, by improving the workability of the brass plated layer by miniaturizing the beta-phase brass structure of poor workability, it is possible to produce an electrode wire having excellent wire workability than the electrode wire coated with the conventional brass alloy layer.

As a result, the wire workability is good and the surface of the electrode wire after the wire drawing is uniform, so that the discharge machining efficiency is improved, thereby increasing the processing speed and the precision of the surface to be processed.

Description

Zr-contained electrode wire for electrical discharge machining and its method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode wire used in a wire electric discharge machine for processing a work piece by partially melting a work piece of a metal material by an electrical spark discharge, and more particularly, a surface of a steel wire having excellent tensile strength. The present invention relates to an electrode wire for wire discharge machining, which is coated with a copper plating layer and coated with a brass plating layer containing an appropriate amount of zirconium thereon to greatly improve wire drawing workability.

1 is an explanatory view schematically showing the discharge processing process of the workpiece using the electrode wire, based on the principle of the discharge processing and processing process as follows.

As shown, the electrode wire 2 released from the supply reel 4 is penetrated through a starting hole 3 made before the start of processing in order to pass the electrode wire 2 into the workpiece 1. The discharge machining preparation is completed by attaching the end of the electrode wire 2 passed through the start hole 3 to the winding reel 5.

The start of the electric discharge machining starts at the same time as the supply reel 4 and the take-up reel 5 of the electrode wire 2 are rotated. An appropriate tensile stress is applied to the electrode wire 2 running perpendicular to the workpiece between the two reels 4 and 5 so as to maintain a constant distance from the workpiece to maintain the accuracy of discharge machining on the workpiece. It is a state. On the other hand, '-' voltage is applied to the electrode wire moving from the supply reel to the winding reel, '+' voltage is applied to the workpiece to be made of metal, and a discharge processing liquid, which is a kind of insulating oil, is supplied between the electrode wire 2 and the workpiece. Between the electrode line 2 and the workpiece 1, an electrical spark discharge occurs and instantaneous heat is generated by the discharge, and the discharge heat is processed by melting the workpiece.

The discharge processing liquid serves to cool the electrode wires and the workpiece and to remove the molten metal from the electrode wires and the workpiece, together with the role of the medium causing the discharge.

When the flame discharge occurs and the machining starts, various types of holes of a desired shape are processed along the trajectory of the workpiece by moving the worktable on which the workpiece is placed in front, rear, left and right with respect to the electrode line.

Tensile stress of a certain magnitude is applied to the electrode wire wound from the supply reel to the take-up reel during the discharge processing, and the electrode wire is heated to a high temperature of about 300 ° C. or higher due to the discharge heat caused by the discharge machining, which causes a decrease in the tensile strength of the electrode wire, thereby reducing the disconnection of the electrode wire. It is triggered. Therefore, in order to prevent disconnection of the electrode wires, the electrode wires must not only have high high temperature strength but also have a small diameter in order to maintain processing accuracy. In addition, since the electrode wire is a disposable consumable, maintenance of an appropriate price level should also be considered as an important matter.

In general, the electrode wire used in the above-described electric wire discharge machining includes copper wire, brass wire and galvanized brass wire having a diameter of 0.03 to 0.40 mm, and tungsten or molybdenum wire is used as a fine wire having a diameter of 0.1 mm or less.

However, the copper wire has a disadvantage in that the cutting edge of the workpiece is not only degraded as well as the electrode wire is easily broken because the tensile strength at high temperature is sharply lowered due to the heat generated during the electrical discharge machining to reduce the tension applied to the electrode wire. The speed of electric discharge machining also decreases.

Brass wire is about 2 times higher in tensile strength at room temperature than copper wire, but the high-temperature characteristics of electrical discharge machining are similar to those of copper wire. Likewise, the galvanized brass wire also improved the discharge safety by the zinc plated layer on the surface, but did not improve the characteristics at high temperatures.

In addition, the tungsten and molybdenum wires have high temperature strength, and thus the above problems are easily solved.

Therefore, a method of solving the above problems at high temperature and considering economical aspects as well as a method of coating a copper or brass plate having excellent conductivity on the surface of the steel wire as a core wire has been devised.

As described above, a conventional electrode wire having a structure in which a coating layer is formed on a surface of the steel wire as a core wire will be described with reference to FIGS. 2A to 2B.

First, Fig. 2A shows a cross-sectional structure of a wire for electric discharge machining in which brass 21 is coated with the steel wire 20 as disclosed in Japanese Patent Application No. 53-80899 as a core wire. Is a structure in which copper 23 is coated on a core wire of steel wire 22 and zinc 24 is coated on the core wire 22, as shown in Japanese Patent Application Laid-Open No. 3-111126. -7689 shows the cross-sectional structure of the wire for electric discharge machining by coating copper (26) on the core wire of steel wire (25) and coating brass (27) with 40 ~ 50% zinc content on the surface. Giving.

Among the three types of conventional electrode wires shown in FIG. 2, the electrode wire of (A) has a problem in that molten copper particles are fused to the processed surface of the workpiece, and the electrode wire of (B) is the electrode wire after two platings are completed. When drawing to final wire diameter, there is a drawback of poor workability due to the properties of the coated zinc.The electrode wire of (C) has a high zinc content of 40 to 50%, and the brass layer is made of β-phase alloy with poor workability. There is also a drawback of low workability.

Therefore, the present invention solves the above problems of the conventional electrode for electric discharge machining, and maintains high tensile strength even at high temperature to enable high speed processing, and improves the freshness, thereby making the electrode wire thin and uniformity of the electrode wire surface. It is an object of the present invention to provide an electrode wire for wire discharge machining that does not increase the manufacturing accuracy of the electrode wire by not only increasing the accuracy of electric discharge machining but also increasing the manufacturing cost of the electrode wire.

1 is a processing schematic diagram of wire discharge machining;

2A to 2C are cross-sectional views of a conventional electrode line.

3 is a cross-sectional view of an electrode line according to the present invention.

((Explanation of symbols for main part of drawing))

3. Start hole 4. Supply reel

5. Reel 20,22,25,31. Liner

21,27,33. Brass plated layer 23,26,32. Copper Plating Layer

24. Galvanized layer

The present invention is to coat the copper with high electrical conductivity on the surface of the steel wire having a tensile strength of a certain level or more at room temperature, and to coat the brass on it again, but to contain a certain amount of zirconium in the brass plating layer so that the freshness does not fall. There is a characteristic.

The coating of copper with good electrical conductivity on the surface of the wire is based on the characteristics of the current, that is, the current gathers to the surface of the conductor when the current flows through the conductor. In order to handle the tensile stress applied to the electrode wire and the copper layer of the core wire outer layer to serve as a conductor to flow the current. Therefore, in order to maximize the surface effect, the thickness of the copper layer must be appropriately set. A method of manufacturing the electrode line for electric discharge machining according to the present invention is as follows. Coating the copper layer to have a cross-sectional area corresponding to 20-50% of the; Plating zinc and zirconium on the surface of the copper layer by one of electroplating and hot dip plating; Cross diffusion by heat occurs at the interface between the copper layer and the zinc-zirconium plating layer, and has a cross-sectional area corresponding to 3 to 10% of the final electrode wire cross-sectional area. The constituents are 60 to 65 wt% copper, 35 to 40 wt% zinc, and zirconium. Comprising a step of forming a brass layer consisting of a weight ratio of 0.03 ~ 0.8wt%.

3 is a cross-sectional view of an electrode line according to an embodiment of the present invention. The electrode line structure and characteristics of the present invention are as follows.

As shown, in order to maintain the tensile strength at high temperature, the present invention uses the steel wire 31 having a tensile strength of 1500 Mpa or more at room temperature as a core wire, and a copper layer 32 having excellent electrical conductivity on the surface thereof. 20 to 50% of the cross-sectional area was covered, and the brass layer 33 was coated on the surface of the copper plating layer so as to be about 3 to 10% of the final electrode wire cross-sectional area.

The brass layer 33, which is the outermost layer of the electrode wire, changes from the α phase structure with low tensile strength and good processability to the β phase structure with high tensile strength but poor processability as the zinc content increases. Therefore, in order to improve the workability while maintaining tensile strength, the composition of the brass layer 33 was adjusted to 60 to 65 wt% of copper and 35 to 40 wt% of zinc to 0.03 to 0.8 wt% of zirconium. The zirconium contained in the brass layer 33 improves the freshness of the brass coating layer by miniaturizing the β-phase brass structure having poor workability.

In the electrode wire of the present invention, the use of a steel wire having a tensile strength of 1500 Mpa or more at room temperature does not increase the tensile strength of the electrode wire due to a decrease in tensile strength at a high temperature in the case of a steel wire having a tensile strength of less than 1500 Mpa. This is because, in the case of more than that, the decrease in tensile strength at high temperature can be sufficiently handled.

In the case of the copper clad layer, which is an intermediate layer of the electrode line, when the cross-sectional area is less than 20% of the cross-sectional area of the electrode line, the current flows through the steel wire, which is the core wire, to increase the surface effect of the current, thereby deteriorating the electrical conductivity, thereby reducing the discharge efficiency. In addition, when the electrical conductivity exceeds 50%, the electrical conductivity is improved, but the tensile strength of the electrode wire is lowered, which may increase the occurrence of disconnection during discharge processing, and the electrode wire manufacturing cost increases.

If the cross-sectional area of the brass cladding layer, which is the outermost layer of the electrode wire, is less than 3% of the total cross-sectional area of the electrode wire, the copper cladding layer, which is an intermediate layer, melts and penetrates the brass layer during discharge processing, thereby causing a problem that copper is fused to the discharge processing surface of the workpiece. There is a possibility that, if the cross-sectional area exceeds 10% there is a problem that the electrical conductivity is worsened and the discharge efficiency is lowered.

In the case of zirconium which is a trace addition element of the brass cladding layer forming the outermost layer of the electrode wire, when the content is less than 0.03wt%, there is little effect of miniaturizing the brass phase of β phase, and when it exceeds 0.8wt%, the phase refinement effect of β phase due to the addition of zirconium Rather decrease.

Embodiments of the present invention are as follows.

After copper was coated on the steel wire having a diameter of 0.6 mm having a tensile strength of 1500 Mpa or more at room temperature, zinc and zirconium were again coated on the copper coating layer by electroplating. After the two coating processes are completed, the wire is heated by an electrical resistance method so that mutual diffusion occurs between copper, zinc, and zirconium. Thus, the outermost layer of the electrode wire made of zinc and a small amount of zirconium contains a small amount of zirconium. The copper wire was changed to a brass layer, and the steel wire having the coating layer formation completed was fresh to a wire diameter of 0.2 mm, and then a residual stress removal heat treatment was performed to prepare an electrode wire having good straightness.

The electrode wire and the conventional electrode wire according to the present invention obtained through the above manufacturing process is drawn together to investigate the effect of the content of zirconium in the brass layer of the electrode wire on the wire workability and the discharge processability according to the improvement of the wire workability, Table 1 and Table 2 show the results of disconnection frequency, discharge machining speed, and precision of workpiece surface.

Cover layered minutes Old recovery rate (%) Brass layer Open frequency (times / 10 ⁵ Km) Coverage% Zinc fraction (%) Zirconium fraction (%) β-phase average particle size (㎛) Electrode line of the present invention 38.5 6.9 38.5 0.01 0.71 2.6 37.2 7.5 39.0 0.03 0.57 1.1 37.6 7.1 37.5 0.06 0.52 0.5 39.1 7.1 38.0 0.09 0.51 0.4 38.5 7.5 38.4 0.11 0.52 0.5 40.2 7.2 38.2 0.15 0.50 0.5 Conventional electrode wire 15.6 5.2 40.8 0.92 7.8 36.2 7.2 38.2 0.89 5.2 42.3 7.5 34.9 0.93 5.6 55.3 12.5 35.2 0.81 4.8

The β phase in the brass layer was confirmed by electron diffraction, and the average particle diameter of the β phase was observed and calculated by a transmission electron microscope.

Looking at Table 1 above, as the zirconium content increases, it becomes clear that the micronized phenomenon of the structure of which the average particle diameter of the β phase decreases. Can be.

Further, in processing a mold having a thickness of 22 mm of SKD-11 material using a conventional electrode wire including the electrode wire of the present invention shown in Table 1 and a brass wire and a copper wire, the processing speed and the precision of the surface to be processed were examined. The precision is divided into 1 class for dimension error less than 0.01mm, 2 class for 0.01 ~ 0.03mm, and 3 class for exceeding 0.03mm. (The dimension error is the difference between the maximum value and the minimum value after processing.)

Cover layered minutes Old recovery rate (%) Acceleration Speed (mm / min) Precision Coverage% Zinc fraction (%) Zirconium fraction (%) Electrode line of the present invention 38.5 6.9 38.5 0.01 1.3 One 37.2 7.5 39.0 0.03 1.8 One 37.6 7.1 37.5 0.06 1.9 One 39.1 7.1 38.0 0.09 1.7 One 38.5 7.5 38.4 0.11 1.8 One 40.2 7.2 38.2 0.15 1.8 One Conventional copper and brass coated wire (brass wire) (copper wire) 15.6 5.2 40.8 1.3 2 36.2 7.2 38.2 1.4 2 42.3 7.5 34.9 1.4 One 55.3 12.5 35.2 1.6 2 1.0 3 0.9 3

In Table 2 above, it can be seen that the electrode wire of the present invention has improved processing speed and precision compared to conventional copper and brass coated wires and pure brass wires or copper wires. The results of Tables 1 and 2 show the trace element zirconium contained in the brass coating layer. This is because the surface of the electrode wire after wire drawing is more uniform than that of the conventional one because the freshness of the electrode wire is improved due to the structure refinement effect by the microstructure.

As described above, the electrode wire for wire discharge machining of the present invention uses a steel wire having a high tensile strength even at a high temperature and forms a zirconium-containing brass layer on the outermost layer of the electrode wire, so that the high temperature strength is different from the conventional coated electrode wire. It is possible to maintain thin wires, and to draw thin wires. The surface of the electrode wires after wire drawing is uniform, so that the discharge processing efficiency is improved.

Therefore, the electrode wire of the present invention has the advantage of increasing the discharge machining speed and improve the accuracy of the surface to be processed than the conventional electrode wire.

Claims (3)

In the electrode wire for electrical discharge machining, the outer peripheral surface is made of a brass layer, the steel wire 31 having a tensile strength of 1500Mpa or more at room temperature; A copper layer 32 uniformly coated on the surface of the steel wire 31 to have a cross-sectional area corresponding to 20-50% of the final electrode wire cross-sectional area; Brass is uniformly formed on the surface of the copper layer 32 to have a cross-sectional area corresponding to 3 to 10% of the final electrode wire cross-sectional area, and consists of a weight ratio of 60 to 65 wt% copper, 35 to 40 wt% zinc and 0.03 to 0.8 wt% zirconium. An electrode wire for electric discharge machining, comprising a layer (33). Coating a copper layer on the surface of the steel wire having a tensile strength of 1500 Mpa or more at room temperature so as to have a cross-sectional area corresponding to 20-50% of the final electrode wire cross-sectional area; Plating zinc and zirconium on the surface of the copper layer by one of electroplating and hot dip plating; Cross diffusion by heat occurs at the interface between the copper layer and the zinc-zirconium plating layer, and has a cross-sectional area corresponding to 3 to 10% of the final electrode wire cross-sectional area, 60 to 65 wt% of copper, 35 to 40 wt% of zinc, and 0.03 to 0.8 wt% of zirconium. Method for producing an electrode wire for electrical discharge machining, characterized in that the step consisting of forming a brass layer consisting of a weight ratio of. delete