KR20040040146A - The electrode wire for electrical discharge machining, and manufacturing method of it - Google Patents

Abstract

PURPOSE: An electrode wire of a wire electro discharge and a manufacturing method are provided not to break the wire due to oxidized substance and to manufacture the electrode wire in low cost. CONSTITUTION: A surface of a core wire(31) is coated with a copper layer(32), a brass layer(33) and a zinc layer(34) successively. A sectional area of the copper layer is between seven to fifteen percent of whole sectional area of an electrode wire(3). The brass layer is between one point one and one micro meter and the zinc layer is between two and fifteen micro meters in thickness. Thereby, breakage of the wire is reduced because strength and modulus of elasticity increase. Electro discharge and safety are improved by settling all coating layers stable.

Description

The electrode wire for electrical discharge machining, and manufacturing method thereof

The present invention relates to an electrode wire used for wire discharge machining, and more particularly, the copper and zinc plating layers are coated on the outer circumferential surface of the steel wire in a sequence, and then mechanically processed at the interface between the copper plating layer and the zinc plating layer through proper drawing. By forming a brass layer through diffusion to improve the discharge processability and durability and at the same time to reduce the manufacturing cost of the electrode wire relates to an electrode wire for electrical discharge machining.

Among various metal processing methods, cutting processing can be largely divided into mechanical and electrical methods. The mechanical method is a method of simply cutting a metal rod or a plate in a straight line with a band saw or sheer knife forming a closed loop, which is a complicated shape, that is, Curved cutting is not possible.

However, the electric cutting method is a method of cutting a metal into a complicated shape using a thin metal wire to which power is applied, and generates discharge heat by generating a discharge in a state in which the metal wire is close to a surface to be cut. The metal wire is melt-cut, and the metal wire continues to move along the surface to be cut.

Looking at the principle and the process of the wire discharge processing for cutting the metal by the electrical discharge heat as described above in detail as follows.

As shown, in order to initially pass the electrode wire 12 through the workpiece 11, a starting hole h made before the start of processing is passed through the electrode wire 12 released from the supply reel R. After the end of the electrode wire 12 is attached to the winding reel R ', preparation for electric discharge machining is completed.

The electric discharge machining starts at the same time as the supply reel R and the winding reel R 'of the electrode wire 12 are rotated, and the workpiece 11 is disposed between the two reels R and R'. In order to maintain a constant distance from the surface to be processed and to maintain the accuracy of discharge processing of the surface to be processed, the electrode wire 12 running vertically has been subjected to an appropriate tensile stress. '-' Voltage is applied to the electrode wire 12 moving to '), and' + 'voltage is applied to the workpiece 11 of metal material, and a kind of insulating oil discharge is discharged between the electrode wire 12 and the workpiece 11. As the processing liquid is supplied, electrical spark discharge occurs between the electrode wire 12 and the workpiece 11, and the instantaneous discharge heat caused by the spark discharge melts the workpiece near the electrode wire so that cutting is performed. do.

The discharge processing liquid serves as a medium for generating a discharge, cools the electrode wire and the workpiece, and removes the molten metal from the electrode wire and the workpiece.

When the flame discharge occurs and the machining starts, the worktable on which the workpiece is placed is moved back, front, left, and right with respect to the electrode line, and thus cutting is performed in various shapes of a desired shape along the trajectory of the workpiece.

The electrode wire wound from the supply reel to the take-up reel during the discharge processing as described above not only acts on the tensile stress of a certain size but also decreases the tensile strength of the electrode wire by the discharge heat for heating the electrode wire to a high temperature of about 300 ° C. or higher, thereby discharging the electrode wire. The heavy electrode wires can be frequently disconnected.

Therefore, in order to prevent the disconnection of the electrode wire as described above, the electrode wire must not only have a high temperature strength but also have a diameter as small as possible in order to improve the processing accuracy. The maintenance should also be considered as an important matter, but conventional electrode wires have a large amount of adhesion to the workpiece, and there are many disadvantages of disconnection during discharge processing at high speed.

In other words, in order to improve the processing speed, it is necessary to flow a large amount of current through the wire electrode. If the resistance of the electrode is high, the wire electrode is disconnected due to heat generation. Therefore, the wire electrode can improve the processing speed and processing accuracy. Although conductivity is required, metal materials generally have high mechanical strength and low conductivity, while high conductivity has low mechanical strength.

Accordingly, methods for coating a core wire having a high mechanical strength with a high conductivity material have been developed so as to achieve the opposite characteristics as described above.

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 sharply lowered tensile strength at high temperature due to heat generated during electric discharge machining, and thus the tension applied to the electrode wire must be reduced, thereby reducing the precision of the cutting edge of the workpiece. There is a problem that the speed is reduced.

In addition, the brass wire, which has excellent stretchability and strength, has a composition of 65% Cu-35% Zn and a wire diameter in the range of 0.07 to 0.3mm, of which 0.2 to 0.3mm wire diameter occupies more than 80% of the entire electrode wire market. Although the tensile strength at room temperature is about 2 times higher than that of copper wire, the high temperature characteristics at the time of electric discharge machining are similar to those of copper wire, and in the case of galvanized brass wire, the discharge safety is improved by the zinc plating layer on the surface, If the high temperature strength falls and the processing speed is increased, the tendency of disconnection increases.

In addition, tungsten and molybdenum wire is excellent in high temperature strength to solve all of the above problems, there is a problem that the cost is expensive and the drawability is low, the manufacturing cost is increased.

Therefore, a method of solving the problems at high temperature and considering economical aspects as well as a method of coating copper or brass having excellent conductivity on the surface of the steel wire has been devised. Thus, the coating layer is formed on the surface of the steel wire as a core wire. Looking at the conventional electrode line of the formed structure based on (a) to (b) of Figure 2 as follows.

First, Fig. 2A shows a cross-sectional structure of a wire for electric discharge machining in which brass 22 is coated, with the steel wire 21 as disclosed in Japanese Patent Application No. 53-80899 as a core wire. Is a wire for electric discharge machining by coating copper 23 on the core wire of steel wire 21 as shown in Korean Patent Publication No. 92-7689 and coating brass 22 having a zinc content of about 40 to 50% on the surface thereof. The cross-sectional structure of the is shown.

Among the 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) has a zinc content of 40 to 50% in the brass layer. As a degree, the alloy has a disadvantage of poor workability due to the β-phase alloy having poor workability.

The main object of the present invention is to coat a relatively low boiling point material such as zinc on a copper-coated steel wire to prevent the cooling effect of the electrode wire due to latent heat of evaporation, and to prevent the occurrence of wire breakage of oxides such as zinc on the surface, and to prevent ordinary brass wire or brass. The present invention provides and manufactures an electrode wire for electric discharge machining at a relatively low price than a zinc coated brass wire having a core wire.

In addition, two kinds of materials suitable for conductivity and discharge stability are laminated and coated on the surface of the core wire, and an alloy layer is formed on the interface of the two materials, thereby compensating the bonding strength between the two coating layers and the rigidity of the coating layer itself, thereby providing a uniform and stable discharge. It is intended to provide an electrode wire that can minimize the occurrence of disconnection with processing.

1 is a conceptual view showing a wire discharge machining method.

2 is a cross-sectional view of a conventional electrode line,

(A) is a cross-sectional view of an electrode wire coated with brass on the core wire surface

(B) is cross-sectional view of electrode wire coated with copper and brass laminated on the surface of core wire.

Figure 3 is a cross-sectional view of an embodiment electrode line of the present invention.

4 is a block diagram of a manufacturing method of the present invention.

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

3,12. Electrode Line 11. Workpiece

21,31. Core wire 22,33. Brass layer

23,32. Copper plating layer 34. Zinc plating layer

The above object of the present invention is achieved by controlling the copper and zinc plating layers and the final drawing reduction ratio.

In the wire discharge machining electrode wire of the present invention, a steel wire is used as a core wire, and a coating layer of copper and zinc is laminated on the surface thereof, and the plated core wire is finally drawn with an appropriate reduction ratio, and at the interface between the two plating layers due to heat and compressive force generated during drawing. There is a technical feature of the present invention in forming a brass layer by diffusion.

As described above, the electrode wire of the present invention has a structure in which three coating layers of copper-brass-zinc are laminated and coated on a surface of the core wire in a series order, and each coating layer has a respective function. Looking at the role of the coating layer, the copper plated layer effectively conducts the current, the zinc plated layer improves the discharge stability, and the brass layer, the diffusion layer increases the bonding strength of copper and zinc to prevent the zinc plated layer from peeling off, thereby reducing the discharge stability. In addition to preventing it from becoming difficult, it also serves to improve the rigidity of the entire coating layer.

In particular, the galvanized layer increases discharge processing speed and reduces servo voltage, thereby suppressing wire breakage, which has a significantly low vaporization energy, and this vaporization energy has a great influence on the removal of metal particles from the workpiece. As a result, the discharge machining speed is increased, and the electrode wire is cooled by the latent heat of evaporation of zinc, thereby suppressing disconnection of the electrode wire.

Further, the copper plating layer uses the characteristics of the current, that is, the surface effect of the current flowing along the surface of the conductor when the current flows along the conductor, so that the steel wire used as the core wire bears the tensile stress applied to the electrode wire. In addition, since the copper plating layer serves as a conductor for flowing a current, the thickness of the copper plating layer must be appropriately set in order to maximize the surface effect.

Further, due to the surface effect, the thickness of the brass layer and the zinc plating layer coated on the surface of the copper plating layer should also be controlled to an appropriate range. If the thickness becomes thicker than necessary, the brass layer and the zinc plating layer having higher resistance than the copper plating layer may flow. As current increases, current efficiency decreases, and disconnection may occur due to self-resistance heat. If the thickness of the brass and zinc plating layers is made too thin in consideration of current efficiency, discharge processability may decrease.

Therefore, the electrode wire of the present invention, after plating the thickness of the copper and zinc plated layer in the range of 20 to 50㎛ and 20 to 45㎛ respectively on the surface of the core wire, the cross-sectional area of the copper plated layer through the final wire is 7 The thickness of the brass layer and the galvanized layer is set to 0.1 to 1 µm and 2 to 15 µm, respectively.

As described above, limiting the thickness of each coating layer, in the case of the copper plating layer, if the area does not reach 7% of the total cross-sectional area of the electrode wire, the amount of current that can flow through the copper plating layer is decreased while the current flows through the steel wire, which is a core wire. This is because the current efficiency and the discharge processability are lowered, and if it exceeds 15%, the production productivity of the electrode line is reduced by over plating, the manufacturing cost is increased more than necessary, and the tensile strength of the electrode line is decreased, thereby increasing the possibility of disconnection.

In the case of the brass layer, if the minimum thickness is less than 0.1 μm, the bonding strength between the copper and the zinc plated layer and the reinforcing effect of the entire coating layer are hardly observed. When the thickness exceeds 1 μm, the copper and zinc plated layers are reduced to increase the current efficiency. If the thickness of the galvanized layer is less than 2 μm, the current becomes unstable, and the effect of improving the discharge stability is insignificant, sufficient discharge performance cannot be obtained, and the machining precision is reduced. Exceeding the current efficiency lowers the electric discharge efficiency and lowers the high temperature strength, which leads to the easy disconnection.

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, the electrode wire 3 of the present invention is a copper plating layer 32, a brass layer 33 and excellent electrical conductivity on the surface of the steel wire 31 as a core wire in order to maintain the tensile strength at high temperature The galvanized layer 34 has a laminated structure in a series of orders.

At this time, the brass layer 32 is formed in the diffusion, not plating, and the composition is divided into parts of the brass layer 55 to 80wt%, zinc 20 to 45wt% by the brass layer, the portion outside the content is copper or zinc It was regarded as a plating layer.

Referring to the method of manufacturing the electrode wire of the present invention in which three coating layers are formed on the surface of the core wire as described above in detail based on the block diagram shown in FIG. 4.

The electrode wire 3 of the present invention comprises the steps of performing a primary pickling and coating process to remove the surface oxidation scale of a rod as a raw material and to improve freshness; Primary drawing (402) the coated rod; Performing a heat treatment (annealing and parting) to control the mechanical properties of the primary fresh wire (403); Performing a second pickling and coating process to remove oxides on the surface of the heat-treated wire and to improve ductility; A secondary fresh step (405); Performing a third pickling to remove surface residues of the wire rod generated during the second drawing and to increase plating efficiency; Plating (407) the surface of the wire rod with an electroplating method in a copper sulfate solution; Annealing (408) to control the mechanical properties of the wire cured by secondary drawing; Performing a fourth pickling to remove oxides and improve plating properties of the wire surface generated during annealing; Plating zinc in the fourth pickled wire in a zinc sulfate plating bath (410); A third step of drawing the galvanized wire to form a brass layer and matching the wire diameter (411); Tensioning in the inert gas atmosphere is made through step 412 of correcting the mechanical properties and straightness of the tertiary fresh wire.

Since each heat treatment, pickling and plating process of the present invention manufacturing method as described above is a technique generally performed in the field of metal processing, description of specific working conditions has been omitted, but the tertiary drawing process forms a brass layer by diffusion. As a step of making, there is a technical feature of the manufacturing method of the present invention to properly control the fresh reduction ratio at this time.

That is, the tertiary drawing is performed in the range of 90 to 98% of reduction rate, and if the reduction rate is less than 90%, it is difficult to form a brass layer. As a result, the fresh workability is lowered and the dropping of the galvanized layer is increased.

The brass plating layer by the tertiary drawing, the lattice defect is introduced into the structure of the wire rod by the deformation of the wire rod generated during the drawing process, the frictional heat is generated between the wire die and the material, the shear deformation under compressive stress As a result of the dominant forced plastic flow, it is formed by diffusion that occurs at the interface between the copper plated layer and the zinc plated layer.

In other words, the interfacial diffusion due to plastic flow under heat and compressive stress during the third drawing plays an important role in forming the diffusion layer of copper and zinc. It is necessary to manage the shape factor (Δ) of Equation 1, which is a function of the contact length between the die and the workpiece wire.

Where r is the reduction ratio and α is the die angle

In the third drawing of the method of the present invention, the shape factor was maintained at 1.6 to 2.8 while adjusting the die angle to 8 to 11 degrees. Generally, in the drawing process, the shape factor is 2.5 to 3.0, the smaller the die angle and the larger the reduction ratio. As hydrostatic pressure acts, compressive stress acts greatly in all parts of the deformation part.

In addition, the zinc plated layer forming the outermost layer of the steel cord of the present invention is not necessarily limited to zinc, and exhibits almost the same discharge processability as zinc, and has cadmium or a copper alloy having a brass alloy state diagram such as copper-zinc. One of tin or aluminum having a state bronze phase diagram may be plated instead of zinc. In this case, a copper-cadnium or a copper-tin or a copper-aluminum alloy layer is formed at the interface between the two plating layers instead of the brass layer.

The characteristics of the electrode line of the present invention manufactured through the above process will be described through the following examples.

Example

After the secondary drawing, a number of wires with a diameter of 1.2 mm were made using 5.5 mm hard wire rod as raw material.The thickness of the copper and zinc plating layers was formed on the surfaces of the wires, respectively, and the third wire (decrease rate of 95.7%) and Through the calibration process, a plurality of electrode lines for electric discharge machining of the embodiment of the present invention having a final wire diameter of 0.25 mm were manufactured, and detailed manufacturing methods are as follows.

In order to remove the iron oxide scale formed on the surface of the 5.5 mm rod, which is a raw material, hydrochloric acid was washed for 60 seconds in a batch hydrochloric acid tank having a concentration of 23% (within 10 to 30%) of hydrochloric acid. Phosphate coating for 5 minutes, neutralization for 5 minutes in quicklime, and then shape factor with a die angle of 13 degrees (within 11 to 15 degrees) in a drawing machine with 84% wire reduction (in the range of 80 to 90%). Was maintained in the range of 2.5 to 3.0, and was drawn up to 1.2 mm at a drawing speed of 300 to 700 m / min.

In order to control the mechanical properties and at the same time to give the primary fresh wire to be drawn up to fine wire, it is annealed at 1000 ℃ (in the range of 920 ~ 1100 ℃) inline and then 520 ℃ (490 ~ 570 ℃). Particleing was conducted for 50 seconds (in the range of 30 to 100 seconds) at the temperature of the range), and in order to remove oxides on the surface of the heat-treated wire and improve the ductility, the concentration of hydrochloric acid was 24% (in the range of 20 to 30%) and the temperature was increased. After the oxidation scale is removed from the inline pickling device at 34 ° C (in the range of 30 to 40 ° C) and subjected to borax treatment, the die angle is 13 degrees (11 to 15) in a drawing machine having a wire reduction ratio of 70% (in the range of 67 to 75%). In the range of 2.5 to 3.0 while maintaining the shape factor in the range of 2.5 to 3.0, and the secondary speed was drawn up to 1.2 mm at a drawing speed of 300 to 700 m / min.

In order to remove the surface residue of wire rod generated during the secondary drawing and improve the plating efficiency, electrolytic sulfate pickling is performed under the condition of current density 23A / dm ² (in the range of 15 ~ 30A / dm ² ), ultrasonic washing, and plating The current density was adjusted within the range of 30 to 80 A / dm ^{2 in} order to adjust the plating thickness to 20 to 50 µm while performing the strike treatment with the copper pyrophosphate plating, which was a pretreatment.

In order to adjust the plating thickness of the zinc sulfate plating layer to 20 ~ 45㎛ after copper plating and washing with water, zinc plating was performed under the condition of current density of 25 ~ 60A / dm ² . After adjusting the final wire diameter while forming a brass layer, the mechanical properties and straightness of the 3rd fresh wire were calibrated while giving tension in an inert gas atmosphere.

Comparative example

A plurality of Comparative Example electrode wires were prepared in the same manner as in Example, but outside the thickness range of the coating layer of the electrode wire of the present invention.

By cutting the workpiece (SKD11) having a thickness of 50mm using the electrode wires and the conventional brass wires and cutting the rectangular plate of 30mm × 40mm, the discharge processing conditions and the results are shown in Tables 1 and 2 below. same.

Applied voltage Downtime Average processing voltage Peak current Sb Index Electrode wire tension Electrode wire velocity 220 A 12sec 5Vav 10A 13 900kgf 2.2 mm / min.

* Sb index is discharged in 1 ~ 16 steps by using stable circuit in discharge processor.

Divided by

division Copper plating rate (%) Zinc / Brass Thickness (㎛) Electrode wire tensile strength (kgf) Processing speed (mm / min) Machining precision Disconnection frequency Example 1 7 2 / 0.2 110 1.8 to 2.3 B B Example 2 7 4 / 0.3 110 1.8 to 2.5 B A Example 3 10 3 / 0.3 110 1.8 to 2.5 A A Example 4 10 5 / 0.4 109 1.8 to 2.5 A A Example 5 12 7 / 0.6 108 1.8 to 2.5 A A Example 6 12 10/1 107 1.8 to 2.5 A A Example 7 14 8 / 0.7 107 1.8 to 2.5 A A Example 7 14 10/1 106 1.8 to 2.3 A B Comparative Example 1 5 2 / 0.2 110 1.8 to 2.0 C C Comparative Example 2 7 14 / 1.4 106 1.8 to 2.5 B C Comparative Example 3 10 1 / 0.1 110 1.8 to 2.3 C B Comparative Example 4 10 12/1 106 1.8 to 2.0 B C Comparative Example 5 17 5 / 0.2 107 1.8 to 2.3 C B Brass line - - 110 1.8 to 2.5 B A

* Machining accuracy is based on the discrimination of the dimensional error of the cut sheet,

A (less than 0.01 mm), B (less than 0.01 to 0.04 mm), and C (0.04 mm or more).

* Disconnection frequency is independent of acceleration within the processing speed range of the workpiece

'A' for no disconnection, 'B' for 2.3mm / min

In case of disconnection at 2.0mm / min, 'C' is indicated.

Looking at Table 2, it can be seen that in the case of Examples 1 and 7 in which the thickness of the coating layer is close to the lower limit and the upper limit, which are defined in the present invention, respectively, the cutting layer is disconnected according to the processing precision or the processing speed. Although the processing accuracy is good, it is thought that the decrease in the tensile strength of the electrode wire promotes the disconnection due to excessive coating of the plating layer.

In addition, the comparative examples made so as to deviate from the limited range of the plating layer of the electrode line of the present invention were shown to increase the tendency to disconnect as the processing speed increases as the overall processing accuracy is lowered.

In conclusion, if the thickness of the zinc plated layer is thin at the same copper plating rate, the machining precision and the surface roughness of the surface to be processed are reduced. If the thickness of the zinc plated layer is increased, the cutting performance increases with the machining speed, but the galvanized layer thickness is increased. When excessively, it may be disconnected by the decrease in tensile strength, and since the cutting performance is not improved by the thickness increase, only the manufacturing cost of the electrode wire is increased.

As described above, since the electrode wire of the present invention uses a core wire as a steel wire, the mechanical strength and the elastic modulus are high, thereby reducing the occurrence of high-temperature disconnection and improving the processing accuracy, and at the same time by the brass plating layer between the copper and zinc plating layers. Since the coating layer is stabilized, discharge processability and stability are improved.

Claims (4)

A wire discharge machining electrode wire having a steel wire as a core wire and having a plating layer coated on the surface thereof, wherein the copper plating layer, the brass layer, and the zinc plating layer are laminated and coated in a sequence on the surface of the core wire. The electrode wire for wire discharge machining according to claim 1, wherein the cross-sectional area of the copper plating layer is 7 to 15% of the total cross-sectional area of the electrode wire, and the thickness of the brass layer and the zinc plating layer is 0.1 to 1 µm and 2 to 15 µm, respectively. . CLAIMS 1. A method for manufacturing an electrode wire for wire discharge machining using a steel wire as a core wire, the method comprising: performing a primary pickling and coating process for removing surface oxide scale of a rod as a raw material and improving freshness; Primary drawing (402) the coated rod; Heat-treating the primary fresh wire (403); Secondary pickling and coating the heat treated wire rod (404); A secondary fresh step (405); Third pickling the second fresh wire rod (406); Plating (407) the copper on the surface of the third pickled wire using a copper sulfate solution; Annealing the copper plated wire rod (408); Fourth pickling the annealed wire rod (409); Galvanizing the fourth pickled wire in a zinc sulfate plating bath (410); Tertiary drawing (411) of galvanized wire; Method for producing a wire electrode for electrical discharge processing, characterized in that it comprises a step (412) for correcting the mechanical properties and straightness while giving tension to the third wire drawn in an inert gas atmosphere. The method for manufacturing an electrode wire for wire discharge machining according to claim 3, wherein the tertiary drawing is performed in a range of 90 to 98% of a reduction ratio.