JPS61146422A - Manufacture of electric discharge machining wire - Google Patents

Abstract

PURPOSE:To stabilize the inter-electrode voltage and the machining current while to reduce adhesion of electrode component to the work by heating Cu-Zn alloy wire under such ambient as Cu is scarcely oxidized but Zn is oxidized. CONSTITUTION:Alloy composed of 28-37wt% of Zn, total 0.2-2wt% of more than one or two kind of Si, Ti, Zr, Al and the remainder of Cu is employed as the core material and in order to form desired film onto the surface of Cu-Zn alloy wire, thermal processing is executed under such ambient where Cu is scarcely oxidized but Zn is oxidized. Preferably, said ambient has the temperature higher than 500 deg.C and the oxygen partial pressure of 10<-2>-10<-2> bar. The heating time is about 45min. Thereafter, the outer diameter is adjusted and the softened wire is hardened then stretched to increase the tensile force.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing an electrode wire used in wire electrical discharge machining.

(Background Art) Wire electrical discharge machining involves intermittent electrical discharge between a workpiece and a linear machining electrode (referred to as an electrode wire) via a machining liquid such as water. This is a method of cutting a workpiece into a desired shape by moving the workpiece relatively to the workpiece, and is used, for example, in manufacturing various molds.

The electrode wire for wire electrical discharge machining usually has a diameter of 0.2~
0.8 silver copper wire or brass wire, 0.03 to 0.1 B tungsten wire, etc. are used. In recent years, advances in processing power supplies mainly due to the emergence of superior high-speed, large-current semiconductors and control of electrical conditions have made it possible to obtain processing speeds of 1 height, and the influence of electrode wires on processing characteristics has also increased. It became so.

From this point of view, materials suitable for electrode wires are being actively developed.

For example, Special Publication No. 59-9298 (hereinafter referred to as precedent 1)
As an electrode wire that can obtain high processing speed,
%Zn, 0.1~4%AI! , an electrode wire with the remainder being Cu has been proposed. For the same purpose, the special public service was established in 1986-564.
No. 8 (hereinafter referred to as precedent 2) states that Zn or Cd
An electrode wire whose core is coated with a metal layer made of an alloy containing at least 50% of
3) proposes an electrode wire in which a core made of a conductive material is coated with a low melting point metal layer, and a nonmetallic thin film having a semiconductor effect is further formed on the core.

As an electrode wire material for wire electrical discharge machining, ■ it must be able to achieve high electrical discharge machining speed without wire breakage, and ■ it must be possible to perform electrical discharge machining with high tension to obtain high machining accuracy, especially in corner machining. , ■ Low manufacturing cost is required. In high-speed wire electrical discharge machining, a phenomenon often occurs in which electrode components are transferred onto the workpiece within the machining groove, and a large amount adheres to the inner surface of the machining groove. Many processing machines have a function of retracting the position of the line via the processing groove when a significant short circuit occurs. In addition to the above-mentioned adhesion phenomenon being a major hindrance to this operation, electrode wires with large adhesion generally have a lower maximum processing speed, so that less adhesion is also an important required characteristic.

Although the above-mentioned examples 1.2 and 3 are aimed at improving these characteristics, they have the following drawbacks. The electrode wire made of brass containing AJ proposed in Reference 1 has excellent strength at high temperatures and can be processed under high tension, but the processing speed obtained is at most the same as that of ordinary brass wire. It is only 1.1 times as large. The electrode wires proposed in Cases 2 and 3 have a soft metal such as Zn or an alloy layer, so the maximum processing speed is 1.3 times or more than that of ordinary brass wire. Due to the presence of the low melting point metal layer, the tensile strength is reduced and the tension applied during processing is also reduced.

Therefore, there has been a need for a method for easily and inexpensively manufacturing an electrode wire that is uniform over its entire length and has excellent characteristics required by electrical discharge machining.

(Disclosure of the Invention) The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to easily and inexpensively manufacture an electrode wire for wire electrical discharge machining that has a high electrical discharge machining speed and is capable of electrical discharge machining with high tension. The purpose is to provide a method.

The present invention uses Zn 28-37 and Si, Ti, Y,
A total of 0.2 to 0.2 or more of one or more of Zr and Al
A Cu-Zn alloy wire containing 2% is heated in an atmosphere that hardly oxidizes Cu but oxidizes zinc to form a coating mainly composed of zinc oxide on the wire surface, which is then drawn. This is a method for manufacturing an electrode wire for wire electrical discharge machining.

In the present invention, Zn28-87% and Si are used as core materials.

The reason for using an alloy consisting of one or more of Ti, Zr, and AJ in a total of 0.2 to 2%, and the balance being Cu, is that these alloys easily lose adhesion under the conditions described below. This is because not only can a film that is good and has an excellent effect on electric discharge machining be obtained, but also these core materials themselves are excellent as electrode wires for wire electric discharge machining in terms of conductivity, strength, etc. Even when a film containing 50% or more of zinc oxide is formed by the method of the present invention, melting and scattering due to electric discharge reaches the core material. Since electrical discharge occurs repeatedly on the surface of the electrode wire, the strength of the core material itself is important for improving the machining speed and machining accuracy of wire electrical discharge machining. The role of conventional brass is not clear, but at the same time it increases the tensile strength under the heat generated by electric discharge during tensile strength, and at the same time improves the electric discharge property, such as the work function and deionization effect, it can improve the electric discharge frequency and concentrated electric discharge. It is estimated that it has a preventive effect. For the same reason, the core material of the electrode wire produced by the manufacturing method of the present invention is also Zn28.
An alloy mainly composed of Cu and less than ~37% is preferred.

If the Zn content is less than 28%, the electrical discharge machining properties will be poor, and a higher Zn concentration is preferable. -J If Zn exceeds 37%, wire drawing becomes extremely difficult and cannot be used industrially. Si
.

Ti, Zr, AI! The main reason for adding one or two of these to the Cu-Zn alloy is that these alloys can easily form a film that has good adhesion and is highly effective against electrical discharge machining. be. For example, in a Zn 35%-Cu 6596 alloy that does not contain these, the film obtained under the conditions described below is thin and most of it peels off during wire drawing. Even if these additive elements are added, if the total amount is less than 0.2%, a film with good adhesion cannot be obtained. Although the combination of these additive elements is arbitrary, if the total exceeds 2%, wire drawing becomes difficult and it is not practical in industry. In addition, all of these additive elements have the effect of improving high-temperature strength, and the core material alone also has the effect of providing higher wire/discharge machining speed and machining accuracy compared to ordinary brass wire. When using other additive elements such as Sn, Pb, Fe, etc., the effect of improving the speed and accuracy of wire electrical discharge machining in the core material itself is extremely small, and it is also difficult to obtain a film with good adhesion.

In the present invention, in order to form a desired film on the surface of such a Cu-Zn alloy wire, heat treatment is performed in an atmosphere that hardly oxidizes Cu but oxidizes Zn. The atmosphere varies slightly depending on the type of Cu-Zn alloy wire, but generally the temperature is 400°C or higher, more preferably 500°C or higher, and the oxygen partial pressure is 10-5 to 10-1 atm, more preferably 10-4 to The pressure is 10-2 atmospheres.

The heating time is generally 45 minutes or more within the above-mentioned more preferable temperature range and oxygen partial pressure range of 500° C. or higher and 10 −4 to 1 O −2 atm. The effects of temperature, oxygen partial pressure, and time on the oxidation of Cu-Zn alloys are complex;
For example, a 65% Cu-35% Zn alloy is heated at 500°C in the atmosphere.
When heat-treated for 30 minutes, the film was thin and the proportion of Cu oxide in the film was high, and after 24 hours, the Zn
The ratio of oxide increases, but the coating becomes easier to peel off. Generally, at temperatures below 400°C or an oxygen partial pressure below 10-5, the film formation rate is extremely slow, and it takes an extremely long time to obtain the desired film thickness, making electrical discharge machining at a high speed in practice. No electrode wire is available. From this point of view, a higher temperature is preferable, but if the temperature is too high, the coating may easily peel off, so a temperature of 400 to 700°C is appropriate.

If the oxygen partial pressure exceeds 10-1 atmospheres, as mentioned above, the film formation rate may decrease or the C in the film may decrease.
The proportion of oxide in u increases, making it impossible to obtain an electrode wire with a high electrical discharge machining speed. Furthermore, if the heating time is less than 45 minutes, it is generally difficult to form a film of the desired thickness.

If the coating thickness of the electrode wire is less than 0.1μ, the electrical discharge machining speed will not exceed 1.1 times that of the case without coating, and 2
If it exceeds μ, it becomes difficult to supply power to the wire and to detect contact to detect the position with the workpiece. More preferably 0
．． 3 to 0.8μ, and with a coating mainly composed of Zn oxide in this range, the electrical discharge machining speed is generally more than 1.2 times that of the case without a coating, and it does not affect power supply or contact detection. .

However, measuring the film thickness requires special analytical equipment such as performing Auger electron spectroscopy while performing sputter etching. In normal management, the film is dissolved in acid,
A method of calculating the adhesion amount from the difference in weight before and after dissolution can be used. The amount of adhesion is preferably 0.6 to 12 P/mJ, and 1.8 to 48 J'/Fn 2 provides the above-mentioned effects preferable as an electrode wire for wire electric discharge machining.

Gases other than oxygen in the atmosphere include N2, kerosene, vacuum, etc.
Non-oxidizing or reducing gases have no effect. Oxidation of Zn progresses in the presence of oxygen even in a reducing gas such as hydrogen.

The composition of the film formed in such an atmosphere is complex, and in particular, in the more preferred method of the present invention, which involves wire drawing after oxidation treatment, a large amount of wire drawing lubricant is impregnated into the film. It comes to include C.

The ratio of zinc oxide in the entire coating to the sum of oxides of Cu, Zn and Cu (ZnO/Cu+Zn+CuO+Cu 20
) is 50% or more, a high electrical discharge machining speed can be obtained.

The coating mainly composed of zinc oxide mentioned in the present invention means such a coating.

Next, electric discharge machining is a machining process that involves repeated small transient electric discharges in gaps of several μm to several tens of μm, and although it is difficult to elucidate the detailed mechanism, zinc oxide formed by the present invention is mainly used. The presence of the film as a component lowers the work function of the surface, making it possible to discharge at a high current density at a relatively low temperature, and preventing the occurrence of sustained discharge due to the deionization effect of zinc. It is estimated that by preventing excessive current generation during a slight short circuit with the workpiece due to an increase in contact resistance, the machining voltage and machining current during electrical discharge machining are significantly stabilized. Further, the adhesion of the electrode components to the workpiece is very slight even under conditions where the electrode wire according to the above-mentioned Example 1 is used and the machining groove is almost completely filled with the adhering material. The maximum electrical discharge machining speed is 2 times faster than that of ordinary brass wire.
It can be improved by 0 to 50%.

If the electrode wire has sufficient tensile strength after this oxidation treatment, it can be used as it is as an electrode wire for electrical discharge machining.

The wire drawing performed in the present invention after film formation is performed in order to adjust the outer diameter and work harden the wire that has been softened during the oxidation treatment described above, so that a high tension can be obtained during wire electrical discharge machining. be. In addition, wire drawing removes or fixes the powder (scum) of the oxide film that exists on the surface of the film.
It works to

The coating obtained by the above-mentioned oxidation treatment is thinly stretched after wire drawing and is retained to a considerable extent. However, the total cross-sectional reduction rate of wire drawing is 60 to 9
9.5% is preferable; if it is less than 60%, high tensile strength cannot be obtained and the surface will be rough; if it is more than 99.5%, the coating will almost disappear, and high-speed, high-precision wire electric discharge machining will not be possible. I can't do it.

Note that in the present invention, the above-described oxidation treatment and wire drawing may be repeated multiple times.

(Example) Brass wires of various sizes containing 35% Zn and various additive elements were oxidized in various atmospheres and treatment conditions shown in Table 1 to form discolored coatings.

The wires other than those processed at the final size (0,2U&) were drawn after processing to obtain wires of 0.200±0.001 tnxw.

Comparative examples x9 to i12 shown in Table 1 are ordinary brass wires treated under various atmospheres and treatment conditions.

Wire electrical discharge machining was performed using the obtained 0.2 tnxi wire as an electrode wire under the following conditions.

Electric discharge machining conditions Machining fluid specific resistance 10X104Ω, α pulse width
3 μsec.

Pause time 3μsec・Power supply voltage 120V Capacitor capacity 2.11tF Processing voltage 40~45V Processing fluid pressure Upper nozzle 15 Kf/cat
”Lower nozzle 1,,.5・Kf/an2 Wire feed rate 25 kph/sec Machining feed rate Set to the maximum value without breaking the workpiece
Table 1 shows the maximum electrical discharge machining speed during electrical discharge machining of a 5KD-10 material having a thickness of 301 JL.

From Table 1, Mu1 to i8 according to the present invention are i9 to i of the comparative example.
It can be seen that the electric discharge machining speed is 10 to 30% higher than that of No. 12.

(Effects of the Invention) The method for manufacturing an electrode wire for wire electrical discharge machining of the present invention configured as described above has the following effects.

(a) Zn 28-37 and Si, Ti, Y, Zr
, one or more of Al in a total amount of 0.2~
Since the Cu-Zn alloy wire containing 2% Cu is heated in an atmosphere that hardly oxidizes Cu and oxidizes Zn, the formation of Cu oxide on the wire surface is extremely small, and the coating is made of zinc oxide. It becomes the main component, and a coating with a uniform and appropriate thickness (for example, 0.01 to 2 μm) can be obtained over the entire length.
During wire electrical discharge machining, although the detailed mechanism is not clear, the voltage between the machining electrodes and the machining current are extremely stable, and there is less adhesion of electrode components to the workpiece, so the electrical discharge machining speed is high and electrical discharge machining can be performed over the entire length. Electrode wires with excellent characteristics can be manufactured.

(b) Since the above-mentioned oxidation treatment can be performed in the same manner as heat treatment by simply adjusting the oxygen partial pressure, manufacturing is easy and manufacturing cost is low.

(c) In order to draw the wire after forming the above-mentioned coating, the wire softened during the oxidation treatment is work-hardened and the tensile strength is improved, so an electrode wire that can be subjected to electrical discharge machining at high tension can be manufactured.

Further, in this case, for the same reason as in item (b), it is possible to perform both the oxidation treatment and the heat treatment for improving wire drawability, so that the wire can be manufactured at a low cost.

In addition, the above-mentioned wire drawing removes or fixes the coating powder (dregs) on the surface of the wire and smoothes the surface, thereby stabilizing the electrical discharge and further improving the electrical discharge machining speed.

Claims (2)

[Claims] (1) Zn28-37%, Si, Ti, Y, Zr, Al
An alloy wire consisting of a total of 0.2 to 2% of one or more of these and the balance Cu is heated in an atmosphere that hardly oxidizes Cu but oxidizes Zn, so that zinc oxide is formed on the wire surface. A method for producing an electrode wire for wire electrical discharge machining, the method comprising forming a film containing as a main component and then drawing the wire. (2) The total cross-sectional reduction rate of wire drawing after film formation is 60 to 99.
5%. The method for manufacturing an electrode wire for wire electrical discharge machining according to claim 1.