Electrode wire

Abstract

An electrode wire (2) suitable for use as an electrode wire for electrical discharge machining, said electrode wire comprising: - a metal core (10) which extends along a longitudinal axis, and - on the metal core, a coating (12) having a mass per unit area of zinc oxide greater than 0.5 g / m2, wherein the zinc oxide is enriched with chlorine, i.e. the composition of the zinc oxide is [Zn 2 +, O 2- 1-x, Cl-2x ], where x is a molar fraction of between 0.01 and 0.25.

Description

[0001] Electrode wire [1] The invention relates to an electrode wire suitable for use as an electrode wire for EDM machining and to a method for manufacturing this electrode wire. [2] Electrode wires are used for cutting metals or electrically conductive materials by EDM in an EDM machine. [3] The well-known method of EDM machining, or spark erosion, makes it possible to remove material from an electrically conductive part by generating sparks in a machining zone between the part to be machined and an electrically conductive electrode wire. The electrode wire runs continuously in the vicinity of the part in the direction of the length of the wire, held by guides, and is gradually moved in the transverse direction towards the part, either by transverse translation of the wire guides or by translation of the part.[4] An electrical generator, connected to the wire electrode by electrical contacts away from the machining area, establishes an appropriate potential difference between the wire electrode and the conductive workpiece to be machined. The machining area between the wire electrode and the workpiece is immersed in a suitable dielectric fluid. The potential difference causes sparks to appear between the wire electrode and the workpiece, which gradually erode the workpiece and the wire electrode. The longitudinal movement of the wire electrode allows the wire diameter to be permanently maintained sufficient to prevent breakage in the machining area. The relative movement of the wire and the workpiece in the transverse direction allows the workpiece to be cut or its surface to be treated, if necessary. [5] The particles detached from the wire electrode and the workpiece by the sparks disperse in the dielectric fluid, where they are evacuated.[6] Achieving machining precision, particularly when making small radius corner cuts, requires the use of small diameter wires with a high mechanical load at break to be tensioned in the machining area and limit the amplitude of vibrations. [7] Most modern EDM machines are designed to use metal wires, generally 0.25 mm in diameter, and with a load at break of between 700 N / mm. 2 and 1000 N / mm 2. [8] When a spark occurs between the electrode wire and the workpiece, the surface of the electrode wire is suddenly heated to a very high temperature for a short time. As a result, the material in the surface layer of the electrode wire at the location of the spark changes from a solid to a liquid or gaseous state and is displaced to the surface of the electrode wire and / or evacuated into the dielectric fluid. It can be seen that the outer face of the electrode wire reached by the spark has been deformed, generally taking on a slightly concave crater shape, with areas where the material has melted and re-solidified. [9] It has been found that the effectiveness of sparks in EDM depends largely on the nature and topography of the surface layer of the electrode wire.For this, considerable progress in the efficiency of electroerosion has been obtained by using electrode wires comprising: - a metal core made of one or more metals or alloys ensuring good conduction of the electric current and good mechanical strength to withstand the mechanical tension load of the wire, and - a coating made of one or more other metals or alloys and / or a particular topography, for example fractures, ensuring better efficiency of electroerosion, for example a higher erosion speed.

[0010] For example, patent JPH026076 discloses the production of an oxide layer on the surface of an electrode wire to accelerate machining. Also known from the state of the art are US8378247B2 and US2022 / 212277A1.

[0011] The invention aims to further improve the machining speed of electrode wires comprising a coating containing oxide and, in particular, zinc oxide.

[0012] The invention is set forth in the attached set of claims.

[0013] The invention will be better understood upon reading the following description, given solely by way of non-limiting example and with reference to the drawings in which: - Figure 1 is a schematic illustration of the cross-section of an electrode wire, - Figures 2, 3 and 4 are flowcharts, respectively, of a first, a second and a third method of manufacturing the electrode wire of Figure 1, - Figure 5 is a partial schematic illustration of a cross-section of another electrode wire, and - Figure 6 is a flowchart of a method of manufacturing the electrode wire of Figure 5.

[0014] In these figures, the same references are used to designate the same elements. In the remainder of this description, the characteristics and functions well known to those skilled in the art are not described in detail.

[0015] Subsequently, in a chapter I, the definitions of certain terms are given. In a chapter II, examples of detailed embodiments are described with reference to the figures. Then, in a chapter III, variants of these embodiments are presented. Finally, in a chapter IV, the advantages of the different embodiments are described.

[0016] Chapter I: Definitions and terminology

[0017] The expression "element made of material A" or "element of material A" designates an element in which material A represents at least 70%, by mass, of this element and preferably, at least 90% or 95% by mass of this element.

[0018] A "copper-zinc alloy" designates an alloy formed solely of copper and zinc, excluding unavoidable impurities. A copper-zinc alloy is also called "brass".

[0019] A "phase" of the copper-zinc alloy refers to a solid phase of the copper-zinc alloy that has a particular crystallographic structure. More specifically, the phases of the copper-zinc system are distinguished from each other by their composition and by their particular crystallographic structure. This particular crystallographic structure makes it possible to distinguish a phase of the copper-zinc alloy from a simple mixture of fine grains of copper and zinc, which mixture would have the same overall composition. Typically, known phases of the copper-zinc alloy are the alpha phase, the beta phase, the gamma phase, the delta phase, the epsilon phase and the eta phase. The particular crystallographic structure of a phase is identifiable by various means.For example, optical microphotographs or metallography of polished samples show different color shades for each phase, provided the sample has been properly etched. Thus, to distinguish the gamma phase from the epsilon phase, an etch with "Nital", which is a 3% solution of nitric acid diluted in ethanol, is carried out. The gamma phase then appears gray when it is low in zinc and gray with shades of brown when it is rich in zinc. The epsilon phase appears darker brown. It is also possible to distinguish the gamma phase from the epsilon phase by observing the sample under a scanning electron microscope, using a backscattered electron detector. It is also possible to identify the phase of a sample by X-ray diffraction. In the latter case, the wire sample is placed under an incident beam of X-rays of a specific wavelength.For example, the Kα line of copper, with an average wavelength of 0.1541 nm, is used. The intensity of the diffracted rays is evaluated for each diffraction angle. The gamma phase has a known X-ray diffraction pattern, which is different from that of the other phases of the copper-zinc system, and from the zinc oxide ZnO, which is often found on the surface of wires. If the copper-zinc alloy is not crystallized in the form of at least one of the alpha, beta, gamma, delta, epsilon, or eta phases, it is amorphous, and the X-ray diffraction pattern then shows flattened bumps rather than sharp peaks. At a given temperature, the different phases of the copper-zinc alloy each correspond to a specific zinc concentration range. The extent of each of these specific zinc concentration ranges varies with temperature.

[0020] The concentration of an element in a sample can be obtained by composition microanalysis and, in particular, by energy-dispersive X-ray spectroscopy (EDS or EDXS). A composition microanalysis is carried out with a scanning electron microscope equipped with a spectrometry probe. An electron beam, accelerated for example in a 20 kV electric field, impacts the surface of the sample and causes an emission of X-rays. These X-rays have an energy spectrum characteristic of the composition of the surface of the sample which has been impacted by the electron beam. With an energy-dispersive spectrometric analysis probe (EDS) or wavelength selection (WDS), the spectrum of the X-rays emitted by the surface of the sample is measured.Algorithms are used to select the elements analyzed (thus eliminating the effect of impurities), and to calculate the composition of the sample impacted by the electron beam, from the measured spectra. It should be noted that due to the interactions between X-rays and matter, the volume analyzed by EDS (or WDS) is generally about one cubic micrometer. At the boundary between two areas of different compositions, an average concentration, which does not actually exist in either area, can be measured. In order to avoid this problem, the compositions indicated are measured in areas larger than one-micrometer cubes and at locations within this analyzed area far from the boundaries with other unanalyzed areas.

[0021] The expression "the concentration of an element within an area is greater than X atomic %" means that the average concentration of this element within this area is greater than X atomic %.An average concentration is for example obtained by measuring the concentration of this element at different locations within this zone and then averaging these concentration measurements. The locations where the measurements are made are located both at the locations where the concentration is likely to be the lowest, at the locations where the concentration is likely to be close to the average, and at the locations where the concentration is likely to be maximum. For this, typically, the locations where the measurements are made are distributed along an axis passing through the axis of the electrode wire.

[0022] The expression "electrical conductor" designates a material whose electrical conductivity, at 20 °C, is greater than 10. 6 S / m and preferably greater than 10 7S / m.

[0023] The longitudinal axis of a wire is the axis along which the wire mainly extends.

[0024] The term "cross-section" refers to a section of the electrode wire perpendicular to its longitudinal axis.

[0025] The term "longitudinal section" refers to a section of the electrode wire made along a plane that contains its longitudinal axis.

[0026] The term "layer" refers to an annular layer of the electrode wire that is located, in each cross-section of the electrode wire, between an inner circular boundary and an outer circular boundary. In reality, these boundaries are not perfect circles. However, as a first approximation, in this text, these boundaries are treated as circles. These circular boundaries are both centered on the axis of the electrode wire. The inner circular boundary is the boundary of the layer that is closest to the axis of the electrode wire.Conversely, the outer circular boundary is the boundary of the layer that is furthest from the axis of the electrode wire. Between these inner and outer circular boundaries, the chemical composition is substantially homogeneous. Conversely, at the inner and outer circular boundaries, the chemical composition changes abruptly. In particular, the change in composition when these circular boundaries are crossed is much greater than the slight changes in composition that can be observed within a layer.

[0027] A "uniform" layer means a layer formed of a material that, in a cross-section of the wire, extends, around the axis of the wire and within this layer, continuously or practically continuously. Thus, a uniform layer does not have a multitude of fractures that partition it into a multitude of blocks separated from each other, in a longitudinal section of the wire, by these very numerous radial fractures.Very numerous radial fractures designates, over a length of 1 mm of the electrode wire, more than ten radial fractures which divide the layer in question into ten blocks mechanically isolated from each other, in the longitudinal section, by these radial fractures.

[0028] The term "fractured layer" designates a layer which comprises a multitude of fractures which partition it into a multitude of blocks separated from each other, in a longitudinal section of the wire, by very numerous radial fractures. The composition of these blocks is different from that of the adjacent layer located under this fractured layer or of the metallic core located immediately under this fractured layer. The majority of the blocks of a fractured layer have a length greater than the thickness of the fractured layer. Here, the majority of the blocks of a fractured layer have a length greater than 5 µm or 10 µm.In this text, the length and width of a block, in a cross-section, are defined as being equal, respectively, to the length and width of the rectangle of smallest area which entirely contains this block.

[0029] A "radial fracture" is a fracture which extends mainly, within a cross-section of the electrode wire, in a radial direction.

[0030] The expression "surface layer" designates the layer of the electrode wire which is located furthest to the outside of the electrode wire. This surface layer may have on its surface a thin film composed of residues such as wire drawing lubricant residues. The outer face of this surface layer is therefore either merged with the outer face of the electrode wire in the absence of the thin film or separated from the outer face of the electrode wire only by this thin film.

[0031] The expression "room temperature" designates a temperature between 15°C and 35°C and, typically, equal to 25°C.

[0032] The average thickness e of a surface layer of zinc oxide is defined by the following relation (1): e = [mi-mf] / [ρ*π*d*L], where: - m. iis the initial mass of a sample of a wire comprising a surface layer of zinc oxide, - mf is the mass of the same sample of wire after being immersed in a bath which completely dissolves the surface layer of zinc oxide, - ρ is the volume density of the zinc oxide enriched or not in chlorine, this density ρ being taken here equal to 5600 kg / m³, - π is the number pi, - d is the initial diameter of the sample of wire before being immersed in the bath which completely dissolves the oxide layer, - L is the length of the sample of wire, and - "*" is the symbol which designates the scalar multiplication.

[0033] The average thickness e is, for example, measured according to the following method: 1) A sample of length L and diameter d of wire is taken then wound in the form of a crown of approximately 5 cm in diameter. The length L is for example equal to 12 m. The diameter d is often equal to 0.25 mm.2) The sample is rinsed with water, then dried and dusted using a jet of compressed air. 3) The initial mass m. i of the sample is measured using a precision balance. 4) The sample is then soaked for 20 to 30 seconds in a stirred aqueous bath of sulfuric acid between 8% and 12% concentration, the temperature of which is between 42°C and 48°C. 5) The sample is rinsed with water. 6) The sample is dried using a jet of compressed air. 7) The final mass mf of the sample is measured using a precision balance. 8) The average thickness e of the sample is calculated using the previous relationship (1). Unless otherwise specified, in the remainder of this text, the term "thickness of the zinc oxide layer" alone designates the average thickness of this zinc oxide layer.

[0034] The average quantity qZnO of zinc oxide contained in a surface layer is defined by the following relation (2): q ZnO = [mi -m f ] / [π*d*L]. The initial masses mi and final masses mf are, for example, measured by implementing the same method as that described for measuring the thickness e of a surface layer of zinc oxide. Subsequently, the quantity q ZnO is expressed in g / m². Since the quantity q ZnO is expressed in g / m², it is a surface mass. Thus, in this text, the terms "quantity qZnO" ​​and "surface mass qZnO" ​​designate the same thing. Unless otherwise specified, in the remainder of this text, the term "quantity of zinc oxide" alone designates the average quantity of zinc oxide calculated using relation (2).

[0035] The average quantity qZnCl2 of zinc chloride (ZnCl2) deposited on the surface of a wire after it has been dipped in an aqueous solution of this salt is defined by the following relation (3): q ZnCl2 = [C / (1+C)]*[m fCl -m iCl] / [π*d*L], where: - C is the zinc chloride concentration of the aqueous solution expressed in kg / l, C being equal to the mass of zinc chloride, expressed in kg, dissolved in 1 liter of water, - mfCl is the final mass of a sample of a wire on the surface of which zinc chloride has been deposited by dipping this wire in an aqueous solution of this salt, - miCl is the initial mass of the same sample of wire before being dipped in the aqueous solution of zinc chloride, - π is the number pi, - d is the initial diameter of the sample of wire before being dipped in the aqueous solution of zinc chloride, - L is the length of the sample of wire.

[0036] The average quantity qZnCl2 is, for example, measured according to the following method: 1) A sample of length L and diameter d of wire is taken and then wound in the form of a crown of approximately 5 cm in diameter. The length L is for example equal to 12 m.2) The sample is rinsed with water, then dried and dusted using a jet of compressed air. 3) The initial mass miCl of the sample is measured using a precision balance. 4) Zinc chloride is then deposited on the surface of this sample by dipping it in an aqueous solution of zinc chloride. 5) The sample is drained to remove the drops of solution that remain attached to the sample. It is not dried, because zinc chloride is too hygroscopic. 6) The final mass m. fCl of the sample is measured using a precision balance. 8) The average quantity qZnCl2 is calculated using the previous relation (3). Subsequently, the quantity qZnCl2 is expressed in g / m². Unless otherwise specified, in the remainder of this text, the term “quantity of zinc chloride deposited on a wire” alone designates the average quantity of zinc chloride calculated using relation (3).

[0037] Chapter: Examples of embodiments

[0038] The figure represents an electrode wire 2 for electroerosion machining as described in the introductory part of this text.

[0039] For this purpose, the electrode wire 2 has a breaking load greater than 400 N / mm² or 700 N / mm² and, generally, less than 1100 N / mm 2. The wire 2 extends along a longitudinal axis 4. The axis 4 is here perpendicular to the plane of the sheet. The length of the wire 2 is greater than 1 m and, typically, greater than 10 m or 50 m.

[0040] The wire 2 has an outer face 6 directly exposed to sparks during the machining of a part by EDM using this wire. The outer face 6 is a cylindrical face which extends along the axis 4. The directrix curve of the face 6 is mainly a circle centered on the axis 4. Thus, the cross-section of the wire 2 is circular. The outer diameter D2 of the wire 2 is typically between 50 µm and 1 mm and, most often, between 70 µm and 400 µm. Here, the diameter D2 is equal to 0.25 mm.

[0041] In this embodiment, the wire 2 comprises: - a central core 10 made of electrically conductive material, and - a coating 12 directly deposited on the core 10.

[0042] The core 10 has the function of ensuring, on its own, the majority of the breaking load of the wire 2. It also has the function of ensuring the electrical conductivity of the wire 2. For this purpose, it is made of an electrically conductive material. Typically, it is made of metal or a metal alloy.

[0043] The core 10 has a mainly cylindrical peripheral face 14 which extends along the axis 4. This peripheral face 14 is made of a copper-zinc alloy. For this purpose, in this exemplary embodiment, the core 10 is entirely made of a single copper-zinc alloy. For example, the single copper-zinc alloy of the core 10 is an α-phase copper-zinc alloy or a copper-zinc alloy formed from a mixture of α and β phases. In particular, the core 10 does not comprise a central part made of copper-zinc alloy of a given phase covered with a layer of copper-zinc alloy in another phase.Typically the zinc concentration in the core 10 is greater than 20 atomic % and, preferably, greater than or equal to 36 atomic % or 40 atomic %. Typically, the zinc concentration of the core 10 is less than 42 atomic %.

[0044] The coating 12 is designed to increase the machining speed and therefore the erosive efficiency of the electrode wire and / or the quality of the faces of the part obtained after EDM machining. The quality of a face cut by EDM is all the better when its roughness is low.

[0045] For this purpose, the coating 12 contains zinc oxide in an amount greater than 0.5 g / m² or 1 g / m². The amount of zinc oxide may also be greater than 3 g / m² or 5 g / m². Generally, the amount of zinc oxide in the coating 12 is less than 100 g / m² or 50 g / m² and, most often, less than 10 g / m².

[0046] In this embodiment, the layer 12 is essentially made of zinc oxide.However, in places, the layer 12 may be crossed by brass peaks. These brass peaks form projections on the peripheral face 14 of the core 10 which pass through the layer 12. These brass peaks form only one block of material with the core 10.

[0047] More precisely, the zinc oxide contained in the coating 12 is zinc oxide enriched in chlorine of formula [Zn. 2+ , O 2-1-x, Cl-2x], where x is a mole fraction between 0.01 and 0.15 or between 0.01 and 0.2 or between 0.01 and 0.25. Preferably, the mole fraction x is greater than 0.02 or 0.03. Also, preferably, the mole fraction x is less than or equal to 0.2 or 0.13. The chlorine-enriched zinc oxide may be partially hydrated or not hydrated. Energy dispersive spectrometry (EDS) or wavelength selection (WDS) analyses give substantially the same results in the case of a chlorine-enriched zinc oxide whether it is hydrated or not. Thus, subsequently, the composition of the chlorine-enriched zinc oxide is given without taking into account the water molecules.

[0048] In this first embodiment, the coating 12 is formed from a single layer of zinc oxide. Thus, subsequently, the same numerical reference is used to designate both the coating 12 and the zinc oxide layer.Layer 12 is the surface layer of the electrode wire 2.

[0049] The average thickness of the layer 12 is very small compared to the diameter D2 of the wire 2, that is to say less than 0.5% of the diameter D2 and, preferably, less than 0.25% of the diameter D2.

[0050] The average thickness e12 of the layer 12 is between 100 nm and 522 nm and, preferably, between 100 nm and 400 nm or between 100 nm and 300 nm.

[0051] Composition analyses carried out using XPS spectra (“X-ray Photoelectron Spectroscopy”) have shown that the zinc oxide of the layer 12 is composed, in atomic percentages: - of more than 90% zinc, oxygen and chlorine, and - the remainder being copper and various manufacturing residues.

[0052] During these composition analyses, the presence of water, carbon and carbon compounds on the surface of layer 12 was not taken into account. Indeed, this carbon comes from the lubricant used during the electrode wire drawing step.According to the analyses carried out, it appears that the zinc oxide corresponds to zincite.

[0053] A first method for manufacturing the wire 2 will now be described with reference to FIG. 2.

[0054] For the implementation of this manufacturing method, typically, the desired thickness e12 is first chosen between 100 nm and 522 nm. For example, here, the thickness e12 is taken to be equal to 200 nm. Then, the value of a coefficient c1 described later is chosen between 1.15 and 6. For example, here, the coefficient c1 is chosen to be equal to two. Finally, a diameter D0 is chosen according to the coefficient c1 previously chosen and the desired final diameter D2 and respecting the constraints stated in the following paragraph. By way of illustration, the final diameter D2 is taken to be equal to 0.25 mm.

[0055] In a step 80, a brass blank wire is first provided. The blank wire is a brass wire having a diameter D0 between 1.15*D2 and 6*D2 and, preferably, between 2*D2 and 6*D2.In this example, the diameter D2 is equal to 0.25 mm so that the diameter D0 is between 0.288 mm and 1.5 mm and, preferably, between 0.5 mm and 1.5 mm. Here, the diameter D0 is taken to be equal to 0.5 mm.

[0056] The zinc concentration of this blank wire is chosen as described previously in the case of the core 10. Here the zinc concentration of the blank wire is 40 atomic %. Indeed, the higher the zinc concentration, the more the performance of the wire 2 is improved.

[0057] In this embodiment, the blank wire having the desired diameter D0 is obtained by drawing a brass wire of standard diameter D0 until the desired diameter D0 is obtained. For example, the diameter D. iniis equal to 1.25 mm.

[0058] Then, during a step 82, the blank wire is oxidized to obtain an oxidized blank wire. The oxidized blank wire has a layer of zinc oxide directly on its peripheral face. This layer of zinc oxide completely covers the peripheral face of the oxidized blank wire. For this purpose, during step 82, the blank wire provided is subjected to a heat treatment in the presence of oxygen and chlorine. This heat treatment is carried out in a gaseous medium containing oxygen and at a pressure greater than 50 kPa or 100 kPa. Here, this heat treatment is simply carried out in the Earth's atmosphere, that is to say in a gaseous medium comprising more than 20%, by volume, of oxygen, at the ambient pressure of approximately 101 kPa.

[0059] To ensure the presence of chlorine during the heat treatment, before the start of this heat treatment, the blank wire is dipped in an aqueous zinc chloride solution whose zinc chloride concentration makes it possible to deposit a quantity of zinc chloride on the outer face of the blank wire greater than 0.5 g / m² or 1 g / m². The quantity of zinc chloride deposited on the outer face of the blank wire is preferably greater than 5 g / m² or 10 g / m². Here, the temperature of the aqueous zinc chloride solution is equal to room temperature and the zinc chloride concentration in the solution is equal to 250 g / l. The blank wire is dipped in this solution for a time greater than 1 s. Here, the dipping time is between 1 s and 10 s and, preferably, between 3 s and 6 s. Throughout the soaking period, the solution is stirred to ensure a homogeneous concentration of zinc chloride.The zinc wire passes through the aqueous zinc chloride solution, for example, at a speed equal to 2 m / s. After being dipped in the zinc chloride solution, the rough wire is drained to remove any drops of solution that may remain on its surface and thus avoid local excesses of zinc chloride on the outer face of the rough wire. Under these conditions, the quantity of zinc chloride ZnCl2 deposited on the outer face of the rough wire is approximately 6 g / m².

[0060] The rough wire coated with zinc chloride is then wound onto a steel coil and then the steel coil is placed in a furnace, under air and at ambient pressure, to apply the heat treatment. Here, the furnace is not airtight and the air is stirred throughout the heat treatment.

[0061] Here, this heat treatment is configured to generate a layer of zinc oxide on the peripheral face of the rough wire whose average thickness e0 is between 115 nm and 600 nm. Indeed, a thickness e0 less than 115 nm does not allow a thickness e12 greater than or equal to 100 nm to be obtained after the drawing step 84 described later. Furthermore, it has been observed that a thickness e0 greater than 600 nm leads to a layer of zinc oxide which does not adhere well and which is torn off, at least in places, during the drawing step 84. This removal of part of the zinc oxide layer during wire drawing step 84 constitutes a waste of material which should be avoided or limited since the removed zinc oxide is not used in the wire 2 produced.

[0062] Within the range [115 nm; 600 nm], the thickness e0 is determined by successive experiments by testing several thicknesses e0 included in this range until the thickness e0 is found which, after wire drawing, makes it possible to obtain the desired thickness e12 of zinc oxide. In particular, to determine the thickness e0, it must be taken into account that, even if the thickness e0 remains less than 600 nm, a fraction of the zinc oxide is torn off during the wire drawing step. It has been evaluated that, currently, this fraction of zinc oxide can reach 45% or 30%. It is emphasized that such a fraction of zinc oxide lost during wire drawing remains much lower than the fraction of zinc oxide lost if the thickness e0 were chosen to be greater than 600 nm or 800 nm. Indeed, for a thickness e0 greater than 600 nm or 800 nm, the fraction of zinc oxide lost during wire drawing is greater than 60% or 75%.Typically, the thicknesses e0 tested are generally chosen in the interval [c1*e12; Min(1.8*c1*e12; 600)] and, preferably, in the interval [1.2*c1*e12; Min(1.8*c1*e12; 600)] and, even more often, in the interval [1.35*c1*e12; Min(1.7*c1*e12; 600)], where: - c1 is equal to the reduction coefficient of the diameter of the rough wire oxidized during the drawing step 84, and - Min(a;b) is the function which returns the smallest of the values ​​a and b.

[0063] The reduction coefficient c1 is defined as being equal to the ratio D0 / D2. Thus, when the thickness e12 is equal to 200 nm and the coefficient c1 is equal to two, the thickness e0 which makes it possible to obtain the desired thickness e12 after wire drawing is typically between 540 nm and 600 nm.

[0064] The parameters of the heat treatment to be configured are the temporal evolution of the temperature Tfour of the furnace during the heat treatment and the total duration Dfour of this heat treatment.Here, to simplify the adjustment of the heat treatment parameters, the temperature Tfour is chosen to be constant throughout the duration Dfour.

[0065] In the temperature range Tfour from 130°C to 260°C, the oxidation kinetics of zinc chloride-coated brass depends little on the temperature. The thickness e0 of the chlorine-doped zinc oxide layer appears to increase as a function of the square root of time, according to the following relationship (4): , where: - K = 2.68*10. -19 m 2 / s, - t is time, - e0 ini is the thickness e0 at time t=0, - the symbol “*” denotes scalar multiplication.

[0066] Using relation (4) it is possible to estimate a theoretical value D fourT of the duration D fourto obtain a given thickness e0. Then, several tests with different values ​​of the duration Dfour chosen around the theoretical value DfourT may be necessary to obtain the precise value of the duration Dfour which allows to obtain exactly the desired thickness e0. Typically, the value of the duration D fourretained at the end of these tests is included in the interval [0.8*DfourT; 1.2*DfourT] or in the interval [0.9*DfourT; 1.1*DfourT] or in the interval [0.95*DfourT; 1.05*DfourT].

[0067] The duration Dfour is advantageously chosen to be greater than four hours or six hours in order to ensure that the temperature is homogeneous in the coil.

[0068] At the end of the duration Dfour, the coil of rough wire is removed from the furnace. At this stage, the rough wire is covered with a layer of zinc oxide of thickness e 0. It is therefore called "oxidized rough wire". After being removed from the furnace, the coil is cooled. For this, conventionally, the coil is exposed to ambient air for the time necessary to cool to ambient temperature. Step 82 is then completed.

[0069] During step 82, the oxidation of the zinc consumes the zinc present in the brass.Thus, the zinc concentration of the brass core of the rough wire near the zinc oxide layer is generally lower than that of the same brass located at the axis 4.

[0070] Then, during a step 84, the rough wire, oxidized and cooled, is cold drawn to obtain the wire 2. By "cold", we mean the fact that the drawing step 84 is carried out without heating the rough wire before reducing its diameter. During step 84, the diameter reduction coefficient c1 makes it possible to bring the diameter D0 of the rough wire to the diameter D2 desired for the wire 2, that is to say here to a diameter of 0.25 mm.

[0071] Here, during step 84, the oxidized rough wire is drawn under the same conditions as those suitable for a non-oxidized brass wire.The diameter reduction is achieved by passing the oxidized blank wire successively through several dies of decreasing diameter so as to progressively reduce the diameter of the oxidized blank wire until the desired diameter D2 is reached. For example, dies with elongations between 15% and 22% are used. When drawing the oxidized blank wire, a water-soluble lubricant is used. For example, here, the lubricant is an aqueous solution containing the water-soluble lubricant.

[0072] It is this drawing that can create the brass peaks that pass through layer 12.

[0073] After step 84, once the diameter D2 is reached, an in-line stress relief annealing is carried out before it is wound. This stress relief annealing makes it possible to minimize the residual stresses in wire 2 and therefore to obtain a fairly straight wire, when a length of one meter is hung vertically, attached to its upper end.This facilitates the threading of the electrode wire into the machining machine. This stress-relieving annealing does not modify the structure of the wire 2 and has little effect on its breaking load. Typically, the temperature for stress-relieving annealing is between 250°C and 450°C and its duration is less than one tenth of a second.

[0074] It is emphasized that during step 82, the temperature T furnace is sufficiently low so that, under the effect of the heat treatment, the brass does not recrystallize so that the breaking load of the oxidized rough wire is greater than 700 N / mm². The coefficient c1 can therefore be as small as desired. On the other hand, to increase the breaking load of the oxidized rough wire, the coefficient c1 is chosen to be greater than or equal to 1.3 or 1.6. The coefficient c1 must also preferably be less than 6 so that the thickness e0 remains less than 600 nm when the thickness e12 is equal to 100 nm.

[0075] To demonstrate the benefit of an electrode wire comprising a surface layer of zinc oxide enriched with chlorine, the following tests were carried out. A reference electroerosion machining job was defined. This involves cutting a punch from a 50 mm high piece of steel with guides located less than 0.2 mm from the piece. The cutting is carried out on a CUT200MS machine marketed by the company "GF Machining Solution". This cutting is carried out in three machining passes, with technology adapted to brass. During each pass, the speed of movement of the part relative to the electrode wire was adapted to cut the punch as quickly as possible with the same final surface condition. Here, this final surface condition corresponds to a roughness Ra of 0.6 µm.More specifically, in the tests carried out, only the speeds of movement of the part relative to the electrode wire of the first and second passes were adapted according to the wire used. The speed of movement of the part relative to the electrode wire during the third pass is the same for all the tests carried out.

[0076] Using the manufacturing method of Figure 2, a first wire was manufactured. Then, a second wire was manufactured by implementing exactly the same manufacturing method as that used to obtain the first wire except that, during step 82, the dipping of the blank wire in the zinc chloride solution was omitted. Thus, the heat treatment implemented to manufacture this second wire is carried out in the absence of chlorine. Because of this, the thickness of the oxide layer of the second wire is different from the thickness e. 12of the first wire.

[0077] The machining times of the punch using the first and second wires were measured. The quantities of zinc oxide in the first and second wires were also measured. To eliminate variations in machining speed that could be explained simply by the fact that the thickness of the zinc oxide layers of the first and second wires are different, for each wire, the machining efficiency E defined by the following relationship was calculated: E = G / qZnO, where G and qZnO are, respectively, the measured time saving and the measured quantity of zinc oxide in this wire. The time saving G is calculated using the following relationship: G = 1- (tu / tref), where: - tu is the measured machining time, - tref is the machining time required to carry out the same machining of the same punch but using a brass wire comprising 40 atomic % zinc and without a coating.

[0078] It was observed that the machining efficiency of the first wire is 1.64 times higher than the machining efficiency of the second wire. This therefore indicates that the first wire machines faster than an identical wire but in which the zinc oxide is not enriched with chlorine.

[0079] Figure 3 shows a second method of manufacturing the wire 2. The method of Figure 3 is identical to the method of Figure 2 except that step 80 is replaced by a step 90 and the final drawing step 84 is omitted.

[0080] Step 90 is identical to step 80 except that the diameter D0 of the supplied brass blank wire is equal to D2 - e12. Then, during step 82, the thickness e0 is chosen equal to the thickness e12. Thus, after step 82, wire 2 of diameter D2 is directly obtained without it being necessary to carry out a wire drawing step to reduce the diameter of the oxidized rough wire.

[0081] In this second method, the elimination of step 84 is possible because during the oxidation step 82 the temperature of the rough wire does not exceed 250°C or 200°C so that even without final drawing, the breaking load remains greater than 700 N / mm². With this second manufacturing method, since there is no final drawing, the thickness e0 can be chosen to be greater than 522 nm or 600 nm, which makes it possible to produce a wire 2 whose thickness e. 12is greater than 522 nm or 600 nm.

[0082] Figure 4 shows a third method for manufacturing wire 2. This method is similar to the previous methods except that the oxidation of zinc and the enrichment in chlorine are not carried out at the same time.

[0083] This method begins with a step 92 of providing a rough wire. This step 92 is identical to step 80 except that the diameter D0 is between 1.3*D2 and 6*D2.

[0084] Then, during a step 94, the rough wire is oxidized to obtain an oxidized rough wire. This step 94 is identical to step 82 except that the heat treatment is carried out in the absence of chlorine. For this, the soaking of the rough wire in the aqueous zinc chloride solution is omitted. Due to the absence of chlorine, in step 94 the oxidation rate of zinc is slower. It was estimated that the values ​​of the parameters k and Q of relation (4) are then equal, respectively, to 2.418*10 -7 m 2 / s and 152 kJ / mol. To compensate for this slower oxidation rate while maintaining an acceptable oven duration D, the temperature Toven is generally chosen between 400°C and 500°C.

[0085] At the end of step 94, the zinc oxide of the oxidized rough wire is not enriched with chlorine.

[0086] Once step 94 is complete, the rough wire, oxidized and cooled, is drawn to the desired diameter D2 during a step 96. Step 96 is, for example, identical to step 84.

[0087] Before step 96 or after step 96, during a step 98, the zinc oxide is enriched with chlorine. In Figure 4, step 98 is illustrated in the case where it is carried out after step 96. In all cases, this step 98 is carried out after the heat treatment, that is to say after the oxidized rough wire has been cooled to room temperature.

[0088] During step 98, the zinc oxide produced during step 94 is placed in the presence of a chlorinated compound.For example, the wire is dipped into a solution containing the chlorine compound, such as an aqueous solution of zinc chloride at room temperature. The wire can also be enclosed in an enclosure containing chlorine gas. The time the zinc oxide is exposed to the chlorine compound is chosen to be long enough for Cl - anions to have time to replace O anions. 2- in zinc oxide of initial composition [Zn 2+ , O 2- ] in order to obtain a zinc oxide enriched in chlorine of composition [Zn 2+ , O 2- 1-x , Cl- 2x], where x is a mole fraction between 0.01 and 0.25. Step 98 can be carried out at room temperature. It can also be carried out at a slightly higher temperature, for example between 100°C and 200°C, while remaining at temperatures lower than those necessary to recrystallize the core 10 of the wire.

[0089] As an example of a chlorinated compound in the gaseous state that can be used during this step 98, mention may be made of hydrogen chloride (HCl) at room temperature. Hydrogen chloride is naturally found in the gaseous state above an aqueous solution of hydrochloric acid, concentrated to approximately 10%, at room temperature. Thus, during step 98, it is possible to place a coil of the wire oxidized during step 94 above such an aqueous solution of hydrochloric acid.After 24 hours, the zinc oxide of this wire is sufficiently enriched in chlorine to obtain a machining speed higher than that of an identical wire except that it has not been exposed to hydrochloric acid vapors.

[0090] Figure 5 represents a part of the cross-section of an electrode wire 100. This wire 100 is identical to wire 2 except that the coating 12 is replaced by a coating 102.

[0091] The coating 102 comprises successively, starting from the core 10 towards the outside: - a layer 104 of copper-zinc alloy in beta phase, and - a surface fractured layer 106.

[0092] The layer 106 is formed of blocks 110 of copper-zinc alloy separated from each other by fractures 112 more or less filled with zinc oxide. In Figure 5, the numerical references 110 and 112 point only, for illustration purposes, to a few examples of blocks and fractures.The majority, and typically, more than 90%, of these blocks are essentially gamma-phase copper-zinc alloy. Optionally, these gamma-phase blocks have a thin beta-phase layer on their faces that were directly exposed to oxygen during the oxidation step 122, described later. This thin beta-phase layer represents only a small fraction of the gamma-phase block. For example, in a transverse or longitudinal section of a gamma-phase block whose length is greater than 5 µm, the thin beta-phase layer represents less than 20% and, generally, less than 10% of the surface area of ​​this block in this section.Since, in all cases, the proportion of beta phase within a gamma phase block is low, the expression "gamma phase block" refers both to a block entirely composed of gamma phase brass and to a block essentially composed of gamma phase brass with, on its surface, a thin layer of beta phase brass.

[0093] The zinc oxide contained in the layer 106 is chlorine-enriched zinc oxide identical to that described previously.

[0094] A method for manufacturing the wire 100 is now described with reference to FIG. 6.

[0095] In a step 120, a blank wire is provided. Here, this blank wire is manufactured by implementing a method in accordance with that described in patent US8378247B2. For example, a brass wire with a diameter of 1.25 mm is first provided. The concentration of zinc in this wire is equal to 40 atomic %.Next, the brass wire is first electrolytically zinc-plated to obtain a zinc-plated brass wire with a 13.4 µm thick zinc layer on its surface. This zinc-plated brass wire is then drawn to obtain a zinc-plated brass wire with a diameter of 0.512 mm and a pure zinc coating thickness of 5.5 µm. This wire is then heat-treated to form a layer of beta-phase copper-zinc alloy surrounded by a surface layer of gamma-phase copper-zinc alloy. For example, a coil of this zinc-plated and drawn brass wire is placed in a furnace initially at room temperature.Then, the temperature of the furnace evolves temporally as follows: - the temperature is raised to 300°C following a ramp of 300°C / h, then - the temperature of the furnace is maintained equal to 300°C for three hours, then - the temperature of the furnace is raised to 330°C following a ramp of 20°C / h, then - the temperature of the furnace is maintained equal to 330°C for seven hours, then - the temperature of the furnace is lowered to 300°C following a ramp of 30°C / h, then - the coil is removed from the furnace and left in the ambient air to cool to ambient temperature.

[0096] Under these conditions, the thicknesses of the beta phase and gamma phase layers obtained are equal, respectively, to 13 µm and 6 µm. A thin film of non-chlorine-enriched zinc oxide is also present on the surface of the gamma-phase layer. The thickness of this thin zinc oxide film is 78 nm.

[0097] Then, the heat-treated wire is drawn.This drawing causes the fracturing of the surface layer in gamma phase while the layer in beta phase remains continuous. The fractures which separate the blocks in gamma phase open outwards.

[0098] This rough wire thus manufactured comprises successively going from the longitudinal axis towards the outside: - the core 10, - the layer 104 of copper-zinc alloy in beta phase, - a fractured layer similar to the fractured layer 106 with blocks of copper-zinc alloy in gamma phase and fractures which are not or practically not filled with zinc oxide. In addition, if zinc oxide is present, at this stage, this zinc oxide is not enriched with chlorine.

[0099] Here, the heat-treated wire is drawn to a diameter of 0.355 mm. The thickness of the 104 layer is then 9 µm, the thickness of the fractured layer is 6 µm and the thickness of the thin zinc oxide film is 52 nm.

[0100] At the end of step 120, during a step 122, the rough wire is oxidized to obtain an oxidized rough wire. For this, during step 122, the rough wire provided is subjected to a heat treatment in the presence of oxygen and chlorine. Here, step 122 is carried out by applying the teachings given in the particular case of oxidation step 82. For example, after having been soaked for 10 s in the aqueous zinc chloride solution, the rough wire is placed in a furnace at 120°C for 24 h. This oxidation step 122 consumes a portion of the zinc present on the surface of the gamma-phase blocks, which causes, in certain cases, the appearance of the thin beta-phase layer on some of the faces of these gamma-phase blocks.

[0101] At the end of step 122, a layer of zinc oxide enriched in chlorine covers the fractured layer. In this example, the thickness of the layer of zinc oxide enriched in chlorine is 1200 nm.

[0102] Finally, during a step 124, the oxidized wire obtained at the end of step 122 is drawn to the desired final diameter. Step 124 is carried out under the same conditions as step 84. For example, the oxidized wire passes successively through four dies to reduce the diameter of the oxidized wire successively to 0.324 mm, 0.296 mm, 0.270 mm and finally 0.25 mm. At the end of step 124, a stress relief annealing, similar or identical to that implemented after step 84, is carried out.

[0103] During the final drawing, a portion of the zinc oxide which is on the surface of the oxidized wire is pushed inside the fractures of the fractured layer. Thus, at the end of step 124, the majority of the fractures 112 between the blocks 110 are at least partially filled with chlorine-enriched zinc oxide. The amount of zinc oxide contained within the fractures 112 depends on the thickness of the zinc oxide layer produced during step 122.The greater the thickness of the zinc oxide layer manufactured during step 122, the more the fractures 112 are filled with chlorine-enriched zinc oxide. At the end of step 124, a portion of the outer faces of the blocks 110 may still be covered with a layer of chlorine-enriched zinc oxide. The outer faces of the blocks 110 are the faces of these blocks facing outwards, i.e. on the side opposite the longitudinal axis of the wire. In the particular case of the manufacturing method detailed here, the thickness of the chlorine-enriched zinc oxide layer obtained after this last drawing is equal to 500 nm.

[0104] The machining speed of the wire 100 was compared to the machining speed of a reference wire manufactured using the same manufacturing method except that the dipping in the aqueous zinc chloride solution was omitted. He observed that the machining speed of wire 100 is 1.1 times higher than the machining speed of the reference wire.

[0105] Chapter III: Variants:

[0106] Variants of the electrode wire:

[0107] The metal core is not necessarily made entirely of brass. For example, as a variant, the metal core comprises only a surface layer of brass. This surface layer of brass typically has a thickness greater than 5 µm or 10 µm. The core of the metal core is made of another material, such as steel, copper or another metal or another metal alloy.

[0108] The outer face of the coating 12 or 102 may be covered with a thin film of the lubricant used during the wire drawing step 84 or 124.

[0109] The thickness of the oxide layer 12 may also be greater than 461 nm. For example, the thickness of the oxide layer 12 may be greater than 500 nm or 600 nm.

[0110] Variants of the manufacturing processes:

[0111] Alternatively, the blank wire provided during steps 80, 90 and 92 comprises a metal core, for example devoid of zinc, covered with a surface layer of zinc. The surface layer of zinc is often deposited on the metal core by electrolysis. In such a case, the electrolysis bath may comprise a chlorinated compound so that at the outlet of the electrolysis bath, residues of this chlorinated compound may remain on the outer face of the zinc layer. However, unless special measures are taken, the residual quantity of this chlorinated compound from the electrolysis bath is too low to obtain, after the oxidation step, zinc oxide enriched in chlorine with a molar fraction x greater than 0.01.Thus, unless special measures are taken to preserve, on the outer face of the zinc layer, a substantial quantity of the chlorinated compound from the electrolysis bath, dipping in the aqueous zinc chloride solution cannot be omitted in this case.

[0112] Alternatively, if the rough wire having the desired diameter D0 is commercially available, during step 80, it is not drawn before performing step 82.

[0113] Other embodiments of oxidation step 82 or 122 are possible. For example, many other solutions containing a chlorinated compound can be used to replace the aqueous zinc chloride solution. For example, a hydrochloric acid solution or a solution containing bleach is also suitable. A solution containing NaCl may also be suitable.

[0114] In another variant, the chlorine is deposited on the wire to be treated not by soaking it in a liquid solution containing a chlorine component but by bringing it into contact with a gas containing a chlorine compound such as dichlorine (Cl2).

[0115] Alternatively, instead of placing an entire coil of the rough wire in a furnace, the rough wire is unwound and then passes through a heating tunnel and is then wound again onto a coil at the exit of this tunnel. Inside the tunnel, the temperature is equal to the temperature Tfurnace. Thus, in this variant, the rough wire is heated to the temperature T. four portion after portion. Therefore, the problem of the time required to obtain a uniform temperature within an entire coil of the blank wire does not arise. In this case, it is possible to use a higher temperature T furnace and a very short duration D furnace. For example, when a heating tunnel is used, the value of the temperature Tfourcan be greater than 300°C or 400°C. The speed of travel of the rough wire inside the tunnel is then adjusted so that the duration D oven, during which a portion of the rough wire remains inside the tunnel, makes it possible to obtain the desired thickness e0.

[0116] To obtain a thickness e12 greater than 522 nm, even in the context of the process of Figure 2, the thickness e0 can be chosen to be greater than 600 nm or 800 nm.

[0117] The oxidation step 82 can also be carried out in a medium other than the Earth's atmosphere. For example, step 82 can also be carried out in a medium containing more than 20% or 30%, by volume, of dioxygen or, on the contrary, depleted in oxygen but with a residual quantity of oxygen sufficient to oxidize the rough wire.

[0118] In another variant of step 82, the temperature T four varies during the duration Dfour. For example, the temperature Tfour increases continuously during the duration Dfour.For example, the manufacturing process is as follows: a 60% copper and 40% zinc brass wire, 1.25 mm in diameter in the annealed state is supplied and then drawn to a diameter of 0.464 mm. The wire, with a diameter equal to 0.464 mm, is then dipped in an aqueous zinc chloride solution at 252 g / l and 20°C (+ / - 5°C), for a period of 5 seconds. After being dipped in the aqueous zinc chloride solution, the wire is wound onto a steel coil and placed in a furnace under atmospheric pressure. The temperature T. fouris then gradually increased from 20°C to 260°C at a rate of 10°C per hour. The duration Dfour is therefore 24 hours. After the duration Dfour, the wire is removed from the furnace and left in the air at room temperature to cool. It is then drawn to a diameter of 0.25 mm using dies with elongations between 15% and 22% and a lubricant consisting of an oil-in-water emulsion at a temperature between 20°C and 80°C. Finally, it undergoes stress-relief annealing. The breaking load of the wire thus obtained is greater than 900 N / mm².

[0119] During step 120, the blocks of the rough wire supplied can be in the gamma phase and in the epsilon phase. To achieve this, during the production of the rough wire, the temperature of the heat treatment which formed the beta and gamma phase layers is lowered to form, instead, a superposition of a gamma phase layer and an epsilon phase layer.For example, for this, the temperature of the heat treatment is lowered to between 130°C and 160°C. The thickness of the epsilon phase layer is sufficiently low so that, during wire drawing, the epsilon phase layer fractures at the same time as the gamma phase layer so that the wire provided has a fractured layer comprising essentially gamma phase and epsilon phase blocks instead of only gamma phase blocks.

[0120] During step 120, the blocks of the blank wire may also be beta phase blocks. For example, for this a blank wire containing gamma phase blocks is first manufactured and then a heat treatment is applied to transform the gamma phase blocks into beta phase blocks. Such a method for manufacturing a wire containing essentially beta phase blocks is described in application US2022212277A1.

[0121] In another variant, step 124 is omitted.In this case, more than 50% or 70% or 90% of the surface of the outer faces of the blocks 110 of the fractured layer is covered with a chlorine-enriched oxide layer. On the other hand, the fractures are not necessarily filled with chlorine-enriched zinc oxide.

[0122] The cooling of the oxidized blank wire can also be carried out differently. For example, the furnace is turned off and the coil is left inside the furnace until it reaches room temperature.

[0123] In a simplified embodiment, the stress-relieving annealing is omitted.

[0124] Several of the variants described above can be combined in a single embodiment.

[0125] Chapter IV: Advantages of the described embodiments:

[0126] The fact that the coating comprises zinc oxide enriched with chlorine improves the machining speed compared to an identical or practically identical wire but in which the zinc oxide is not enriched with chlorine.

[0127] The fact that the chlorine-enriched zinc oxide is mainly located inside the fractures of a fractured layer makes it possible to both improve the machining speed while also improving the electrical contact between this wire and the electrodes used when machining a part with this wire.

[0128] The fact that the thickness of the oxide layer is greater than 100 nm improves the machining speed and makes it possible, in particular, to obtain machining speeds equal to or greater than that of an electrode wire comprising a fractured coating of gamma-phase copper-zinc alloy such as that described in US8378247B2.

[0129] The fact that the thickness of the zinc oxide layer is less than 522 nm makes it possible to manufacture this zinc layer on a rough wire and then to draw it to the final diameter D2 with very little loss of zinc oxide during this drawing.

[0130] The fact that the zinc oxide layer is directly formed on the peripheral face of the metal core makes it possible to manufacture this zinc oxide layer by simple oxidation of the brass peripheral face of a blank wire. Thus, it is not necessary to deposit a zinc layer on the peripheral face of the blank wire as, for example, in the case of the manufacture of a wire in accordance with the teaching given in patent US8378247B2. In particular, it is emphasized that the deposition, by electrodeposition, of a zinc layer on a blank wire consumes much more energy than the heat treatment step. Thus, the electrode wire in which the oxide layer is directly formed on the brass core can be manufactured by simpler and more economical processes.

[0131] Carrying out the oxidation of zinc in the presence of chlorine makes it possible to obtain a zinc oxide enriched in chlorine which increases the machining speed of the manufactured electrode wire.

[0132] The presence of chlorine during the heat treatment carried out to oxidize the zinc also makes it possible to accelerate the oxidation reaction. Thus, the duration of the heat treatment is shorter and / or the temperature of the heat treatment is lower than, respectively, the duration and / or the temperature necessary to obtain the same quantity of zinc oxide but in the absence of chlorine. Therefore, the presence of chlorine during the oxidation makes it possible to accelerate the manufacturing process and / or to reduce the temperature of the heat treatment.

[0133] Obtaining the desired quantity of zinc oxide using a heat treatment which does not exceed 250°C makes it possible not to degrade the breaking load of the wire during the implementation of this heat treatment.Thus, it is no longer necessary to subject the oxidized rough wire obtained at the end of this heat treatment to an additional drawing step with a high coefficient c1 to give it an acceptable breaking load. In addition, such a method makes it possible to simply and efficiently manufacture an electrode wire whose thickness e12 of the oxide layer is greater than 522 nm or 600 nm.

[0134] Oxidizing the zinc first in the absence of chlorine and then transforming this non-chlorine-enriched zinc oxide into chlorine-enriched zinc oxide makes it possible to carry out the chlorine enrichment with very little heating or without heating, that is to say, for example, at room temperature.

Claims

Claims 1. Electrode wire (2; 100) suitable for use as an electrode wire for electroerosion machining, this electrode wire comprising: - a metal core (10) which extends along a longitudinal axis, and - on the metal core, a coating (12; 102) having a surface mass of zinc oxide greater than 0.5 g / m², characterized in that the zinc oxide is enriched in chlorine, i.e. the composition of the zinc oxide is [Zn 2+ , O 2- 1-x , Cl- 2x], where x is a mole fraction between 0.01 and 0.

25.

2. Electrode wire according to claim 1, wherein: - the coating comprises a fractured layer (106) comprising blocks (110) of copper-zinc alloy and fractures (112) which separate the blocks from each other and from adjacent layers, and - the majority of the fractures (112) are at least partially filled with chlorine-enriched zinc oxide.

3. Electrode wire according to any one of the preceding claims, in which: - the coating comprises a fractured layer comprising blocks (110) of copper-zinc alloy and fractures (112) which separate the blocks from each other, the composition of these blocks being different from that of an adjacent layer located under this fractured layer or of the metallic core located immediately under this fractured layer, and - the chlorine-enriched zinc oxide covers at least 50% of the surface of the faces of the blocks facing outwards. 4.The electrode wire of claim 3 or 4, wherein the majority of the copper-zinc alloy blocks are gamma-phase copper-zinc alloy blocks (110).

5. Electrode wire according to claim 1, wherein the coating (12) comprises a layer of chlorine-enriched zinc oxide whose average thickness is greater than 100 nm.

6. Electrode wire according to claim 5, wherein the average thickness of the layer (12) of zinc oxide is less than 522 nm.

7. Electrode wire according to any one of claims 5 to 6, wherein: - the metal core (10) is made of a single copper-zinc alloy, and - the layer (12) of zinc oxide is directly formed on the peripheral face of the metal core.

8. Electrode wire according to any one of the preceding claims, wherein the mole fraction x is between 0.01 and 0.

15. 9.A method of manufacturing an electrode wire according to any one of the preceding claims, this method comprising the following steps: - providing (80; 90; 120) a blank wire whose outer periphery contains zinc or a zinc alloy, then - oxidizing (82; 122) the outer periphery of the blank wire to form a coating having a surface mass of zinc oxide greater than 0.5 g / m², characterized in that the oxidation (82; 122) of the outer periphery is carried out in the presence of a chlorinated compound so that the zinc oxide obtained at the end of the oxidation step is a zinc oxide enriched in chlorine.

10. A method according to claim 9, wherein the oxidation (82; 122) of the outer periphery of the blank wire is carried out by subjecting the blank wire to a heat treatment in the presence of oxygen and chlorine. 11.Method according to claim 10, in which: - the supply (80; 90) of the blank wire comprises the supply of a blank wire comprising a metallic core made of a single copper-zinc alloy, and. - the temperature to which the rough wire is heated during the heat treatment remains below 250°C.

12. Method according to any one of claims 10 to 11, in which to ensure the presence of chlorine during the heat treatment, before the start of this heat treatment, the rough wire is dipped in an aqueous solution of zinc chloride whose zinc chloride concentration makes it possible to deposit a quantity of zinc chloride on the outer face of the rough wire greater than 0.5 g / m². 13.

14. A method of manufacturing an electrode wire according to any one of claims 1 to 8, this method comprising the following steps: - providing (92) a blank wire whose outer periphery contains zinc or a zinc alloy, then - oxidizing (94), in the absence of a chlorine compound, the outer periphery of the blank wire to form a coating having a surface mass of zinc oxide greater than 0.5 g / m², this zinc oxide being free of chlorine, characterized in that, after the oxidation step, the method comprises a step (98) of enriching the zinc oxide with chlorine during which the chlorine-free zinc oxide is placed in the presence of a chlorine compound so as to transform the zinc oxide obtained at the end of the oxidation step into a zinc oxide enriched in chlorine.A method according to any one of claims 9 to 13, wherein: - providing (120) the blank wire comprises providing a blank wire comprising a fractured layer of copper-zinc alloy, the outer face of which forms the outer periphery of the blank wire, - then, once the chlorine-enriched zinc oxide has been obtained on the outer face of the fractured layer, the method comprises drawing (124) the blank wire to push the chlorine-enriched zinc oxide inside the fractures of the fractured layer.

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