ELECTRODE LEAD WITH A POROUS LAYER FOR ELECTRICAL DISCHARGE MACHINING

Abstract

According to the invention, the electrode wire (1) for electric discharge machining comprises a metal core (2), in one or more layers of metal or metal alloy. On the metal core (2), a coating (3) having an alloy different from that of the metal core (2) contains more than 50 wt % zinc. The coating (3) comprises copper-zinc alloy (3a) of fractured γ phase, and covers the majority of the metal core (2). The coating (3) contains covered pores (5a, 5b, 5c, 5d, 5e) larger than 2 μm.

Claims

1-15. (canceled)

16. An electrode wire for electric discharge machining, said electrode wire comprising: a metal core, in one or more layers of metal or metal alloy, on the metal core, a coating having an alloy different from that of the metal core and containing more than 50 wt % zinc, in which: the coating comprises copper-zinc alloy of fractured γ phase, wherein: the coating contains covered pores larger than 2 μm, some or all of the pores are covered with one or more alloys of copper and zinc with more than 58% and less than 100% zinc by weight.

17. The electrode wire as claimed in claim 16, wherein the coating covers the metal core at a coverage greater than 85% when the diameter of the electrode wire is about 0.30 mm, at a coverage greater than 75% when the diameter of the electrode wire is about 0.25 mm, at a coverage greater than 65% when the diameter of the electrode wire is about 0.20 mm.

18. The electrode wire as claimed in claim 16, wherein the coating covers the metal core at a coverage greater than 85% when the diameter of the electrode wire is 0.25 mm.

19. The electrode wire as claimed in claim 16, wherein some or all of the pores are covered with one or more alloys of copper and zinc with more than 78% and less than 100% zinc by weight.

20. The electrode wire as claimed in claim 16, wherein some or all of the pores are covered with a mixture of alloys of copper and zinc of ε phase and η phase.

21. The electrode wire as claimed in claim 16, wherein the coating comprises on average, in each complete cross section of the electrode wire, at least 3 covered pores larger than 2 μm.

22. The electrode wire as claimed in claim 16, wherein the coating comprises on average, in each complete cross section of the electrode wire, at least 5 covered pores larger than 2 μm.

23. The electrode wire as claimed in claim 16, wherein the coating contains covered pores larger than 3 μm.

24. The electrode wire as claimed in claim 16, wherein the coating contains covered pores larger than 4 μm.

25. The electrode wire as claimed in claim 16, wherein the core comprises a metal core and an intermediate layer of alloy of copper and zinc of β phase.

26. The electrode wire as claimed in claim 25, wherein the core is of copper or copper alloy.

27. A method of manufacturing an electrode wire as claimed in claim 16, comprising the sequence of steps: taking a core of brass with 63% copper and 37% zinc, with a diameter of 1.25 mm, depositing a first layer of zinc with a thickness of 20 μm on this core, drawing to 0.30 mm, carrying out a diffusion heat treatment at 180° C. for 2 hours for partially transforming the outer layer of zinc into a layer of γ-phase brass; the coating then comprises a layer of γ phase near the core, and an outer layer of ε phase, drawing to 0.25 mm.

28. A method for producing an electrode wire as claimed in claim 16, comprising the steps: taking a core of brass with 80% copper and 20% zinc, with a diameter of 1.20 mm, depositing a first layer of zinc with a thickness of 30 μm on this core, carrying out a first heat treatment of 20 hours at 385° C. to obtain: a sublayer of R phase about 60 μm thick, and an outer layer of γ phase about 15 μm thick, drawing to 0.62 mm; the γ phase fractures, making a coating of 3 μm of zinc on the fractured γ phase, degreased and deoxidized beforehand, drawing to 0.25 mm, carrying out a heat treatment of 5 hours at 130° C.

29. A method for producing an electrode wire as claimed in claim 16, comprising the steps: taking a core of brass with 80% copper and 20% zinc, with a diameter of 1.20 mm, depositing a first layer of zinc 38 μm thick on this core, carrying out a first heat treatment of 22 hours at 395° C. to obtain: a sublayer of β phase about 76 μm thick, and an outer layer of γ phase about 15 μm thick, drawing to 0.62 mm; the γ phase fractures, carrying out a second heat treatment of 7 hours at 327° C.; we obtain a layer of β-phase brass 39 μm thick, and an 8 μm layer of blocks of fractured γ-phase brass also containing β phase, making a coating of 6.5 μm of zinc on the fractured γ phase, degreased and deoxidized beforehand, drawing to 0.42 mm, carrying out a third heat treatment of 32 hours at 145° C., at the end of which a coating is obtained comprising an inner layer of β-phase brass 16 μm thick and a surface layer of γ-phase brass 14 μm thick, drawing to 0.25 mm.

30. A method for producing an electrode wire as claimed in claim 16, comprising the steps: taking a core of brass with 60% copper and 40% zinc, with a diameter of 1.20 mm, depositing a layer of zinc 13 μm thick on this core, drawing this wire to 0.464 mm, the layer of zinc then being 5 μm thick, subjecting the blank thus obtained to a diffusion heat treatment comprising a rise in temperature over 4 hours from room temperature up to a stationary phase of 11 hours at 140° C., followed by a fall in temperature over 5 hours down to room temperature; the coating then comprises an inner layer of γ-phase brass of about 6 μm, and a surface layer of ε-phase brass about 2 μm thick, without trace of zinc, gradually drawing down to a final diameter, said final diameter advantageously being 0.20 mm, 0.25 mm or 0.30 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Other aims, features and advantages of the present invention will become clearer from the following description of particular embodiments, referring to the appended figures, where:

[0068] FIG. 1 is a schematic perspective view of an electrode wire for electric discharge machining according to the present invention;

[0069] FIG. 2 is a schematic cross section, on a larger scale, of the electrode wire in FIG. 1, according to a first embodiment of the core of the electrode wire;

[0070] FIG. 3 is a schematic cross section, on a larger scale, of the electrode wire in FIG. 1, according to a second embodiment of the core of the electrode wire;

[0071] FIG. 4 is a schematic partial view in longitudinal section, on a larger scale, of a segment of the electrode wire according to FIG. 1;

[0072] FIG. 5 shows an example of a phase equilibrium diagram of the copper-zinc system:

[0073] FIG. 6 is a partial cross-sectional view of a wire of the prior art according to document U.S. Pat. No. 8,067,689;

[0074] FIG. 7 is a schematic partial cross-sectional view of a wire sample A according to example No. 1 of the present description;

[0075] FIG. 8 is a schematic partial cross-sectional view of a wire sample B according to example No. 2 of the present invention;

[0076] FIG. 9 is a schematic partial cross-sectional view of a wire sample E according to example No. 5 of the present invention;

[0077] FIG. 10 is a schematic partial cross-sectional view of a wire sample F according to example No. 6 of the present invention;

[0078] FIG. 11 is a light microscope photograph of a cross section of the wire sample B according to the present invention;

[0079] FIG. 12 is a light microscope photograph of a longitudinal section of the wire sample B in FIG. 11;

[0080] FIG. 13 is a light microscope photograph of a cross section of a wire sample G with a diameter of 0.25 mm according to the present invention;

[0081] FIG. 14 is a light microscope photograph of a longitudinal section of the wire sample G in FIG. 13;

[0082] FIG. 15 is a light microscope photograph of the surface of the wire sample G in FIG. 13; and

[0083] FIG. 16 is a light microscope photograph of a cross section of a wire sample G with a diameter of 0.30 mm according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0084] In the embodiments illustrated in the figures, an electrode wire 1 for electric discharge machining comprises a metal core 2, covered with a coating 3 of thickness E.sub.3 comprising fractured γ-phase brass.

[0085] In the embodiment illustrated in FIG. 2, the metal core 2 comprises a single layer of metal or metal alloy, for example an alloy with 63% copper and 37% zinc, or an alloy with 80% copper and 20% zinc.

[0086] In the embodiment illustrated in FIG. 3, the metal core 2 comprises two different layers of metal or metal alloy, which differ by the presence of a metal core 2a, for example of α-phase brass, and an intermediate layer 2b of alloy of copper and zinc of β phase.

[0087] In this same embodiment in FIG. 3, the coating 3 comprises an inner layer 3a of alloy of copper and zinc of fractured γ phase, i.e. in the form of blocks, and further comprises an outer layer 3b of thickness E.sub.4 of zinc or alloy of zinc and copper of a phase.

[0088] Let us now consider FIG. 4, which shows, schematically and on a larger scale, a partial view in longitudinal section of a segment of length L of the electrode wire 1 in FIG. 1, in the radial region of the coating 3 covering the core 2.

[0089] The coating 3, with fractured structure, contains covered pores 5a, 5b, 5c, 5d and 5e.

[0090] FIG. 4 shows the size of the covered pores. We can see, for example in the covered pores 5a and 5b, an internal cavity, in which a circle 7 can be drawn. When the circle 7 comes into contact with opposite walls of the cavity, the diameter of the circle 7 defines the size of the pore.

[0091] The pores, for example pore 5b, are said to be “covered” as the radial straight lines such as the straight line D1, starting from the axis I-I of the electrode wire and passing through said circle 7, only leave the wire after again passing through solid matter 6. Similarly, the pore will be said to be “covered” when said circle 7 is covered with solid matter 6.

[0092] In the illustration in FIG. 4, the pores 5c, 5d and 5e are completely covered, in the sense that no radial straight line passing through them emerges from the wire without passing through solid matter again. In other words, observation of the outside surface of the electrode wire in a radial direction cannot discern the internal cavity constituting the volume of the pore. In contrast, the pores 5a and 5b are covered, but only partially, in the sense that radial straight lines passing through them in the spaces illustrated by the lengths L1 and L2 can emerge from the pore without passing through solid matter again. In other words, observation of the outside surface of the electrode wire in a radial direction can then at least partly discern the internal cavity constituting the volume of the pore 5a or 5b.

[0093] FIG. 4 also illustrates the degree of longitudinal coverage Tc according to which the coating 3 covers the metal core 2. In the longitudinal section of wire observed, with total length L, the length of the core 2 not covered by the coating 3 is equal to the sum of the lengths L1 and L2 of the spaces according to which radial straight lines passing through the pores 5a and 5b can emerge from the pore without passing through solid matter. The degree of coverage Tc is then defined by the formula:

Tc=[(total length)−(length uncovered)]/(total length)=1−(L1+L2)/L

[0094] Several embodiment examples of electrode wires of this kind comprising covered pores will now be described.

[0095] In all these examples, the wiredrawing steps were carried out with injection of an emulsion of 5 to 10 vol % of oil in water in the wiredrawing dies. The heat treatment steps were carried out in the free atmosphere, without special precautions to avoid the presence of oxides on the outside surface of the electrode wire.

Example No. 1

[0096] In this first example, the electrode wire (sample A) was produced by the following method: [0097] take a core of brass with 63% copper and 37% zinc, with a diameter of 1.25 mm, [0098] deposit a first layer of zinc with a thickness of 6 μm on this core. [0099] draw to 0.46 mm. [0100] carry out diffusion heat treatment to obtain an outer layer of γ-phase brass, about 4 μm thick; in practice, the heat treatment may be about 6 hours at 180° C. [0101] draw to 0.30 mm: the γ phase fractures into blocks of about 5 μm, leaving voids between said blocks, [0102] deposit a layer of zinc about 2 μm thick, [0103] draw to 0.25 mm.

[0104] A wire sample A of this kind is shown schematically in partial cross section in FIG. 7.

[0105] It was found that, in a wire A of this kind, covered pores 5a are observable in cross sections of the wire. In fact, in the coating 3 covering the core 2, the ductile zinc of the outer layer 3b has only partially filled the voids present between the blocks of layer 3a of γ-phase brass. However, the covered pores 5a are few in number, and of small size (less than about 2 μm).

[0106] With a subsequent heat treatment at low temperature (about 60° C. for 48 hours), a wire was produced (sample A′) in which the outer layer 3b of zinc covering the pores 5a was converted by diffusion into ε-phase brass, without the core 2 being recrystallized, and without causing the covered pores to disappear.

Example No. 2

[0107] In this second example, the electrode wire (sample B) was produced by the following method: [0108] take a core of brass with 63% copper and 37% zinc, with a diameter of 1.25 mm, [0109] deposit a first layer of zinc with a thickness of 20 μm on this core, [0110] draw to 0.30 mm, [0111] carry out diffusion heat treatment at 180° C. for 2 hours for partially transforming the outer layer of zinc into a 6 μm layer of γ-phase brass; the coating then comprises a layer of γ-phase brass near the core, and a 5 μm outer layer of ε-phase brass, [0112] draw to 0.25 mm.

[0113] A wire sample B of this kind is shown schematically in partial cross section in FIG. 8.

[0114] It was found that, in a wire B of this kind, covered pores 5a, 5b, 5c are observable in cross sections of the wire. In the coating 3 covering the core 2 of the wire, the γ phase of the layer 3a fractured into blocks during the second wiredrawing. The outer layer 3b of ε phase has only very partially filled the voids created between the blocks of the layer 3a of γ phase, leaving behind covered pores 5a, 5b, 5c that are more numerous and larger (possibly exceeding 4 μm). The degree of longitudinal coverage was greater than 90%.

[0115] With a subsequent heat treatment at low temperature (at a temperature of about 180° C. for 4 hours), the outer layer 3b of c phase covering the pores can be converted to γ-phase brass, without the core 2 being recrystallized, and without causing the covered pores 5a, 5b, 5c to disappear.

[0116] In FIG. 8, a crack 8 is illustrated schematically, which is clearly different from the covered pores according to the present invention with respect to its shape and its volume, and which opens onto the surface of the wire.

[0117] The photographs in FIGS. 11 and 12 illustrate the presence of covered pores in a longitudinal section and a cross section of the wire B, respectively.

Example No. 3

[0118] In this third example, the electrode wire (sample C) was produced by the following method: [0119] take a core of brass with 80% copper and 20% zinc, with a diameter of 1.20 mm, [0120] deposit a first layer of zinc with a thickness of 30 μm on this core, [0121] carry out a first heat treatment of 20 hours at 385° C. to obtain: a sublayer of phase about 60 μm thick, and an outer layer of γ phase about 15 μm thick, [0122] draw to 0.62 mm; the γ phase fractures, [0123] make a coating of 3 μm of zinc on the fractured γ phase, degreased and deoxidized beforehand, [0124] draw to 0.25 mm, [0125] carry out a heat treatment of 5 hours at 130° C.

[0126] The surface zinc was transformed into ε-phase brass.

[0127] It was found that, in a wire C of this kind, the degree of longitudinal coverage that was obtained was about 90%. Covered pores are observable in cross sections of the wire. Some of these pores may be larger than 3 μm. On average, more than 3 covered pores are observed per complete cross section of the wire.

Example No. 4

[0128] In this fourth example, the electrode wire (sample D) was produced by the following method: [0129] take a core of brass with 80% copper and 20% zinc, with a diameter of 1.20 mm, [0130] deposit a first layer of zinc with a thickness of 38 μm on this core, [0131] carry out a first heat treatment of 22 hours at 395° C. to obtain: a sublayer of β phase about 76 μm thick, and an outer layer of γ phase about 15 μm thick, [0132] draw to 0.62 mm; the γ phase fractures, [0133] carry out a second heat treatment of 7 hours at 327° C.; we obtain a layer of β-phase brass 39 μm thick, and an 8 μm layer of blocks of fractured γ-phase brass also containing β phase, [0134] make a coating of 6.5 μm of zinc on the fractured γ phase, degreased and deoxidized beforehand, [0135] draw to 0.42 mm, [0136] carry out a third heat treatment of 32 hours at 145° C., at the end of which a coating is obtained comprising an inner layer of β-phase brass 16 μm thick and a layer of γ-phase brass 14 μm thick, [0137] draw to 0.25 mm.

[0138] It was found that, in a wire D of this kind, the degree of longitudinal coverage that was obtained was about 86%. Covered pores are observable in cross sections of the wire. Some of these pores may be larger than 4 μm. On average, more than 5 covered pores larger than 2 μm are observed per complete cross section of the wire.

Example No. 5

[0139] In this fifth example, the electrode wire (sample E) was produced by the following method: [0140] take a brass wire with 63% copper and 37% zinc, with a diameter of 1.25 mm, [0141] deposit a first layer of zinc 14 μm thick on this core, [0142] draw this wire to 0.827 mm, [0143] subject the blank thus obtained to diffusion heat treatment until the coating no longer has zinc at the surface; in practice, the heat treatment may be of 4 hours at 180° C.; we obtain a layer of about 13 μm of γ-phase brass, and a surface layer of ε-phase brass about 7 μm thick, without a trace of zinc, [0144] draw to 0.25 mm.

[0145] A wire sample E of this kind is shown schematically in partial cross section in FIG. 9.

[0146] It was found that, in a wire E of this kind, the degree of longitudinal coverage that was obtained was about 86%. The layer 3a of γ-phase brass is fractured, comprising blocks of brass of variable thickness, which may reach 12 μm. Covered pores 5a, 5b, 5c, 5d are observable in cross sections of the wire. Some of these pores may be larger than 4 μm. On average, in the coating 3 covering the core 2, more than 5 covered pores larger than 2 μm are observed per complete cross section of the wire.

[0147] A crack 8 is illustrated schematically in FIG. 9, which is clearly different from the covered pores according to the present invention with respect to its shape and its volume, and which opens onto the surface of the wire.

Example No. 6

[0148] In this sixth example, the electrode wire (sample F) was produced by the following method: [0149] take a core of brass with 63% copper and 37% zinc, with a diameter of 1.25 mm, [0150] deposit a first layer of zinc with a thickness of 20 μm on this core. [0151] draw to 0.827 mm, [0152] carry out a first heat treatment of 5 hours at 180° C. to obtain: a sublayer of alloy of copper and zinc of γ phase about 15 μm thick, an intermediate layer of alloy of copper and zinc of ε phase of about 6 μm, and an outer layer of lightly alloyed copper and zinc alloy of η phase about 6 μm thick, [0153] draw to 0.25 mm; the γ phase fractures, and the coating covering the core is a mixture of blocks of alloy of copper and zinc of γ phase, with, between the blocks, pores covered with a mixture of alloys of copper and zinc of ε phase and η phase.

[0154] A wire sample F of this kind is shown schematically in partial cross section in FIG. 10.

[0155] It was found that, in a wire F of this kind, the degree of longitudinal coverage that was obtained was greater than about 90%. Covered pores 5a, 5b, 5c are observable in cross sections of the wire. Some of these pores may be larger than 4 μm. On average, more than 5 covered pores larger than 2 μm are observed per complete cross section of the wire.

[0156] With a subsequent heat treatment at low temperature (about 60° C. for 48 hours), a wire was produced (sample F′) in which the outer layer 3b of zinc covering the pores was converted by diffusion into ε-phase brass, without the core 2 being recrystallized, and without causing the covered pores 5a, 5b, 5c to disappear.

[0157] With a second subsequent heat treatment at about 180° C. for 2 hours, a wire was produced (sample F″) in which the outer layer 3b of alloy of copper and zinc of ε phase covering the pores was converted by diffusion into alloy of copper and zinc of γ phase, without the core 2 being recrystallized, and without causing the covered pores 5a, 5b, 5c to disappear.

Example No. 7

[0158] In this seventh example, the electrode wire (sample G) was produced by the following method: [0159] take a brass wire with 60% copper and 40% zinc, with a diameter of 1.20 mm, [0160] deposit a layer of zinc 13 μm thick on this core, [0161] draw this wire to 0.464 mm, the layer of zinc then being 5 μm thick, [0162] subject the blank thus obtained to a diffusion heat treatment comprising a rise in temperature over 4 hours from room temperature up to a stationary phase of 11 hours at 140° C., followed by a fall in temperature over 5 hours down to room temperature; the coating then comprises an inner layer of γ-phase brass of about 6 μm, and a surface layer of ε-phase brass about 2 μm thick, without trace of zinc, [0163] gradually draw down to a final diameter, for example by using 5 successive dies down to a final diameter of 0.30 mm, or by using 8 successive dies down to a final diameter of 0.25 mm, or by using 10 successive dies down to a final diameter of 0.20 mm.

[0164] FIGS. 13, 14 and 15 are optical microscope photographs of a sample wire G 0.25 mm in diameter, respectively in cross section, in longitudinal section, and as a surface view. FIG. 16 is an optical microscope photograph of a sample wire G 0.30 mm in diameter in cross section. The following have been marked out on these photographs: the core 2, the inner layer 3a of alloy of copper and zinc of fractured gamma phase, the outer layer 3b of alloy of copper and zinc of ε phase, and covered pores 5a.

[0165] It could be seen that, in such a wire G, the degree of longitudinal coverage which was obtained was about 88% when the diameter of the electrode wire is 0.30 mm. The degree of longitudinal coverage was about 77% when the diameter of the electrode wire is 0.25 mm. The degree of longitudinal coverage was about 66% when the diameter of the electrode wire is 0.20 mm. The layer of γ-phase brass is fractured, comprising blocks of brass of substantially constant thickness. Covered pores 5a are observable in sections of the wire. Some of these pores are larger than 2 μm. On average, in the coating covering the core, more than 5 covered pores larger than 2 μm are observed per complete cross section of the electrode wire.

[0166] The sample B of the second example, and the sample G of the seventh example, are obtained by methods particularly suitable for industrial production as just one heat treatment is necessary. In the case of the sample G, this heat treatment is carried out on a wire diameter which is markedly greater than the final diameter, which is even more favorable in industrial production.

[0167] Tests

[0168] Comparative machining tests were carried out, demonstrating the advantageous effect of the present invention.

[0169] The machining tests were carried out with the electrode wires A, A′, B, C, D, E, F, F′, F″ and G whose manufacture is described above, comparing them with: [0170] a wire (sample LA) with a diameter of 0.25 mm of bare brass with 63% copper and 37% zinc, [0171] a wire (sample T) with a diameter of 0.25 mm having a core of copper-zinc alloy with 63% copper and 37% zinc, a coating covering practically 100% of the surface of the core and comprising blocks of alloy of copper and zinc of fractured γ phase, said blocks being embedded in a matrix of alloy of copper and zinc of c phase that fills the interstices between the blocks of γ phase; this wire is as described in document U.S. Pat. No. 8,067,689 B2 according to the embodiment with e phase, [0172] a wire (sample SD2) with a diameter of 0.25 mm having a core of alloy of copper and zinc at 63% copper and 37% zinc, a coating having a sublayer of alloy of copper and zinc of β phase and an outer layer of alloy of copper and zinc of fractured γ phase, i.e. having open pores, [0173] a wire (sample SE) with a diameter of 0.25 mm having a core of alloy of copper and zinc at 80% copper and 20% zinc, a coating having a sublayer of alloy of copper and zinc of β phase and an outer layer of alloy of copper and zinc of fractured γ phase, i.e. having open pores, [0174] a wire (sample SA) with a diameter of 0.25 mm having a core of alloy of copper and zinc at 63% copper and 37% zinc, a coating of alloy of copper and zinc of fractured γ phase having blocks of alloy of substantially constant thickness and revealing the core in the fractures, i.e. having open pores.

[0175] All the machining tests were carried out using a GFMS P350 machine, on a steel workpiece with a height of 50 mm, with detached nozzles of 4.4 mm at the bottom and 5.0 mm at the top, with AC CUT VS+0.25 mm technology (ACO=0), with I changed from 17 to 18, P changed from 54 to 45 to give about 10 A of machining current, and with FW changed from 17 to 10.

[0176] Regarding the comparative tests for evaluating the production or powder during machining, a length of wire of about 1000 linear meters, tensioned at 10 N, was passed through a ceramic wire guide of an electric discharge machine, the powder was collected under the wire guide on an adhesive surface, and the amounts of powder deposited were compared. Comparison was essentially visual, with the naked eye, adopting five thresholds of amount, namely an undetectable amount, a very small amount, a medium amount, a large amount, and a very large amount. The standard for amount is obtained with SA, SD2 and SE wires, which are mass-produced wires that have been marketed by the applicant for several years. The SA wire produces only an undetectable amount of powder during electric discharge machining. The SD2 and SE wires are completely satisfactory thanks to the fact that they produce only a very small amount of powder during electric discharge machining.

[0177] The results are presented in the following table.

TABLE-US-00001 Machining speed Amount of State of Wire (mm.sup.2/min) powder surface Wire LA 83.8 medium Wire SD2 99.8 very small Wire SE 106.6 very small Wire SA 90 undetectable excellent (0.16 μm) Wire T 96.0 very large 0.20 μm Wire A 94.2 medium Wire A′ 96.0 medium Wire B 100.3 very small g (0.20 μm) Wire C 107.1 large Wire D 110.1 very small Wire E 101.9 medium mediocre Wire F 97.0 very small mediocre Wire F′ 108 mediocre Wire F″ 110 large mediocre Wire G 95 undetectable excellent (0.25 mm) (0.15 μm)

[0178] The covered pores of wires A and A′ are apparently too small to have an advantageous effect on the machining speed notably relative to wire SD2.

[0179] However, comparison of the machining speeds of wires A and A′ shows the advantage of the ε phase relative to pure zinc or of η phase.

[0180] On examining wires B and E with covered pores of sufficient size, we find an increase in rough machining speed relative to wires having an identical core structure of brass CuZn37 and having a coating with open pores or with small covered pores (wires SD2, A, A′).

[0181] In particular, wire E, which was produced by depositing the same amount of zinc as wire A′, shows the advantage of the presence of covered pores of more than 4 μm in the coating. Compared to wire E, wire A′ only has pores with diameter less than 2 μm.

[0182] Wire B gave low roughness values in finishing, of the order of 0.20 μm of Ra. It generates little powder when it passes through the wire guides of the machine. Wire B demonstrates that, to reconcile a high machining speed, a low roughness value, and little release of powder, it may be advantageous to produce covered pores of more than 4 μm covered with alloy of copper and zinc of ε phase between fractured blocks of regular thickness of alloy of copper and zinc of γ phase. In comparison with wire SD2, the core of which has the same composition, wire B demonstrates the advantage of the presence of large covered pores.

[0183] On examining wire D with covered pores of sufficient size, we find an increase in rough machining speed relative to wires having an identical core structure of brass CuZn20 and having a coating with open pores (wire SE).

[0184] Wire F has a relatively low machining speed, despite the presence of the coating layer of fractured γ phase, of ε phase, and of covered pores. The presence of zinc of r phase seems to be the cause of this result.

[0185] In comparison with wire F, wire F′ demonstrates the advantage of having covered pores of more than 3 μm in a coating of alloy of copper and zinc of ε phase without r phase.

[0186] Wire G gave very low roughness values in finishing. The amount of powder produced when it passes through the wire guides of the machine is virtually undetectable. Wire G demonstrates that, to reconcile a high machining speed, a very low roughness value and a virtually undetectable release of powder, it may be advantageous to produce covered pores of more than 2 μm covered with alloy of copper and zinc of γ phase between fractured blocks of regular thickness of alloy of copper and zinc of γ phase. In comparison with wire SA, which exhibits the same structure having fractured blocks of regular thickness of alloy of copper and zinc of γ phase, wire G demonstrates the advantage of the presence of covered pores for increasing the machining speed.

[0187] The present invention is not limited to the embodiments that have just been described explicitly, but includes the several variants and generalizations thereof that are within the scope of the claims given hereunder.