Electrode wire for spark erosion cutting

Abstract

The invention relates to an electrode wire for spark erosion cutting, comprising a core (2) comprising a metal or a metal alloy and a covering layer (3) surrounding the core (2), the core (2) comprising regions having a morphology corresponding to block-shaped particles, the block-shaped particles being separated from one another and / or by cracks in the core material at least in a portion of the periphery, characterised in that, observed in a cross section of the wire perpendicular or parallel to the longitudinal axis of the wire, more than 50% of the surface area of ​​the region having the morphology of block-shaped particles contains a copper-zinc alloy having a zinc concentration of 58.5-67 wt.-%, wherein, observed in a view perpendicular to the wire surface, the surface proportion formed by the block-shaped particles is more than 20% and less than 50% of the total surface area of ​​the electrode wire and in each case has a surface area of ​​25-200 μm 2 The bulk particles within the range account for more than 50% of the total surface area of ​​all bulk particles.

Description

Technical Field

[0001] The invention relates to an electrode wire for electric spark erosion cutting and a manufacturing method thereof. Background Art

[0002] The spark erosion method (electrical discharge machining, EDM) is used to separate electrically conductive workpieces and involves removing material by spark discharges between the workpiece and a tool. To this end, a controlled spark discharge is generated in a dielectric liquid such as deionized water or oil by applying a voltage pulse between the respective workpiece and a tool, which is held at a short distance from the workpiece and serves as an electrode. In this way, workpieces made of metal, electrically conductive ceramics or composite materials, for example, can be machined regardless of their hardness. The electrical energy for the spark discharge is provided by a pulse generator in the erosion machine.

[0003] A special spark erosion method is spark erosion cutting or wire erosion, in which the tool consists of a thin, tensioned wire, typically with a diameter of approximately 0.02 to 0.4 mm. The wire is consumed during the erosion process due to material removal; it must be continuously drawn through the cutting or processing area and can only be used once, meaning that the wire is continuously consumed. The desired cut contour is initially made with a high discharge energy in a so-called main cut. To improve the contour accuracy and surface roughness of the workpiece, one or more so-called trim cuts can be performed after the main cut, with successively lower discharge energies. During these trim cuts, the electrode wire engages only a portion of its periphery. Machine-specific settings for the main and trim cuts, such as open-circuit voltage, pulse current, pulse duration, pause duration, gap width adjustment parameters, wire pretension, wire withdrawal speed, flushing pressure, etc., are combined in so-called techniques or erosion or cutting technologies. Corresponding erosion technologies are available for erosion machines commonly used in the industry, tailored to the type of material to be processed, workpiece height, wire type, wire diameter, and quality targets.

[0004] In practice, coated and uncoated wires or electrode wires are used, which are now usually produced based on brass or copper. Uncoated electrode wires, also called bare wires, consist of a homogeneous material, while coated electrode wires have a covered or coated core. In the prior art, coated electrode wires are usually constructed so that a sheath or covering consisting of one covering layer or a plurality of successively superimposed covering layers is used for the actual corrosion process, while the core of the electrode wire, for example, imparts the tensile strength required for threading and prestressing the wire as well as the necessary electrical and thermal conductivity.

[0005] Bare wire typically consists of brass with a zinc content of 35 to 40 wt.%, while most coated wires have a core of red copper or brass and one or more covering layers of zinc or copper-zinc alloy. Zinc and brass, the materials involved in the actual corrosion process, have lower evaporation temperatures due to the presence of zinc, resulting in higher removal rates and corrosion process efficiency, as well as the potential for very low pulse energy transfer. This advantage is particularly relevant for fine machining of workpiece surfaces, i.e., machining to produce the smallest possible surface roughness. In this context, for fine machining, electrode wires with a covering composed primarily or entirely of zinc are often used.

[0006] It is known that the removal rate or cutting performance can be improved by using wire having a coating comprising one or more zinc-containing alloys, compared to bare wire and wire having a coating consisting primarily or entirely of zinc. This includes wire having a coating containing brass in one or more of the β or β', γ and ε phases, respectively.

[0007] To achieve high cutting performance, it has proven advantageous to produce a coating from a brittle alloy (such as brass in the gamma phase), giving it a diameter larger than the final diameter by diffusion, and then drawing it to its final size by cold forming. As a result, the brittle hard layer cracks, leading to the formation of dents and continuous cracks therein, with the underlying material penetrating (see US Pat. No. 5,945,010, US Pat. No. 6,306,523). These cracks and dents increase the surface area of ​​the wire. This allows the latter to be better cooled by the surrounding dielectric, and also facilitates the removal of dislodged particles from the gap. Furthermore, due to the excessive increase in the electric field, discharges preferentially form at the edges where the cracks are created. This improves the ignition properties of the electrode wire, thereby enhancing cutting performance. According to US Pat. No. 5,945,010, good corrosion results in terms of cutting performance and surface quality are achieved if the coating covers less than 100% and more than 50% of the wire surface.

[0008] This and further developments for improving cutting performance are also based on the combination of variously designated covering layers (optionally with further layers) in a multilayer coating. Occasionally, as may be necessary due to diffusion processes occurring during the respective production process, jackets with brass covering layers containing, for example, a phase mixture of α and β phases or β and γ phases are also proposed.

[0009] US Pat. No. 7,723,635 proposes an electrode wire having a core and a first covering layer of a brass alloy containing approximately 37-49.5 wt.% zinc. Uniformly distributed so-called grains, which are separated from one another and contain a brass alloy containing approximately 49.5-58 wt.% zinc, are embedded in the covering layer. Such an electrode wire is intended to enhance corrosion resistance while improving electrical conductivity and strength.

[0010] According to EP-A-2 193 867, at least one of the several covering layers comprises a predominantly fine-grained mixture of beta and gamma brass. By incorporating gamma brass into the beta brass matrix, the gamma brass is not lost too quickly during corrosion, but is instead released in small quantities into the corrosion gaps by efficient removal.

[0011] In EP-A-1 846 189a wire electrode is proposed which contains a firstlayer ofβbrass as well as a torn layer ofγbrass, in the holes of which thelayer ofβbrass emerges.

[0012] EP-A-1 846 189 proposes an electrode wire comprising a first layer of beta brass and a tear layer of gamma brass, in the pores of which the layer of beta brass emerges.

[0013] EP-A-2 517 817 describes an electrode wire having two alloy layers formed by diffusion. Core material emerges along cracks in the second alloy layer, forming a multiplicity of granular structures on the surface. The granules contain the core material and are arranged approximately perpendicular to the longitudinal direction of the electrode wire. This improves both cutting performance and surface quality.

[0014] However, for coatings of brittle phases such as the gamma phase, it has been shown that, on the one hand, an increase in the layer thickness does not necessarily lead to a further improvement in the properties (see EP-A-1 295 664) and, on the other hand, the formability of thicker layers limits economic production capabilities (see US 5,945,010).

[0015] A significant drawback of the aforementioned electrode wires is that they often fail to achieve the required precision and / or surface quality of the components being machined, even on erosion machines that do not have the erosion technology specifically matched to these wires, but only standard technology for bare brass wire. While the remedy here could be to adapt or optimize the existing erosion technology, companies in the erosion industry are often unable or unwilling to invest the necessary time for this.

[0016] Particularly in the case of multi-step etching processes with one or more finishing steps to achieve reduced surface roughness, it is known that the use of electrode wires, such as those according to US Pat. No. 5,945,010 (see comparative tests in EP-A-1 949 995), can result in the formation of undesirable grooves parallel to the wire's travel speed. To address this problem, EP-A-1 949 995 proposes an electrode wire having a covering layer formed from block-like structures ("blocks"), wherein the blocks have a very uniform thickness, a zinc content exceeding 50 wt.%, and cover more than 50% of the wire surface. Furthermore, the cracks generated between the blocks follow a preferred orientation, forming an angle exceeding 45% with the longitudinal axis of the wire. These characteristics are achieved by having an approximate covering layer thickness of 7 μm or less before the final drawing process and a ratio between the final diameter and the intermediate diameter before the final drawing process of 0.4 to 0.8. However, this requires galvanizing the electrode wire at a correspondingly smaller diameter, or requiring another intermediate drawing after galvanizing at a larger diameter. Both would undermine the economic viability of electrode wire production.

[0017] Purpose of the Invention

[0018] One object of the present invention is to provide an electrode wire which, on the one hand, has a higher cutting performance than bare brass wire, thereby improving the economic viability of wire etching technology, and, on the other hand, achieves an equivalent or higher precision and surface quality than bare brass wire and the above-mentioned coated wire.

[0019] Furthermore, it is an object of the present invention to provide an electrode wire that can be subjected to etching techniques on bare brass wire, in particular those involving multiple cuts, thereby achieving a higher cutting performance than that of bare brass wire and achieving the same or higher precision and surface quality on the assembly than that of bare brass wire and the above-mentioned coated wire.

[0020] Another object of the present invention is to provide an electrode wire having the above-mentioned advantages, which can be produced with as little manufacturing effort as possible. Summary of the Invention

[0021] To achieve this object, an electrode wire is used having the features of claim 1. Advantageous embodiments of the electrode wire are the subject matter of the respective dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A cross section (perpendicular to the longitudinal axis) of a first embodiment of an electrode wire according to the invention is schematically shown.

[0023] Figure 2An optical microscope picture showing a cutout of the outer periphery of an electrode wire according to the invention in a cross section perpendicular to the longitudinal axis of the wire body.

[0024] Figure 3 Shows Figure 1 The outer periphery of the electrode wire of the present invention is cut in a cross section perpendicular to the longitudinal axis.

[0025] Figure 4 An optical microscope picture of the surface of an electrode wire according to the present invention is shown.

[0026] Figure 5 Shows the Figure 3 Optical microscope picture of a particle with a rectangular reference frame for determining the degree of coverage of bulk particles or clusters formed therefrom.

[0027] Figure 6 Shows the Figure 3 Optical microscope image of the line, in which the longitudinal axis and linear blocky particle clusters are marked.

[0028] Figure 7 An optical microscope picture of the surface of a first electrode line not according to the present invention is shown.

[0029] Figure 8 An optical microscope picture of the surface of a second electrode line not according to the present invention is shown. DETAILED DESCRIPTION

[0030] According to the present invention, an electrode wire for spark erosion cutting has a core comprising a metal or a metal alloy. Preferably, the core consists of one or more metals and / or one or more metal alloys in an amount exceeding 50 wt.%, more preferably entirely or substantially entirely. Specifically, the core can thus consist entirely of one metal or one metal alloy. The core can be formed homogeneously or, for example, in the form of a plurality of layers of a single metal or a metal alloy of different compositions superimposed on one another, with properties varying in the radial direction. As used herein, "substantially" means that the wire according to the present invention, or its layers, or its core, consists of the respectively disclosed composition and / or has the disclosed properties, taking into account production and measurement tolerances, such as the presence of unavoidable impurities, as is familiar to the expert.

[0031] The metal is in particular red copper and the metal alloy is in particular a copper-zinc alloy having a zinc content of 20-42 wt.-%.

[0032] Around the core, for example in the form of a coating, a sheath (hereinafter also referred to as "covering layer") is provided. The covering layer wears away during the wire corrosion process and serves to influence the corrosion properties.

[0033] The covering layer of the electrode wire according to the invention comprises areas with a granular appearance (morphology), which are characterized in particular by irregular contours, which sometimes contain sharp corners with a corner radius of less than 2 μm, and lines whose straightness deviates from an ideal straight line by less than 2 μm. Therefore, these areas are described as areas whose morphology corresponds to blocks or block-shaped particles. In the following, the layer containing these areas is also referred to as "covering layer with block-like morphology", and the areas, whose morphology corresponds to blocks or block-shaped particles, are also referred to as "block-like particles" or "block-shaped particles" for short. The core material can appear between the block particles. The block particles are in turn separated in a part of their surroundings, from each other and / or by cracks in the core material. The block particles themselves can contain cracks.

[0034] The cracks are typically about 2 μm wide, predominantly about 1 μm, and can be imaged using a scanning electron microscope under standard conditions, for example, based on backscattered electrons (20 kV). If a larger crack width (e.g., 1 to 2 μm) appears along the crack line, this structure is also considered a crack within the meaning of the present invention. In contrast, wider spacings between the blocky particles (typically extending radially inward from the outer surface of the line) are referred to as indentations or gaps.

[0035] Observed in a cross section of the wire perpendicular or parallel to the longitudinal axis of the wire (also referred to as the "wire longitudinal axis" or simply the "wire axis"), the majority (i.e., more than 50% of the surface area of ​​the bulk particles) comprises a copper-zinc alloy with a zinc content of 58.5-67 wt.%. According to the phase diagram for the CuZn system, the alloy is present in this portion of the surface area as the γ phase. At the boundaries between adjacent materials of the wire, "seams" of β and / or β' phases can form (if red copper or α-brass is used as the core material). These seams are usually recognizable using an optical microscope (or can be determined using other methods known to experts, such as SEM / EDX, as described in detail below) and are not considered bulk particles.

[0036] The surface of the electrode wire is formed by the "joints" of the bulk particles, the core material and the optional β and / or β' phases. Figures 4 to 6 As shown (perpendicular to the circumference of the wire, as seen radially at the point closest to the observer (microscope)), the surface proportion formed by the blocky particles, i.e. the coverage, accounts for more than 20% and less than 50% of the entire surface of the electrode wire. These values ​​can be determined according to Figure 5 are described and represented in the figure itself by a suitable reference surface area. Figure 5The image is defined by a light-colored reference frame 6, which has a size of approximately 400 μm x 50 μm and is symmetrical with respect to the longitudinal axis of the line body.

[0037] In the above view perpendicular to the wire surface, the surface area is 25–250 μm 2 The bulk particles within the range account for more than 50% of the total surface area of ​​all bulk particles.

[0038] In the above view perpendicular to the wire surface, the blocky particles are arranged in linear clusters of four or more particles, which account for a significant proportion and are particularly dominant. Within these clusters, the spacing between particles is less than 15 μm. Adjacent particles that meet this spacing criteria are also referred to as adjacent particles.

[0039] The term "line-shaped" refers to a uniform structural characteristic in which particles are arranged in adjacent "rows." This arrangement may have some irregularity (in terms of particle size and spatial arrangement). However, the characteristic feature of a line-shaped cluster is that it has a preferred orientation, i.e., it is arranged in a row (=line) in the longitudinal direction, and in the transverse direction, along this line, there are no or only a few directly adjacent particles, i.e., particles with a spacing of less than 15 μm, as described above.

[0040] In particular, there are only a few arrangements of blocky particles, which are adjacent to each other in the form of fluffy "piles", or strip-like arrangements, formed by several linear clusters, which are directly adjacent to each other in most of the longitudinal range, that is, so close that the spacing between the particles in the (vertical) transverse direction is less than 15 μm.

[0041] The clusters thus have a "scattered" appearance, i.e., they have only a few "contact points" with other clusters, e.g. Figure 6 The cases of clusters (a) and (b) shown in .

[0042] This characteristic morphological appearance of the clusters can be quantified as follows.

[0043] The 25–250 μm 2 An arrangement of bulk particles of a surface area containing so many particles of such size that they can be connected in a straight line (longitudinal axis), wherein the longitudinal axis must connect or touch all particles of the cluster meeting the above size criteria, and the spacing between adjacent particles (of such size) defined in this way in this longitudinal direction is less than 15 μm, or can be separated by very small particles without violating the spacing criteria of less than 15 μm.

[0044] As the starting and ending points of the vertical axis, the endpoints of the particles that are farthest apart in the cluster determined according to the above criteria are selected.

[0045] The majority of the linear clusters, i.e. more than 50%, form an angle of less than 45° with the longitudinal axis of the electrode line, independently of the viewing direction along the longitudinal axis of the electrode line, see e.g. Figure 6 Clusters (a) and (c) in .

[0046] As mentioned above, the clusters appear in a dispersed manner, i.e. several linear clusters are generally not immediately adjacent to each other (i.e. in the transverse direction, thus perpendicular to the longitudinal direction of the clusters, with a spacing of less than 15 μm). This can also be exemplified by Figure 6 This can be seen from the arrangement of clusters (a) and (b).

[0047] More than two-thirds of the blocky particles have a thickness measured in the radial direction that is greater than 0.8% and less than 2% of the total diameter of the electrode wire when viewed in a cross section of the wire perpendicular or parallel to the longitudinal axis of the wire.

[0048] The metal contained in the core and coating may contain unavoidable impurities.

[0049] According to the prior art, if the broken layer of an electrode wire contains blocky particles with a zinc content of more than 50 wt.-%, but the degree of coverage of such particles is less than 50%, and there is no preferential orientation of the cracks essentially perpendicular to the longitudinal axis of the wire, then the cutting properties and the surface quality of the electrode wire are not particularly favorable.

[0050] However, it has been demonstrated that using the electrode wire of the present invention, particularly when using the erosion technique on bare brass wire, very good results can be achieved in terms of cutting performance and surface quality. Without being bound by a particular theory, it is believed that the following features or a combination thereof contribute to achieving very uniform feed in various cuts during spark erosion machining:

[0051] - have a coverage of less than 50% and greater than 20%,

[0052] -Surface area between 25–250 μm 2 The bulk particles within the range account for more than 50% of the total surface area of ​​all bulk particles, and

[0053] -Furthermore, the arrangement of blocky particles in linear clusters of at least 4 particles is significant or dominant in number.

[0054] Furthermore, during the main cutting and the entire machining process, machining time is significantly reduced compared to bare brass wire.

[0055] In addition, due to the targeted setting of the thickness of the block particles, in the case of at least two-thirds of the block particles, the thickness of the block particles is greater than 0.8% and less than 2% of the total diameter of the electrode wire. Combined with the above characteristics, very good surface quality can be obtained, and grooves parallel to the wire running speed are rarely formed.

[0056] Production

[0057] The starting materials for the production of the electrode wire according to the invention comprise one or more metals and / or one or more metal alloys in an amount exceeding 50 wt.-%, more preferably all or substantially all. Thus, for example, starting from a starting material, one can make Cu, CuZn 37 or CuZn 40 (brass containing 37 or 40 wt.-% zinc, respectively) in the form of a uniform wire with a diameter of, for example, 1.20 mm. Starting from this starting material, the production of the electrode wire according to the invention ideally comprises only three process steps: zinc coating, diffusion annealing and finally stretching with integrated stress relief annealing. The starting material diameter before diffusion annealing is selected so that a 20-25-fold reduction in cross-sectional area is achieved during stretching to the final diameter. In a first step, the starting material is coated with zinc, for example by an electrodeposition process. The thickness of the zinc layer before diffusion annealing is determined by the zinc content of the selected core material. For example, if a core material consisting of CuZn is selected, 37 The thickness of the zinc layer is preferably 0.8 to 1.6% of the desired final diameter. For example, if a core composed of CuZn is selected 40 For a homogeneous core composed of the alloy, the zinc layer thickness is preferably 0.6-1.4% of the desired final diameter.

[0058] The zinc-coated wire is then diffusion annealed, resulting in a coating consisting primarily of a copper-zinc alloy with a zinc concentration of 58.5–67 wt. %. According to the CuZn phase diagram, this alloy exists as a gamma phase.

[0059] Diffusion annealing can be performed in a static manner (e.g., in a bell-type furnace) and in a continuous process (e.g., by resistance heating). Diffusion annealing can be performed, for example, in a bell-type furnace in an ambient atmosphere or a protective gas, preferably at 180-230°C for 4-12 hours, wherein the average heating rate is preferably at least 80°C / h and the average cooling rate is preferably at least 60°C / h. Alternatively, the operation can be performed, for example, by resistance heating continuously passed through in an ambient atmosphere or a protective gas, wherein the average heating rate is preferably at least 10°C / s, the maximum line temperature is preferably 600 to 800°C, the annealing time is preferably 10-200s, and the average cooling rate is preferably at least 10°C / s. The above-mentioned annealing time relates to the time period from leaving room temperature to returning to room temperature.

[0060] In the final step, the wire is tapered to its final diameter, preferably by cold forming and stress-relief annealing. This final diameter lies in the range of 0.02–0.40 mm. During this process, the brittle, hard brass layer in the gamma phase tears apart, resulting in the formation of bulk particles. These bulk particles are spatially separated from one another, so that core material can be present between them. The bulk particles themselves may contain cracks.

[0061] Due to the thickness of the zinc layer before the diffusion annealing selected in a targeted manner as described above and the cross-sectional reduction during drawing to the final diameter selected in a targeted manner, the resulting blocky particles have a diameter of 25-250 μm in each case in a view perpendicular to the wire surface. 2 The surface area of ​​the electrode wire accounts for more than 50% of the total surface area of ​​all bulk particles, and further, when viewed perpendicular to the wire surface, a significant number, and particularly a predominant number, of at least four types of particles are arranged in linear clusters. The spacing between particles in these clusters is less than 15 μm. A majority of the linear clusters, i.e., more than 50%, form an angle of less than 45° with the longitudinal axis of the electrode wire. The degree of coverage of the bulk particles is between less than 50% and more than 20% of the entire surface of the electrode wire. For further details on clusters, please refer to the above description.

[0062] Furthermore, the formation of linear clusters is promoted by the cross-sectional reduction at each drawing step, which is approximately 8–12% at least in the last 12 drawing steps.

[0063] If more than two thirds of the bulk particles have a thickness of less than 0.8% of the final diameter of the electrode wires and bulk particles, wherein their surface area in each case is between 25 and 250 μm 2 range, which together account for less than 50% of the surface area of ​​all bulk particles, this embodiment does not provide a significant improvement in cutting performance compared to bare brass wire.

[0064] On the other hand, if the coating thickness after diffusion annealing is too large, exceeding 2% of the final diameter in a view perpendicular to the wire surface and exceeding 250 μm in surface area, 2 After drawing to the final diameter, the resulting lumpy grains gradually form. Furthermore, the thickness of these lumpy grains varies significantly because the brittle, hard layer of the gamma-phase brass breaks more intensively in the radial direction during the cold forming process. While this design significantly improves cutting performance compared to bare brass wire during the main cut, it increasingly leads to short circuits and unintended discharges during the trim cut. This not only reduces cutting performance but also impairs the surface quality of the component.

[0065] Alternatively, the coating can be carried out first and then intermediate drawing can be carried out before the wire is diffusion annealed. This can be an economical alternative for producing electrode wires with a diameter of 0.02-0.15 mm, for example, according to the invention.

[0066] Overall, the electrode wire of the present invention can be produced with minimal manufacturing effort. If, in particular, a copper-zinc alloy containing 37–40 wt.% zinc is selected as the core material, the necessary zinc layer thickness is only 0.6–1.6% of the final diameter. For a final diameter of, for example, 0.25 mm, the necessary zinc layer thickness is 1.5–4 μm. This allows for relatively high production speeds during the zinc coating process. Furthermore, the aforementioned necessary zinc layer thickness range allows for relatively short processing times during diffusion annealing. Finally, a coverage of more than 20% and less than 50% reduces wear on the wire drawing tools compared to electrode wire according to the prior art.

[0067] Preferred embodiments

[0068] The portion of the bulk particles, viewed in a cross section perpendicular to or parallel to the longitudinal axis of the wire (also referred to as the "wire longitudinal axis" or simply the "wire axis"), preferably comprises more than 75%, more preferably more than 90%, of the surface area of ​​the bulk particles, preferably comprising a copper-zinc alloy having a zinc concentration of 58.5 to 67% by weight. More preferably, the bulk particles consist essentially entirely of a copper-zinc alloy having a zinc concentration of 58.5 to 67% by weight. With regard to the formation of "joints" of copper-zinc alloy having a lower zinc concentration at the boundaries with adjacent wires, reference is made to the above description.

[0069] In a view perpendicular to the wire surface, the proportion of the surface formed by the blocky particles, ie, the coverage, as defined above, is preferably 30% or more and 45% or less of the entire surface of the electrode wire.

[0070] Preferably, the surface area is between 25–200 μm in a view perpendicular to the wire surface. 2 The bulk particles within the range account for more than 50% of the total surface area of ​​all bulk particles.

[0071] More preferably, the surface area is between 50 and 200 μm in a view perpendicular to the surface of the wire. 2 The bulk particles within this range account for more than 50% of the total surface area of ​​all bulk particles.

[0072] The block-like particles are arranged in large numbers and in particular mainly in linear clusters of preferably five or more particles. In the linear clusters, the spacing between the block-like particles is preferably less than 10 μm.

[0073] As mentioned above, although the clusters are present in significant numbers, in particular predominantly, they are still "scattered", i.e. several linear clusters are not usually located next to each other (i.e. in the transverse direction, thus perpendicular to the longitudinal direction of the clusters as defined above, with a spacing of less than 15 μm, preferably less than 10 μm). Figure 6The distribution of clusters (a) and (b) in FIG is shown by way of example. A linear cluster preferably comprises particles of adjacent clusters for less than 50% of their length, as defined above.

[0074] The majority of the linear tufts, i.e. more than 50%, preferably form an angle of less than 40°, more preferably less than 35° with the longitudinal axis of the electrode wire. Preferably, more than 75% of the linear tufts form an angle of less than 45° with the longitudinal axis of the electrode wire.

[0075] Preferably more than 75% and more preferably more than 90% of the blocky particles have a thickness measured in the radial direction of more than 0.8% and less than 2% of the total diameter of the electrode wire, viewed in a wire cross section perpendicular or parallel to the wire longitudinal axis.

[0076] The electrode wire according to the invention has a structure preferably composed of the alloy CuZn 37 or CuZn 40 The wire core.

[0077] The structure and composition of the electrode wire of the present invention can be determined by, for example, a scanning electron microscope (SEM) with an energy dispersive X-ray spectrometer (EDX). For this purpose, the surface and cross-sectional polishing of the electrode wire were investigated. The production of the cross-sectional polishing of the wire can be achieved, for example, by the so-called ion beam beveling method, in which the wire body is covered with a mask and an Ar + Ion irradiation is used to remove the material from the wire body, where the material is removed from the portion outside the mask. This method allows the preparation of samples without mechanical deformation. Thus, through such treatment, the structure of the electrode wire coating of the present invention is maintained. Therefore, the structure of the coating of the electrode wire of the present invention can be represented by SEM images. Point, line, and surface EDX analysis can be used to determine the composition of the electrode wire of the present invention.

[0078] The present invention will be explained in more detail below with reference to the accompanying drawings.

[0079] Figure 1 The electrode wire 1 shown in cross section in FIG has a wire core 2 surrounded by a covering. In the exemplary embodiment shown, the core 2 is formed uniformly, completely or substantially completely, from copper or a copper-zinc alloy, with a zinc content preferably of 20 to 40 wt.%. The covering is formed from block-shaped particles 3, which are spatially separated from one another or from the material of the core 2, for example by cracks (not shown).

[0080] Figure 2 The cross section perpendicular to the longitudinal axis shows the Figure 1Optical microscope image of a cutout of the periphery of an electrode wire according to the invention, having a wire core and block-shaped particles. The more precise shape of the block-shaped particles (dark gray areas) and the fact that they are separated from one another or from the adjacent material of the core (light gray areas) by cracks (black areas) over part or all of their periphery (seen in this cross-section) are visible.

[0081] Figure 3 The cross section perpendicular to the longitudinal axis shows the Figure 1 A cutout of the outer periphery of an electrode wire according to the invention, comprising a wire core 2 and block-shaped particles 3. The block-shaped particles are identifiable over a portion of their periphery (viewed in this cross-section) as being separated from one another and from the adjacent material of the core (light grey area) by cracks and indentations or gaps 4. Furthermore, cracks 4' contained within the block-shaped particles themselves are identifiable.

[0082] Figure 4 An optical microscope picture of the surface of an electrode wire according to the invention is shown, with a magnification of 500. Blocky particles (dark grey areas) as well as cracks and indentations or gaps (black areas) of the covering layer are recognizable.

[0083] Figure 5 Shows the Figure 4 An optical microscope image of the surface of an electrode wire according to the present invention is shown. To determine the degree of coverage, a rectangular reference frame 6 measuring 400 x 50 μm is drawn, symmetrically about the axis 5 of the electrode wire. The degree of coverage can be determined, for example, by using an image processing program to calculate the surface area formed by the bulk particles based on the specific colors within the reference frame and to correlate this with the surface area of ​​the reference frame. The surface area of ​​individual bulk particles within the reference frame can also be calculated, for example, using an image processing program.

[0084] Figure 6 It also shows that according to Figure 4 Optical microscope image of the surface of an electrode wire according to the present invention. Linear clusters 7 of four or more blocky particles are marked with a dashed line. The central axis 5 of the electrode wire, also shown, clearly shows that the linear clusters form an angle of less than 45° with the longitudinal axis of the electrode wire.

[0085] Figure 7 An optical microscope picture of the surface of an electrode wire not according to the invention according to comparative sample V2 is shown at a magnification of 500.

[0086] Figure 8 An optical microscope picture of the surface of an electrode wire not according to the invention according to comparative sample V3 is shown at a magnification of 500.

[0087] Example

[0088] The advantages of the electrode wire of the present invention are described below by comparing the two embodiments with different electrode wires in the prior art. The production of the wire sample is carried out in the following order:

[0089] Comparison Sample V1:

[0090] - Initial wire material: CuZn 40 , d=1.20mm

[0091] - Stretched to d = 0.25 mm and stress relief annealed

[0092] Comparison Sample V2:

[0093] - Initial wire material: CuZn 37 , d=1.20mm

[0094] - Electrodeposited 1.5μm zinc

[0095] -Diffusion annealing was performed in a bell furnace at 180°C for 9 hours under ambient atmosphere

[0096] - Stretched to d = 0.25 mm and stress relief annealed

[0097] Comparison sample V3:

[0098] - Initial wire material: CuZn 40 , d=1.20mm

[0099] - Electrodeposited 7μm zinc

[0100] -Diffusion annealing was performed in a bell furnace at 180°C for 9 hours under ambient atmosphere

[0101] - Stretched to d = 0.25 mm and stress relief annealed

[0102] Sample E1 of the present invention:

[0103] - Initial wire material: CuZn 37 , d=1.20mm

[0104] - Electrodeposition of 3μm zinc

[0105] -Diffusion annealing was performed in a bell furnace at 180°C for 9 hours under ambient atmosphere

[0106] - Stretched to d = 0.25 mm and stress relief annealed

[0107] Sample E2 of the present invention:

[0108] - Initial wire material: CuZn 40 , d=1.20mm

[0109] - Electrodeposition of 2μm zinc

[0110] -Diffusion annealing was performed in a bell furnace at 180°C for 9 hours under ambient atmosphere

[0111] - Stretched to d = 0.25 mm and stress relief annealed

[0112] The relative cutting performance achieved by each electrode wire in the case of spark erosion during the main cut and in the case of the main cut and three trim cuts is shown in Table 1. The spark erosion was performed on a commercial wire erosion system with deionized water as the dielectric. A 60 mm high workpiece of hardened cold-worked steel type X155CrVMo12-1 was machined. A square with a side length of 10 mm was selected as the cutting profile. CuZn was selected. 40 Composite materials are processed on the machine side with bare brass wire.

[0113] Table 1

[0114]

[0115] The cutting performance achieved by comparative sample V1 in the main cut and the main cut and 3 trim cuts was set to 100% in each case.

[0116] Comparative sample V2 has a coating consisting of massive particles. These particles have a zinc content of 60-63 wt.%, consisting primarily of gamma brass. The coverage is approximately 35%. In a view perpendicular to the wire surface, the surface area in each case is between 25–250 μm². 2 The bulk particles in the range account for about 45% of the total surface area of ​​all bulk particles (see Figure 7 For the comparative sample, in the case of more than two-thirds of the blocky particles, the thickness measured in the radial direction of the wire cross section was less than 0.8% of the final diameter. Compared with the comparative sample V1, the cutting performance was improved by 1% and 4%, respectively.

[0117] Comparative sample V3 also has a coating consisting of massive particles. These particles have a zinc content of 60-63 wt.%, consisting primarily of gamma brass. The coverage is approximately 60%. In a view perpendicular to the wire surface, the surface area is between 25–250 μm. 2 The bulk particles within the range account for less than 45% of the total surface area of ​​all bulk particles (see Figure 8 ). Surface area exceeds 250μm 2 The presence of lumps, whose thickness, measured in the radial direction of the wire cross-section, exceeded 2% of the final diameter, increased. Furthermore, the thickness of these lumps varied significantly. Using this comparative sample, cutting performance improved by 5% and 3%, respectively, compared to comparative sample V1.

[0118] Sample E1 according to the invention has a covering layer consisting of blocky particles. The blocky particles are spatially separated from each other and from the core material by cracks and indentations (gaps) at least along a portion of their periphery. The zinc content of the blocky particles is 60-63 wt.-%, consisting primarily of gamma copper. The coverage is approximately 40%. In a view perpendicular to the wire surface, their surface area is in each case between 25 and 250 μm. 2 The bulk particles within the range account for about 90% of the total surface area proportion of all bulk particles. In the view perpendicular to the wire surface, the bulk particles are mainly arranged in linear clusters of four or more particles. In these clusters, the spacing between the particles is less than 15μm. More than 50% of the linear clusters form an angle of less than 40° with the longitudinal axis of the electrode wire. In the case of 80% of the bulk particles, the thickness measured radially on the wire cross section is in the range of 3-4.5μm, that is, 1.2-1.8% of the wire diameter. Using sample E1 of the present invention, the cutting performance is improved by 5% and 11% respectively compared with comparative sample 1.

[0119] Sample E2 according to the invention has a covering layer consisting of blocky particles. The blocky particles are spatially separated from each other and from the core material by cracks and indentations (gaps) at least along a portion of their periphery. The blocky particles have a zinc content of 60-64 wt.% and consist primarily of gamma brass. The coverage is approximately 45%. In a view perpendicular to the wire surface, their surface area is in each case between 25 and 250 μm. 2 The bulk particles within the range account for about 85% of the total surface area of ​​all bulk particles. In the view perpendicular to the surface of the wire, the bulk particles are mainly arranged in linear clusters of four or more particles. In these clusters, the spacing between the particles is less than 15μm. More than 50% of the linear clusters form an angle of less than 40° with the longitudinal axis of the electrode wire. For 80% of the bulk particles, the thickness measured radially on the cross section of the wire is in the range of 3.5-4.5μm, which is 1.2-1.8% of the wire diameter. Using sample E1 of the present invention, the cutting performance is improved by 5% and 12% respectively compared with comparative sample 1.

[0120] In order to evaluate the suitability for finishing, spark erosion machining with main cutting and 7 finishing cuts was performed on the comparative samples V1 and V3 and the samples E1 and E2 according to the invention. The spark erosion machining was carried out on a wire erosion system commonly used in the commercial industry with deionized water as the dielectric. 50 mm high workpieces of X155CrVMo12-1 type solidified cold-worked steel were machined. A square with a side length of 10 mm was selected as the cutting profile. The machine side technology for zinc-coated brass wire was selected as the machining technology. The target value of the arithmetic mean deviation of the roughness curve Ra was 0.13 μm. The measurement of the roughness on the eroded stamp-shaped parts was carried out by means of a stylus instrument. The measuring direction was perpendicular to the wire running direction. The evaluation of the groove formation was carried out purely qualitatively with the naked eye. The measurement of the profile deviation was carried out by means of a micrometer screw gauge on two axes and three different heights (top, middle, bottom) on the component. The results are shown in Table 2.

[0121] Comparison sample V1's R a The Ra value of the comparative sample V3 is 0.23 μm. Visual evaluation of the component also shows strong groove formation. The profile deviation is 5 μm. This result can be explained by the presence of thicker block particles compared to samples E1 and E2, as well as the more strongly varying thickness of the block particles.

[0122] For samples E1 and E2 of the present invention, R a The surface roughness was 0.13 μm, which deviated only slightly from the target value. The formation of grooves was minimal. The profile deviation in both cases was 3 μm, which is at the level of Comparative Sample V1.

[0123] Table 2

[0124]

[0125] Reference Numbers

[0126] 1: Electrode wire

[0127] 2: Wire core

[0128] 3: Blocky particles

[0129] 4: Cracks surrounding blocky particles

[0130] 4': Cracks inside blocky particles

[0131] 5: Center axis of the electrode line (vertical axis)

[0132] 6: Reference Frame

[0133] 7: Linear clusters of massive particles

[0134] Cited Documents

[0135] US 5,945,010

[0136] US 6,306,523

[0137] US 7,723,635

[0138] EP-A-2 193 867

[0139] EP-A-1 846 189

[0140] EP-A-2 517 817

[0141] EP-A-1 295 664

[0142] EP-A-1 949 995.

Claims

1. An electrode wire for electric spark erosion cutting, comprising - a core (2) comprising a metal or a metal alloy, wherein the metal is copper and the metal alloy is a copper-zinc alloy, and - a covering layer (3), surrounding the core (2), comprising regions having a morphology corresponding to massive particles, said massive particles being spatially separated from one another and / or from the core material by cracks at least over a portion of their periphery, characterised in that, viewed in a cross section of the wire perpendicular or parallel to the longitudinal axis of the wire, a portion representing more than 50% of the surface area of ​​the region having the morphology of massive particles comprises a copper-zinc alloy having a zinc concentration of 58.5 to 67 wt %, wherein: In a view perpendicular to the surface of the wire, the surface formed by the blocky particles accounts for more than 20% and less than 50% of the entire surface of the electrode wire, and, in each case, the surface area is between 25 and 250 μm 2 The blocky particles within the range account for more than 50% of the total surface area of ​​all blocky particles.

2. The electrode wire according to claim 1, wherein more than 75% of the surface area of ​​the block particles comprises a copper-zinc alloy having a zinc concentration of 58.5-67 wt%. 3 . The electrode wire according to claim 1 , wherein a ratio of a surface formed by the block-shaped particles to an entire surface of the electrode wire is 30% or more and 45% or less.

4. The electrode wire according to claim 1, wherein In a view perpendicular to the wire surface, the surface area is 25–200 µm 2 The bulk particles within the range account for more than 50% of the total surface area of ​​all bulk particles.

5. The electrode wire according to claim 1, wherein the block-shaped particles are present in linear clusters of four or more particles, wherein the distance between two particles is less than 15 μm. The electrode wire according to claim 5 , wherein the distance between two particles within the linear cluster is less than 10 μm.

7. The electrode wire according to claim 5 or 6, wherein a majority of the linear clusters form an angle of less than 45° with the longitudinal axis of the electrode wire.

8. The electrode wire according to claim 7, wherein a majority of the linear clusters form an angle of less than 40° with the longitudinal axis of the electrode wire.

9. The electrode wire according to claim 1, wherein More than two-thirds of the block-shaped particles have a thickness measured in the radial direction of more than 0.8% and less than 2% of the total diameter of the electrode wire when viewed in a cross section perpendicular or parallel to the longitudinal axis of the wire. 10 . The electrode wire according to claim 9 , wherein more than 75% of the block-shaped particles have a thickness measured in the radial direction of not less than 0.8% and not more than 2% of the total diameter of the electrode wire.

11. The electrode wire according to the preceding claim 1, wherein the core (2) is formed of red copper or a copper-zinc alloy having a zinc content of 20 to 40 wt%.

12. The electrode wire according to claim 1, wherein the core (2) is made of the alloy CuZn 37 or CuZn 40 form.

13. The electrode wire according to the preceding claim, wherein the region with the blocky grain morphology has internal cracks (4').

Images