Machining tool or other workpiece comprising a ceramic-metal composite material, machining process, motion transmission process, machining machine and complex element

Abstract

The invention relates to a machining tool and to a surface finishing process using the DL method, said tool comprising a ceramic-metal composite material having a homogeneous surface polishing. In some embodiments, the machining tool demonstrates, after polishing, a compressive tension of less than -500 MPa or equal to or greater than 40% of the compressive stresses generated during the grinding process. In some embodiments of the invention, the machining tool has a homogeneous surface polishing along the cutting edge, i.e. a perfect planarity between the metal elements and the ceramic elements of the tool, in such a way that the roughness of the cutting edge of the tool is of the submicrometric order. In some cases, the machining tool has a change in roughness between the cutting edge and the faces adjacent to the cutting edge along the homogeneous or regular cutting edge of the tool.

Description

[0001] DESCRIPTION

[0002] MACHINING TOOL OR OTHER TYPE OF PART THAT INCLUDES A CERAMIC-METAL COMPOSITE MATERIAL, MACHINING PROCESS, MOTION TRANSMISSION PROCESS, MACHINING MACHINE AND COMPLEX ELEMENT

[0003] FIELD OF APPLICATION OF THE INVENTION

[0004] The present invention can be applied to all types of parts made from a polished ceramic-metal composite material where the durability of the part is an important consideration. The ceramic-metal composite may be present only on part of the surface of the part, or on the entire surface. In some examples, the ceramic-metal composite is a surface coating on a part made from another material.

[0005] An example is machining tools, which are generally made of a polished ceramic-metal composite material and allow a part or material to be shaped by removing, extracting, separating or deforming material, for example, by chip removal, abrasion or cutting.

[0006] In this patent, the concept of machining tool should be understood in a broad sense, including, for example, sharp tools, excavator blades, cutting inserts for tunnel boring machines, or percussion tools.

[0007] Machining tools are an important example, but there are other parts made from a polished ceramic-metal composite material, where durability is important, which are also protected by this patent.

[0008] For example, motion transmission elements such as gears or cams can also be made of a ceramic-metal composite material, which are exposed to friction that causes wear. Another example is parts for the aeronautical sector, which are exposed to constant friction that causes wear. The durability of parts is a key aspect in the maintenance and repair of complex elements, such as machining machines or aircraft. In the maintenance and repair of complex elements, the replacement of parts that are about to reach the end of their useful life is scheduled. Replacing these parts often involves downtime of the complex element, with the associated economic costs.

[0009] In conclusion, an increase in the durability of the part comprising a polished ceramic-metal composite material implies a longer useful life of the same and reduces the need for replacement, as well as the economic costs linked to the operation of the complex element that includes the part comprising a polished ceramic-metal composite material, such as a machine or an aircraft.

[0010] BACKGROUND OF THE INVENTION

[0011] Machining is a manufacturing process that involves a set of operations for shaping parts by removing, extracting, separating or deforming material, for example, by chip removal, abrasion or cutting.

[0012] A type of machining is one in which material is removed or cut with a machining tool, resulting in waste or chips. The machining tool generally consists of one or more cutting edges or blades that remove chips from the workpiece with each pass.

[0013] Some machining tools are the drill or bit, the cutting tool of a mortiser, the broach of a broaching machine, the blade of a lathe, or the cutter of a milling machine.

[0014] Machining tools are usually made from ceramic-metal composite materials (inorganic composite materials), such as cemented carbide, also known as hard metal, widia (German: widia), metal carbide, or tungsten carbide.

[0015] Tungsten carbide is a composite material with a heterogeneous distribution of hard ceramic particles of tungsten carbide (WC) embedded in a metallic matrix, usually cobalt (Co). The ceramic particles provide the final material with high hardness and wear resistance, while the metallic binder provides high fracture toughness. Furthermore, tungsten carbide is also resistant to intermediate / high temperatures.

[0016] For all the reasons mentioned above, tungsten carbide is widely used to manufacture machining tools or other types of parts where durability is an important aspect.

[0017] Parts made from ceramic-metal composite materials, such as machining tools, are post-processed primarily by grinding, which uses an abrasive, typically a rotating abrasive wheel, to remove small shavings of material from the part being manufactured. The grinding process generates surface compressive stresses (ranging from the initial 10 to 20 µm) of approximately -1500 to -2000 MPa, depending on the metal binder content (known as binder) and the size of the reinforcing phase (ceramic phase), which can range from ultra-fine to coarse (also known as coarse).

[0018] These compressive stresses increase the durability of the parts under service conditions, however, the roughness induced by the grinding process (of the order of 0.1 to 0.6 .m in R a), generates surface defects, such as local oxidative effects or nanoprotuberances due to preferential polishing of the softer phase. These surface defects, for example, prevent proper chip removal by the machining tool under operating conditions and therefore lead to a reduction in tool life.

[0019] For this reason, it is necessary to achieve a compromise between surface quality in terms of remaining compressive stresses and the final degree of roughness of parts made from ceramic-metal composite materials.

[0020] Therefore, today, parts made from ceramic-metal composite materials, such as machining tools, that have been ground are subsequently polished.

[0021] Due to the extreme hardness of the ceramic-metal composite material, parts made from this material, such as machining tools, are typically polished using mechanical systems, chemo-mechanical polishing processes (CMP), chemical systems, or electrochemical systems.

[0022] Some known polishing processes significantly reduce (or even eliminate) the compressive stress layer, as these processes remove tens of microns from the surface. Specifically, the compressive stresses generated during the grinding process in the part, which are typically between -1500 and -2000 MPa, are reduced by 60 to 80%. Consequently, the durability of the part after polishing is reduced because it only exhibits 20 to 40% of its initial compressive stresses.

[0023] When parts made from a ceramic-metal composite material are polished chemically or electrochemically, due to the differences in mechanical properties between the ceramic particles and the metallic binder, the polishing is not homogeneous, producing different degrees of polishing at the interface between the two components. Furthermore, due to the pH of the polishing liquid or the medium used in the electrochemical process, a localized selective attack occurs on the metallic binder, completely dissolving said metallic element in the surface layers of the material to be polished, eroding said interface to a depth of a few nanometers to a few microns, and in some cases, reaching tens of microns. This phenomenon is known as "leaching."

[0024] After polishing a ceramic-metal composite part using a standard chemical or electrochemical process, the ceramic elements of the composite material protrude relative to the metallic elements, and therefore, the ceramic elements bear the brunt of the stress generated during the machining process. This ceramic phase of the material, being the most brittle, can act as the starting point for a fracture crack or as a stress concentration element.

[0025] Ceramic-metal composite materials can be composed of more than two phases, known as gamma phases. These phases present precipitates that are harder than WC, such as TiC, TaC, NbC, among others; the most common being WC-(W,Ti,Ta,Nb)C-Co. These high-hardness particles can be carbides of tungsten, titanium, niobium, tantalum, among others. During the mechanical finishing of parts that present these gamma phase particles in their microstructure, the significant difference between their mechanical properties and those of the rest of the matrix generates heterogeneities and spalling that can reduce the mechanical properties of the tool surface, decreasing its performance under operating conditions, along with the tool's useful life.

[0026] The heterogeneous polishing of the surface in a specific area of ​​the cutting tool comprising a ceramic-metal composite material, such as the tool edge, causes a considerable reduction in the mechanical properties of the tool and consequently a reduction in the durability of the tool by not being able to homogeneously transmit the stresses generated in the cutting edge to the rest of the tool during the machining process.

[0027] After a thorough analysis at a micro- or submicrometric scale of both the geometry and the resulting microstructure of a machining tool comprising a ceramic-metal composite material and polished by conventional polishing (for example: mechanical, CMP, chemical or electrochemical), a reduction in the compressive stresses generated in the machining tool after the grinding process is observed, as well as heterogeneous polishing within an area of ​​the machining tool when it has a heterogeneous and / or complex geometry as a result of greater extraction of the metallic elements with respect to the ceramic elements.

[0028] Conventional techniques do not uniformly reduce roughness inside the cutting edge and result in inconsistent chip removal under working conditions, creating hot spots inside the flute, which reduces its durability.

[0029] Similarly, in a machining tool comprising a ceramic-metal composite material and polished by conventional polishing (for example: mechanical, CMP, chemical or electrochemical), a heterogeneous or irregular change in roughness is observed between the cutting edge and the faces adjacent to the cutting edge along the cutting edge of the tool.

[0030] In the particular case of drill bits or milling cutters, the service performance of these cutting tools depends on a property known as the K factor ( -factor). The -factor, which is a parameter that characterizes the micrometric geometry of the cutting angle, is defined as the ratio between the rake surface and the main clearance surface (S Y / Sa). Its optimum value depends on the material to be machined with the tool, K = 0.7-0.8 being the optimum for tungsten carbide drills or milling cutters for machining titanium alloys and K = 1 for tungsten carbide drills or milling cutters for machining other metals, such as aluminium, iron, etc., as well as their respective alloys. Achieving these K factors while maintaining flatness between the different metallic and ceramic constituents present in the microstructure of composite materials is impossible using conventional polishing methods.

[0031] For some specific applications, a coating is applied after the machining and polishing or finishing stages to enhance the mechanical performance of cutting tools. Typically, to increase the tool's cutting capacity and durability under extreme operating conditions (e.g., temperature, lubricating agents, etc.), these coatings exhibit greater hardness and corrosion resistance than the ceramic-metal substrate, which in turn compromises its toughness. The fragility inherent in coatings makes them susceptible to crack nucleation and propagation, which can penetrate the substrate, generating a catastrophic defect for the tool itself.Therefore, there are methods for reducing and / or eliminating defects, such as droplets, which are the result of the deposition process before they penetrate the tool matrix. If the area containing the critical defect can be eliminated without compromising the integrity of the rest of the tool during this process, the tool can be put back into use after the previously pickled area has been coated. In these processes, using conventional methods, such as mechanical processes, there is a high possibility of propagation that could compromise the mechanical or surface integrity of the tool. This means a low probability of success during the recovery or repair process of a cutting tool with a defect in its coating.

[0032] Another problem generated during the polishing of a part comprising a ceramic-metal composite material is the heterogeneity of the polishing between different areas of the part, for example, between the cutting edge of the machining tool and the chip evacuation areas, which are usually concave.

[0033] During the chemical or electrochemical polishing process, areas with higher electrolyte mobility are polished more than areas with lower electrolyte mobility. The roughness change between the areas of a cutting tool polished using a chemical and / or electrochemical polishing process is heterogeneous or irregular. This situation also causes the stresses applied to the cutting edge to be transmitted heterogeneously or irregularly to the rest of the machining tool, thereby reducing its durability.

[0034] In addition to tool durability, a lack of homogeneity or regularity in the cutting edge and / or a lack of homogeneity or regularity in the roughness change between the areas of a tool can lead to a reduction in machining accuracy, as well as an increase in machining time and energy used to perform the machining.

[0035] Parts made from other ceramic-metal composite materials, such as Ti(C,N)-FeN¡, among other composite materials or cermets, present the same problems once polished by mechanical, CMP, chemical or electrochemical polishing.

[0036] Thus, the objective of this invention is a new machining tool or other type of part comprising a polished ceramic-metal composite material with greater durability than those polished using conventional processes.

[0037] OBJECT AND SUMMARY OF THE INVENTION

[0038] The present invention can be applied to all types of parts made from a polished ceramic-metal composite material where the durability of the part is an important aspect. Machining tools are an important example, but there are others such as motion transmission parts, such as a gear, cam, or bearing, or parts intended for the aeronautical sector.

[0039] The invention also covers parts manufactured with materials that have two or more distinct phases and that present a great difference in terms of their chemical nature and consequently their physical, mechanical and electrochemical properties, resulting in a heterogeneous surface treatment or leveling depending on the speed of interaction between the medium and each constituent. Some examples may be, for example, iron castings or aluminum alloys with a high concentration of silicon. The object of this invention is a machining tool or other type of part comprising a ceramic-metal composite material, which maintains the highest percentage of compressive stresses generated by the grinding process after post-processing (polishing), with the aim of thus increasing the durability of the cutting tool or other type of part, its precision, while reducing the time and energy required in the machining process.

[0040] Also the subject of this invention is a machining process carried out with a machining tool with a ceramic-metal composite material, a motion transmission process with a part with a ceramic-metal composite material, a machining machine comprising a machining tool with a ceramic-metal composite material and a complex element of a part with a ceramic-metal composite material, such as an aircraft.

[0041] The durability of parts is a key aspect in the maintenance and repair of complex elements, such as machining machines or aircraft. In the maintenance and repair of complex elements, the replacement of parts that are nearing the end of their useful life is scheduled. Replacing these parts often involves a shutdown of the machine or complex element, with the associated financial costs.

[0042] In conclusion, an increase in the durability of the part comprising a polished ceramic-metal composite material implies a longer useful life of the same and thus reduces the need for replacement, as well as the economic costs linked to the operation of the complex element that includes the part comprising a polished ceramic-metal composite material, such as a machine or an aircraft.

[0043] The invention relates, at least in part, to a machining tool, including a cutting and / or drilling tool comprising a metal-ceramic composite material, or another type of part comprising a homogeneous surface polish.

[0044] The invention also encompasses the polishing method, comprising both the process and the electrolyte, by which said tool is polished, achieving the benefits detailed herein. In the present description, "machining tool" is understood to include applications, features, and uses such as turning, drilling and milling, profiling, planing, sawing, cutting, and broaching.

[0045] A homogeneous surface polish according to the present invention includes, in some embodiments, a ceramic-metal interface with a roughness between 20 and 100 nm. In some embodiments, the roughness is less than 20 nm. Examples of homogeneous roughness according to the present invention include a roughness less than 15 nm, less than 10 nm, or less than or equal to 5 nm.

[0046] A surface or surface refers to any part of the tool in contact with its surroundings, such as the workpiece being machined. In particular, homogeneous surface polishing includes polishing the cutting edge and / or the surface surfaces adjacent to the cutting edge.

[0047] The object of the present invention includes a cutting and / or drilling tool comprising a ceramic-metal composite material that maintains the highest percentage of compressive stresses generated by the grinding process after the polishing process and allows the stresses applied to the cutting edge during its use to be transmitted homogeneously to the rest of the tool and indirectly through the polishing process used increases the durability of the same under service conditions.

[0048] Also the subject of this invention is a machining process carried out with a machining tool with a ceramic-metal composite material, a motion transmission process with a part with a ceramic-metal composite material, a machining machine comprising a machining tool with a ceramic-metal composite material and a complex element that includes a part with a ceramic-metal composite material, such as an aircraft.

[0049] EXPLANATION OF THE INVENTION

[0050] According to the present invention, the machining tool comprises a ceramic-metal composite material, including in some embodiments, tungsten carbide (WC), W(Ti,Ta), W-Co or Ti(C,N)-FeN¡, among others, and a homogeneous surface polish. In some embodiments, the metallic binder included in the matrix comprises metallic binders based on cobalt, nickel, iron, chromium or combinations thereof in different proportions.

[0051] In particular, the machining tool or other type of part comprising a ceramic-metal composite material object of the invention comprises, after polishing, a compressive stress of less than -400 MPa. Preferably, the compressive stress after polishing is less than -500 MPa, less than -1000 MPa, less than -1500 MPa, less than -2000 MPa. In a specific embodiment of the invention, the compressive stress after polishing is between -1600 and -1800 MPa.

[0052] The grinding process generates compressive stresses in the workpiece of between -1500 and -2000 MPa, generally between -1600 and -1800 MPa. The machining tool or other type of workpiece comprising a ceramic-metal composite material object of the invention comprises, after polishing following grinding, a compressive stress of at least 25% of the initial compressive stresses prior to polishing. Preferably, the compressive stress after polishing is at least 40, or 50, or 60, or 70, or 80, or 90, or 99% of the initial compressive stresses. In a specific embodiment of the invention, the compressive stress after polishing is between 80 and 90% of the compressive stresses generated during the grinding process.

[0053] In some preferred embodiments, the parts comprising a ceramic-metal composite material object of the invention comprise compressive stresses after the grinding and subsequent polishing process of between -1280 and -1620 MPa. Consequently, the durability of the cutting tool is not reduced to the degree that it was when polishing said part by the traditional polishing process, this being the standard mechano-chemical polishing process.

[0054] Compressive stresses can be measured in the part using X-ray diffraction techniques (XRD) and analyzed using the sine wave method. 2 \| / .

[0055] The polishing process for obtaining the part object of the invention preferably comprises a step of ionic transport between the part to be polished and a set of solid particles comprising a liquid electrolyte inside and water coated with a liquid that is less conductive than the solid particles and immiscible. In some cases, in said polishing process, two solid particles come into contact or one solid particle comes into contact with the part to be polished, an ionic exchange occurs, thus allowing electrical conductivity between solid particles or between the solid particle and the part to be polished.

[0056] Unlike other electrochemical methods, restricting ionic transport to surface protrusions, due to contact between conductive particles and these protrusions, results in more precise polishing, resulting in less material removal to achieve the desired surface finish. Furthermore, this polishing process modifies the surface state (whether for applications in tribological conditions, impact, etc.), without modifying internal stresses or any other microstructural condition.

[0057] In tools that have a coating after the machining and polishing or finishing stage, cracks may appear in the coating and their propagation towards the substrate may compromise its structural integrity under service conditions, possibly reducing its durability. By means of polishing methods comprising conductive solid particles, according to the present invention, it is possible to remove said layer once it is detected that the coating has one or more cracks, without damaging the substrate, allowing its reuse through a coating process and thus increasing the useful life of the tool and reducing the associated costs. The present invention covers treatments to extend the useful life of tools comprising a ceramic-metal matrix and a coating.In some cases, the tools are coated with monolayer or multilayer coatings with different bilayer periods as well as with different ceramic systems such as binary (e.g.: CrN, TiN, ZrN, etc.), ternary (e.g.: TiAlN, TiSiN, AlCrN, etc.) and / or quaternary (e.g.: AlCrSiN, etc.).

[0058] Figure 3 shows that a workpiece after a grinding process presents a compressive stress of approximately -1800 MPa. If this same workpiece is polished after the grinding process using an EDM process, the compressive stresses are completely eliminated and tensile stresses are generated. If this same workpiece is polished after the grinding process using a chemo-mechanical polishing process (or polishing - P), the residual stresses after the polishing process are approximately -400 MPa. Finally, it is observed that if this same workpiece is polished after the grinding process using a DL process, the residual stresses after the polishing process are approximately -1600 MPa.

[0059] Figure 4a shows a schematic representation of the different damages obtained in the piece under spherical indentation tests for the most common surface states at an industrial level: a grinding process, an electrical discharge machining process (EDM), mechanical polishing (P) after grinding or with polishing using conductive solid particles, according to the present invention, after grinding.

[0060] Figure 4b shows the number of cracks generated in the piece under spherical indentation tests for the most common surface states at an industrial level: a grinding process, an electrical discharge machining process (EDM), a mechanical polishing (P) after grinding or with a polishing using conductive solid particles, according to the present invention, after grinding.

[0061] Figure 4c shows the length of the cracks generated in the piece under spherical indentation tests for the most common surface states at an industrial level: a grinding process, an electrical discharge machining process (EDM), a mechanical polishing (P) after grinding or with a polishing using conductive solid particles, according to the present invention, after grinding.

[0062] It can be observed that the durability (lower number of cracks and shorter crack length) of a piece polished by means of conductive solid particles, according to the present invention, after the grinding process, is greater than the same piece polished by EDM or P after the grinding process.

[0063] In particular, when the polished part comprising a ceramic-metal composite material object of the invention is a machining tool, said tool exhibits flatness along the cutting edge between the metal and ceramic elements of the tool. In this invention, flatness is understood to mean a roughness of the submicron order, i.e., equal to or less than one micron, in particular, less than 20 nm. This characteristic allows the stresses applied to the cutting edge to be transmitted uniformly to the rest of the cutting tool, thereby increasing the durability of the cutting tool.

[0064] Preferably, the machining tool has a roughness on the cutting edge below 20 nm, below 15 nm, below 10 nm or below 8 nm.

[0065] Preferably, the machining tool exhibits a homogeneous or regular roughness change between the cutting edge and the faces adjacent to the cutting edge along the cutting edge of the tool.

[0066] Again, this feature allows the stresses applied to the cutting edge to be transmitted evenly to the rest of the cutting tool, thus increasing its durability.

[0067] Polishing methods using conductive solid particles are especially effective in homogeneously reducing the roughness of all constituents present in the surface microstructure of the material. This includes, in some cases, precipitates known as gamma phase, which have high hardness. The tools according to the present invention sometimes feature homogeneous polishing without presenting defects related to the difference between the properties of said particles and the rest of the phases present in the matrix.

[0068] As explained above, the K factor is a critical variable when defining the in-service performance of cutting tools. The object of the present invention is a polished cutting tool comprising a composite material of a metal-ceramic matrix with the required K factor depending on each inventive embodiment as detailed herein, depending on the material to be machined, and which, in turn, retains at least 40%, or 50%, or 60%, or 70%, or 80%, or 90%, or 99% of the compressive stresses prior to the polishing process.

[0069] In particular, the invention comprises a polished cutting tool comprising a composite material of a metal-ceramic matrix with the required K factor depending on each inventive embodiment as detailed herein, depending on the material to be machined, and which, in turn, retains at least 40%, or 50%, or 60%, or 70%, or 80%, or 90%, or 99% of the compressive stresses prior to the polishing process. In some embodiments, said tools have a height difference between the different constituent phases on the order of a few nanometers, a nanometric or even lower leveling between the different microconstituents of the matrix. More particularly, the invention covers said tool, presenting the aforementioned degree of flatness, minimizing regrowth defects or localized attack in the metal matrix.

[0070] BRIEF DESCRIPTION OF THE DRAWINGS

[0071] To complement the description being made and in order to help better understand the characteristics of the invention, some sheets of drawings are attached as an integral part of the same, in which, for illustrative and non-limiting purposes, the following has been represented:

[0072] Figure 1 shows a perspective section of an area of ​​a machining tool, showing the cutting edge and the adjacent faces. This figure shows that the change in roughness between the cutting edge and the adjacent faces is not constant along the tool's cutting edge.

[0073] Figure 2 shows a top view of a section of a machining tool, showing the cutting edge and the adjacent surfaces. This figure shows that the change in roughness between the cutting edge and the adjacent surfaces is constant along the tool's cutting edge, and that the grinding is homogeneous within the cutting edge area.

[0074] Figure 3 shows a representation of the stress generated in a ceramic-metal sample for the three most common types of surface finishes, together with the one described in the present invention; a grinding and EDM process, and the residual compressive stresses after the polishing process P or by means of conductive solid particles, according to the present invention (DL) on the surface of a piece starting in both cases from a ground surface (same compressive stresses as those presented in the graph for sample -G).

[0075] Figure 4 shows a schematic representation of the different damages obtained in a piece under spherical indentation tests based on radar maps P, (b) and (c) comparing the damage induced for the different surface states (after a grinding and EDM process, and after a polishing process using conductive solid particles, according to the present invention (DL), based on the number of cracks and the length of the cracks, respectively.

[0076] Figure 5 shows a drill bit comprising a ceramic-metal composite material with a homogeneous polish.

[0077] Figure 6 shows a set of gears comprising a ceramic-metal composite material with a homogeneous polish.

[0078] Figure 7 shows an excavator blade comprising a ceramic-metal composite material with a homogeneous polish, according to the present invention.

[0079] Figure 8 shows micrographs taken using a scanning electron microscope on the cutting surfaces of a machining cutter made of tungsten carbide, in which the surface result obtained can be compared, in terms of polishing penetration and level of flatness between constituents, after being processed while maintaining the electrical parameters constant and as the only variable using four different electrolytes (L800, L803, L807 and L808) described later in the examples, according to the present invention.

[0080] Figure 9 shows micrographs taken using a scanning electron microscope on the cutting surfaces of a micro drill, made of tungsten carbide, in which the surface result obtained can be compared, in terms of polishing penetration and level of flatness between constituents, after being processed keeping the electrical parameters constant and as the only variable using four different electrolytes (L800, L803, L807 and L808) described later in the examples, according to the present invention.

[0081] Figure 10 shows the evolution of the increase in the cutting radius of a tungsten carbide tool as a function of the polishing time, according to the present invention.

[0082] Figure 11 shows the evolution of the stripping level of a titanium nitride (TiN) coating deposited on a tungsten carbide substrate as a function of polishing time, according to the present invention.

[0083] A preferred embodiment of obtaining the machining tool of the invention is through an electrochemical polishing process comprising an ion transport step between the workpiece to be polished and a set of solid ion transport particles that, in some cases, comprise a liquid electrolyte inside. In some embodiments, the particles include water. In some embodiments, the particles are coated with a liquid that is less conductive than the solid particles, and in some cases is not miscible with any of the other constituents.

[0084] In this polishing process, two solid particles come into contact or a solid particle comes into contact with the workpiece to be polished. An ionic exchange occurs, thus allowing electrical conductivity between solid particles or between the solid particle and the workpiece to be polished.

[0085] The solid particles, according to the polishing method encompassed by the present invention DL, can be ceramic, polymeric, organic, inorganic, of plant origin, etc.

[0086] The conductive particles are preferably made of ion-exchange resin, as this promotes ionic conductivity. More preferably, the particles are made of cation-exchange resin, as this allows them to capture metal ions extracted during electropolishing processes and maintain their initial properties.

[0087] Typically, ion exchange particles with macroporosity are called macroporous particles, and those with microporosity are called gel-like particles. Both types are suitable for use in this invention.

[0088] Preferably, the particles have a liquid retention capacity of between 20 and 100% by weight of water relative to the total mass, particularly between 40% and 100% by weight of water relative to the total mass, more particularly between 40% and 70% by weight of water relative to the total mass.

[0089] In some embodiments, the particles retain an acid to promote ion exchange. The functional groups present on the exchange resin may be cation exchange groups such as sulfonic acid / sulfonate, carboxylic acid / carboxylate; anion exchange groups such as amine / ammonium, quaternary ammonium; or chelating groups such as iminodiacetic acid, aminophosphonic acid, polyamine, 2-picolylamine, thiourea, amidoxime, isothiouronium, or bispicolylamine, since these groups are suitable for ion capture and contribute to electropolishing.

[0090] The base polymer can be a polymer based on monomers such as styrene and derivatives, such as divinylbenzene, acrylate type, methacrylate and their derivatives with different functional groups, or phenolic resins, among others. Preferably, the solid particles are resins of a copolymer of styrene and sulfonated divinylbenzene, whether with a gel-like structure, a macroporous structure, or another, since they are capable of capturing ions and exhibit good electrical, chemical, and mechanical stability.

[0091] When electrolytic media is used in electropolishing processes, transmission occurs at the particle-surface contact points, i.e., only at the surface roughness peaks. Therefore, the effect of the electrolytic media can be adjusted by particle shape.

[0092] The particles can flow over the surface of the workpiece to be polished to produce a homogeneous effect across its entire surface. A shape that generally favors particle movement over the surface to be polished is the spherical shape. In some cases, the particles are substantially spherical or have a spherical geometry, as this facilitates their rolling over a wide variety of geometries. Preferably, the set of spheres has a central diameter between 50 micrometers and 2 mm. Due to their geometry, this measurement favors the elimination of roughness inherent in tool machining.

[0093] Preferably, a set of spheres with a bimodal particle size distribution can be used to obtain the velocity provided by the large particles and the detail polishing provided by the smaller particles.

[0094] Depending on the geometry of the surface to be polished, it may be useful to use other shapes that better suit that need. These include discs, cylinders, bars, fibers, cones, pointed shapes, etc. In some cases, it is preferable to use crushed particle fragments, which facilitate access to areas with a small radius in their concavity.

[0095] Commercially available are gel-type or macroporous sulfonated poly(styrene-divinylbenzene) cation exchange resin spheres that are preferred for use in this invention. In some cases, the electrolyte used in the present invention includes chemical activity moderating particles capable of neutralizing galvanic residues emitted during the polishing process, such as, for example, weak-base anion exchange resins composed of an acrylic backbone crosslinked with divinylbenzene and functionalized with a tertiary amine.

[0096] Below are some of the components that are included in the electrolytes used in some embodiments of the invention, DL.

[0097] - Retained water:

[0098] Solid electrolyte particles retain a certain amount of water. This retained water is responsible for dissolving oxides and salts that form on the surface to be polished during the electropolishing process. Furthermore, it is water, or rather the combination of water and particles, that transmits electrical conductivity, probably through an ionic transport mechanism.

[0099] Before preparing the electrolytic medium, the solid particles capable of retaining liquid are preferably washed with distilled water and partially dried so that they are capable of retaining the liquid. After this process, the particles still contain a certain amount of water, which is retained in the electrolyte particles and not free; that is, after this process, in some cases, the particles do not drip the retained water. In some embodiments of the invention, the particles are washed once or several times with water at a temperature between 60 and 200°C, preferably between 60 and 150°C, particularly above the boiling point. The resins are washed to eliminate any excess acid residues present in the solid structure. In some cases, it is preferable to carry out the washing process until the pH of the wash water is between 4 and 7, particularly between 5 and 7, and in particular 5.4 or similar. Preferably, the ion exchange resin particles retain a quantity of water between 10 and 50% of the total mass. This quantity ensures that there is sufficient liquid to produce a salt-solubilizing effect.

[0100] The water retained in the particles can come from a particle cleaning process. That is, a set of particles with the ability to retain liquid is subjected to a washing process that includes a final washing step with water. The water used in washing is preferably distilled water with a conductivity of less than 10 microS / cm. This low conductivity keeps the electrochemical process under control.

[0101] - Less conductive liquid:

[0102] The main characteristic of this liquid is that it is less electrically conductive than the conductive particles. The conductivity of the less conductive liquid is, for example, 90%, 50%, 20%, 5%, or 1% lower than the conductivity of the conductive particles.

[0103] As it is involved in electrochemical processes, the least conductive liquid, in some cases it presents high chemical and thermal stability, due to the high temperatures located during the electropolishing process.

[0104] The least conductive liquid is, in some cases, immiscible in water so that it does not mix or diffuse with the water retained in the particles.

[0105] In other cases the non-conducting liquid is water, and in others it is a mixture, in some cases miscible, and in other cases immiscible, of water and other non-conducting liquids.

[0106] Furthermore, this less conductive liquid must be kept in a liquid or fluid state within the operating range. Since the process involves distilled water, the operating range is, in some cases, between 0 and 100°C at most. The operating range is preferably below 60°C.

[0107] Since solid particles behave like granular materials, in some cases it is desirable for the less conductive liquid to act as a lubricant or fluidizer, or a combination of both. The lubricating effect of the less conductive liquid helps reduce the friction force between two bodies. On the one hand, the friction between two conductive particles, and on the other, the friction between the conductive particles and the workpiece being polished. In both cases, the amount of less conductive liquid expelled when a conductive particle comes into contact with another conductive particle or with the workpiece being polished is reduced. This results in a less aggressive and more controlled polishing process, resulting in a lower intensity polishing process.

[0108] The fluidifying effect of the less conductive liquid favors a decrease in the viscosity of the conductive particle array. By modifying the theoretical properties of the array, it is possible to modify the fluid dynamics of the conductive particles as they circulate over the metal surface. By increasing the proportion of liquid (less conductive) to conductive particles, it is possible to reduce the viscosity of the array, to the detriment of conductivity. The greater the amount of liquid (less conductive), the lower the density of conductive particles that transmit the electric field from the cathode to the anode, resulting in a slower surface treatment speed.

[0109] Less conductive liquids that can be used in this application include, but are not limited to, aliphatic and / or aromatic hydrocarbons, silicones, organic solvents, fluorinated solvents, fatty acids, fatty alcohols, glycols, sulfoxides, among others. In some cases, these less conductive liquids can be mixed with a solvent, such as distilled water (in some cases, the liquid, such as the silicone hydrocarbon, will be less conductive than the distilled water).

[0110] The ratio of solvent to hydrocarbon is, for example, 5:1 although it can be lower such as 4:1, 3:1.

[0111] Due to their electrical, chemical and thermal stability properties, silicones are of particular interest in this application.

[0112] Liquid silicones exhibit high thermal and chemical stability, and act as electrical insulators and have lubricating properties. These characteristics make them an excellent candidate for this application. All of this contributes to their effect in the solid electropolishing processes of this invention. In this text, silicones are understood broadly to encompass all those compounds, oligomers or polymers that comprise the siloxane group, general formula [- OSiR 2-] n, whether linear, branched or cyclic. The R group is preferably a hydrocarbyl group, such as, but not limited to, methyl, ethyl, n-propyl, / s0-propyl, t / f-butyl, n-hexyl, cyclohexyl, phenyl, among others.

[0113] A group of preferred liquid silicones are those containing poly(dimethylsiloxane), as they have a low viscosity and are nontoxic. Lower viscosity liquid silicones with a dynamic viscosity of less than 20 cP, preferably in the range of 1 to 10 cP at 25°C, are preferred.

[0114] Cyclic liquid silicones such as octamethylcyclotetrasiloxane D4, decamethylcyclopentasiloxane D5, or dodecamethylcyclohexasiloxane D6 are also preferred due to their excellent solvent properties. Due to their volatility, cyclohexanes are preferred for low-temperature applications.

[0115] The amount of silicone added to the particles can vary depending on the dimensions and shape of the workpiece being polished. Surfaces with cavities and corners that result in low particle mobility achieve better results with a higher proportion of silicone.

[0116] When polishing cavities, the less conductive liquid tends to accumulate in the valleys (cavities) of the polished parts, while the electrically charged solid particles accumulate in the peaks. This situation means that polishing with the conductive solid particles within a less conductive liquid does not polish cavities evenly.

[0117] Hydrophobic elements, such as hydrocarbons (for example, aliphatic hydrocarbons), are another less conductive liquid that is useful for polishing parts with cavities. Thanks to its physicochemical characteristics, the hydrophobic element binds the particles together, allowing them to penetrate the cavities of the parts and thus achieve a more homogeneous polish.

[0118] The non-conductive liquid comprising a hydro-repellent element allows for the production of an electrolytic medium (a set of conductive particles plus a less conductive liquid) that combines two antagonistic phases. On the one hand, the hydro-repellent element is water-repellent, and on the other, the solid particles with water inside are hydrophilic. This combination contributes to the electrolytic medium (a set of conductive particles plus a less conductive liquid with a hydro-repellent element) being more cohesive and penetrating more evenly into the cavities of the workpiece to be polished, achieving a more even polishing result.

[0119] In one embodiment, the less conductive liquid with water-repellent element further comprises a surfactant element.

[0120] The surfactant element varies the effect of maintaining conductivity between the solid particles, depending on the separation between them. The surfactant element helps adjust the morphology of the meniscus of the conductive liquid, usually contained within the solid particles, which is generated between two solid particles when they are in contact or close together. This characteristic helps adjust conductivity, or the flow of electrical current, between the solid particles.

[0121] An example of the application of an electrolytic medium composed of a set of particles containing an acid and water, the particles being surrounded by a less conductive liquid comprising a hydro-repellent element is the following:

[0122] Electrolytic medium for polishing ceramic-metal composite materials, and in particular carbides: less conductive liquid (200g of aqueous medium + 40g of aliphatic hydrocarbon) + 500g of solid particles containing an acid and 50% aqueous medium.

[0123] Polishing of parts using an electrolytic medium composed of a set of particles and water, the particles being surrounded by a less conductive liquid comprising a hydro-repellent element, can be done by immersing the part in a bucket with electrolytic medium, but it can also be done by projecting the electrolytic medium onto the part to be polished.

[0124] In addition to hydrocarbons, surfactants, and silicones, other chemical elements can be used that do not make a significant contribution to conductivity, as defined above. Some chemical compounds have demonstrated synergy between conductive solid particles, their distribution and mobility in water, and their ability to coat metal surfaces. These compounds are used to protect the metal surface from excessive attacks that may occur during the polishing process, acting as a resistive layer. Compounds that exhibit such synergies include, for example, fatty acids (C8-C20), fatty alcohols (C2-C20), glycols (C2-C20), and organosulfur compounds such as sulfoxides (C2-C20), particularly dimethyl sulfoxide (DMSO).Other compounds with properties similar to those detailed below also fall within the scope of protection of the present invention.

[0125] In some embodiments of the invention, the elements included in the less conductive phase have the following properties. A molecular mass between 50 and 300 g / mol and a polarity (Dipole, D) between 4.5 and 1. In some cases, its melting point is between 150 and 300 °C and melting point between 0 and 60 °C. In some embodiments of the invention, said substances have a dielectric constant between 1 and 50. In some cases, the substances used in the present invention have an acid / base character, both Acid (PKa = 4 - 5), slightly acidic (pKa = 14 - 16), and approximately neutral, and with a hydrophilicity that is either high, moderate, or low.

[0126] Liquids with high solvent properties for salts or ionic compounds, particularly sulfoxides, more particularly dimethyl sulfoxide (DMSO), are used in some embodiments of the present invention. Sulfoxides are organosulfur compounds with the general formula RS(=O)-R'. In DMSO, both R groups are methyl (CH3), resulting in the formula (CH3)2SO. This molecule exhibits polarization, distribution and homogeneous dissolution in water, and properties that make it an excellent candidate for addition to the water present in the non-conductive fluid surrounding the conductive solid particles and coating the metal part, forming a resistive layer around the part during the work pulse, thereby generating greater polishing homogeneity and fewer defects due to localized attack or regrowth of the metallic ligand phase present in the microstructure.The addition of DMSO not only modulates the resistivity of the polishing process, but also affects the viscosity of the assembly, providing it with a shape memory, particularly interesting in applications or parts that present an extrusion or revolution geometry.

[0127] A fatty acid is an organic molecule with a long hydrocarbon chain and a terminal carboxyl group, which exhibits non-zero polarization. They are found in natural fats and oils. They can be saturated, with no double bonds, such as stearic acid or octanoic acid, and unsaturated, with one or more double bonds. These are divided into monounsaturated, with a single double bond, such as oleic acid, and polyunsaturated, with two or more double bonds, such as linoleic acid.The properties discussed above, together with their high polarity, make these molecules an excellent candidate to be added to the water present in the non-conductive fluid surrounding the conductive solid particles, in some embodiments of the present invention, and to coat the metal piece, forming micelles and structures capable of migrating towards the metal surface under an electric field and coating it with a resistive layer during the work pulse, consequently generating greater polishing homogeneity and fewer defects due to localized attack or regrowth of the metallic binder phase present in the microstructure. Fatty acids, depending on their proportion with respect to the polar and non-polar liquids present in the non-conductive fluid surrounding the conductive solid particles, can alter the fluidity of the assembly depending on their proportion and the length of the hydrogen-carbonate chains.In small proportions (0.1 - 10% by weight) and short chains ( <C10) actúan como lubricantes, sin embargo, a mayores proporciones y cadenas más largas, pueden tener el efecto contrario. Todo ello puede abarcar un espectro en cuanto a la profundidad del pulido a lo largo de geometrías concretas, en función del tiempo de pulido.

[0128] In some embodiments of the present invention, fatty alcohols, such as dodecanol or hexadecanol, and glycols, such as ethylene glycol or propylene glycol, are included, which consist of hydrocarbon chains containing one or more hydroxyl groups, respectively. Fatty alcohols can be saturated or unsaturated and have properties similar to fatty acids. Glycols are known for their high solubility in water and are commonly used as solvents; they have properties similar to sulfoxides. They are also molecules that have a dipole moment and have the necessary properties to act as resistive protectors of the metal surface.

[0129] Furthermore, as mentioned above, a second aspect of the present invention relates to a dry electropolishing method using the described electrolytic medium.

[0130] The electrolytic medium described above is not, by itself, sufficient to produce a satisfactory electropolishing effect on inorganic composite materials. The electrolytic medium is complemented by the method, especially with the type of current applied, to obtain optimal results. In some embodiments, said solid particles are projected onto the tool to be polished. In other embodiments, the tool is immersed in a granular compound that includes said particles. In some cases and regions of the compound, said granular compound includes a gaseous element between groups of particles. In other embodiments, the granular compound is immersed in a liquid medium. Examples of liquid medium include an electrolyte liquid identical to or different from that of the solid particles, or a moderator liquid that is electrically neutral or has lower conductivity than a conventional electrolyte.

[0131] The polishing process of the tool using a process that includes electrically charged solid particles, such as the aforementioned DL method, allows the radius of the cutting area to be modulated, as well as generating a profile or a homogeneous polishing front (see Figures 1, 8 and 9) and in this way being able to establish a tolerance between the cutting edge and the roughness change boundary.

[0132] Examples of DL polishing processes, apparatus, and systems used in this technology include polishing using electrically charged solid particles, for example, porous solid particles that include, for example, by absorption, a liquid that provides said solid particles with electrical conductivity. These examples of the method and electrolyte used to polish said tool are detailed in the examples section.

[0133] Example 1 describes the polishing method for a tungsten carbide milling cutter and a micro drill. The results after polishing with different electrolytes can be seen in Figures 8 and 9 respectively. Micrographs taken using a secondary electron detector emitted by a scanning electron microscope show the level of flatness obtained after all treatments to be in the micron range. After applying the different polishing processes, the resulting radius is 8 micrometres for the cutting wire of the milling cutter and 3 micrometres for the micro drill. The micrographs show that the electrolyte with the greatest microstructural homogeneity, with the greatest levelling and the fewest defects, is the treatment described in Example 1.2, which comprises an electrolyte based on DMSO in its non-conductive liquid phase.On the other hand, the treatment that offers the greatest polishing depth and therefore the greatest speed in terms of reducing machining marks is the one described in example 1.3, which comprises an electrolyte based on octanoic acid in its non-conductive liquid phase. Therefore, an optimal method to obtain a good compromise between the speed of machining scratch removal and the homogeneity and microstructural leveling of the polished surface involves a multi-step process, comprising a first step of longer polishing time depending on the radius requirement of the cutting wire using an electrolyte based on octanoic acid in its non-conductive liquid phase and a final step (shorter polishing time) using an electrolyte based on DMSO or ethylene glycol in its non-conductive liquid phase.

[0134] As can be seen in Figure 10, the final cutting radius can be varied depending on the polishing time. Increasing the polishing time increases the radius. This also has a similar correlation with the K factor.

[0135] According to the present invention, a tool with homogeneous surface polishing comprises in some embodiments a radius in the cutting area between 2 and 20 microns, in some embodiments between 2 and 10 microns, and in some cases it even incorporates a radius with a value around 5 microns.

[0136] According to the present invention, the tolerance between the cutting edge and the boundary of the roughness change of the tool in question comprises values ​​between 100 and 2000 nm, for example, tolerance values ​​between 250 and 750 nm and, in some embodiments, a tolerance around 500 nm.

[0137] The object of this invention is a machining tool or other type of part manufactured with a ceramic-metal composite material, which comprises, after polishing, a compressive stress of less than -400 MPa with the objective of increasing the durability of the cutting tool or other type of part, its precision, while reducing the time and energy required in the machining process. Preferably, the compressive stress after polishing is less than -500 MPa, less than -1000 MPa, less than -1500 MPa, less than -2000 MPa. In a specific embodiment of the invention, the compressive stress after polishing is between -1600 and -1800 MPa.

[0138] The grinding process generates compressive stresses in the workpiece of between -1500 and -2000 MPa, generally between -1600 and -1800 MPa. The machining tool or other type of workpiece comprising a ceramic-metal composite material object of the invention comprises, after polishing following grinding, a compressive stress of at least 25% of the compressive stresses prior to the polishing process. Preferably, the compressive stress after polishing is at least 40%, or 50%, or 60% or 70% or 80% or 90%, or even 99% of the compressive stresses prior to polishing. In a specific embodiment of the invention, the compressive stress after polishing is between 80 and 90% of the compressive stresses generated during the grinding process.

[0139] In some embodiments, the machining tool or other type of part made of a ceramic-metal composite material has compressive stresses of at least 25% of the compressive stresses prior to the polishing process compared to other tools with an equivalent roughness but polished by other polishing methods. Preferably, the compressive stress of the machining tool or other type of part made of a ceramic-metal composite material after polishing is at least 40%, or 50%, or 60%, or 70%, or 80%, or 90%, or even up to 99% of the compressive stresses prior to polishing. In a specific embodiment of the invention, the compressive stress of the machining tool or other type of part made of a ceramic-metal composite material after polishing is between 80 and 90% of the compressive stresses generated during the grinding process.

[0140] An embodiment of the invention is shown in Figure 5 and Figure 7, where a machining tool is observed, specifically a tool for removing material, such as a drill bit in Figure 5 and an excavator shovel in Figure 7, which comprises a ceramic-metal composite material with a homogeneous polishing such as that described in this specification. In this embodiment, the tool for removing material, such as a drill bit in Figure 5 and an excavator shovel in Figure 7, has, after polishing, a compressive stress of less than -400 MPa with the aim of thus increasing the durability of the cutting tool or other type of part, its precision, while reducing the time and energy required in the machining process. Preferably, the compressive stress after polishing is less than -500 MPa, less than -1000 MPa, less than -1500 MPa, less than -2000 MPa.In a specific embodiment of the invention, the compressive stress after polishing is between - 1600 and -1800 MPa.

[0141] This homogeneous polishing of the drill bit results in a machining tool, for example, a drill bit or an excavator shovel, with greater durability than those polished using previously known methods. The durability of machining tools is a key aspect in the maintenance and repair of machining machines. Maintenance and repair of machining machines includes the scheduled replacement of machining tools that are nearing the end of their useful life. Replacing these machining tools often involves a machine shutdown, with the associated financial costs.

[0142] Furthermore, thanks to the homogeneous polishing of the machining tool, such as the drill shown in Figure 5, a machining tool with greater precision and efficiency is obtained, which allows reducing the time and energy required in the machining process compared to machining processes where polished machining tools are used with the processes known to date.

[0143] Another embodiment of the invention is shown in Figure 6, which shows a motion transmission part, specifically a set of gears, comprising a ceramic-metal composite material with a homogeneous polishing process as described in this specification. In this embodiment, the motion transmission part, specifically a set of gears, has, after polishing, a compressive stress of less than -400 MPa in order to increase the durability of the motion transmission part, specifically a set of gears. Preferably, the compressive stress after polishing is less than -500 MPa, less than -1000 MPa, less than -1500 MPa, less than -2000 MPa. In a specific embodiment of the invention, the compressive stress after polishing is between -1600 and -1800 MPa.

[0144] Thanks to this homogeneous polishing of a motion-transmitting part, such as a gear set, a motion-transmitting part is obtained with greater durability than those polished using methods known to date. The durability of motion-transmitting parts is a key aspect in the maintenance and repair tasks of the complex elements that comprise them. In the maintenance and repair tasks of complex elements that comprise them, such as an aircraft, the replacement of motion-transmitting parts that are about to reach the end of their useful life is scheduled. The replacement of these motion-transmitting parts generally involves a shutdown of the complex element that comprises them, such as an aircraft, with the economic costs that such a shutdown entails.

[0145] Also the subject of this invention is a machining machine comprising a machining tool with a ceramic-metal composite material and a complex element comprising a part, for example, a motion transmission part, such as an aircraft, with a ceramic-metal composite material with a homogeneous polishing such as that described elsewhere in the specification. The machining tool, with a ceramic-metal composite material, comprised in the machining machine and the part, for example, a motion transmission part with a ceramic-metal composite material, comprised by the complex element, such as an aircraft, has after polishing, a compressive stress of less than -400 MPa with the aim of thus increasing the durability of the motion transmission part, specifically a set of gears.Preferably, the compressive stress after polishing is less than -500 MPa, less than -1000 MPa, less than -1500 MPa, or less than -2000 MPa. In a specific embodiment of the invention, the compressive stress after polishing is between -1600 and -1800 MPa.

[0146] In some embodiments, the machining tool comprising a ceramic-metal composite material comprised by the machining machine and the homogeneously polished motion transmission part comprising a ceramic-metal composite material comprised in a complex element, such as an aircraft, have compressive stresses of at least 25% of the pre-polishing compressive stresses compared to other tools with equivalent roughness but polished by other polishing methods. Preferably, the compressive stress of the machining tool or other type of part made of a ceramic-metal composite material after polishing is at least 40%, or 50%, or 60%, or 70%, or 80%, or 90%, even up to 99% of the pre-polishing compressive stresses.In a specific embodiment of the invention, the compressive stress of the machining tool or other type of part made of a ceramic-metal composite material after polishing is between 80 and 90% of the compressive stresses generated during the grinding process. Machining machines or complex elements comprising a machining tool or a part comprising a homogeneously polished ceramic-metal composite material are more efficient compared to other machining machines or complex elements.

[0147] Machining machines, as well as complex elements comprising a machining tool with a homogeneously polished ceramic-metal composite material or a complex element, a part, for example, a motion transmission part, with a homogeneously polished ceramic-metal composite material, do not have to be stopped so frequently to perform the task of replacing the machining tool or the part comprising a homogeneously polished ceramic-metal composite material, as it enjoys greater durability.

[0148] In maintenance and repair tasks involving machining machines or complex components, such as aircraft, the replacement of machining tools or motion transmission parts that are nearing the end of their useful life is scheduled. Replacing these parts often involves a shutdown of the machining machine or the complex component it comprises, such as aircraft, with the associated financial costs.

[0149] As shown in Figure 11, there are machining tools made of a ceramic-metal composite material that are polished and subsequently coated with, for example, ternary coatings such as TiAlN-TiSiN. In particular, the case depicted in Figure 11 illustrates the ability of a polishing method using conductive solid particles to remove a titanium nitride (TiN) coating, increasing the polishing process. This makes it possible to locally eliminate any areas where the coating may have defects (e.g., drops, etc.), while coating the rest of the tool. This prevents catastrophic crack propagation into the tool die, so that after subsequent coating, the tool can be re-ground under operating conditions.

[0150] In some cases, particularly where the part to be machined by the tool comprises titanium alloys, the tool has a K factor = 0.7 - 0.8, while retaining at least 40%, or 50%, or 60%, or 70%, or 80%, or 90%, or 99% of the compressive stresses prior to polishing, and having a height difference between constituents (also known as flatness) of the nanometric order and minimizing regrowth defects or localized attack in the metal matrix, the characteristics discussed above. Particularly, the invention provides a tool for machining titanium alloys with a K factor = 0.7 - 0.8, with a nanometric flatness between the different constituents, having compressive stresses of approximately between -500 and -1800 MPa. Particularly presenting compressive stresses between -1000 and -1750MPa, more particularly between -1400 and -1700MPa, specifically between -1600 and -1700MPa.In other cases, particularly in those where the part to be machined by the tool comprises another type of alloy, such as aluminium alloys, the tool has a factor of approximately K = 1, whilst retaining at least 40%, or 50%, or 60%, or 70%, or 80%, or 90%, or 99% of the compressive stresses prior to polishing, and having a nanometric levelling between the different constituents, minimising regrowth defects or localised attack in the metal matrix. In particular, the invention provides a tool for machining titanium alloys with a factor of approximately K = 1, with a nanometric flatness between the different constituents, having compressive stresses of approximately between -500 and -1800 MPa. Particularly presenting compressive stresses between -1000 and -1750MPa, more particularly between -1400 and -1700MPa, specifically between -1600 and -1700MPa.

[0151] In tools that have two ceramic phases embedded in a metallic matrix, known as gamma phases, polished tools that do not present defects related to the finish due to differential polishing between the different constituents also fall within the scope of protection.

[0152] Finally, this invention also relates to a machining process performed with a machining tool using a ceramic-metal composite material, as well as a motion transmission process using a workpiece made of a ceramic-metal composite material. These processes are more efficient than processes not performed with a machining tool or workpiece using a ceramic-metal composite material, polished homogeneously as described in the specification, because said processes do not need to be stopped as often, as said workpieces enjoy greater durability. Replacing said workpieces often involves stopping the machining process or the motion transmission process of the machining machine or the complex element comprising it, with the associated economic costs.

[0153] The machining tool, with a ceramic-metal composite material, used in a machining process and the workpiece, for example, a motion transmission part with a ceramic-metal composite material, used in a motion transmission process, have after polishing, a compressive stress of less than -400 MPa with the aim of increasing the durability of the motion transmission part, specifically a set of gears. Preferably, the compressive stress after polishing is less than -500 MPa, less than -1000 MPa, less than -1500 MPa, less than -2000 MPa. In a specific embodiment of the invention, the compressive stress after polishing is between -1600 and -1800 MPa.

[0154] In some embodiments, the machining tool having a ceramic-metal composite material used in a machining process and the motion transmission part having a homogeneous polishing of a ceramic-metal composite material used in a motion transmission process have compressive stresses of at least 25% of the compressive stresses prior to polishing compared to other tools with an equivalent roughness but polished by other polishing methods. Preferably, the compressive stress of the machining tool or other type of part made of a ceramic-metal composite material after polishing is at least 40%, or 50%, or 60%, or 70%, or 80%, or 90%, or 99% of the compressive stresses prior to polishing.In a specific embodiment of the invention, the compressive stress of the machining tool or other type of part made of a ceramic-metal composite material after polishing is between 80 and 90% of the compressive stresses generated during the grinding process. Having sufficiently described the nature of the present invention, as well as how to put it into practice, it is not considered necessary to explain it further so that any person skilled in the art can understand its scope and the advantages derived from it.

[0155] EXAMPLES

[0156] In order to exemplify the characteristics of some cutting tools that are included within the scope of the present invention, together with their corresponding polishing process, the following cases or examples will be described below:

[0157] Example 1

[0158] An electropolishing process using conductive solid particles (Dry Electropolishing) has been carried out on a machining cutter and on a micro drill, manufactured using a ceramic-metal composite material based on WC tungsten carbide and with a cobalt metallic binder.

[0159] The part, connected to the first pole of a power supply, was immersed in a tank filled with dry electrolyte, along with a platinum-coated titanium mesh perimeter cathode connected to the second pole of the power supply. A rotational vibration of 1 mm amplitude and 10 Hz frequency was applied to the tank along its longitudinal axis to ensure the movement or recirculation of the conductive solid particles of the dry electrolyte located inside the cylindrical tank, with a capacity of 1 L.

[0160] Two synchronized cyclic movements were performed; the first, linear in the direction of the longitudinal axis of the tool and perpendicular to the direction of the dry electrolyte surface, with a frequency of 30 rpm and an amplitude of the order of the tool length; at the same time, the second, a rotational movement around the longitudinal axis of the workpiece, of 180° and also at a frequency of 30 rpm.

[0161] Specific electrical parameters were applied: 20 V during an anodic pulse, taking the part as a reference and lasting 20 microseconds. 50 V during a cathodic pulse, taking the part as a reference and lasting 160 microseconds. A 0 V time period was established between each polarity change, lasting 10 microseconds.

[0162] The composition of the electrolyte with which the pieces have been polished is detailed below, named as different versions of example 1:

[0163] Example 1.1

[0164] The polishing process described in the Example, using an electrolyte called L800, with the following composition:

[0165] - 500 g of conductive solid particles comprising: o 95.65% by weight of sulfonated styrene divinylbenzene gel particles (Mitsubishi Relite CFH) of 0.3 to 1.18 mm in diameter with a hydration of 55% by weight in water after a washing process using deionized water (at a temperature above 100 °C) until a pH of the washing water is obtained between 4.5 - 6, and a subsequent drying process. o 4.35% of a weak base anion exchange resin composed of an acrylic backbone crosslinked with divinylbenzene and functionalized with a tertiary amine (Dupont Amberlite IRA67 Resin) with a hydration of 55% by weight, acting as a chemical moderator particle. - 239 g of a non-conductive fluid comprising: o 90.91% by weight of distilled water o 9.09% by weight of polydimethylsiloxane (PDMS)

[0166] The result obtained can be seen in Figures 8 and 9.

[0167] Example 1.2

[0168] The polishing process described in the Example, using an electrolyte called L803, with the following composition:

[0169] - 500 g of conductive solid particles comprising: o 89.11% by weight of sulfonated styrene divinylbenzene gel particles (Mitsubishi Relite CFH) of 0.3 to 1.18 mm in diameter with a hydration of 55% by weight in water after a washing process using deionized water (at a temperature above 100 °C) until obtaining a pH of the washing water between 4.5 - 6, and a subsequent drying process. or 9.90% by weight of sulfonated styrene divinylbenzene gel particles (Lewatit Relite CFH) of 0.3 mm diameter with a hydration of 55% by weight in water after an acidification process using sulfuric acid and after a subsequent washing using deionized water (at a temperature above 100 °C) until obtaining a pH of the washing water between 4.5 - 6, and a subsequent drying process.or 0.99% of a weak base anion exchange resin composed of an acrylic backbone crosslinked with divinylbenzene and functionalized with a tertiary amine (Dupont Amberlite IRA67 Resin) with a hydration of 55% by weight, acting as a chemical moderator particle.

[0170] 167 g of a non-conductive fluid comprising: o 33.33% by weight of distilled water o 66.67% by weight of Dimethyl sulfoxide (DMSO)

[0171] The result obtained can be seen in Figures 8 and 9.

[0172] Example 1.3 The polishing process described in the Example, using an electrolyte called L807, with the following composition:

[0173] - 500 g of conductive solid particles comprising: o 90% by weight of sulfonated styrene divinylbenzene gel particles (Mitsubishi Relite CFH) of 0.3 to 1.18 mm in diameter with a hydration of 55% by weight in water after a washing process using deionized water (at a temperature above 100 °C) until a pH of the washing water is obtained between 4.5 - 6, and a subsequent drying process. o 1% of a weak base anion exchange resin composed of an acrylic backbone crosslinked with divinylbenzene and functionalized with a tertiary amine (Dupont Amberlite IRA67 resin) with a hydration of 55% by weight, acting as a chemical moderator particle.

[0174] - 233 g of a non-conductive fluid comprising: o 43.48% by weight of distilled water o 56.52% by weight of Octanoic Acid of 98% purity.

[0175] The result obtained can be seen in Figures 8 and 9.

[0176] Example 1.4

[0177] The polishing process described in the Example, using an electrolyte called L808, with the following composition:

[0178] - 500 g of conductive solid particles comprising: o 72.36% by weight of sulfonated styrene divinylbenzene gel particles (Mitsubishi Relite CFH) of 0.3 to 1.18 mm in diameter with a hydration of 55% by weight in water after a washing process using deionized water (at a temperature above 100 °C) until obtaining a pH of the washing water between 4.5 - 6, and a subsequent drying process. or 16.06% by weight of sulfonated styrene divinylbenzene gel particles (Mitsubishi Relite CFH) of 0.3 to 1.18 mm in diameter, crushed into different shapes and sizes by means of two rolling rollers, with a hydration of 55% by weight in water after a washing process using deionized water (at a temperature above 100 °C) until obtaining a pH of the washing water between 4.5 - 6, and a subsequent drying process.or 8.04% by weight of sulfonated styrene divinylbenzene gel particles (Lewatit Relite CFH) of 0.3 mm diameter with a hydration of 55% by weight in water after an acidification process using sulfuric acid and after a subsequent wash using deionized water (at a temperature above 100 °C) until obtaining a pH of the wash water between.

[0179] 4.5 - 6, and a subsequent drying process. or 3.23% by weight of glass microspheres (Silicon oxide) with a diameter between 0.04 and 0.07 micrometers. or 0.31% of a weak base anion exchange resin composed of an acrylic backbone crosslinked with divinylbenzene and functionalized with a tertiary amine (Dupont Amberlite IRA67 resin) with a hydration of 55% by weight, acting as a chemical moderator particle.

[0180] - 5 g of a non-conductive fluid containing 99% pure octanoic acid. The results can be seen in Figures 8 and 9.

Claims

CLAIMS 1. Machining tool or other type of part comprising a ceramic-metal composite material characterized in that it comprises a homogeneous surface polish.

2. Machining tool or other type of part according to claim 1, characterized by having a homogeneous surface polish along the cutting edge, that is, a flatness between the metallic elements and the ceramic elements of the tool, such that the roughness of the cutting edge of the tool is of the submicrometric order.

3. Machining tool or other type of part according to claim 1, characterized in that the roughness of the surface polishing is below 20 nm.

4. Machining tool or other type of part according to claim 1, characterized in that the roughness of the surface polishing is below 15 nm.

5. Machining tool or other type of part according to claim 1, characterized in that the roughness of the surface polishing is below 10 nm.

6. Machining tool or other type of part according to claim 1, characterized in that the roughness of the surface polishing is below 9 nm.

7. Machining tool or other type of part according to any of the previous claims, characterized in that the ceramic-metal material is one or more of the following group of materials: tungsten carbide ((WC), W(Ti,Ta)C-Co, Ti(C,N)-FeN¡, among other carbides with metal binders based on cobalt, nickel, iron, chromium or combinations of them in different proportions.

8. Machining tool or other type of part according to any of the preceding claims, characterized in that the change in roughness between the cutting edge and the faces adjacent to the cutting edge along the cutting edge of the tool is homogeneous or regular.

9. Machining tool or other type of part according to any of the preceding claims, characterized in that it has, after polishing, a compressive stress of less than -500 MPa or more than 25% of the compressive stresses generated during the grinding process.

10. Machining process using a machining tool comprising a ceramic-metal composite material characterized in that the machining tool comprises a homogeneous surface polishing.

11. Machining process according to claim 10, characterized in that the machining tool has a homogeneous surface polish along the cutting edge, i.e. perfect planarity between the metal elements and the ceramic elements of the tool, such that the roughness of the cutting edge of the tool is in the submicrometric order.

12. Machining process according to claim 11, characterized in that the machining tool has a homogeneous surface polishing along the cutting edge below 20 nm.

13. Machining process according to claim 12, characterized in that the machining tool has a homogeneous surface polishing along the cutting edge below 15 nm.

14. Machining process according to claim 13, characterized in that the machining tool has a homogeneous surface polishing along the cutting edge of less than 10 nm.

15. Machining process according to claim 14, characterized in that the machining tool has a homogeneous surface polishing along the cutting edge below 9 nm.

16. Machining process according to any of claims 10-15, characterized in that the ceramic-metal material of the tool machining is one or more of the following group of materials: tungsten carbide ((WC), W(Ti,Ta)C-Co, Ti(C,N)-FeN¡, among other carbides with metallic binders based on cobalt, nickel, iron, chromium or combinations of them in different proportions.

17. Machining process according to any of claims 10-16, characterized in that the change in roughness between the cutting edge and the faces adjacent to the cutting edge along the cutting edge of the tool is homogeneous or regular.

18. Machining process according to any of claims 10-16, characterized in that the tool has, after polishing, a compressive stress of less than -500 MPa or more than 25% of the compressive stresses generated during the grinding process.

19. Process for transmitting motion by means of a motion transmission part comprising a ceramic-metal composite material, characterized in that the motion transmission part comprises a homogeneous surface polish.

20. Motion transmission process according to claim 19, characterized in that the ceramic-metal material of the machining tool is one or more of the following group of materials: tungsten carbide ((WC), W(Ti,Ta)C-Co, Ti(C,N)-FeN¡, among other carbides with metallic binders based on cobalt, nickel, iron, chromium or combinations of them in different proportions.

21. Motion transmission process according to claim 19, characterized in that the motion transmission part presents, after polishing, between 80 and 90% of the compressive stresses generated during the grinding process.

22. Machining machine characterized in that it comprises a machining tool with a homogeneous surface polish.

23. Machining machine according to claim 22, characterized in that the machining tool has a homogeneous surface polish along the cutting edge, i.e. a flatness between the metallic elements and the ceramic elements of the tool, such that the roughness of the cutting edge of the tool is of the submicrometric order.

24. Machining machine according to claim 22, characterized in that the roughness of the surface polishing of the machining tool is below 20 nm, below 15 nm, below 10 nm or below 9 nm.

25. Machining machine according to any of claims 22-24, characterized in that the machining tool for the ceramic-metal material is one or more of the following group of materials: tungsten carbide ((WC), W(Ti,Ta)C-Co,Ti(C,N)-FeN¡, among other carbides with metal binders based on cobalt, nickel, iron, chromium or combinations thereof in different proportions.

26. Machining machine according to any of claims 22-25, characterized in that the machining tool has a change in roughness between the cutting edge and the faces adjacent to the cutting edge along the cutting edge of the tool that is homogeneous or regular.

27. Machining machine according to any of claims 22-26, characterized in that the machining tool presents, after polishing, between 80 and 90% of the compressive stresses generated during the grinding process.

28. Complex element, such as an aircraft, characterized in that it comprises a motion transmission part with a homogeneous surface polish.

29. Complex element according to claim 28, characterized in that a motion transmission part has at least part of its surface a homogeneous surface polish, i.e. a planarity between the metallic elements and the ceramic elements of the tool, such that the roughness of the cutting edge of the tool is of the submicrometric order.

30. Complex element according to claim 28, characterized in that the roughness of the surface polishing of the motion transmission part is below 20 nm, below 15 nm, below 10 nm or below 9 nm.

31. Complex element according to any of claims 28-30, characterized in that the machining tool because the ceramic-metal material is one or more of the following group of materials: tungsten carbide ((WC), W(Ti,Ta)C-Co, Ti(C,N)-FeN¡, among other carbides with metallic binders based on cobalt, nickel, iron, chromium or combinations thereof in different proportions.

32. Complex element according to any of claims 28-31, characterized in that the machining tool has, after polishing, a compressive stress of less than -500 MPa or more than 25% of the compressive stresses generated during the grinding process.

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