Method of manufacturing of a spark plug electrode with platinum group metal tip produced using additive manufacturing

Abstract

The invention relates to a spark plug electrode (1) comprising an electrode base body (2) and an additively manufactured layer-by-layer electrode tip (3) containing a platinum group metal, wherein the spark plug electrode (1) has a bonding zone (4) formed by melting and solidification, wherein the bonding zone (4) has a thickness (S) of a maximum of 400 µm, and wherein the bonding zone (4), the electrode base body (2), and the electrode tip (3) outside the bonding zone (4) fulfill at least one of the requirements A, B, and C: A) in the bonding zone (4) at least 1 atom% nickel and at least 1 atom% platinum group metal, and outside less nickel or less platinum group metal; B) in the bonding zone (4) a higher total crack length per µm² of cracks than outside the bonding zone; and C) in the bonding zone (4) a larger mean pore diameter than outside the bonding zone.The invention also relates to a method for producing a spark plug electrode (1), a spark plug electrode (1) produced by such a method, a spark plug comprising a spark plug electrode (1) and a method for producing a spark plug.

Description

[0001] The invention relates to a method for manufacturing a spark plug electrode comprising an electrode base body made of nickel or a nickel-based alloy and an electrode tip, wherein the electrode tip consists at least on a distal side pointing away from the electrode base body of a platinum group metal or a platinum group metal-based alloy.

[0002] The process for manufacturing a spark plug electrode, in which an electrode base body made of a nickel-based alloy is provided, a spark plug electrode manufactured by such a process, a spark plug comprising such a spark plug electrode and a process for manufacturing a spark plug.

[0003] Currently, spark plug electrodes are usually manufactured from two metallic materials by welding a conventionally produced precious metal blank, for example made of IrRh2.5Zr or IrRh, as the electrode tip onto an electrode base made of a less expensive metallic material such as nickel or a nickel-based alloy, or another non-precious metal. Such spark plug electrodes and methods for their manufacture are known, for example, from WO 00 / 013274 A1, US 2020 / 0321756 A1, EP 2133968 B1, EP 3378593 A1, JP 4392130 B2, and DE 10 2019 203 431 A1. The weld seam produced between the electrode tip and the electrode base has the disadvantages that an uneven joining zone is created with regard to thickness and homogeneity, and that only defined and uniform geometries, such as...Cylinders are possible as a geometric shape for the spark plug electrode and that, depending on the welding process used, only a weld seam is produced around the outer edge, so that the connection only takes place at the edge of the surface of the electrode base body (see . Figure 8 This weakens the transition between the electrode tip and the electrode base, impairing the durability (service life) and mechanical stability of the spark plug electrode. The same problem arises with the electrode tip sintered from two metallic materials according to US 2017 / 0085061 A1, which is also welded to an electrode base after its manufacture.

[0004] Further disadvantages of the methods and spark plug electrodes known from the prior art are that an expensive manufacturing process for the precious metal discs, namely rolling a sheet to the desired thickness and eroding or alternatively wire production and cutting to length, makes the production of the electrode tip costly.

[0005] Furthermore, lengthy manufacturing processes are required because the electrode tip must be machined from ingots or sheets. Additionally, only malleable precious metal alloys can be used. There is also a loss of precious metal due to sawing the precious metal blank before welding, and the capital tied up in precious metals through processing losses and subsequent recycling is also considerable.

[0006] Furthermore, the possibilities for shaping the electrode tip are limited.

[0007] Methods for manufacturing a spark plug electrode using additive manufacturing (AM), such as 3D printing, are known from WO 2019 / 025795 A1, US 2022059999 A1, and US 2006 / 028106 A1. In these processes, an electrode tip is built up layer by layer from a precious metal onto an electrode base. This method is intended to, and can, enable the fabrication of more complex geometries than electrode tips on the electrode base. However, precious metals for spark plug applications cannot be reliably bonded to nickel-based alloys such as Inconel® using additive manufacturing processes. In a standard 3D printing process, the first layer of powder is exposed to high volume energy. This is necessary to melt the precious metal and create a dense body in the bonding zone.A disadvantage of this method is that spark plug electrodes manufactured in this way do not exhibit good durability and service life, or even have reduced durability and service life compared to welded precious metal electrode tips. The connection between the electrode base and the electrode tip therefore still represents a weak point. Within the scope of the present invention, it was found that in additive manufacturing processes for applying the electrode tip to the electrode base, where the electrode tip material is melted onto the electrode base using radiation, thermal stresses from the melting and resolidification process cause cracks in the area of ​​the connection zone that forms the transition between the electrode base and the electrode tip, thus weakening the connection zone. Furthermore, pores can form in the connection zone, which further weaken it.It was further found within the scope of the present invention that the pores are formed by evaporation of the material, in particular by evaporation of nickel.

[0008] Additive manufacturing processes such as 3D printing precious metals onto nickel or nickel-based alloys present the following problems: firstly, some material from the electrode substrate (e.g., nickel) evaporates, causing porosity in the bonding zone; and secondly, stresses develop in the interface between the nickel / nickel-based alloy and the precious metal due to differing coefficients of thermal expansion. These stresses can lead to cracking and thus weaken the bonded area.

[0009] The use of precious metal electrodes manufactured with conventional parameters is not possible due to the voltage and the lack of quality of the connection.

[0010] The object of the invention is therefore to overcome the disadvantages of the prior art. In particular, a method for manufacturing such a spark plug electrode is to be found that can be implemented as cost-effectively and variably as possible and is suitable for cost-effective mass production, so that the spark plug electrode is stable and durable and thus has a long and improved service life.

[0011] The objects of the invention are solved by a method for manufacturing a spark plug electrode according to independent claim 1, wherein a spark plug electrode comprises an electrode base body made of nickel or a nickel-based alloy and an electrode tip, the electrode tip consisting at least on a distal side facing away from the electrode base body of a platinum group metal or a platinum group metal-based alloy, the electrode tip being manufactured layer by layer on the electrode base body by additive manufacturing from a base material containing at least one platinum group metal by melting and solidifying, the spark plug electrode having a connection zone at a transition between the electrode base body and the electrode tip, the connection zone being formed by the melting and solidifying during additive manufacturing.wherein the connection zone has a maximum thickness of 400 µm and wherein the connection zone, as well as the electrode base body and the electrode tip outside the connection zone, fulfill at least one of requirements A, B and C: , A) in the connection zone, a composition containing at least 1 atom % nickel and at least 1 atom % platinum group metal is present, and outside the connection zone, in the electrode tip, a composition containing less nickel is present than in the connection zone, and outside the connection zone, in the electrode body, a composition containing less platinum group metal is present than in the connection zone; B) in the connection zone, a higher total crack length per µm 2< of cracks in a cross-section of the spark plug electrode is present than outside the connection zone in the electrode body and in the electrode tip; and C) in the connection zone, a larger mean pore diameter is present than outside the connection zone in the electrode body and in the electrode tip.

[0012] A spark plug electrode comprising an electrode base body and a layer-by-layer additively manufactured electrode tip containing a platinum group metal, wherein the spark plug electrode has a bonding zone formed by melting and solidification, wherein the bonding zone has a maximum thickness of 400 µm, and wherein the bonding zone, the electrode base body, and the electrode tip outside the bonding zone satisfy at least one of requirements A, B, and C: A) in the connection zone at least 1 atomic percent nickel and at least 1 atomic percent platinum group metal and outside less nickel or less platinum group metal; B) in the connection zone higher total crack length per µm² of cracks than outside the connection zone; and C) in the connection zone larger mean pore diameter than outside the connection zone.

[0013] The total crack length can preferably be determined using an imaging technique. When determining the total crack length, care must be taken during the preparation of the cross-section to ensure that no cracks are created during preparation. Preferably, the total crack length can be determined in an optically polished cross-section of the spark plug electrode.

[0014] An optically polished cross-section is understood to be a flat axial cross-section of the spark plug electrode, which is finished with a polishing compound whose grain size is smaller than the wavelength of visible light, preferably with a grain size of no more than 200 µm, so that the final polishing produces grooves with a depth and width of no more than 200 nm. The cross-section includes an axis that runs parallel to the layer-by-layer 3D build direction of the additive manufacturing of the electrode tip. The cross-section, or cross-sectional area, of the spark plug electrode is defined along this axis, which preferably forms a central axis of symmetry of the spark plug electrode extending from the center of a proximal base of the electrode body to the distal tip of the electrode, with the central axis of symmetry of the spark plug electrode lying within the cross-sectional area.

[0015] The mean pore diameter can preferably be determined using an imaging method, wherein preferably the pore diameters of pores in an optically polished cross-section of the spark plug electrode are determined.

[0016] The cross-section can be produced by grinding or by cutting and subsequent polishing of the spark plug electrode. This applies both to the cross-section for determining the mean pore diameter and to the cross-section for determining the total crack length.

[0017] Platinum group metals are the chemical elements ruthenium (Ru), rhodium (Rh), and palladium (Pd), as well as osmium (Os), iridium (Ir), and platinum (Pt). Preferred platinum group metals are the chemical elements Ru, Rh, Pd, Ir, and Pt. Particularly preferred platinum group metals are the chemical elements Rh and Ir. The most preferred platinum group metal is iridium, and an iridium-based alloy is preferred as a platinum group metal base alloy. Iridium and rhodium exhibit particularly high long-term stability in spark plug tips compared to other metals and even compared to other platinum group metals.

[0018] The platinum group metal can, of course, contain impurities resulting from the manufacturing process. The same applies to nickel and nickel-based alloys.

[0019] A nickel-based alloy is defined as a metallic alloy containing at least 50 atomic percent nickel. Similarly, a platinum group-based alloy is defined as a metallic alloy containing at least 50 atomic percent of at least one of the chemical elements selected from the group consisting of ruthenium, rhodium, palladium, osmium, iridium, and platinum. An iridium-based alloy is defined as a metallic alloy containing at least 50 atomic percent iridium.

[0020] A copper core may be arranged in or on the electrode base body. The electrode base body, with the exception of the optional copper core, may preferably consist of nickel or a nickel-based alloy.

[0021] According to one embodiment, the connection zone, as well as the electrode base body and the electrode tip outside the connection zone, fulfill requirements A and B.

[0022] According to another embodiment, the connection zone, as well as the electrode base body and the electrode tip outside the connection zone, fulfill requirements A and C.

[0023] According to another embodiment, the connection zone, as well as the electrode base body and the electrode tip outside the connection zone, fulfill requirements B and C.

[0024] According to another embodiment, the connection zone, as well as the electrode base body and the electrode tip outside the connection zone, fulfill requirement A.

[0025] According to another embodiment, the connection zone, as well as the electrode base body and the electrode tip outside the connection zone, fulfill requirement B.

[0026] According to yet another embodiment, the connection zone, as well as the electrode base body and the electrode tip outside the connection zone, fulfill requirement C.

[0027] It can be provided that the connection zone contains a composition containing at least 5 atomic percent nickel and at least 5 atomic percent platinum group metal, and that outside the connection zone, in the electrode body and in the electrode tip, there is less nickel or less platinum group metal than in the connection zone, wherein preferably the content of nickel and platinum group metal refers to an average over a standard area of ​​at least 50 µm by 50 µm of an optically polished cross-section of the spark plug electrode, and the connection zone has a mixture of nickel and platinum group metal in each standard area of ​​at least 50 µm by 50 µm in this area.or in the connection zone a composition containing at least 10 atomic percent nickel and containing at least 10 atomic percent platinum group metal is present, and outside the connection zone in the electrode body and in the electrode tip, less than 10 atomic percent nickel or less than 10 atomic percent platinum group metal is present, wherein preferably the content of nickel and platinum group metal refers to the averaging over a standard area of ​​at least 50 µm by 50 µm of an optically polished cross-section of the spark plug electrode, and the connection zone has a mixture of nickel and platinum group metal in each standard area of ​​at least 50 µm by 50 µm in this area.

[0028] This ensures that the compound zone is defined by a mixture of chemical elements.

[0029] The precise measurement method is suitable regardless of its penetration depth into the standard surface of the optically polished cross-section. For example, energy-dispersive X-ray analysis (EDX), wavelength-dispersive X-ray analysis (WDX), or X-ray fluorescence analysis can be used to determine the chemical composition in the cross-section. As long as the same method is always used, the measurements are comparable and therefore suitable. Furthermore, with the described manufacturing process, it is not expected that the composition in the plane of the cross-section will differ from that in the bulk material.

[0030] Furthermore, it can be provided that the electrode base body and the electrode tip are connected to each other via a connecting surface, wherein the connecting surface is arranged within the connecting zone, wherein the connecting zone is bounded by a first interface in the electrode base body and by a second interface in the electrode tip, wherein the first interface and the second interface are parallel to the connecting surface between the electrode base body and the electrode tip, wherein the first interface is defined bythat within a volume of 1 µm thickness starting from the first interface in the direction of the distal side of the electrode tip in the electrode base body, a composition containing a proportion of the platinum group metal or platinum group metals of at least 5 atomic% is contained, and in each volume section of 1 µm thickness starting from the first interface in the direction away from the connection surface in the electrode base body, a composition containing a proportion of the platinum group metal or platinum group metals of less than 5 atomic% is contained, and wherein the second interface is defined bythat within a volume of 1 µm thickness extending from the second interface towards the connection surface in the electrode tip, a composition containing at least 5 atomic percent nickel is present, and in each volume section of 1 µm thickness extending from the second interface away from the connection surface in the electrode tip, a composition containing less than 5 atomic percent nickel is present, wherein the thickness of the connection zone is the distance between the first interface and the second interface.

[0031] This ensures a particularly easy-to-understand and easily measurable strength of the connection zone.

[0032] Preferably, the connecting surface can be a partial surface of the original surface of the electrode base body before the additive application (manufacturing) of the electrode tip onto this surface of the electrode base body.

[0033] Preferably, the contact surface can be a flat surface that, on average, approximates the microscopically potentially uneven interface between the electrode base and the electrode tip as closely as possible. The position of the flat contact surface can be determined, for example, by regression. However, the exact position of the contact surface is not critical. It is sufficient to estimate the position of the contact surface even very roughly, since the first and second interfaces are determined within an accuracy of 1 µm, independent of the exact positioning of the contact surface.

[0034] The nickel and platinum group metal content can be determined using energy-dispersive X-ray analysis (EDX) or wavelength-dispersive X-ray analysis (WDX) with an electron microscope or by X-ray fluorescence. Other possible analytical methods are known to those skilled in the art.

[0035] Furthermore, it can be provided that the electrode base body and the electrode tip are connected to each other via a connecting surface, wherein the connecting surface is arranged within the connecting zone, wherein the thickness of the connecting zone is determined by means of an X-ray analysis to determine a platinum group metal content or a nickel content using a scanning electron microscope (SEM) or by means of X-ray fluorescence, wherein for this purpose a polished cross-section through the spark plug electrode running parallel to the 3D build-up direction is analyzed, wherein a first boundary line runs in the cross-section of the electrode base body and a second boundary line runs in the cross-section of the electrode tip and wherein the connecting surface forms a connecting line in the cross-section of the spark plug electrode.wherein the first boundary line and the second boundary line are arranged parallel to the connecting line in the cross-section between the electrode base body and the electrode tip, wherein the first boundary line is defined in that within a distance of 1 µm thickness starting from the first boundary line in the direction of the distal side of the electrode tip, the electrode base body contains a composition with a proportion of the platinum group metal or platinum group metals of at least 5 atomic percent, and in each area section of 1 µm distance starting from the first boundary line in the direction away from the connecting line, the electrode base body contains a composition with a proportion of the platinum group metal or platinum group metals of less than 5 atomic percent, and wherein the second boundary line is defined in thatthat within a distance of 1 µm thickness starting from the second boundary line in the direction of the connection line in the electrode tip, a composition with a nickel content of at least 5 atomic percent is contained, and in each surface section of 1 µm distance starting from the second interface in the direction away from the connection line in the electrode tip, a composition with a nickel content of less than 5 atomic percent is contained, wherein the thickness of the connection zone is the distance of the first boundary line from the second boundary line.

[0036] This ensures a particularly easy-to-understand and simple-to-measure strength of the connection zone using SEM.

[0037] It may be provided that a longitudinal axis of the electrode tip lies in the plane of the cross-section, with the longitudinal axis passing through the center of gravity of the electrode tip and through the geometric center of the connecting surface.

[0038] The strength of the connection zone can also be referred to as the thickness of the connection zone. However, the term "thickness" has been avoided here to distinguish the strength of the connection zone from the thickness of the interface.

[0039] The scanning electron microscope (SEM) can preferably be a Zeiss Ultra 55 Gemini SEM, operated with a field emission cathode and an accelerating voltage of 20 kV. An Oxford "AZtec" analyzer can be used as the detector for the EDX measurements.

[0040] The measurement is preferably carried out integrally over the aforementioned area with a thickness of 1 µm or integrally in sections of areas with an edge length of 1 µm, wherein the content of platinum group metal(s) or nickel is determined from the sections by averaging.

[0041] The cross-section is preferably polished with sandpaper with a grit size of less than 100 µm and then finished with a diamond paste down to 3 µm.

[0042] Preferably, wavelength-dispersive X-ray analysis (WDX), X-ray fluorescence analysis, or energy-dispersive X-ray analysis (EDX) can be used as a measurement method; particularly preferably, an Oxford analyzer "AZtec" can be used as EDX.

[0043] Preferably, the connecting line lies in the plane of the original surface of the electrode base body before the additive application of the electrode tip.

[0044] Preferably, the connecting line can be a straight line that, on average, provides the best possible approximation to the microscopically uneven boundary between the electrode base and the electrode tip. The straight connecting line can be determined computationally, for example, using linear regression, by selecting the straight line where the sum of the squares of the points on the uneven boundary that deviate from the line is smallest. The first boundary is preferably also a straight first boundary, and the second boundary is preferably also a straight second boundary.

[0045] The boundary line can also simply be a straight line between two corner points of the cross-section, where the electrode tip, the electrode base, and the outer boundary (i.e., the area surrounding the spark plug electrode) meet at each corner point. It can also be provided that the electrode tip covers only a portion of a flat surface of the electrode base, preferably with this portion forming a contact surface between the electrode tip and the electrode base. This allows for a stable connection between the electrode tip and the electrode base.

[0046] According to a further development, it can be provided that the connection zone has a thickness of a maximum of 350 µm, preferably a thickness of a maximum of 300 µm, and particularly preferably a thickness of a maximum of 250 µm.

[0047] This results in a more durable and stable spark plug electrode.

[0048] The smaller the contact zone, the more stable and durable the spark plug electrode.

[0049] It is also preferred that the connection zone has a thickness of at least 50 µm, preferably a thickness of at least 100 µm, and particularly preferably a thickness of at least 150 µm.

[0050] In additive manufacturing processes, connecting zones with even smaller thicknesses can only be produced with great difficulty, so the minimum thicknesses mentioned ensure cost-effective production of the spark plug electrode.

[0051] Furthermore, the connection zone can be provided to have a thickness of at least 50 µm and at most 350 µm, preferably a thickness of at least 100 µm and at most 300 µm, and particularly preferably a thickness of at least 150 µm and at most 250 µm. It can also be provided that the connection zone has a thickness of at least 50 µm and at most 350 µm, preferably a thickness of at least 50 µm and at most 300 µm, and particularly preferably a thickness of at least 50 µm and at most 250 µm. According to a preferred embodiment, it can be provided thatthat only in the connection zone is a total crack length per µm²< of cracks measurable in an optically polished cross-section of the spark plug electrode, and outside the connection zone in the electrode base body and in the electrode tip no cracks are measurable for determining the total crack length per µm²< in the optically polished cross-section of the spark plug electrode, or the connection zone has a higher total crack length per µm²< of cracks in an optically polished cross-section of the spark plug electrode compared to the electrode tip and the electrode base body outside the connection zone, wherein preferably the total crack length per µm²< of cracks of the optically polished cross-section in the connection zone is at least 50% higher than the average total crack length per µm²< of an optically polished cross-section of the electrode tip at a distance of more than 10 µm from the connection zone,particularly preferred is the total crack length per µm² of cracks in the optically polished cross-section in the connection zone being at least twice as high as the average total crack length per µm² of an optically polished cross-section in the electrode tip at a distance of more than 10 µm from the connection zone.

[0052] A thin bonding zone (thickness less than 400 µm) with an increased total crack length per µm 2< can provide a more stable and durable spark plug electrode compared to a spark plug electrode with a thicker bonding zone.

[0053] The total crack length per µm²< is defined as the sum of all crack lengths measured in a standard area (for example, a square with a side length of 1 µm) using a defined and standardized method, relative to the area of ​​the standard area. The crack lengths can be determined, for example, by light microscopy or electron microscopy on the optically polished cross-section. The precise method of length determination is not critical, as only a relative total crack length per µm²< is used to determine the junction zone – namely, the total crack length per µm²< within the junction zone compared to the total crack length per µm²< outside the junction zone in the electrode body and at the electrode tip.Therefore, the same measuring method (possibly with the same sample preparation for the optically polished cross-section) must always be used to determine the total crack length per µm 2< in the connection zone and in the electrode tip and in the electrode base body.

[0054] When determining the total crack length per µm², it is preferable that at least one total crack length per µm² of at least 1 µm / µm² be measurable within the connection zone. The measurement method can then be considered particularly well-suited for determining the total crack length per µm². For example, an optically polished cross-section can be imaged with a reflected-light microscope (e.g., Leica DM6000M) at a magnification between 50x and 500x, preferably at a magnification of 200x, and subsequently evaluated with image analysis software. An optically polished surface exhibits grooves caused by the polishing compound with a width of less than 200 nm, which are fundamentally distinguishable from cracks.The crack length can be determined computationally, for example, through a corresponding microstructure analysis, such as by calculating the length of a polygon along a dark line in a light microscopy image. Software such as Imagic IMS can be used for this evaluation.

[0055] It may be provided that the total crack length per µm 2< is determined by analyzing and summing the crack lengths of cracks on images of optically polished cross sections using a light microscope or a scanning electron microscope (SEM).

[0056] This makes it particularly easy to standardize the value of the total crack length per µm 2<.

[0057] Furthermore, it can be provided that the total crack length per µm 2< in the connection zone is a maximum of 0.1 µm / µm 2<, preferably a maximum of 0.05 µm / µm 2<, and particularly preferably a maximum of 0.02 µm / µm 2<.

[0058] A low total crack length per µm 2< results in higher durability and longevity of the spark plug electrode.

[0059] It can also be provided that the total crack length per µm 2< in the connection zone is at least 0.001 µm / µm 2<, preferably at least 0.005 µm / µm 2<, particularly preferably at least 0.01 µm / µm 2<.

[0060] This allows the connection zone to be clearly distinguished from its surroundings.

[0061] The measurement is preferably carried out using a light microscope, Leica DM6000M, with reflected light at a magnification of 200 on an optically polished surface of a cross-section of the spark plug electrode.

[0062] The crack length per µm 2< is preferably determined using the software from Imagic "Imagic IMS".

[0063] The connection zone may be provided with a larger mean pore diameter compared to the electrode tip outside the connection zone, preferably with a mean pore diameter at least 50% larger than the mean pore diameter of the electrode tip at a distance of more than 10 µm from the connection zone, and particularly preferably with a mean pore diameter at least twice as large as the mean pore diameter of the electrode tip and the electrode base body at a distance of more than 10 µm from the connection zone. This allows for a more precise specification and definition of the connection zone.

[0064] The mean pore diameter can be determined, for example, by calculating the average of all mean or maximum diameters of all visible pores, or of all pores with a minimum diameter. The pore diameters can be determined, for example, using light microscopy or electron microscopy in an optically polished cross-section. The precise method used to determine the pore diameters is not critical, as only a relative mean pore diameter is used to determine the bonding zone and its thickness—that is, a comparison of the mean pore diameters inside and outside the bonding zone. Therefore, the only requirement is that the same standardized measurement procedure (possibly with the same sample preparation) is always used to determine the mean pore diameter in the bonding zone, at the electrode tip, and in the electrode body.

[0065] When determining the mean pore diameter, at least 5 pores per 0.0625 mm² should preferably be measurable within the junction zone. The measurement method can then be considered well-suited for determining the mean pore diameter. For example, an optically polished flat cross-section can be imaged using a reflected-light microscope (e.g., Leica DM6000M) at a magnification between 50 and 500x, preferably at a magnification of 200x. An optically polished surface exhibits grooves caused by the polishing compound with a width smaller than the wavelength of the light used, for example, less than 200 nm. This can be achieved, for example, by using sandpaper or a polishing paste with abrasive particles of a maximum diameter of 100 nm.The mean pore diameter can be calculated, for example, through a corresponding microstructure analysis, such as by determining the maximum and minimum diameters of dark-appearing pores in a light microscope image. Software such as Imagic IMS from Imagic can be used for the evaluation.

[0066] It can also be provided that the mean pore diameter in the connection zone is a maximum of 50 µm, preferably a maximum of 35 µm, and particularly preferably a maximum of 25 µm.

[0067] This provides a more stable connection zone and therefore a more stable spark plug electrode.

[0068] Furthermore, it can be provided that the mean pore diameter in the connection zone is at least 3 µm, preferably at least 5 µm, and particularly preferably at least 10 µm.

[0069] This allows the connection zone to be clearly distinguished from its surroundings.

[0070] The measurement was performed using a Leica DM6000M light microscope with reflected light at a magnification of 200x on an optically polished cross-section of a spark plug electrode. The mean pore diameter was determined using Imagic IMS software by calculating the average of the maximum diameter of all measurable pores.

[0071] Furthermore, it can be provided that the nickel-based alloy contains at least 50 wt% nickel, preferably at least 80 wt% nickel.

[0072] Such nickel-based alloys are particularly well-suited for use as electrode substrates. Furthermore, the nickel-based alloy can be an Inconel alloy or a nickel-based alloy with chromium as the second most abundant minor component, wherein the nickel-based alloy with chromium as the second most abundant minor component preferably also contains at least one of the chemical elements selected from the group consisting of iron, molybdenum, niobium, cobalt, manganese, copper, aluminum, titanium, silicon, carbon, sulfur, phosphorus, and boron.

[0073] Such nickel-based alloys are particularly well suited for use as electrode substrates.Preferably, the platinum group metal may also be selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir) and platinum (Pt), or the platinum group metal or metals of the platinum group metal base alloy may be selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir) and platinum (Pt), wherein preferably the platinum group metal is selected from the group consisting of rhodium (Rh) and iridium (Ir), or the platinum group metal or metals of the platinum group metal base alloy may be selected from the group consisting of rhodium (Rh) and iridium (Ir), wherein the electrode tip is particularly preferably made of an iridium base alloy, most preferably of an iridium base alloy containing rhodium as the second most abundant component and at least 0.1 wt% to a maximum of 1 wt% zirconium.

[0074] These platinum group metals are particularly well suited for use as electrode tips and ensure high durability and longevity of the spark plug electrodes manufactured with them.

[0075] Furthermore, it can be provided that the electrode tip outside the connection zone consists of the platinum group metal or of the platinum group metal base alloy, wherein preferably the electrode tip consists of the platinum group metal and a platinum group metal base alloy or of a platinum group metal base alloy.

[0076] The fact that the electrode tip outside the junction zone consists of the platinum group metal or the platinum group metal base alloy means that, apart from impurities, the electrode tip outside the junction zone consists of the platinum group metal or the platinum group metal base alloy. Those skilled in the art know that a certain degree of impurities cannot be prevented, or not with reasonable effort. This results in a high degree of stability for the spark plug electrode.

[0077] Furthermore, it can be provided that a base material from which the electrode tip is additively manufactured is a powder, preferably a metallic powder, and particularly preferably a powder made of a platinum group metal or of several platinum group metals or of at least one platinum group metal base alloy.

[0078] This simplifies the manufacturing of the electrode tip.

[0079] The powder may also contain impurities that are unavoidable or cannot be avoided with reasonable effort.

[0080] It may be provided that the electrode tip has a larger diameter in the area of ​​the connection to the electrode base body than the remaining areas of the electrode tip.

[0081] This results in a further reduction in crack formation.

[0082] According to the invention, the spark plug electrode is manufactured using a method described below.

[0083] The problems underlying the present invention are solved by a method for manufacturing a spark plug electrode according to independent claim 1, the method comprising the following steps: A) Providing an electrode substrate made of nickel or a nickel-based alloy; B) Applying a layer of a base material made of a platinum group metal or a platinum group metal-based alloy to a surface of the electrode substrate; C) Fusing the layer of base material to the electrode substrate by means of radiation with a volume energy in a lower volume energy range to produce a first layer of the platinum group metal or the platinum group metal-based alloy on the surface of the electrode substrate;D) Applying further layers of the base material to the first layer of the platinum group metal or platinum group metal base alloy and fusing the further layers of the base material with the underlying already fused layer of the platinum group metal or platinum group metal base alloy by means of radiation with a volume energy in the lower volume energy range to produce a transition zone of the platinum group metal or platinum group metal base alloy;and E) Applying further layers of the base material to the transition zone and fusing the powder with the underlying already fused layer of the platinum group metal or the platinum group metal base alloy by means of radiation with a volume energy in an upper volume energy range to produce the remaining electrode tip from the platinum group metal or the platinum group metal base alloy, wherein the volume energies in the upper volume energy range are on average at least 5% higher than the volume energies in the lower volume energy range.

[0084] Volume energy is the power delivered per unit volume (per mm³) and per unit time (per second) by the radiation into the layer of the base material and possibly also into part of the underlying material. Volume energy is calculated as the laser power divided by the laser scanning speed multiplied by the laser track spacing multiplied by the layer thickness (the layer in which the energy is absorbed) and has the unit W / (mm / s) * mm * mm, which corresponds to the unit J / mm³.

[0085] Preferably, the volume energies in the upper volume energy range are on average at least 6% higher than the volume energies in the lower volume energy range. Particularly preferably, the volume energies in the upper volume energy range are on average 8% higher than the volume energies in the lower volume energy range.

[0086] The volume energy can be reduced in the lower volume energy range by reducing the power at which the radiation source, such as, for example, and preferably, a laser, is operated, or by changing the hatch spacing, or by changing the speed at which the radiation is guided over the surface of the layers of the base material, or by a combination of at least two of these three measures. Preferably, the nickel-based alloy contains at least 70 wt% nickel, more preferably at least 80 wt% nickel.

[0087] It may also be provided that the nickel-based alloy is an Inconel alloy or a nickel-based alloy with chromium as the second most common minor component.

[0088] Particularly preferred is a nickel-based alloy with chromium as the second most abundant minor component and additionally contains at least one of the chemical elements selected from the group consisting of iron, molybdenum, niobium, cobalt, manganese, copper, aluminum, titanium, silicon, carbon, sulfur, phosphorus, and boron. Preferably, a spark plug electrode according to the invention is produced using the method. In the methods according to the invention, it can be provided that in steps C) and D) the radiation is passed over the powder with a first hatch spacing, and in step E) the radiation is passed over the powder with a second hatch spacing, wherein the second hatch spacing is smaller than the first hatch spacing.

[0089] This reduces the volume energy in steps C) and D) compared to the volume energy in step E), thus implementing the inventive method in a simple manner. The hatch spacing is the distance between two parallel scan vectors and is the distance between two lines along which the powder is locally melted by the radiation, in particular by a laser beam or an electron beam.

[0090] It can also be provided that at least 2 and at most 30 layers of the base material are fused in steps C) and D) with the volume energy in the lower volume energy range and at least 2 layers of the base material are fused in step E) with the volume energy in the upper volume energy range, wherein preferably at least 10 and at most 25 layers of the base material are fused in steps C) and D) with the volume energy in the lower volume energy range and wherein particularly preferably 20 layers of the base material are fused in steps C) and D) with the volume energy in the upper volume energy range.

[0091] This makes it possible to form a stable connection between the electrode tip and the electrode base while keeping the thickness of the connection zone as low as possible.Furthermore, it may be provided that the platinum group metal is selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir) and platinum (Pt), or that the platinum group metal or platinum group metals of the platinum group metal base alloy are selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir) and platinum (Pt), wherein preferably the platinum group metal is selected from the group consisting of rhodium (Rh) and iridium (Ir), or that the platinum group metal or platinum group metals of the platinum group metal base alloy are selected from the group consisting of rhodium (Rh) and iridium (Ir), wherein the powder is particularly preferably made of an iridium base alloy, most preferably of an iridium base alloy containing rhodium as the second most abundant component and at least 0.1 at% to a maximum of 1 at% zirconium.

[0092] These platinum group metals are particularly well suited for use as electrode tips and ensure high durability and longevity of the spark plug electrodes manufactured with them.

[0093] Furthermore, it can be provided that the volume energies of the lower volume energy range are at a maximum of 13.75 J / mm 3< and the volume energies of the upper volume energy range are above 14.17 J / mm 3<, wherein preferably the lower volume energy range extends from a minimum of 12.5 J / mm 3< to a maximum of 13.75 J / mm 3< and the upper volume energy range extends from a minimum of 14.17 J / mm 3< to a maximum of 16.7 J / mm 3<.

[0094] These volume energy ranges are particularly well suited for the application of common additive manufacturing processes such as laser zone melting.

[0095] It can also be provided that the base material from which the electrode tip is additively manufactured is a powder, preferably a metallic powder, and particularly preferably a powder made of a platinum group metal or of several platinum group metals or of at least one platinum group metal base alloy.

[0096] Such powders are particularly easy to apply as a base material and can be easily bonded to the underlying layers by local melting.

[0097] It can be provided that the powder has particle sizes in the range between 0.1 µm and a maximum of 100 µm, preferably the powder has particle sizes in the range between 5 µm and a maximum of 50 µm.

[0098] Powders of these particle sizes are easy to process.

[0099] The particle distributions can be determined, for example, using sieve fractions by passing the powder through sieves (especially a sieve tower) with different (especially decreasing) mesh sizes, each retaining powder above or below a certain particle size. Alternatively, the particle sizes can be determined by laser diffraction in a liquid medium or in dry conditions, e.g., with a Mastersizer 3000.

[0100] According to the invention, it can also be provided that the merging is carried out with a laser beam or with an electron beam, preferably with a laser beam.

[0101] The radiation from a laser can be used to melt the base material in a highly localized and well-controlled manner.

[0102] Preferably, the method may be used to produce a spark plug electrode according to the invention.

[0103] The problems underlying the present invention are also solved by a spark plug electrode produced using a method according to the invention, by a spark plug comprising a spark plug electrode according to the invention, and by a method for producing a spark plug in which a spark plug electrode according to the invention is produced using a method according to the invention and is subsequently attached adjacent to a second spark plug electrode, preferably adjacent to and opposite a second spark plug electrode.

[0104] Preferably, the second spark plug electrode is also produced using a method according to the invention.

[0105] The invention is based on the surprising finding that, through a process of at least two stages in the additive application / manufacturing of the electrode tip onto the electrode base body, in which the first layer(s) of the electrode tip made of the platinum group metal is melted onto the electrode base body with a reduced volume energy, it is possible to ensure a bonding zone with a thinness of a maximum of 400 µm or less, wherein the spark plug electrode within the bonding zone is weakened by cracks, pores and / or the material transition as such (i.e. a gradient in the mixture of the chemical elements of the electrode base body with the electrode tip) and is not weakened or is weakened less so outside in the electrode base body and in the electrode tip.The comparatively small thickness of the connection zone results in a more durable spark plug electrode with a longer service life compared to spark plug electrodes known from the state of the art and manufactured using additive manufacturing.

[0106] Since it was found within the scope of the present invention that the connection zone represents a weak point of the spark plug electrode and adversely affects its service life, an improvement can be achieved according to the invention by making the connection zone as thin as possible. However, a way had to be found first for manufacturing such a thinner connection zone.

[0107] A connection zone with reduced volume energy is printed onto the electrode base body made of nickel or a nickel-based alloy. Small ridges can be formed in this connection zone, parallel to the interface between the electrode base body and the electrode tip. These ridges then connect the proximal underside of the electrode tip to the distal top side of the electrode base body (as a build plate). This reduces mechanical stresses that arise due to the different coefficients of thermal expansion between the electrode tip and the electrode base body.

[0108] According to the invention, the first layers in additive manufacturing can be exposed or irradiated with reduced energy and / or a larger hatch spacing, ideally such that the radiation power is sufficient to bond the platinum group metal of the electrode tip to the nickel or nickel-based alloy, but not so high that too much nickel evaporates from the electrode base. Preferably, only after a few layers (between 2 and 30 layers) is the energy density or volume energy increased to the values ​​that are optimal for the remaining structure of the electrode tip.The advantage is that in the transition zone of the connection, no metals evaporate from the electrode base, or at least little or no nickel evaporates. Therefore, the connection zone is less porous, and the thermally induced mechanical stresses, and consequently the formation of cracks, are not as high. As a result, fewer cracks appear in the connection zone, as will be shown in the following investigations.

[0109] To manufacture a spark plug electrode using a method according to the invention, less precious metal is required, and less precious metal bonding is necessary (due to the standardized manufacturing of the precious metal electrode tip from a sheet). Furthermore, manufacturing steps are eliminated because the electrode tip is not welded to the electrode base. This results in more cost-effective manufacturing of the spark plug electrode. The method according to the invention also enables more specialized geometries for the spark plug electrode through the application of additive manufacturing techniques such as 3D printing. For example, the electrode tip can be manufactured as a cylinder, a point, a cone, or a truncated cone without having to remove any part of the electrode tip.Our own tests showed comparable technical performance with regard to the wear gradient compared to currently commercially available spark plug electrodes, such as the spark plug electrodes from "Federal Mogul", Z212, 14FR-4 DIU and "Denso" GE2-3 M14DDI with welded-on precious metal electrode tips made of IrRh10. The welded joints of conventionally manufactured precious metal spark plugs always represent a weak point that can be avoided through additive manufacturing.

[0110] The following are exemplary embodiments of the invention, illustrated by eight schematic figures and a flowchart, without limiting the invention. These figures show: Figure 1 : a schematic cross-sectional view of a spark plug electrode produced using a method according to the invention; Figure 2: a SEM image of a partial area of ​​a cross-section through a spark plug electrode according to the invention, produced using a method according to the invention; Figure 3 : a light microscopic image of a section of a cross-section of a spark plug electrode, produced using a method according to the invention, in the area of ​​the connection zone; Figure 4 : a SEM image of a partial area of ​​a cross-section through an additively manufactured spark plug electrode according to the state of the art for comparison; Figure 5 : a light microscopic image of a section of a cross-section through the spark plug electrode according to the state of the art for comparison with Figure 4 in the area of ​​the connection zone as a comparison; Figure 6 : Four photographs of a spark plug electrode after operation of the spark plug electrode with different numbers of ignition events and initial and final weight; Figure 7: Four photographs of a state-of-the-art spark plug electrode after operation of the spark plug electrode with different numbers of ignition events for comparison and initial and final weight; Figure 8 : a light microscopic image through a spark plug electrode produced by welding on a precious metal electrode tip according to the state of the art; and Figure 9 : a flowchart to illustrate a method according to the invention.

[0111] In the figures, the same reference symbols are sometimes used for identical or similar parts. For example, the thickness of the connection zones 4, 24, 44 is always indicated by the letter S in different embodiments and comparison examples, and thus the two embodiments according to Figure 2 and Figure 3 The same reference symbols were used to improve the comparability of the exemplary embodiments.

[0112] Figure 1Figure 1 shows a schematic cross-sectional view of a spark plug electrode 1 produced according to the invention. The cross-section includes the longitudinal axis of the spark plug electrode 1. The spark plug electrode 1 has an electrode base body 2 made of nickel or a nickel-based alloy. Alternatively, a copper core (not shown) can also be arranged in the electrode base body.

[0113] A layered electrode tip 3 can be printed onto a distal (and preferably flat) surface 8 of the electrode base body 2, wherein the electrode tip 3 consists of at least one platinum group metal or a platinum group metal base alloy. The electrode base body 2 and the electrode tip 3 are approximately cylindrical in shape. The printing of the electrode tip 3 creates a bonding zone 4 characterized by a mixture of the chemical elements of the electrode base body 2 and the electrode tip 3, in particular nickel, with the at least one platinum group metal, and / or by a higher porosity and / or a higher total crack length (per µm 2< ) compared to the remaining areas of the electrode tip 3 and the electrode base body 2.

[0114] In the ignition electrode 1 and in the method according to the invention, at least the first two layers of the electrode tip 3 on the distal surface 8 of the electrode base body 2 are melted with a lower volume energy using radiation (preferably a laser beam, although an electron beam is also possible) than the subsequent layers that form the electrode tip 3 up to a distal front face 7 of the electrode tip 3. For producing the layers of the electrode tip 3, for example, powdered particles of at least one platinum group metal or a platinum group metal base alloy can be applied as a base material to the distal surface 8 of the electrode base body 2 or to layers already bonded to the electrode base body 2 and melted at least partially with the radiation. Such methods are known to those skilled in the art from 3D printing.The volume energies in an upper volume energy range for producing the distal side of the electrode tip 3 are on average at least 5% higher than the volume energies in a lower volume energy range for producing the proximal side of the electrode tip 3 on the distal surface 8 of the electrode base body 2. The input of the volume energy can, for example, take place in two stages or increase with the number of layers already applied.

[0115] The areas of the electrode tip 3 produced with the first layers, which are printed with reduced volume energy, preferably have a larger diameter than the remaining areas of the electrode tip 3. This results in an additional reduction of crack formation.

[0116] The connection zone 4 can be subdivided into a mixing zone 5 in the electrode base body 2 and a transition zone 6 in the electrode tip 3.

[0117] The mixing zone 5 is formed by the melting of the distal surface 8 of the electrode base 2 during the melting of the first few layers of the electrode tip 3. The mixing zone 5 can be bounded by a first interface 10, up to which mixing of the chemical elements of the electrode tip 3 and the electrode base 2 is evident, and / or by increased cracking and / or porosity formation compared to adjacent areas outside the mixing zone 5 in the electrode base 2. The first interface 10 is arranged parallel to a connection surface that forms a partial surface of the distal surface 8 of the electrode base 2 and that connects the electrode base 2 to the electrode tip 3. Pores can form through the evaporation of nickel from the mixing zone 5 of the electrode base 2.The lower volume energy used in the production of the first layers (the proximal underside) of the electrode tip 3 reduces the penetration depth of the radiation and keeps the depth of the mixing zone 5 in the electrode base body 2 small.

[0118] The transition zone 6 in the electrode tip 3 is formed by the mixing of the electrode tip 3 material with the electrode base material 2 during the melting of the first few layers. The transition zone 6 can be bounded by a second interface 12, up to which a mixing of the chemical elements of the electrode tip 3 and the electrode base 2 and / or increased cracking and / or porosity formation compared to adjacent areas outside the transition zone 6 in the electrode tip 3 is evident and can be distinguished from the surrounding area in the electrode tip 3. The second interface 12 is arranged parallel to the connection surface, which forms a partial surface of the distal surface 8 of the electrode base 2 and which connects the electrode base 2 and the electrode tip 3.Pores can form due to incomplete melting of the electrode tip 3 material, and cracks can form due to thermally induced mechanical stresses during the cooling of the first layers on the electrode base body 2, caused by different coefficients of thermal expansion of the materials of the electrode base body 2 and the electrode tip 3.

[0119] Due to the lower volume energy, the thickness S of the connection zone 4 is lower than in known methods with printed electrode tips and in known spark plug electrodes with printed electrode tips. This is demonstrated below by comparative measurements.

[0120] Figure 2 shows a SEM image of a partial area of ​​a cross-section through a spark plug electrode, produced using a method according to the invention and Figure 3A light microscopic image of a section of a cross-section through a spark plug electrode produced by a method according to the invention, in the region of its connection zone 24. The cross-section includes the longitudinal axis of the spark plug electrode. The spark plug electrodes of the Figures 2 and 3 were produced using the same parameters regarding volume energy, powder used, and layer thicknesses. The spark plug electrode of the Figure 2 The manufacturing process differs from that of a spark plug electrode. Figure 3 by having a base area in the connection to the boundary surface.

[0121] The spark plug electrode after the Figures 2 and 3 The electrode base body 22 has a nickel-based core. Alternatively, a copper core (not shown) can also be arranged in the electrode base body.

[0122] On a distal (and preferably flat) surface 28 of the electrode base body 22, an electrode tip 23 can be printed layer by layer, wherein the electrode tip 23 is made of an IrRh10 alloy consisting of iridium and rhodium in a weight ratio of 9:1 iridium / rhodium, as well as impurities of the metals iridium and rhodium due to the manufacturing process. The electrode base body 22 and the electrode tip 23 are approximately cylindrical in shape. However, other geometries, particularly for the electrode tip 23 but also for the electrode base body 22, are readily possible according to the invention.

[0123] The areas of the electrode tip 23 produced with the first layers, which are printed with reduced volume energy, preferably have a larger diameter than the remaining areas of the electrode tip 23. The electrode tip 23 can thus have two cylindrical areas with different diameters. This results in a further reduction of crack formation.

[0124] During the printing process of the electrode tip 23, the connection zone 24 is formed, which is characterized by a mixing of the chemical elements of the electrode base body 22 and the electrode tip 23, in this case nickel with iridium and rhodium, and / or can be easily delineated by a higher porosity and / or total crack length (per µm 2< ) compared to the remaining areas of the electrode tip 23 and the electrode base body 22. The transition is particularly clearly visible in SEM and thus easily delineated.

[0125] At the ignition electrodes after the Figures 2 and 3 In the inventive method, at least the first twenty layers of the electrode tip 23 on the distal surface 28 of the electrode base body 22 were melted with a lower volume energy using laser radiation (alternatively, an electron beam is also possible) than the subsequent layers that form the electrode tip 23 up to a distal front face 27 of the electrode tip 23. Alternatively, more or fewer of the first layers can also be produced with reduced volume energy, preferably between two and thirty of the first layers.

[0126] To produce the layers of the electrode tip 23, powdered particles of an IrRh10 alloy were applied as a base material to the distal surface 28 of the electrode base body 22 or to layers already bonded to the electrode base body 22 and melted, at least partially, using laser radiation. Such methods are known to those skilled in the art from 3D printing. The volume energies in an upper volume energy range for producing the distal side of the electrode tip 23 were approximately 9% higher at 14.6 J / mm³ than the volume energies of 13.42 J / mm³ for producing the first twenty layers of the proximal side of the electrode tip 23 on the distal surface 28 of the electrode base body 22. Alternatively, the volume energy can also be successively increased from 13.42 J / mm³ to 14.6 J / mm³.

[0127] The connection zone 24 can be subdivided into a mixing zone 25 in the electrode base body 22 and a transition zone 26 in the electrode tip 23.

[0128] The mixing zone 25 is formed by the melting of the distal surface 28 of the electrode base body 22 during the melting of the first and the first few layers of the electrode tip 23. The mixing zone 25 can be limited by a first interface 30, up to which mixing of the chemical elements of the electrode tip 23 and the electrode base body 22 and / or increased cracking and / or pore formation compared to adjacent areas outside the mixing zone 25 in the electrode base body 22 is evident. The first interface 30 is arranged parallel to a connection surface that forms a partial surface of the distal surface 28 of the electrode base body 22 and that forms the connection between the electrode base body 22 and the electrode tip 23. Pores 36 (see Figure 3These can be formed by the evaporation of nickel from the mixing zone 25 of the electrode base body 22. The lower volume energy used in the production of the first layers (the proximal underside) of the electrode tip 23 reduces the penetration depth of the radiation and keeps the depth of the mixing zone 25 in the electrode base body 22 small.

[0129] The transition zone 26 in the electrode tip 23 is formed by the mixing of the electrode tip material 23 with the electrode base material 22 during the melting of the first layers of the electrode tip material 23. The transition zone 26 can be bounded by a second interface 32, up to which a mixing of the chemical elements of the electrode tip 23 and the electrode base 22 and / or increased cracking and / or porosity formation compared to adjacent areas outside the transition zone 26 in the electrode tip 23 is evident. The second interface 32 is arranged parallel to the connection surface, which forms a partial surface of the distal surface 28 of the electrode base 22 and which forms the connection between the electrode base 22 and the electrode tip 23.Pores can be caused by incomplete melting of the electrode tip material 23 and cracks 34 by thermally induced mechanical stresses during the cooling of the first layers on the electrode base body 22, which are caused by different coefficients of thermal expansion of the materials of the electrode base body 22 and the electrode tip 23.

[0130] Due to the lower volume energy in the first twenty layers of the electrode tip 23, the thickness S of the connection zone 24 is approximately 250 µm lower than in known methods with printed electrode tips and in known spark plug electrodes with printed electrode tips, as can be seen in comparison with the Figures 4 and 5 This can be seen in a SEM image of a partial area of ​​a cross-section through a spark plug electrode according to the state of the art with an additively printed electrode tip at constant volume energy ( Figure 4 ) and a light microscopic image ( Figure 5 ) of a section of a cross-section through the spark plug electrode Figure 4 The cross-section shows the area of ​​the connection zone for comparison. It includes the longitudinal axis of the spark plug electrode.

[0131] The spark plug electrode after the Figures 4 and 5 has an electrode base body 42 which consists of a nickel-based alloy.

[0132] On a distal surface 48 of the electrode base body 42, an electrode tip 43 is printed layer by layer. The electrode tip 43 is made of an IrRh10 alloy consisting of iridium and rhodium in a ratio of 9:1 iridium / rhodium, as well as impurities of the metals iridium and rhodium due to the printing process. During the printing of the electrode tip 43, the bonding zone 44 is formed. This zone is characterized by a mixture of the chemical elements of the electrode base body 42 and the electrode tip 43, in this case nickel (from the nickel-based alloy) with iridium and rhodium, and / or by a higher porosity and / or total crack length (per µm²) compared to the remaining areas of the electrode tip 43 and the electrode base body 42. [The last sentence appears to be incomplete and requires context to be translated accurately.] Figure 4 and 5All layers of the electrode tip 43 on the distal surface 48 are melted with the same volume energy using laser radiation. To produce the layers of the electrode tip 43, powdered particles of IrRh10 alloy were applied as a base material to the distal surface 48 of the electrode base body 42 or to layers already bonded to the electrode base body 42 and melted, at least partially, with the laser radiation. Such methods are known to those skilled in the art from 3D printing. In this process, the volume energies for producing the electrode tip 43 were higher, at 175 watts radiation power in the first twenty layers, compared to the method used in the previous calculation. Figures 2 and 3 Spark plug electrode produced using a method according to the invention and in comparison to the volume energy in a method according to the invention.

[0133] The connection zone 44 can be subdivided into a mixing zone 45 in the electrode base body 42 and a transition zone 46 in the electrode tip 43.

[0134] The mixing zone 45 is formed by the melting of the distal surface 48 of the electrode base body 42 during the melting of the first and the first few layers of the electrode tip 43. The mixing zone 45 can be limited by a first interface 50, up to which mixing of the chemical elements of the electrode tip 43 and the electrode base body 42 and / or increased cracking and / or pore formation compared to adjacent areas outside the mixing zone 45 in the electrode base body 42 is evident. The first interface 50 is arranged parallel to a connection surface that forms a partial surface of the distal surface 58 of the electrode base body 42 and that forms the connection between the electrode base body 42 and the electrode tip 43. Pores 56 (see Figure 5These layers can be formed by the evaporation of nickel from the mixing zone 55 of the electrode base body 42. Due to the higher volume energy during the production of the first twenty layers (the proximal underside) of the electrode tip 43 compared to the inventive method, the depth of the mixing zone 45 in the electrode base body 42 is comparatively greater.

[0135] The transition zone 46 in the electrode tip 43 is formed by the mixing of the electrode tip material 43 with the electrode base material 42 during the melting of the first few layers of the electrode tip material 43. The transition zone 46 can be bounded by a second interface 52, up to which a mixing of the chemical elements of the electrode tip 43 and the electrode base 42 and / or increased cracking and / or porosity formation compared to adjacent areas outside the transition zone 46 in the electrode tip 43 is evident. The second interface 52 is arranged parallel to the connection surface, which forms a partial surface of the distal surface 48 of the electrode base 42 and which forms the connection between the electrode base 42 and the electrode tip 43.Pores can be caused by incomplete melting of the electrode tip material 43 and cracks 54 by thermally induced mechanical stresses during the cooling of the first layers on the electrode base body 42, which are caused by different coefficients of thermal expansion of the materials of the electrode base body 42 and the electrode tip 43.

[0136] Due to the higher volume energy during the printing of the first twenty layers of the electrode tip 43, the thickness S of the connection zone 44 is approximately 450 µm higher than in the inventive method and in the inventive spark plug electrodes 1 with printed electrode tips 3, 23.

[0137] Due to the reduced thickness S of the connection zone 4, 24, the service life (the service life) of the spark plug electrodes 1 according to the invention is increased. Furthermore, the spark plug electrodes according to the invention exhibit the following properties: Figures 2 and3 Significantly fewer cracks, a more homogeneous microstructure, and smaller pores (due to reduced evaporation) compared to the state-of-the-art spark plug electrode. Figures 4 and 5 .

[0138] For the spark plug electrodes according to the invention, Figures 2 and 3 This results in individual crack lengths of less than 100 µm and a total crack length in the connection zone 24 of 1000 / 90000 µm / µm² < = 1 / 90 µm / µm² < as well as maximum pore diameters of up to 20 µm. In comparison, conventionally printed spark plug electrodes according to the Figures 4 and 5 Crack lengths of more than 150 µm and a total crack length in the connection zone 44 of 3000 / 150000 µm / µm 2< = 1 / 50 µm / µm 2< as well as maximum pore diameters of up to 40 µm.

[0139] The values ​​were geometrically measured using SEM. Maximum lengths and maximum pore diameters were determined across the entire joining zone. The crack lengths per µm were calculated for each joining procedure from 5 surfaces of the joining zone per height of the joining zone S (24, 44) and a width of 200 µm as the mean value.

[0140] The following is a comparison of spark plug electrodes manufactured according to the invention, in which an IrRh10 alloy is used as the electrode tip on an electrode base body made of Inconel (nickel-based alloy Inconel 600 = commercially defined alloy) analogous to the one described above. Figures 2 and 3 printed using the inventive method described above, with a conventional commercially available spark plug "Denso" GE2-3 M14DDI, (electrode section, spark plug welded IrRh10 tip welded onto Inconel (nickel-based alloy)).

[0141] Figure 6Figure 1 shows four photographs of the spark plug electrode according to the invention after operation of the spark plug electrode with different numbers of ignition processes, which are referred to as events. This results in a wear gradient per 10⁶ events of -1.520 * 10⁻³ mm³ / 10⁶ events, and converted to -3.948 * 10⁻³ mm / 10⁶ events. Figure 7 This shows four photographs of the "Denso" GE2-3 M14DDI spark plug electrode according to the state of the art after operation with different numbers of ignition cycles, referred to as events. This results in a wear gradient of -1.821*10⁻³ mm³ / 10⁶ events and -4.731*10⁻³ mm³ / 10⁶ events.

[0142] The aforementioned measurements were taken on an IAV ignition test bench. This test bench is used to examine ignition systems or components under conditions closely residing in an engine.

[0143] The test bench equipment for carrying out the aforementioned measurements consists of the following components: NGK spark plug connectors with 5 kΩ interference suppression resistor; Beru high-voltage ignition cables (dielectric strength up to 38 kV, 300 mm length / 1 kΩ); Fixed contact from ignition module to ignition cable; Integration of the secondary voltage tap into a housing; Active cooling of the ignition coil; Ignition coil: VW standard ignition coil approx. 90 mJ (active); ECU: IAV FI2re (open ECU); Measurement technology: o Counting of ignition events on the primary side using an industrial counter; o Measurement of the secondary voltage using a PINTEK HVP39pro

[0144] The test chamber is connected to a blower via a closed piping system. The interior of the entire system can be pressurized up to 40 bar using a gas cylinder; in this test, the pressure was 10 bar. All non-explosive gases and gas mixtures are suitable. In this application, synthetic air was used. The flow velocity through the chamber can be precisely controlled between 0 and 30 m / s by adjusting the blower speed; in this test, it was 20 m / s. The gas temperature in the chamber is approximately 30°C, resulting from heat exchange with the surroundings.

[0145] Printed and commercially available material samples with a diameter of 0.7 mm (as is commonly used in spark plugs for passenger car applications) were installed in the test chamber. The plastic used also serves as an insulator to withstand the breakdown voltages of up to approximately 26 kV. These sensors are then inserted into the test chamber's access points.

[0146] For the endurance tests presented here, representative average values ​​were chosen for the number of (ignition) events as well as for the boundary conditions gas density and flow velocity. The following assumptions were made for this purpose: Assumed mileage: 25,000 km; Average speed: 50 km / h; Average engine speed: 2,600 rpm

[0147] Based on these assumptions, this results in 39 million (ignition) events. The events are counted using a pulse counter on the primary side of the ignition coil.

[0148] Transformed to engine conditions, this operating point corresponds to a typical boundary condition of a gasoline engine at the time of ignition.

[0149] A flow velocity of 20 m / s was set to represent spark drifts, which lead to further subsequent breakthroughs after the initial breakthrough sparks until the ignition coil discharges.

[0150] The ignition energy is provided by standard VW ignition coils with approximately 90 mJ. To limit the ignition current (EMC), a spark plug connector with 5 kΩ impedance and Beru high-voltage ignition cables with 1 kΩ impedance are used.

[0151] Before the material samples are placed in the sample holders, they are weighed on a precision balance. They are then placed in the sample holder. This holder is installed in the sample carrier, and the electrode spacing of 0.7 mm is adjusted by sliding the material samples relative to each other. A photograph is then taken using a reflected-light microscope of the sample end face (facing the spark), i.e., the distal front of the electrode tips and the two adjacent sides of the casing, for each sample holder with a material sample. Finally, the sample holders are mounted in the test chamber.

[0152] The test begins with a measurement of the breakdown voltage for each sample holder (one electrode pair). For this purpose, the voltage in the secondary circuit is measured using a probe from PinTEC and recorded at 25 ms. The spark rate is 55.5 [1 / s]. At specific intervals, the endurance test is interrupted for interim evaluation after 8.3, 18.7, 30.8, and 39.1 million events: Secondary voltage measurements and photographic recordings of the wear progression are performed. To prevent excessively high electrode wear and a consequent increase in the electrode gap, the electrode gap resulting from the endurance test is determined using a feeler gauge with an accuracy of ±0.05 mm and, if necessary, readjusted to 0.7 mm.At the end of the endurance test, after 31.9 million events, in addition to measuring the secondary stress, taking photographs, and determining the electrode gap, the material samples are weighed. The weight difference allows the density of the alloy to be used to determine the volume removed. This parameter provides a better indication of the wear condition (wear gradient) than measuring the electrode gap alone.

[0153] The results show a comparable wear gradient with respect to erosion and cycles for the spark plug electrode according to the invention and the conventional "Denso" GE2-3 M14DDI spark plug. The manufacturing process according to the invention therefore does not lead to a reduced service life (lifespan) of the spark plug electrode according to the invention.

[0154] Figure 8Figure 1 shows a light micrograph through a spark plug electrode "Federal Mogul", Z212, 14FR-4 DIU, produced by welding on a precious metal electrode tip, which is comparable to the "Denso" GE2-3 M14DDI spark plug according to the prior art. The spark plug electrode has an electrode base 62 made of Inconel and an electrode tip 63 made of an iridium alloy. The electrode tip 63 is welded to a distal surface 68 of the electrode base 62 by a weld 65. A distal surface 67 of the electrode tip 63 is designed for spark ignition.

[0155] Figure 9Figure 1 shows a flowchart illustrating a method according to the invention. First, an electrode base body made of nickel or a nickel-based alloy, preferably with a clean and flat distal surface, is provided. The electrode base body is then installed in an additive manufacturing device, such as a powder bed-based 3D printer.

[0156] Subsequently, several layers of a base material made of at least one platinum group metal or of a platinum group metal base alloy are applied and each layer is fused individually and successively on the respective substrate with a first volume energy E1 reduced compared to the optimal bonding of the layers.

[0157] Once the desired layer thickness of the bonding zone is reached, further layers of the base material are applied and each individually and successively fused onto the respective support with a volume energy E2 > E1, wherein the second volume energy E2 preferably enables optimal bonding of the layers and is at least 5% higher than the first volume energy E1. A specific shape of the electrode tip can also be created in this process.

[0158] Once the electrode tip has been finished using the additive process, the spark plug electrode produced in this way, with the electrode tip printed on the electrode base, can be removed and optionally cleaned.

[0159] Subsequently, one or more such spark plug electrodes can be installed in a spark plug. Reference symbol list

[0160] 1 Spark plug electrode 2, 22, 42 Electrode base body 3, 23, 43 Electrode tip 4, 24, 44 Joint zone 5, 25, 45 Mixing zone 6, 26, 46 Transition zone 7, 27, 47 Distal front face of electrode tip 8, 28, 48 Distal flat surface of electrode base body 9, 29, 49 Joint surface 10, 30, 50 First interface 12, 32, 52 Second interface 34, 54 Crack 36, 56 Pore 62 Electrode base body 63 Electrode tip 65 Weld 67 Distal front face of electrode tip 68 Distal flat surface of electrode base body Strength of the joint zone E1 First volume energy E2 Second volume energy

Claims

1. A method for producing a spark plug electrode (1), the method comprising the following steps: A) providing an electrode main body (2, 22) made of nickel or of a nickel base alloy; B) applying a layer of a base material made of a platinum group metal or of a platinum group metal base alloy to a surface (8, 28) of the electrode main body (2, 22); C) fusing the layer of the base material with the electrode main body (2, 22) by means of radiation having a volume energy in a lower volume energy range in order to produce a first layer of the platinum group metal or of the platinum group metal base alloy on the surface (8, 28) of the electrode main body (2, 22); D) applying further layers of the base material to the first layer of the platinum group metal or of the platinum group metal base alloy and fusing the further layers of the base material with the underlying, previously fused layer of the platinum group metal or of the platinum group metal base alloy by means of radiation having a volume energy in the lower volume energy range in order to produce a transition zone from the platinum group metal or the platinum group metal base alloy; and E) applying further layers of the base material to the transition zone and fusing the powder with the underlying previously fused layer of the platinum group metal or of the platinum group metal base alloy by means of radiation having a volume energy in an upper volume energy range in order to produce the remaining electrode tip (3, 23) from the platinum group metal or the platinum group metal base alloy, wherein the volume energies in the upper volume energy range are on average at least 5% higher than the volume energies in the lower volume energy range.

2. The method according to claim 1, characterized in that in step C) and in step D), the radiation is passed over the powder at a first hatch distance and in step E), the radiation is passed over the powder at a second hatch distance, the second hatch distance being smaller than the first hatch distance.

3. The method according to either of claims 1 or 2, characterized in that at least 2 and at most 30 layers of the base material are fused in steps C) and D), with the volume energy in the lower volume energy range, and at least 2 layers of the base material are fused in step E), with the volume energy in the upper volume energy range, preferably at least 10 and at most 25 layers of the base material being fused in steps C) and D), with the volume energy in the lower volume energy range, and particularly preferably 20 layers of the base material being fused in steps C) and D), with the volume energy in the upper volume energy range.

4. The method according to any of the preceding claims, characterized in that fusing is carried out using a laser beam or an electron beam, preferably using a laser beam.

5. The method according to any of the preceding claims, characterized in that the volume energies of the lower volume energy range are at most 13.75 J / mm3 and the volume energies of the upper volume energy range are above 14.17 J / mm3, the lower volume energy range preferably ranging from at least 12.5 J / mm3 to at most 13.75 J / mm3 and the upper volume energy range preferably ranging from at least 14.17 J / mm3 to at most 16.7 J / mm3.

6. The method according to any of the preceding claims, characterized in that the base material from which the electrode tip (3, 23) is additively manufactured is a powder, preferably a metal powder, particularly preferably a powder made of a platinum group metal or of multiple platinum group metals or of at least one platinum group metal base alloy.

7. The method according to claim 6, characterized in that the powder has particle sizes in the range between 0.1 µm and a maximum of 100 µm, particularly preferably the powder has particle sizes in the range between 5 µm and a maximum of 50 µm.

8. The method according to any of the preceding claims, characterized in that a spark plug electrode (1) is produced via the method, the spark plug electrode (1) comprising an electrode main body (2, 22) made of nickel or of a nickel base alloy, and an electrode tip (3, 23), the electrode tip (3, 23) consisting, at least on a distal side facing away from the electrode main body (2, 22), of a platinum group metal or a platinum group metal base alloy, the electrode tip (3, 23) being manufactured by melting and solidifying layer by layer on the electrode main body (2, 22) by means of additive manufacturing from a base material containing at least one platinum group metal, the spark plug electrode (1) comprising a connection zone (4, 24) at a transition between the electrode main body (2, 22) and the electrode tip (3, 23), the connection zone (4, 24) being formed by melting and solidifying during additive manufacturing, the connection zone (4, 24) having a thickness (S) of at most 400 µm and the connection zone (4, 24) as well as the electrode main body (2, 22) and the electrode tip (3, 23) outside the connection zone (4, 24) satisfying at least one of requirements A, B and C: A) in the connection zone (4, 24) there is a composition containing at least 1 atom% nickel and at least 1 atom% platinum group metal, and outside the connection zone (4, 24) in the electrode tip (3, 23) there is a composition containing less nickel than in the connection zone (4, 24), and outside the connection zone (4, 24) in the electrode main body (2, 22) there is a composition containing less platinum group metal than in the connection zone (4, 24), B) in the connection zone (4, 24) there is a higher total crack length per µm2 of cracks (34) in a transverse microsection of the spark plug electrode (1) than outside the connection zone (4, 24) in the electrode main body (2, 22) and in the electrode tip (3, 23), and C) in the connection zone (4, 24), there is a larger mean pore diameter than outside the connection zone (4, 24) in the electrode main body (2, 22) and in the electrode tip (3, 23).

9. A spark plug electrode (1) produced via a method according to any of the preceding claims.

10. A spark plug comprising a spark plug electrode (1) according to claim 9.

11. A method for producing a spark plug, in which a spark plug electrode (1) is produced via a method according to any of claims 1 to 8 and is subsequently attached adjacent to a second spark plug electrode (1).

12. The method according to claim 11, characterized in that the spark plug electrode (1) is attached opposite the second spark plug electrode (1).

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