Method and composite preform for the production of a shaped metal product

Abstract

The present invention relates to a method for producing a shaped metal product, wherein a metal preform containing an internal sacrificial element in a cavity is formed to smaller dimensions and the sacrificial element is subsequently removed. The invention further comprises a composite material for producing a shaped metal product and its use. The metal products can be used to manufacture an implantable medical device.

Description

[0001] The present invention relates to a method for producing a shaped metal product, wherein a metal preform containing an internal sacrificial element in a cavity is formed to smaller dimensions and the sacrificial element is subsequently removed. The invention further comprises a composite material for producing a shaped metal product and its use. The metal products can be used to manufacture an implantable medical device. Background of the invention

[0002] Electrodes or electrode components for medical devices, preferably both active and passive implantable medical devices, are generally very small, with the trend in this technical field being towards further miniaturization.

[0003] Conventional medical electrodes or electrode components require very expensive and complex manufacturing equipment and processes with many individual steps. For example, ring electrodes for medical devices are often machined from a bar stock using processes such as turning, and the excess material inside the ring is removed, for example, by electrical discharge machining (EDM). Such conventional manufacturing methods are costly and can reach their limits in terms of the shape of the electrode or a part thereof and the achievable degree of miniaturization.

[0004] EP 3 950 046 A1 describes a method for manufacturing a formed metal product, which involves providing an outer sacrificial element, an inner sacrificial element, and a metal preform arranged between the outer and inner sacrificial elements. After a forming process and the removal of a composite preform disc, the sacrificial elements are removed, leaving the formed metal product. A disadvantage of the described method is that, during the forming process, which is advantageously a drawing process, geometric deformations occur, particularly in the metal preform, which uncontrollably alter the geometry of the final formed metal product.Due to the small dimensions of the formed metal products, which are preferably used as electrodes or electrode components in medical devices, these geometric deformations result in a high production reject rate, as the formed metal products no longer meet the high requirements for low manufacturing tolerances.

[0005] There is therefore a market demand for an improved manufacturing process for such shaped metal products, for example for medical devices, with the lowest possible manufacturing tolerances. In particular, the present invention is directed to providing a method for manufacturing a shaped metal product that offers high flexibility with regard to the dimensions, geometry, and / or shape of a ring electrode or a segmented electrode for a medical device. The method of the present invention can be used, in particular, for the manufacture of electrodes or segmented electrodes for medical devices, especially for electrical stimulation and / or in sensor technology. Tasks

[0006] One object of the present invention is to overcome at least some of the disadvantages arising from the prior art.

[0007] A further object of the invention is to provide a method for producing a shaped metal product which has the highest possible flexibility with regard to the dimensions, geometry and / or shape of the shaped metal products for a medical device and at the same time has the lowest possible manufacturing tolerances, i.e. high process stability. Preferred embodiments of the invention

[0008] The features of the independent claims contribute to at least partially fulfilling at least one of the aforementioned tasks. The dependent claims provide preferred embodiments that contribute to at least partially fulfilling at least one of the tasks.

[0009] A first embodiment of the invention is a method for producing a shaped metal product, preferably for a medical device, in particular for producing an electrode or part of an electrode for a medical device, comprising the following method steps: a) Providing a metal preform with a cavity A; b) Providing, at least, one internal sacrificial element; c) Producing a composite preform by inserting the inner sacrificial element into the cavity A of the metal preform; d) Machining the composite preform produced in process step c) to obtain a form-fitting preform, wherein in the form-fitting preform the metal preform is essentially in a form-fitting manner against the inner sacrificial element; e) Diffusion annealing of the form-fitting preform produced in process step d) to obtain a composite preform with an outer diameter D1; f) Shaping the composite preform obtained in process step e) to obtain a shaped composite preform with a smaller outer diameter D2 than the outer diameter D1 of the composite preform obtained in process step e); g) Separation of a composite preform disc from the shaped composite preform obtained in process step f); h) Removal of the inner sacrificial element from the composite preform disc obtained in process step g), while retaining the formed metal product.

[0010] In a preferred embodiment of the method, in process step b) an outer sacrificial element with a cavity B is additionally provided; process step c) comprises producing a composite preform by inserting the metal preform into the cavity B of the outer sacrificial element and inserting the inner sacrificial element into the cavity A of the metal preform; in process step d) the composite preform is machined such that, in the form-fitting preform, the metal preform essentially forms a positive fit with the inner and outer sacrificial elements; and in process step h) the outer sacrificial element is additionally removed. This embodiment is a second embodiment of the invention, which preferably depends on the first embodiment of the invention.

[0011] In a preferred embodiment of the method, the processing in process step d) comprises a drawing operation, wherein the drawing operation is preferably carried out with a deformation factor between 5% and 40% and / or with a drawing die having an inclusion angle 2α in a range of 5° to 20°, or the processing in process step d) comprises a pressing operation, in particular isostatic pressing. This embodiment is a third embodiment of the invention, which preferably depends on the first or second embodiment of the invention.

[0012] In a preferred embodiment of the method, the diffusion annealing in process step e) is carried out in a temperature range of 450°C to 1200°C, preferably in a temperature range of 450°C to 1150°C. This embodiment is a fourth embodiment of the invention, which preferably depends on one of the preceding embodiments of the invention.

[0013] In a preferred embodiment of the method, the diffusion annealing in process step e) is carried out over a period of time in the range of 15 min to 300 min, preferably in the range of 20 min to 260 min. This embodiment is a fifth embodiment of the invention, which preferably depends on one of the preceding embodiments of the invention.

[0014] In a preferred embodiment of the method, the forming process in step f) comprises a drawing operation, wherein the drawing operation is preferably carried out with a deformation factor between 5% and 40% and / or with a drawing die having an inclusion angle 2α in a range of 5° to 20°. This embodiment is a sixth embodiment of the invention, which preferably depends on one of the preceding embodiments of the invention.

[0015] In a preferred embodiment of the method, the drawing process in process step f) comprises 3 to 50 individual drawing steps. This embodiment is a seventh embodiment of the invention, which preferably depends on the sixth embodiment of the invention.

[0016] In a preferred embodiment of the method, the composite preform is annealed between the individual drawing steps in process step f). This embodiment is an eighth embodiment of the invention, which preferably depends on the sixth or seventh embodiment of the invention.

[0017] In a preferred embodiment of the method, the metal preform comprises a metal selected from the group consisting of platinum, iridium, steel, titanium, hafnium, niobium, cobalt, nickel, chromium, zirconium, rhenium, tungsten, molybdenum, and alloys of at least one of these metals, preferably selected from the group consisting of nickel-cobalt alloys, steel, platinum, and platinum-iridium alloys. This embodiment is a ninth embodiment of the invention, which preferably depends on one of the preceding embodiments of the invention.

[0018] In a preferred embodiment of the method, the composite preform is shaped to have smaller dimensions without substantially altering its overall geometry. This embodiment is a tenth embodiment of the invention, which preferably depends on one of the preceding embodiments of the invention.

[0019] An eleventh embodiment of the invention is a composite preform for the production of a shaped metal product, comprising a) a metal preform with a cavity A', b) an internal sacrificial element which is arranged in the cavity A' of the metal preform, characterized in that an inner diffusion zone with a thickness in the range of 1µm to 15µm is formed at an interface between the metal preform and the inner sacrificial element.

[0020] In a preferred embodiment of the composite preform, the inner diffusion zone comprises an intermetallic phase. This embodiment is a twelfth embodiment of the invention, which preferably depends on the eleventh embodiment of the invention.

[0021] In a preferred embodiment of the composite preform comprising an outer sacrificial element with a cavity B', wherein the metal preform is arranged in the cavity B' of the outer sacrificial element and an outer diffusion zone with a thickness in the range of 1 µm to 15 µm is formed at an interface between the metal preform and the outer sacrificial element. This embodiment is a thirteenth embodiment of the invention, which preferably depends on the eleventh or twelfth embodiment of the invention.

[0022] In a preferred embodiment of the composite preform, the outer diffusion zone comprises an intermetallic phase. This embodiment is a fourteenth embodiment of the invention, which preferably depends on the thirteenth embodiment of the invention.

[0023] A fifteenth embodiment of the invention relates to the use of a composite preform according to one of the eleventh to fourteenth embodiments of the invention for the manufacture of a medical device, preferably for the manufacture of a medical ring electrode or a segmented medical electrode. General

[0024] For each of the embodiments described herein, whose elements "have" or "comprise" a certain feature (e.g., a material), a further embodiment is always considered in which the element in question consists solely of the feature, i.e., it does not include any other components. The word "comprise" or "comprise" is used synonymously with the word "have" or "have" herein.

[0025] If an element in an embodiment is designated in the singular, an embodiment containing several such elements is also considered. The use of a plural term for an element generally also includes an embodiment containing only a single corresponding element.

[0026] Unless otherwise stated or clearly excluded from the context, it is generally possible, and hereby expressly considered, that features of different embodiments may also be present in the other embodiments described herein. Likewise, it is generally considered that all features described herein in connection with a method are also applicable to the products and devices described herein, and vice versa. For the sake of brevity, not all of these considered combinations are explicitly listed in every case. Technical solutions that are known to be equivalent to the features described herein are also generally considered to be within the scope of the invention.

[0027] In this description, range specifications also include values ​​referred to as limits. A specification of the form "in the range of X to Y" with respect to a quantity A therefore means that A can take on the values ​​X, Y, and values ​​between X and Y.

[0028] One-sided limited areas of the type "up to Y" for a size A accordingly mean as a value Y and smaller than Y.

[0029] Some of the described characteristics are linked to the term "essentially." The term "essentially" means that, under real-world conditions and manufacturing techniques, a mathematically exact interpretation of terms such as "superposition," "perpendicular," "diameter," or "parallelism" can never be exact, but only within certain manufacturing tolerances. For example, "essentially perpendicular axes" include an angle of 85 to 95 degrees to each other, and "essentially equal volumes" encompass a deviation of up to 5% by volume. A "device consisting essentially of plastic," for example, comprises a plastic content of ≥95% to ≤100% by weight. "An essentially complete filling of volume B," for example, encompasses a filling of ≥95% to ≤100% by volume of the total volume of B. Detailed description

[0030] A first object of the invention relates to a method for producing a shaped metal product, preferably for a medical device, comprising the following process steps: a) Providing a metal preform with a cavity A; b) Providing an internal sacrificial element; c) Producing a composite preform by inserting the inner sacrificial element into the cavity A of the metal preform; d) Machining the composite preform produced in process step c) to obtain a form-fitting preform, wherein in the form-fitting preform the metal preform is essentially in a form-fitting manner against the inner sacrificial element; e) Diffusion annealing of the form-fitting preform produced in process step d) to obtain a composite preform with an outer diameter D1; f) Shaping the composite preform obtained in process step e) to obtain a shaped composite preform with a smaller outer diameter D2 than the outer diameter D1 of the composite preform obtained in process step e); g) Separation of a composite preform disc from the shaped composite preform obtained in process step f); h) Removal of the inner sacrificial element from the composite preform disc obtained in process step g), while retaining the formed metal product.

[0031] The process serves to produce a shaped metal product, which can preferably be flexibly designed in its dimensions, geometry, and / or shape. With this process, it is possible to uniformly deform a, preferably monolithic, metal preform, particularly in the longitudinal direction, to produce a shaped metal product that has essentially the same geometry and / or shape as the metal preform but with a reduced diameter. This is achieved by forming a composite preform by diffusion annealing. This composite preform comprises the metal preform and at least one internal sacrificial element and can be stretched with low manufacturing tolerances while maintaining its geometry and / or shape to obtain a reduced diameter.

[0032] It goes without saying that the desired final geometry and shape of the formed metal product can be fully produced at the level of the highly scaled metal preform. Thus, the method according to the invention enables access to miniaturized metal products with any desired geometry and / or shape. With conventional methods, such metal products would only be accessible, if at all, through very complex and costly processes.

[0033] In process step a), a metal preform is provided. The metal preform comprises at least one cavity A. The cavity can have any shape when viewed in a radial cross-section. For example, the cavity can have a circular cross-section. Furthermore, the cavity A, when viewed in a radial cross-section, can have, for example, a C-shaped, U-shaped, or V-shaped cross-section. This refers to a shape that resembles the aforementioned character.

[0034] The metal preform can, in principle, have any possible shape. Preferably, the metal preform has a homogeneous shape along a longitudinal axis, i.e., it has a fixed cross-sectional profile.

[0035] The metal preform can have a closed shape, such as a hollow cylindrical shape with a circular cross-section, or an open shape. In one embodiment, the outer shape of the metal preform, seen in a radial cross-section, has either an open or a closed outer shape. An "open outer shape" means that the metal preform includes a cavity A that is not completely enclosed by the material of the metal preform in the radial cross-section. For example, a metal preform with a C-shaped radial cross-section is considered to have an open outer shape, while a metal preform with a completely circular or O-shaped radial cross-section is considered to have a closed outer shape. A closed shape of the metal preform can have a cross-sectional shape selected from the list of oval, polygonal, cubic, rectangular, and round.The metal preform can, for example, consist of a tube enclosing cavity A. Such a tube can, for example, have an oval, polygonal, cubic, rectangular, or circular radial cross-sectional shape.

[0036] In another embodiment, the metal preform has an open outer shape, such as a U-shape, L-shape, T-shape, S-shape, or H-shape. This refers to a shape that resembles the aforementioned characters.

[0037] In another variation of the process, the internal shape of the metal preform, as can be seen in a radial cross-section, is not circular. The "internal shape" of the monolithic metal preform refers to the cross-sectional areas of the metal preform that do not face outwards. For example, the internal shape may have an open recess, depression, indentation, or an open or closed cavity.

[0038] The metal preform can be provided in various ways. For example, the metal preform can be manufactured and provided using one or more processes selected from the group consisting of electrically discharge machining (EDM), additive manufacturing processes such as laser melting or selective electron beam melting, deep hole drilling, turning, and milling.

[0039] The material of the metal preform can be any metal suitable for producing the desired shaped metal product. Preferably, the metal of the metal preform is a biocompatible metal. The term "biocompatible" as used in the present invention refers to a material that a person skilled in the art considers safe to come into contact with a living organism, such as a human being, for a certain period of time, for example, when used in an implantable medical device. A person skilled in the art knows or can determine whether a metal is biocompatible or not. The biocompatible metal can, for example, be a biocompatible metal according to EN ISO 10993.

[0040] Preferably, the metal preform comprises a metal selected from the group consisting of platinum, gold, iridium, steel, titanium, hafnium, niobium, tantalum, cobalt, nickel, chromium, zirconium, rhenium, tungsten, molybdenum, and alloys of at least one of these metals. Preferably, the metal is selected from the group consisting of nickel-cobalt alloys, steel, platinum, platinum-iridium alloys, and Nitinol. Preferably, the steel is stainless steel. Preferably, the nickel-cobalt alloy is MP35N. Preferably, the platinum-iridium alloy is PtIr10 or PtIr20, particularly preferably PtIr10.

[0041] MP35N is a nickel-cobalt alloy containing nickel, cobalt, chromium, and molybdenum. A variant of MP35 is described in the industry standard ASTM F562-13. In one embodiment, MP35 is an alloy containing 33% to 37% Co, 19% to 21% Cr, 9% to 11% Mo, and 33% to 37% Ni.

[0042] PtIr10 is an alloy consisting of 88% to 92% platinum and 8% to 12% iridium. PtIr20 is an alloy consisting of 78% to 82% platinum and 18% to 22% iridium. Nitinol is a shape-memory nickel-titanium alloy with an ordered cubic crystal structure and a nickel content of approximately 45–60%, with the remainder being titanium. Nitinol exhibits good biocompatibility and corrosion resistance.

[0043] Unless otherwise stated, all percentages contained herein are to be understood as mass percentages (weight percent).

[0044] In process step b), an inner sacrificial element is provided. The inner sacrificial element preferably has an outer shape which essentially corresponds to the inner shape, i.e., the cavity A, of the metal preform.

[0045] The material of the inner sacrificial element can be chosen arbitrarily, as long as it can be selectively removed from the composite preform disc by the material of the metal preform. Therefore, the material of the inner sacrificial element must be selected depending on the material of the metal preform.

[0046] In one embodiment of the method, the inner sacrificial element comprises a base metal or a base metal alloy, preferably consisting of a base metal or a base metal alloy. A "base" metal or a "base" metal alloy within the meaning of the present invention is a metal not selected from the group consisting of ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, gold, mercury, and alloys of the aforementioned metals.

[0047] The base metal or base metal alloy is preferably selected from the group consisting of zinc, tin, nickel, copper, steel, and alloys of any of these metals. The base metal or base metal alloy is capable of reacting with acids, preferably with strong acids (e.g., sulfuric acid, hydrochloric acid, nitric acid).

[0048] In a preferred embodiment of the method, the inner sacrificial element comprises a metal selected from the group consisting of nickel, copper, steel and alloys of one of these metals; preferably, the inner sacrificial element consists of one of these metals or of one of these alloys.

[0049] In process step c) of the process, a composite preform is produced by inserting the inner sacrificial element into the cavity A of the metal preform. For example, the metal preform has a hollow cylindrical shape into which an inner sacrificial element in the form of a solid cylinder is inserted. Preferably, the metal preform and the inner sacrificial element have a similar axial extent, so that the cavity A is filled with the inner sacrificial element substantially along its entire length.

[0050] The person skilled in the art knows how the insertion in process step c) can be carried out.

[0051] To produce a shaped metal product with the lowest possible manufacturing tolerance, the combination of the two process steps d) and e) is particularly noteworthy.

[0052] In process step d), the composite preform is machined such that the metal preform and the inner sacrificial element are in essentially positive contact with each other. If more than one inner sacrificial element is present, it is preferred that each inner sacrificial element is in essentially positive contact with the metal preform. An essentially positive contact is achieved when there is essentially no gap or void, such as an air inclusion, between the metal preform and the inner sacrificial element. Gaps between the metal preform and the inner sacrificial element can arise, for example, from a diameter discrepancy between cavity A and the inner sacrificial element.To ensure that the inner sacrificial element can be inserted into cavity A in process step c) smoothly and without damage, such as scratches or abrasions, its outer diameter is preferably slightly smaller than the diameter of cavity A. This means that the inner sacrificial element has an approximate net shape of cavity A. Preferably, the outer diameter of the inner sacrificial element is smaller than the diameter of cavity A of the metal preform by a factor of 0.01% to 5%, more preferably by a factor of 0.01% to 3%. If the element has a non-circular cross-section, its maximum width in a radial cross-section is considered the "diameter".

[0053] In process step d), this discrepancy in diameters is essentially completely eliminated. This can be achieved, for example, through a pressing process, in particular isostatic pressing, or a drawing process, which presses the metal preform onto the inner sacrificial element, thus essentially eliminating all gaps or spaces between the two components.

[0054] In process step e), the form-fitting preform provided in process step d) is subjected to a diffusion annealing step, resulting in a composite preform. The diffusion annealing is designed such that significant solid-state diffusion intentionally occurs between the metal preform and the internal sacrificial element, regardless of whether this is ductile diffusion (i.e., zone solid solution formation) or non-ductile diffusion (i.e., the formation of intermetallic phases).The aim of diffusion annealing is to improve the adhesion of the metal preform to the internal sacrificial element by forming a diffusion zone, preferably with a thickness in the range of 1 µm to 15 µm, between the two components. This ensures that the original shapes of the components are preserved as faithfully as possible during subsequent process steps, particularly the forming process in step f), resulting in the lowest possible manufacturing tolerances in the final product. Without diffusion annealing, internal relative movements of the components can occur, which negatively affect the original shape and / or geometries of the components, especially the metal preform, and thus lead to larger manufacturing tolerances.

[0055] Diffusion annealing should not be confused with an annealing step between two drawing steps, as the latter does not result in significant solid diffusion due to insufficient temperature exposure, both in terms of temperature level and / or duration. The precise temperature ranges and durations at which diffusion annealing occurs depend on the materials used. A temperature range that can induce diffusion annealing with one material combination, for example, may not do so with a second. A person skilled in the art knows under which conditions diffusion annealing occurs, or does not occur, with a given material combination. Therefore, a person skilled in the art can determine whether diffusion annealing or merely an intermediate annealing step should be performed.

[0056] In process step f), the composite preform is transformed into a shaped composite preform, whereby its outer diameter D1 is reduced to an outer diameter D2. This can be done, for example, using an extrusion process. Extrusion is a process in which a block of material is pressed through a die with a desired cross-section in a chamber. The pressing can be carried out, for example, using a mechanical or hydraulic press.

[0057] In process step g), a composite preform disc is separated from the previously obtained shaped composite preform. This separation serves to adjust the desired dimensions, in particular the desired axial length of the final formed metal product. This process step can also include further shaping steps for the resulting composite preform disc. For example, the composite preform disc, especially the portion of the metal preform within the composite preform disc, can be milled or drilled to create desired structural features in the final metal product. For instance, the metal preform material within the composite preform disc can be provided with an axial bore through the composite preform disc, creating an axially extending passage in the final metal product.

[0058] In process step h), the inner sacrificial element is removed while retaining the formed metal product with the desired dimensions, geometry, and / or shape. Removal of the inner sacrificial element can be achieved, for example, by melting, chemical etching, or electroplating. In one embodiment, removal is based on exploiting the different melting points of the materials used. For example, the material of the inner sacrificial element can have a lower melting point than the material of the metal preform and be removed by selective melting. In another preferred embodiment, removal of the inner sacrificial element is achieved by wet chemical etching, for example, using a strong acid such as nitric acid, sulfuric acid, hydrochloric acid, or a mixture of these acids.

[0059] Preferably, wet chemical etching is carried out using a strong, preferably aqueous, acid, such as nitric acid, sulfuric acid, hydrochloric acid, or a mixture of these acids, at a temperature in the range of 18 °C to 120 °C. Preferably, process step h) is carried out under the influence of ultrasound, preferably in an ultrasonic bath. It may be preferred to carry out process step h) under reduced pressure.

[0060] Preferably, in addition to the inner sacrificial element, the diffusion zone formed by the diffusion annealing is also removed, preferably using the same method.

[0061] For the production of a shaped metal product with a circular outer surface, the exclusive use of one or more internal sacrificial elements may be sufficient. If a shaped metal product with a non-circular outer surface is to be produced, it is preferred to additionally use an outer sacrificial element. For example, it may be preferable to use an outer sacrificial element if the metal preform has a protrusion or a depression, such as a fin or a groove, on or in its outer surface. The outer sacrificial element thus serves to protect the outer surface of the metal preform during the manufacturing process, particularly if it is non-circular.

[0062] One embodiment of the method is characterized in that, in process step b), an outer sacrificial element with a cavity B is additionally provided, process step c) comprises producing a composite preform by inserting the metal preform into the cavity B of the outer sacrificial element and inserting the inner sacrificial element into the cavity A of the metal preform, in process step d) the composite preform is processed in such a way that, in the form-fitting preform, the metal preform essentially forms a positive fit with the inner sacrificial element and the outer sacrificial element, and in process step h) the outer sacrificial element is additionally removed.

[0063] The method according to this embodiment comprises the following process steps: a) Providing a metal preform with a cavity A; b) Providing an outer sacrificial element with a cavity B and an inner sacrificial element; c) Producing a composite preform by inserting the metal preform into cavity B of the outer sacrificial element and inserting the inner sacrificial element into cavity A of the metal preform; d) Machining the composite preform produced in process step c) to obtain a form-fitting preform, wherein in the form-fitting preform the metal preform is essentially in a form-fitting manner against the inner sacrificial element and the outer sacrificial element; e) Diffusion annealing of the form-fitting preform produced in process step d) to obtain a composite preform with an outer diameter D1; f) Shaping the composite preform obtained in process step e) to obtain a shaped composite preform with a smaller outer diameter D2 than the outer diameter D1 of the composite preform obtained in process step e); g) Separation of a composite preform disc from the shaped composite preform obtained in process step f); h) Removal of the outer sacrificial element and the inner sacrificial element from the composite preform disc obtained in process step g), retaining the formed metal product.

[0064] Preferably, the outer sacrificial element completely surrounds the metal preform in a radial cross-sectional view. The outer sacrificial element can have a hollow cylindrical shape. The outer shape of the outer sacrificial element preferably has a circular or oval cross-section. The inner shape of the outer sacrificial element, i.e., the cavity B, can have any shape, but preferably corresponds substantially to a negative of the outer shape of the metal preform.

[0065] Preferably, the inner sacrificial element and the outer sacrificial element comprise the same material; more preferably, the inner sacrificial element and the outer sacrificial element consist of the same material.

[0066] As already mentioned, the machining in process step d) can be carried out in various ways to achieve a substantially positive fit of the metal preform to the inner sacrificial element, and, if present, to the outer sacrificial element. For example, the machining can be carried out by a pressing operation, preferably using an isostatic press.

[0067] One embodiment of the method is characterized in that the processing in process step d) comprises a drawing operation, for example, a wire drawing operation. Preferably, the drawing operation is carried out with a deformation factor between 5% and 40%, more preferably between 10% and 30%. It is further preferred that the drawing operation is carried out with a drawing die having an inclusion angle 2α in a range of 5° to 20°, more preferably from 5° to 15°. It is further preferred that the drawing operation is carried out with a deformation factor between 5% and 40%, more preferably between 10% and 30%, and with a drawing die having an inclusion angle 2α in a range of 5° to 20°, more preferably from 5° to 15°.

[0068] Due to the drawing process, the form-fitting preform has a greater length and a smaller outer diameter compared to the composite preform.

[0069] Depending on the material combination of metal preform, inner sacrificial element and, if present, outer sacrificial element, the diffusion annealing in process step e) can take place in different temperature ranges.

[0070] One embodiment of the method is characterized in that the diffusion annealing in process step e) is carried out in a temperature range of 450°C to 1200°C, preferably in a temperature range of 450°C to 1150°C.

[0071] Depending on the material combination of metal preform, inner sacrificial element and, if present, outer sacrificial element, the diffusion annealing in process step e) can take place over different time periods.

[0072] One embodiment of the method is characterized in that the diffusion annealing in process step e) is carried out over a period of time in a range of 15 min to 300 min, preferably in a range of 20 min to 260 min.

[0073] Diffusion annealing can also be divided into two or more individual steps, each of which is carried out for a period of time in the range of 15 min to 300 min, preferably in the range of 20 min to 260 min. For example, the diffusion annealing takes place in two individual steps, each of which is carried out at a temperature of 800 °C for a period of time of 30 min.

[0074] To a certain extent, the temperature used and the duration of the diffusion annealing are related. For example, the duration of a diffusion anneal can be reduced if it is carried out at higher temperatures.

[0075] As already described, the forming process in step f) can be carried out in different ways.

[0076] One embodiment of the method is characterized in that the forming process in step f) includes a drawing operation. The drawing operation can comprise a single drawing step or a plurality, i.e., at least two, preferably 3 to 50, individual drawing steps. Preferably, the drawing operation is carried out with a deformation factor between 5% and 40%, more preferably between 10% and 30%, per individual drawing step. Preferably, the drawing operation is carried out with a drawing die having an inclusion angle 2α in a range of 5° to 20°. Most preferably, the drawing operation is carried out with a deformation factor between 5% and 40%, more preferably between 10% and 30%, per individual drawing step and with a drawing die having an inclusion angle 2α in a range of 5° to 20°. It is known to those skilled in the art how such a drawing operation can be carried out.

[0077] One embodiment of the method is characterized in that the composite preform is annealed in process step f) between at least one, and preferably between all individual drawing steps if more than one drawing step is performed. This annealing serves to largely eliminate material stresses that may be present in the composite preform after a drawing step. The annealing must be selected such that essentially no solid diffusion occurs between the metal preform and the inner sacrificial element, and, if present, also the outer sacrificial element. The exact annealing conditions depend on the materials used, taking into account the degree of deformation of the drawing step, and are known to those skilled in the art.

[0078] The shaped metal products manufactured according to the inventive method are preferably suitable for use in a medical device, in particular in an active implantable medical device. Preferred active medical devices include, for example, pacemakers, cardiac defibrillators, neurostimulators, cochlear implants, implantable cardioverters, nerve, brain, organ or muscle stimulators, as well as implantable monitoring devices, hearing aids, retinal implants, muscle stimulators, implantable drug pumps, artificial hearts, bone growth stimulators, prostate implants, gastric implants or similar devices. Preferably, the active medical device is a pacemaker, a system for electroporation (pulse-field ablation), or a neuromodulator.

[0079] Preferably, the shaped metal product is used as an electrode, preferably as a ring electrode or as a segmented electrode, in one of the medical devices described above.

[0080] Another aspect of the invention relates to a composite preform for the production of a shaped metal product, comprising a) a metal preform with a cavity A', b) an internal sacrificial element which is arranged in the cavity A' of the metal preform, characterized in that an inner diffusion zone with a thickness in the range of 1 µm to 15 µm is formed at an interface between the metal preform and the inner sacrificial element.

[0081] The composite preform is preferably produced using an embodiment of the method described above.

[0082] The composite preform has an internal diffusion zone at an interface between the metal preform and the inner sacrificial element, preferably at the entire interface between the metal preform and the inner sacrificial element. This internal diffusion zone has a thickness in the range of 1 µm to 15 µm, preferably in the range of 1 µm to 10 µm, and most preferably in the range of 2 µm to 9 µm. The internal diffusion zone comprises elements of both the metal preform and the inner sacrificial element, preferably in the form of a ductile diffusion zone, i.e., comprising solid solutions of the elements, or a non-ductile diffusion zone, i.e., comprising intermetallic phases of the elements.The inner diffusion zone ensures improved adhesion of the metal preform and the inner sacrificial element, so that the original shapes of the components remain as unchanged as possible through the subsequent process steps for manufacturing the formed metal product, and a formed metal product with the lowest possible manufacturing tolerance can be produced.

[0083] The described thickness ranges of the inner diffusion zone have proven advantageous, as they represent a good compromise between sufficient adhesion of the metal preform to the inner sacrificial element and the smallest possible diffusion zone thickness. Thinner diffusion zones are easier to remove and result in tighter manufacturing tolerances during removal. Preferably, the final formed metal product has essentially no inner diffusion zone.

[0084] If the composite preform has more than one internal sacrificial element, it is preferred that an internal diffusion zone is formed between all internal sacrificial elements and the metal preform.

[0085] A person skilled in the art knows how to determine a diffusion zone and its thickness. For example, the diffusion zone and its thickness in a cross-section of the composite preform can be determined using energy-dispersive X-ray spectroscopy (EDX).

[0086] One embodiment of the composite preform is characterized in that the inner diffusion zone comprises an intermetallic phase.

[0087] One embodiment of the composite preform is characterized in that the composite preform comprises an outer sacrificial element with a cavity B', wherein the metal preform is arranged in the cavity B' of the outer sacrificial element and an outer diffusion zone with a thickness in a range of 1 µm to 15 µm, preferably in a range of 1 µm to 10 µm, most preferably in a range of 2 µm to 9 µm, is formed at an interface between the metal preform and the outer sacrificial element.

[0088] The outer diffusion zone comprises both the elements of the metal preform and the outer sacrificial element, preferably in the form of a ductile diffusion zone, i.e., comprising solid solutions of the elements, or a non-ductile diffusion zone, i.e., comprising intermetallic phases of the elements. The outer diffusion zone ensures improved adhesion between the metal preform and the outer sacrificial element, so that the original shapes of the components remain as unchanged as possible during the subsequent process steps for manufacturing the formed metal product, and a formed metal product with the lowest possible manufacturing tolerance can be produced.

[0089] The described thickness ranges of the outer diffusion zone have proven advantageous, as they represent a good compromise between sufficient adhesion of the metal preform to the outer sacrificial element and the smallest possible diffusion zone thickness. Thinner diffusion zones are easier to remove and result in tighter manufacturing tolerances during removal. Preferably, the final formed metal product has essentially no outer diffusion zone.

[0090] If the composite preform has more than one outer sacrificial element, it is preferred that an outer diffusion zone is formed between all outer sacrificial elements and the metal preform.

[0091] One embodiment of the composite preform is characterized in that the outer diffusion zone comprises an intermetallic phase.

[0092] Another aspect of the invention relates to the use of the aforementioned composite preform for the manufacture of a medical device, preferably for the manufacture of a medical ring electrode or a segmented medical electrode. Example

[0093] An exemplary shaped metal product was manufactured using the following process steps and under the following conditions.

[0094] A cylindrical outer sacrificial element, 230 mm long, with an outer diameter of 14.5 mm and an internal square cavity B with an edge length of 7.91 mm, was manufactured from a block of nickel using electrical discharge machining (EDM). Two inner sacrificial elements, one rectangular (3.78 x 3.78 mm) and one isosceles triangular (5.87 x 4.15 mm), were also manufactured from the same material using EDM. Both had a length of 230 mm.

[0095] A rectangular metal preform with a square cavity A1 and an isosceles triangular cavity A2 was manufactured from a platinum-iridium alloy with a weight content of 10% iridium (Ptlr10) using electrical discharge machining (EDM). The outer edge length of the metal preform was 7.91 x 7.91 mm, the outer edge length of cavity A1 was 3.81 mm, and the triangular cavity A2 had an edge length of 5.9 x 4.18 mm. The length of the metal preform was 230 mm.

[0096] The two inner sacrificial elements were arranged in the cavity A1 and A2 of the metal preform, and these were arranged in the cavity B of the outer sacrificial element to obtain a composite preform.

[0097] The composite preform was subjected to a pressing process using a drawing operation, which essentially eliminated the gap between the components. This pressing process transformed the composite preform into a form-fitting preform. Subsequently, the form-fitting preform was diffusion annealed at a temperature of 600 °C for 120 minutes, resulting in a composite preform. This process formed a diffusion zone approximately 5 µm thick between the metal preform and the adjacent sacrificial element.

[0098] The composite preform was subjected to a drawing process. In a first drawing step, the diameter of the composite preform was reduced from 13.1 mm to a final diameter of 1.74 mm in multiple drawing steps. After each 60% reduction in the total degree of deformation, the composite was annealed for 30 minutes at 500°C to restore the material to a ductile state for the subsequent forming steps.

[0099] A shaped metal product was produced by separating a composite preform disc from the shaped composite preform and removing the sacrificial elements by etching, as described in US 2019 / 0255317A1.

[0100] As a comparative example, another shaped metal product was manufactured using the above-described method and with the same dimensions, omitting the diffusion annealing step.

[0101] The following table compares the dimensions of the example and the comparison example, and a shrinkage factor was calculated from the respective dimensions of the starting components and the measured dimensions of the formed composite preform (once with and once without diffusion annealing). This shrinkage factor calculated by measurements was compared against a theoretical shrinkage factor derived from the initial and final dimensions of the outer sacrificial element. Table 1: Dimensions of the comparison example and the exemplary shaped metal product. Comparative example (shaped composite preform without diffusion annealing) Shrinkage factor comparison example Example (shaped composite preform with diffusion annealing) Shrinkage factor example Outer diameter of the sacrificial element 1,740 mm 8,33 / 1 1,740 mm 8,33 / 1 Outer edge metal preform 0.952 mm 8,31 / 1 0.951 mm 8,32 / 1 Edge length 1 rectangular inner sacrificial element 0.458 mm 8,25 / 1 0.454 mm 8,32 / 1 Edge length 2 rectangular inner sacrificial element 0.458 mm 8,25 / 1 0.454 mm 8,32 / 1 Edge length 1 isosceles triangular inner sacrifice element 0.710 mm 8,26 / 1 0.705 mm 8,33 / 1 Edge length 2 isosceles triangular inner sacrificial element 0.504 mm 8,23 / 1 0.499 mm 8,32 / 1 Edge length 3 isosceles triangular inner sacrificial element 0.504 mm 8,23 / 1 0.499 mm 8,32 / 1 Smallest shrinkage factor 8.23 / 1 8,32 / 1 Largest shrinkage factor 8.33 / 1 8,33 / 1 Average shrinkage factor 8.27 / 1 8,32 / 1

[0102] Table 1 shows the improved manufacturing tolerance of the process with diffusion annealing compared to the same process without diffusion annealing. The theoretical shrinkage factor is 8.33, which corresponds to the ratio of the initial to the final diameter of the outer sacrificial element (see first row with measured values). The process stability shown here is calculated from the ratio of the minimum to the maximum actually achieved shrinkage factor. The test setup without diffusion annealing results in a process stability of 98.7%. In comparison, the test setup described here with diffusion annealing results in a process stability of 99.9%. Figures

[0103] The invention is further illustrated below by means of figures. The invention is not limited to the figures.

[0104] The Fig.Figures 1 to 6 illustrate an exemplary process for manufacturing a shaped metal product.

[0105] They show Fig. 1 an exemplary metal preform with a cavity A for the production of a shaped metal product, Fig. 2 a composite preform comprising the metal preform made of Fig. 1 as well as an inner sacrificial element and an outer sacrificial element, Fig. 3 a by machining the composite preform from Fig. 2. Retained form-fitting sacrificial element, Fig. 4 a composite preform produced by diffusion annealing Fig. 3 obtained composite preforms, Fig. 5 a composite preform formed by shapes Fig. 4 received shaped composite preforms, Fig. 6 the shaped metal product, and Fig.7 An exemplary flowchart of a process for manufacturing a shaped metal product. Description of the characters

[0106] Fig. Figure 1 shows an exemplary metal preform 200 for the production of a shaped metal product in a front view along a longitudinal axis of the metal preform 200. In the embodiment shown, the metal preform 200 has a hollow cylindrical shape which encloses a cylindrical cavity A 210.

[0107] The metal preform 200 in the embodiment shown is made of a platinum-iridium alloy with a weight fraction of 90 weight percent platinum and 10 weight percent iridium (PtIr10).

[0108] Fig. Figure 2 shows a composite preform 400 as an intermediate product in the process for manufacturing the shaped metal product in a front view. The composite preform 400 comprises the metal preform 200 made of Fig.1, wherein within the cavity A 210 (see Fig. 1) A cylindrical inner sacrificial element 300 is arranged in the metal preform 200. The composite preform 400 also has a hollow cylindrical outer sacrificial element 350, wherein the metal preform 200 and the inner sacrificial element 300 are arranged within a cavity B 360 of the outer sacrificial element. A gap 410 exists between the metal preform 200 and the inner sacrificial element 300, as well as between the metal preform 200 and the outer sacrificial element 350, which results from a diameter discrepancy between the components 200, 300, 350 of the composite preform 400. The diameter discrepancy allows for simplified and non-destructive assembly of components 200, 300, and 350 to form the composite preform 400. The inner sacrificial element 300 and the outer sacrificial element 350 are made of nickel in the illustrated configuration.

[0109] Fig.Figure 3 shows a result of machining the composite preform 400 from Fig. 2. Form-fitting preform 500 obtained. In contrast to the composite preform 400 made of Fig. 2. The individual components 200, 300, 350 are positively engaged with one another, i.e., the inner sacrificial element 300 is positively engaged with the metal preform 200, and the metal preform 200 is positively engaged with the outer sacrificial element 350. A positive engagement exists if there is essentially no gap between the components 200, 300, 350 (cf. Fig. 2) is present. The machining does not essentially result in a material-bonded connection between components 200, 300, 350.

[0110] In the embodiment shown, the form-fitting preform 500 was obtained by isostatic pressing of the composite preform 400.

[0111] Fig. Figure 4 shows a form-fitting preform 500 made by diffusion annealing. Fig.3. The resulting composite preform 600. Diffusion annealing resulted in the formation of an inner diffusion zone 610 between the metal preform 200 and the inner sacrificial element 300, and an outer diffusion zone 620 between the metal preform 200 and the outer sacrificial element 350. In the embodiment shown, the diffusion annealing took place at a temperature of 650 °C for a period of 120 minutes, resulting in the formation of a diffusion zone 610, 620 with a thickness of 5 µm. Due to the material combination of the metal preform 200 and the two sacrificial elements 300, 350, the diffusion zones 610, 620 each comprise solid solutions.

[0112] The composite preform 600 has an outer diameter D1 650.

[0113] Fig. Figure 5 shows a shaped composite preform 700, produced by forming the composite preform 600 from Fig. 4. Due to the forming process, the formed composite preform 700 has a diameter of 650 mm compared to the outer diameter D1 (see below). Fig. 4) reduced outer diameter D2 750. The formed composite preform 700 is "stretched" along the longitudinal axis compared to the composite preform 600, i.e., it has a greater axial extent than the composite preform 600. In the embodiment shown, the forming was carried out by a drawing process.

[0114] Fig. Figure 6 shows the manufactured shaped metal product 100. The shaped metal product 100 was made from the in Fig. The shaped composite preform 700 shown in Figure 5 was produced by separating a composite preform disc with the desired axial extent from the shaped composite preform 700 and subsequently the inner sacrificial element 300, the outer sacrificial element 350, the inner diffusion zone 610 and the outer diffusion zone 620 (see Figure 5). Fig. 4 and Fig. 5) was removed. In the design shown, these elements were etched away using wet chemical methods.

[0115] Fig.Figure 7 shows a flowchart of an exemplary process 800 for the production of a shaped metal product 100 comprising process steps 810 to 880.

[0116] In process step 810, a metal preform 200 with a cavity A 210 is provided. The metal preform 200 can have only one cavity A 210 or more than one. If several cavities A 210 are present, they can be isolated from each other or connected to each other.

[0117] In process step 820, at least one inner sacrificial element 300 is provided. The inner sacrificial element 300 preferably has a different material than the metal preform 200. In one embodiment of process step 820, this also includes providing at least one outer sacrificial element 350 with a cavity B 360. The outer sacrificial element 350 preferably has a different material than the metal preform 200, and preferably the same material as the inner sacrificial element 300.

[0118] In process step 830, a composite preform 400 is produced by inserting or sliding the inner sacrificial element 300 into the cavity A 210 of the metal preform 200. If an outer sacrificial element 350 is used, the metal preform 200 and the inner sacrificial element 300 are also arranged in the cavity B 360 of the outer sacrificial element 350. To facilitate the production of the composite preform 400, the diameters of the components 200, 300, and, if present, 350 are selected such that a gap 410 exists between them.

[0119] In process step 840, the composite preform 400 is machined to obtain a positive-locking preform 500. In the positive-locking preform, the gap 410 between the metal preform 200 and the inner sacrificial element 300, and, if present, between the metal preform 200 and the outer sacrificial element 350, is substantially eliminated by the machining. Preferably, the machining is a pressing operation from the outside onto the composite preform 400 and / or a drawing operation on the composite preform 400. The machining serves in particular to prepare process step 850.

[0120] In process step 850, the form-fitting preform 500 undergoes diffusion annealing to obtain a composite preform 600. The composite preform has an inner diffusion zone 610 between the metal preform 200 and the inner sacrificial element 300. If an outer sacrificial element 350 is used, the composite preform 600 has an outer diffusion zone 620 between the metal preform and the outer sacrificial element 350. The inner diffusion zone 610 and, if present, the outer diffusion zone 620 improve the adhesion of the components 200, 300, and, if present, 350, so that their geometry is essentially undistorted by the subsequent process steps and a formed metal product 100 can be produced with the lowest possible manufacturing tolerances.

[0121] In process step 860, the composite preform 600 is formed into a formed composite preform 700. In this process, the outer diameter D1 650 of the composite preform 600 is reduced to an outer diameter D2 750 of the formed composite preform 700. The forming preferably includes a drawing operation.

[0122] In process step 870, a composite preform disc is separated from the formed composite preform 700 with a desired thickness of the formed metal product 100. The separation preferably includes cutting, for example, by means of a laser. Preferably, a plurality, for example 50 to 10,000, of composite preform discs can be separated from a single composite preform 700. This simplifies the production of the formed metal product 100 and thus reduces manufacturing costs.

[0123] In a process step 880, the inner sacrificial element 300 and, if present, the outer sacrificial element 350, preferably including all diffusion zones 610, 620, are removed from the composite preform disc, yielding the formed metal product 100. Preferably, the removal includes an etching process using an acid or a base. Reference sign 100 formed metal products 200 metal preforms 210 Cavity A 300 inner sacrificial element 350 outer sacrificial element 360 Cavity B 400 compound preform 410 gap 500 form-fitting preforms 600 composite preform 610 inner diffusion zone 620 outer diffusion zone 650 outer diameter D1 700 shaped composite preforms 750 outer diameter D2 800 procedures 810 Provide metal preform 820 Provide inner sacrificial element 830 Manufacturing compound preform 840 Processing compound preform 850 Diffusion annealing 860 shapes 870 Detach 880 Remove

Claims

[1] Method (800) for producing a shaped metal product (100), preferably for a medical device, comprising the following process steps: a) Providing (810) a metal preform (200) with a cavity A (210); b) Providing (820) an inner sacrificial element (300); c) Producing (830) a composite preform (400) by inserting the inner sacrificial element (300) into the cavity A (210) of the metal preform (200); d) Machining (840) the composite preform (400) produced in process step c) to obtain a form-fitting preform (500), wherein in the form-fitting preform (500) the metal preform (200) is substantially in contact with the inner sacrificial element (300); e) Diffusion annealing (850) of the form-fitting preform (500) produced in process step d) to obtain a composite preform (600) with an outer diameter D1 (650); f) Shaping (860) the composite preform (600) obtained in process step e) to obtain a shaped composite preform (700) with a smaller outer diameter D2 (750) than the outer diameter D1 (650) of the composite preform (600) obtained in process step e); g) Separating (870) a composite preform disc from the shaped composite preform (700) obtained in process step f); h) Removal (880) of the inner sacrificial element (300) from the composite preform disk obtained in process step g) while retaining the formed metal product (100). [2] Method (800) according to claim 1, wherein in method step b) an outer sacrificial element (350) with a cavity B (360) is additionally provided, method step c) comprises producing (830) a composite preform (400) by inserting the metal preform (200) into the cavity B (360) of the outer sacrificial element (350) and inserting the inner sacrificial element (300) into the cavity A (210) of the metal preform (200), in method step d) the composite preform (400) is processed (840) such that in the form-fitting preform (500) the metal preform (200) is substantially form-fitting to the inner sacrificial element (300) and to the outer sacrificial element (350), and in method step h) the outer sacrificial element (350) is additionally removed (880). [3] Method (800) according to claim 1 or 2, wherein the processing (840) in process step d) comprises a drawing operation, wherein the drawing operation is preferably carried out with a deformation factor between 5% and 40% and / or with a drawing die having an inclusion angle 2α in a range of 5° to 20° or wherein the processing (840) in process step d) comprises a pressing operation, in particular isostatic pressing. [4] Method (800) according to one of the preceding claims, wherein the diffusion annealing (850) in process step e) is carried out in a temperature range of 450 °C to 1200 °C, preferably in a temperature range of 450 °C to 1150 °C. [5] Method (800) according to one of the preceding claims, wherein the diffusion annealing (850) in process step e) is carried out over a period of time in a range of 15 min to 300 min, preferably in a range of 20 min to 260 min. [6] Method (800) according to one of the preceding claims, wherein the forming (860) in process step f) comprises a drawing operation, wherein the drawing operation is preferably carried out with a deformation factor between 5% and 40%, preferably between 10% and 30% per individual drawing step and / or with a drawing die having an inclusion angle 2α in a range of 5° to 20°. [7] Method (800) according to claim 6, wherein the drawing process in method step f) comprises 3 to 50 individual drawing steps. [8] Method (800) according to one of claims 6 or 7, wherein the composite preform (600) is annealed in process step f) between the individual drawing steps of the drawing process. [9] Method (800) according to any one of the preceding claims, wherein the metal preform (200) comprises a metal selected from the group consisting of platinum, gold, iridium, steel, titanium, hafnium, niobium, cobalt, nickel, chromium, zirconium, rhenium, tungsten, molybdenum and alloys of at least one of these metals, preferably selected from the group consisting of nickel-cobalt alloys, steel, platinum and platinum-iridium alloys. [10] Method (800) according to one of the preceding claims, wherein the composite preform (600) is formed in the method (800) such that it assumes a smaller dimension without substantially changing its overall geometry. [11] Composite preform (600) for the production of a shaped metal product (100), comprising a) a metal preform (200) with a cavity A', b) an inner sacrificial element (300) which is arranged in the cavity A' of the metal preform (200), characterized by, that an inner diffusion zone (610) with a thickness in a range of 1 µm to 15 µm is formed at an interface between the metal preform (200) and the inner sacrificial element (300). [12] Composite preform (600) according to claim 11, wherein the inner diffusion zone (610) comprises an intermetallic phase. [13] Composite preform (600) according to claim 11 or 12, comprising an outer sacrificial element (350) with a cavity B', wherein the metal preform (200) is arranged in the cavity B' of the outer sacrificial element (350) and an outer diffusion zone (620) with a thickness in a range of 1 µm to 8 µm is formed at an interface between the metal preform (200) and the outer sacrificial element (350). [14] Composite preform (600) according to claim 13, wherein the outer diffusion zone (620) comprises an intermetallic phase. [15] Use of a composite preform (600) according to any one of claims 11 to 14 for the manufacture of a medical device, preferably for the manufacture of a medical ring electrode or a segmented medical electrode.

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