3D printed metal component

Abstract

There is provided a 3D printed metal component having a metal body and an internal cavity within said metal body, the component comprising a 3D printed electrode within the internal cavity, the 3D printed electrode having lower density than the metal body.

Description

[0001] 3D PRINTED METAL COMPONENT

[0002] FIELD OF THE INVENTION

[0003] The present application relates generally to 3D printed metal components, and in particular to 3D printed metal components having a metal body and an internal cavity within said metal body.

[0004] BACKGROUND OF THE INVENTION

[0005] 3D printing includes a collection of manufacturing processes that affords layer-by-layer growth of three-dimensional physical objects from a digital design. The inherent simplicity of 3D printing can efficiently afford production of objects having complex 3D geometries.

[0006] 3D printing can successfully be adopted to print 3D metal components. However, as- fabricated metal components have high surface roughness, which can significantly impair their mechanical characteristics and shelf-life. 3D printed metal components must therefore undergo surface finish procedures before being implemented into devices of practical use. Smooth surface finish of metal components is beneficial to prolong the service lifespan of the component, as well as necessary for applications demanding tight geometric tolerances. Also, smooth surfaces can prevent corrosion and improve the resistance to fatigue failure of the component.

[0007] There exist various polishing procedures for the post-print reduction of the surface roughness of an as-printed metal component. Those procedures include electropolishing, chemical polishing, and mechanical polishing. While existing procedures are for the most part effective to polish exterior surfaces of 3D printed metal components, the polishing of the surface of inner cavities and crevices of components having complex geometries is challenging. Mechanical polishing is inevitably limited by the dimensions of existing machining tools. This makes it complex and extremely impractical, if not impossible, to achieve homogeneous polishing of internal surfaces of cavities with intricate geometries.

[0008] On the other hand, chemical polishing can be successfully implemented to polish cavities with simple geometry. Nevertheless, chemical polishing can also be ineffective due to the limited ability of polishing solutions to permeate the internal volume of components having complex geometries.

[0009] Electropolishing may also be hindered by the limited reach of electrical field within the electropolishing solution, even when said solution homogeneously permeates the cavities of a 3D component with complex geometries. In some instances, for example when a metal component has a simple geometry (e.g. a straight metal pipe), electropolishing of the inner surface of the component may be achieved by inserting an electrode into the internal cavity of the component, which will act as the cathode during electropolishing. However, that approach is not immediately applicable to 3D printed metal components having geometries that depart, even minimally, from that of a simple straight metal pipe.

[0010] There remains therefore an opportunity to address one or more problems associated with post-printing polishing procedures of 3D printed metal components.

[0011] SUMMARY OF THE INVENTION

[0012] The present invention provides a 3D printed metal component having a metal body and an internal cavity within said metal body, the component comprising a 3D printed electrode within the internal cavity, the 3D printed electrode having lower density than the metal body.

[0013] The present invention also provides a method of making a metal component, the method comprising 3D printing (i) a metal body having an internal cavity therein and (ii) an electrode within the internal cavity, the electrode having lower density than the metal body. The 3D printed electrode in the component of the invention can effectively act as built-in electrode. By having a 3D printed electrode within an internal cavity, the 3D printed metal component can undergo straightforward and effective electropolishing of the surface of said cavity when the electrode is used as a cathode in an electropolishing procedure. Also, since the electrode is 3D-printed, the electrode can be advantageously designed to have geometric shape and dimensions that are conformal to those of the internal cavity, ensuring that subsequent electropolishing can be thorough and homogeneous throughout the entire surface of the cavity. In addition, the lower density of the 3D printed electrode relative to that of the metal body affords straightforward and effective removal of the electrode after electropolishing, for example by mechanical breakage, with minimal risk of residual electrode material remaining trapped within the cavity.

[0014] The 3D printed metal components of the invention is therefore highly suitable to undergo effective and homogeneous electropolishing of the entire surface of any of its internal cavities, irrespective of the cavities' geometry and dimensions.

[0015] In some embodiments, the electrode and the metal body are co-printed. By being "coprinted", the electrode and the metal body result from being fabricated during the same printing session. As a result, the 3D printed metal component can undergo effective electropolishing of its internal surfaces shortly after printing.

[0016] Advantageously, the electrode can have any shape and geometry that is conducive to effective and homogeneous electropolishing of the surface of the internal cavities of the metal component. In that regard, it was found that increasing the surface area of the electropolishing electrode can effectively improve electropolishing efficiency. Accordingly, the electrode of the invention can be characterised by higher surface area than conventional electropolishing cathodes. In some embodiments, the 3D printed electrode has a surface area of at least 300 mm2 / g. Large surface areas of the 3D printed electrode may be provided by the electrode having a complex geometrical shape. For example, the 3D printed electrode may have a lattice structure. The 3D printed metal component of the invention can undergo electropolishing of an internal cavity by operating the 3D printed electrode as cathode and the metal body as anode in an electropolishing procedure.

[0017] Depending on the specific design of the 3D printed component, prior to electropolishing the 3D electrode may need to be electrically insulated from the metal body. For instance, the electrode and the metal body may be 3D printed to be connected to one another, for example by sacrificial connective metal, resulting in a continuous discrete 3D metal component. In those instances, the electrode would have to be physically disconnected from the metal body before the electropolishing, for example by rupturing any sacrificial connective metal between the electrode and the metal body. Accordingly, in some embodiments the method of making a metal component may comprise electrically insulating the electrode from the metal body.

[0018] The method of the invention may also therefore comprise a step of electropolishing the internal cavity. Specifically, said electropolishing comprises (i) using the 3D printed electrode as cathode, and (ii) flowing an electropolishing solution through the internal cavity.

[0019] By flowing the electropolishing solution through the internal cavity of the metal component, electropolishing efficiency can significantly be improved over conventional electropolishing procedures, for example those that use a static electropolishing solution (e.g. by merely immersing the component into the solution, or by sealing the solution within the cavity).

[0020] Flowing the electropolishing solution through the internal cavity of the metal component during electropolishing is believed to be unique in its own right. Accordingly, the present invention is also directed to a method of electropolishing an internal cavity of a 3D printed metal component, the metal component comprising a 3D printed metal body defining said internal cavity and a 3D printed electrode within the internal cavity, said electropolishing comprising (i) using the electrode as cathode, and (ii) flowing an electropolishing solution through the internal cavity. The present invention affords the production of 3D printed metal components with highly polished external and internal surfaces, irrespective of the degree of complexity of the component's geometry. Said components can be successfully implemented in complex structures for high-end applications, and represent per se an advancement over the inherent limitations posed by design complexity in current 3D-printed objects.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Embodiments of the invention will be now described with reference to the following nonlimiting drawings, in which:

[0023] Figure 1 shows a schematic diagram of a partial cross-sectional view of a 3D printed hollow metal component section with a lattice structured electrode connected to the metal component,

[0024] Figure 2 shows a schematic diagram of a partial cross-sectional view of a 3D printed hollow metal component section with a lattice structured cathode connected to the metal component by non-conductive resin,

[0025] Figure 3 shows a block diagrammatic view of an example of an electropolishing setup, for use whit an embodiment of the 3D printed metal component of the invention,

[0026] Figure 4 shows a schematic of an embodiment 3D printed metal component shaped as a bent pipe, having a 3D printed electrode coaxial with the internal cavity of the pipe, and

[0027] Figure 5 shows a schematic of the CAD model of the 3D printed metal component used in Example 1.

[0028] DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention provides a 3D printed metal component. By being "3D printed", the component of the invention is manufactured with 3D printing. As used herein, the expression "3D printing" (also known as "additive manufacturing") indicates a process of joining materials to make physical objects from 3D model data, usually layer upon layer, as opposed to "subtractive manufacturing" methodologies, in which the end object is obtained by removing material form a starting block. 3D printing is a collection of additive processes where successive layers of material are laid down in different shapes using a heat source. This is in comparison to traditional machining techniques, which mostly rely on the removal of material by methods such as cutting, machining, or milling. 3D printing is sometimes known as “additive manufacturing”, “additive layer manufacturing” (ALM) or “rapid prototyping”.

[0030] By being 3D printed, the metal component of the invention inherently presents different characteristics from metal components fabricated by conventional subtractive manufacturing based on top-down cutting away from a solid block of metal (e.g. through cutting, drilling, milling, lathing, etc.). This is believed to be linked to local atom-scale recrystallisation rearrangement within the metal micro structure promoted during 3D printing procedures. As a result, 3D printed metal components can have improved specific strength, fatigue resistance, fracture toughness and hot- strength relative to metal components formed using conventional mechanical manufacturing.

[0031] 3D printing techniques suitable for use in the invention embrace all those known to a skilled person for the 3D printing of metal components, for example those that require the use of a metal powder feedstock.

[0032] For example, suitable 3D printing techniques may encompass those in which a heat source (such as a laser beam) is used to form a spatially confined melt pool on either a metallic substrate or on a previously deposited metal layer. A metal powder feedstock is fed into the melt pool using a carrier gas, where it melts to form a deposit that is fusion bonded to the substrate or on the previously deposited metal layer. Other suitable 3D printing techniques may embrace those in which a metal powder feedstock is first spread on a metallic substrate or on a previously deposited metal layer. The feedstock is then locally melted using a heat source (such as a laser or electron beam) under a process gas, causing the feedstock particulate to coalesce and fuse to the substrate or on the previously deposited metal layer.

[0033] Further suitable 3D printing techniques may include processes in which a print head deposits a liquid binding agent onto selected areas of subsequent layers of metal particles, thereby building a three-dimensional object of metal particles joined by the binder. The object is subsequently consolidated by sintering to form the final metal article.

[0034] Accordingly, the 3D printing suitable in the present invention may comprise powder bedbased processes such as selective laser sintering (SLS), selective laser melting (SLM), laser powder bed fusion (LPBF), direct metal laser sintering (DMLS), direct metal laser melting (DMLM), binder jet printing (BJP), electron beam melting (EBM) and blown powder processes named laser engineered net shaping (LENS), direct laser forming (DLF), or directed energy deposition (DED).

[0035] A skilled person would be aware of specific devices and operational parameters for the 3D printing of a metal component given a metal feedstock of the kind described herein.

[0036] The 3D printed metal component of the invention has a metal body.

[0037] The term "metal" is used herein in accordance to its broadest meaning to encompass materials that (i) comprise at least one metal element, and (ii) can be processed by additive manufacturing. As such, the term will be understood to include elemental metals as well as metal alloys. By "metal alloy" is meant herein a combination comprising either (i) two or more metal elements or (ii) one metal element and one or more non-metal alloying element(s).

[0038] Accordingly, the metal body may be made of any metal that can be processed by additive manufacturing. In some embodiments the metal comprises titanium, aluminium, magnesium, nickel, iron, copper, gold, silver, bismuth, manganese, zinc, chromium, molybdenum, platinum, zirconium, iridium, yttrium, vanadium, niobium, tantalum, tungsten, cobalt, tin, lead, gallium, or an alloy of one or more thereof.

[0039] Accordingly, in some embodiments the metal body of the 3D component is made of titanium, aluminium, magnesium, nickel, iron, copper, gold, silver, bismuth, manganese, zinc, chromium, molybdenum, platinum, zirconium, iridium, yttrium, vanadium, niobium, tantalum, tungsten, cobalt, tin, lead, gallium, or an alloy of one or more thereof.

[0040] The expression “titanium alloy” used herein encompasses alloys in which the major element is titanium. The expression may also encompass proprietary titanium alloy systems as well as titanium alloys based on titanium powder metallurgy and titanium compounds, and may also encompass alloy systems such as titanium gum metal. The expression may encompass, for example, alpha titanium alloys, near alpha titanium alloys, alpha-beta titanium alloys, beta titanium alloys and titanium alloys strengthened by small additions of oxygen, nitrogen, carbon and iron. Examples of typical titanium alloys used herein include, for example, Ti- 1.50, Ti-0.2O, Ti-0.3O, Ti-0.20-0.2Pd, Ti-3A1-2.5V, Ti-6A1-4V, Ti-6A1-4V ELI (Extra Low Interstitials) and Ti-6Al-4V-0.06Pd. In some embodiments, the titanium alloy is an alpha titanium alloy (e.g. Ti-5Al-2Sn-ELI, Ti-8Al-lMo-lV). In some embodiments, the titanium alloy is a near-alpha titanium alloy (e.g. Ti-6Al-2Sn-4Zr-2Mo, Ti-5Al-5Sn-2Zr- 2Mo, IMI 685, Ti 1100). In some embodiments, the titanium alloy is an alpha-beta titanium alloy (e.g. Ti-6A1-4V, Ti-6A1-4V ELI, Ti-6Al-6V-2Sn, Ti-6Al-7Nb). In some embodiments, the titanium alloy is a beta-near beta titanium alloy (e.g. Ti-10V-2Fe-3Al, Ti-29Nb-13Ta- 4.6Zr, Ti-13V-l lCr-3Al, Ti-8Mo-8V-2Fe-3Al, Beta C, Ti-15-3).

[0041] In some embodiments, the metal is an alloy selected from 1000, 2000, 3000, 4000, 5000, 6000, 7000 and 8000 series aluminium alloy.

[0042] In some embodiments, the metal is AlSilOMg, Ti-6A1-4V, or Inconel 718. In some embodiments, the metal is high- strengthening-phase nickel superalloy.

[0043] The 3D component of the present invention comprises an internal cavity.

[0044] By the term cavity is meant herein an unfilled volume in the mass of the metal body. By being "internal" to the metal body, the cavity is therefore an unfilled space located within the external boundaries of the metal body. Examples of internal cavities for the purpose of this invention include interior channels of a metal component that are open to the outside, such as the interior channel of a pipe. Herein, and unless otherwise stated, the internal cavity will be referred also as "cavity", for convenience.

[0045] In some embodiments, the internal cavity is an open internal cavity. By the internal cavity being "open" is meant that the unfilled space within the internal cavity is in fluid communication with the exterior of the metal body through an opening in the metal body.

[0046] Accordingly, the present invention may also be taken to provide a 3D printed metal component having a metal body and an internal open cavity within said metal body, the component comprising a 3D printed electrode within the internal cavity, the 3D printed electrode having lower density than the metal body.

[0047] The cavity of the 3D printed component may have any shape or dimensions conducive to accommodate a 3D printed electrode of the kind described herein. In some embodiments, the cavity is in the form of a channel passing through the component.

[0048] The 3D component of the present invention comprises a 3D printed electrode within the internal cavity.

[0049] As skilled person will appreciate, by the term "electrode" is meant herein a component that can function as an electrode of an electrochemical cell under an applied electric potential between the electrode and a suitable counter-electrode. Under those circumstances, the 3D printed electrode of the invention can function as an electrical conductor used to make contact with a non-metallic part of a circuit (e.g. an electrolyte solution such as an electropolishing solution surrounding the electrode).

[0050] The 3D printed electrode may be made of any electrode material making it suitable to operate as an electrode under an applied electric potential between said electrode and a suitable counter-electrode. For example, the 3D printed electrode may be made of any of the metals described herein.

[0051] Accordingly, in some embodiments the 3D printed electrode comprises titanium, aluminium, magnesium, nickel, iron, copper, gold, silver, bismuth, manganese, zinc, chromium, molybdenum, platinum, zirconium, iridium, yttrium, vanadium, niobium, tantalum, tungsten, cobalt, tin, lead, gallium, or an alloy of one or more thereof.

[0052] In some embodiments, the 3D printed electrode and the metal body are 3D co-printed elements. In these instances, the 3D printed electrode and the metal body have been printed simultaneously. Accordingly, under those circumstances the 3D printed electrode and the metal body may be typically made of the same metal. Also, by being co-printed, the electrode and the metal body may be connected to one another in the as-printed component. For example, the electrode and the metal body may be connected by sacrificial connective metal, which can be broken or removed to electrically insulate the electrode from the metal body for subsequent electropolishing.

[0053] The 3D printed electrode may be of any shape and dimensions that are conducive to the electrode fitting in the cavity of the metal component. In some embodiments, the 3D printed electrode has a conformal shape to that of the cavity. For example, if the cavity is the internal channel of a pipe-shaped component, the 3D electrode may have an elongated cylindrical shape such that the electrode fits within the channel, for instance in coaxial arrangement with the channel. A schematic example of one such arrangement is shown in Figure 4.

[0054] In some embodiments, the 3D printed electrode is electrically insulated from the metal body. By the electrode and the metal body being "electrically insulated", free direct flow of electrons between the electrode and the metal body is not allowed. For example, the electrode and the metal body may be electrically insulated by not being in physical contact with one another. In other instances, the electrode and the metal body may be electrically insulated by having an electrically insulating material provided therebetween.

[0055] In some embodiments, the 3D printed electrode has an external shape that is conformal to that of the cavity. In those instances, the main external surface of the 3D printed electrode faces the surface of the cavity, for example such that there is a constant space gap between the 3D printed electrode and the surface of the cavity. Each one of Figures 1-4 shows a schematic example of one such arrangement. In Figures 1-3, the 3D printed electrode is depicted as having a lattice structure, while in Figure 4 the 3D printed electrode is in the form of a rod coaxial with the internal channel of a pipe. Accordingly, in some embodiments the 3D printed electrode has a rod-like shape. In some embodiments, the 3D printed electrode is in the form of a rod.

[0056] In some aspects of the present invention, the 3D printed electrode has lower density than the metal body.

[0057] As used herein, the term "density" in the context of a 3D printed metal element refers broadly to the density of the printed unit volume of said element, as opposed to the density of the bulk metal per se. In a more general sense, density herein is akin to a "bulk density", i.e. a measurement of mass of material per unit of volume. Accordingly, density of the 3D printed electrode would be understood broadly to encompass density of the electrode structure (e.g. a lattice structure being less dense than a block structure), but also density of printed metal as it results from printing metal powder feedstock.

[0058] By having lower density than the metal body, the 3D printed electrode is mechanically weaker than the metal body. This affords removal of the 3D printed electrode from within the cavity of the metal component, for example following completion of the electropolishing procedure, by mechanical breakage of the 3D printed electrode. This is particularly advantageous when the 3D printed electrode is shaped to fit within a cavity having intricate geometry, in that the proposed density relation facilitates breakage and minimises the chance of residual electrode material remaining trapped within the cavity after removal of the electrode.

[0059] It will be therefore understood that the density of an element is herein intended to be linked to the inherent mechanical rigidity of the element itself. For instance, when both the 3D printed metal body and the 3D printed electrode have a lattice structure, the 3D printed electrode would have lower density than that of the metal body such that the electrode is mechanically weaker than the metal body and break preferentially over the metal body under applied mechanical stress.

[0060] The electrode as a whole having lower density than the metal body is a particularly advantageous arrangement, for example, over electrode elements which may be printed to have pre-formed stress raisers in specific positions of the electrode structure. Under mechanical stress, said stress raisers act as primary breaking points. Nevertheless, the provision of localised stress raisers does not eliminate the risk of residual electrode portions remaining trapped within the cavity upon removal of the electrode.

[0061] The 3D printed electrode of the invention has lower density than the metal body by having a less dense unit structure. For example, the 3D printed electrode may have lower density than the metal body by having higher porosity than the metal body. In that context, the 3D printed electrode may be characterised by any degree of porosity resulting in the 3D printed electrode being mechanically weaker than the metal body. As used herein, the term "porosity" refers to the ratio of the volume of empty space over the volume of a unit volume structure.

[0062] In some embodiments, the 3D printed electrode has a porosity of more than 1% and less than 99%, relative to the volume of the electrode. For example, the 3D printed electrode may have a porosity of between 5% and 99%, between 10% and 99%, between 20% and 99%, between 30% and 99%, between 40% and 99%, between 50% and 99%, between 60% and 99%, between 70% and 99%, between 80% and 99%, or between 90% and 99%, relative to the volume of the electrode.

[0063] Advantageously, the electrode can be 3D printed to have a complex geometry, providing for larger surface area over corresponding electrodes having simpler geometry. In some embodiments, the 3D printed electrode has a surface area of at least 300 mm2 / g. For example, the 3D printed electrode may have a surface area of at least 500 mm2 / g, at least 750 mm2 / g, at least 1,000 mm2 / g, at least 2,500 mm2 / g, at least 5,000 mm2 / g, at least 10,000 mm2 / g, or at least 50,000 mm2 / g. In some embodiments, the 3D printed electrode has a surface area of from 300 mm2 / g to 50,000 mm2 / g.

[0064] High surface areas may be achieved by having the electrode 3D printed into any complex shape that is conducive to development of surface over weight unit.

[0065] In some embodiments, the 3D printed electrode has a lattice structure.

[0066] Typically, a lattice structure is an open framework containing regular, repeating patterns which can be defined by a certain unit cell. Said unit cell is itself the simplest repeat unit of the pattern. As a result, a lattice structure is essentially spatially defined by a plurality of unit cells. Said unit cell may have any shape achievable by 3D printing. Examples of such shapes include triclinic, monoclinic, orthorhombic, tetragonal, rhombohedral, hexagonal, and cubic. Typical unit cells of a lattice structure suitable for the purpose of the invention may have a volume ranging from 1 to 10,000 mm3, for example from 10 to 5,000 mm3, from 50 to 5,000 mm3, or from 50 to 2,000 mm3. A lattice structure for the purpose of the invention may be visualised as a reticulated structure having the form and / or appearance of a net or grid.

[0067] For the purpose of the invention, the lattice structure of the electrode may be provided with varying unit cell geometries, varying unit cell dimensions and / or varying structure densities. In some embodiments, the lattice structure is defined by a plurality of unit cells with a size between 1 and 20 mm. Unit elements of the lattice may be in the form of strips, bars, girders, beams or the like, which are contacting, crossing or overlapping in a regular pattern. The strips, bars, girders, beams or the like may have a straight shape, but may also have a curved shape. The lattice is not necessarily made of longitudinal beams or the like, and may for example consist of interconnected spheres, pyramids, etc. Said strips, bars, girders, beams or the like may have a thickness or diameter of 0.1 mm or more. In some embodiments, said unit elements have a thickness or diameter of 0.2 mm, 0.4 mm, 0.6 mm, 0.8 mm, 1 mm, 1.5 mm, 2 mm, 3 mm, or 5 mm or more.

[0068] In some embodiments, the 3D printed electrode has a lattice structure selected from a triply periodic minimal surface (TPMS) lattice, a strut lattice, and a planar lattice.

[0069] In some embodiments, the 3D printed electrode has a TPMS lattice structure. As a skilled person would know, TPMS lattices are created when a trigonometric equation is used to generate the unit cell. For instance, a gyroid TPMS cell would be made up of all the points inside the cell for which the following equation holds true: sin(x)cos(y) + sin(y)cos(z) + sin(z)cos(x) = 0. Different, but similar, equations like this produce the different TPMS lattice types.

[0070] In some embodiments, the 3D printed electrode has a strut lattice structure. These structures are made up of interconnected beams, joined in various patterns as defined by the unit cell. The struts can be joined by the vertices of the cubic cell, the edges, and the faces, and different combinations of these connection points produce the different types.

[0071] In some embodiments, the 3D printed electrode has a planar lattice structure. Planar lattice structures are the simplest type of lattice and are created when a 2D unit cell is extruded in 3D. A common type of planar lattice is a honeycomb structure.

[0072] In some embodiments, the cavity of the metal body has an axial length. In those instances, the cavity has an elongated shape along a main direction. In its simple form, a cavity with an axial length may be visualised as the internal channel of a straight pipe. In some embodiments, the cavity and the electrode are co-axial. This configuration is achievable when the cavity has an elongated shape characterised by a main directional axis. Those include, for example, cavities with rotation geometry about a main axis. Suitable examples in that regard include cylindrical shape, tubular shape, conical shape, etc. In those instances, the electrode can be shaped such that it shares its main axis with the cavity to be co-axial. Examples of some such configurations are shown in the schematics of Figures 1- 4.

[0073] Aspects of the invention also relate to a method of making a metal component, the method comprising 3D printing (i) a metal body having an internal cavity therein and (ii) an electrode within the internal cavity, the electrode having lower density than the metal body.

[0074] In the context of said method, it will be understood that the metal component, the metal body, the cavity and the electrode may be a metal component, a metal body, a cavity and an electrode of the kind described herein.

[0075] The method of the invention comprises 3D printing a metal body. Provided the 3D printing results in a component of the kind described herein, the 3D printing may be effected in accordance to any procedure known to the skilled person that is effective for the 3D printing of a metal component. In that regard, a skilled person would be aware of specific devices and operational parameters (e.g. printing speed, power of the heat source, mass-feeding rate of powder feedstock, etc.) for the effective additive manufacturing of a metal component of the kind described herein.

[0076] The method of the invention comprises the 3D printing of an electrode within the internal cavity, the electrode having lower density than the metal body.

[0077] Different density of the 3D printed electrode relative to the metal body may be achieved by any means known to the skilled person. Said density differential may be achieved, for example, by acting on the operative parameters of the 3D printer (such as power input, laser intensity, etc.), and / or by adopting 3D printing patterns resulting in differential infill of the electrode relative to the metal body.

[0078] In some embodiments, the method of making a metal component comprises co-printing the electrode and the metal body. In these instances, the electrode and the metal body are printed during the same printing session. Accordingly, under those circumstances the method provides for the electrode and the metal body to be made of the same metal. Also, co-printing the electrode and the metal body can also ensure mechanical connection between the electrode and the metal body in the as-printed component. For example, the electrode and the metal body may be connected by sacrificial connective metal, which can be broken or removed to electrically insulate the electrode from the metal body for subsequent electropolishing.

[0079] The 3D printed electrode in the 3D printed metal component of the invention is intended for use as cathode during a post-printing electropolishing procedure. Accordingly, in some embodiments the method of making a metal component further comprises electropolishing the cavity.

[0080] As a skilled person would know, electropolishing is an electrochemical surface finishing process aimed at removing a thin layer of material from a metal surface, to provide smooth finish. This process can dissolve extremely small, tightly controlled amounts of metal, resulting in micron-level thickness of surface removal. More specifically, electropolishing is performed by inducing an electric potential between an anode and a cathode in contact with an electrolyte solution.

[0081] In a typical electropolishing procedure, the anode is positively charged by being connected to the positive terminal of a DC power rectifier, while the cathode is connected to the negative terminal of the DC power rectifier. Electrical current from the rectifier is conducted from the anode to the cathode through the electrolyte. The electrical current causes metal ions on the surface of the anode to oxidize and dissolve into the electrolyte, meanwhile reduction reaction accompanied with gas evolution occur at the surface of the cathode. This promotes gradual dissolution of a thin layer of the anode material, typically in the form of metal ions, into the electrolyte solution to leave a shiny, smooth, ultra-clean surface finish on the anode material. In the process of electropolishing, burrs and other peaks of surface roughness on the metal surface attract greater electrical current density and erode first, in a phenomenon known as "anodic levelling". The preferential removal of protruding portions of the surface structure leads to a smoother metal surface. In this context, electropolishing are also known as "electrochemical polishing", "anodic polishing" or "electrolytic polishing".

[0082] The 3D printed metal component of the invention can therefore be implemented in an electropolishing procedure in which the 3D printed electrode is used as cathode while the metal body of the component is used as the anode of the electropolishing circuit.

[0083] Accordingly, in some embodiments the 3D printed electrode functions as cathode during electropolishing.

[0084] Due to the specific shape and location of the 3D printed electrode within a cavity of the metal body, the electropolishing procedure will result in the homogeneous polishing of the surface of the cavity, irrespective of the cavity geometry and dimensions. The 3D printed metal component of the invention is therefore particularly advantageous as it is provided with a "built-in" cathode for post-printing electropolishing of its internal cavities.

[0085] As a skilled person would appreciate, the 3D printed electrode and the 3D printed metal body would have to be electrically insulated to ensure they can effectively function as cathode and anode, respectively. As discussed herein, electrical insulation may be achieved by any means known to the skilled person, for example mechanical breakage and the interposition of a non-conductive resin. As such, in some embodiments the method of making a metal component further comprises electrically insulating the electrode from the metal body. For instance, the electrode and the metal body may be 3D printed to be connected to one another, for example by sacrificial connective metal, resulting in a continuous discrete 3D component. In those instances, electrical insulation between the electrode and the metal body may be achieved by physically disconnecting the electrode from the metal body, for example by rupturing any sacrificial connective metal between the electrode and the metal body.

[0086] Other means to impart electric insulation between the 3D printed electrode and the 3D printed metal body include the interposition of a non-conductive resin between the electrode and the metal body. Advantageously, said non-conductive resin may also function as physical connector between the electrode and the metal body to ensure they are fixed relative to one another. This setup is schematically shown in Figure 2.

[0087] Electropolishing of the cavity in the method of making the metal component in accordance to the present invention may be achieved by any means known to a skilled person.

[0088] A typical electropolishing procedure includes the provision of an electrolyte solution into the cavity, for example by having the metal component immersed in the electrolyte solution.

[0089] Electrolyte solutions (which may also be referred to herein as "electropolishing solutions") for metal electropolishing are usually mixtures containing concentrated strong acids completely dissociated in water, such as mineral acids. In this context, strong acids are categorized as those that are stronger in aqueous solution than the hydronium ion (H3O). Typically, the formulation and composition of the electropolishing solution would be determined based on the nature of the target metal (i.e. the anode material).

[0090] Examples of suitable strong acids for use an electropolishing solution for use in the invention include sulfuric acid, hydrochloric acid, perchloric acid, and nitric acid. Electropolishing solutions containing strong acids are particularly effective to electropolish ferrous components. For example, the electrolyte solution may contain a mixture of sulfuric acid and phosphoric acid. Altematively, the electrolyte solution may also be an aqueous solution of a weak acid, for example an acid from the carboxylic acid group such as formic acid, acetic acid, butyric acid, and citric acid. These electrolyte solutions may provide several advantageous results in electropolishing of non-ferrous metals, particularly titanium and titanium alloys. Certain organic compounds, such as alcohols, deep eutectic solvents, amines, or carboxylic acids may be used in mixtures with strong acids to moderate the dissolution etching reaction to avoid excess etching of the anode material.

[0091] Either before or after the provision of the electropolishing solution, the metal body is electrically connected to the positive terminal of a DC power supply, and the electrode to the negative terminal of the DC power supply. Once the electropolishing solution is provided, the DC power supply can be activated to apply an electrical potential between the electrodes, resulting in electrical current flowing from the anode to the cathode through the electrolyte.

[0092] As used herein, the term "power supply" is taken to mean a unit capable of supplying a continuous voltage for a period of time. Typically, the power supply is setup to supply a positive voltage to the anode (that is, the 3D printed metal body) and a negative voltage to the cathode (that is, the 3D printed electrode). Suitable voltages provided by the power supply may range from 1 to 50 V, 5 to 40, 10 to 30 V, for example 12 or 24 V. The power supply would typically provide a direct current (DC), typically from 0.1 to 5 Amps, for example from 1 to 2.5 Amps or 1.5 to 2 Amps.

[0093] Electrical current generated during the electropolishing procedure may vary relative to the chemical composition of the electrolyte solution. Accordingly, said current may also be expressed in terms of surface current density (A / cm2), i.e. Ampere per unit surface of the electrode. A typical range of surface current density for use in the electropolishing procedure of the invention may be 0.01 A / cm2- 0.3 A / cm2.

[0094] During electropolishing, electrical current from the power supply is conducted from the anode to the cathode through the electrolyte. Said electrical current causes metal ions to form on the surface of the part to oxidize and dissolve into the electrolyte. This process can dissolve extremely small, tightly controlled amounts of metal, resulting in micron-level thickness of surface removal.

[0095] The amount of metal surface removal during electropolishing may be controlled by parameters such as the chemical composition of the electropolishing solution, the temperature of the electropolishing solution, the duration of electropolishing, the density of electrical current, and the composition of the metal body.

[0096] In certain embodiments, the electrolyte solution may be made to flow through the cavity during electropolishing. In these instances, the internal cavity will be understood as being an internal open cavity in fluid communication with the exterior of the metal body. Flowing the electrolyte solution through the cavity may be achieved by any means known to a skilled person. For example, the electrolyte solution may be pumped through the cavity.

[0097] Having the electrolyte solution flowing through the cavity during electropolishing is particularly advantageous, in that electropolishing efficiency significantly increases over procedures in which the electropolishing solution is static relative to the anode. At an atomic scale, a flowing solution over the surface of the anode can afford homogeneous polishing as it assists with the steady removal of metal ions from the anode. As a result, diffusion of metal ions away from the anode can be homogeneous and steady-state. On a macroscopic level, a flowing electrolyte solution can also afford mechanical removal of unwanted debris that may form on the anode during the procedure.

[0098] Flowing the electropolishing solution through the cavity is particularly advantageous over conventional procedures in which the solution is maintained static within the cavity, for example by merely immersing the component into the solution or by sealing off the cavity after filling it with the electropolishing solution. Of those conventional procedures, electropolishing using a solution that is sealed off inside the cavity is particularly inadequate. Gaseous by-products forming during the electropolishing can accumulate within the sealed cavity and pressurize the polishing reservoir. The accumulation of gas by-products within the cavity can have dangerous consequences as well as resulting in a drastic degradation of the polishing efficiency. In addition, the seal used to seal off the electropolishing solution can impair the net-shape capability of the 3D printing, not to mention that many internal channels are not sealable in the first place.

[0099] The electropolishing solution may be flown through the cavity at any flow rate conducive to effective electropolishing. In that regard, the flow rate of the electropolishing solution can be adjusted to modulate the efficiency of the overall process, depending also on the specific geometric features of the cavity. In some embodiments, the method comprises flowing the electropolishing solution through the internal cavity at a flow rate of at least 0.1 1 / min, at least 1 1 / min, at leastlO 1 / min, or at least 100 1 / min. In some embodiments, the flow rate is from about 10 1 / min to about 100 1 / min. For example, the flow rate may be from about 10 1 / min to about 100 1 / min.

[0100] The electropolishing solution may contain any amount of electrolyte that is conducive to effective electropolishing of the surface of the internal cavity. For example, the electropolishing solution may contain the electrolyte in an amount of at least 1 g / L, at least 2 g / L, at least 5 g / L, at least 10 g / L, at least 25 g / L, at least 50 g / L, at least 100 g / L, at least 250 g / L, at least 500 g / L, or at least 750 g / L. In some embodiments, the electropolishing solution may contain the electrolyte in an amount of from 1 g / L to 990 g / L.

[0101] In the method of the invention, electropolishing may be performed for any duration of time that is conducive to effective electropolishing of the whole surface of the internal cavity. For instance, electropolishing may be performed for at least 5 seconds, at least 10 seconds, at least 30 seconds, at least 1 minute, at least 5 minutes, at least 10 minutes, at least 15 minutes, or at least 20 minutes. In some embodiments, electropolishing is performed for a duration of from 10 seconds to 20 minutes.

[0102] Electropolishing may be performed at any temperature that is conducive to effective electropolishing of the whole surface of the internal cavity. For instance, electropolishing may be performed at a temperature of the electropolishing solution of at least 50°C, at least 70°C, at least 75°C, or at least 90°C. Typically, the temperature of the electropolishing solution would be selected to be lower than the boiling point of the solution itself, for safety. In some embodiments, electropolishing is performed at a temperature of the electropolishing solution of from 70°C to 90°C.

[0103] Electropolishing results in a decrease of the average roughness of the surface of the cavity. In the invention, electropolishing may be conducted under conditions (e.g. concentration of electrolyte, electropolishing duration, temperature, etc.) that are conducive to provide an average superficial roughness Raof the internal cavity of less than 2 pm. In some embodiments, electropolishing results in an average superficial roughness Raof the internal cavity of less than 1.5 pm, less than 1 pm, or less than 0.5 pm.

[0104] Once the electropolishing process is completed, the cathode can be extracted from the components. In the present invention, extraction of the cathode following electropolishing is favoured by the cathode being less dense than the metal body. By being less dense, the cathode is mechanically weaker than the metal body and can be extracted by mechanical rupture. When the internal cavity and the cathode have particularly complex geometries, the cathode can be mechanically broken at any location that is conducive to effective removal of the cathode from the cavity. This is advantageous over instances in which the cathode is only provided with pre-formed stress raisers in specific positions of the cathode structure. Under mechanical stress, said stress raisers act as primary breaking points. Nevertheless, even with the provision of localised stress raisers the risk of residual cathode portions remaining trapped within the cavity upon removal of the cathode remains significant.

[0105] Figure 1 shows a schematic diagram of a partial cross-sectional view of a 3D printed hollow metal component section having a lattice structured electrode 2 connected to the metal body 4. The 3D model of the metal body (or anode) 4 with an internal cavity 1 is designed for the 3D printing process. The 3D model of the lattice- structured electrode (cathode) 2 is created and coaxially positioned within internal cavity 1. The 3D model of electrode (cathode) 2 is connected to an external side of the metal body 4 with designed anchors 3. The purpose of the anchors 3 is to secure the position of electrode (cathode) 2, hence keeping it coaxial to the internal cavity 2 during and after the 3D printing process.

[0106] For the design of the lattice structured electrode (cathode) 2, the contour and the dimension of the electrode (cathode) is corresponding to the internal cavity 1 defined by the metal body 4. In this embodiment, the lattice structure of the electrode 2 is a type of periodic cellular structure with a unit cell. The shape of the lattice can be strut-based or minimal surface designs. Typically, the porosity of the lattice structure, for example that of the structure in Figure 1, may be larger than 0% and smaller than 100%. This corresponds to a material fraction of the lattice structure smaller than 100% and larger than 0%, respectively. The corresponding total surface area is dependent on the unit cell of the lattice structure.

[0107] The positioning of the electrode (cathode) 2 is co-axial with the internal cavity 1 of the metal body (anode) 4. The diameter of the electrode (cathode) 2 is proportionally downscaled to the diameter of the internal cavity 1 of the metal body (anode) 4. Once the 3D printing process is finished, the metal body 4 and the electrode (cathode) 2 can be cut off from the 3D printer substrate together. The anchors 3 in between the electrode (cathode) 2 and the metal body 4 can then be disconnected, for example by using mechanical cutting tools. This prevents short-circuiting during the electropolishing process. The gap in between the electrode (cathode) 2 and the internal cavity 1 of the metal body (anode) 4 allows for the flowing of the electropolishing solution through the internal cavity during electropolishing. The metal parts, the anchors 3, and the lattice-structured cathode 2 may be made by the same material, this material can be iron-based, nickel-based, titanium-based, aluminium-based, cobalt-based, copper-based material.

[0108] Figure 2 is a schematic diagram of a partial cross-sectional view of the 3D printed metal component section shown in Figure 1, in which the lattice structured electrode (cathode) is re-attached to the metal component by non-conductive resin 5, for example light curing resin. In this configuration, the component can undergo electropolishing of the surface of the internal cavity, since the electrode (functioning as cathode) is electrically insulated from the metal body. Figure 3 shows a is a diagrammatic view of an example of an electropolishing setup for electropolishing an embodiment of the 3D printed metal component of the invention as the one depicted in Figures 1-2. Once the electrode (cathode) 2 is resecured with non-conductive resin 5 to the metal body (anode) 4, the positive terminal of an electric power unit 8 can be connected to the metal body 4, working as the anode, and the negative terminal of the electric power unit 8 can be connected to the electrode 2 (working as the cathode).

[0109] A conductive polishing solution 6 provided in an external reservoir can subsequently be pumped through the internal cavity 1 of the metal body 4 using a pump 7. The flow rate of the polishing solution 6 can be adjusted. Once the flowing of the polishing solution 6 is stable, electropolishing can be initiated by switching on the electric power unit 8. Once the polishing process is finished, electrode (cathode) 2 can be extracted from the metal part 4, by rupturing it at the connection points. The electropolishing procedure as described in this disclosure ensures the polishing solution 6 is free of moving using pump 7.

[0110] Figure 4 depicts a schematic of a 3D printed metal component in the form of a bent metal pipe 9, with a 3D printed electrode rod 10 located within, and co-axial with, the pipe channel. The left image represent a schematic of an external view of the pipe component showing an end of the rod electrode protruding out of the pipe channel. Metal pipe 9 may be used to function as anode, with electrode rod 10 functioning as built-in cathode. The right image shows a transparent view of the metal component, allowing to appreciate the extension and shape of the internal channel and the shape of the rod electrode located within the channel. In the schematic, the metal body (i.e. tube) and the rod electrode are electrically insulated in that they are not in physical contact.

[0111] As discussed herein, flowing the electropolishing solution through the internal cavity of the metal component to electropolish the surface of the internal cavity is particularly advantageous over conventional electropolishing procedures, for instance those in which the electropolishing solution is sealed within the cavity. It is therefore believed that an electropolishing procedure of an internal cavity of a 3D printed metal component by flowing the electropolishing solution through the cavity would be unique in its own rights.

[0112] Accordingly, the present invention also provides a method of electropolishing an internal cavity of a 3D printed metal component, the metal component comprising a 3D printed metal body defining said internal cavity and a 3D printed electrode within the internal cavity, said electropolishing comprising (i) using the electrode as cathode, and (ii) flowing an electropolishing solution through the internal cavity.

[0113] In the electropolishing method of the invention, the 3D printed metal component, the 3D printed metal body, and the 3D printed electrode may be a 3D printed metal component, a 3D printed metal body, and a 3D printed electrode of the kind described herein.

[0114] Also, flowing the electropolishing solution through the internal cavity of the metal body in the electropolishing method of the invention may be achieved by any means described herein. For example, the electropolishing solution may be pumped through the internal cavity.

[0115] In some embodiments of the electropolishing method, the 3D printed electrode has lower density than the metal body. As explained herein, by having lower density than the metal body, the 3D printed electrode is mechanically weaker than the metal body. This affords removal of the 3D printed electrode from within the cavity of the metal component, for example following completion of the electropolishing procedure, by mechanical breakage of the 3D printed electrode. This is particularly advantageous when the 3D printed electrode is shaped to fit within a cavity having intricate geometry, in that the proposed density relation minimises the chance of residual electrode material remaining trapped within the cavity after removal of the electrode.

[0116] The 3D printed electrode may have a lower density than the metal body by being more porous than the metal body. In some embodiments, the 3D printed electrode in the electropolishing method of the invention has a porosity of more than 1% and less than 99%, relative to the volume of the electrode. For example, the 3D printed electrode may have a porosity of between 5% and 99%, between 10% and 99%, between 20% and 99%, between 30% and 99%, between 40% and 99%, between 50% and 99%, between 60% and 99%, between 70% and 99%, between 80% and 99%, or between 90% and 99%, relative to the volume of the electrode.

[0117] Advantageously, the electrode can be 3D printed to have a complex geometry, providing for larger surface area over corresponding electrodes having simpler geometry. In some embodiments, the 3D printed electrode has a surface area of at least 300 mm2 / g. For example, the 3D printed electrode may have a surface area of at least 500 mm2 / g, at least 750 mm2 / g, at least 1,000 mm2 / g, at least 2,500 mm2 / g, at least 5,000 mm2 / g, at least 10,000 mm2 / g, or at least 50,000 mm2 / g. In some embodiments, the 3D printed electrode has a surface area of from 300 mm2 / g to 50,000 mm2 / g.

[0118] The method of claim 19 or 20, wherein the metal body and the electrode are co-printed. As explained herein, in these instances the 3D printed electrode and the metal body have been printed simultaneously. As a result, the 3D printed electrode and the metal body may be made of the same metal.

[0119] In the electropolishing method of the invention, the metal body may be made of any metal that can be processed by additive manufacturing. In some embodiments, said metal comprises titanium, aluminium, magnesium, nickel, iron, copper, gold, silver, bismuth, manganese, zinc, chromium, molybdenum, platinum, zirconium, iridium, yttrium, vanadium, niobium, tantalum, tungsten, cobalt, tin, lead, gallium, or an alloy of one or more thereof.

[0120] Also, in the electropolishing method of the invention the 3D printed electrode may be made of any electrode material making it suitable to operate as an electrode under an applied electric potential between said electrode and a suitable counter-electrode. For example, the 3D printed electrode may be made of any of the metals described herein. Accordingly, in some embodiments, the 3D printed electrode in the electropolishing method of the invention comprises titanium, aluminium, magnesium, nickel, iron, copper, gold, silver, bismuth, manganese, zinc, chromium, molybdenum, platinum, zirconium, iridium, yttrium, vanadium, niobium, tantalum, tungsten, cobalt, tin, lead, gallium, or an alloy of one or more thereof.

[0121] Electropolishing in the electropolishing method of the invention may be performed under any of the conditions (e.g. concentration of electrolyte, electropolishing duration, temperature, etc.) described herein.

[0122] For instance, electropolishing in the electropolishing method of the invention may be performed for any duration of time that is conducive to effective electropolishing of the whole surface of the internal cavity. For instance, electropolishing may be performed for at least 5 seconds, at least 10 seconds, at least 30 seconds, at least 1 minute, at least 5 minutes, at least 10 minutes, at least 15 minutes, or at least 20 minutes. In some embodiments, electropolishing is performed for a duration of from 10 seconds to 20 minutes.

[0123] Also, electropolishing in the electropolishing method of the invention may be performed at any temperature that is conducive to effective electropolishing of the whole surface of the internal cavity. For instance, electropolishing may be performed at a temperature of the electropolishing solution of at least 50°C, at least 70°C, at least 75°C, or at least 90°C. Typically, the temperature of the electropolishing solution would be selected to be lower than the boiling point of the solution itself, for safety. In some embodiments, electropolishing is performed at a temperature of the electropolishing solution of from 70°C to 90°C.

[0124] Electropolishing in the electropolishing method of the invention results in a decrease of the average roughness of the surface of the cavity. In the invention, electropolishing may be conducted under conditions (e.g. concentration of electrolyte, electropolishing duration, temperature, etc.) that are conducive to provide an average superficial roughness Raof the internal cavity of less than 2 pm. In some embodiments, electropolishing results in an average superficial roughness Raof the internal cavity of less than 1.5 pm, less than 1 pm, or less than 0.5 pm.

[0125] Upon completion of the electropolishing procedure, it may be required to remove residual electrolyte and by-products of the electrochemical reaction and dry the metal to prevent staining (Post Treatment). Depending on the nature of the electrolyte, chemical by-products may include phosphates and sulfates of heavy metals, which should be removed to ensure a consistent surface finish and sterilized product.

[0126] The invention is also described with reference to the following non-limiting examples.

[0127] EXAMPLES

[0128] EXAMPLE 1

[0129] 3D printing a hollow metal component with a coaxial electrode

[0130] A full dense nickel-based superalloy Hastelloy-X (HX) hollow tube (anode) along with a coaxial porous electrode (cathode) and sacrificial connective metal were designed using CAD software and then 3D printed using the laser powder bed fusion (LPBF) method at the same session.

[0131] Figure 5 schematically illustrated the CAD model of the component involved in the 3D printing.

[0132] The LPBF machine is market available. The associated LPBF parameters to 3D print the component including: laser power at 290 W, laser scanning speed at 1000 mm / s, laser scanning spacing at 0.01 mm, layer thickness at 0.04 mm, cast iron build substrate, and Argon protective gas was used. By finishing the 3D printing procedure, the 3D printed component was cut off from the build substrate using a market-available electric-discharge machine. EXAMPLE 2

[0133] Electropolishing the 3D printed metal hollow component

[0134] To start the electropolishing process of the HX tube component as described in Example 1, the sacrificial connective metal was first disconnected from the anode using abrasive cutting tool. This is to achieve electrical insulation between the cathode and the anode. Light curing resin was applied to the disconnected point of the sacrificial connective metal and cured for at least 30 minutes. This is to ensure the cathode coaxially positioned with the anode during the following electropolishing process.

[0135] The electropolishing electrolyte was prepared using a fully organic compound, comprising a mixture of Choline Chloride and Ethylene Glycol with a molar ratio of 1:2. For the electropolishing process, a 30V DC power supply unit was used with its positive terminal connected to the HX tube component as the anode, and its negative terminal connected to the porous electrode as the cathode. The electrolyte was kept in a 1 L PYREX beaker and was constantly heated at 70 °C. Once the temperature of the electrolyte is stable, a pump was used to pump the electrolyte from the beaker to into the channel of the anode at a flow rate of 1.1 L / min. Once the flow of the electrolyte is stable the electropolishing process started by turning on the DC power supply. The DC power was set at a constant current of 1.5 A. The electropolishing process stopped at 5 minutes by turning off the DC power supply.

[0136] Throughout this specification and the claims which follow, unless the context requires otherwise, the word ‘comprise’, and variations such as ‘comprises’ and ‘comprising’, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0137] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A 3D printed metal component having a metal body and an internal cavity within said metal body, the component comprising a 3D printed electrode within the internal cavity, the 3D printed electrode having lower density than the metal body.

2. The 3D printed metal component of claim 1, wherein the 3D printed electrode is electrically insulated from the metal body.

3. The 3D printed metal component of claim 1 or 2, wherein the electrode has a porosity of more than 10% and less than 90%.

4. The 3D printed metal component of any one of claims 1-3, wherein the electrode has a surface area of at least 300 mm2 / g.

5. The 3D printed metal component of any one of claims 1-4, wherein the electrode has a lattice structure.

6. The 3D printed metal component of any one of claims 1-5, wherein the electrode and the metal body are 3D co -printed elements.

7. The 3D printed metal component of any one of claims 1-6, wherein the metal body and the electrode comprise iron, nickel, titanium, cobalt, aluminium, copper, or an alloy of any one thereof.

8. The 3D printed metal component of any one of claims 1-7, wherein the internal cavity and the electrode are coaxial.

9. The 3D printed metal component of any one of claims 1-8, wherein the electrode functions as cathode during electropolishing.

10. A method of making a metal component, the method comprising 3D printing (i) a metal body having an internal cavity therein and (ii) an electrode within the internal cavity, the electrode having lower density than the metal body.

11. The method of claim 10, further comprising electrically insulating the electrode from the metal body.

12. The method of claim 11, comprising 3D printing the electrode with a surface area of at least 300 mm2 / g.

13. The method of claim 10 or 11, comprising 3D printing the electrode with a porosity of more than 10% and less than 90%.

14. The method of any one of claims 10-13, comprising co-printing the metal body and the electrode.

15. The method of any one of claims 10-14, wherein the metal body and the electrode comprise iron, nickel, titanium, cobalt, aluminium, copper, or an alloy of any one thereof.

16. The method of any one of claims 10-15, wherein the internal cavity and the electrode are coaxial.

17. The method of any one of claims 10-16, further comprising electropolishing the internal cavity, said electropolishing comprising (i) using the electrode as cathode, and (ii) flowing an electropolishing solution through the internal cavity.

18. The method of any one of claims 10-17, the method further comprising extracting the electrode from the internal cavity.

19. A method of electropolishing an internal cavity of a 3D printed metal component, the metal component comprising a 3D printed metal body defining said internal cavity anda 3D printed electrode within the internal cavity, said electropolishing comprising (i) using the electrode as cathode, and (ii) flowing an electropolishing solution through the internal cavity.

20. The method of claim 19, wherein the 3D printed electrode has lower density than the metal body.

21. The method of claim 19 or 20, wherein the metal body and the electrode are coprinted.

22. The method of any one of claims 19-21, wherein electropolishing results in the internal cavity having an average superficial roughness Raof less than 2pm.

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