Hybrid extrusion die and a method of repairing damaged extrusion die

Abstract

The disclosure relates to an aluminium extrusion die including a male bridge part comprising a two or more portholes and at least one mandrel with a mandrel die bearing, and a die plate part with a die plate bearing, and the male bridge part, or the die plate part, or both, is comprised of a die substrate portion obtained by subtractive manufacturing, and a die functional portion obtained by additive manufacturing, wherein the die substrate portion has a surface acting as an attachment surface for the die functional portion, and the die functional portion comprises a die bearing. The disclosure further comprises a method of repairing a damaged aluminium extrusion die including a male bridge part comprising a two or more portholes and at least one mandrel, and a die plate part.

Description

[0001] HYBRID EXTRUSION DIE AND A METHOD OF REPAIRING DAMAGED EXTRUSION DIE

[0002] Technical field

[0003] The present disclosure relates to the field of hot metal extrusion. More specifically, the disclosure relates to an extrusion die made of steel including a male bridge part comprising two or more portholes and at least one mandrel, and a die plate part as defined in the introductory parts of the independent claims. The present disclosure further relates to a method of repairing damaged aluminium extrusion die made of steel including a male bridge part comprising two or more portholes and at least one mandrel, and a die plate part.

[0004] Background art

[0005] The present invention relates to an extrusion tool or die for hot metal extrusion of metallic materials, in particular extrusion of aluminium or alloys thereof, or other non-ferrous metals such as copper and alloys thereof. The document US2010 / 0095731A1 illustrates an example of an extrusion die. By means of extrusion, preheated material is pushed through an extrusion die to create solid or hollow objects of a desired cross-sectional profile. Extrusion allows manufacture of complex cross-sections, and finished parts having excellent surface finish can be obtained. In some cases, the desired cross-sectional shape of the extruded object may be very complex, which puts high demand on the extrusion die and can make it difficult and expensive to manufacture.

[0006] The present invention also relates to a method of repairing used extrusion dies for hot metal extrusion of metallic materials, in particular extrusion of aluminium or alloys thereof. Extrusion dies for hollow profiles or complex cross-sections comprises a male bridge part comprising two or more portholes and webs between the portholes, and at least one mandrel with a mandrel die bearing. A multi-hollow profile normally comprises several portholes and webs, and a mandrel with mandrel bearing for each hollow. Extrusion dies for hollow and complex cross-sections are subjected to damages, such as cracks, distortions and general wear of the mandrel die bearings, leading to end of lifetime for the die part. It is therefore desired to repair damaged extrusion dies extending the operational lifetime for the extrusion tool part. Repairing extrusion dies, especially bridge parts in large dies will save significant amounts of steel as only the damaged parts need to be replaced leading to lower CO2 footprint and lower tool cost. The present disclosure aims at providing an extrusion die that can be used for extrusion of complex and very complex profile shapes. The present disclosure also provides an extrusion die that can be used for extrusion of very complex extruded profile shapes, which extrusion die can be manufactured to a reasonable cost, and demonstrates a long die lifetime. Furthermore, there is a need for an extrusion die that enables increased or high production efficiency of complex extruded profiles while maintaining a long die lifetime of production capacity. The present disclosure also provides a repaired extrusion die, having the said performance and advantages. Lastly, the present disclosure provides a method for repairing damaged extrusion dies.

[0007] The aluminium extrusion die according to the present disclosure is made of steel and includes a male bridge part comprising two or more portholes, separated by webs, and at least one mandrel, and a die plate part, where one of the male bridge part, or the die plate part, or both, is comprised of a die substrate portion obtained by subtractive manufacturing, and a die functional portion obtained by additive manufacturing, wherein the die substrate portion has a surface acting as an attachment surface for the die functional portion, and the die functional portion comprises a die bearing, wherein, for the male bridge part, the portholes extend through the die substrate portion such that porthole openings are present on a surface thereof, said surface acting as the attachment surface for the die functional portion of the male bridge part, which die functional portion includes a base portion and a mandrel portion, wherein the base portion has through porthole openings corresponding to the substrate porthole openings.

[0008] The male bridge part and / or the die plate part may optionally comprise die cooling channels located within the die functional portion, and / or located in the interface between the die substrate portion and the die functional portion. Suitably, these cooling channels have been obtained during additive manufacturing of the die functional portion, and are configured to form a part of a cooling circuit in the extrusion die.

[0009] The attachment surface of the die substrate portion of the male bridge part and / or the die plate part may be substantially flat, and the cooling channels may be located entirely in the functional portion of the male bridge part and / or the die plate part. Alternatively, the attachment surface of the die substrate portion of the male bridge part and / or the die plate part may include one or more recesses obtained by subtractive working, which partially form cooling channels, and the die functional portion obtained by additive manufacturing may then include the remaining part of the cooling channels.

[0010] The functional portion of the male bridge part may comprise male bridge cooling channels for cooling the mandrel die bearing, connecting the base portion with the mandrel portion, said cooling channels having been obtained during additive manufacturing of the male bridge functional portion, and being configured for form a part of a cooling circuit in the extrusion die. By including the cooling channels in the base portion of the functional part, the cooling circuit to the mandrel die bearing run via the webs that separate the porthole. This configuration allows high flexibility of the cooling circuit, and enables cooling of male bridge parts with a complex design, e.g. two or more mandrels with mandrel dies bearings.

[0011] The base portion of the male bridge functional portion may have a circumference edge surface, which is inclined toward a central axis of the extrusion die, and / or the die plate functional portion may have a circumference edge surface which is inclined toward a central axis of the extrusion die.

[0012] A spacer part may be arranged between the male bridge part and the die plate part, and being configured to be in contact with the male bridge part and the die plate part. This spacer part may suitably be obtained by subtractive manufacturing. The spacer part may comprise one or more through channels having inlet and outlet openings that are positioned so as to correspond to inlet and outlet openings of the cooling channels arranged in the male bridge functional portion and / or the die plate functional portion, so that the cooling channels in the male bridge functional portion and / or the die plate functional portion are connected so as to form one or more cooling circuit, which can be configured to be connected to at least one cooling fluid supply source via inlet and outlet channels arranged in one or more of the die plate part, in the male bridge part, or in the spacer part.

[0013] The outlet channels arranged in the male bridge functional portion and / or the die plate functional portion may comprise a plurality of cooling fluid flushing channels arranged immediately after the mandrel die bearing and / or the die plate bearing, relative to an extrusion direction.

[0014] The extrusion die according to the present disclosure may be a repaired or restored die in which the die substrate portion of the male bridge part, or the die plate part, or both, is made up of a previously used extrusion die.

[0015] The present disclosure further provides a method for repairing a damaged aluminium extrusion die made of steel, where the extrusion die comprises a die plate part with a die plate bearing, and a male bridge part comprising two or more portholes, separated by webs, and at least one mandrel with a mandrel die bearing, wherein the method comprises the following steps:

[0016] (a) removing damaged parts from the die plate part, and / or from the male bridge part, thereby obtaining a die substrate portion with a surface acting as an attachment surface for depositing a reconstructed part,

[0017] (b) depositing a reconstructed part on the attachment surface of the die substrate portion using additive manufacturing, (c) heat-treating the die substrate portion with the reconstructed part deposited thereon,

[0018] (d) machining the reconstructed part to a final shape.

[0019] In an embodiment comprising repairing a damaged male bridge part, the step (a) may comprise removing the at least one mandrel with the mandrel die bearing, and optionally parts of a surface surrounding the portholes including parts of a surface of webs between the portholes.

[0020] When repairing a damaged male bridge part where the mandrel part and / or the mandrel die bearing is damaged, e.g. worn or distorted, step (a) may comprise removing the at least one mandrel with the mandrel die bearing, and optionally parts of a surface surrounding the portholes including parts of a surface of the webs separating the portholes. When repairing a damaged male bridge part where one or more of the webs separating the portholes is damaged, step (a) comprises removing parts of a surface surrounding the portholes including parts of a surface of the webs between the portholes and the at least one mandrel.

[0021] In an embodiment comprising repairing a damaged die plate part, step (a) may comprise removing the die plate bearing.

[0022] The step (a) of removing damaged parts may be done by subtractive machining, comprising one or more of cutting, turning, milling, grinding and erosion.

[0023] The depositing of the reconstructed part in step (b) may be performed by using powder bed fusion (PBF) or directed energy deposition (DED) using powdered or wire feedstock material. Preferably, the depositing step (b) is performed by using DED with wire feedstock material and laser as heat source. Using DED with wire as feedstock is especially advantageous for reconstructing a male bridge part where the webs are damaged and / or in cases where the reconstructed part to be deposited is large. Furthermore, DED does not require a flat substrate and may therefore be a preferred deposition AM method compared with powder bed fusion for repairing both a male bridge part and a die plate part.

[0024] Cooling channels may be formed in the reconstructed part deposited by additive manufacturing. Thus, it is possible to add additional functions in the repaired extrusion die improving the performance and possible lifetime of the extrusion die returned into operation. The male bridge part and / or the die plate part may comprise die cooling channels located within the additively manufactured reconstructed part, and / or located in the interface between the die substrate portion and the additively manufactured reconstructed part. Suitably, the cooling channels may be configured to form a part of a cooling circuit in the extrusion die, which can be configured to be connected to at least one cooling fluid supply source via inlet and outlet channels. The reconstructed part of the male bridge part may comprise male bridge cooling channels for cooling the mandrel die bearing, connecting a base portion including parts of the webs, with the mandrel portion, said cooling channels having been obtained during additive manufacturing of the reconstructed male bridge part, and being configured for form a part of a cooling circuit in the extrusion die. Outlet channels arranged in the male bridge reconstructed part and / or the die plate reconstructed part may comprise a plurality of cooling fluid flushing channels arranged immediately after the mandrel die bearing and / or the die plate bearing, relative to an extrusion direction.

[0025] The heat-treating in step (c) may comprise tempering for softening the AM deposited part.

[0026] The machining step (d) may further comprise machining the substrate portion if needed to obtain the final shape. The machining step (d) may comprise erosion to final shape. After the machining to final shape, the extrusion die is preferably subjected to a polishing step.

[0027] Brief iption of the

[0028] The present extrusion die will now be described with reference to the accompanying drawings, in which preferred example embodiments of the disclosure are shown. The extrusion die may, however, be embodied in other forms and should not be construed as limited to the herein disclosed embodiments.

[0029] Figure 1 is a schematic cross-sectional view of an extrusion die according to the present disclosure;

[0030] Figure 2 is a perspective view of a male bridge part for another example of an extrusion die according to the present disclosure;

[0031] Figure 3 is a cross-sectional view along the line B-B in Fig. 2;

[0032] Figure 4 is a perspective view of a die plate part for a further example of an extrusion die according to the present disclosure;

[0033] Figure 5 is a cross-sectional view along the line C-C in Fig. 4;

[0034] Figure 6 is a perspective view of a spacer adapted for use together with a die plate part as illustrated in Figs. 4-5.

[0035] Figure 7 is a flowchart illustrating a conventional manufacturing process for an extrusion die.

[0036] Figure 8 is a flowchart illustrating method steps of a process according to the present disclosure, for the manufacturing of an extrusion die.

[0037] Figure 9 is a flowchart illustrating method steps for a process for repairing an extrusion die according to the present disclosure. Figure 10 shows measured temperatures in a die bearing from trials using a cooled hybrid extrusion die according to the present disclosure.

[0038] Figure 11 shows measured profile temperature of extrusions during trials comprising extrusion of several billets and with different extrusion speeds.

[0039] Figure 12 illustrates a die taken out of service where damaged parts are removed (a) and after being repaired by additive manufacturing (b).

[0040] Detailed description

[0041] The present disclosure relates to an extrusion die of the of the type that includes a male bridge part comprising two or more portholes and at least one mandrel, and a die plate part. This type of extrusion dies is typically used in the manufacture of hollow extruded profiles and the shape of the extruded profile is determined by the shape of the mandrel bearings, defining the inner profile shape, and the die plate bearing, defining the outer profile shape. Extrusion allows very complicated profile geometries to be manufactured, which requires complicated extrusion die geometries. Such dies may be difficult to manufacture, or at least difficult to obtain at a reasonable cost, with conventional die manufacturing CNC machining technologies, such as cutting, drilling, boring and / or turning (collectively denoted "subtractive manufacturing"). A flowchart of a conventional die manufacturing process is illustrated in Fig. 7, comprising steps 1-6, which will be further explained in the following.

[0042] Step 1; the starting material is an annealed hot work tool steel blank. A typical steel can be AISI H13 / 1.2343 / X40CrMoV5 having a hardness of 220-260 HB.

[0043] Step 1-2; a design of the part is done, usually made with a 3D CAD software. CAM programs are then made for the steps 2 and 4.

[0044] Step 2; the blank is turned and milled to gross dimensions of the part.

[0045] Step 3; a typical heat treatment for hot work tool steel is done. Normally the heat treatment comprises a solutionizing step, a quenching step followed by two or three tempering steps to achieve the correct mechanical properties and targeted hardness. Conventional heat treatment scheme comprises annealing at about 700 °C, austenitizing (solutionizing) at about 1020 °C, and quenching. Tempering may normally be carried out at about 600°C, with cooling between each tempering step.

[0046] Step 4; after the heat treatment, most of the die part is finished to net shape with milling. In step 4-1 a specific CAD is generated to erode the part with cupper electrode, graphite electrode or wire.

[0047] Step 5; erosion is used to fully finish the die part to net shape. Step 6; the die is polished, usually with a polishing machine to decrease the surface roughness.

[0048] The present disclosure aims at providing an extrusion die that can have a complicated geometry, which is difficult or practically impossible to obtain with the conventional die manufacturing technologies, while at the same time being reasonably inexpensive. An extrusion die thus provided includes a male bridge part with two or more portholes which are separated by webs and one or more mandrels, and a die plate part. One or both of the male bridge part and the die plate part includes a die substrate portion obtained by subtractive manufacturing, and a die functional portion obtained by additive manufacturing. The die substrate portion has a surface acting as an attachment surface for the die functional portion, and the die functional portion comprises at least one die bearing. The attachment surface of the die substrate portion of the male bridge part or the die plate part, or both, may suitably be substantially flat to allow effective manufacture of the die substrate portion.

[0049] Examples of additive manufacturing methods (also denoted AM or 3D printing in the present disclosure) that are suitable in the manufacture of the functional portion of the extrusion die according to the present disclosure are Powder Bed Fusion (PBF) or Directional Energy Deposition (DED) technologies as described by ISO / ASTM52900, however the AM methods are not limited to these. In PBF technology, parts are made in successive horizontal layers, and for each layer, metal powder is spread on a production platform, and a high-energy heat source applied to specific areas is used to melt and fuse the powder material. The high-power heat source can be a laser beam or electron beam. SLS (selective laser sintering) and SLM (selective laser melting) are the preferred PBF methods. In DED objects are formed by melting powder or wire feedstock material with a focused energy source, such as a laser, electron beam, or plasma arc, as it is deposited by a nozzle on a surface, as the nozzle is moved to deposit material in specific locations. DED method does not require a flat substrate, and may be a preferred AM method in cases where the substrate portion is not substantially flat, which will be further described below.

[0050] Additive manufacturing methods are generally more expensive than using conventional subtractive manufacturing methods. In the extrusion die of the present disclosure, the die parts are only partially formed by means of AM, so that only the portion that is most difficult to manufacture with subtractive methods is made by an AM method. This additively manufactured portion is referred to as the functional portion in this context. Thus, by manufacturing as large a portion as possible by a less expensive method, and using that portion as a substrate for the additively manufactured functional portion, the cost for the die can be reduced even though very complicated die geometries are needed.

[0051] The portholes of the male bridge portion extend through the substrate portion of the male bridge part, from the rear end surface to the front-end surface, viewed in an extrusion direction, thus the porthole openings are present on the surface thereof. The partition walls between the portholes are generally denoted webs. The surface (in this context; the front-end surface of the substrate portion) comprising the porthole openings and the webs will then act as the attachment surface for the functional portion of the male bridge part deposited on the substrate surface. The additively manufactured male bridge functional portion may include a base portion and a mandrel portion, wherein the base portion has through porthole openings corresponding to, and being an extension of, the substrate porthole openings. In this way the portholes can be partially located in the substrate portion, so that the functional portion need only include details and geometries that are difficult to obtain by conventional subtractive working, such as the mandrel(s) and the mandrel die bearing(s). Hence the mass of the part manufactured by AM is as small as possible which leads to a cost efficient hybrid extrusion die. In addition, being able to fine tune the configuration of the functional parts of the extrusion die by the high precision of AM may also enable better performance of the extrusion die allowing increased production efficiency of extruded profiles, such as higher extrusion speed, and longer die lifetime.

[0052] The base portion of the male bridge functional portion may suitably have a circumference edge surface, which is inclined toward a central axis of the extrusion die. Similarly, the die plate functional portion may have a circumference edge surface which is inclined toward a central axis of the extrusion die. Such inclined circumference edge surface provides a small space between the functional portion and adjacent parts of the extrusion die, which may have the effect of reducing the risk of stress and cracks in the functional portion.

[0053] The additively manufactured base portion of the male bridge functional portion and / or the die plate functional portion may suitably have a thickness of 2-100 mm in a direction parallel to the central axis of the extrusion die.

[0054] The extrusion die can advantageously include a spacer part arranged between the male bridge part and the die plate part, and configured to be in contact with the male bridge part at one end and the die plate part at the opposite end. The spacer part can be used to assemble the male bridge part and the die plate part, as well as defining the welding chamber volume. The spacer part may have a rather simple shape that can advantageously be obtained by subtractive manufacturing, and thus even less of the extrusion die needs to be made by additive manufacturing, thus further reducing the manufacturing cost. Suitably, the spacer may include a connection means, such as a recess, on one or both sides or ends configured to receive a mating connection means, such as a protruding part of the substrate portion or the functional portion of the male bridge part and / or the die plate part. By having a recess and mating protrusion the substrate portion or the functional portion of the male bridge part and / or the die plate part can abut a bottom surface of the recess ensuring correct orientation of the parts. The functional portions of the male bridge part and / or the die plate part may have specific circumference edge shapes, and the connection recess may suitably have a mating circumference shape to receive the protruding part of the functional portion.

[0055] In hot metal extrusion, the material is pushed through the extrusion die at considerable speed and force. Due to the forming heat and heat generated by friction and shear there is an increase in the temperature during extrusion, and the process must be controlled to avoid to too high temperature in the extruded profile exiting the extrusion die. Too high temperatures may result in surface defects in the extruded profiles. Very high loads on the extrusion die, especially the die bearings may also reduce the die lifetime. It is thus important to keep control of the heat in the extrusion die, and a common method is to reduce the extrusion speed. Cooling extrusion dies with liquid nitrogen between backer and bolster is also known to cool the die, however such cooling is more global and does not have much impact on the walls of an extruded profile. In an embodiment of the extrusion die according to the present disclosure, the male bridge part or the die plate part, or both, may include conformal die cooling channels. The cooling channels are preferably located within the die functional portion or in the interface between the die substrate portion and the die functional portion, or both. Such cooling channels can effectively be obtained during additive manufacturing of the die functional portion, and are suitably configured to form a part of a cooling circuit in the extrusion die, which is adapted to be connected to a source of cooling medium. The cooling channels may be located entirely in the functional portion of the male bridge part and / or the functional portion of the die plate part, which means that they are entirely made by additive manufacturing. For example, the male bridge part may comprise cooling channels for local cooling of the die bearing located on the mandrel, which also leads to effective cooling of the extruded profile. Male bridge cooling channels are beneficially in connection with cooling channels in the male bridge base portion, which are preferably formed on the webs, so that cooling medium can be led from the male bridge base portion to the mandrel die bearing. Cooling channels in the webs enables a high flexibility of the cooling circuits, such as bringing cooling fluids to two or more mandrels and mandrel die bearings. Similarly, the die plate part may comprise die plate cooling channels for cooling the die plate bearing, which correspondingly also lead to effective cooling of the extruded profile.

[0056] The extruded profile can be further cooled immediately after the die bearing exit by flushing the cooling fluid onto the extrusion profile via several cooling flushing exit channels around the profile. The cooling flushing exit channels can be located about 1-20 mm, preferably 2-10 mm, from the bearing exits, in the extrusion direction.

[0057] By cooling the die bearings in either the mandrel, or the die plate part, or both, the temperature of the profile is significantly reduced. Enhanced cooling of the profile may be obtained by the said flushing of cooling fluid on the extruded profile. By effecting localized cooling of the extruded profile, the extrusion speed can be increased without inducing surface defects on the extruded profile, hence the production speed can be significantly increased without compromising the quality of the extruded profile. Extrusion dies with cooling channels as described herein are especially beneficial in dies for extrusion of hard alloys where productivity is low due to tearing limitations.

[0058] Alternatively, the cooling channels can entirely or partially be formed in the interface between the attachment surface of the die substrate portion of the male bridge part and / or the die plate part and the respective functional portion. This can be obtained by including one or more recesses obtained by subtractive working in the attachment surface of the die substrate portion, where the recess forms a part of a cooling channel, while the remaining part of the cooling channel is located in the functional portion. Accordingly, the cooling channels may be entirely located in the interface between substrate portion and functional portion, entirely in the functional portion, or a combination thereof, thus giving flexibility in designing various extrusion die types.

[0059] When a spacer part is included in the extrusion die, the spacer part may preferably comprise one or more through channels having inlet and outlet openings that are positioned so as to correspond to inlet and outlet openings of cooling channels arranged in the male bridge functional portion and / or the die plate functional portion. Thereby, the cooling channels in the male bridge functional portion and / or the die plate functional portion can be connected so as to form one or more cooling circuit(s). In case connection recesses are present in the spacer on one or both sides thereof, the cooling channel(s) can suitably be located in the part of the spacer where the recess(es) are. The die plate bearing and the mandrel die bearing may be connected to the same or different cooling circuits as desired. Suitably, the cooling circuit can be configured to be connected to a cooling fluid supply source via inlet and outlet channels arranged in the die plate part or in the spacer part, which allow access to the extrusion die in a convenient manner. One or more cooling channels may be in the form of flushing channels with exit immediately after the bearing exit, e.g. 1-20 mm, preferably 2-10 mm, after the mandrel die bearing exit, and / or the die plate bearing exit.

[0060] In all described embodiments, the cooling fluid is preferably air, nitrogen gas or liquid nitrogen, however not limited to these as other cooling fluids may be used.

[0061] Trials have been conducted comprising extrusion of AA6063 aluminium alloy billets in a 7" (178 mm) press into a profile with three cavities by use of hybrid extrusion dies according to the present disclosure, where the die bearings were provided with cooling channels 5-6 mm distance from the die bearings and using N2 gas as cooling fluid. The trials showed consistently a speed increase of 15-20 %, compared to running the extrusion using the same equipment without N2 gas cooling. The extruded profiles had an excellent surface quality. Also, the die lifetimes for the test runs were high (>100 days) and comparable to regular extrusion dies despite the significantly increased extrusion speed. It is believed that cooling with liquid nitrogen and decreasing the distance from the cooling channels to the bearings will improve cooling, and the productivity can be increased even more.

[0062] The extrusion die according to the present disclosure is suitably made of steel. The substrate portion may be made from a moulded first precipitation-hardening tool steel and the functional portion is obtained by depositing a second precipitation-hardening tool steel onto the substrate portion by using additive manufacturing (AM) method, thereby forming a hybrid part comprising the substrate portion and the AM functional portion. The AM method comprises providing a substrate blank, which may be an annealed hot work tool steel blank correspondingly as in the conventional die manufacture. The method comprises forming CAD / CAM of the die for the manufacturing, wherein the design of the extrusion die is made, including the substrate portion and the functional portion. The substrate blank is shaped and prepared for additive manufacturing deposition. Machining techniques such as turning, grinding and milling are used for gross dimensions. For the surface preparation of the interface between the substrate part and the AM part, the preparation may include grinding and milling, and slight polishing. A 2D slicing data file is generated of the 3D AM part by using a slicing software, which is generally known in the field. Such slicing data file specifies layer thickness, toolpaths and supports, and optionally other parameters, to be used by the AM printing machine.

[0063] The substrate is positioned in the AM printing machine and aligned with the machine coordinate system. The AM printing may be performed according to known methods in the field. Performing AM by using PBF technology, the bed is filled with hot-work tool steel powder, and the laser (or alternatively an EB) builds layer by the layer the additive part on top of the substrate. If AM is performed by DED technology, the wire or powder is directly melted on the substrate building layer by layer. After the AM printing is finished, supports can be removed and the hybrid die part, i.e. the substrate portion including the AM functional portion deposited thereon, is removed from the machine for further treatments.

[0064] The further treatment may include heat treatment the hybrid die part. The heat treatment may comprise annealing of the hybrid die part to decrease internal stress in the material, followed by a solutionizing treatment, quenching and tempering. The tempering may comprise 2 or 3 tempering treatments for obtaining the desired hardness of the hybrid die part. The heat treatment may be performed according to established heat treatment procedures for tool steels, such as described above in Step 3 for a conventional die manufacturing process; e.g. a heat treatment comprising annealing at about 700 °C, austenitizing (solutionizing) at about 1020 °C, and quenching. Tempering may typically be carried out at about 600°C, with cooling between each tempering. It should however be noted that different tool steels may have other heat treatment temperatures profiles, as is known to the skilled person in the field. It has been found that performing the AM at an elevated temperature, e.g. using preheating temperature in the AM machine in the range of 350-550 °C, preferably in the range of 400- 500 °C, it has been observed that less internal stress is developed in the hybrid die part, and the annealing step may be omitted.

[0065] The first precipitation-hardening tool steel may be a tool steel which, when moulded and subjected to said heat treatments, obtains a ductility of at least 8% elongation before rupture. The first precipitation-hardening tool steel may be a tool steel which, when moulded and subjected to said heat treatments, obtains a yield strength of at least 1100 MPa. The first precipitation-hardening tool steel may be a tool steel which, when moulded and subjected to said heat treatments, obtains a tensile strength of at least 1400 MPa. The first precipitation-hardening tool steel, constituting the substrate portion, preferably obtains a hardness in the range of 45-57 HRC, when subjected to the above heat treatments.

[0066] The first precipitation-hardening tool steel may have the following composition, in weight%: C 0.30-0.55, Cr 2.40-5.50, Mo 1.05-3.50, V 0.30-1.40, Mn 0.20-0.55, Si 0.20-1.25, Ni+Cu 0-0.80, balance Fe and unavoidable impurities, or alternatively the following composition, in weight%: C 0.32-0.52, Cr 4.3- 5.3, Mo 1.3-3.2, V 0.5-1.2, Mn 0.20-0.55, Si 0.15-1.10, Ni+Cu 0-0.80, balance Fe and unavoidable impurities. Examples of standard steel types suitable as the first precipitation-hardening tool steel for the substrate blank may be an annealed hot work steel chosen from the group comprising; AISI H13 corresponding to 1.2344 (EN steel number); AISI Hll corresponding to 1.2343 and 1.2367 (EN steel number); BOHLER W360; Dievar by Uddeholm or TQl steel (Hitachi Metals), all having a hardness of 220- 260 HB.

[0067] The second precipitation-hardening tool steel may be a tool steel which, when deposited by means of said additive manufacturing and subjected to said heat treatments obtains a ductility of at least 8% elongation before rupture. The second precipitation-hardening tool steel may be a tool steel which, when deposited by means of said additive manufacturing and subjected to said heat treatments obtains a yield strength of at least 1100 MPa. The second precipitation-hardening tool steel may be a tool steel which, when deposited by means of said additive manufacturing and subjected to said heat treatments obtains a tensile strength of at least 1400 MPa. The second tool steel, constituting the AM functional portion, preferably obtains a hardness in the range of 45-57 HRC when subjected to the said heat treatments.

[0068] The second precipitation-hardening tool steel is in the form of a steel alloy powder suitable for additive manufacturing, and may have the following composition, in weight%: C 0.30-0.55, Cr 2.40-5.50, Mo 1.05-3.50, V 0.30-1.40, Mn 0.20-0.55, Si 0.20-1.25, Ni+Cu 0-0.80, balance Fe and unavoidable impurities, or alternatively the following composition, in weight%: C 0.32-0.52, Cr 4.3-5.3, Mo 1.3-3.2, V 0.5-1.2, Mn 0.20-0.55, Si 0.15-1.10, Ni+Cu 0-0.80, balance Fe and unavoidable impurities. Examples of standard steel types suitable for the second precipitation-hardening tool steel for the additive manufacturing are hot work steel chosen from the group comprising; AISI H13 corresponding to 1.2344 (EN steel number); AISI Hll corresponding to 1.2343 and 1.2367 (EN steel number); BOHLER W360; Dievar by Uddeholm or TQl steel (Hitachi Metals).

[0069] Mechanical properties as measured according to standards ISO 6892-1 for room temperature, and ISO 6892-2 for elevated temperatures.

[0070] It is further disclosed a method of repairing or restoring a used and damaged aluminium extrusion die. The damaged aluminium extrusion die may be a conventionally manufactured extrusion die, made by using traditional subtractive manufacturing, or a hybrid extrusion die manufactured both by using subtractive manufacturing and additive manufacturing, as disclosed above. Extrusion dies are especially subjected to wearing and damage on the parts exposed to the highest forces, such as the die plate bearings and the mandrel die bearings. In addition, for the male bridge parts, common damages may be in the form of cracks in the webs separating the portholes and deformation or breakage of the mandrel part in addition to wear at the bearing. A defect extrusion die would typically be taken out of service and scrapped. Thus, it is desired to repair and restore extrusion dies that are taken out of service due to wear or damage. The hybrid extrusion die according to the present disclosure may therefore be a repaired die, wherein the substrate portion of the male bridge part and / or the substrate portion of the die plate part is made up of a used extrusion die part.

[0071] The method disclosed above for additively manufacturing functional portions of extrusion dies may also be used for repairing used extrusion dies. The extrusion die taken out of service will typically be of the same type of precipitation-hardening hot work tool steel as disclosed above, having a composition, in weight%: C 0.30-0.55, Cr 2.40-5.50, Mo 1.05-3.50, V 0.30-1.40, Mn 0.20-0.55, Si 0.20- 1.25, Ni+Cu 0-0.80, balance Fe and unavoidable impurities, or alternatively the following composition, in weight%: C 0.32-0.52, Cr 4.3-5.3, Mo 1.3-3.2, V 0.5-1.2, Mn 0.20-0.55, Si 0.15-1.10, Ni+Cu 0-0.80, balance Fe and unavoidable impurities. However, differently from the above disclosed method, in the method for repairing a damaged extrusion die, the start material is a heat-treated steel material.

[0072] The first step of the method for repairing the extrusion die may be inspecting the die and damaged parts and potential damaged parts. A 3D CAD can be made for the design of the die, comprising the design of the AM part and part to be removed from the used die. The design of the AM part may comprise cooling channels having corresponding configuration as described above. CAM programs are preferably made for machining steps. The damaged parts, and any potential damaged parts, of the used extrusion die may be removed by machining techniques. Such machining techniques may include milling, grinding, turning, erosion and / or cutting, e.g. wirecutting, or other machining technique known in the field. In a repairing case where the die plate is damaged, such as deformation, breakage or wear of the die plate bearing, the damaged die plate bearing is removed, leaving a die plate substrate portion with a surface acting as an attachment surface for depositing a reconstructed part by use of AM.

[0073] In a repairing case where the male bridge part is damaged, such as deformations, wear or breakage of a mandrel and / or cracks in the webs between the portholes, the damaged parts of the male bridge part are removed. If the damage is located only on the mandrel part, it may be sufficient to remove only the mandrel, or mandrels if more than one, however, parts of an area surrounding porthole openings and upper surface of webs may also be removed. Removing parts of a base surrounding the mandrel and portholes enables formation of cooling channels via the webs. In case there are deformations or cracks in the webs, the area surrounding the porthole openings and upper surface parts of the webs are removed in addition to the mandrel, or mandrels if more than one mandrel. The male bridge substrate obtained by removal of the damaged parts has a surface acting as an attachment surface for depositing a reconstructed part by use of AM.

[0074] After removal of the damaged parts the die substrate portion may be annealed, however annealing is not required before depositing the repairing part by use of AM. On the contrary, when repairing a used extrusion die, the substrate part already is a hardened steel with net shape, and it may be preferred to avoid annealing and do full heat treatment after AM to avoid distortion of the substrate dimensions. After removing the damaged part(s) from the used extrusion die, the attachment surface forming the interface between the substrate portion and the functional AM part may further be prepared before AM deposition, e.g. by grinding, milling and slight polishing.

[0075] The AM process may include depositing a second precipitation-hardening tool steel in the form of a steel alloy powder suitable for additive manufacturing, and following heat treatment process for the repair method may correspond with the process as disclosed above. The steel compositions and mechanical properties of a repaired extrusion die may typically be the same as disclosed above for the manufacturing of the hybrid extrusion die, hence the second precipitation-hardening steel alloy powder may have the following composition, in weight%: C 0.30-0.55, Cr 2.40-5.50, Mo 1.05-3.50, V 0.30-1.40, Mn 0.20-0.55, Si 0.20-1.25, Ni+Cu 0-0.80, balance Fe and unavoidable impurities, or alternatively the following composition, in weight%: C 0.32-0.52, Cr 4.3-5.3, Mo 1.3-3.2, V 0.5-1.2, Mn 0.20-0.55, Si 0.15- 1.10, Ni+Cu 0-0.80, balance Fe and unavoidable impurities. The heat treatment may be performed according to established heat treatment procedures for tool steels, such as described above in Step 3 for a conventional die manufacturing process; e.g. a heat treatment comprising annealing at about 700 °C, austenitizing (solutionizing) at about 1020 °C, and quenching. Tempering may typically be carried out at about 600°C, with cooling between each tempering. It should however be noted that different tool steels may have other heat treatment temperatures profiles, as is known to the skilled person in the field. Performing the AM at an elevated temperature, e.g. using preheating temperature in the AM machine in the range of 350-550 °C, preferably in the range of 400-500 °C, less internal stress may be developed in the hybrid die part, and the annealing step may be omitted. Both the AM functional portion and the substrate portion of the used extrusion die preferably obtain a hardness in the range of 45-57 HRC when subjected to the heat treatments.

[0076] Alternatively, and as mentioned above, it may be desired to avoid doing a full heat treatment of the repaired extrusion die to avoid any distortion of the dimensions of the hardened substrate already having net shape. Therefore, according to a preferred embodiment of the method for repairing a damaged extrusion die, the AM deposition may be performed by using DED with metal wire as feedstock, which is melted by a heat source and deposited on the used extrusion die substrate layer by layer. The metal wire may be a steel alloy wire suitable for additive manufacturing. The steel compositions of the steel alloy wire may be, in weight%: C 0.30-0.55, Cr 2.40-5.50, Mo 1.05-3.50, V 0.30-1.40, Mn 0.20-0.55, Si 0.20-1.25, Ni+Cu 0-0.80, balance Fe and unavoidable impurities, or alternatively the following composition, in weight%: C 0.32-0.52, Cr 4.3-5.3, Mo 1.3-3.2, V 0.5-1.2, Mn 0.20-0.55, Si 0.15-1.10, Ni+Cu 0-0.80, balance Fe and unavoidable impurities. Wire based DED is especially suitable for repairing large extrusion dies where large parts are deposited by AM due to the high deposition rate and more flexible equipment compared with powder bed fusion AM. Wire based DED is also especially suitable for repairing male die bridge parts since with DED a flat interface between the AM part and substrate part is not needed. DED allows an interface with various geometry and angle, thus it can be adapted to a variety of attachment surfaces obtained after removing damaged parts. The heat source for melting the steel wire is preferably laser beam, although other known heat sources may be used.

[0077] After the wire DED the die substrate part with the functional AM part should preferably be heat treated to obtain desired hardness of the AM part, preferably in the range of 46-50 HRC. When the AM part is deposited on a hardened, net shape die substrate the heat treatment preferably comprises tempering to lower the hardness of the AM part, such as twice with cooling between each tempering. Tempering temperature should be according to appropriate heat treatment temperature profile for the specific steel, typically around 600°C, however not limited to this specific temperature.

[0078] Wire based DED provides dense and strong parts with good mechanical properties meeting extrusion die requirements. Wire based DED may provide near net shape, thus, AM parts deposited by wire DED on the die substrate may need more extensive post-processing to obtain the final shape of the repaired extrusion die compared with PBF AM parts. The post-processing of the AM functional part may be done by milling and grinding. A specific CAD may be generated to erode the part with cupper electrode, graphite electrode or wire to obtain the final shape. As the final step the die may be polished to decrease the surface roughness. Repairing damaged aluminium extrusion dies saves significant amounts of die steel material compared with scrapping damaged dies. For large extrusion dies the steel savings may be up to about a ton of die steel. Extrusion dies can be repaired repeatedly, thus reducing the consumption of hot tool steel material, leading to less CO2 footprint for the extrusion industry.

[0079] Description of example embodiments

[0080] Fig. 1 shows an extrusion die 1 including a male bridge part 2 comprising two or more portholes (not shown) and a mandrel 4, and a die plate part 5. In this embodiment, the male bridge part 2 and the die plate part 5 are both comprised of a die substrate portion 7,14 obtained by subtractive manufacturing, and a die functional portion 8,15 obtained by additive manufacturing. The die substrate portion 7,14 has a surface acting as an attachment surface for the die functional portion 8,15, and the die functional portion comprises a die bearing 8', 15'. Figs. 2-3 illustrates a mandrel die bearing 8' and Figs. 4-5 illustrate a die plate bearing 15'. As illustrated in Fig. 1, the extrusion die further may include a spacer part 18 arranged between the male bridge part 2 and the die plate part 5, which is configured to be in contact with the male bridge part and the die plate part.

[0081] Figs. 2-3 shows an embodiment where only the male bridge part 2 includes a die substrate portion 7 obtained by subtractive manufacturing, and a die functional portion 8 obtained by additive manufacturing, whereas the die plate part 5 is made entirely by subtractive manufacturing.

[0082] Figs. 4-5 shows an embodiment where the die plate part 5 includes a die substrate portion 14 obtained by subtractive manufacturing, and a die functional portion 15 obtained by additive manufacturing.

[0083] In all the illustrated embodiments, die cooling channels 16, 17 are included in the die functional portion 8 of the male bridge part and mandrel, and / or the die functional portion of the die plate part 15. These cooling channels have been obtained during additive manufacturing of the die functional portion, and may be configured to form a part of a cooling circuit in the extrusion die. In these illustrated cases, the attachment surface of the die substrate portion 7, 14 of the male bridge part 2 and / or the die plate part 5 is substantially flat, and the cooling channels are located entirely in the functional portion of the male bridge part 2 and / or the die plate part 5. The male bridge cooling channels 16 for cooling the die bearing 8' located on the mandrel can connect the mandrel portion 12 with the male bridge functional base portion 11 and can be configured to form a part of a cooling circuit in the extrusion die.

[0084] Alternatively (not shown), the cooling channels forming part of a cooling circuit may be located in the interface between the die substrate portion 7, 14 and the die functional portion 8, 15 of the male bridge and / or the die plate part, and the attachment surface of the die substrate portion 7,14 of the male bridge part 2 and / or the die plate part 5, may then include one or more recesses obtained by subtractive working, which partially form cooling channels, and the die functional portion 8,15 obtained by additive manufacturing includes the remaining part of the cooling channels.

[0085] The portholes of the male bridge part suitably extend through the substrate portion 7 of the male bridge part 2, such that the porthole openings are present on a surface 10 thereof. This surface acts as an attachment surface for the functional portion 8 of the male bridge part 2, which is arranged on the substrate surface. The male bridge functional portion thus includes a base portion 11 and a mandrel portion 12, and the base portion 11 has through porthole openings 13 that correspond to the substrate porthole openings.

[0086] The base portion 11 of the male bridge functional portion 8 can have a circumference edge surface 25, which is inclined toward a central axis A of the extrusion die, and / or the die plate functional portion 15 can have a circumference edge surface 26 which is inclined toward a central axis A of the extrusion die.

[0087] As illustrated in Fig. 1 a spacer part 18 can be arranged between the male bridge part 2 and the die plate part 5. The spacer part is suitably obtained by subtractive manufacturing, and can, as illustrated in Fig. 1, include one or more through channels 19 having inlet and outlet openings 20,21 that are positioned so as to correspond to inlet and outlet openings 22,23 of the cooling channels arranged in the male bridge functional portion 8 and / or the die plate functional portion 15. Thereby, the cooling channels in the male bridge functional portion 8 and / or the die plate functional portion 15 can be connected so as to form a cooling circuit. Fig. 6 shows an example of a spacer part having a shape adapted to the shape of the die plate shown in Fig. 4.

[0088] The cooling circuit is configured to be connected to a cooling fluid supply source (not shown) via inlet and outlet channels arranged in the die plate part 5 or in the spacer part 18.

[0089] Fig. 8 is a flowchart illustrating a process of manufacturing an extrusion die according to the present disclosure. Dashed lines illustrate flow of digital data, while solid lines illustrate flow of parts. The starting material in Step 1 is an annealed hot work tool steel blank. Step 1-2 is CAD / CAM of die for machining, where the design of the part, including a substrate and a functional part, is done. The CAM programs are made for the steps 2 and 4. In Step 2, the blank is turned and milled to gross dimensions of the substrate part. The steps of additive manufacturing is illustrated in the block 3. In 3-1 the surfaces of the substrate from Step 2, which forms the interface between the substrate and the functional AM part, is prepared. Preparation may include grinding of sharp edges, and grinding or milling the surface. The surface preparations may also include slight polishing. 3-1-1 illustrates slicing the 3D of the AM part in 2D layers by use of slicing software. The slicing software generates a file that may specify layer thickness, toolpaths and supports, used by the AM 3D printer. Step 3-2 illustrates the 3D printing step on substrate part. The 3D printing can be done e.g. by EB-PBF, LB-PBF or DED. The substrate is positioned in the 3D printing machine and aligned with the machine coordinate system. The sliced file is loaded in the machine. In an AM machine based on PBF technology, the bed is filled with alloyed hot work steel powder. During the AM the laser, or electron beam, will build up layer-by-layer forming the AM part on top of the substrate. In an AM machine based on DED technology, the laser will directly melt a wire or powder on the substrate. If supports are used or created during the AM, such supports can be removed at stage 3-3, or alternatively at Step 4 or Step 5. Step 3-4 represents a heat treatment step, wherein the combined parts including the substrate and the AM part on the substrate is heat treated. The heat treatment comprises annealing of the combined part, followed by a solutionizing treatment, quenching and 2 or 3 temperings for hardening of the steel. As discussed in the present disclosure, the annealing step of the heat treatment may be omitted. After the heat treatment, the part is milled to near net shape in Step 4. Step 4-1 represents generation of CAD / CAM of die for erosion, wherein a specific CAM is generated to erode with cupper electrode, graphite electrode or wire, or other means used for such erosion. In Step 5 erosion is used to obtain the finished net shape. Step 6 represents the polishing step, wherein the die is polished to decrease surface roughness.

[0090] Fig. 9 illustrates a flowchart for repairing a used extrusion die having damaged parts. In the process for repairing a damaged extrusion die, the starting material in Step 1' is a used extrusion die, thus the die steel is normally a hardened steel having a net shape. Step 1' comprises inspection of a damaged die. In Step 1-2' a 3D CAD of the extrusion die is made, hence comprising the design of the AM part and parts to be removed from the damaged die. CAM programs for the Steps 2' and 4 are thus made. In Step 2' the damaged part to be repaired is removed, generally including removal of the part by milling, grinding and / or cutting, e.g. wirecutting. By removal of the damaged part it is obtained a die substrate consisting of the used die with a surface for depositing a repaired part replacing the removed part. The steps of additive manufacturing is illustrated in the block 3. In step 3-1 the surfaces of the substrate from Step 2', which forms the interface between the substrate and the functional AM part, is prepared. Preparation may include grinding of sharp edges, and grinding or milling the surface. The surface preparations may also include slight polishing. Step 3-1-1 illustrates the software for the AM process. In an AM process using DED, such as wire based DED, the AM software in step 3-1-1 may be a tool path generation for the laser head. Step 3-2 illustrates the AM deposition step on the substrate part. The substrate may be positioned on a 3D printing machine base plate or fixture and aligned with the machine coordinate system. In an AM machine based on PBF technology, the bed is filled with alloyed hot work steel powder. During the AM the laser, or electron beam, will build up layer-by-layer forming the AM part on top of the substrate. In an AM machine based on DED technology, a heat source, such as a laser, directly melts a wire or powder on the substrate building the part layer by layer. For large dies requiring large AM functional parts, and for repairing male bridge parts, it is preferred to use wire based DED. If supports are used or created during the AM, such supports can be removed at stage 3-3, or alternatively at Step 4 or Step 5. Step 3-4 represents a heat treatment step, wherein the combined parts including the substrate and the AM part on the substrate is heat treated. After the heat treatment, the part is milled to near net shape in Step 4. Step 4-1 represents generation of CAD / CAM of die for erosion, wherein a specific CAM is generated to erode with cupper electrode, graphite electrode or wire, or other means used for such erosion. In Step 5 erosion is used to obtain the finished net shape of the repaired die. Step 6 represents the polishing step, wherein the die is polished to decrease surface roughness.

[0091] List of reference numbers used in drawings:

[0092] 1. Extrusion die.

[0093] 2. Male bridge part.

[0094] 4. Mandrel.

[0095] 5. Die plate part.

[0096] 7. Die substrate portion (male bridge part).

[0097] 8. Die functional portion (male bridge part).

[0098] 8'. Die bearing (mandrel die bearing).

[0099] 10. Surface of die substrate portion (male bridge part).

[0100] 11. Base portion of die functional portion (male bridge part).

[0101] 12. Mandrel portion of die functional portion (male bridge part).

[0102] 13. Porthole openings.

[0103] 14. Die substrate portion (die plate part).

[0104] 15. Die functional portion (die plate part).

[0105] 15'. Die bearing (die plate bearing).

[0106] 16. Male bridge cooling channels.

[0107] 17. Die plate cooling channels.

[0108] 18. Spacer part.

[0109] 19. Through channels (spacer part).

[0110] 20. Inlet / outlet openings (spacer part).

[0111] 21. Inlet / outlet openings (spacer part).

[0112] 22. Inlet / outlet openings (cooling channels 16 and / or 17).

[0113] 23. Inlet / outlet openings (cooling channels 16 and / or 17).

[0114] 25. Circumference edge (male bridge part).

[0115] 26. Circumference edge (die plate part).

[0116] 102. Used male bridge part.

[0117] 103. Used die substrate portion (male bridge part). 104. Defect part including mandrel, mandrel bearings, parts of webs and portholes of used male bridge part.

[0118] 105. Surface of used die substrate portion (male bridge part).

[0119] 106. Used die plate part.

[0120] 107. Used die substrate portion (die plate part).

[0121] 108. Defect part of used die plate part, including die plate bearings.

[0122] 109. Surface of used die substrate portion (die plate part).

[0123] 110. Repaired male bridge die part.

[0124] 111. Base portion of AM deposited die functional portion including parts of webs and portholes (repaired male bridge part).

[0125] 112. AM deposited mandrel die bearing (repaired male bridge part).

[0126] 113. AM deposited mandrel (repaired male bridge part).

[0127] 114. Substrate portion of repaired die (male bridge part).

[0128] 115. Repaired die plate part.

[0129] 116. Repaired die functional portion, including die plate bearing (die plate part).

[0130] 117. Substrate portion of repaired die (die plate part).

[0131] A trial comprising extrusion of 40 billet of a 6063 alloy in a 7" extrusion press was conducted to test cooling capacity and surface quality of the extruded profiles. The extrusion die comprised a hybrid die according to the present disclosure, with cooling channels in the functional part of the bearings, 6 mm distance from the bearings. In addition, flushing channels were provided around the profile immediately after the bearing exit. Cooling fluid was nitrogen gas. Extrusion billet temperature was 465 °C initially, and reduced to 450 °C at billet no. 15 and thereafter kept constant.

[0132] Fig. 10 shows the temperature in the die bearings measured with a thermocouple a couple of millimetres away from the surface of the bearings. The three first billets were run without cooling reaching a peak die temperature of about 529 °C, at the thermocouple position close to the bearings. Opening the GN2 (nitrogen gas) valve decreased the die temperature by 12°C. Increasing the speed to 62 m / min while decreasing the billet temperature led to an increase of the die temperature by 6°C. Above 65 m / min, the billet oven could not follow, and longer dead cycle led to a stronger decrease of the minimum die temperature and a larger temperature variation within the extrusion cycle. Increasing the speed up to 70 m / min increased the max die temperature by 2°C. When closing the GN2 valve, the max die temperature increased by 12°C after 1 billet and 4°C more after 6 billets. Fig. 11, shows the profile temperature of each billet extruded at the die exit, and with different extrusion speeds, as shown by the dotted line which is the average of puller speed. As shown in Fig. 11, the exit temperature was stable and could be trusted. The increase of speed from 38 m / min to 52 m / min between billets 5 and 10 lead to 10°C increase of the exit temperature, however only 4°C at the bearing area. Between billet 11 and 23, the exit temperature was rather stable around 602°C despite an increase speed from 52m / min to 62m / min. At 70m / min, despite longer dead cycle, the exit temperature increased to 604°C-606°C (2-4°C increase). Closing the GN2 valve brought the exit temperature to 606- 609°C (2-3°C increase in average). No increase of the extrusion force was noticed during the trials. The surface quality of the profiles had no tearing or other defects. Die inspection after the trials did not show critical damages.

Claims

CLAIMS1. An aluminium extrusion die (1) made of steel including a male bridge part (2) comprising two or more portholes and at least one mandrel (4), and a die plate part (5), characterised in that the male bridge part (2), or the die plate part (5), or both the male bridge part (2) and the die plate part (5), comprise- a subtractively manufactured die substrate portion (7,14); and- an additively manufactured die functional portion (8,15); wherein the die substrate portion (7,14) has a surface acting as an attachment surface for the die functional portion (8,15); the die functional portion (8,15) comprises a die bearing (8', 15'), wherein, for the male bridge part (2), the portholes extend through the die substrate portion (7) such that porthole openings are present on a surface (10) thereof, said surface acting as the attachment surface for the die functional portion (8) of the male bridge part (2), which die functional portion (8) includes a base portion (11) and a mandrel portion (12), wherein the base portion (11) has through porthole openings (13) corresponding to the substrate porthole openings.

2. The aluminium extrusion die of claim 1, wherein the male bridge part (2) and / or the die plate part (5) comprises die cooling channels (16,17) located within the die functional portion (8,15), and / or located in an interface between the die substrate portion (7,14) and the die functional portion (8,15), said die cooling channels (16,17) having been obtained by additive manufacturing of the die functional portion (8,15), and being configured to form a part of a cooling circuit in the extrusion die.

3. The aluminium extrusion die of any one of the preceding claims, wherein the functional portion (8) of the male bridge part (2) comprises male bridge cooling channels (16) for cooling the mandrel die bearing (8'), connecting the male bridge base portion (11) with the mandrel portion (12), said cooling channels having been obtained during additive manufacturing of the male bridge functional portion (8), and being configured for form a part of a cooling circuit in the extrusion die.

4. The aluminium extrusion die of any one of the preceding claims, further including a spacer part (18) arranged between the male bridge part (2) and the die plate part (5), and being configured to be in contact with the male bridge and the die plate part.

5. The aluminium extrusion die of claim 4, wherein the spacer part (18) comprises one or more through channels (19) having inlet and outlet openings (20,21) that are positioned so as to correspond to inlet and outlet openings (22,23) of the cooling channels arranged in the male bridge functional portion (8) and / or the die plate functional portion (15), so that the cooling channels in the male bridge functional portion (8) and / or the die plate functional portion (15) are connected so as to form a cooling circuit.

6. The aluminium extrusion die of any one of the preceding claims, wherein the cooling circuit is configured to be connected to a cooling fluid supply source via inlet and outlet channels arranged in one or more of the die plate part (5), the male bridge part (2), or in the spacer part (18).

7. The aluminium extrusion die of any one of the preceding claims, wherein the cooling channels comprise a plurality of cooling fluid flushing channels arranged immediately after the mandrel die bearing (8') and / or the die plate bearing (15'), relative to an extrusion direction.

8. The aluminium extrusion die according to any one of the preceding claims, wherein the extrusion die is a repaired die in which the die substrate portion (7,14) of the male bridge part (2), or the die plate part (5), or both, is made up of a previously used extrusion die.

9. A method for repairing a damaged aluminium extrusion die made of steel, the extrusion die comprises a die plate part with a die plate bearing, and a male bridge part comprising two or more portholes, separated by webs, and at least one mandrel (4) with a mandrel die bearing, the method comprises the steps:(a) removing damaged parts from the die plate part, and / or from the male bridge part, thereby obtaining a die substrate portion with a surface acting as an attachment surface for depositing a reconstructed part;(b) depositing a reconstructed part on the attachment surface of the die substrate portion using additive manufacturing;(c) heat treating the die substrate portion with the reconstructed part deposited thereon;(d) machining the deposited reconstructed part to a final shape.

10. The method according to claim 9, wherein, when repairing a damaged male bridge part where the mandrel and / or the mandrel die bearing is damaged, step (a) comprises removing the mandrel with the mandrel die bearing, and optionally parts of a surface surrounding the portholes including parts of a surface of the webs separating the portholes.

11. The method according to claim 9, wherein, when repairing a damaged male bridge part where at least one of the webs separating the portholes is damaged, step (a) comprises removing parts of a surface surrounding the portholes including parts of a surface of the webs separating the portholes and the at least one mandrel.

12. The method according to claim 9, wherein, when repairing a damaged die plate part, step (a) comprises removing the die plate bearing.

13. The method according to any one of claims 9-12, wherein the step (a) of removing damaged parts is done by subtractive machining, comprising one or more of cutting, turning, milling, grinding and erosion.

14. The method according to any one of claims 9-13, wherein the depositing of step (b) is performed by using powder bed fusion (PBF) or directed energy deposition (DED) using powdered or wire feedstock material.

15. The method according to claim 14, wherein the additive manufacturing depositing step (b) is performed by using DED with wire feedstock material and laser as a heat source.

16. The method according to any one of claims 9-15, wherein the depositing of step (b) includes forming die cooling channels located within the additively manufactured reconstructed part, and / or located in an interface between the die substrate portion and the additively manufactured reconstructed part.

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