Method for forming a magnet and magnet

Abstract

Method (100) for forming a magnet (10), wherein the method (100) comprises: Forming a slurry (20) comprising magnetic powder material, binder material, and a solvent; Producing a first crude layer (14a') from the slurry (20), wherein the first crude layer (14a') is viscous and flowable; Applying a magnetic field (24) to the first raw layer (14a') to align the magnetic powder material contained in the first raw layer (14a') in a desired direction; Hardening of the first raw layer (14a') to form a hardened first layer (14a) by focusing a laser beam (28) on sections of the first raw layer (14a') that are to be part of the magnet (10) while the magnetic field (24) is applied to the first raw layer (14a'); after the first raw layer (14a') has hardened, a second raw layer (14b') is produced from the slurry (20) in contact with the hardened first layer (14a), wherein the second raw layer (14b') is viscous and flowable; Applying a magnetic field (24) to the second raw layer (14b') to align the magnetic powder material contained in the second raw layer (14b') in the desired direction; Curing the second raw layer (14b') to form a cured second layer (14b) by focusing a laser beam (28) on sections of the second raw layer (14a') that are to be part of the magnet (10) while the magnetic field (24) is applied to the second raw layer (14b'), whereby the cured second layer (14b) adheres to the cured first layer (14a); wherein the generation of the slurry (20) comprises homogeneously mixing the magnetic powder material and the binder, wherein the method (100) further comprises: Providing the magnetic powder material comprising at least one rare earth metal selected from neodymium, iron and boron, and at least one from dysprosium and terbium; Providing the binder, which is organic and comprises at least one of: polyvinyl alcohol (PVA), stearic acid, carnauba wax, phenolic resin, epoxy resin, nylon, polypropylene, polystyrene and poly(methyl methacrylate) (PMMA); Providing the slurry (20) with a viscosity of less than 10 Pascal-seconds; Sintering of the cured first and second layers (14a, 14b); and The cured first and second layers (14a, 14b) are subjected to an isostatic hot pressing (HIP) process.

Description

[0001] The present description relates generally to permanent magnets and methods for forming anisotropic permanent magnets that can be used in electric motors, wind turbines, electric bicycles and devices.

[0002] Permanent magnets are widely used in a variety of devices, including traction motors for hybrid and electric vehicles, wind turbines, air conditioning systems, and other mechanized equipment. Such permanent magnets can be ferrite, Nd-Fe-B, CmCo, CmFeN, Alnico, etc.

[0003] For Nd-Fe-B magnets, the manufacturing processes begin with initial preparation, including testing and weighing the starting materials for the desired material compositions. The materials are then vacuum induction melted and continuously cast to form thin pieces (less than one mm) several centimeters in size. This is followed by hydrogen decrepitation, where the thin pieces absorb hydrogen at about 25°C to about 300°C for about 5 to about 20 hours, are dehydrated at about 200°C to about 400°C for about 3 to about 25 hours, and then subjected to hammer milling and grinding and / or mechanical pulverization or nitrogen milling (if necessary) to form a fine powder suitable for further powder metallurgy processing.This powder is typically sieved for size classification and then blended with other alloy powders for the final desired magnetic material composition.

[0004] In one method, the magnetic powder is mixed with binders to produce green parts (typically in the shape of a cube) by a suitable pressing process in a mold. The powder may be weighed prior to forming into a cubic block or other shape. The formed part is then vacuum-packed and subjected to isostatic pressing, after which it is sintered (for example, at about 800°C to about 1100°C for about 1 to about 30 hours under vacuum) and aged if necessary (for example, at about 300°C to about 700°C for about 5 to about 20 hours under vacuum). Typically, a number of blocks, weighing a total of about 100 kg to about 800 kg, are sintered at the same time as a batch.

[0005] The magnet pieces are then cut and machined into a final shape based on the desired final shape of the magnets from the larger block. A cutting machine with numerous thin blades is used to cut the desired shapes from the magnet block. A large portion of the material is lost during the cutting process, and the thin blades require maintenance. The cutting and machining process to produce the magnets with the desired shape typically results in a relatively large amount of material loss, with the yield typically being about 55 to 75 percent (i.e., about 25 to 45 percent material loss).

[0006] The high material losses during manufacturing and machining have significantly increased the cost of finished rare earth element magnets. These costs have been exacerbated by a dramatic increase in the price of rare earth elements in recent years. Accordingly, there are significant challenges associated with the production of low-cost magnets containing rare earth elements.

[0007] CN 1 05 405 636 A describes a process for producing NdFeB magnets in which magnetic powder is sprayed onto a heated model table.

[0008] DE 34 18 482 A1 describes a magnetic recording medium made of a non-magnetic carrier material with at least one magnetic layer.

[0009] CN 1 07 225 248 A describes a process for producing parts from magnetic material by dual-curing 3D gel printing.

[0010] US 2016 / 0 375 492 A1 describes an additive manufacturing system comprising a carrier, a dispenser which provides metallic powder on the carrier, an energy source to fuse at least one layer of the metallic powder, and a magnet which exposes the layer of metallic powder to a magnetic field during processing of the powder.

[0011] It can be considered as a task to provide an improved method for forming magnets.

[0012] The present disclosure provides a novel method for manufacturing magnets that involves printing magnetic powder material into a desired final magnet shape by printing a series of thin layers of magnetic powder material in a slurry into a three-dimensional shape, which does not require the magnet to be machined into a different final shape. This results in a material savings typically lost during the cutting and machining process of the magnet. Furthermore, by printing the magnetic material in a slurry, a magnetic field can be applied to the slurry to orient the magnetic material in a desired direction before and during curing, and the viscosity from the wetness of the slurry helps maintain the material in the anisotropic orientation before and during curing.

[0013] To align the magnetic powder material in a desired direction, a magnetic field can be applied. Creating layers of magnetic powder material under a magnetic field can cause the magnetic powder material to move significantly due to the magnetic field. However, the present description contemplates a wet slurry containing magnetic powder material and a binder, with the slurry form of the material keeping the magnetic powder intact. The slurry can then be cured by any suitable means, such as a laser, to harden layers of the magnetic layer layer by layer.

[0014] In a form that may be combined with or separate from the other forms described herein, a method of forming a magnet is provided. The method of the invention includes forming a slurry comprising a magnetic powder material, a binder, and a solvent. The method includes creating a first green sheet from the slurry, the first green sheet being viscous and flowable. The method further includes applying a magnetic field to the first green sheet to substantially align the magnetic powder material contained in the first green sheet in a desired direction, and curing the first green sheet to form a cured first layer by focusing a laser beam onto portions of the first green sheet that are to be part of the magnet while the magnetic field is applied to the first green sheet.After curing the first green layer, the method includes creating a second green layer from the slurry on and in contact with the cured first layer, wherein the second green layer is viscous and flowable. The method includes applying a magnetic field to the second green layer to substantially orient the magnetic powder material contained in the second green layer in the desired direction, and curing the second green layer to form a cured second layer by focusing a laser beam onto portions of the second green layer that are to be part of the magnet while applying the magnetic field to the second green layer, wherein the cured second layer adheres to the cured first layer.The method further comprises: homogeneously mixing the magnetic material and the binder material to produce the slurry; wherein the magnetic powder material comprises at least one rare earth metal; wherein the magnetic powder material comprises neodymium, iron, and boron; wherein the magnetic powder material comprises dysprosium and / or terbium; providing the binder, which is organic and comprises at least one of: polyvinyl alcohol (PVA), stearic acid, carnauba wax, phenolic resin, epoxy resin, nylon, polypropylene, polystyrene, and poly(methyl methacrylate) (PMMA); providing the slurry having a viscosity of less than 10 Pascal-seconds; sintering the cured first and second layers; and subjecting the cured first and second layers to a hot isostatic pressing (HIP) process.

[0015] Additional features may be provided, including, but not limited to: the step of applying the magnetic field to each completed green layer while the same green layer is curing; the step of applying the magnetic field to each further completed green layer for a predetermined period of time prior to curing the same green layer to enable the magnetic powder material contained in the respective green layer to be substantially oriented in the desired direction; disposing a plurality of additional layers, layer by layer, on the cured second layer; each additional layer being formed from the slurry; disposing each additional layer therebetween, curing a last-disposed additional layer to form a plurality of attached cured layers; providing the magnetic field having a magnetism in the range of 0.5 to 4 Teslas; providing a base;the step of creating the first green layer from the slurry, comprising printing the first green layer onto the base; the step of creating the second green layer from the slurry, comprising printing the second green layer onto the first layer; the step of disposing the plurality of additional layers layer by layer onto the second cured layer, comprising printing each additional layer; and removing residual slurry before disposing each additional layer.

[0016] Further additional features may be provided, including, but not limited to, the following: the slurry further comprising an organic-based solvent; wherein the curing steps are performed with a laser; wherein the binder comprises polyamide; the slurry has a magnetic material to binder ratio of at least 1.5:1; sintering the cured first and second layers and the plurality of bonded cured layers; subjecting the cured first and second layers and the plurality of bonded cured layers to either a sintering and / or a hot isostatic pressing (HIP) process; and / or each layer having a thickness in the range of 5 to 500 micrometers. The HIPing process can be either encapsulated with a metal foil or container, or unencapsulated, depending on whether the pores are interconnected or not.

[0017] Additionally, the present description provides a magnet formed by any version of the methods described herein. Fig. 1A is a plan view of an exemplary magnet according to the principles of the present description; Fig. Figure 1B is a perspective view of the magnet of Fig. 1A according to the principles of this description; Fig. Figure 1C is a cross-sectional side view of a portion of the magnet of the Fig. 1A-1B along the line 1C-1C in Fig. 1B according to the principles of the present description; Fig. 2 is a block diagram illustrating a method of forming a magnet according to the principles of the present description; Fig. Figure 3A is a schematic cross-sectional view of an apparatus for forming the magnet of the Fig. 1A-1C in an initial step in a process for forming the magnet of the Fig. 1A-1C according to the principles of this description; Fig. Figure 3B is a schematic cross-sectional view of a device of Fig. 3A at a step in a method of forming the magnet of the Fig. 1A-1C, after the step described in Fig. 3A according to the principles of the present description; Fig. Figure 3C is a schematic cross-sectional view of a device of the Fig. 3A-3B at a step in a method of forming the magnet of the Fig. 1A-1C, after the step described in Fig. 3B according to the principles of the present description; and Fig. 3D is a schematic cross-sectional view of a device of the Fig. 3A-3C at a step in a method for forming the magnet of the Fig. 1A-1C, after the step described in Fig. 3C according to the principles of the present description.

[0018] The present disclosure provides a permanent magnet and a method for manufacturing permanent magnets in a manner that reduces material loss and produces a magnet with anisotropic properties. The method greatly reduces or eliminates the need for subsequent machining operations and allows the magnetic powder material to be oriented in a desired direction (an anisotropic orientation) without causing loss of magnetic powder material.

[0019] With reference to the Fig. 1A-1B, a permanent magnet is shown and generally designated 10. In this variant, the permanent magnet 10 has a three-dimensional semicircular shape with a thickness t; however, the permanent magnet 10 could have any other desired shape without departing from the spirit and scope of the present description. The permanent magnet 10 could be useful in electric motors and the like, or in any other desired application.

[0020] Magnet 10 may be a ferromagnetic magnet having an iron-based composition, and magnet 10 may include any number of rare earth metals. For example, magnet 10 may have an Nd-Fe-B (neodymium, iron, and boron) configuration. Magnet 10 may also include Dy (dysprosium) and / or Tb (terbium), if desired. It is also contemplated that magnet 10 may include additional or alternative materials without departing from the spirit and scope of the present description.

[0021] Referring to Fig. 1C, the permanent magnet 10 is formed from a plurality of layers 12, each containing magnetic powder materials. Each of the layers 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h of the multiple layers 12 can be produced by 3D printing or otherwise arranging the layers 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h contiguously or layer by layer to form the shape of the permanent magnet 10. Thus, the magnet 10 is produced as one layer 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h, respectively, until substantially the desired final shape. Although in Fig. 1C depicts eight layers 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h, any desired number of layers 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h can be provided. For example, as many layers 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h as 300 can be provided.

[0022] In some variations, each layer 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h may have a height or thickness in the range of approximately 5-500 micrometers; for example, each layer 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h may have a height in a range of 3-100 micrometers. Thus, the magnet 10 may have a large variety of layers, such as 300 layers, resulting, for example, in a magnet having a thickness t of approximately 3 mm. Other thicknesses t could range from about 1 to about 10 mm for electric motors, or any other desired magnet thickness t. Magnets used in windmills are much larger.

[0023] With reference now to Fig. 2, the present description provides a method 100 for near-net-shape formation of a magnet, such as magnet 10. The method 100 includes a step 102 of forming a slurry comprising a magnetic powder material and a binder. The magnetic powder material may comprise any magnetic powder, such as powders of the materials described above (iron, neodymium, iron, boron, dysprosium, terbium, etc.). The slurry further contains a solvent to make the slurry viscous and flowable. The solvent may be water-based, but in a preferred form, the solvent is an organic-based solvent, such as kerosene or alcohol (e.g., ethanol or methanol), to prevent oxidation of the magnetic powder material. A binder, which may be organic or inorganic, is also mixed into the slurry.The binder can help hold the magnetic powder material together until it is heat-treated and / or sintered. The binder can contain a polyamide and / or the binder can be a non-magnetic polymer-based material configured to enable the bonding of powder particles of the magnetic powder material. The binder is organic and includes one or more of the following components: polyvinyl alcohol (PVA), stearic acid, carnauba wax, phenolic resin, epoxy resin, nylon, polypropylene, polystyrene, and poly(methyl methacrylate) (PMMA).In some forms, a photopolymerizing material (optional) may also be included to enable curing by light or other electromagnetic radiation; for example, ultraviolet (UV) light-curing organic binders (with photopolymerization reactions) may also be used, such as 2-hydroxyethyl acrylate and polyethylene glycol 200 diacrylate, etc. Two commercially available UV-curable resins can be used as binders: XC11122 (DSM) and UV-A 2137 (Sadechaf).

[0024] In some forms, the slurry may be viscous, such as having a viscosity of 2 or 3 Pascal-seconds, but preferably no more than 10 Pascal-seconds. The slurry may be formed by homogeneously mixing the magnetic material and the photopolymerizing material, as well as a solvent. Efforts may be made to reduce the viscosity of the slurry. For example, the use of diluents and a heating system may reduce the viscosity of the slurry to some extent.

[0025] The binder is generally undesirable due to cost or other side effects. These binders should be kept to a minimum to avoid contamination or a reduction in magnetic properties. Thus, in some variations, the slurry has a ratio of at least 1.5:1 of magnetic material to binder, and in some cases, the ratio of magnetic material to binder can be at least 2:1.

[0026] Once the slurry is created, the method 100 includes a step 104 of creating a green (uncured) first layer 14a' from the slurry. The green first layer 14a' may be created, for example, by 3D printing, or the green first layer 14a' may be created from the slurry in any other suitable manner.

[0027] With reference to Fig. 3A, a base 16 is provided in a mold, and a first raw layer 14a' of the slurry 20 can be applied to the base 16 with a knife 23, wherein the knife 23 can be used to remove residual sludge, and the knife 23 can then be moved away and the first raw layer 14a' can be dried.

[0028] With reference to the Fig. 2 and Fig. 3B, the method 100 includes a step 106 of applying a magnetic field (indicated by arrow 24 in Fig. 3B) to the first green layer 14a' to align the magnetic powder material contained in the first green layer 14a' substantially in a desired direction. The method 100 includes a step 108 of curing the first green layer 14a to form a cured first layer 14a (shown in Fig. 1C and the Fig. 3C-3D). Curing 108 is performed using a laser device 26 that focuses a laser beam 28 onto the portions of the first green sheet 14a' that are to be part of the magnet 10. The step 108 of applying the magnetic field 24 to the first green sheet 14a' is performed during the curing of the first green sheet 14a'. The step 106 of applying the magnetic field 24 to the first green sheet 14a' may further be performed for a first predetermined period of time prior to curing the first green sheet 14a' in order to be able to align the magnetic powder material contained in the first green sheet 14a' substantially in the desired direction prior to curing the slurry 20 of the first green sheet 14a', since the curing process begins to fix the orientation of the magnetic powder materials.Thus, the magnetic field 24 is preferably applied for at least a short period of time prior to curing, and the magnetic field 24 is applied during curing. The magnetic field 24 is preferably provided with a magnetism in the range of 0.5 to 4 Tesla, or 1 to 3 Tesla, or about 2 Tesla, for example. In some forms, the magnetic field 24 may be applied while the first green layer 14a' is being printed or deposited onto the base 16, and / or the magnetic field 24 may be applied continuously throughout the printing process, and each layer of the magnet 10 may be cured as needed. Providing the magnetic field orients the magnetic powder materials in the slurry of the first green layer 14a' to align them in a desired direction while the layer 14a' is cured, and then the magnetic materials are fixed in that position after curing.When the magnetic field 24 is applied during the curing step for each layer, the magnet 10 has an anisotropic orientation whose magnetic properties in a particular direction may be, for example, 30% stronger than those of an otherwise similar isotropic magnet.

[0029] As stated above, the curing step 108 may be performed with a laser beam 28, although any other desirable type of curing, such as an electron beam, ultraviolet light, visible light, or another form of electromagnetic radiation, may alternatively be performed. The cured first layer 14a may be a cured shape based on a path of the laser beam 28 formed by a computer-aided design (CAD) input for the magnet 10.

[0030] With reference to the Fig. 2 and Fig. 3C, after the first green layer 14a' has cured, the first green layer 14a' becomes the cured first layer 14a. The method 100 then includes a step 110 for creating a second green layer 14b' from the slurry 20 in contact with the previous layer, which in this case is the cured first layer 14a, and the knife 23 can be used to remove the residual slurry 20 from the second green layer 14b'. It should be noted that each green layer 14a', 14b' is applied evenly with the sharp knife 23 (preferably with a thickness in the range of a few micrometers to one millimeter). After the second green layer 14b' has been applied, the knife 23 can then be moved away, and the second green layer 14b' can dry.

[0031] With reference to the Fig. 2 and Fig. 3D, the method 100 includes a step 112 of applying a magnetic field 24 to the second green layer 14b' to substantially align the magnetic powder material contained in the second green layer 14b' in a desired direction. The method 100 includes a step 114 of curing the second green layer 14b' to form a cured second layer 14b (illustrated in Fig. 1C). The curing 114 of the second layer is performed with the laser device 26, which focuses a laser beam 28 onto the portions of the second green layer 14b' that are to be part of the magnet 10, or the curing step 114 may be performed in any other suitable manner.

[0032] The step 112 of applying the magnetic field 24 to the second green layer 14b' is performed during the curing of the second green layer 14b'. The step 112 of applying the magnetic field 24 to the second green layer 14b' may further be performed for a first predetermined period of time before the curing of the second green layer 14b' in order to be able to align the magnetic powder material contained in the second green layer 14b' substantially in the desired direction before the slurry 20 of the second green layer 14b cures, since the curing process begins to fix the orientation of the magnetic powder materials. Thus, the magnetic field 24 is preferably applied for at least a short period of time before curing, and the magnetic field 24 is applied during curing. As with the first layer 14a', the magnetic field 24 is preferably applied in a range of 0.5 to 4 Teslas.In some forms, the magnetic field 24 may be applied while the second green layer 14b' is being printed or deposited on the base 16, and / or the magnetic field 24 may be applied continuously throughout the printing process and each layer of the magnet 10 may be cured as needed.

[0033] After the second green layer 14b' is baked into the cured second layer 14b, the cured second layer 14b is attached to the cured first layer 14c.

[0034] The method 100 may iteratively repeat steps 110, 112, and 114 to form additional layers on the other layers and to form the entire magnet 10. Thus, the plurality of additional layers 14c, 14d, 14e, 14f, 14g, 14h may be initially applied in green form, layer by layer, to the cured second layer 14b, with each additional layer formed from the slurry 20, and each additional layer therebetween, with a last-deposited additional layer being cured under application of the magnetic field 24 to form a plurality of attached cured layers 14c, 14d, 14e, 14f, 14g, 14h, as shown in Fig. 1C, in a similar or identical manner to the above-described production of the first and second layers.

[0035] After forming each of the cured layers 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h by arranging them in green form and then curing them under a magnetic field 24 to form the magnet 10, the magnet 10 (including all of its layers 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h) is then sintered and subjected to a hot isostatic pressing (HIP) process.

[0036] Thus, a magnet 10 is formed which includes a plurality of layers 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h comprising magnetic powder material oriented in a desired direction.

[0037] The method 100 for forming the magnet 10 may include further optional steps, such as an initial preparation step, including testing and weighing the starting materials for the desired material compositions. The method 100 may include vacuum induction melting and continuously casting the starting materials to form thin pieces (less than one mm) several centimeters in size. Hydrogen decrepitation may then be performed, in which the thin pieces absorb hydrogen at about 25°C to about 300°C for about 5 to about 20 hours and are then dehydrogenated at about 200°C to about 400°C for about 3 to about 25 hours.The process 100 may include pulverization, which may include hammer milling and grinding and / or mechanical pulverization or cold grinding with nitrogen (if necessary) to form a fine powder suitable for further powder metallurgical processing.

[0038] The process 100 may include mixing medium-sized powder, milling, blending fine powder, and blending various magnetic powders. For example, if the magnet 10 is manufactured based on an Nd-Fe-B configuration in which at least a portion of the Nd is to be replaced by Dy or Tb, the powder components may include the aforementioned iron-based powder containing Dy or Tb, as well as an Nd-Fe-B-based powder. In one form, for example, for automotive or truck applications including traction motors, the finished rare-earth permanent magnets have a Dy content of approximately 8 or 9 percent. In other applications, such as wind turbines, the total Dy or Tb concentration may need to be on the order of 3 to 4 percent by weight.In any case, the use of permanent magnets in such motors, which could benefit from improved magnetic properties (such as coercivity), is considered within the scope of the present description. Additional ingredients, such as the binders mentioned above, may also be included in the blended mixture, although such binders should be kept to a minimum to avoid contamination or a reduction in magnetic properties. In one form, blending may involve the use of an iron-based alloy powder of Dy or Tb (for example, between about 15 wt.% and about 50 wt.% Dy or Tb) blended with an Nd-Fe-B-based powder.

[0039] The magnetic powder can be sieved for size classification and then blended with other alloy powders for the final desired magnetic material composition, along with the binder material, to form a well-mixed or homogeneous material. The solvent can then be added to form the slurry 20.

[0040] Thereafter, the plurality of layers 12 are printed, such as by a three-dimensional printer as explained above. This may involve the use of the Fig.3A-3D above or the use of another 3D printing process. As described above, the layer printing steps 104, 110 may include printing the plurality of layers 12 into a desired final shape of the magnet 10, with little cutting and machining required thereafter. Each layer is cured while the magnetic field 24 is applied to the respective layer to substantially align the magnetic powder material in a desired direction to create an anisotropic magnet 10. Thus, the magnetic powder material is oriented under a magnetic field 24 capable of producing magnetism in the range of about 0.5 to 4 Tesla, preferably about 2 Tesla. The magnetic field 24 will cause the individual magnetic particles of the mixture to align such that the finished magnet 10 has a preferred direction of magnetization.Thus, the finished magnet 10 can be provided, the component of which is magnetic material arranged in an anisotropic orientation.

[0041] After laser curing / scanning, the magnetic powders are bonded. Once the entire "green" parts are manufactured, they can be heated for thermal curing for increased strength. Bonded magnets do not require sintering, and significant organic binders remain in the magnets. However, in the production of sintered magnets, the thermal curing process removes most (or almost all) of the organic binder, and they then undergo solid-state sintering.

[0042] In some molds, the hardened layers 14a, 14b, 14c, 14d, 14e, 14f, 14g can be heated to a curing temperature that is lower than the sintering temperature. For example, the curing temperature can be less than 400°C for all molds, although this step may not be required for all molds. The curing step can result in "cured green parts" or "brown parts" that still do not have the final strength and microstructure, as these should be subjected to sintering for complete curing. After curing, the magnet 10 is slightly hardened, but not as hard as the magnet 10 after sintering. However, this step burns off most of the binder, leaving a pure magnet composition and microstructure, which is desirable for improved magnetic properties.

[0043] During sintering, the magnet 10 is sintered at a temperature in the range of approximately 750°C to approximately 1100°C. Sintering may be performed and aged in a vacuum for approximately 1 to approximately 30 hours, and optionally, may alternatively be subjected to another heat treatment, which may be performed at approximately 300°C to approximately 700°C for approximately 3 to approximately 20 hours in a vacuum.

[0044] Sintering can be carried out in a vacuum or in an inert atmosphere (e.g., N2 or Ar) to prevent oxidation. A typical sintering vacuum is in the range of about 10 -3 and about 10 -5Pascal to achieve up to 99 percent theoretical density. Longer sintering times can further improve the sintered density. If the sintering time is too long, it can negatively impact both the mechanical and magnetic properties due to oversized grains in the microstructure. As with other forms of powder metallurgy processing, a cooling schedule can be used in which the sintered component is cooled over the course of several hours. Sintering 104 may also involve exposing the layers 12 to a SiC heating element and high-power microwaves.

[0045] Sintering is used to promote metallurgical bonding through heating and solid-state diffusion. Therefore, sintering, where the temperature is slightly below the temperature required to melt the magnetic powder material, is understood to be different from other high-temperature processes in which the powder material is melted. Heat isostatic pressing (HIPping) can be used prior to sintering to improve the magnet density and simplify the subsequent sintering process.

[0046] Additional secondary operations after sintering may also be applied, including minor machining and surface treatment or coating.

[0047] Additionally, HIPping can be applied to increase magnet density before or after sintering or to minimize porosity. HIPping may involve subjecting the magnet 10 to a hot isostatic pressing (HIP) process. In an alternative configuration, hot forging may be used instead of the HIP process. In some variations, minor machining, such as polishing (e.g., with ceramic or metal powder) and / or grinding, may be performed if desired.

[0048] In certain situations, the surface treatment can then be achieved by adding an oxide or a corresponding coating. For example, a protective layer or coating can be added. The protective layer can be applied to the finished magnets.

[0049] Laser heating is achieved using a CO2 laser gun as an example. The typical power is 110 V and 20 A. The build-up rate can be 16 cm 3 / hr or 1 in 3 / hr. Electron beam heating can also be used.

Claims

[1] A method (100) for forming a magnet (10), the method (100) comprising: Forming a slurry (20) comprising magnetic powder material, binder material, and a solvent; Producing a first raw layer (14a') from the slurry (20), wherein the first raw layer (14a') is viscous and flowable; Applying a magnetic field (24) to the first green layer (14a') to align the magnetic powder material contained in the first green layer (14a') in a desired direction; Curing the first green layer (14a') to form a cured first layer (14a) by focusing a laser beam (28) on portions of the first green layer (14a') that are to be part of the magnet (10) while applying the magnetic field (24) to the first green layer (14a'); after curing the first green layer (14a'), producing a second green layer (14b') from the slurry (20) in contact with the cured first layer (14a), the second green layer (14b') being viscous and flowable; Applying a magnetic field (24) to the second green layer (14b') to align the magnetic powder material contained in the second green layer (14b') in the desired direction; Curing the second green layer (14b') to form a cured second layer (14b) by focusing a laser beam (28) on portions of the second green layer (14a') that are to be part of the magnet (10) while applying the magnetic field (24) to the second green layer (14b'), the cured second layer (14b) adhering to the cured first layer (14a); wherein producing the slurry (20) comprises homogeneously mixing the magnetic powder material and the binder, the method (100) further comprising: Providing the magnetic powder material comprising at least one rare earth metal selected from neodymium, iron and boron and at least one of dysprosium and terbium; Providing the binder which is organic and comprising at least one of: polyvinyl alcohol (PVA), stearic acid, carnauba wax, phenolic resin, epoxy resin, nylon, polypropylene, polystyrene and poly(methyl methacrylate) (PMMA); Providing the slurry (20) having a viscosity of less than 10 Pascal-seconds; Sintering the cured first and second layers (14a, 14b); and Subjecting the cured first and second layers (14a, 14b) to a hot isostatic pressing (HIP) process. [2] The method (100) of claim 1, wherein the step of applying the magnetic field (24) to the first green layer (14a') is further performed for a first predetermined period of time prior to curing the first green layer (14a') in order to be able to align the magnetic powder material contained in the first green layer (14a') in the desired direction, and the step of applying the magnetic field (24) to the second green layer (14b') is further performed for a second predetermined period of time prior to curing the second green layer (14b') in order to align the magnetic powder material contained in the second green layer (14b') substantially in the desired direction, the method (100) further comprising arranging a plurality of additional layers (14c, 14d, 14e, 14f, 14g, 14h) layer by layer on the cured second layer (14b), each additional layer (14c, 14d, 14e, 14f, 14g, 14h) is formed from the slurry (20),and in between, arranging each additional layer (14c, 14d, 14e, 14f, 14g, 14h), curing a last arranged additional layer (14c, 14d, 14e, 14f, 14g, 14h) to form a plurality of attached cured layers (14c, 14d, 14e, 14f, 14g, 14h). [3] The method (100) of any preceding claim, further comprising providing the magnetic field (24) with a magnetism in the range of 0.5 to 4 Tesla. [4] Method (100) according to one of the preceding claims, further comprising: Providing a base (16), wherein the step of producing the first green layer (14a') from the slurry (20) comprises printing the first green layer (14a') onto the base (16), the step of producing the second green layer (14b') from the slurry (20) comprises printing the second green layer (14b') onto the cured first layer (14a), and the step of arranging the plurality of additional layers (14c, 14d, 14e, 14f, 14g, 14h) layer by layer onto the second cured layer (14b) comprises printing each additional layer (14c, 14d, 14e, 14f, 14g, 14h); and Removing the residual slurry (20) before applying each additional layer (14c, 14d, 14e, 14f, 14g, 14h). [5] The method (100) of any preceding claim, further comprising providing the slurry (20) further comprising an organic-based solvent. [6] The method (100) of any preceding claim, wherein the curing steps are performed using at least one of the following: a laser, an electron beam, and electromagnetic radiation. [7] The method (100) of any preceding claim, further comprising providing the slurry (20) having a ratio of at least 1.5:1 of magnetic powder material to binder material. [8] A method according to any one of the preceding claims, wherein the method further comprises: Sintering the cured first and second layers (14a, 14b) and the plurality of attached cured layers (14c, 14d, 14e, 14f, 14g, 14h); and Subjecting the cured first and second layers (14a, 14b) and the plurality of attached cured layers (14c, 14d, 14e, 14f, 14g, 14h) to a hot isostatic pressing (HIP) process. [9] Magnet (10) formed by the method (100) according to any one of the preceding claims.

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