Method for forming a magnet and a magnet

Abstract

Method (100) for forming a magnet (10), wherein the method (100) comprises: Forming a viscous and flowable slurry (20) comprising a magnetic powder material and a photopolymerizing powder material as well as a solvent; Producing a first crude layer (14a') from the viscous and flowable slurry (20); Hardening the first raw layer (14a') with electromagnetic radiation to form a hardened first layer (14a); after the hardening of the first raw layer (14a'), producing a second raw layer (14b') from the viscous and flowable slurry (20) in contact with the hardened first layer (14a); Hardening the second raw layer (14b') with electromagnetic radiation to form a hardened second layer (14b), wherein the hardened second layer (14b) adheres to the hardened first layer (14b); Sintering of the hardened first and second layers (14a, 14b); Subjecting the hardened first and second layers (14a, 14b) to a hot isostatic pressing (HIP) process; Providing the slurry (20) with a viscosity of at least 3 Pascal-seconds; Providing a magnetic field in the range of 0.5 to 4 Tesla; Providing the magnetic powder material comprising at least one rare earth metal; and Providing the magnetic powder material comprising neodymium, iron and boron and at least one of dysprosium and terbium, wherein the generation of the slurry (20) comprises the homogeneous mixing of the magnetic material and the photopolymerizing material as well as the solvent.

Description

[0001] The present description relates generally to permanent magnets and methods for forming isotropic or 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 (e.g., 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 from the larger block into a final shape based on the desired final shape of the magnets. The magnet pieces are then surface treated, if desired. 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 07 225 248 A describes a method for producing parts from magnetic material by dual-curing 3D gel printing.

[0008] DE 34 18 482 A1 describes a method for producing a flexible, magnetic recording medium.

[0009] US 2003 / 0 044 547 A1 describes an ultraviolet light-curable ferromagnetic composition and a process for producing such a composition for producing a ferromagnetic coating on a suitable substrate.

[0010] It can be considered as an object to provide an improved method for forming a magnet.

[0011] 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 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.

[0012] 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. The present disclosure provides a slurry comprising a magnetic powder material and a photosensitive resin or photopolymer, wherein the slurry form of the materials maintains the powder intact and can then be cured with electromagnetic radiation, such as a light source, to harden layers of the magnet layer by layer.

[0013] The inventive method for forming a magnet comprises forming a viscous and flowable slurry comprising a magnetic powder material and a photopolymerizing powder material, as well as a solvent. The method then comprises forming a first green layer from the viscous and flowable slurry and curing the first green layer with electromagnetic radiation to form a cured first layer. After curing the first green layer, the method comprises forming a second green layer from the viscous and flowable slurry in contact with the first cured layer and curing the second green layer with electromagnetic radiation to form a cured second layer, wherein the cured second layer adheres to the cured first layer.The method further comprises: sintering the cured first and second layers and the plurality of adherent cured layers; subjecting the cured first and second layers and the plurality of adherent cured layers to a hot isostatic pressing (HIP) process; providing the slurry having a viscosity of at least 3 Pascal-seconds, providing the magnetic field in the range of 0.5 to 4 Tesla; providing the magnetic powder material comprising at least one rare earth metal; providing the magnetic powder material comprising neodymium, iron, and boron; and providing the magnetic powder material comprising at least one of dysprosium and terbium, wherein forming the slurry comprises homogeneously mixing the magnetic material and the photopolymerizing material, as well as the solvent.

[0014] Additional functions may be provided, including, but not limited to, the following: applying a magnetic field to the first green layer while curing the first green layer; applying a magnetic field to the second green layer while curing the second green layer, wherein the application of the magnetic field substantially orients the magnetic powder material in a desired direction; disposing a plurality of additional layers, layer by layer, on the cured second layer, each additional layer being formed from the slurry, and, between the disposing of each additional layer, curing by exposing a last-disposed additional layer to form a plurality of adherent cured layers; the slurry further comprises an organic-based solvent; the electromagnetic radiation is visible light;Providing the visible light through a light-emitting diode (LED), providing a base; providing a flat, shallow tray containing the slurry, while the slurry layer of a few micrometers to one millimeter is evenly applied to the flat tray with a sharp knife, lowering the base towards the slurry and touching the slurry to arrange the first green layer on the base before the first green layer cures, raising the base after the first green layer cures with the desired curing shape, which is an image of the electromagnetic radiation formed by the computer-aided design (CAD) for the magnet; removing the remaining slurry and then applying a new slurry layer with approximately the same thickness as the first layer;Lowering the base toward the slurry and contacting the slurry to place the second green layer on the cured first layer before curing the second green layer; raising the base after curing the second green layer; placing the LED with the desired radiation pattern under the tray, wherein the tray has a translucent bottom or a transparent bottom; sintering the cured first and second layers and the plurality of adhered cured layers; subjecting the cured first and second layers and the plurality of adhered cured layers to a hot isostatic pressing (HIP) process; wherein creating the slurry comprises homogeneously mixing the magnetic material, the photopolymerizing material, and the solvent.

[0015] According to the invention, a magnet is provided that contains a plurality of layers comprising magnetic powder material. Each layer comprises cured photosensitive resin. The magnet has an anisotropic orientation and is manufactured according to the method of the invention.

[0016] Additional features of the magnet may include, but are not limited to: the magnet comprises at least one rare earth metal, each layer being in the range of 10 to 1000 microns thick, wherein the magnet comprises neodymium, iron, boron, and dysprosium and / or terbium.

[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 perspective view of the magnet of Fig. 3A according to the principles of this description; Fig. Figure 3C is a schematic cross-sectional view of a device of the Fig. 3A-3B in one 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. 3D is a schematic cross-sectional view of a device of the Fig. 3A-3C in one step in a method for forming the magnet of the Fig. 1A-1C, after the step described in Fig. 3C is illustrated in accordance with the principles of the present description; Fig. Figure 3E is a schematic cross-sectional view of a device of the Fig. 3A-3D in one step in a method for forming the magnet of the Fig. 1A-1C after the step described in Fig. 3D according to the principles of the present description; Fig. Figure 3F is a schematic cross-sectional view of a device of the Fig. 3A-3E in one step in a method of forming the magnet of the Fig. 1A-1C, after the step described in Fig. 3E according to the principles of the present description; Fig. Figure 3G is a schematic cross-sectional view of a device of the Fig. 3A-3F in one step in a method for forming the magnet of the Fig. 1A-1C after the step described in Fig. 3F according to the principles of the present description; Fig. Figure 3H is a schematic cross-sectional view of a device of the Fig. 3A-3G in one step in a method for forming the magnet of the Fig. 1A-1C, after the step described in Fig. 3G is illustrated in accordance with the principles of the present description;

[0018] The present description provides a permanent magnet and a method for manufacturing permanent magnets in a manner that reduces material loss. 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 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, 14e, 14h can be provided. For example, as many layers 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h as 300 can be provided.

[0022] Each layer 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h may have a height or thickness in the range of approximately 5-500 µm; for example, each layer 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h may have a height in the range of 3-100 µm. Thus, the magnet 10 may have a large number of layers, for example, 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 photopolymerizable powder material. 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 render 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 avoid oxidation of the magnetic powder material. Typical magnetic binders, which may be organic or inorganic, may be included but are optional.The binder can help hold the magnetic powder material together until it is heat-treated and / or sintered. The binder can be a polymer-based, non-magnetic material configured to allow powder particles of the magnetic powder material to adhere to one another. In some forms, the slurry can be viscous, e.g., having a viscosity of at least 2 or 3 Pascal-seconds or much higher. The slurry is formed by homogeneously mixing the magnetic material and the photopolymerizing material, as well as a solvent.

[0024] The photopolymerizing material is included to enable the magnetic slurry to be formed into layers and cured with electromagnetic radiation, such as light, as explained in more detail below. The photopolymerizing material, or photosensitive resin or photopolymer, is a composition that can be selectively polymerized and / or crosslinked upon imagewise exposure to light radiation or other electromagnetic radiation, such as ultraviolet light.

[0025] In general, photopolymers can comprise multiple components, including binders, photoinitiators, additives, chemical agents, plasticizers, and colorants. In some forms, photopolymerizing material formulations can comprise polymers, oligomers, monomers, and / or additives. Polymer bases for photopolymers can include acrylics, polyvinyl alcohol, polyvinyl cinnamate, polyisoprene, polyamides, epoxies, polyimides, styrenic block copolymers, nitrile rubber, or other base materials. In some examples, the polymeric base material can be dissolved in the solvent carrier, such as the organic solvent used in the slurry. An included monomer can include multifunctional acrylates and methacrylates combined with a non-polymeric component to reduce volume shrinkage.

[0026] In some variations, the photopolymer may consist of 50-80% of a binder or oligomer, such as oligomers of the styrene family (e.g., styrene tetramer alpha-cumyl terminated oligomer, α-methylstyrene dimer (1), α-methylstyrene tetramer, etc.), methacrylates (e.g., acrylic acid oligomers, methyl methacrylate oligomers, methyl methacrylate tetramer, etc.), vinyl alcohols (e.g., vinyl alcohol trimer, vinyl acetate trimer, vinyl acetate oligomer, etc.), olefins (e.g., polyisobutylene), glycerols (e.g., triglycerol), polypropylene glycols (e.g., polypropylene glycol (dihydroxy terminated), etc.).

[0027] The photopolymer can also consist of one or more monomers, such as an acrylate- or methacrylate-based monomer, comprising, for example, 10-40% of its composition. Multifunctional monomers and / or monofunctional monomers are used in the polymerization process. Multifunctional monomers can act as both diluents and crosslinkers, while monofunctional monomers can act as either diluents or crosslinkers. Some examples of monofunctional and multifunctional monomers include acrylic acid, methacrylic acid, isodecyl acrylate, N-vinylpyrrolidone, trimethylpropane triacrylate (TMPTA), ethoxylated TMPTA, trimethylpropane trimethacrylate, and hexanediol diacrylate.

[0028] Photoinitiators are also included in the photopolymerizing material, which can convert light energy into chemical energy by forming free radicals or cations through electromagnetic radiation (such as visible or ultraviolet light). Upon such exposure, the photoinitiators break down into two or more particles, and at least one of the particles reacts with the monomers or oligomers, bonding them together.

[0029] Photoinitiators can be, for example, free radicals or cationic photoinitiators. In free radical photopolymerization, radicals or ions disrupt the initiators when electromagnetic radiation reacts, and ions then begin to react with monomers to initiate polymerization. In the cationic reaction, strong acid is released from the initiator, which starts a bonding process. Some examples of radical photoinitiators include isopropylthioxanthone, benzophenone, and 2,2-azobisisobutyronitrile. Examples of cationic photoinitiators include diaryliodonium salts and triarylsulfonium salts.

[0030] Other examples of photopolymerizing materials that can be used or combined with others include hydroxycyclohexylphenyl ketones with acrylates, titanocene photoinitiator with epoxy resin or acrylates, N-methyl-2-pyrrolidone (NMP) with tetrahydrofuran (THF), and esters of cinnamic acid (C9H8O2). Photopolymer resins with mechanical properties similar to engineering plastics such as ABS, nylon, and polycarbonate can also be used in the slurry.

[0031] Once the slurry is created, the method 100 includes a step 104 of creating a green (uncured) first layer 14a' from the slurry. This may involve 3D printing the green first layer 14a', or the green first layer 14a' may be created from the slurry in any other suitable manner.

[0032] In one form, with reference to Fig. 3A, a base 16 is provided, and a shallow tray 18 is provided beneath the base, with the slurry contained within the tray 18 and designated by reference numeral 20. The bottom 22 of the tray 18 is formed of a transparent or translucent material, and a source of electromagnetic radiation is located beneath the tray 18, adjacent the bottom 22. In the illustrated example, the source of electromagnetic radiation is a visible light source, such as one or more light-emitting diodes (LEDs) 24; however, alternatively, the electromagnetic radiation source could provide ultraviolet light, infrared light, or any other desired source capable of effectively curing the photopolymer.

[0033] In some molds, a light modulator may be included to vary the intensity of the light 24, and an exposure field may be created at the bottom 22 of the container to produce a desired shape for the particular layer that will be cured next. The desired shape is determined by computer-aided design (CAD) input for 3D printing or manufacturing and implemented by the exposure field in the bottom 22, whereby each layer is cured by the light 24.

[0034] Referring to the Fig. 3A-3B, the flat, shallow tray 18 contains the slurry 20, while the slurry layer (with a thickness in the range of a few micrometers to one millimeter) is evenly applied to the flat tray with a sharp knife 23.

[0035] Referring to Fig. 3C, the method 100 may include lowering the base 16 toward and into the slurry 20 to deposit a first green layer 14a' on the base 16 prior to curing the first green layer 14a'. The first green layer 14a' is then disposed between the bottom 22 of the tray 18 and a bottom surface 26 of the base 16.

[0036] With reference to Fig. 3D and with further reference to Fig. 2, the method 100 then includes a step 104 of curing the first green layer 14a' with electromagnetic radiation to form a cured first layer 14a adhered to the underside 26 of the base 16. In preferred variations, the method 100 includes applying a magnetic field to the first green layer 14a' during curing of the first green layer 14a'. The magnetic field may, for example, be provided with magnetism in the range of 0.5 to 4 Tesla, or approximately 1-3 Tesla. 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 subsequently, the magnetic materials are fixed in this position after curing.When the magnetic field is applied to each layer during the curing step, the magnet 10 has an anisotropic orientation, whose magnetic properties in a particular direction can be, for example, 30% stronger than those of an otherwise similar isotropic magnet. Layer 14a is a hardened shape based on an image of the electromagnetic radiation, formed using computer-aided design (CAD) for the magnet.

[0037] With reference to Fig. 3E, after curing the first green layer 14a', the base 16 can be lifted out of the tray 18 to form the cured first layer 14a, with the cured first layer 14a adhering to the underside 26 of the base 16.

[0038] Referring to Fig. 3F and with continued reference to Fig. 2, the method 100 then returns to step 102 to form another layer of the slurry. In the example of Fig. 3A-3F, the method 100 may include removing the remainder of the previous remaining slurry and then applying a fresh layer of slurry to form the second green layer by scraping the shallow tray 18 with a thin knife and lowering the base 16 with the adhered cured first layer 14a toward and into the slurry 20 to deposit a second green layer 14b' on the cured first layer 14a prior to curing the second green layer 14b'. The second green layer 14b' is then disposed between the bottom 22 of the tray 18 and the cured first layer 14a.

[0039] With reference to Fig. 3G and with continued reference to Fig. 2, the method 100 continues with the layer curing step 104, this time involving the second green layer 14b'. Like the first green layer 14a', the second green layer 14b' is cured with electromagnetic radiation, such as from the LED light source 24, to form a cured second layer 14b adhered to the cured first layer 14a. In preferred variations, the method 100 also includes applying a magnetic field to the second green layer 14b' while the second green layer 14b' is curing to orient the magnetic powder material contained in the slurry in the desired direction while the layer 14b' is curing.

[0040] With reference to Fig. 3H, after curing the second green layer 14b' to form the second cured layer 14b, the base 16 can be lifted out of the shell 18, with the cured first layer 14a still adhering to the underside 26 of the base 16 and with the cured second layer 14b being adhered to the underside 28 of the cured first layer 14a in the manufacturing orientation shown in Fig. 3H is shown.

[0041] The method 100 may iteratively repeat steps 102 and 104 to form additional layers on the other layers and to form the entire magnet 10. If necessary, additional volume of the slurry 20 may be added to the shell 18. Thus, the plurality of additional layers 14c, 14d, 14e, 14f, 14g, 14h may first be deposited in green form, layer by layer, on the underside 30 of the cured second layer 14b, with each additional layer being formed from the slurry 20, and between the depositing of each additional layer, the last deposited additional layer is cured with the light 24 to form a plurality of attached cured layers 14c, 14d, 14e, 14f, 14g, 14h disposed in Fig. 1C. Upon curing each layer, a magnetic field may be applied during the light-curing process, as explained above.

[0042] After forming each of the hardened layers 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h by arranging them in green form and then hardening them to form the magnet 10, the magnet 10 (including all of its layers 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h) can then be sintered and subjected to a hot isostatic pressing (HIP) process.

[0043] Thus, a magnet 10 comprising a plurality of layers 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h containing a magnetic powder material is formed, each layer 14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h also comprising cured photosensitive resin.

[0044] 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 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 may include pulverization, which may include hammer grinding and milling and / or mechanical pulverization or cold grinding with nitrogen (if necessary) to form a fine powder suitable for further powder metallurgical processing.

[0045] The process 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 a motor, 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.

[0046] In one step, the powder is sieved for size classification and then mixed with other alloy powders for the final desired composition of the magnetic material, along with binders (if desired, as explained above). The photopolymerizing material can also be mixed with the magnetic material and any other binders to form a well-mixed or homogeneous powder material. The solvent can then be added to form the slurry.

[0047] Thereafter, the plurality of layers 12 of magnetic powder material are printed in step 102, such as by a three-dimensional printer as explained above. This may involve using the method comprising the base 16 and the shell 18 or using another 3D printing method. As described above, the step 102 of printing the layers 14a, 14b, ... may involve printing multiple layers 12 into a desired final shape of the magnet, with only minimal cutting and machining required thereafter. Each layer 14a, 14b, 14c, 14d, 14e, 14f, 14g is preferably cured with the light 24 while a magnetic field is applied to the respective layer to substantially orient the magnetic powder material in a desired direction to create an anisotropic magnet.Thus, the magnetic powder material is oriented under a magnetic field ranging from approximately 0.5 to 4 Tesla, and preferably approximately 2 Tesla. The magnetic field will cause the individual magnetic particles of the mixture to align so that the finished magnet 10 has a preferred magnetization direction. Thus, the magnetic powder material can be provided in an anisotropic orientation.

[0048] In some molds, the hardened layers 14a, 14b, 14c, 14d, 14e, 14f, 14g can be heated to a curing temperature 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. In other words, 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.

[0049] 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.

[0050] 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, 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.

[0051] Sintering is used to promote metallurgical bonding through heating and solid-state diffusion. Therefore, sintering—where the temperature is slightly below that required to melt the magnetic powder material—is considered different from other high-temperature processes that melt the powder material. Heat isostatic pressing (HIPping) can be used prior to sintering to improve magnet density and simplify the subsequent sintering process.

[0052] Additional secondary operations after sintering may also be applied, including minor machining and surface treatment or coating.

[0053] 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.

[0054] 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 after sintering.

Claims

[1] A method (100) for forming a magnet (10), the method (100) comprising: Forming a viscous and flowable slurry (20) comprising a magnetic powder material and a photopolymerizing powder material and a solvent; Producing a first raw layer (14a') from the viscous and flowable slurry (20); Curing the first green layer (14a') with electromagnetic radiation to form a cured first layer (14a); after curing the first green layer (14a'), producing a second green layer (14b') from the viscous and flowable slurry (20) in contact with the cured first layer (14a); Curing the second green layer (14b') with electromagnetic radiation to form a cured second layer (14b), the cured second layer (14b) adhering to the cured first layer (14b); Sintering the hardened first and second layers (14a, 14b); Subjecting the cured first and second layers (14a, 14b) to a hot isostatic pressing (HIP) process; Providing the slurry (20) having a viscosity of at least 3 Pascal-seconds; Providing the magnetic field in the range of 0.5 to 4 Tesla; Providing the magnetic powder material comprising at least one rare earth metal; and Providing the magnetic powder material comprising neodymium, iron and boron and at least one of dysprosium and terbium, wherein producing the slurry (20) comprises homogeneously mixing the magnetic material and the photopolymerizing material as well as the solvent. [2] The method (100) of claim 1, further comprising applying a magnetic field to the first green sheet (14a') while curing the first green sheet (14a') and applying a magnetic field to the second green sheet (14b') while curing the second green sheet (14b') to substantially orient the magnetic powder material in a desired direction. [3] The method (100) of any preceding claim, further comprising disposing 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) being formed from the slurry (20), and curing by exposing a last-disposed additional layer (14c, 14d, 14e, 14f, 14g, 14h) between the disposition of each additional layer (14c, 14d, 14e, 14f, 14g, 14h) to form a plurality of adherent cured layers (14c, 14d, 14e, 14f, 14g, 14h), wherein the electromagnetic radiation is visible light (24). [4] The method (100) of any preceding claim, wherein the slurry (20) further comprises an organic-based solvent. [5] The method (100) of claim 3, further comprising: Providing the visible light (24) by a light-emitting diode (LED); Providing a base (16); Providing a tray containing the slurry (20); Lowering the base (16) to the slurry (20) to place the first green layer (14a') onto the base (16) prior to curing the green layer (14a'); Lifting the base (16) after hardening of the first raw layer (14a'), Removing the residual slurry (20); applying a second fresh layer of the slurry (20) by scraping with a knife; Lowering the base (16) towards the slurry (20) to place the second green layer (14b') on the cured first layer (14a) prior to curing the second green layer (14b'); and Lifting the base (16) after hardening of the second raw layer (14b'), wherein the method (100) comprises disposing the LED beneath the tray, wherein the tray has either a translucent bottom or a transparent bottom. [6] Method (100) according to one of the preceding claims, further comprising: Sintering the hardened first and second layers (14a, 14b) and the plurality of adherent hardened layers (14c, 14d, 14e, 14f, 14g, 14h); Subjecting the cured first and second layers (14a, 14b) and the plurality of adhered cured layers (14c, 14d, 14e, 14f, 14g, 14h) to a hot isostatic pressing (HIP) process. [7] A magnet (10) comprising a plurality of layers (14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h) comprising a magnetic powder material, each layer (14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h) comprising cured photosensitive resin, the magnet (10) having an anisotropic orientation, and the magnet being manufactured by the method of claim 1. [8] A magnet (10) according to claim 7, comprising at least one rare earth metal, wherein each layer (14a, 14b, 14c, 14d, 14e, 14f, 14g, 14h) is in the range of 10 to 100 µm thick. [9] Magnet (10) according to claim 8, comprising neodymium, iron and boron and at least one of dysprosium and terbium.

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