Patent Description:
Permanent magnets with high energy products, such as neodymium-iron-boron magnets, are conventionally produced with a modified powdered metallurgical process in simple geometrical forms like discs, cuboids and parallelepiped. A conventional process of manufacturing an exemplary combination of metals, neodymium-iron-boron, is shown and described with reference to <FIG>.

First, powdered metals are created. To do this, the appropriate amounts of neodymium, iron, and boron are combined and heated to the melting point under vacuum. As used herein, "alloy" is used to refer to the resulting substance in both liquid and solid states. The vacuum prevents any chemical reaction between air and the melting materials that might contaminate the final metal alloy. Once the metal alloy has cooled and solidified, it is broken up and crushed into small pieces, which are ground into a fine powder creating a powdered metal alloy.

Next, the powdered metal alloy is pressed. In this process, the powder is placed in a die that has the shape of the finished magnet. A magnetic field is applied to the powder to line up the powder particles. While the magnetic force is being applied, the powder is pressed from the top and bottom with hydraulic or mechanical rams to compress it to within about <NUM> inches (<NUM>) of its final intended thickness. Typical pressures are about <NUM>,<NUM> psi to <NUM>,<NUM> psi (<NUM> MPa to <NUM> MPa). Some shapes are made by placing the powder in a flexible, air-tight, evacuated container and pressing it into shape with liquid or gas pressure. This is known as isostatic compaction.

Once compressed, the powdered metal alloy is heated. The metal alloy is removed from the die and placed in an oven for sintering, which fuses the powder into a solid piece. The process usually consists of three stages. In the first stage, the alloy is heated at a low temperature to slowly drive off any moisture or other contaminants that may have become entrapped during the pressing process. In the second stage, the temperature is raised to about <NUM>-<NUM>% of the melting point of the metal alloy and held there for a period of several hours or several days to allow the small particles to fuse together. Finally, the alloy is slowly cooled down in controlled, step-by-step temperature increments.

The sintered metal alloy then undergoes a second controlled heating and cooling process known as annealing. This process removes any residual stresses within the alloy and strengthens it.

Then, a finishing process takes place. The annealed metal alloy is very close to the finished shape and required dimensions. A final machining process removes any excess material and produces a smooth surface. The alloy is then given a protective coating to seal the surfaces.

Once in its finished form, the metal alloy is magnetized. Up to this point, the metal alloy is just a piece of compressed and fused metal. Even though it was subjected to a magnetic force during pressing, that force did not magnetize the alloy, it simply lined up the loose powder particles. To turn it into a magnet, the alloy is placed between the poles of a powerful electromagnet and oriented in the desired direction of magnetization. The electromagnet is then energized for a period of time. The magnetic force aligns the groups of atoms, or magnetic domains, within the material to transform the alloy into a strong permanent magnet.

Each step of the conventional manufacturing process is monitored and controlled. The sintering and annealing processes are especially critical to the final mechanical and magnetic properties of the magnet, and the variables of time and temperature must be closely controlled.

The standard geometrical forms produced by this conventional method are insufficient for many applications. More complex shapes and magnetization directions are needed. For example, Halbach arrays formed from permanent magnets use complex shapes and magnetization directions. To create permanent magnets for Halbach arrays using conventional methods either complex molds (dies) are needed to produce the permanent magnets or the standard geometrical forms have to be machined to yield the required shapes. Both of these manufacturing processes are complex and expensive. Machining of permanent magnet materials, in particular, is difficult, since the material is very hard and brittle, causing wear-out and breakage of cutting tools. The manufacture of large permanent magnet arrays is further complicated by a difficult assembly process, in which substantial repulsive or attractive magnetic forces have to be overcome during manufacturing processes. <CIT> discloses a method of producing a rare earth magnet using hot working. The method produces an R-T-B-based rare earth magnet by: molding a powder of an R-T-B-based rare earth alloy (Rare earth element, T: Fe or Fe part of which is substituted by Co) to form a bulk, then hot working the bulk and, before molding, mixing with the powder of the R-T-B-based rare earth alloy either a metal which forms a liquid phase in copresence with R at a temperature lower than the hot working temperature, or an alloy which forms a liquid phase at a temperature lower than the hot working temperature. <CIT> discloses a method producing a radial anisotropic bond magnet; in the method a magnetic powder is made of a binder and a magnetic anisotropic powder, which is an alloy powder exhibiting a magnetic anisotropy and whose major phase is R2 TM1 4B. R is one or more types of rare-earth element, containing Y; TM is a substitution of Co for Fe or a part of Fe, and B is boron. The average crystal particle size of the magnetic powder is <NUM>-<NUM>, and its average particle size is <NUM>-<NUM>. The particles of the powder are cylindrical; anisotropy is imparted in a radial direction.

<CIT> discloses a manufacturing method of a rare-earth magnet including: manufacturing a first sealing body by filling a graphite container with a magnetic powder to be a rare-earth magnet material and by sealing the graphite container; manufacturing a sintered body by sintering the first sealing body to manufacture a second sealing body in which the sintered body is accommodated; and manufacturing a rare-earth magnet by performing hot plastic working on the second sealing body to give magnetic anisotropy to the sintered body.

Therefore, what is needed in the art is a more efficient manufacturing method that can create permanent magnets of more complex shapes and magnetization directions and results in permanent magnets which are more structurally robust and are able to resist structural failure under point or distributed loads that may be experienced during manufacture, shipping, assembly and use.

In accordance with the teachings disclosed herein, embodiments related to a method of manufacturing permanent magnets are disclosed.

The invention is a novel and enabling process for economical production of permanent magnets, having the potential to revolutionize permanent magnet manufacturing; lower cost product, lower cost and safer assembly of magnet-based products, enabler for the application of future permanent magnet materials and enabling new magnet-based products having potential for high-impact solutions for energy, medical, transportation and environmental industries. The novel Permanent Magnet (PM) manufacturing technology of the invention, termed PM-Wire, overcomes many inherent issues with conventional magnet production methods. The process of the invention enables mass-produced, cost-effective PM products, which are more robust, easily assembled into products and enables new "wire like" shapes and significantly increases energy density. The novel process comprises a "powder-in-tube" process that is continuous and may utilize drawing, packing and shaping processes, allows for mass production of permanent magnets of any desired shape or cross section, produces permanent magnets continuously that may be cut to any length, and may, in an embodiment, result in magnets with a desired magnetization direction.

In an embodiment, a method manufacturing a permanent magnet is provided, as defined in claim <NUM>. The plurality of magnetic metals may be, for example, neodymium, iron and boron. The process of compressing the metal alloy powder comprises swaging the metal alloy powder and the container. The metal alloy may comprise NdFeB. The container may have original outer dimensions that depend on a desired diameter of the resulting container. The magnetizing of the sintered metal alloy powder may comprise placing the sintered metal alloy powder while in the container between the poles of an electromagnet and energizing the electromagnet. The permanent magnet may have a diameter small enough to be described as wire.

In another embodiment, a permanent magnet is prepared by the above process.

The accompanying drawings, which are incorporated into and form a part of the specification, illustrate one or more embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating the preferred embodiments of the invention and are not to be construed as limiting the invention. In the drawings:.

In the figures, like item callouts refer to like elements.

A detailed description of the embodiments for a method of manufacturing permanent magnets will now be presented with reference to <FIG>. One of skill in the art will recognize that these embodiments are not intended to be limitations on the scope, and that modifications are possible. In certain instances, well-known methods, procedures and components have not been described in detail.

As used herein, "tube" includes within its definition any desired shape enclosing an interior volume.

As used herein, "PM Wire" is used to refer to any permanent magnet shape or configuration produced by the inventive method, and is therefore not limited only to "wire" constructs or shapes.

Embodiments of the manufacturing process disclosed herein overcome some of the inherent issues with the conventional manufacturing method and, in particular, enable cost effective manufacturing of complex magnetic arrays, such as Halbach arrays. Embodiments of the manufacturing process enable mass production of permanent magnets that are more mechanically robust than conventional permanent magnets and more easily assembled into complex arrays. In some cases, permanent magnets created can be bent into arcs.

An exemplary embodiment of the inventive process for manufacturing a permanent magnet is shown and described with reference to <FIG>. An exemplary list of magnetic metals that may be used in the apparatus and method are neodymium, iron, cobalt, boron, gadolinium, dysprosium and alloys such as steel that contain ferromagnetic metals, alone or in any combination. These identified magnetic metals listed of should not be taken as limiting. Any magnetic material can be used in the process of the invention to produce permanent magnets of a desired magnetic material or combination of materials. In particular, various novel magnetic materials, currently under development, which are not based on rare-earth materials, can be used.

Referring now to <FIG>, in a first step <NUM>, powdered metals are created. To do this, the appropriate amounts of magnetic materials such as, for example and not by way of limitation, neodymium, iron and boron are combined and heated to their melting point under vacuum. The vacuum prevents any chemical reaction between air and the melting materials that might contaminate the final metal alloy. Once the metal alloy has cooled and solidified, it is broken up and crushed into small pieces, which are ground into a fine powder creating a powdered metal alloy.

Still referring to <FIG>, in a second step <NUM>, pressure is applied to the powdered metal alloy. In this process, the powder is inserted into a tube or other-shaped container of a non-magnetic metal depicted as <NUM> in <FIG>. The non-magnetic metal tube or other-shaped container may be, for example, stainless steel or titanium. The material has to be non-magnetic to allow unhampered penetration of magnetic flux through the tube or other shaped container wall. While the powder is being exposed to a magnetic field to align crystals, swaging is used to compress the powder. The resulting shape can vary depending on the swaging process. Exemplary resulting tube shapes include cylindrical, rectangular prism, square prism, and pie-shaped. Cross-sectional and perspective views of a cylindrical tube are shown in <FIG>, respectively. Cross-sectional and perspective views of a rectangular prism-shaped tube are shown in <FIG>, respectively. Cross-sectional and perspective views of a square prism-shaped tube are shown in <FIG>, respectively. The outer dimensions of the original tube or other-shaped container can vary depending on the desired diameter of the resulting tubes after swaging. The length of the tube can also vary and can be significant. For example, a resulting tube may be one meter long and have a diameter or cross-sectional length of two centimeters or more. Even tubes with very small diameter that can be described as wires are producible by the process of the invention. While the enclosed volume is described herein as a tube for convenience, the container of the invention may take any desired shape as long as it has an interior volume able to contain the powdered metal alloy as described herein.

Still referring to <FIG>, in a third step <NUM>, once compressed, the powdered metal alloy is heated. The powdered metal alloy, still in its tube, is sintered with the appropriate temperature profile. The alloy is then slowly cooled down.

As an alternative to the sintering process of steps <NUM> and <NUM>, a bonding agent, such as a chemical bonding agent, epoxy, or the like may be mixed with the powdered metal alloy. The bonding agent is then cured, producing a permanent magnet of a desired shape that is ready for final finishing.

Still referring to <FIG>, after cool-down, the alloy, still in its tube or other-shaped container (<FIG>), is magnetized <NUM>. For most applications the magnetization direction will be chosen to be perpendicular to the tube axis. For shorter tube sections, the magnetization direction may also be along the tube axis.

With this powder-in-tube process depicted in <FIG>, no annealing and machining of the sintered alloy is needed, and no further surface coating, as required for conventional permanent magnets, is required. This is but one of many reasons the inventive method and product produced by the method is an improvement in the state of the art of permanent method manufacture. It can be seen that the inventive method of producing permanent magnets of <FIG> comprises fewer steps and is therefore more efficient than the conventional method of producing permanent magnets depicted in <FIG>.

Using the resulting tubes of permanent magnets, complex assemblies such as, for example, Halbach arrays can be produced. The surrounding support tube, or other-shaped container, provides mechanical strength, which aids in the handling of the permanent magnets created using the powder-in-tube process. Included within the scope of the invention are Halbach arrays comprising permanent magnets produced by the processes and methods described herein.

For powder-in-tube magnets with large aspect ratios of tube length to diameter, for example a length of <NUM> and an outer tube diameter of <NUM>, or wires, a slight bending of the final magnet is possible, creating an arc.

Referring now to <FIG>, and <FIG>, an application of the inventive method for producing a permanent magnet which results in a permanent magnet wire (PM-Wire) of pie-shaped cross section is depicted. It is to be understood that the example PM Wire cross section depicted in these figures is one of many cross sections of the PM Wire that may be produced by the process of the invention and that numerous other cross sectional shapes are within the scope of the invention. Further, the exemplary dual Halbach array application depicted in <FIG> is but one of many applications of the process and permanent magnet(s) that may be produced by the process. The exemplary application depicted in <FIG> is a dual-Halbach array electric motor that may be used in electric engines for aircraft propulsion. One advantage of the pie-shaped PM Wire produced by the process of the invention, as depicted in <FIG> and <FIG>, is the enablement of smaller diameter electric engines producing magnetic field strengths of up to <NUM> tesla, or greater. This is especially true when stator <NUM> is a double-helix or direct double helix conductor configuration as described in <CIT>, <CIT>, or <CIT>. To demonstrate the advantage over the prior art, a permanent magnet A produced by traditional means is shown for reference in <FIG>, and an array of permanent pie-shaped traditional magnets A such as may be used to form a segment of a Halbach array is shown for reference in <FIG>. In contrast to these traditional permanent magnets, a pie-shaped cross section PM Wire produced by the continuous process may be defined as having an inner radius R2' and outer radius R1' of the invention is depicted in <FIG>. The outer radius R1' of the PM Wire may be, for example much less than the outer diameter R1 of the traditional permanent magnet, allowing for a smaller diameter engine. Also, the length L' of the PM Wire produced by the process of the invention may much longer than the length L of a traditional permanent magnet A because the process of the invention is continuous, allowing less expensive and much easier construction of a longer engine comprising, for example, dual coaxial Halbach arrays (or a single Halbach array, if desired) because the for assembling together a plurality of pie-shaped permanent magnets along the axial direction, as would be required to construct a motor of length L' using traditional pie-shaped permanent magnets as shown in <FIG>, is eliminated. This is yet a further distinct advantage of the process of the invention - the elimination of the need to assemble a plurality of traditional permanent magnets in the longitudinal direction in order to construct a Halbach array of desired length L' as shown in <FIG>. Assembly of such a plurality of traditional magnets A into an array forming a long pie-shaped magnet is difficult, expensive, and requires special tooling because of the magnetic forces acting on the individual magnets A. In contract, by using pie-shaped PM Wire produced by the process of the invention, the need for this assembly tooling is eliminated because the pie-shaped PM Wire may be produced and cut to the desired length, and the individual pie-shaped PM Wire segments of desired length are easily assembled together and the tubes may be affixed by any mechanical means known in the art. For example, the pie-shaped PM Wire segments may be assembled into place and welded together using known fabrication techniques such as electron beam welding. If the Curie temperature can be exceeded in the welding process the PM Wires must be glued together. The result is lower cost and higher speed fabrication and assembly. The sintered, magnetized powdered metal alloy <NUM> is contained with the pie-shaped tube <NUM> as shown in <FIG>.

In <FIG>, an outer Halbach array comprises a plurality of PM Wire segments <NUM>, and an inner Halbach array comprises a plurality of pie shaped PM Wire segments <NUM>. The two Halbach arrays, the outer shell, stator <NUM> and engine shaft <NUM> are coaxial with the longitudinal axis of the engine.

Referring now to <FIG>, the steps of an exemplary embodiment of the process for producing PM Wire are pictorially depicted. In the embodiment shown, step <NUM> comprises placing the powdered metal alloy, such as, for example, NdFeB powder <NUM>, into a tube of any desired cross sectional shape or length <NUM>. The tube with powdered metal alloy inside is then drawn through a die <NUM> and subsequently swaged <NUM> and pre-magnetized <NUM>. Then, in step <NUM>, the powder-in-tube is sintered <NUM> and magnetized with powerful electromagnets <NUM>, producing a permanent magnet of a desired cross sectional shape and desired magnetization.

Having now described the invention, the construction, the operation and use of preferred embodiments thereof, and the advantageous new and useful results obtained thereby, the new and useful constructions, and reasonable mechanical equivalents thereof obvious to those skilled in the art, are set forth in the appended claims.

Claim 1:
A method of manufacturing a permanent magnet, the method comprising:
heating a plurality of magnetic metals to their melting point under vacuum to create a metal alloy;
allowing the metal alloy to cool and solidify;
grinding the metal alloy into a powder (<NUM>);
characterized by
placing the metal alloy powder (<NUM>) into a non-magnetic metal container (<NUM>), the container being a tube of any desired cross sectional shape;
aligning the metal alloy powder (<NUM>) by applying a magnetic field (<NUM>) to the metal alloy powder while compressing (<NUM>) the metal alloy powder (<NUM>) and the container (<NUM>);
sintering (<NUM>) the metal alloy power (<NUM>) while in the container (<NUM>);
cooling the sintered metal alloy powder (<NUM>) and the container (<NUM>); and
magnetizing (<NUM>) the sintered metal alloy powder (<NUM>) while in the container (<NUM>);
wherein compressing the metal alloy powder comprises swaging the metal alloy powder (<NUM>) and the container (<NUM>); and
the permanent magnet comprises the magnetizing sintered metal alloy powder in the container.