Layer-by-layer manufacturing method of dense permanent magnets

Abstract

The application relates to a layer-by-layer manufacturing method of a dense permanent magnet, which comprises the following steps: 1) laying a layer of samarium iron nitride powder on the bottom of a lower mold; 2) vibrating the powder layer; 3) applying downward mechanical pressure on the powder by a pressing block to compact the powder; 4) using ultra-short laser pulses to impact the compacted samarium iron nitride powder with a certain coverage rate to solidify the samarium iron nitride powder layer; 5) laying a next layer of samarium iron nitride powder on the surface of the impacted samarium iron nitride material, and re-executing steps 2) to 4) to solidify the samarium iron nitride powder of the current layer by using the ultra-short laser pulse impact; and 6) repeatedly executing steps 2) to 5) to obtain a dense samarium iron nitride block material. The application can realize layer-by-layer manufacturing of a permanent magnet block material, and meanwhile, can avoid the decline of magnetic performance caused by a thermal process.

Description

Technical Field

[0001] This invention relates to the fields of permanent magnet materials, near-net-shape manufacturing, and additive manufacturing. Specifically, this invention relates to a layer-by-layer manufacturing method for dense permanent magnet bulk materials. Background Technology

[0002] Permanent magnet materials are important materials in energy, power, electronics, and communications. They can be used in electric motors, engines, satellites, traveling wave tubes and circulators in radar, and other electronic instruments. Currently, rare earth permanent magnets have been applied to many fields, including clean grids, automobiles, home appliances, electronic instruments, nuclear magnetic resonance imaging (MRI) scanners, audio equipment, micromotors, and mobile phones.

[0003] The most widely used rare-earth permanent magnet material is neodymium iron boron (NdFeB). Compared with traditional ferrites, NdFeB has higher magnetic properties, and when applied to micromotors, the magnet volume can be much smaller than that of corresponding ferrites. This gives permanent magnet motors many advantages such as small size, light weight, low inertia, high power, and high efficiency.

[0004] Based on manufacturing processes, neodymium iron boron (NdFeB) magnets can be divided into bonded NdFeB magnets and sintered NdFeB magnets. The raw material for bonded NdFeB magnets is typically a mixture of NdFeB magnetic powder and a binder in a specific volume fraction. This mixture can be molded into magnets with a certain mechanical strength using either compression molding or injection molding. Bonded NdFeB magnets offer high dimensional accuracy and can be manufactured into complex magnetic components. However, due to the need for non-magnetic binders (such as resins or plastics), the magnetic properties of bonded NdFeB magnets are often far lower than the theoretical values ​​for NdFeB magnets.

[0005] In recent years, neodymium iron boron (NdFeB) magnets have emerged based on additive manufacturing (sometimes referred to as 3D printing) technology. This includes techniques such as Selective Laser Sintering (SLS), Laser Directed Energy Deposition (LDED), and Laser Powder Bed Fusion (LPBF). Existing additive manufacturing technologies for magnetic materials typically require the use of mixed organic binders as raw materials, falling under the category of Fused Deposition Modeling (FDM). However, in some cutting-edge explorations of NdFeB additive manufacturing, it is possible to achieve high density in NdFeB magnetic powder without mixing with organic binders. Nevertheless, regardless of SLS, LDED, or LPBF technologies, high-temperature treatment is required when solidifying the magnetic powder (e.g., the sintering temperature of NdFeB powder typically reaches 1000℃). During the high-temperature processing, some of the magnetically endowed crystalline phases of the NdFeB powder may decompose, resulting in the magnetic properties of the manufactured NdFeB bulk material not being as expected.

[0006] Furthermore, samarium iron nitride (SFeNi) is a promising new type of permanent magnet material. Microscopic analysis shows that SFeNi grains exhibit better intrinsic magnetic properties compared to neodymium iron boron (NdFeB) grains. For example, the magnetic energy product of micron-sized SFeNi particles can reach as high as 60 MGOe. However, SFeNi is a magnetic material that decomposes at 600℃. Currently, SFeNi permanent magnets are mostly manufactured using bonding techniques, where polymers or metals (such as zinc) at relatively low temperatures are used as binders to bond SFeNi powder into magnets. Low-temperature sintering methods, such as spark plasma sintering and laser sintering, are also used to prepare SFeNi magnets; however, their magnetic properties are far from reaching theoretical values ​​(see document: DT Zhang, M. Yue & J.X. Zhang, Study on bulk Sm2Fe). 17 N x sintered magnets prepared by spark plasma sintering,Powder Metallurgy,2007,50(3):215-218, and M.,Fim RGT,Quispe LTet al.,On the feasibility ofusing Sm2Fe 17 N xPowders obtained via HDDR process, for laser powder bed fusion of bonded permanent magnets, Journal of Magnetism and Magnetic Materials, 2023, 565:170273. In general, the magnetic properties of commercially available samarium iron nitride (SMR) bulk materials are often lower than those of neodymium iron boron (NdFeB) bulk materials. Research on additive manufacturing methods for SMR bulk materials is also relatively limited.

[0007] Shinobu Takagi et al. prepared samarium iron nitride (SMR) magnets using an explosive method. The main idea of ​​this technique is as follows: a cylindrical inner container is placed inside a larger cylindrical outer container. The inner container has a movable cover. A compacted SMR powder blank is placed inside the inner container. An explosive is detonated to create a high pressure of tens of GPa inside the outer container, driving the cover to subject the SMR powder blank inside the inner container to a high-intensity impact. When the impact pressure reaches tens of GPa or higher, the magnet density reaches 7.65 g / cm³. 3 Magnetic energy product (BH) max Reaching 116–144 kJ / m 3 (i.e., 14.5-18.0 MGOe). Reference: Shinobu Takag, Koichi Morii, Takahiko Iriyama, et al., Evaluation of Practicality for Fully Dense Isotropic Sm-Fe-N Magnets Made by Shock-Wave Consolidation Method, IEEE Transactions on Magnetics, 2023, 59(11):2101205. This is the highest volume density and magnetic energy product value reported to date for bulk samarium iron nitrogen. However, it is difficult to manufacture permanent magnets with complex shapes using the explosion method. This is because the shock wave pressure generated by the explosion method is uneven and decreases with the increase of the bulk material volume. When the permanent magnet has a complex shape, the above-mentioned disadvantages will cause more serious negative effects. Furthermore, the aforementioned explosive-based techniques require detonating explosives, and the container needs a high-pressure resistant outer shell. To more efficiently transfer the explosive energy to the samarium iron nitride powder blank to achieve higher magnet density, it is also necessary to design complex moving structures capable of operating under high pressure (such as a piston-type movable cover plate on the top of the inner container) and multi-layered container structures. Therefore, this explosive method is difficult to combine with existing samarium iron nitride additive manufacturing methods to obtain dense permanent magnet blocks with complex shapes.

[0008] Unlike additive manufacturing of general metals or alloys, additive manufacturing of permanent magnets requires consideration of not only their mechanical properties, such as density, but also their magnetic properties. Current additive manufacturing methods for dense permanent magnet blocks require high-temperature treatment of the magnetic powder to transform it from a powder state to a dense, solidified state. This process easily causes grain decomposition of the magnetic powder, leading to a decrease in magnetic properties. On the other hand, recent research has shown that explosive methods for fabricating samarium iron nitride (SMR) blocks can achieve a relatively high volume density and energy product, but this explosive method is difficult to use to create dense permanent magnet blocks with complex shapes.

[0009] Therefore, in summary, in the field of additive manufacturing of permanent magnets, there is an urgent need to solve the technical problem of magnetic performance degradation caused by thermal processes.

[0010] Furthermore, among other functional materials besides permanent magnets, there are also some temperature-sensitive materials whose corresponding functions may be lost or weakened due to thermal processes during their molding. Therefore, people are looking forward to solving the technical problem of performance degradation caused by thermal processes during the molding of such temperature-sensitive materials.

[0011] On the other hand, the solution proposed in this application draws on the principle of laser shockpeening (LSP). Laser shock peening, also known as laser impact strengthening, is a widely used laser surface treatment technology in industry. It typically utilizes nanosecond-level short-pulse lasers to create plasma on a material, generating explosive shock waves that alter the microstructure of the material's surface and generate residual compressive stress, thereby improving its performance, such as increasing the material's fatigue strength. However, LSP usually requires a thin film to be coated on the surface of the material being treated. The explosive plasma formed by the laser acting on the bulk material is suppressed by the film, allowing the reverse shock wave from the plasma to act on the bulk material. To further suppress the film, LSP needs to be performed underwater, making this method of impacting powder materials almost unacceptable. However, if ultrashort-pulse lasers, especially femtosecond pulse lasers, are used, due to their narrow pulse width and high peak power, laser shock strengthening can be performed directly on metallic materials in the atmosphere without the need for masks or water media, and the shock wave pressure can reach over 100 GPa. For details, please refer to: T. Kawashima, T. Sano, A. Hirose, et al., Femtosecond laser peening of friction stir welded 7075-T73 aluminum alloys, Journal of Materials Processing Technology, 2018, 262: 111-122. However, it should be noted that existing laser peening technology is mainly used for laser surface treatment of pre-formed bulk materials. Summary of the Invention

[0012] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for manufacturing permanent magnets layer by layer that can avoid the degradation of magnetic properties caused by the thermal process.

[0013] To solve the above-mentioned technical problems, the present invention provides a layer-by-layer manufacturing method for dense permanent magnets, comprising the following steps: Step 1) preparing a mold, the mold comprising a base, a side frame, a pressing block, and a top cover, the base and the side frame being combined to form an open lower mold with a receiving cavity, and laying a layer of samarium iron nitride powder at the bottom of the lower mold; Step 2) vibrating the lower mold to make the samarium iron nitride powder layer reach a preset compaction density; Step 3) inserting the pressing block into the lower mold, then sealing the opening of the lower mold with the top cover, driving the pressing block to move downward and applying downward mechanical pressure to the samarium iron nitride powder, so that the samarium iron nitride powder is compacted; Step 4) opening the top cover and removing the pressing block, and using an ultrashort laser pulse to compact the powder with a preset coverage rate. The samarium iron nitride powder is subjected to ultrashort pulse laser shock to further increase its density and thus solidify the samarium iron nitride powder layer. The ultrashort pulse laser shock is performed by irradiating the surface of the compacted samarium iron nitride powder with an energy of at least 20 μJ, a pulse width of more than 200 fs and not more than 800 fs, and a spot diameter of 40-120 μm, thereby inducing a plasma shock wave to impact the compacted samarium iron nitride powder layer; 5) a new layer of samarium iron nitride powder is placed on the surface of the impacted samarium iron nitride material; steps 2) to 4) are repeated to solidify the current layer of samarium iron nitride powder using ultrashort laser pulse shock; 6) steps 2) to 5) are repeated to obtain a dense samarium iron nitride bulk material.

[0014] The layer-by-layer manufacturing method further includes a pre-processing step: before making the samarium iron nitrogen (SFI) block, its three-dimensional graphic is sliced ​​into layers, with each slice having a thickness of Δh; then, based on the thickness h1 of the compacted SFI powder, the specified weight of SFI powder in each slice is calculated, and a specified weight of SFI powder is weighed for each slice; wherein, Δh is less than h1; in steps 1) and 5), the corresponding weighed portion of SFI powder with the specified weight is loaded into the lower mold, thereby completing the laying of the current layer of SFI powder; in step 4), after each ultrashort laser pulse impact on the current layer of SFI powder, the worktable mounted on the mold is lowered by Δh, while the laser head position remains unchanged; or the laser head used for ultrashort laser pulse impact is raised by Δh, while the worktable position remains unchanged.

[0015] In step 4), by adjusting the coverage and laser pulse energy, the samarium iron nitrogen material after impact reaches more than 98% of its theoretical density.

[0016] In step 2), the method of vibrating the mold is to strike, rock, or a combination of both, so that the samarium iron nitrogen powder layer reaches the preset tap density.

[0017] The side frame is fitted onto the base, on which a non-magnetic metal substrate is placed. A first layer of samarium iron nitride powder is laid and compacted onto the substrate, and subsequent layers of samarium iron nitride powder are laid and compacted onto the previous layer that has been impacted by an ultrashort pulse laser. The side frame is cylindrical, rectangular, square, or has a frame shape with other outlines. The shapes of the base, the top cover, and the pressing block match the shapes of the side frame. The top cover and the pressing block are integrated.

[0018] The mold is surrounded by coils or coils that can extend into the lower mold. In step 3), a pulse current with a peak value exceeding 1kA is applied to the coil during the compaction process to generate a thin magnetic field of more than 30kOe in the region of the samarium iron nitrogen powder in the current layer of the mold. The samarium iron nitrogen powder being compacted and not subjected to laser shock achieves magnetic orientation under the action of the thin magnetic field.

[0019] In step 3), the coil generates a horizontal or vertical pulsed magnetic field in the region where the samarium iron nitrogen powder layer is located; while the pulsed magnetic field is applied, the pressing block hammers the samarium iron nitrogen powder layer to compact it, wherein the timing of the pulsed current being applied to the coil is controlled so that the time difference between the duration of the pulsed magnetic field and the time when the pressing block contacts the samarium iron nitrogen powder does not exceed 1ms.

[0020] The side frame is fitted onto the base, and a non-magnetic insulating substrate is placed on the base. A first layer of samarium iron nitrogen powder is laid and compacted on the substrate, and subsequent layers of samarium iron nitrogen powder are laid and compacted on the previous layer that has been impacted by an ultrashort pulse laser. The substrate, the base, the side frame, and the pressing block are all made of corundum.

[0021] The samarium iron nitrogen powder has a particle size distribution D. 50 It is a polygonal or spherical powder with a diameter of 3–50 μm.

[0022] Steps 1) to 6) are carried out in a gas-protected environment, wherein the protective gas in the gas-protected environment is an inert gas or nitrogen; the pressure of the gas-protected environment is equal to atmospheric pressure, the humidity is ≤30%, and the temperature is room temperature; the protective environment is obtained by directly filling the air with protective gas, or by first drawing a vacuum and then filling it with protective gas.

[0023] Compared with the prior art, this application has at least one of the following technical effects:

[0024] 1. This application draws on the principle of laser peening, utilizing ultrashort laser pulses to impact compacted samarium iron nitrogen powder, causing it to solidify under the action of the shock wave. One of the key aspects of this application is that, compared to common additive manufacturing technologies for permanent magnets, such as SLS, LDED, LPBF, and FDM, this application replaces laser sintering, laser directional energy deposition, and laser powder bed fusion processes with ultrashort laser pulse impact. To address the problem of decreased magnetic properties due to thermal processes in additive manufacturing, the inventors of this application have tried numerous solutions, such as low-temperature laser sintering in a high-pressure environment; and a two-step forming scheme involving pre-sintering (i.e., preliminary sintering) followed by density strengthening of the pre-sintered body. After numerous trials and continuous evolution, the inventors finally proposed a one-step forming scheme that completely replaces laser sintering with ultrashort laser pulse impact. In this method, samarium iron nitride powder layers are laid one by one in a mold with a receiving cavity and solidified under room temperature and high pressure to obtain a layer-by-layer samarium iron nitride bulk material with extremely high density. This application can achieve additive manufacturing (which is more conducive to the production of permanent magnets with complex shapes than the explosive method) while avoiding the problem of samarium iron nitride powder being easily decomposed by heat, thereby helping to improve its magnetic properties.

[0025] 2. In some embodiments of this application, the thickness h1 of the symmetrically weighed samarium iron nitrogen powder and the slice layer thickness Δh (which corresponds to the rise of the laser head or the fall of the worktable, and will be further described in detail below) are distinguished and processed accordingly. This allows for more precise application of ultrashort pulse laser impact to the surface of the compacted powder layer, preventing a decrease in yield due to errors between the laser focus point and the irradiation location. Furthermore, this precise distinction also helps ensure that the size and shape of the permanent magnet produced by this application are more consistent with the designed size and shape.

[0026] 3. In some embodiments of this application, anisotropic permanent magnets can be fabricated by magnetically orienting the powder layer during the compaction process, thereby further increasing the magnetic properties of the samarium iron nitride permanent magnets, such as their energy product. Further details will be provided below.

[0027] 4. Besides samarium iron nitride permanent magnets, there are other temperature-sensitive functional materials whose corresponding functions may be lost or weakened due to thermal processes during molding. Therefore, the concept of this application can be extended to the molding technology of such temperature-sensitive functional materials to solve the problem of performance degradation caused by thermal processes during molding. Attached Figure Description

[0028] Figure 1 A schematic flowchart of a layer-by-layer manufacturing method for a dense permanent magnet according to an embodiment of this application is shown;

[0029] Figure 2 A schematic diagram of the mold structure in one embodiment of this application is shown;

[0030] Figure 3 A schematic diagram of the compaction step in one embodiment of this application is shown;

[0031] Figure 4 A schematic diagram of an ultrashort pulse laser shock step in one embodiment of this application is shown;

[0032] Figure 5 A schematic diagram of the overlapping method between laser irradiation points in the ultrashort pulse laser shock step of one embodiment of this application is shown;

[0033] Figure 6 A schematic flowchart of a layer-by-layer manufacturing method for samarium iron nitride permanent magnets with an added magnetic orientation step is shown in one embodiment of this application.

[0034] Figure 7 A schematic diagram of an embodiment of this application in which a horizontal magnetic field is arranged inside a mold is shown;

[0035] Figure 8 It shows the use of Figure 7 A schematic diagram of the coil performing horizontal magnetic orientation and simultaneously compacting the powder layer;

[0036] Figure 9 A schematic diagram of an embodiment of this application in which a vertical magnetic field is arranged inside a mold is shown;

[0037] Figure 10 It shows the use of Figure 9 A schematic diagram of the coil being vertically magnetically oriented and the powder layer being compacted simultaneously;

[0038] Figure 11 A schematic diagram of an embodiment of this application in which a horizontal magnetic field is arranged outside the mold is shown;

[0039] Figure 12 It shows the use of Figure 11 A schematic diagram of the coil performing horizontal magnetic orientation and simultaneously compacting the powder layer;

[0040] Figure 13 A schematic diagram of an embodiment of this application in which a vertical magnetic field is arranged outside the mold is shown;

[0041] Figure 14 It shows the use of Figure 13 A schematic diagram of the coil being vertically magnetically oriented and the powder layer being compacted simultaneously;

[0042] Figure 15 A schematic diagram of a small square pressing block according to one embodiment of this application is shown;

[0043] Figure 16 This demonstrates how an external coil performs magnetic orientation while utilizing... Figure 15 A three-dimensional schematic diagram of a small square pressing block simultaneously compacting a powder layer. Detailed Implementation

[0044] To better understand this application, various aspects of this application will be described in more detail with reference to the accompanying drawings. It should be understood that these detailed descriptions are merely illustrative of exemplary embodiments of this application and are not intended to limit the scope of this application in any way. Throughout the specification, the same reference numerals refer to the same elements. The expression "and / or" includes any and all combinations of one or more of the associated listed items.

[0045] It should be noted that in this specification, the terms "first," "second," etc., are used only to distinguish one feature from another and do not imply any limitation on the features. Therefore, without departing from the teachings of this application, the first subject discussed below may also be referred to as the second subject.

[0046] In the accompanying drawings, the thickness, size, and shape of the objects have been slightly exaggerated for ease of illustration. The drawings are for illustrative purposes only and are not drawn to scale.

[0047] It should also be understood that the terms "comprising," "including," "having," "containing," and / or "comprising," when used in this specification, indicate the presence of the stated features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or combinations thereof. Furthermore, when expressions such as "at least one of..." appear after a list of listed features, they modify the entire listed feature, not individual elements in the list. Additionally, when describing embodiments of this application, the word "may" is used to mean "one or more embodiments of this application." And the term "exemplary" is intended to refer to an example or illustration.

[0048] As used herein, the terms “basically,” “approximately,” and similar terms are used as terms of approximation rather than terms of degree, and are intended to describe inherent biases in measured or calculated values ​​that will be recognized by those skilled in the art.

[0049] Unless otherwise specified, all terms used herein (including technical terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms (e.g., those defined in common dictionaries) shall be interpreted as having the meaning consistent with their meaning in the context of the relevant art and shall not be interpreted in an idealized or overly formal sense unless expressly so specified herein.

[0050] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0051] This application proposes a layer-by-layer manufacturing method for dense permanent magnets, such as... Figure 1 As shown, it includes the following steps: Step 1) Prepare a mold, such as Figure 2 As shown, the mold includes an upper cover 11, a pressing block 12, a side frame 13, and a base 16. The base 16 and the side frame 13 are combined to form an open lower mold with a receiving cavity. In this step, a layer of samarium iron nitride powder is laid on the bottom of the lower mold to form a samarium iron nitride powder layer 14. A substrate 15 can be provided at the bottom of the lower mold to facilitate the separation of the formed samarium iron nitride block from the mold. Step 2) Vibrate the lower mold to make the samarium iron nitride powder layer 14 reach a preset compaction density. Step 3) Insert the pressing block 12 into the lower mold, then seal the opening of the lower mold with the upper cover 11, drive the pressing block 12 to move downward and apply downward mechanical pressure to the samarium iron nitride powder, so that the samarium iron nitride powder is compacted, such as... Figure 3 As shown. Step 4) Open the upper cover 11 and remove the pressing block 12. Use an ultrashort laser pulse to perform ultrashort pulse laser shock on the compacted samarium iron nitrogen powder with a certain coverage, so as to further increase the density of the samarium iron nitrogen powder and thus solidify the samarium iron nitrogen powder layer. Reference Figure 4 The aforementioned implementation of ultrashort pulse laser shock involves focusing the beam emitted from laser head 18 onto the surface of the samarium iron nitride powder layer. This is achieved using an ultrashort pulse laser with a single pulse energy of at least 20 μJ, a pulse width of 200 fs or more but not exceeding 800 fs, and a spot diameter of 40-120 μm (i.e.,...). Figure 4 The laser beam 19 shown irradiates the surface of the compacted samarium iron nitride powder (i.e., the surface of the samarium iron nitride powder layer), inducing a plasma shock wave to impact the compacted samarium iron nitride powder layer. After the impact, the samarium iron nitride powder layer solidifies into a samarium iron nitride bulk material 20. 5) A new layer of samarium iron nitride powder is laid on the surface of the impacted samarium iron nitride material. For the currently laid samarium iron nitride powder layer (also referred to as the current samarium iron nitride powder layer), steps 2) to 4) are repeated to solidify the current layer of samarium iron nitride powder using an ultrashort laser pulse impact. 6) Steps 2) to 5) are repeatedly executed until a dense samarium iron nitride bulk material with the designed three-dimensional shape is obtained; that is, new samarium iron nitride layers are continuously laid and solidified on the currently solidified samarium iron nitride material, ultimately obtaining a dense samarium iron nitride bulk material with the designed three-dimensional shape.

[0052] One of the key aspects of this application lies in its borrowing of the principle of laser shock peening (LSP). It utilizes ultrashort laser pulses to subject compacted samarium iron nitrogen powder to ultrashort pulse laser shock at a specific coverage rate. Laser shot peening, also known as laser shock peening, is a widely used laser surface treatment technology in industry. It typically uses nanosecond-level short-pulse lasers to create plasma on a material, generating explosive shock waves that alter the microstructure of the material's surface and generate residual compressive stress, thereby improving its performance, such as increasing the material's fatigue strength. However, laser shock peening usually requires a thin film to be coated on the surface of the material being treated. The explosive plasma formed by the laser acting on the bulk material is suppressed by the film, allowing the reverse shock wave of the plasma to act on the bulk material. To further compress the film, laser shock peening needs to be carried out underwater. Using this method to impact powder materials is almost unacceptable.

[0053] This application utilizes an ultrashort pulse laser. Ultrashort pulse lasers, especially femtosecond pulse lasers, due to their narrow pulse width and high peak power, can directly perform laser shock peening on metallic materials in the atmosphere without the need for a mask or water medium. For details, please refer to: T. Kawashima, T. Sano, A. Hirose, et al., Femtosecond laser peening of friction stir welded 7075-T73 aluminum alloys, Journal of Materials Processing Technology, 2018, 262:111-122. Using an ultrashort pulse laser with a single pulse energy of at least 20 μJ, a pulse width of 200 fs or more but not exceeding 800 fs, and a spot diameter of 40-120 μm, irradiating the surface of the compacted samarium iron nitrogen powder can induce the surface samarium iron nitrogen powder to ionize into plasma, forming a plasma shock wave that reverse-impacts the underlying samarium iron nitrogen powder. The pressure of this plasma shock wave can reach tens to hundreds of GPa. Experiments have shown that samarium iron nitride powder can be solidified at room temperature without high-temperature heat treatment under high-pressure impact of tens of GPa. Furthermore, the samarium iron nitride magnets obtained under this high-pressure impact achieve strengths of 116–144 kJ / m³. 3(i.e., 14.5-18.0 MGOe). For details, please refer to the following reference: Shinobu Takag, Koichi Morii, Takahiko Iriyama, et al., Evaluation of Practicality for FullyDense Isotropic Sm-Fe-N Magnets Made by Shock-Wave Consolidation Method, IEEE Transactions on Magnetics, 2023, 59(11):2101205. Therefore, under the laser shock strengthening treatment implemented by the above ultrashort pulse laser, the compacted samarium iron nitrogen powder can be consolidated under high pressure shock of tens of GPa. Moreover, under the laser shock strengthening implemented by the above ultrashort pulse laser, only a small amount of powder on the surface is heated and ionized into plasma. The heat does not spread to most of the powder in the lower layer, so that the powder in the lower layer can still be kept at room temperature during the laser shock strengthening process. Therefore, the problem of samarium iron nitrogen powder being easily decomposed by heat is avoided. Meanwhile, in this application, an ultrashort pulse laser performs point-by-point laser impact on mechanically compacted powder, scanning the impact with a certain coverage rate. This allows for the convenient depiction of the desired shape, and by stacking layers, the desired three-dimensional graphic shape can be obtained. Therefore, compared with samarium iron nitride magnets produced by the explosive method, the samarium iron nitride permanent magnets produced by the method of this application can have more complex shapes. Furthermore, this layer-by-layer manufacturing scheme based on ultrashort pulse lasers can make the impact force on the powder in different regions more consistent and uniform, thus contributing to further improvement of the magnetic properties of samarium iron nitride powder.

[0054] Furthermore, in one embodiment of this application, the layer-by-layer manufacturing method of the dense permanent magnet further includes a pre-processing step. This pre-processing step is performed before step 1). The pre-processing step involves: before fabricating the samarium iron nitride (SFI) block, performing layered slicing on its three-dimensional graphic in software, with each slice having a layer thickness of Δh; then calculating the specified weight of SFI powder in each slice based on the compacted thickness h1 of the SFI powder, and subsequently weighing a specified weight of SFI powder for each slice. In this embodiment, in steps 1) and 5), the corresponding weighed portion of SFI powder with the specified weight is loaded into the lower mold, thereby completing the laying of the current layer of SFI powder. In step 4), after each ultrashort laser pulse impact on the current layer of SFI powder, the worktable carrying the mold is lowered by Δh or the laser head used for ultrashort laser pulse impact is raised by Δh. It should be noted that research has found that during the process of compacting the powder layer under ultrashort pulse laser impact, the powder layer undergoes thickness reduction under the enormous impact force. That is, if the thickness of the compacted samarium iron nitride (SFI) powder layer is h1, and the thickness of the final solidified SFI layer after ultrashort pulse laser impact treatment is Δh, then Δh will actually be less than h1. In this embodiment, when weighing the SFI corresponding to each slice, the thickness h1 of the compacted SFI powder is used. When moving the worktable or laser head to perform ultrashort pulse laser impact treatment on the next layer of SFI powder, the amount of movement is Δh. Δh is the thickness of the worktable (e.g., h1) after completing one layer of printing. Figure 4 The worktable 21) or laser head (e.g.) Figure 4 The amount of movement in the height direction of the laser head 18) is also the amount of rise of the powder block compared to the previous layer after being impacted by the femtosecond pulsed laser. In this embodiment, distinguishing and processing the thickness h1 and Δh accordingly allows for more precise application of ultrashort pulsed laser impact to the surface of the compacted powder layer, preventing a decrease in yield due to errors between the laser focus point and the irradiation location. On the other hand, this precise distinction also helps to ensure that the size and shape of the permanent magnet produced by this application are more consistent with the design size and shape.

[0055] Furthermore, in one embodiment of this application, in step 4), by adjusting the coverage and pulse energy, the samarium iron nitrogen material after impact reaches more than 98% of its theoretical density. Figure 5 As shown, in the ultrashort pulse laser shock step, the laser irradiation points overlap to continuously and uniformly cover the area of ​​the samarium iron nitrogen powder layer that needs to be compacted and cured. Figure 5In this context, the overlap width of the laser spot, i.e., the overlap spacing D2, can be adjusted by changing the ratio of the overlap spacing D2 to the spot diameter D1 to control the coverage of the laser shock. The ultrashort pulse laser beam is typically a Gaussian beam; selecting an appropriate coverage rate can make the impact force on the powder layer more uniform and consistent. Furthermore, as mentioned earlier, using an ultrashort pulse laser with a single pulse energy of at least 20 μJ, a pulse width of 200 fs or more but not exceeding 800 fs, and a spot diameter of 40-120 μm to irradiate the surface of the compacted samarium iron nitride powder can induce the surface samarium iron nitride powder to ionize into plasma, forming a plasma shock wave that impacts the underlying samarium iron nitride powder in the opposite direction. This plasma shock wave applies a pressure of GPa or even higher to the compacted powder layer. However, direct and precise measurement of plasma shock waves is difficult. Therefore, in this embodiment, the coverage and pulse energy (laser pulse energy depends on the pulse width, duty cycle, frequency, and even waveform, especially the rise edge) are adjusted by measuring the density of the impacted samarium iron nitride material, allowing these parameters to be optimized. Studies have shown that when the impacted samarium iron nitride material reaches more than 98% of its theoretical density, the resulting permanent magnet (or permanent magnet block) can possess excellent mechanical and magnetic properties.

[0056] Furthermore, in some embodiments of this application, in step 2), the method of vibrating the mold is to strike, rock, or a combination of both alternately. Specifically, the powder can be poured into the mold first and spread evenly with a scraper (or other method), at which point the powder density is the loose density. Vibrating the mold will further compact the powder, increasing its density, which is called the tapped density. Using an ultrashort pulse laser to impact the powder further compacts it (actually approaching the theoretical density), resulting in the bulk density. In step 2), a non-contact method can also be used to achieve the tapped density. For example, in other embodiments, ultrasound or microwaves can be used to act on the samarium iron nitride powder layer to achieve a preset tapped density.

[0057] Further, in one embodiment of this application, the side frame is fitted onto the base, and a non-magnetic metal substrate is placed on the base. A first layer of samarium iron nitride powder is laid and compacted on the substrate, and subsequent layers of samarium iron nitride powder are laid and compacted on the previous layer impacted by an ultrashort pulse laser. The side frame can be cylindrical, rectangular, square, or a frame with other shapes. The shapes of the base, the top cover, and the pressing block match the shapes of the side frame. Placing a non-magnetic metal substrate on the base prevents the magnet from sticking to the mold base after impact. In this embodiment, the top cover and the pressing block can be integrated. They can be connected by threads or screws, so that rotating the top cover can drive the pressing block to move downward, thereby applying the required mechanical pressure to the powder layer under the pressing block. In another embodiment, the top cover and the pressing block can be fixedly connected. In this case, a hydraulic device can be used to drive the top cover and the pressing block to move downward, thereby applying the required mechanical pressure to the powder layer under the pressing block.

[0058] Furthermore, in one embodiment of this application, when the three-dimensional graphic of the samarium iron nitride block to be manufactured has a hollow structure, in the case where the area of ​​the latter layer exceeds that of the former layer, the hollow area can be filled by an auxiliary support column so that a new samarium iron nitride powder layer can be laid on top and solidified.

[0059] Furthermore, in one embodiment of this application, a pulse coil is arranged around the mold; in step 3), a pulse current with a peak value exceeding 1kA is applied to the pulse coil during the compaction process to generate a thin magnetic field of more than 30kOe in the region of the samarium iron nitrogen powder in the current layer within the mold, and the samarium iron nitrogen powder being compacted and not subjected to laser shock achieves magnetic orientation under the action of the thin magnetic field.

[0060] Furthermore, in some embodiments of this application, the samarium iron nitrogen powder may have a particle size distribution D 50 It is a polygonal or spherical powder with a diameter of 3–50 μm.

[0061] Furthermore, in some embodiments of this application, steps 1) to 7) are carried out in a gas-protected environment, wherein the protective gas in the gas-protected environment is an inert gas or nitrogen; the pressure of the gas-protected environment is equal to atmospheric pressure, the humidity is ≤30%, and the temperature is room temperature; the protective environment is obtained by directly filling the air with protective gas, or by first evacuating the air and then filling it with protective gas. The manufacturing process of samarium iron nitride (SFIN) blocks is completed in a gas-protected environment. A substrate is placed at the bottom of a mold of a simple shape, a specified weight of SFIN powder is added, the mold is covered, the SFIN powder is compacted mechanically, the mold is opened, and an ultrashort pulse laser is used to scan the SFIN layer with a certain coverage along a set path. The plasma shock wave induced by the ultrashort pulse laser further compacts the SFIN layer. On top of this layer, a specified weight of samarium iron nitrogen powder is added, the mold cover is closed, mechanical compaction is performed, the cover is opened, and the laser repeats the above path to impact and compact this layer of powder again; ..., this cycle is repeated, layer by layer, until an isotropic samarium iron nitrogen permanent magnet with a density of more than 98% of the theoretical value is finally obtained.

[0062] In the above embodiments, the mold can consist of a base, side frames, a top cover, and a pressure block. The side frames are fitted onto the base, and a substrate is placed on the base as the foundation for the powder and the future molded part. This substrate will be removed together with the molded part. The pressure block is then placed on top, and pressure is applied to the top cover. The pressure is transmitted to the powder through the pressure block, compacting the powder placed therein. The compacted thickness h1 is used as the basis for calculating the weight of each portion of samarium iron nitrogen. The first layer of samarium iron nitrogen powder is laid and compacted on a non-magnetic high-strength metal substrate, and subsequent layers of samarium iron nitrogen powder are laid and compacted on the previous layer after being impacted by an ultrashort pulse laser. The vibration method is usually tapping, rocking, or a combination of both repeatedly. The side frames of the mold can be cylindrical, rectangular, square, etc. The shapes of the base, top cover, and pressure block should match the shapes of the side frames to ensure that the powder is compacted in the mold. The amount of powder added to the mold each time varies with the thickness of the compacted layer. The mold material is a high-strength, non-magnetic material, such as metal, engineering plastics, ceramics, carbon fiber, etc. The substrate is a non-magnetic, high-strength metal material, such as 316 stainless steel.

[0063] Furthermore, considering that some other functional materials besides samarium iron nitride permanent magnets are also temperature-sensitive, their corresponding functions may be lost or weakened due to thermal processes during molding. Therefore, the concept of this application can be extended to the molding technology of such temperature-sensitive functional materials to solve the problem of performance degradation caused by thermal processes during molding. Based on this, in one embodiment of this application, a molding method for temperature-sensitive functional materials is provided, which includes the following steps: Step 1) Prepare a mold, the mold including a top cover, a pressing block, a side frame and a base, the base and the side frame combined to form an open lower mold with a receiving cavity. In this step, a layer of functional material powder is laid on the bottom of the lower mold to form a powder layer, wherein a substrate can be provided at the bottom of the lower mold to facilitate the separation of the molded functional material block from the mold. Step 2) Vibrate the lower mold to make the powder layer reach a preset compaction density. Step 3) Insert the pressing block into the lower mold, then seal the opening of the lower mold with the upper cover, drive the pressing block downward and apply downward mechanical pressure to the powder layer, so that the functional material powder is compacted. Step 4) Open the upper cover and remove the pressing block. Use an ultrashort laser pulse to perform ultrashort pulse laser shock on the compacted functional material powder with a certain coverage, so as to further increase the density of the functional material powder and thus solidify the functional material powder layer. The ultrashort pulse laser shock is performed by aiming the laser head at the surface of the functional material powder layer. Using an ultrashort pulse laser with a single pulse energy of at least 20 μJ, a pulse width of more than 200 fs and not more than 800 fs, and a spot diameter of 40-120 μm, the surface of the compacted functional material powder (i.e., the surface of the functional material powder layer) is irradiated, inducing a plasma shock wave to impact the compacted functional material powder layer. After the impact, the functional material powder layer solidifies into a functional material block. 5) After impact, a layer of functional material powder is deposited on the surface of the functional material. For the currently deposited functional material powder layer (also referred to as the current functional material powder layer), steps 2) to 4) are repeated to solidify the current layer of functional material powder using ultrashort laser pulse impact. 6) Steps 2) to 5) are repeated continuously until a dense functional material block with the designed three-dimensional shape is obtained; that is, new functional material layers are continuously deposited and solidified on the currently solidified functional material to ultimately obtain a dense functional material block with the designed three-dimensional shape. Here, the functional material refers to the material whose grains decompose or are damaged in other ways due to excessively high temperatures during the process of forming the material from powder to block, resulting in the loss or weakening of its corresponding function. For example, samarium iron nitride (SFI) has magnetism, and magnetism is its function. If the temperature is too high during the process of forming SFI from powder to block (e.g., excessively high temperature during sintering), the SFI grains may decompose, leading to the loss or significant weakening of magnetism.

[0064] The details of this application will now be further described with reference to a more specific embodiment.

[0065] refer to Figure 6 In this embodiment, a layer-by-layer manufacturing method for permanent magnets that can avoid the decrease in magnetic properties caused by the thermal process is provided, which includes the following steps: (1) In a gas-protected environment, fine samarium iron nitrogen powder is weighed according to a specified weight, divided into several portions, and packaged in various containers. (2) A three-dimensional model of the permanent magnet to be manufactured is designed in the software, and the model is sliced ​​and path planned in layers. The three-dimensional model is decomposed into two-dimensional graphics and paths that can be laser-impacted. (3) A mold of a simple shape is placed in a gas-protected environment, and a non-magnetic high-strength substrate is placed at the bottom of the mold. A portion of samarium iron nitrogen powder is poured in, and the mold is vibrated to increase the compaction density of the powder and minimize the gaps in the powder before laser impact. (4) The mold cover is closed, and the powder is compacted by mechanical pressure. (5) During the compaction process, the powder is magnetically oriented by a coil, wherein the thickness of the orientation is basically the same as the thickness of the compacted powder. (6) Open the mold cover, use the laser pointer to aim at the starting point to be impacted, turn on the femtosecond laser, and at the same time move the worktable or laser head according to the path specified by the software to perform ultra-short pulse laser impact on the samarium iron nitrogen powder with a certain coverage, so that the density of the samarium iron nitrogen powder is further increased to reach more than 98% of the theoretical value. (7) Open the mold cover, pour in a portion of samarium iron nitrogen powder, vibrate the mold to increase the compaction density of the powder, and minimize the gap of the powder before laser impact. (8) Determine whether a complete three-dimensional shape has been obtained. If the determination is no, repeat steps (4)-(7) to realize the manufacturing of the designed anisotropic samarium iron nitrogen permanent magnet. If the determination is yes, then end. When the manufactured product is an isotropic samarium iron nitrogen permanent magnet, the aforementioned step (5) is not executed, and in step (8), it is determined whether a complete three-dimensional shape has been obtained. If the determination is no, repeat steps (4), (6), and (7). If the determination is yes, then end.

[0066] In this embodiment, the gas in the protective gas environment can be an inert gas, such as argon, helium, or nitrogen. The pressure of the protective environment is equal to atmospheric pressure, the humidity is ≤30%, and the temperature is room temperature, typically 15-30℃. The protective environment can be obtained by directly filling with argon to replace air, or by first evacuating and then filling with nitrogen, helium, or argon. The specified weight depends on the cross-sectional area of ​​the mold, the volume determined by the thickness of each layer, and the density of samarium iron nitride (SMR). That is, the amount of powder added corresponds to the thickness of each layer. This thickness refers to the thickness of the powder after spinning, not the thickness after laser impact. The fine SMR powder is generally micron-sized, i.e., particle size distribution D... 50It is a polygonal or spherical powder with a diameter of 3–50 μm. In step (1), the container can be made of non-magnetic materials such as glass, metal, plastic, or ceramic that do not chemically react with samarium iron nitrogen in a protected environment.

[0067] In this embodiment, the software comprises two parts: design and manufacturing. The design part can be general-purpose mechanical graphic design software, such as AutoCAD or CAXA. The manufacturing part is 3D printing (additive manufacturing) specialized software, such as Materialis or CATIYA, or it can be self-developed 3D printing (additive manufacturing) specialized software. The movement of the worktable or laser head according to the path specified by the software refers to the working path during femtosecond laser impact, which is a three-dimensional motion, including two-dimensional planar motion and vertical lifting motion. The height of the rise or fall is equal to the increase in height Δh of the samarium iron nitride magnet after laser impact. When the laser head is stationary, the worktable lowers by Δh; if the worktable is stationary, the laser head rises by Δh.

[0068] Furthermore, in some embodiments, to improve processing efficiency, multiple ultra-short pulse lasers can be used simultaneously for impact compaction, with each laser scanning area only overlapping at the interface as required by the process, rather than repeating (or overlapping each other).

[0069] In step (5) of the aforementioned embodiment, the powder is magnetically oriented using a coil during compaction. This coil is a pulse coil. The preferred shape of the magnetic field generated by the pulse coil is a thin-sheet two-dimensional magnetic field. However, the fabrication of such a two-dimensional magnetic field is difficult. In the actual magnetic powder compaction process, an approximate magnetic field shape (which can be called an approximate magnetic field) can be used instead of a thin-sheet two-dimensional magnetic field. When using an approximate magnetic field, spatially, the position of the pulse coil can be adjusted to select an area with a large and uniformly distributed magnetic field strength, and this area can be coupled with the magnetic powder layer (i.e., the samarium iron nitride powder layer) currently being compacted. Temporally, the action time of the approximate magnetic field is shortened as much as possible while fully improving the orientation degree of the currently compacted magnetic powder layer. In this way, the approximate magnetic field acts on the current magnetic powder layer in both time and space, with less interference to other solidified samarium iron nitride blocks.

[0070] Magnetic orientation involves aligning the easy magnetization axes of the magnetic powder particles with the designed direction, thereby aligning the easy magnetization directions of the particles to approximately match or nearly match the final magnetization direction in the permanent magnet's design direction (i.e., improving its orientation degree). After step (6), the magnetic powder particles are solidified together and exist as grains in the samarium iron nitride bulk material. The easy magnetization axis direction of the magnetic powder particles rearranged through magnetic orientation in step (5) is also fixed. By adding the magnetic orientation step, the layer-by-layer manufacturing method of the permanent magnet in the above embodiment can produce magnetically anisotropic samarium iron nitride bulk materials, thereby further enhancing their magnetic energy product (BH). max Isomagnetic properties. Reference Figure 7 and Figure 8 During the compaction process, the horizontal orientation coil 17 can be placed inside the lower mold, and magnetic orientation and compaction operations are performed synchronously to maximize the orientation degree while ensuring compaction. Specifically, the coil 17 can be placed inside the lower mold (i.e., inside the mold side frame 13), with the outer diameter of the coil 17 matching the inner diameter of the mold. The pressing block 12 is placed inside the coil 17, with its outer diameter matching the inner diameter of the coil 17. A pulsed current is passed through the coil 17 to generate a pulsed magnetic field in a horizontal direction. Simultaneously, the pressing block 12 moves downward and hammers the samarium iron nitride powder layer 14 below. The timing of the pulsed current passing through the coil 17 is controlled so that the time difference between the duration of the pulsed magnetic field and the time when the pressing block contacts the samarium iron nitride powder does not exceed 1 ms, thereby ensuring the synchronization of magnetic orientation and compaction operations. For example, the duration of the pulsed magnetic field can be 0–10 ms, and the time when the pressing block hammers the samarium iron nitride powder layer can be 1–9 ms. The process of the pressing block hammering the samarium iron nitride powder layer can be a single hammer blow or multiple hammer blows at a certain frequency. When performing multiple hammering operations at a certain frequency, it is necessary to ensure that all hammering occurs within a time period of 1 to 9 ms. For example, the briquette is hammered 8 times at a frequency of 1 kHz within a time period of 1 to 9 ms. In this embodiment, the pulsed magnetic field can generate a thin magnetic field of more than 30 kOe in the region where the samarium iron nitrogen powder is located, thereby causing the easy magnetization axis of the powder particles to turn in the horizontal direction and improving the orientation of the powder layer.

[0071] refer to Figure 9 and Figure 10 In another embodiment, a coil-embedded vertical orientation scheme is also provided. In this vertical orientation scheme, the coil 17 is placed inside the lower mold, and the direction of its pulsed magnetic field is perpendicular to the powder layer surface, hence it can be called a vertical magnetic field. In this embodiment, magnetic orientation and compaction operations are performed simultaneously to maximize the degree of orientation while ensuring compaction. The specific method can be compared with a coil-embedded horizontal orientation scheme (i.e.,... Figure 7 and Figure 8 The corresponding embodiment is the same, except that a vertical magnetic field is used in this embodiment.

[0072] In other embodiments of this application, the orientation coil can be externally placed, that is, the orientation coil can be arranged outside the lower mold. In this configuration, the pressure head 12 does not need to avoid the coil 17, which can prevent the samarium iron nitride powder at the edge from being difficult to compact. Figure 11 and Figure 12 In one embodiment, the coil 17 for orientation is located outside the mold side frame, with its inner diameter matching the mold's outer diameter. The pressure block is located inside the side frame, with its outer diameter matching the mold side frame's inner diameter. In this embodiment, magnetic orientation and compaction operations are performed simultaneously to maximize orientation while ensuring compaction. Specifically, a pulsed current is passed through the coil 17 to generate a horizontally oriented pulsed magnetic field. Simultaneously, the pressure block 12 moves downward and hammers the samarium iron nitride powder layer 14 below. The timing of the pulsed current passing through the coil 17 is controlled so that the time difference between the duration of the pulsed magnetic field and the time the pressure block contacts the samarium iron nitride powder does not exceed 1 ms, thus ensuring the synchronization of magnetic orientation and compaction operations. For example, the duration of the pulsed magnetic field can be 0–20 ms, and the time the pressure block hammers the samarium iron nitride powder layer can be 1–19 ms. The process of the pressure block hammering the samarium iron nitride powder layer can be a single hammer blow or multiple hammer blows at a certain frequency. When performing multiple hammering operations at a certain frequency, it is necessary to ensure that all hammering occurs within a time period of 1–19 ms. For example, the compact can be hammered 18 times at a frequency of 1 kHz within a time period of 1–19 ms. Alternatively, when the duration of the pulsed magnetic field is 0–10 ms, the hammering period of the samarium iron nitride powder layer can be 1–9 ms, and the compact can be hammered 16 times at a frequency of 2 kHz within this 1–9 ms time period. In this embodiment, the pulsed magnetic field can generate a thin magnetic field of over 30 kOe in the region where the samarium iron nitride powder is located, thereby causing the easy magnetization axis of the powder particles to align horizontally and improving the orientation of the powder layer.

[0073] refer to Figure 13 and Figure 14 In another embodiment, a vertical orientation scheme with an externally placed coil is also provided. In this vertical orientation scheme, the coil 17 is placed outside the lower mold, and the direction of its pulsed magnetic field is perpendicular to the powder layer surface, hence it can be called a vertical magnetic field. In this embodiment, magnetic orientation and compaction operations are performed simultaneously to maximize the degree of orientation while ensuring compaction. The specific method can be compared with the horizontal orientation scheme with an externally placed coil (i.e.,...). Figure 11 and Figure 12 The corresponding embodiment is the same, except that a vertical magnetic field is used in this embodiment.

[0074] This application also provides an embodiment of synchronous compaction based on a small-area square compactor and an accompanying pulsed magnetic field. (Reference) Figure 15 and Figure 16The orientation coil is located outside the mold side frame. The mold and coil 17 are square, with the outer dimensions of the mold matching the inner dimensions of the coil. The cross-section of the pressing block is also square, with its outer dimensions smaller than the inner dimensions of the mold. A pulsed current is passed through coil 17, generating a horizontal pulsed magnetic field of 30 kOe as shown in the figure, lasting from 0 to 10 ms. Within 1-9 ms, the pressing block is hammered 16 times at a frequency of 2 kHz, while the pressing block 12 moves at a certain horizontal speed, hammering the entire plane 22 containing the powder layer with a certain coverage.

[0075] Figures 7 to 16 In the corresponding embodiments, the pressing block, substrate, mold, etc., are made of non-magnetic insulating materials. Preferably, the pressing block, substrate, base, and side frame are all made of corundum. It should be noted that... Figures 7 to 16 This is for illustrative purposes only, and the dimensions of the components do not represent actual dimensions. For example, the actual size of the coil in the thickness direction may be much smaller than the size shown in the diagram. In the actual magnetic alignment process, the coil is positioned as close as possible to the powder layer. When the coil is positioned inside the side frame, it is positioned slightly higher than the powder layer to avoid direct contact with the powder. When the coil is positioned outside the side frame, it can be positioned flush with the powder layer so that the area of ​​the coil with a higher and more uniform magnetic field strength can better couple with the magnetic powder layer (i.e., the samarium iron nitride powder layer) being compacted.

[0076] It is important to note that magnetic orientation is different from magnetization. At a more microscopic level, each magnetic powder particle or each grain in the bulk material obtained after laser impact contains a large number of magnetic domains. Each magnetic domain is a tiny region containing multiple atoms or molecules, and the atomic magnetic moments within this tiny region are aligned in a specific direction, exhibiting uniform spontaneous magnetization. Before magnetization, within each grain of the bulk material obtained after laser impact, the magnetic moments of each magnetic domain are in different directions, resulting in mutual cancellation and a vector sum of zero, making the overall magnetic moment of the object zero. In other words, magnetic materials do not exhibit magnetism under normal circumstances. Only after the magnetic material is magnetized can it exhibit magnetism. In this embodiment, oriented magnetic powder during compaction allows the easily magnetized axes of the magnetic powder particles (which may be polygonal, circular, or, in the case of polygons, prisms, hexagonal rods, strips, etc.) to align in the same direction, thus facilitating subsequent magnetization. For example, when the easy magnetization axis of the grains is aligned with or approximately aligned with the final magnetization direction, a smaller magnetic field strength and a shorter magnetization time can be used to achieve saturation magnetic induction in the permanent magnet. Conversely, if the final magnetization direction is located along the difficult magnetization axis of the grains, a larger magnetic field strength and a longer magnetization time are required to achieve magnetization. In this embodiment, magnetic orientation during the compaction process can be used to rearrange the easy magnetization axes of grains in different regions of the permanent magnet according to the designed direction, thereby facilitating the magnetization of permanent magnets with complex pole distributions and shapes.

[0077] Furthermore, it should be noted that during the magnetic alignment process based on the pulsed coil (i.e., rearranging magnetic powder particles), the magnetic powder particles may become partially magnetized. If the resulting bulk material still retains magnetism after impact, it may affect the subsequent laying of magnetic powder. In this embodiment, the residual magnetism introduced into the samarium iron nitride bulk material by the magnetic alignment operation can be eliminated by reversing the pulsed coil. That is, after the pulsed laser impact is completed, the pulsed coil is reversed to demagnetize the samarium iron nitride bulk material obtained after the pulsed laser impact, thereby facilitating the subsequent laying of magnetic powder. In another embodiment, the residual magnetism introduced by the magnetic alignment operation can also be eliminated by thermal demagnetization (i.e., using a thermal demagnetization module to eliminate the residual magnetism in the samarium iron nitride bulk material obtained after the pulsed laser impact). It should be noted that the demagnetization of the samarium iron nitride bulk material restores the multiple magnetic domains inside its grains to a state where their magnetic moments are different and cancel each other out, without changing the orientation of the easy magnetization axis of the grain.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for manufacturing a dense permanent magnet layer by layer, characterized in that, Includes the following steps: Step 1) Prepare a mold, which includes a base, side frame, pressure block and top cover. The base and side frame are combined to form an open lower mold with a receiving cavity. A layer of samarium iron nitrogen powder is laid on the bottom of the lower mold. Step 2) Vibrate the lower mold to make the samarium iron nitrogen powder layer reach the preset tap density; Step 3) Insert the pressing block into the lower mold, then seal the opening of the lower mold with the upper cover, drive the pressing block to move downward and apply downward mechanical pressure to the samarium iron nitrogen powder, so that the samarium iron nitrogen powder is compacted; Step 4) Open the top cover and remove the compactor block. Use an ultrashort laser pulse to perform ultrashort pulse laser shock on the compacted samarium iron nitrogen powder with a pre-set coverage rate, so as to further increase the density of the samarium iron nitrogen powder and thus solidify the samarium iron nitrogen powder layer. The ultrashort pulse laser shock is performed by using an ultrashort pulse laser with a single pulse energy of at least 20 μJ, a pulse width of more than 200 fs and not more than 800 fs, and a spot diameter of 40-120 μm to irradiate the surface of the compacted samarium iron nitrogen powder, thereby inducing a plasma shock wave to impact the compacted samarium iron nitrogen powder layer. Step 5) Deposit a layer of samarium iron nitrogen powder on the surface of the impacted samarium iron nitrogen material; repeat steps 2) to 4) to solidify the current layer of samarium iron nitrogen powder by impacting with an ultrashort laser pulse; Step 6) Repeat steps 2) to 5) to obtain dense samarium iron nitrogen blocks.

2. The method for manufacturing a dense permanent magnet layer by layer according to claim 1, characterized in that, The layer-by-layer manufacturing method also includes Preprocessing steps: Before fabricating the samarium iron nitride (SFI) blocks, the 3D graphic is sliced ​​into layers, with each slice having a thickness of [missing information]. Δh; Then, based on the thickness after compaction of the samarium iron nitrogen powder... h 1 The specified weight of samarium iron nitrogen powder for each slice is calculated, and then a specified weight of samarium iron nitrogen powder is weighed for each slice; wherein, Δh Less than h 1 ; In steps 1) and 5), the corresponding weighed portion of samarium iron nitrogen with a specified weight is loaded into the lower mold, thereby completing the laying of samarium iron nitrogen powder in the current layer; In step 4), after each ultrashort laser pulse impact on the samarium iron nitrogen powder of the current layer, the worktable carrying the mold is lowered. Δh The laser head remains stationary; or the laser head used for ultrashort laser pulse impact is raised. Δh The workbench remains stationary.

3. The method for manufacturing a dense permanent magnet layer by layer according to claim 1, characterized in that, In step 4), by adjusting the coverage and laser pulse energy, the samarium iron nitrogen material after impact reaches more than 98% of its theoretical density value.

4. The method for manufacturing a dense permanent magnet layer by layer according to claim 1, characterized in that, In step 2), the method of vibrating the mold is to strike, rock, or use a combination of both alternately, so that the samarium iron nitrogen powder layer reaches the preset tap density.

5. The method for manufacturing a dense permanent magnet layer by layer according to claim 1, characterized in that, The side frame is fitted onto the base, on which a non-magnetic metal substrate is placed. A first layer of samarium iron nitride powder is laid and compacted onto the substrate, and subsequent layers of samarium iron nitride powder are laid and compacted onto the previous layer that has been impacted by an ultrashort pulse laser. The side frame is cylindrical, rectangular, square, or has a frame shape with other outlines. The shapes of the base, the top cover, and the pressing block match the shapes of the side frame. The top cover and the pressing block are integrated.

6. The method for manufacturing a dense permanent magnet layer by layer according to claim 1, characterized in that, The mold is surrounded by coils or is provided with coils that can extend into the lower mold; In step 3), a pulsed current with a peak value exceeding 1 kA is applied to the coil during the compaction process to generate a thin magnetic field of more than 30 kOe in the region of the samarium iron nitrogen powder in the current layer within the mold. The samarium iron nitrogen powder being compacted, which has not been subjected to laser shock, achieves magnetic orientation under the action of the thin magnetic field.

7. The method for manufacturing a dense permanent magnet layer by layer according to claim 6, characterized in that, In step 3), the coil generates a horizontal or vertical pulsed magnetic field in the region where the samarium iron nitrogen powder layer is located; while the pulsed magnetic field is applied, the pressing block hammers the samarium iron nitrogen powder layer to compact it, wherein the timing of the pulsed current being applied to the coil is controlled so that the time difference between the duration of the pulsed magnetic field and the time when the pressing block contacts the samarium iron nitrogen powder does not exceed 1ms.

8. The method for manufacturing a dense permanent magnet layer by layer according to claim 6, characterized in that, The side frame is fitted onto the base, and a non-magnetic insulating substrate is placed on the base. A first layer of samarium iron nitrogen powder is laid and compacted on the substrate, and subsequent layers of samarium iron nitrogen powder are laid and compacted on the previous layer that has been impacted by an ultrashort pulse laser. The substrate, the base, the side frame, and the pressing block are all made of corundum.

9. The method for manufacturing a dense permanent magnet layer by layer according to claim 1, characterized in that, The samarium iron nitrogen powder has a particle size distribution D. 50 It is a polygonal or spherical powder with a diameter of 3~50μm.

10. The method for manufacturing a dense permanent magnet layer by layer according to claim 1, characterized in that, Steps 1) to 6) are carried out in a gas-protected environment, wherein the protective gas in the gas-protected environment is an inert gas or nitrogen; the pressure of the gas-protected environment is equal to atmospheric pressure, the humidity is ≤30%, and the temperature is room temperature; the protective environment is obtained by directly filling the air with protective gas, or by first drawing a vacuum and then filling it with protective gas.

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