CN118023541A

CN118023541A - Layer-by-layer manufacturing method of compact permanent magnet

Info

Publication number: CN118023541A
Application number: CN202410179091.3A
Authority: CN
Inventors: 李正阳; 陆俊
Original assignee: Beijing Photoelectric Technology Co ltd
Current assignee: Beijing Photoelectric Technology Co ltd
Priority date: 2024-02-17
Filing date: 2024-02-17
Publication date: 2024-05-14

Abstract

The invention relates to a layer-by-layer manufacturing method of a compact permanent magnet, which comprises the following steps: 1) Paving a layer of samarium iron nitrogen powder at the bottom of the lower die; 2) Compacting the powder layer; 3) Applying downward mechanical pressure to the powder with a briquette to compact it; 4) Performing ultrashort pulse laser impact on the compacted samarium iron nitrogen powder with a certain coverage rate by utilizing ultrashort laser pulses to solidify a samarium iron nitrogen powder layer; 5) The surface of the impacted samarium-iron-nitrogen material is provided with a next layer of samarium-iron-nitrogen powder; re-executing the steps 2) to 4), so that the samarium-iron-nitrogen powder of the current layer is solidified by utilizing ultra-short laser pulse impact; 6) And (5) repeatedly executing the steps 2) to 5) to obtain the compact samarium-iron-nitrogen block material. The invention can realize the layer-by-layer manufacture of the permanent magnet blocks, and simultaneously avoid the magnetic property reduction caused by the thermal process.

Description

Layer-by-layer manufacturing method of compact permanent magnet

Technical Field

The invention relates to the technical fields of permanent magnet materials, near-net forming manufacturing and additive manufacturing, in particular to a layer-by-layer manufacturing method of compact permanent magnet blocks.

Background

The permanent magnetic material is an important material in energy power and electronic technology communication, and can be used in travelling wave tubes, circulators and other electronic instruments in the aspects of motors, engines, satellites and radars. At present, rare earth permanent magnet application is permeated into various aspects such as clean power grids, automobiles, household appliances, electronic instruments, nuclear magnetic resonance imagers, acoustic equipment, micro-motors, mobile phones and the like.

The most widely used rare earth permanent magnet material is neodymium iron boron (NdFeB) permanent magnet material. Compared with the traditional ferrite, the neodymium iron boron has high magnetic performance, and the volume of the magnet can be much smaller than that of the corresponding ferrite when the neodymium iron boron is applied to a micro motor, so that the permanent magnet motor has the advantages of small volume, light weight, small inertia, high power, high efficiency and the like.

The neodymium-iron-boron magnet can be classified into a bonded neodymium-iron-boron magnet and a sintered neodymium-iron-boron magnet according to the production process. The production raw material of the bonded NdFeB is usually mixed powder obtained by mixing NdFeB magnetic powder and a binder according to a certain volume fraction. The mixed powder can be made into a magnet with certain mechanical strength by compression molding or injection molding. The bonded NdFeB magnet has high dimensional accuracy and can be manufactured into a magnetic element with a relatively complex shape. However, the magnetic properties of bonded NdFeB tend to be much lower than the theoretical values of NdFeB magnets due to the need to use non-magnetic binders (e.g., resins, plastics, etc.).

Neodymium-iron-boron magnets manufactured based on additive manufacturing (additive manufacturing, which is sometimes also referred to as 3D printing) technology have emerged in recent years. Selective laser sintering (SELECTIVE LASER SINTERING, abbreviated SLS), laser directed energy deposition techniques (LASER DIRECTED ENERGY deposition, abbreviated LDED), and laser powder bed fusion techniques (laserpowder bed fusion, abbreviated LPBF), among others. Existing magnetic material additive manufacturing techniques typically require the use of mixed organic binders as raw materials, belonging to the fused deposition (Fused Deposition Modelling, abbreviated FDM) category. However, in some front-edge exploration of neodymium-iron-boron additive manufacturing, an organic binder is not mixed in the neodymium-iron-boron magnetic powder, so that higher density can be obtained. However, high temperature processing is required to consolidate the magnetic powder (e.g., sintering temperatures of neodymium iron boron powder typically up to 1000 ℃), whether by SLS, LDED or LPBF techniques. During the heat treatment at high temperature, part of the crystalline phase of the neodymium iron boron powder with magnetic endowment may be decomposed, so that the magnetic performance of the manufactured neodymium iron boron block is not as expected.

In addition, samarium iron nitrogen is a novel permanent magnet material with good prospect. From microscopic analysis, samarium iron nitrogen grains have better intrinsic magnetic properties than neodymium iron boron grains. For example, the magnetic energy product of micron-sized samarium-iron-nitrogen particles can be as high as 60MGOe. However, samarium iron nitrogen is a magnetic material that decomposes at 600 ℃, and currently, samarium iron nitrogen permanent magnets are mostly manufactured by bonding a powder of samarium iron nitrogen into a magnet by using a polymer or a metal (e.g., zinc) having a relatively low temperature as a bonding phase. Low temperature sintering methods are also available, such as: samarium-iron-nitrogen magnets prepared by spark plasma sintering, laser sintering and other methods have magnetic properties far below theoretical values (see, for example, reference ：D.T.Zhang,M.Yue&J.X.Zhang,Study on bulk Sm₂ Fe₁₇ N_xsintered magnets prepared by spark plasma sintering,Powder Metallurgy,2007,50(3):215-218, and referenceM.,Fim R.G.T,Quispe L.T.et al.,On the feasibility of using Sm₂Fe₁₇N_x powders 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 the samarium iron nitrogen blocks on the market are often lower than those of neodymium iron boron blocks. The research on the additive manufacturing method of the samarium iron nitrogen block material is relatively less.

The high xylon et al prepared samarium iron nitrogen magnets by an explosion method. The main idea of the technology is as follows: disposing a cylindrical inner container inside a larger cylindrical outer container, the inner container having a removable cover on top thereof, the compact of samarium iron nitrogen powder being disposed in the inner container; the high pressure of tens GPa is formed in the outer container by detonating the explosive, and the cover plate is driven to perform high-strength impact on the samarium-iron-nitrogen powder blank in the inner container. When the impact pressure reaches more than tens GPa, the magnet density reaches 7.65g/cm ³, and the magnetic energy product (BH) _max reaches 116-144kJ/m ³ (namely 14.5-18.0 MGOe). Reference is made to: shinobu Takag1 (Gaohan), koichi Morii (Senwell Hao), takahiko Iriyama (Shangshan Gongyan), etc. ,Evaluation ofPracticality for Fully Dense Isotropic Sm-Fe-N Magnets Made by Shock-Wave Consolidation Method,IEEE Transactions on Magnetics,2023,59(11):2101205. are the maximum bulk density and magnetic energy product values achieved by the samarium iron nitrogen block reported so far. However, it is difficult to manufacture permanent magnets having complicated shapes by explosion. Since the shock wave pressure generated by the explosion method is not uniform and decays with the increase of the volume of the bulk material, the above-mentioned adverse factors will cause more serious adverse effects when the permanent magnet has a complex shape. In addition, in the above-mentioned technology based on the explosion method, it is required to detonate the explosive, the container is required to have a high pressure resistant housing, and in order to make the explosion energy more efficiently transferred to the samarium-iron-nitrogen powder compact to obtain a higher magnet density, it is also required to design a relatively complex moving structure (for example, a piston type movable cover plate on the top of the inner container) and a multi-layered container structure capable of operating in a high pressure environment. Therefore, the explosion method is difficult to be combined with the existing samarium iron nitrogen additive manufacturing method to obtain compact permanent magnet blocks with complex shapes.

Unlike additive manufacturing of general metals or alloys, additive manufacturing of permanent magnets needs to consider not only mechanical properties such as compactness but also magnetic properties. The existing additive manufacturing schemes of the compact permanent magnet material all need to carry out high-temperature treatment on the magnetic powder of the permanent magnet material to promote the magnetic powder to be converted into a compact consolidation state from a powder state, and the process is easy to cause the grain decomposition of the magnetic powder of the permanent magnet material, so that the magnetic property of the magnetic powder is reduced. On the other hand, in the latest research results, the samarium iron nitrogen block manufactured by the explosion method can reach a larger bulk density and a higher magnetic energy product value, but the compact permanent magnet block with a more complex shape is difficult to manufacture by the explosion method.

Therefore, in view of the above, in the technical direction of additive manufacturing of permanent magnets, there is an urgent need to solve the technical problem of the magnetic performance degradation caused by the thermal process.

Further, there are some temperature sensitive materials in other functional materials besides the permanent magnet, and the corresponding function is lost or weakened due to the thermal process in the molding process, so that it is expected to solve the technical problem that the performance of the temperature sensitive materials is reduced due to the thermal process in the molding process of the temperature sensitive materials.

On the other hand, the solution proposed by the present application lends itself to the principle of laser peening (laser shockpeening, abbreviated as LSP). Laser peening, also known as laser shock peening, is a widely used laser surface treatment technique in industry. The method generally utilizes nanosecond short pulse laser to act on substances to form explosion shock waves generated by plasmas, changes the microstructure of the surface layers of the substances and generates residual compressive stress, thereby improving the performances of the substances, such as: the fatigue strength of the material is improved. However, laser shock peening generally requires a film to be coated on the surface of the material to be treated, explosion plasma generated by laser acting on the bulk material is suppressed by the film, reverse shock wave of the plasma can be applied to the bulk material, and laser shock peening needs to be performed in water in order to further press the film, and it is almost unacceptable to impact the powder material by this method. If ultra-short pulse laser, especially femtosecond pulse laser, is used, the laser shock strengthening can be directly carried out on the metal material in the atmosphere due to narrow pulse width and high peak power, and the shock wave pressure can reach more than 100GPa without mask and water medium. Reference is made in particular to ：T.Kawashima,T.Sano,A.Hirose,et al.,Femtosecond laser peening offriction stir welded 7075-T73 aluminum alloys,Journal of Materials Processing Technology,2018,262:111-122. but it should be noted that existing laser peening techniques are used primarily for laser surface treatment of shaped blocks.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a layer-by-layer manufacturing method of a permanent magnet, which can avoid the magnetic property degradation caused by a thermal process.

In order to solve the technical problems, the invention provides a layer-by-layer manufacturing method of a compact permanent magnet, which comprises the following steps: step 1) preparing a die, wherein the die comprises a base, a side frame, a pressing block and an upper cover, the base and the side frame are combined into an open lower die with a containing cavity, and a layer of samarium iron nitrogen powder is paved at the bottom of the lower die; step 2) vibrating the lower die to enable the samarium iron nitrogen powder layer to reach preset tap density; step 3) the pressing block stretches into the lower die, then an upper cover is used for sealing an opening of the lower die, the pressing block is driven to move downwards, and downward mechanical pressure is applied to the samarium-iron-nitrogen powder, so that the samarium-iron-nitrogen powder is compacted; step 4) opening an upper cover, taking out the pressing block, and applying ultrashort pulse laser impact to the compacted samarium-iron-nitrogen powder with a preset coverage rate by utilizing ultrashort laser pulse to further improve the density of the samarium-iron-nitrogen powder and further solidify a samarium-iron-nitrogen powder layer; wherein, the implementation ultrashort pulse laser impact is as follows: irradiating the surface of the compacted samarium-iron-nitrogen powder with ultra-short pulse laser with single pulse energy of at least 20 muJ, pulse width of more than 200fs and not more than 800fs and spot diameter of 40-120 mu m, and inducing plasma shock waves to impact the compacted samarium-iron-nitrogen powder layer; 5) The surface of the impacted samarium-iron-nitrogen material is provided with a next layer of samarium-iron-nitrogen powder; re-executing the steps 2) to 4), so that the samarium-iron-nitrogen powder of the current layer is solidified by utilizing ultra-short laser pulse impact; 6) And (5) repeatedly executing the steps 2) to 5) to obtain the compact samarium-iron-nitrogen block material.

Wherein the layer-by-layer manufacturing method further comprises a pretreatment step of: before the samarium-iron-nitrogen block is manufactured, layering slicing treatment is carried out on the three-dimensional graph of the samarium-iron-nitrogen block, and the layer thickness of each slice is delta h; then, measuring and calculating the specified weight of the samarium-iron-nitrogen powder of each slice according to the thickness h ₁ of the compacted samarium-iron-nitrogen powder, and further weighing one part of samarium-iron-nitrogen powder with the specified weight for each slice; wherein Δh is less than h ₁; in the step 1) and the step 5), the corresponding weighed samarium iron nitrogen with the specified weight is filled into the lower die, so that the laying of the samarium iron nitrogen powder of the current layer is completed; in the step 4), after the ultra-short laser pulse impact to the samarium iron nitrogen powder of the current layer is completed each time, the workbench carrying the die is lowered by delta h, and the position of the laser head is kept still; or the laser head for the ultra-short laser pulse impact is lifted by delta h, and the position of the workbench is kept still.

In the step 4), the coverage rate and the laser pulse energy are adjusted to enable the density of the impacted samarium-iron-nitrogen material to reach more than 98% of the theoretical density value.

In the step 2), the method of vibrating the die is knocking, rolling or the combination of the knocking and the rolling alternately, so that the samarium iron nitrogen powder layer reaches the preset tap density.

The side frame is sleeved on the base, a nonmagnetic metal substrate is placed on the base, a first layer of samarium-iron-nitrogen powder is paved and compacted on the substrate, and a subsequent layer of samarium-iron-nitrogen powder is paved and compacted on a previous layer impacted by the ultrashort pulse laser; the side frames are cylindrical, long square frames, square frames or frame shapes with outlines of other shapes, and the shapes of the base, the upper cover and the pressing block are matched with the shapes of the side frames; wherein, the upper cover and the pressing block are connected into a whole.

Wherein, the periphery of the die is provided with a coil or a coil which can extend into the lower die; in the step 3), pulse current with peak value exceeding 1kA is applied to the coil in the compaction process so as to generate a thin-layer magnetic field of more than 30kOe in the area of the samarium-iron-nitrogen powder of the current layer in the die, and the samarium-iron-nitrogen powder which is not impacted by laser and is being compacted realizes magnetic orientation under the action of the thin-layer magnetic field.

In the step 3), the coil generates a horizontal pulse magnetic field or a vertical pulse magnetic field in the area where the samarium-iron-nitrogen powder layer is located; the compact hammers the samarium-iron-nitrogen powder layer to compact it while the pulsed magnetic field is applied, wherein a time difference between a duration of the pulsed magnetic field and a period in which the compact contacts the samarium-iron-nitrogen powder is not more than 1ms by controlling a timing of applying a pulsed current to the coil.

The side frame is sleeved on the base, a non-magnetic insulating substrate is placed on the base, a first layer of samarium-iron-nitrogen powder is paved and compacted on the substrate, and a subsequent layer of samarium-iron-nitrogen powder is paved and compacted on a previous layer impacted by the ultrashort pulse laser; the base plate, the base, the side frames and the pressing blocks are all made of corundum.

Wherein the samarium iron nitrogen powder is polygonal powder or spherical powder with the particle size distribution D ₅₀ of 3-50 mu m.

Wherein, the steps 1) to 6) are carried out under a gas protection environment, and the protection gas in the gas protection environment is inert gas or nitrogen; the pressure of the gas protection environment is equal to the atmospheric pressure, the humidity is less than or equal to 30%, and the temperature is room temperature; the protection environment is obtained by directly filling the protection gas to replace air, or by vacuumizing and then filling the protection gas.

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

1. The application uses the principle of laser shot blasting to impact the compacted samarium-iron-nitrogen powder by using ultrashort laser pulse, so that the compact samarium-iron-nitrogen powder is solidified under the action of shock waves. One of the key points of the application is that: compared with the common technology for permanent magnet additive manufacturing, such as SLS, LDED, LPBF, FDM, the ultra-short laser pulse impact is used for replacing the processes of laser sintering, laser directional energy deposition, laser powder bed fusion and the like. To solve the problem of the decrease of magnetic properties caused by thermal processes in additive manufacturing, the inventors of the present application have tried several solutions successively, such as laser sintering at a lower temperature in a high pressure environment; and for example, a two-step molding scheme in which the pre-sintered body is pre-sintered (i.e., primary sintered) and then the density of the pre-sintered body is enhanced. After multiple attempts and continuous evolution, the inventor finally proposes a one-step forming scheme for thoroughly replacing laser sintering by using ultra-short laser pulse impact. In the scheme, samarium iron nitrogen powder layers are laid layer by layer in a die provided with a containing cavity and are solidified under the action of normal temperature and high pressure, so that samarium iron nitrogen blocks with extremely high density manufactured layer by layer are obtained. The application can avoid the problem that samarium iron nitrogen powder is easy to be decomposed by heating while realizing additive manufacturing (compared with an explosion method, the method is more beneficial to manufacturing permanent magnets with complex shapes), thereby helping to improve the magnetic performance of the samarium iron nitrogen powder.

2. In some embodiments of the present application, the thickness h1 and slice thickness Δh (which are consistent with the elevation of the laser head or the lowering of the table, and further described in detail below) used for weighing samarium-iron-nitrogen powder are differentiated and processed correspondingly, so that the surface of the compacted powder layer can be more precisely subjected to ultra-short pulse laser impact, and the reduction of yield due to errors between the focus point of the laser and the position to be irradiated is prevented. On the other hand, the precise distinction also helps to make the size and shape of the permanent magnet manufactured by the scheme of the application more consistent with the design size and shape.

3. In some embodiments of the present application, the anisotropic permanent magnet may be fabricated by magnetically orienting the powder layer during compaction, thereby further increasing the magnetic properties of the samarium-iron-nitrogen permanent magnet, such as its magnetic energy product. Further details are described below.

4. In addition to samarium iron nitrogen permanent magnets, there are other temperature sensitive functional materials, and the corresponding function may be lost or weakened due to the thermal process during the forming process. Therefore, the concept of the application can be expanded into the molding technology of the temperature-sensitive functional material so as to solve the problem of performance degradation caused by the thermal process in the molding process.

Drawings

FIG. 1 shows a schematic flow chart of a layer-by-layer manufacturing method of a dense permanent magnet according to one embodiment of the application;

FIG. 2 shows a schematic structural view of a mold in one embodiment of the application;

FIG. 3 shows a schematic representation of a compaction step in one embodiment of the application;

FIG. 4 shows a schematic diagram of an ultrashort pulse laser shock step in one embodiment of the present application;

FIG. 5 shows a schematic diagram of a method of overlap between laser irradiation points in an ultrashort pulse laser impingement step in one embodiment of the present application;

FIG. 6 is a flow chart of a layer-by-layer manufacturing method of a samarium-iron-nitrogen permanent magnet with the addition of a magnetic orientation step in one embodiment of the application;

FIG. 7 shows a schematic view of an embodiment of the present application in which a horizontal magnetic field is arranged inside a mold;

FIG. 8 shows a schematic diagram of horizontal magnetic orientation and simultaneous compaction of a powder layer using the coil of FIG. 7;

FIG. 9 shows a schematic view of an embodiment of the present application in which a vertical magnetic field is arranged inside a mold;

FIG. 10 shows a schematic diagram of perpendicular magnetic orientation and simultaneous compaction of a powder layer using the coil of FIG. 9;

FIG. 11 shows a schematic view of an embodiment of the present application in which a horizontal magnetic field is arranged outside the mold;

FIG. 12 shows a schematic diagram of horizontal magnetic orientation and simultaneous compaction of a powder layer using the coil of FIG. 11;

FIG. 13 shows a schematic view of an embodiment of the present application in which a vertical magnetic field is arranged outside the mold;

FIG. 14 shows a schematic diagram of perpendicular magnetic orientation and simultaneous compaction of a powder layer using the coil of FIG. 13;

FIG. 15 shows a schematic view of a small area square compact in one embodiment of the application;

fig. 16 shows a schematic perspective view of the simultaneous compaction of a powder layer with the small area square compacts of fig. 15 while the external coils are magnetically oriented.

Detailed Description

For a better understanding of the application, various aspects of the application will be described in more detail with reference to the accompanying drawings. It should be understood that the detailed description is merely illustrative of exemplary embodiments of the application and is not intended to limit the scope of the application in any way. Like reference numerals refer to like elements throughout the specification. The expression "and/or" includes any and all combinations of one or more of the associated listed items.

It should be noted that in this specification, the expressions first, second, etc. are only used to distinguish one feature from another feature, and do not represent any limitation of the feature. Accordingly, a first body discussed below may also be referred to as a second body without departing from the teachings of the present application.

In the drawings, the thickness, size and shape of the object have been slightly exaggerated for convenience of explanation. The figures are merely examples and are not drawn to scale.

It will be further understood that the terms "comprises," "comprising," "includes," "including," "having," "containing," and/or "including," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Furthermore, when a statement such as "at least one of the following" appears after a list of features that are listed, the entire listed feature is modified instead of modifying a separate element in the list. Furthermore, when describing embodiments of the present application, the use of "may" means "one or more embodiments of the present application. Also, the term "exemplary" is intended to refer to an example or illustration.

As used herein, the terms "substantially," "about," and the like are used as terms of a table approximation, not as terms of a table level, and are intended to illustrate inherent deviations in measured or calculated values that would be recognized by one of ordinary skill in the art.

Unless otherwise defined, all terms (including technical terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

It should be noted that, without conflict, the embodiments of the present application and features of the embodiments may be combined with each other.

The application provides a layer-by-layer manufacturing method of a compact permanent magnet, which is shown in fig. 1 and comprises the following steps: step 1) a mold is prepared, as shown in fig. 2, wherein the mold comprises an upper cover 11, a pressing block 12, a side frame 13 and a base 16, and the base 16 and the side frame 13 are combined into an open lower mold with a containing cavity. In this step, a layer of samarium iron nitrogen powder is laid on the bottom of the lower die to form a samarium iron nitrogen powder layer 14, wherein a substrate 15 can be arranged on the bottom of the lower die to facilitate separation of the formed samarium iron nitrogen block from the die. Step 2) vibrating the lower die to enable the samarium iron nitrogen powder layer 14 to reach a preset tap density. Step 3) the pressing block 12 is stretched into the lower die, then the upper cover 11 is used for sealing the opening of the lower die, the pressing block 12 is driven to move downwards, and downward mechanical pressure is applied to the samarium iron nitrogen powder, so that the samarium iron nitrogen powder is compacted, as shown in fig. 3. And 4) opening the upper cover 11, taking out the pressing block 12, and applying ultrashort pulse laser impact to the compacted samarium-iron-nitrogen powder with a certain coverage rate by utilizing ultrashort laser pulse to further improve the density of the samarium-iron-nitrogen powder and further solidify the samarium-iron-nitrogen powder layer. Referring to fig. 4, the implementation of ultrashort pulse laser shock is described as follows: the beam of light from the laser head 18 is focused onto the surface of the samarium iron nitrogen powder layer. The surface of the compacted samarium-iron-nitrogen powder (i.e., the surface of the samarium-iron-nitrogen powder layer) is irradiated with an ultra-short pulse laser having a pulse width of 200fs or more and not more than 800fs and a spot diameter of 40-120 μm (i.e., the laser beam 19 shown in fig. 4) with a single pulse energy of at least 20 muj, and a plasma shock wave is induced to impact the compacted samarium-iron-nitrogen powder layer. After impact, the samarium iron nitrogen powder layer is solidified into a samarium iron nitrogen block 20. 5) And (3) arranging a next layer of samarium-iron-nitrogen powder on the surface of the impacted samarium-iron-nitrogen material, and re-executing the steps 2) to 4) for the currently paved samarium-iron-nitrogen powder layer (also called the current samarium-iron-nitrogen powder layer), so that the samarium-iron-nitrogen powder of the current layer is solidified by utilizing ultrashort laser pulse impact. 6) Continuously repeating the steps 2) to 5) until a compact samarium-iron-nitrogen block with a designed three-dimensional shape is obtained; that is, new samarium iron nitrogen layers are continuously paved and consolidated on the current consolidated samarium iron nitrogen material, and finally the compact samarium iron nitrogen block with the designed three-dimensional shape is obtained.

One of the keys of the application is to use the principle of laser shot blasting (laser shockpeening, abbreviated as LSP) to apply ultrashort pulse laser impact to compacted samarium-iron-nitrogen powder with a certain coverage rate by utilizing ultrashort laser pulses. Laser peening, also known as laser shock peening, is a laser surface treatment technique commonly used in the industry. The method generally utilizes nanosecond short pulse laser to act on substances to form explosion shock waves generated by plasmas, changes the microstructure of the surface layers of the substances and generates residual compressive stress, thereby improving the performances of the substances, such as: the fatigue strength of the material is improved. However, laser shock peening generally requires a film to be coated on the surface of the material to be treated, explosion plasma generated by laser acting on the bulk material is suppressed by the film, reverse shock wave of the plasma can be applied to the bulk material, and laser shock peening needs to be performed in water in order to further press the film, and it is almost unacceptable to impact the powder material by this method.

The application uses ultrashort pulse laser. The ultra-short pulse laser, especially the femtosecond pulse laser, can directly perform laser shock reinforcement on the metal material in the atmosphere due to narrow pulse width and high peak power, and does not need mask and aqueous medium. Specifically, reference ：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. discloses that by irradiating the surface of the compacted samarium-iron-nitrogen powder with ultra-short pulse laser having a pulse width of 200fs or more and not more than 800fs and a spot diameter of 40-120 μm with a single pulse energy of at least 20 muj, the surface samarium-iron-nitrogen powder can be induced to be ionized into plasma, and a plasma shock wave can be formed to reversely impact the underlying samarium-iron-nitrogen powder. The pressure of the plasma shock wave can reach tens to hundreds GPa. Experiments prove that under the high-pressure impact of tens of GPa, the samarium iron nitrogen powder can be solidified at normal temperature without high-temperature heat treatment. And the samarium-iron-nitrogen magnet obtained under high-pressure impact of tens GPa reaches 116-144kJ/m ³ (namely 14.5-18.0 MGOe). Specific reference may be made to: reference is made to: shinobu Takag1 (Gaohan), koichi Morii (Senwell Hao), takahiko Iriyama (Shangshan Gong yan) and the like ,Evaluation ofPracticality for Fully Dense Isotropic Sm-Fe-N Magnets Made by Shock-Wave Consolidation Method,IEEE Transactions on Magnetics,2023,59(11):2101205., the compacted samarium-iron-nitrogen powder can be consolidated under high-pressure impact of tens of GPa levels under the laser impact strengthening treatment performed by the ultrashort pulse laser. In addition, under the laser shock peening performed by the ultrashort pulse laser, only a small amount of powder on the surface is heated and ionized into plasma. The heat is not largely transmitted to most of the powders located in the lower layers, so that the powders in the lower layers can be maintained in a normal temperature state during the laser shock peening process. Therefore, the problem that samarium iron nitrogen powder is easy to be decomposed by heating is avoided. Meanwhile, in the application, the ultra-short pulse laser performs point-by-point laser impact on the powder compacted by the mechanical method, and scans the impact with a certain coverage rate, so that the required shape can be conveniently depicted, and the required three-dimensional graph shape can be obtained by stacking the powder layer by layer, therefore, compared with the samarium iron nitrogen magnet manufactured by the explosion method, the samarium iron nitrogen permanent magnet manufactured by the method can have a more complex shape. In addition, the layer-by-layer manufacturing scheme based on the ultra-short pulse laser can enable the impact force born by the powder in different areas to be more consistent and uniform, so that the magnetic performance of the samarium-iron-nitrogen powder is further improved.

Further, in one embodiment of the present application, the layer-by-layer manufacturing method of the compact permanent magnet further comprises a pretreatment step. This preprocessing step is performed before said step 1). The pretreatment steps are as follows: before samarium iron nitrogen blocks are manufactured, layering slicing treatment is carried out on three-dimensional graphs in software, and the layer thickness of each slice is delta h; and then measuring and calculating the regulated weight of the samarium-iron-nitrogen powder of each slice according to the thickness h ₁ of the compacted samarium-iron-nitrogen powder, and further weighing one part of samarium-iron-nitrogen powder with the regulated weight for each slice. In this embodiment, in the step 1) and the step 5), the corresponding weighed samarium iron nitrogen having the predetermined weight is charged into the lower mold, thereby completing the laying of the samarium iron nitrogen powder of the current layer. In the step 4), after completing the ultra-short laser pulse impact to the samarium iron nitrogen powder of the current layer, the workbench carrying the die is lowered by delta h or the laser head for the ultra-short laser pulse impact is raised by delta h. It is noted that it has been found that during the impact of the compacted powder layer with the ultra-short pulse laser, the powder layer undergoes a thickness reduction under the influence of a large impact force. That is, if the thickness of the compacted samarium iron nitrogen powder layer is h ₁ a and the thickness of the consolidated samarium iron nitrogen layer after the final ultrashort pulse laser shock treatment is Δh, Δh will be actually less than h ₁. In this embodiment, when the samarium iron nitrogen corresponding to each slice is weighed, the thickness h ₁ of the compacted samarium iron nitrogen powder is used, and the moving amount of the compacted samarium iron nitrogen powder is Δh when the table or the laser head is moved to perform the ultrashort pulse laser impact treatment on the samarium iron nitrogen powder on the next layer. Δh is the amount of movement in the height direction of a stage (e.g., stage 21 in fig. 4) or a laser head (e.g., laser head 18 in fig. 4) after printing one layer, and is the amount of elevation of the powder from the previous layer after being impacted by the femtosecond pulsed laser. In this embodiment, the thicknesses h ₁ and Δh are distinguished and processed correspondingly, so that the surface of the compacted powder layer can be more accurately subjected to ultrashort pulse laser shock, and the yield is prevented from being reduced due to errors between the laser focusing point and the position to be irradiated. On the other hand, the precise distinction also helps to make the size and shape of the permanent magnet manufactured by the scheme of the application more consistent with the design size and shape.

Further, in one embodiment of the present application, in the step 4), the coverage rate and the pulse energy are adjusted so that the samarium-iron-nitrogen material after the impact reaches more than 98% of the theoretical density value. As shown in fig. 5, in the ultra-short pulse laser impact step, overlapping is performed between laser irradiation points to continuously and uniformly cover the area to be solidified of the samarium-iron-nitrogen powder layer to be compacted. In fig. 5, the overlapping width of the light spots, i.e., the overlapping distance D2, and the coverage of the laser shock can be adjusted by adjusting the ratio of the overlapping distance D2 to the diameter D1 of the light spots. The beam of the ultra-short pulse laser is usually a Gaussian beam, and the proper coverage rate is selected, so that the powder layer can be subjected to impact force more uniformly and consistently. Further, as described above, irradiation of the surface of the compacted samarium-iron-nitrogen powder with ultra-short pulse laser having a pulse width of 200fs or more and not more than 800fs and a spot diameter of 40-120 μm with single pulse energy of at least 20 μj can induce the surface samarium-iron-nitrogen powder to be ionized into plasma and form a plasma shock wave to reversely impact the samarium-iron-nitrogen powder on the lower layer thereof. The plasma shock wave applies pressure of the order of GPa or even higher to the compacted powder layer. However, it is difficult to make a direct accurate measurement of the plasma shockwave, so in this embodiment, the coverage and pulse energy (the laser pulse energy depends on the pulse width, duty cycle, frequency, and even also on its waveform, in particular its rising edge) are adjusted by measuring the density of the shocked samarium-iron-nitrogen material, so that these parameters can be optimized. Research shows that when the density of the impacted samarium iron nitrogen material reaches more than 98% of the theoretical density value, the obtained permanent magnet (or permanent magnet blocks) can have excellent mechanical properties and magnetic properties.

Further, in some embodiments of the present application, in the step 2), the method of vibrating the mold is beating, rolling, or a combination of both. Specifically, the powder may be poured into a mold and laid flat with a doctor blade (or other means) where the powder density is bulk. The powder will be further densified by vibrating the die, where the powder density will increase, known as tap density. The powder is further densified (actually approaching the theoretical density) by the impact of ultra-short pulse laser, and the bulk density is obtained. In said step 2), it is also possible to use a non-contact means to bring the powder to tap density. For example, in other embodiments, ultrasonic waves or microwaves may be applied to the samarium iron nitrogen powder layer to achieve a predetermined tap density.

Further, in one embodiment of the present application, the side frame is sleeved on the base, a non-magnetic metal substrate is placed on the base, a first layer of samarium-iron-nitrogen powder is paved and compacted on the substrate, and a subsequent layer of samarium-iron-nitrogen powder is paved and compacted on a previous layer impacted by the ultrashort pulse laser; the side frame can be cylindrical, rectangular, square or frame with outline of other shapes, and the shapes of the base, the upper cover and the pressing block are matched with those of the side frame. A non-magnetic metal substrate is placed on the base, so that the magnet after impact can be prevented from being adhered to the die base. In this embodiment, the upper cover and the pressing block may be integrally connected. They may be movably connected by threads or screws so that rotating the upper cover drives the compacts down, thereby applying the required mechanical pressure to the powder layer under the compacts. In another embodiment, the upper cover and the compacts may be fixedly connected, in which case hydraulic means may be used to drive the upper cover and compacts downwardly so as to apply the required mechanical pressure to the powder layer under the compacts.

Further, in one embodiment of the application, when the three-dimensional graph of the samarium-iron-nitrogen block to be manufactured has a hollowed-out structure, for the situation that the physical area of the later layer exceeds the former layer, the hollowed-out area can be filled by adopting an auxiliary support column method so as to lay a new samarium-iron-nitrogen powder layer above and solidify the same.

Further, in one embodiment of the present application, a pulse coil is disposed around the mold; in the step 3), pulse current with peak value exceeding 1kA is applied to the pulse coil in the compacting process so as to generate a thin-layer magnetic field with the thickness of more than 30kOe in the area of the samarium-iron-nitrogen powder of the current layer in the die, and the samarium-iron-nitrogen powder which is not impacted by laser and is being compacted realizes magnetic orientation under the action of the thin-layer magnetic field.

Further, in some embodiments of the present application, the samarium iron nitrogen powder may be polygonal powder or spherical powder having a particle size distribution D ₅₀ of 3 to 50 μm.

Further, in some embodiments of the present application, the steps 1) to 7) are performed in a gas-shielded environment, wherein the shielding gas in the gas-shielded environment is inert gas or nitrogen gas; the pressure of the gas protection environment is equal to the atmospheric pressure, the humidity is less than or equal to 30%, and the temperature is room temperature; the protection environment is obtained by directly filling the protection gas to replace air, or by vacuumizing and then filling the protection gas. The manufacturing process of the samarium iron nitrogen block material is completed in a gas protection environment. Placing a substrate at the bottom of a mould with a simple shape, adding a part of samarium iron nitrogen powder with a specified weight, covering the upper cover of the mould, compacting the samarium iron nitrogen powder by a mechanical method, opening the upper cover of the mould, moving according to a set path by using ultra-short pulse laser, scanning the layer of samarium iron nitrogen with a certain coverage rate, and compacting the samarium iron nitrogen layer further by using plasma shock waves induced by the ultra-short pulse laser. Adding a part of samarium iron nitrogen powder with a specified weight on the layer, covering the upper cover of the die, mechanically compacting, opening the upper cover, repeating the path by laser, and compacting the layer of powder by impact again; …, and finally obtaining the isotropic samarium-iron-nitrogen permanent magnet with the density reaching more than 98% of the theoretical value by stacking layer by layer in the circulating way.

In the above embodiment, the mold may be composed of a base, a side frame, an upper cover, and a pressing block, wherein the side frame is sleeved on the base, and a substrate is placed on the base, and is taken out together with the forming piece as a basis for powder and future forming pieces. The pressing block is put in, the upper cover is pressed, the pressing block transmits the pressure to the powder, and the powder arranged between the pressing block and the upper cover is compacted. The compacted thickness h ₁ is used as a measuring and calculating basis for weighing each part of the specified samarium iron nitrogen. The first layer of samarium-iron-nitrogen powder is laid and compacted on a non-magnetic high-strength metal substrate, and the subsequent samarium-iron-nitrogen powder is laid and compacted on the previous layer impacted by the ultrashort pulse laser. The vibration method is usually repeated by knocking, rolling or a combination of the two. The side frames of the die can be cylindrical, rectangular frames, square frames and the like, and the shapes of the base, the upper cover and the pressing block are matched with the shapes of the side frames, so that the powder is compacted in the die. The amount of powder added to the mold at a time varies with the thickness of the compacted layer. The mold material is a high-strength nonmagnetic material, such as: metal, engineering plastic, ceramic, carbon fiber, etc. The substrate is made of nonmagnetic high-strength metal materials, such as: 316 stainless steel.

Further, considering that some temperature sensitive materials exist in other functional materials besides the samarium-iron-nitrogen permanent magnet, the corresponding function may be lost or weakened due to the thermal process during the forming process. Therefore, the concept of the application can be expanded into the molding technology of the temperature-sensitive functional material so as to solve the problem of performance degradation caused by the thermal process in the molding process. Based on this, in one embodiment of the present application, there is provided a molding method of a temperature-sensitive functional material, including the steps of: step 1) preparing a die, wherein the die comprises an upper cover, a pressing block, a side frame and a base, and the base and the side frame are combined into an open lower die with a containing cavity. In the step, a layer of functional material powder is paved at the bottom of the lower die to form a powder layer, wherein a substrate can be arranged at the bottom of the lower die, so that the formed functional material blocks can be conveniently separated from the die. And 2) vibrating the lower die to enable the powder layer to reach a preset tap density. And 3) stretching the pressing block into the lower die, and then sealing the opening of the lower die by using an upper cover, driving the pressing block to move downwards and applying downward mechanical pressure to the powder layer so as to compact the functional material powder. And 4) opening the upper cover, taking out the pressing block, and applying ultrashort pulse laser impact to the compacted functional material powder with a certain coverage rate by utilizing ultrashort laser pulse to further improve the density of the functional material powder and further solidify the functional material powder layer. The implementation of the ultrashort pulse laser impact is as follows: the laser head is aligned to the surface of the functional material powder layer. Irradiating the surface of the compacted functional material powder (i.e., the surface of the functional material powder layer) with an ultrashort pulse laser having a pulse width of 200fs or more and not more than 800fs and a spot diameter of 40-120 μm with a single pulse energy of at least 20 μj, and inducing a plasma shock wave to impact the compacted functional material powder layer. After impact, the functional material powder layer is consolidated into a functional material block. 5) And (3) arranging a next layer of functional material powder on the surface of the functional material after impact, and re-executing the steps 2) to 4) for the currently laid functional material powder layer (also called the current functional material powder layer), so that the functional material powder of the current layer is solidified by utilizing ultra-short laser pulse impact. 6) Continuously repeating the steps 2) to 5) until a compact functional material block with a designed three-dimensional shape is obtained; that is, new functional material layers are continuously laid and consolidated on the current consolidated functional material, and a compact functional material block having a designed three-dimensional shape is finally obtained. The functional material refers to a material which is subjected to crystal grain decomposition or other forms of damage caused by overhigh temperature in the process of forming the material into a block material from a powder form, so that the corresponding function is lost or weakened. For example, samarium iron nitrogen materials have magnetism, which is the function of the magnetism, and powder-state samarium iron nitrogen materials can be decomposed to cause the loss or obvious weakening of magnetism if the temperature is too high (for example, the temperature is too high during sintering) during the process of forming the powder-state samarium iron nitrogen materials into blocks.

The various details of the application are further described below in connection with a more specific embodiment.

Referring to fig. 6, in the present embodiment, there is provided a permanent magnet layer-by-layer manufacturing method capable of avoiding degradation of magnetic properties due to a thermal process, comprising the steps of: (1) In a gas protection environment, weighing the fine samarium iron nitrogen powder according to a specified weight, dividing the powder into a plurality of parts, and subpackaging the parts in various vessels. (2) And designing a three-dimensional model of the permanent magnet to be manufactured in software, carrying out layered slicing and path planning on the model, and decomposing the three-dimensional model into a two-dimensional graph and a path capable of carrying out laser impact. (3) A mold of a simple shape is placed in a gas-shielded environment, and a nonmagnetic high-strength substrate is placed at the bottom of the mold. Pouring a part of samarium iron nitrogen powder, and vibrating the die to improve the tap density of the powder, so as to reduce the gap of the powder before laser impact as much as possible. (4) And (5) covering the upper cover of the die, spinning, and compacting the samarium-iron-nitrogen powder by using mechanical pressure. (5) During compaction of the powder, it is magnetically oriented with the coil, wherein the thickness of the orientation is guaranteed to be substantially the same as the thickness of the compacted powder. (6) Opening the upper cover of the die, aiming at a starting point needing impact by using the indicating light of the laser, opening the femtosecond laser, enabling the workbench or the laser head to move according to a path appointed by software, and implementing ultrashort pulse laser impact on samarium iron nitrogen powder with a certain coverage rate, so that the density of the samarium iron nitrogen powder is further improved, and the density reaches more than 98% of a theoretical value. (7) And opening the upper cover of the die, pouring one part of samarium iron nitrogen powder, vibrating the die to improve the tap density of the powder, and reducing the gap of the powder before laser impact as much as possible. (8) And (5) judging whether the complete three-dimensional shape is obtained, if not, repeating the steps (4) - (7) to realize the manufacture of the designed anisotropic samarium-iron-nitrogen permanent magnet, and if yes, ending. When the isotropic samarium-iron-nitrogen permanent magnet is manufactured, the step (5) is not executed, and in the step (8), whether the complete three-dimensional shape is obtained is judged, if not, the steps (4), (6) and (7) are repeated, and if yes, the process is finished.

In this embodiment, the gas in the gas-protecting environment may be an inert gas, such as: argon, helium, or nitrogen. The pressure of the environment is equal to the atmospheric pressure, the humidity is less than or equal to 30 percent, and the temperature is room temperature, and is usually 15 to 30 ℃. The environment protection can be achieved by directly filling argon to replace air, or by vacuumizing and then filling nitrogen, helium or argon. The stated weight depends on the volume determined by the cross-sectional area of the die and the thickness of each layer and the density of samarium iron nitrogen, i.e. how much powder is added to each layer, which is the thickness of the powder after spinning and not after laser shock. The fine samarium-iron-nitrogen powder is generally micron-sized powder, namely polygonal powder or spherical powder with the particle size distribution D ₅₀ of 3-50 mu m. In the step (1), the vessel can be made of materials which are non-magnetic and do not react with samarium iron nitrogen in a protective environment, such as glass, metal, plastic, ceramic and the like.

In this embodiment, the software includes two parts, i.e. design and manufacture, and the design part may be general mechanical graphic design software, such as: autoCAD, tianhe (CAXA). The manufacturing section is 3D printing (additive manufacturing) dedicated software such as: MATERIALIS, CATIYA, or self-developed 3D printing (additive manufacturing) specific software. The motion of the workbench or the laser head according to the path designated by software refers to a working path during femtosecond laser impact, and the motion is three-dimensional, including two-dimensional plane motion and vertical lifting motion, and the lifting or lifting height is equal to the increased height delta h of the samarium-iron-nitrogen magnet after laser impact. When the laser head is motionless, the workbench is lowered by delta h; if the table is stationary, the laser head is raised by Δh.

Further, in some embodiments, multiple ultrashort pulse lasers may be used to simultaneously impact compact the workpiece, with each laser scanning area overlapping only the process requirements at the interface instead of overlapping (or overlapping each other).

In step (5) of the previous embodiment, the powder is magnetically oriented with the coil during compaction. The coil is a pulse coil. The preferred shape of the magnetic field generated by the pulse coil is a lamellar two-dimensional magnetic field. However, the manufacturing difficulty of the two-dimensional magnetic field is high, and in the actual magnetic powder compacting process, an approximate magnetic field shape (which can be called an approximate magnetic field) can be adopted to replace a lamellar two-dimensional magnetic field. When using an approximate magnetic field, the position of the pulse coil can be spatially adjusted, and a region of relatively large magnetic field strength and uniform distribution can be selected to couple the region with the layer of magnetic powder currently being compacted (i.e., the samarium-iron-nitrogen powder layer). On the time scale, the acting time of the approximate magnetic field is shortened as much as possible on the premise of fully improving the orientation degree of the currently compacted magnetic powder layer. Thus, the approximate magnetic field acts on the current magnetic powder layer in a concentrated way in time and space, and has less interference on other solidified samarium-iron-nitrogen blocks.

The magnetic orientation is to turn the easy magnetization axis of the magnetic powder particles in a designed direction, so that the easy magnetization direction of the magnetic powder particles is aligned so as to be substantially identical or nearly identical to the final magnetization direction in the design direction of the permanent magnet (i.e., to promote the degree of orientation thereof). After the step (6) is completed, the magnetic powder particles are solidified together and exist in the samarium iron nitrogen block in the form of crystal grains. The direction of the easy axis of magnetization after the magnetic powder particles in step (5) are rearranged by magnetic orientation is also fixed. After the magnetic orientation step is added, the layer-by-layer manufacturing method of the permanent magnet can manufacture the samarium-iron-nitrogen block with magnetic anisotropy, so that the magnetic properties such as a magnetic energy product (BH) _max and the like are further enhanced. Referring to fig. 7 and 8, during compaction, a horizontally oriented coil 17 may be placed in the lower mold with magnetic orientation synchronized with the compaction operation to maximize the degree of orientation while ensuring compaction. Specifically, the coil 17 may be placed inside the lower mold (i.e., inside the mold side frame 13), the outer diameter of the coil 17 being matched to the inner diameter of the mold, and the compact 12 being inside the coil 17, the outer diameter thereof being matched to the inner diameter of the coil 17. The coil 17 is supplied with a pulsed current to generate a pulsed magnetic field in a horizontal direction, and the compact 12 moves downward and hammers the underlying samarium-iron-nitrogen powder layer 14. The time of the pulse current is controlled in the coil 17, so that the time difference between the duration of the pulse magnetic field and the time period of the pressing block contacting the samarium iron nitrogen powder is not more than 1ms, thereby ensuring the synchronism of magnetic orientation and compaction operation. For example, the duration of the pulsed magnetic field may be 0-10 ms, and then the period of time for the compact to hammer against the samarium iron nitrogen powder layer may be 1-9 ms. The process of hammering the samarium iron nitrogen powder layer by the pressing block can be single hammering or multiple hammering with a certain frequency. When hammering is performed several times at a certain frequency, it is necessary to ensure that all hammering occurs within a period of 1 to 9ms. For example, the briquette is hammered 8 times at a frequency of 1kHz for a period of 1 to 9ms. In this embodiment, the pulsed magnetic field may generate a thin magnetic field of 30kOe or more in the region where the samarium-iron-nitrogen powder is located, so that the easy axis of magnetization of the powder particles is turned to the horizontal direction, and the degree of orientation of the powder layer is improved.

Referring to fig. 9 and 10, in another embodiment, a vertically oriented solution with a built-in coil is also provided. In this vertically oriented version, the coil 17 is placed in the lower die with its pulsed magnetic field oriented perpendicular to the surface of the powder layer, and thus may be referred to as a vertical magnetic field. In this embodiment, the magnetic orientation is performed in synchronization with the compaction operation to maximize the degree of orientation while ensuring compaction. The specific method may be the same as the coil-in-coil horizontal orientation scheme (i.e., the embodiment corresponding to fig. 7 and 8), except that the present embodiment employs a vertical magnetic field.

In other embodiments of the present application, the orientation coil may be externally positioned, i.e., disposed outside of the lower mold. Under such a scheme, the pressure head 12 does not need to avoid the coil 17, and the phenomenon that samarium iron nitrogen powder at the edge is difficult to compact can be avoided. In fig. 11 and 12, in one embodiment, the coil 17 for orientation is located outside the mold side frame with an inner diameter matching the outer diameter of the mold and the compact is inside the side frame with an outer diameter matching the inner diameter of the mold side frame. In this embodiment, the magnetic orientation is performed in synchronization with the compaction operation to maximize the degree of orientation while ensuring compaction. Specifically, the coil 17 is supplied with a pulse current to generate a pulse magnetic field in a horizontal direction, and the compact 12 moves downward to hammer the samarium-iron-nitrogen powder layer 14 therebelow. The time of the pulse current is controlled in the coil 17, so that the time difference between the duration of the pulse magnetic field and the time period of the pressing block contacting the samarium iron nitrogen powder is not more than 1ms, thereby ensuring the synchronism of magnetic orientation and compaction operation. For example, the duration of the pulsed magnetic field may be 0-20 ms, and then the period of time for the compact to hammer against the samarium iron nitrogen powder layer may be 1-19 ms. The process of hammering the samarium iron nitrogen powder layer by the pressing block can be single hammering or multiple hammering with a certain frequency. When hammering is performed several times at a certain frequency, it is necessary to ensure that all hammering occurs within a period of 1 to 19ms. For example, the briquette is hammered 18 times at a frequency of 1kHz for a period of 1 to 19ms. For another example, when the duration of the pulsed magnetic field is 0 to 10ms, then the period in which the compact hammers the samarium iron nitrogen powder layer may be 1 to 9ms, and the compact may be hammered 16 times at a frequency of 2kHz for the period of 1 to 9ms. In this embodiment, the pulsed magnetic field may generate a thin magnetic field of 30kOe or more in the region where the samarium-iron-nitrogen powder is located, so that the easy axis of magnetization of the powder particles is turned to the horizontal direction, and the degree of orientation of the powder layer is improved.

Referring to fig. 13 and 14, in another embodiment, a vertically oriented solution with an external coil is also provided. In this vertically oriented version, the coil 17 is placed outside the lower die with its pulsed magnetic field oriented perpendicular to the surface of the powder layer, and thus may be referred to as a vertical magnetic field. In this embodiment, the magnetic orientation is performed in synchronization with the compaction operation to maximize the degree of orientation while ensuring compaction. The specific method may be the same as the horizontal orientation scheme (i.e., the embodiment corresponding to fig. 11 and 12) with the coil being externally positioned, except that the present embodiment employs a vertical magnetic field.

The application also provides an embodiment for synchronous compaction based on the accompanying pulse magnetic field of the small-area square press block. Referring to fig. 15 and 16, the orientation coil is located outside the side frame of the die, the die and coil 17 are square, the outer dimension of the die matches the inner dimension of the coil, the cross section of the compact is also square, and the outer dimension of the compact is smaller than the inner dimension of the die. A pulse current is applied to the coil 17, and the coil 17 generates a pulse magnetic field 30kOe in the horizontal direction as shown, and the duration is 0 to 10ms. Within 1-9ms, the compact was hammered 16 times at a frequency of 2kHz while the compact 12 was moved at a horizontal velocity to hammer through the entire plane 22 of the powder layer with a degree of coverage.

In the embodiments corresponding to fig. 7 to 16, the pressing block, the substrate, the mold, etc. are made of non-magnetic insulating materials, and preferably, the pressing block, the substrate, the base, and the side frame are made of corundum. It should be noted that fig. 7 to 16 are only schematic views, wherein the dimensions of the respective components do not represent the actual dimensions. For example the actual dimensions of the coil in the thickness direction may be much smaller than those shown in the figures. In the actual magnetic orientation step, the coil arrangement is located as close as possible to the powder layer. When the coil is arranged on the inner side of the side frame, the arrangement position of the coil is slightly higher than the powder layer, so that the coil is prevented from being in direct contact with the powder. When the coil is arranged outside the side frame, the coil may be arranged flush with the powder layer so that the region of the coil where the magnetic field strength is large and evenly distributed is better coupled with the magnetic powder layer being compacted, i.e. the samarium iron nitrogen powder layer.

Note that the magnetic orientation is different from magnetization. From a more microscopic level, each magnetic particle or each grain in the resulting bulk material after laser shock has a large number of magnetic domains inside. Each magnetic domain is a tiny region containing a plurality of atoms or molecules, and the atomic magnetic moments within the tiny region are aligned in a specific direction, exhibiting uniform spontaneous magnetization. Before magnetization, the directions of magnetic moment of magnetic domains are different in each grain of each magnetic powder particle or block obtained after laser impact, and the magnetic moment of the whole object is zero. That is, the magnetic material does not normally exhibit magnetism to the outside. Only after the magnetic material is magnetized, it can exhibit magnetism to the outside. In this embodiment, during compacting, the magnetic powder is oriented, so that the easy magnetization axes of the magnetic powder particles (the magnetic powder particles may be polygonal, circular, in the case of polygonal, may be prismatic, hexagonal rod, bar, etc.) are aligned in the same direction, thereby facilitating subsequent magnetization. For example, when the direction of the easy axis of magnetization of the crystal grains coincides or is approximately coincident with the final magnetization direction, then the saturation induction of the permanent magnet can be achieved with a smaller magnetic field strength and a shorter magnetization time. Conversely, if the final magnetization direction is in the hard axis direction of the grains, a larger magnetic field strength and longer magnetization time are required to achieve magnetization. In this embodiment, the grains in different regions in the permanent magnet can be rearranged in the easy axis according to the designed direction by the magnetic orientation during the compaction process, so as to facilitate the magnetization of the permanent magnet with complex magnetic pole distribution and complex shape.

Further, it is noted that the magnetic particles may be partly magnetized during the process of rearranging the magnetic particles based on the magnetic orientation of the pulse coil, which may affect the subsequent laying of the magnetic particles if the resulting block is still magnetic after impact. In this embodiment, residual magnetism introduced into the samarium-iron-nitrogen block for the magnetic orientation operation can be eliminated by reverse energization of the pulse coil. The pulse coil is reversely electrified after pulse laser impact is finished, so that the samarium iron nitrogen block obtained after pulse laser impact is demagnetized, and subsequent magnetic powder paving is facilitated. In another embodiment, the residual magnetism introduced for the magnetic orientation operation can also be eliminated by thermal demagnetization (i.e., using a thermal demagnetization module to eliminate residual magnetism in the resulting samarium-iron-nitrogen block after pulsed laser impact). It should be noted that demagnetization of samarium iron nitrogen block is to restore a plurality of magnetic domains in the crystal grain to a state that magnetic moment directions are different and offset each other, and the direction of the easy axis of magnetization of the crystal grain is not changed.

Finally, it should be noted that the above embodiments are only for illustrating the technical solution of the present invention and are not limiting. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made thereto without departing from the spirit and scope of the present invention, which is intended to be covered by the appended claims.

Claims

1. A method for layer-by-layer fabrication of a dense permanent magnet, comprising the steps of:

Step 1) preparing a die, wherein the die comprises a base, a side frame, a pressing block and an upper cover, the base and the side frame are combined into an open lower die with a containing cavity, and a layer of samarium iron nitrogen powder is paved at the bottom of the lower die;

step 2) vibrating the lower die to enable the samarium iron nitrogen powder layer to reach preset tap density;

Step 3) the pressing block stretches into the lower die, then an upper cover is used for sealing an opening of the lower die, the pressing block is driven to move downwards, and downward mechanical pressure is applied to the samarium-iron-nitrogen powder, so that the samarium-iron-nitrogen powder is compacted;

step 4) opening an upper cover, taking out the pressing block, and applying ultrashort pulse laser impact to the compacted samarium-iron-nitrogen powder with a preset coverage rate by utilizing ultrashort laser pulse to further improve the density of the samarium-iron-nitrogen powder and further solidify a samarium-iron-nitrogen powder layer; wherein, the implementation ultrashort pulse laser impact is as follows: irradiating the surface of the compacted samarium-iron-nitrogen powder with ultra-short pulse laser with single pulse energy of at least 20 muJ, pulse width of more than 200fs and not more than 800fs and spot diameter of 40-120 mu m, and inducing plasma shock waves to impact the compacted samarium-iron-nitrogen powder layer;

Step 5), arranging a next layer of samarium iron nitrogen powder on the surface of the impacted samarium iron nitrogen material; re-executing the steps 2) to 4), so that the samarium-iron-nitrogen powder of the current layer is solidified by utilizing ultra-short laser pulse impact;

And 6) repeatedly executing the steps 2) to 5) to obtain the compact samarium-iron-nitrogen block.

2. The layer-by-layer manufacturing method of a dense permanent magnet according to claim 1, further comprising

Pretreatment: before the samarium-iron-nitrogen block is manufactured, layering slicing treatment is carried out on the three-dimensional graph of the samarium-iron-nitrogen block, and the layer thickness of each slice is delta h; then, measuring and calculating the specified weight of the samarium-iron-nitrogen powder of each slice according to the thickness h ₁ of the compacted samarium-iron-nitrogen powder, and further weighing one part of samarium-iron-nitrogen powder with the specified weight for each slice; wherein Δh is less than h ₁;

In the step 1) and the step 5), the corresponding weighed samarium iron nitrogen with the specified weight is filled into the lower die, so that the laying of the samarium iron nitrogen powder of the current layer is completed;

In the step 4), after the ultra-short laser pulse impact to the samarium iron nitrogen powder of the current layer is completed each time, the workbench carrying the die is lowered by delta h, and the position of the laser head is kept still; or the laser head for the ultra-short laser pulse impact is lifted by delta h, and the position of the workbench is kept still.

3. The method according to claim 1, wherein in the step 4), the coverage rate and the laser pulse energy are adjusted so that the density of the impacted samarium-iron-nitrogen material reaches more than 98% of the theoretical density value.

4. The method of claim 1, wherein in step 2), the vibration die is alternatively used by knocking, rolling or a combination of both to make the samarium-iron-nitrogen powder layer reach a preset tap density.

5. The method for manufacturing a dense permanent magnet layer by layer according to claim 1, wherein the side frames are sleeved on the base, a nonmagnetic metal substrate is placed on the base, a first layer of samarium-iron-nitrogen powder is paved and compacted on the substrate, and a subsequent layer of samarium-iron-nitrogen powder is paved and compacted on a previous layer impacted by the ultrashort pulse laser; the side frames are cylindrical, long square frames, square frames or frame shapes with outlines of other shapes, and the shapes of the base, the upper cover and the pressing block are matched with the shapes of the side frames; wherein, the upper cover and the pressing block are connected into a whole.

6. A method of layer-by-layer manufacture of a compact permanent magnet according to claim 1, characterized in that the mould is provided with coils around or into the lower mould;

In the step 3), pulse current with the peak value exceeding 1 kA is applied to the coil in the compaction process so as to generate a thin-layer magnetic field of more than 30 kOe in the area of the samarium-iron-nitrogen powder of the current layer in the die, and the samarium-iron-nitrogen powder which is not impacted by laser and is being compacted is magnetically oriented under the action of the thin-layer magnetic field.

7. The method of layer-by-layer fabrication of a dense permanent magnet according to claim 6, wherein in step 3), the coil generates a horizontal pulsed magnetic field or a vertical pulsed magnetic field in the region where the samarium-iron-nitrogen powder layer is located; the compact hammers the samarium-iron-nitrogen powder layer to compact it while the pulsed magnetic field is applied, wherein a time difference between a duration of the pulsed magnetic field and a period in which the compact contacts the samarium-iron-nitrogen powder is not more than 1ms by controlling a timing of applying a pulsed current to the coil.

8. The method of layer-by-layer fabrication of a dense permanent magnet according to claim 6, wherein the side frame is sleeved on the base, 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 a subsequent layer of samarium-iron-nitrogen powder is laid and compacted on a previous layer after the ultrashort pulse laser is impacted; the base plate, the base, the side frames and the pressing blocks are all made of corundum.

9. The method for producing a dense permanent magnet layer by layer according to claim 1, wherein the samarium iron nitrogen powder is a polygonal powder or a spherical powder having a particle size distribution D ₅₀ of 3 to 50 μm.

10. The layer-by-layer manufacturing method of a dense permanent magnet according to claim 1, wherein steps 1) to 6) are performed in a gas-shielded environment, wherein the shielding gas in the gas-shielded environment is inert gas or nitrogen gas; the pressure of the gas protection environment is equal to the atmospheric pressure, the humidity is less than or equal to 30%, and the temperature is room temperature; the protection environment is obtained by directly filling the protection gas to replace air, or by vacuumizing and then filling the protection gas.