Magnetic ring manufacturing device and preparation method of hot-pressed neodymium iron boron radiation magnetic ring

Abstract

The invention provides a magnetic ring manufacturing device and a preparation method of a hot-pressed neodymium iron boron radiation magnetic ring, and belongs to the technical field of magnetic ring manufacturing. The core rod can move in the axis direction of the female die and comprises a first core shaft and a second core shaft which are fixedly arranged in the axis direction; the upper punch can stretch into the forming cavity and move in the axis direction of the female die, and a containing cavity allowing the first mandrel to stretch into is formed in the upper punch; the ejection punch is arranged outside the second core shaft in a sleeving manner, and the ejection punch can also extend into the forming cavity and move in the axis direction of the female die; and the punching force of the ejection punch or the upper punch is adjustable. The forming die has the advantages that the hot stamping function and the heat flow forming function are integrated in the same die system, materials are driven to flow through the pressure difference between the upper punch and the ejection punch, densification and radiation orientation forming can be continuously completed after one-time heating, and intermediate cooling, transferring and reheating links are omitted.

Description

Technical Field

[0001] This invention belongs to the field of magnetic ring manufacturing technology, and particularly relates to a magnetic ring manufacturing apparatus and a method for preparing a hot-pressed neodymium iron boron radiating magnetic ring. Background Technology

[0002] With the rapid development of emerging fields such as humanoid robots, drones, and high-precision micromotors, stringent requirements have been placed on their core driving components—rare-earth permanent magnets—for high magnetic energy product, high temperature resistance, and lightweight design. Magnetic rings, as a key component, directly determine the efficiency and performance of micromotors. Among various permanent magnet materials, anisotropic radially oriented magnetic rings can provide the most optimized magnetic flux path along the radial direction, making them an ideal choice for achieving the aforementioned high-performance requirements.

[0003] Currently, the mainstream technologies for manufacturing anisotropic NdFeB radiating rings include sintering and hot pressing. For sintered radiating rings, it is necessary to apply magnetic fields in the inner and outer diameter directions to orient the easy magnetization axis of the magnetic powder particles along the radial direction of the ring. However, for small-diameter rings (especially those with high aspect ratios, i.e., the ratio of length to outer diameter ≥ 3), due to physical space limitations, it is difficult to establish a sufficiently strong and uniform orientation magnetic field within the cavity. This results in a low degree of orientation (Ra) of the grains inside the magnet, making it impossible to obtain an ideal high magnetic energy product and limiting its performance upper limit.

[0004] Hot pressing / thermorheology, as a near-net-shape forming technology, uses pressure rather than a magnetic field for grain orientation. Theoretically, it is not limited by the size of the magnetic ring, offering a possibility for solving the orientation problem of small-diameter radiation rings. However, the traditional hot pressing radiation ring manufacturing process has inherent defects. As is well known in the art (see patents CN101145442B, CN101299363B, etc.), its standard process usually includes three independent steps: first, cold pressing pre-forming; then, hot pressing densification of the cold-pressed blank (heating to 700-800℃); and finally, reheating the densified blank for thermorheology forming (heating to 800-900℃) to achieve the final shape and radiation orientation. This serial process of "cold pressing-hot pressing-thermorheology" requires the magnet to undergo two high-temperature heating cycles.

[0005] This repeated heating process has led to several serious problems:

[0006] 1. Abnormal Grain Coarsening: Hot-pressed NdFeB magnets use rapidly quenched magnetic powder as raw material, which has a nanocrystalline structure (grain size typically <100nm) and is extremely sensitive to temperature. The two high-temperature heating processes provide conditions for abnormal grain growth. Once the grains coarsen, it will directly lead to a significant decrease in the rheological properties and final magnetic properties (such as coercivity and energy product) of the magnet.

[0007] 2. Poor uniformity of structure: For small-diameter magnetic rings with low powder content and light weight, the heating process of the front and rear ends of the magnetic rings differs under repeated thermal shocks, which can easily lead to uneven internal structure of the magnet, larger deviation in performance, and difficulty in guaranteeing the yield.

[0008] 4. Low production efficiency and high cost: Two independent hot processes mean a longer production cycle and higher energy consumption. In addition, the high-temperature mold is more prone to wear and thermal adhesion in the two independent processes, which increases equipment maintenance costs and downtime, and is not conducive to large-scale automated stable production.

[0009] Therefore, there is an urgent need in this field for a new manufacturing method and equipment that can overcome the above-mentioned defects and efficiently and stably produce high-performance, especially small-sized, high aspect ratio anisotropic hot-pressed NdFeB radiation magnetic rings, while avoiding grain coarsening. Summary of the Invention

[0010] The purpose of this invention is to address the aforementioned problems in existing technologies by proposing a magnetic ring manufacturing apparatus and a method for preparing a hot-pressed neodymium iron boron radiating magnetic ring.

[0011] The objective of this invention can be achieved through the following technical solution: a magnetic ring manufacturing apparatus, comprising:

[0012] A female mold, which has a forming cavity inside;

[0013] The mandrel is movable along the axial direction of the female mold and includes a first mandrel and a second mandrel fixedly disposed along the axial direction.

[0014] The upper punch is capable of extending into the forming cavity and moving along the axial direction of the female mold. The upper punch is provided with a receiving cavity for the first mandrel to extend into.

[0015] The ejector punch is fitted over the second mandrel and can also extend into the molding cavity and move along the axial direction of the female mold.

[0016] The punching force of the ejector punch or the upper punch is adjustable, thereby creating a pressure difference between the upper punch and the ejector punch.

[0017] In the aforementioned magnetic ring manufacturing apparatus, the punching force of the ejector punch is configured to be independently adjustable.

[0018] The second objective of this invention is to provide a method for preparing a hot-pressed neodymium iron boron radiation magnetic ring, which is prepared using a magnetic ring manufacturing apparatus. The preparation method specifically includes the following steps:

[0019] S1. Cold pressing pre-pressing: Pre-pressing the rapidly quenched magnetic powder to obtain the billet;

[0020] S2, Hot pressing and rheological forming: The blank obtained in S1 is placed in a magnetic ring manufacturing device and subjected to hot pressing and hot rheological forming processes in sequence to obtain a blank.

[0021] S3. Demolding process: The upper punch is depressurized and retracted, and the ejector punch is kept under pressure to eject the blank and demold it. After cutting according to the design dimensions, a hot-pressed neodymium iron boron radiating magnetic ring is obtained.

[0022] In one of the above preparation methods, the parameters for pre-pressing in step S1 are as follows: pressure of 200-600 MPa, pressing time of 3-10 s, and billet density of 5.3-6.1 g / cm³. 3 .

[0023] In one of the above preparation methods, in step S2, the blank is preheated before hot pressing. The parameters of the preheating treatment are as follows: temperature is 500-700℃, and heating rate is 2-15℃ / s.

[0024] In one of the above preparation methods, step S2 includes coating the surface of the blank with a release agent before preheating.

[0025] In one of the above preparation methods, in step S2, the hot pressing process is carried out by microwave heating, and the hot pressing temperature is 700-800℃.

[0026] In one of the above preparation methods, the specific steps of hot pressing are as follows: the ejector punch moves upward to close the forming cavity, and the upper punch moves downward to extrude the blank to make it dense, wherein the stroke of the upper punch is ≥ 30% of the height of the blank, the extrusion stress is ≥ 300MPa, and the extrusion speed is 0.5-2mm / s.

[0027] In one of the above preparation methods, in step S2, the temperature of the thermorheological treatment is 800-900℃, and the specific steps of the thermorheological treatment are as follows: the upper punch applies extrusion stress to the blank that has been hot-pressed, while the ejector punch releases pressure to 5-30% of the upper punch stress. The pressure difference formed between the upper punch and the ejector punch pushes the hot-pressed blank into the forming cavity. The narrowing of the forming cavity width forms a uniform radial orientation of the compressive stress formed on the blank, resulting in a blank. The extrusion stress of the upper punch is ≥200MPa, and the extrusion speed is 2-10mm / s.

[0028] In one of the above preparation methods, the compression ratio is 50-90%, and the compression ratio = 100 - {(D2)} 2 -d2 2 ) / (D1 2 -d1 2 )*100};wherein,

[0029] D2 is the diameter of the heat flow edge region in the molding cavity;

[0030] d2 is the diameter of the second mandrel in the mandrel;

[0031] D1 is the diameter of the hot stamping zone in the forming cavity;

[0032] d1 is the diameter of the first mandrel in the mandrel. Attached Figure Description

[0033] Figure 1 This refers to the existing method for manufacturing hot-pressed NdFeB radiating magnetic rings;

[0034] Figure 2 This refers to the abnormal grain growth (coarsening) phenomenon in existing thermo-pressed radiation rings;

[0035] Figure 3 This is a schematic diagram of the manufacturing equipment;

[0036] Figure 4 This is a schematic diagram illustrating the data of the manufacturing equipment;

[0037] Figure 5 This is a process diagram illustrating the fabrication of the hot-pressed neodymium iron boron radiating magnetic ring of the present invention;

[0038] Figure 6 This is a diagram showing the shape and internal microstructure of the product after hot pressing / rheology in Embodiment 1 of the present invention.

[0039] Figure 7 This is a comparison diagram of the magnetic properties of the hot-pressed NdFeB radiative magnetic ring prepared in Example 1 and the conventional hot-pressed radiative ring prepared in Comparative Example 1.

[0040] In the figure, the female mold is 100; the forming cavity is 101; the mandrel is 200; the first mandrel is 201; the second mandrel is 202; the upper punch is 300; the receiving cavity is 301; and the ejector punch is 400. Detailed Implementation

[0041] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings. However, the present invention is not limited to these embodiments.

[0042] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0043] Figure 1The manufacturing method for existing hot-pressed NdFeB radial magnetic rings includes the following steps: 1. Pressing NdFeB rapidly quenched magnetic powder into a cylindrical shape (post-extrusion) or a ring shape (pre-extrusion); 2. Heating the cold-pressed blank to above the softening temperature of the magnet grain boundary phase and pressing it to increase the density of the blank to near or reach the theoretical density of the NdFeB magnet; 3. Thermorheology: Reheating the hot-pressed blank to the hot-pressing temperature or higher, and extruding the blank through a punch to form a cup-shaped blank (post-extrusion: the direction of the punch movement is opposite to the direction of the magnet being extruded) or a cup-shaped blank with a central hole at the bottom (pre-extrusion: the direction of the punch movement is the same as the direction of the magnet being extruded). At the same time, the micro-grain structure inside the magnet undergoes plastic deformation and slippage under the compressive stress, and the easy magnetic axis direction (the direction of least deformation resistance) of the grains deflects radially towards the cup wall, ultimately forming a uniform radial arrangement. Then, the bottom of the cup is removed by post-processing, and the blank is cut into a radial ring of the designed size.

[0044] like Figure 2 As shown, current hot-pressed NdFeB radiation magnetic rings typically use rapidly quenched magnetic powder manufactured by ultra-rapid cooling process as raw material. The interior of the rapidly quenched powder has a polycrystalline structure with a grain size of typically <100nm. Due to the fine grain size, it has high coercivity (high temperature resistance). However, because the rapid cooling rate on one side of the rapidly quenched powder surface (the roller-contacting surface) is too fast, the surface layer has an amorphous structure. Since the amorphous structure lacks grain boundary phase constraints, it has high temperature sensitivity. When the heating temperature is high and the heating time is long, the grains on the roller-contacting surface are prone to abnormal growth (coarsening), thereby reducing the rheological ability and magnetic properties of the magnet.

[0045] To address the problems existing in the prior art, this invention provides a magnetic ring manufacturing apparatus and a method for preparing hot-pressed NdFeB radiant magnetic rings. By innovatively designing a one-stop hot-pressing / rheological mold with a variable pressure ejector punch 400, and integrating the two processes of hot-pressing densification and thermorheological orientation into a single heating process, the invention effectively avoids the problem of grain coarsening caused by repeated heating of the magnet, significantly improves the uniformity and consistency of the magnetic ring performance, and simultaneously increases production efficiency and product yield.

[0046] like Figures 3-7 As shown, a magnetic ring manufacturing apparatus includes:

[0047] A female mold 100, which has a molding cavity 101 inside;

[0048] The mandrel 200 is movable along the axial direction of the female mold 100 and includes a first mandrel 201 and a second mandrel 202 fixedly disposed along the axial direction.

[0049] The upper punch 300 is able to extend into the forming cavity 101 and move along the axial direction of the female mold 100. The upper punch 300 is provided with a receiving cavity 301 into which the first mandrel 201 extends.

[0050] The ejector punch 400 is fitted outside the second mandrel 202 and can also extend into the forming cavity 101 and move along the axial direction of the female mold 100.

[0051] The punching force of the ejector punch 400 or the upper punch 300 is adjustable, thereby creating a pressure difference between the upper punch 300 and the ejector punch 400.

[0052] In this application, by integrating hot stamping and hot flow forming functions into the same mold system, and using the pressure difference between the upper punch 300 and the ejector punch 400 to drive material flow, densification and radiation orientation forming can be continuously completed after one heating, eliminating intermediate cooling, transfer and reheating links, significantly shortening the production cycle and improving equipment utilization and production efficiency.

[0053] It is worth mentioning that during the manufacturing process, the forming cavity 101 is divided into a connected hot stamping zone and a thermorheological zone. By adjusting the positions of the upper punch 300, the ejector punch 400 and the mandrel 200 in the female mold 100, the product is pushed to complete hot stamping and thermorheological transformation in the corresponding areas.

[0054] Furthermore, at least one of the upper punch 300 and the ejector punch 400 has an adjustable punching pressure function, which can form a controllable pressure gradient during the forming process. In the thermorheological stage, by controlling the upper punch 300 to maintain high pressure while depressurizing the ejector punch 400, a net extrusion force from top to bottom is formed, pushing the billet into the narrow thermorheological cavity. During this process, the material is subjected to high-proportion compression, and the grains slip and rotate along the grain boundaries at high temperature, causing its easily magnetized axis (c-axis) to tend to align radially, achieving a highly oriented radial texture and significantly improving the anisotropy of the magnetic ring.

[0055] The punching force of the ejector punch 400 is configured to be independently adjustable. This allows the pressure difference required to drive material flow to be created by actively reducing the pressure of the ejector punch 400 during the thermal flow forming stage, without further increasing the pressure of the upper punch 300.

[0056] During the hot-press densification process, the upper punch 300 and the ejector punch 400 need to apply high pressure simultaneously to fully compact the billet. If the pressure of the upper punch 300 is further increased to seek extrusion driving force, the entire mold will be subjected to excessive clamping force, which can easily cause structural damage such as cracking of the female mold 100, bending of the mandrel 200, or jamming of the guide components, seriously affecting the mold life and forming stability. This invention adopts a control strategy of stabilizing the pressure of the upper punch and independently depressurizing the lower punch. While keeping the pressure of the upper punch 300 constant, the ejector punch 400 is depressurized, thereby creating a directional pressure gradient to drive the material into the thermorheological cavity. This ensures both densification quality and extrusion power, while avoiding mold overload and mechanical failure caused by excessive pressure.

[0057] like Figure 3 As shown, the present invention also provides a method for preparing a hot-pressed neodymium iron boron radiation magnetic ring, which is prepared using a magnetic ring manufacturing device. The preparation method specifically includes the following steps:

[0058] S1. Cold pressing pre-pressing: Pre-pressing the rapidly quenched magnetic powder to obtain the billet;

[0059] S2, Hot pressing and rheological forming: The blank obtained in S1 is placed in a magnetic ring manufacturing device and subjected to hot pressing and hot rheological forming processes in sequence to obtain a blank.

[0060] S3. Demolding process: Depressurize and retract the upper punch 300, and maintain the pressure rise of the ejector punch 400 to eject the blank and demold it. After cutting according to the design dimensions, the hot-pressed neodymium iron boron radiation magnetic ring is obtained.

[0061] The core advantage of the above-mentioned preparation method in this invention lies in the technological breakthrough achieved through a "one-stop" integrated process. This method innovatively integrates the two key processes—"hot pressing densification" and "hot flow forming"—which are traditionally separate and require two separate high-temperature heating processes, into a single heating cycle. This integrated process fundamentally avoids the problem of abnormally coarsened nanocrystals caused by repeated thermal cycling of the magnet, thus effectively ensuring the high magnetic properties and high coercivity of the final product. Simultaneously, single heating significantly reduces the uneven heating between the front and rear ends of the magnetic ring during processing, especially in small-diameter, high aspect ratio products, greatly improving the uniformity of the internal structure of the magnet, performance consistency, and product yield. Furthermore, this solution simplifies production steps, shortens the cycle time, and reduces energy consumption and mold wear, providing a reliable path for the stable, efficient, and large-scale production of high-performance hot-pressed radiation rings.

[0062] In specific operation, the parameters for pre-pressing in step S1 are as follows: pressure 200-600 MPa, pressing time 3-10 s, and billet density 5.3-6.1 g / cm³. 3 .

[0063] The aforementioned pre-compression parameters are precisely designed to meet the requirements of the subsequent one-stop hot-pressing rheological process. The resulting billet possesses moderate structural strength and an optimized internal pore structure, ensuring that the billet maintains its shape integrity and does not crack during the transfer and initial pressurization stages. It also provides the necessary physical conditions for the full flow and redistribution of grain boundary phases in the subsequent hot-pressing stage, as well as the plastic deformation, slip, and radial orientation of grains in the thermorheological stage. This forms a solid foundation for ultimately obtaining a high-density, high-performance radial ring.

[0064] In specific operation, in step S2, the billet undergoes preheating before hot pressing. The preheating parameters are as follows: temperature 500-700℃, heating rate 2-15℃ / s. This preheating scheme, through a gentle and controllable heating process, ensures that the billet reaches a uniform transition temperature, effectively avoiding severe thermal stress caused by subsequent rapid microwave heating or direct contact with a high-temperature mold, thus preventing billet cracking. Simultaneously, this preheating prepares for the initial softening of the grain boundary phase in the subsequent hot pressing stage, ensuring a smooth start to the densification process and providing crucial temperature assurance for achieving "one-stop" continuous forming.

[0065] In specific operation, step S2 includes coating the surface of the billet with a release agent before preheating. Applying the release agent before preheating aims to form an effective heat insulation and lubrication barrier on the billet surface. This barrier not only significantly prevents thermal adhesion and mold sticking between the billet and the mold during subsequent high-temperature and high-pressure forming, ensuring smooth demolding and mold life, but also reduces heat loss from the billet within the mold, helping to maintain internal temperature uniformity and creating favorable conditions for uniform grain rheological orientation. The release agent can be the technical solution described in patent CN117253688 B.

[0066] In specific operation, step S2 involves microwave heating for hot pressing, with the temperature ranging from 700-800℃. The advantage of microwave heating lies in its ability to achieve rapid, bulk heating of the billet, ensuring that its internal and external temperatures quickly and uniformly reach the grain boundary softening point. This highly efficient heating method significantly shortens the total residence time of the billet in the high-temperature zone, suppressing the tendency for nanocrystal coarsening at its source. This provides crucial microstructure assurance for achieving high coercivity and is fundamental to achieving high performance.

[0067] In practical operation, the specific steps of hot pressing are as follows: the ejector punch 400 moves upward to close the forming cavity 101, and the upper punch 300 moves downward to extrude the blank and densify it. The stroke of the upper punch 300 is ≥ 30% of the blank height, the extrusion stress is ≥ 300 MPa, and the extrusion speed is 0.5-2 mm / s. This scheme, by limiting the combination of the upper punch 300 stroke, extrusion stress, and speed, ensures that the blank can achieve sufficient and uniform densification at a suitable temperature and strain rate. A moderate extrusion speed avoids the risk of internal stress concentration and cracking caused by excessively rapid pressurization, while sufficient stroke and stress ensure that the blank density can be effectively increased to the high-density foundation necessary for the subsequent thermorheological stage, which is the core of achieving a smooth transition between the two steps.

[0068] In specific operation, in step S2, the temperature of the thermorheological treatment is 800-900℃, and the specific steps of the thermorheological treatment are as follows: the upper punch 300 applies extrusion stress to the blank that has been hot-pressed, while the ejector punch 400 releases pressure to 5-30% of the stress of the upper punch 300. The pressure difference formed between the upper punch 300 and the ejector punch 400 pushes the hot-pressed blank into the forming cavity 101. The narrowing of the forming cavity 101 forms a uniform radial orientation of the compressive stress formed on the blank, resulting in a blank. The extrusion stress of the upper punch 300 is ≥200MPa, and the extrusion speed is 2-10mm / s.

[0069] This scheme precisely controls the pressure relief ratio of the ejector punch 400, working in conjunction with the upper punch 300 to create a precise pressure difference. This is crucial for driving the billet to undergo stable and controllable thermorheology. A higher extrusion temperature ensures sufficient softening of the grain boundary phase to lubricate the grains, while sufficient extrusion stress and speed achieve a high compression ratio and promote efficient radial orientation of the grains, while minimizing the residence time of the billet in the highest temperature region. Ultimately, this efficiently forms a highly oriented radial ring structure while avoiding grain coarsening and die sticking.

[0070] In one of the above preparation methods, the compression ratio is 50-90%, and the compression ratio = 100 - {(D2)} 2 -d2 2 ) / (D1 2 -d1 2 )*100};wherein,

[0071] D2 is the diameter of the heat flow edge region in the forming cavity 101;

[0072] d2 is the diameter of the second mandrel 202 in the mandrel 200;

[0073] D1 is the diameter of the hot stamping zone in the forming cavity 101;

[0074] d1 is the diameter of the first mandrel 201 in the mandrel 200.

[0075] As shown in the following formula, since the performance of the magnetic ring is proportional to the internal grain orientation uniformity (Ra), the thermorheological cavity needs to apply sufficient compressive stress to the blank:

[0076] (BH)max∝(Br / 2)2∝Js·V·Ra; where Js is saturation magnetization, V is magnetite volume fraction, and Ra is orientation degree.

[0077] Its compression ratio is ≥50%, but when the compression ratio is ≥90%, the probability of the billet sticking to the mold increases and the performance decreases.

[0078] The following is a further explanation based on specific embodiments.

[0079] Example 1

[0080] This embodiment provides a hot-pressed neodymium iron boron radiation magnetic ring, which is prepared through the following steps:

[0081] S1. Cold pressing pre-pressing: The rapidly quenched magnetic powder is held under a pressure of 200MPa for 3 seconds to prepare the billet;

[0082] S2, Hot-pressure rheoforming:

[0083] S2.1 Apply a release agent to the surface of the cold-pressed blank;

[0084] S2.2 Preheat the billet by heating it to 500℃ at a rate of 15℃ / s;

[0085] S2.3. The preheated billet is transferred into the magnetic ring manufacturing device and heated by microwave. It is then hot-pressed at 700°C: the ejector punch 400 moves upward to close the cavity, and the upper punch 300 moves downward at a speed of 2 mm / s. The extrusion stress is 300 MPa, and the stroke is 30% of the billet height, so that the billet is densified to 80% of the theoretical density.

[0086] S2.4 Perform thermorheological treatment: Heat to 800℃, apply an extrusion stress of 200MPa to the upper punch 300, and at the same time, release the pressure to 30% of the stress by the ejector punch 400 to form a pressure difference. Push the blank through the cavity at a speed of 10mm / s. The cavity compression ratio is 50% to form a blank.

[0087] S3. Demolding process: The upper punch 300 is depressurized and retracted, and the ejector punch 400 rises to eject the blank. After cutting, a hot-pressed neodymium iron boron radiation magnetic ring is obtained.

[0088] Example 2

[0089] This embodiment provides a hot-pressed neodymium iron boron radiation magnetic ring, which is prepared through the following steps:

[0090] S1. Cold pressing pre-pressing: The rapidly quenched magnetic powder is held under a pressure of 400MPa for 6 seconds to prepare a cold-pressed blank.

[0091] S2, Hot-pressure rheoforming:

[0092] S2.1 Preheat the blank by heating it to 600℃ at a rate of 8℃ / s;

[0093] S2.2 Transfer the preheated billet into the magnetic ring manufacturing device, use microwave heating, and perform hot pressing at 750℃: the ejector punch 400 moves upward to close the cavity, the upper punch 300 moves downward at a speed of 1mm / s, the extrusion stress is 400MPa, the stroke is 50% of the billet height, so that the billet is densified to 90% of the theoretical density.

[0094] S2.3 Perform thermorheological treatment: Heat to 850℃, apply an extrusion stress of 300MPa to the upper punch 300, and at the same time, release the pressure to 10% of the stress by the ejector punch 400 to form a pressure difference. Push the blank through the cavity at a speed of 5mm / s. The cavity compression ratio is 70% to form a blank.

[0095] S3. Demolding process: The upper punch 300 is depressurized and retracted, and the ejector punch 400 rises to eject the blank. After cutting, a hot-pressed neodymium iron boron radiation magnetic ring is obtained.

[0096] Example 3

[0097] This embodiment provides a hot-pressed neodymium iron boron radiation magnetic ring, which is prepared through the following steps:

[0098] S1. Cold pressing pre-pressing: The rapidly quenched magnetic powder is held under a pressure of 600MPa for 10 seconds to prepare the billet;

[0099] S2, Hot-pressure rheoforming:

[0100] S2.1 Apply a release agent to the surface of the blank;

[0101] S2.2 Transfer the blank coated with release agent into the magnetic ring manufacturing device, use microwave heating, and perform hot pressing at 800℃: the ejector punch 400 moves upward to close the cavity, the upper punch 300 moves downward at a speed of 0.5mm / s, the extrusion stress is 500MPa, the stroke is 60% of the blank height, so that the blank is densified to more than 95% of the theoretical density.

[0102] S2.3 Perform thermorheological treatment: Heat to 900℃, apply an extrusion stress of 400MPa to the upper punch 300, and at the same time, release the pressure to 5% of the stress by the ejector punch 400 to form a pressure difference. Push the blank through the cavity at a speed of 2mm / s. The cavity compression ratio is 90% to form a blank.

[0103] S3. Demolding process: The upper punch 300 is depressurized and retracted, and the ejector punch 400 rises to eject the blank. After cutting, a hot-pressed neodymium iron boron radiation magnetic ring is obtained.

[0104] Comparative Example 1

[0105] This comparative example provides a conventional thermo-pressed radiation ring, which employs... Figure 1 It is produced by the existing manufacturing method shown.

[0106] Figure 6 The product shape and internal microstructure after hot pressing / rheology in Embodiment 1 of the present invention are shown below. Figure 6 It can be seen that there are no obvious defects such as cracks or chipping on the inner and outer walls of the product, and the perpendicularity and concentricity of the inner and outer holes are good. The interior of the product has a nanocrystalline texture, with uniform structure, no obvious coarse grains, and good orientation consistency.

[0107] Figure 7 To compare the magnetic properties of the hot-pressed NdFeB radiation magnetic ring prepared in Example 1 with those of the conventional hot-pressed radiation ring prepared in Comparative Example 1, from... Figure 7 It can be seen that the radiation ring obtained in Example 1 has superior magnetic properties (remanence Br, intrinsic coercivity Hcj, magnetic energy product (BH)max, and squareness Hk / Hcj) compared with the traditional radiation ring.

[0108] As can be seen from the above comparison, this invention innovatively integrates the two key processes of hot pressing densification and hot flow forming into a mold with adjustable pressure difference, and completes the process in a one-stop continuous process. This fundamentally avoids the problem of nanocrystal coarsening caused by repeated heating in traditional multi-process production. At the same time, through the synergistic effect of preheating treatment, microwave heating, and precise control of temperature, stress, and speed parameters at each stage, while ensuring high density and excellent radiation orientation of the billet, it significantly improves the uniformity, consistency, and production efficiency of the magnetic ring performance, and realizes the stable and reliable manufacturing of high-performance, especially small-sized, hot-pressed NdFeB radiation magnetic rings.

[0109] It should be noted that in this invention, the use of terms such as "first," "second," and "a" is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified. The terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two elements or the interaction between two elements, unless otherwise explicitly specified. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0110] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0111] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A magnetic ring manufacturing apparatus, characterized in that, include: A female mold, which has a forming cavity inside; The mandrel is movable along the axial direction of the female mold and includes a first mandrel and a second mandrel fixedly disposed along the axial direction. The upper punch is capable of extending into the forming cavity and moving along the axial direction of the female mold. The upper punch is provided with a receiving cavity for the first mandrel to extend into. The ejector punch is fitted over the second mandrel and can also extend into the molding cavity and move along the axial direction of the female mold. The punching force of the ejector punch or the upper punch is adjustable, thereby creating a pressure difference between the upper punch and the ejector punch.

2. The magnetic ring manufacturing apparatus according to claim 1, characterized in that, The punching force of the ejector punch is configured to be independently adjustable.

3. A method for preparing a hot-pressed neodymium iron boron radiation magnetic ring, characterized in that, The magnetic ring is prepared using the magnetic ring manufacturing apparatus according to any one of claims 1-2, and the preparation method specifically includes the following steps: S1. Cold pressing pre-pressing: Pre-pressing the rapidly quenched magnetic powder to obtain the billet; S2, Hot pressing and rheological forming: The blank obtained in S1 is placed in a magnetic ring manufacturing device and subjected to hot pressing and hot rheological forming processes in sequence to obtain a blank. S3. Demolding process: The upper punch is depressurized and retracted, and the ejector punch is kept under pressure to eject the blank and demold it. After cutting according to the design dimensions, a hot-pressed neodymium iron boron radiating magnetic ring is obtained.

4. The preparation method according to claim 3, characterized in that, In step S1, the pre-pressing parameters are as follows: pressure 200-600 MPa, pressing time 3-10 s, and billet density 5.3-6.1 g / cm³. 3 .

5. The preparation method according to claim 3, characterized in that, In step S2, the blank is preheated before hot pressing. The parameters of the preheating treatment are as follows: temperature is 500-700℃, and heating rate is 2-15℃ / s.

6. The preparation method according to claim 5, characterized in that, In step S2, before the preheating treatment, the blank also includes a process of coating the surface of the blank with a release agent.

7. The preparation method according to claim 3, characterized in that, In step S2, the hot pressing process is performed by microwave heating, and the temperature of the hot pressing process is 700-800℃.

8. The preparation method according to claim 7, characterized in that, The specific steps of hot pressing are as follows: the ejector punch moves upward to close the forming cavity, and the upper punch moves downward to extrude the blank to make it dense. The stroke of the upper punch is ≥ 30% of the height of the blank, the extrusion stress is ≥ 300MPa, and the extrusion speed is 0.5-2mm / s.

9. The preparation method according to claim 3, characterized in that, In step S2, the temperature of the thermorheological treatment is 800-900℃, and the specific steps of the thermorheological treatment are as follows: the upper punch applies extrusion stress to the billet that has been hot-pressed, while the ejector punch releases pressure to 5-30% of the upper punch stress. The pressure difference formed between the upper punch and the ejector punch pushes the hot-pressed billet into the forming cavity. The narrowing of the forming cavity width forms a uniform radial orientation of the compressive stress formed on the billet, resulting in a blank. The extrusion stress of the upper punch is ≥200MPa, and the extrusion speed is 2-10mm / s.

10. The preparation method according to claim 9, characterized in that, The compression ratio is 50-90%, and the compression ratio = 100 - {(D2)} 2 -d2 2 ) / (D1 2 -d1 2 )*100};wherein, D2 is the diameter of the heat flow edge region in the molding cavity; d2 is the diameter of the second mandrel in the mandrel; D1 is the diameter of the hot stamping zone in the forming cavity; d1 is the diameter of the first mandrel in the mandrel.

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