Die, device and method for preparing large-size oblique orientation sintered neodymium iron boron

Abstract

The invention discloses a mold, device and method for preparing large-size oblique orientation sintered neodymium iron boron. The device comprises an electric cylinder, a transverse press, a shoulder leaning block, a traction platform and oil cylinders, and the oil cylinders are arranged on the two sides of the transverse press; an electric cylinder is arranged at one end of the transverse press, the end of the electric cylinder is connected with a traction platform, a die is arranged on the traction platform, an adjusting screw is arranged on the traction platform, and the end of the adjusting screw abuts against the shoulder leaning block. According to the method for preparing the large-size oblique orientation sintered NdFeB, large-size oblique orientation can be directly formed, splicing and other processes are not needed, and the performance of a finished product is not lost. The oblique orientation is formed by using the mode, so that the utilization rate of materials is improved, the machining process difficulty is reduced, the process steps are reduced, and the efficiency and benefits are improved.

Description

Technical Field

[0001] The invention relates to the technical field of sintered NdFeB material preparation, and in particular to a mold, a device and a method for preparing large-size obliquely oriented sintered NdFeB. Background Art

[0002] In the preparation of obliquely oriented sintered NdFeB materials, the mold designed in the prior art is a conventional vertical press mold. The mold structure is installed on a conventional press, and the demolding method is that the lower press head is ejected. This movement method has certain limitations. Because the stroke of the lower cylinder of the vertical press and the center position of the pole head of the press magnetizing coil are relatively fixed, the height of the female mold designed for this type of mold is limited (the female mold height is basically between 60 and 160 mm).

[0003] CN102847938A discloses a magnetic material powder molding die. By making the saturated polarization intensity of at least one side material of the female mold cavity consistent with the saturated polarization intensity of the magnetic material powder to be molded, the edge distortion of the magnetic field is transferred from the magnetic material powder to the side of the female mold cavity made of the material, thereby ensuring that the magnetic field of the magnetic material powder is a uniform magnetic field and the performance of the material made by the mold is guaranteed.

[0004] CN116978684A discloses a female mold, a mold and an orientation method for preparing an obliquely oriented blank magnet. The angle of the obliquely oriented material is first determined, and then a mold cavity with a parallelogram cross-section is designed based on the angle and the shrinkage ratio of the material. The mold cavity is made of non-magnetic material, and highly aligned adjustment blocks are embedded in the four corners of the mold cavity. The adjustment blocks are made of magnetic conductive material to form a setting surrounding the mold cavity. Then, by adjusting the shape of the adjustment blocks and the thickness of the mold cavity wall, the orientation of the magnetic powder inside the blank pressed in the mold cavity by applying an external oriented magnetic field is uniform.

[0005] CN 218447535U discloses a mold for preparing obliquely oriented NdFeB magnets. The mold mainly consists of two blocks, one of which is a first cavity formed by four internal fixing blocks, and the other is a second cavity penetrating the internal fixing block, and the magnetic permeability of the internal fixing block is the same as that of the NdFeB powder. The uniformity of the powder under an external magnetic field and the oblique orientation angle of the formed green body are adjusted by replacing the internal fixing block with the second cavity.

[0006] CN220420428U discloses an oblique orientation mold for sintering NdFeB magnets.

[0007] The mold structure disclosed in 218447535U is similar, the inner fixed block is divided into a fixed block with inner teeth, a forming block with outer teeth and a worm with adjustable rotation angle, so that the structure has an adjustable angle worm gear mechanism, and finally the oblique orientation angle is changed by adjusting the worm gear angle, without the need for CN

[0008] The green billet angle can be changed by replacing the internal fixing block as in 218447535U, which has better applicability.

[0009] The above-designed molds are all conventional vertical press molds that press up and down and magnetize left and right.

[0010] At present, with the iteration and update of various technologies, large-scale oblique-oriented materials will be used in many fields such as new energy vehicles, wind power generation, and medical equipment. In the past, the production samples were formed by segmenting the material, and then the required large-scale oblique-oriented materials were finally obtained by splicing. However, there will be magnetic line faults at the joints of the spliced ​​products, which will affect the comprehensive performance of the materials and cause a large loss of magnetic energy product. If you need to obtain materials with specified performance, the performance of the materials used for splicing will have to be improved by 1 to 2 grades to meet the requirements of the spliced ​​products, which will increase the manufacturing cost of the materials. Summary of the invention

[0011] In order to solve the above technical problems, the present invention provides a mold, device and method for preparing large-size obliquely oriented sintered NdFeB, which can directly form large-sized obliquely oriented green billets without the need for subsequent splicing and other processes, and the performance of the finished product is not lost, which is beneficial to improving material utilization, reducing the difficulty of machining technology, reducing process steps, and improving efficiency and benefits.

[0012] A mold for preparing large-size obliquely oriented sintered NdFeB, comprising an upper cover plate, an upper mold cavity plate, side plates placed inside the oil cylinders on both sides of a transverse press, a lower mold cavity plate, positioning pins and a lower cover plate; the upper cover plate and the lower cover plate are arranged opposite to each other up and down, the upper mold cavity plate and the lower mold cavity plate are respectively arranged on opposite sides of the upper cover plate and the lower cover plate, the upper mold cavity plate and the lower mold cavity plate surround an obliquely oriented mold cavity, and the side plate is connected between the side portions of the upper cover plate and the lower cover plate;

[0013] The steps of designing the contour of the mold cavity include:

[0014] 1) The three sides of the material are A, B, and C, the angle between each side is 90°, M is the orientation direction of the magnetization axis, and the angle between the side length A and the orientation direction of the magnetization axis is α, and the length of C is 0 to 200 mm;

[0015] 2) Rotate the material clockwise at an angle (90°-α) around its center point;

[0016] 3) Determine the actual sintering shrinkage ratio in each direction, set the sintering shrinkage ratio in the direction of the magnetization axis as m, the sintering shrinkage ratio in the left and right direction perpendicular to the magnetization axis as n, and the sintering shrinkage ratio in the front and back direction perpendicular to the magnetization axis as v; then enlarge the material according to the corresponding sintering shrinkage ratios in the three directions to obtain the mold cavity profile.

[0017] Preferably, the sides of the upper cover plate and the lower cover plate extend toward each other, the side plates are provided with vertical through holes, the positioning pins pass through the vertical through holes, and the ends are respectively inserted into the holes of the upper cover plate and the lower cover plate.

[0018] Preferably, the upper cover plate is magnetic, the upper mold cavity plate is non-magnetic, and the two are connected by non-magnetic screws; the lower mold cavity plate is non-magnetic, the lower cover plate is magnetic, and the two are connected by non-magnetic screws.

[0019] Preferably, the upper cover plate and the upper mold cavity plate are an integral structure and are made of magnetic conductive material; the lower mold cavity plate and the lower cover plate are an integral structure and are made of magnetic conductive material.

[0020] Preferably, the distance from the top of the mold cavity to the upper cover plate is T=8-15 mm, the thickness of the top of the depression of the upper cover plate is T1=(1.5-2.5)×T, and the distance extending from both sides of the upper cover plate toward the lower cover plate is T2=(2-3.5)×T.

[0021] A device for preparing large-size obliquely oriented sintered NdFeB, comprising an electric cylinder, a transverse press, a shoulder block, a traction platform, and an oil cylinder, wherein oil cylinders are arranged on both sides of the transverse press;

[0022] The transverse press is provided with a press outer frame, and the traction platform is located inside the press outer frame; an electric cylinder is provided at one end of the transverse press, and the end of the electric cylinder is connected to the traction platform. Through the movement of the electric cylinder, the traction platform can be dragged to the loading station and the forming station. At the forming station, the center of the traction platform coincides with the center of the pole head of the magnetizing coil distributed at the upper and lower positions of the press;

[0023] The mold is placed on a traction platform, which is provided with an adjusting screw for positioning. The adjusting screw is threadedly connected to a crossbeam arranged on the traction platform, and the end of the adjusting screw abuts against a shoulder block, which is arranged at one end of the mold.

[0024] A method for preparing large-sized obliquely oriented sintered NdFeB comprises the following steps:

[0025] 1) Mold assembly: Combine two side plates, lower mold cavity plate, positioning pins, lower cover plate and two side pressure heads into a mold unit, and place it on the traction platform of the loading workstation; ensure that the mold center is aligned with the platform center, and the two side pressure heads are kept centered and symmetrical to achieve uniform filling of powder, and the target density is set to ρ; first add half of the total required powder amount, then perform 3 to 15 uniform powder insertion operations to spread over the pressing area, then add the remaining powder, and use a long scraper to sort it out to form a pre-formed hill-like structure;

[0026] 2) Preliminary mold closing: Install the upper cover plate and the upper mold cavity plate, complete the mold closing, and prepare to enter the molding stage; the traction platform is driven by the rear servo of the horizontal press to the molding station;

[0027] 3) Molding and pressing.

[0028] Preferably, the molding and pressing is divided into three stages:

[0029] The first stage: The hydraulic cylinders on both sides simultaneously apply pressure to the center of the mold until the powder density in the mold cavity reaches ρ1, satisfying 1.1ρ≤ρ1≤1.25ρ, and this state is maintained for 1 to 5 seconds. During this period, preliminary charging and demagnetization treatment is carried out to ensure that the magnetic field strength is controlled within the range of 1.2 to 1.4 Tesla, and the charging and demagnetization are completed;

[0030] The second stage: continue to apply pressure until the powder density in the mold cavity reaches ρ2, satisfying 1.35ρ≤ρ2≤1.45ρ, and pause again for 1 to 5 seconds. At this time, the magnetic field is increased to 1.5-1.8 Tesla, and the second charging and demagnetization is carried out;

[0031] The third stage: Final pressure is applied until the powder density in the mold cavity reaches ρ3, satisfying 1.55ρ≤ρ3≤1.65ρ, with a short delay of 0.1 to 2 seconds. At the same time, high-intensity magnetization is performed to the molding size, and the magnetization magnetic field strength is ≥1.8 Tesla. After molding is completed, the final demagnetization step is performed.

[0032] Preferably, the sintering basin method for large-sized obliquely oriented sintered NdFeB is as follows: a layer of gauze is laid flat on the bottom of the graphite basin, the mesh diameter D is between 0.25 and 1.5 mm, the mesh spacing L meets the requirement of 1.5D≤L≤5D, and then the isostatically pressed green body is placed vertically on the laid mesh.

[0033] This technical method is to form obliquely oriented materials on a transverse press, which is essentially different from conventional vertical press molds in terms of mold structure, demoulding method, powder filling method, and sintering swing basin. The molding mode of the transverse press is left-right pressing, upper-lower magnetization, and the molding pressure head does not need to be fixed, so there are fewer restrictions on the molding pressing size. Therefore, the maximum size of the green body formed by the transverse press is 1.5 to 2.5 times larger than the maximum size of the green body formed by the conventional vertical press. The present invention provides a method for preparing large-sized obliquely oriented sintered NdFeB, which can directly form large-sized obliquely oriented green bodies without the need for subsequent splicing and other processes, and the performance of the finished product is not lost. Using this method to form oblique orientation is beneficial to improving the utilization rate of materials, reducing the difficulty of machining technology, reducing process steps, and improving efficiency and benefits.

[0034] The present invention successfully obtains the required large-scale oblique-oriented sintered NdFeB material, thereby improving production efficiency and product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the material structure.

[0036] Figure 2 This is a schematic diagram of rotating the material clockwise by an angle about its center point.

[0037] Figure 3 Schematic diagram of the mold cavity outline.

[0038] Figure 4 This is a schematic structural diagram of the mold of Example 1 of the present invention.

[0039] Figure 5 This is a schematic structural diagram of the mold of Example 2 of the present invention.

[0040] Figure 6 The schematic diagram of the structure of the device for preparing large-sized oblique-oriented sintered NdFeB according to the present invention.

[0041] Figure 7 This is a performance test diagram of the 38SH material in the embodiment of the present invention.

[0042] Figure 8 It is a magnetic circuit simulation diagram of the present invention.

[0043] In the figure: 1. upper cover plate 1, 2. upper cavity plate, 3. side plate, 4. cavity, 5. lower cavity plate, 6. positioning pin, 7. lower cover plate, 8. electric cylinder, 9. adjusting screw 9, 10. press frame, 11. shoulder block, 12. mold, 13. traction platform, 14. oil cylinder, 15. molding station, 16. loading station. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0045] The present invention provides a method for preparing large-sized obliquely oriented sintered NdFeB, which is mainly used for NdFeB products in motors. The patented product specification is a finished product 1-out-1 method;

[0046] The equipment used in the present invention is a transverse press, which is provided with a press outer frame 10; in addition to the two traditional left and right pressing oil cylinders 14, the rear end of the transverse press is modified and optimized, and a servo electric cylinder 8 and a set of traction platforms 13 are added to the rear end of the transverse press. The electric cylinder 8 is connected to the traction platform 13. Through the movement of the electric cylinder 8, the traction platform 13 can be dragged to the loading station 16 and the forming station 15. At the forming station 15, the center of the traction platform 13 will coincide with the center of the pole head of the magnetizing coil distributed at the upper and lower positions of the press. There is a position for placing the mold 12 on the traction platform 13. According to the different widths of the mold 12 used, the adjusting screw 9 at the rear end of the traction device can be adjusted to make the shoulder block 11 move to ensure that the center of the mold 12 coincides with the center of the traction platform 13. The special mold 12 provided is formed in such a modified transverse press to obtain the required large-sized obliquely oriented green blank.

[0047] The present invention provides two mold structures: Figure 4 Provide a mold structure, wherein 2 is Figure 5 Provide mold structure, the difference between the two is Figure 4 The upper cover plate 1 (magnetic), the upper mold cavity plate 2 (non-magnetic), the lower mold cavity plate 5 (non-magnetic), and the lower cover plate 7 (magnetic) are made of different materials and connected by non-magnetic screws. Figure 5 The upper cover plate and the upper cavity plate are an integral structure, made of magnetic conductive material, and the lower cavity plate and the lower cover plate are an integral structure, also made of magnetic conductive material. The two molds use the same molding process, and the molded green body Figure 4 The structure is better than Figure 5 Structural molds, Figure 4 The green powder of the structural mold is evenly distributed and the density is consistent everywhere. Figure 5 There is less powder at the upper and lower corners of the magnetization direction of the green body formed by the structural mold, resulting in extremely low density at these locations and failure to form.

[0048] The present invention proposes an innovative powder filling and molding process for the manufacture of large-sized obliquely oriented sintered NdFeB. The specific steps are as follows:

[0049] 1). Mold assembly: Assemble the two side plates 3, the lower mold cavity plate 5, the positioning pins 6, the lower cover plate 7 and the pressure heads on both sides into a mold unit, and place it on the traction platform 13 of the loading workstation. Ensure that the mold center is accurately aligned with the platform center, and the pressure heads on both sides are centered and symmetrical to achieve uniform powder filling. The target density is set to 1.6g / cm 3 , recorded as ρ. First, half of the total required powder amount is added, followed by 3 to 15 uniform powder insertion operations to spread over the pressing area, followed by the remaining powder being added and arranged with a long scraper to form a preformed hill-like structure.

[0050] 2) Initial mold closing: The upper cover plate 1 and the upper mold cavity plate 2 complete the mold closing and prepare to enter the molding stage. The traction platform 13 is driven by the rear servo of the horizontal press to the molding station 15.

[0051] 3). Three stages of molding and pressing:

[0052] The first stage: the double-sided oil cylinders 14 simultaneously apply pressure to the center of the mold until the powder density in the mold cavity reaches ρ1, satisfying 1.1ρ≤ρ1≤1.25ρ, and maintain this state for 1 to 5 seconds. During this period, preliminary charging and demagnetization treatment is carried out to ensure that the magnetic field strength is controlled within the range of 1.2 to 1.4 Tesla, and the charging and demagnetization are completed.

[0053] The second stage: continue to apply pressure to make the powder density in the mold cavity reach ρ2, satisfying 1.35ρ≤ρ2≤1.45ρ, and pause again for 1 to 5 seconds. At this time, the magnetic field is increased to 1.5-1.8 Tesla, and the second charging and demagnetization is carried out.

[0054] The third stage: Final pressure is applied until the powder density in the mold cavity reaches ρ3, satisfying 1.55ρ≤ρ3≤1.65ρ, with a short delay of 0.1 to 2 seconds. At the same time, high-intensity magnetization is performed to the molding size, and the magnetization magnetic field strength is ≥1.8 Tesla. After molding is completed, the final demagnetization step is performed.

[0055] Through the above optimization process, the required large-sized oblique-oriented green billets were successfully obtained, improving production efficiency and product quality.

[0056] The present invention provides a sintering basin swinging method for large-sized obliquely oriented sintered NdFeB materials. Since the specifications of this material are large, uneven sintering may occur, resulting in slight cracking of the material. The project team lays a layer of gauze on the bottom of the graphite basin, with a mesh diameter D between 0.25 and 1.5 mm and a mesh spacing L that meets the requirement of 1.5D≤L≤5D. The green body after isostatic pressing is then placed vertically on the laid mesh, and the problem of cracking caused by sintering shrinkage is reduced by reducing the contact area and the large weight of the large material itself.

[0057] Figure 1 A, B, and C are the three side lengths of the required material, M is the orientation direction of the magnetization axis, the angle between the side length A and the orientation direction of the magnetization axis is α, the angle between the side length A and the side length B is 90°, and the length of C is 0 to 200 mm. Relying on the structural characteristics of the transverse press, a mold suitable for the transverse press to form obliquely oriented green billets is developed, and then the process of filling the inner cavity of the mold with powder, mold assembly, magnetization molding and other processes are implemented to finally realize the method of oblique orientation process molding. This method has a large length of green billets, and can achieve a pressing molding size between 0 and 200 mm. The molding size range of oblique oriented materials developed by existing processes and patents is 0 to 65 mm. If long-specification material production is required, the splicing method is basically used to solve the problem of insufficient molding size length, and this process has certain disadvantages. If a method of using a transverse press to form obliquely oriented green billets is used, such problems can be solved.

[0058] The present invention provides a method for designing a mold cavity profile.

[0059] 1. Material structure: such as Figure 1 As shown, A, B, and C are the three sides of the required material, the angle between each side is 90°, M is the orientation direction of the magnetization axis, the angle between the side length A and the orientation direction of the magnetization axis is α, and the length of C is 0 to 200 mm.

[0060] 2. Cavity contour design: The position of the horizontal press pole is distributed in the upper and lower positions of the press, and the direction of the material magnetization axis must be consistent with the magnetization direction, so it is necessary to adjust the angle position of the material during design. Figure 1, the angle between side A and the magnetization axis is α, so before designing, the material needs to be rotated clockwise by an angle (90°-α) at ​​its center point to obtain the following Figure 2 As shown. According to the material grade, molding density, sintering temperature and other factors, the actual sintering shrinkage ratio in each direction can be determined. The sintering shrinkage ratio in the direction of the magnetizing axis (up and down) is set as m, the sintering shrinkage ratio in the direction perpendicular to the magnetizing axis (left and right) is set as n, and the sintering shrinkage ratio in the direction perpendicular to the magnetizing axis (front and back) is set as v. Then, according to the corresponding sintering shrinkage ratios in the three directions, the material is enlarged to obtain the following Figure 3 The shape shown is the mold cavity outline.

[0061] 3. Mold structure design: Design the mold structure according to the mold cavity contour, such as Figure 4 As shown, the mold structure consists of an upper cover plate 1 (magnetic), an upper mold cavity plate 2 (non-magnetic), a side plate 3 (non-magnetic), a lower mold cavity plate 5 (non-magnetic), a positioning pin 6 (non-magnetic), and a lower cover plate 7 (magnetic), wherein the mold cavity 4 is surrounded by the above components. The upper mold cavity plate 2 is embedded in the upper cover plate 1 and connected by non-magnetic screws to form a component, the lower mold cavity plate 5 is embedded in the lower cover plate 7 and connected by screws to form a component, and the side plate 3 and the positioning pin 6 are formed into a component through interference fit. The cross-sections of the upper mold cavity plate 2 and the lower mold cavity plate 5 are basically single pieces that can overlap each other by rotating 180°. The size of the mold cavity plate T = 8 ~ 15mm, the size of the cover plate T1 = (1.5 ~ 2.5) × T, T2 = (2 ~ 3.5) × T.

[0062] Example:

[0063] The 38SH brand powder was selected for testing, and the required performance was Br: 12.2~12.6kGs, Hcj:>20kOe, (BH)max: 36.06~40.96MGOe. According to the above patent method, the present invention develops a set of material specifications of 40×31×150+42°. The mold is formed and sintered to obtain the required material, and the two ends and the middle of the material in the length direction of 150mm are selected along the magnetization axis to take out the long sample column, and then the three sections of the long sample column are divided into three sizes of upper, middle and lower The standard sample column was tested for magnetic properties (the equipment used was an ultra-high coercive force magnetometer, and the temperature of the installed test rod needed to be controlled within 20°±0.1°). The test data are shown in Table 1 (see Appendix Figure 7 Test image)

[0064] Table 1 Performance data of various parts of 38SH material

[0065]

[0066] Analyzing the above data, we can draw the following conclusions:

[0067] 1) The obliquely oriented material formed by the present invention does not cause loss of magnetic properties such as Br and Hcj.

[0068] 2) The molding material of the present invention has a relatively long length of 150 mm in the pressing direction, and there may be a problem of large deviation in magnetic properties. Therefore, the performance test of the sampling column was carried out at nine positions, including the two ends, the middle, and the top, middle, and bottom of each position in the pressing direction. The performance measured at each position met the test requirements, and the performance fluctuation at each position was small, with good consistency.

[0069] 3) The present invention is a method for forming obliquely oriented NdFeB materials by a transverse press, and the mold cavity is a special shape, and the mold structure material has large differences in physical properties, which will cause large differences in the orientation of the material. Therefore, the orientation degree (Br / JSat) of the material is calculated, and the value is between 0.965 and 0.97, with good consistency.

[0070] The successful development of obliquely oriented special-shaped materials by transverse presses provides more options for the molding of obliquely oriented special-shaped materials. In the past, the molding of obliquely oriented special-shaped materials was produced by conventional presses, but now it can also be well realized on transverse presses, and the pressing direction has greater advantages than conventional vertical presses. The pressing direction of conventional vertical presses is generally ≤60mm, while the method of developing the obliquely oriented materials by transverse presses in the present invention expands the pressing direction to ≤150mm, which is more than twice the pressing direction of vertical presses. This will enable the molding of more types of materials, and has made great progress in the development of material diversity.

[0071] Compared with the prior art, the present invention forms obliquely oriented materials on a transverse press, while the existing designed molds are all conventional vertical press molds, which are essentially different from the mold structure, demoulding method, powder filling method, and sintering swing basin. The mold structure developed by the prior art is installed on a conventional press, and the demoulding method is that the lower pressure head is ejected. This movement method has certain limitations, because the stroke of the lower cylinder of the vertical press and the center position of the pole head of the press magnetizing coil are relatively fixed, which makes the height of the female mold of this mold design limited (the height of the female mold is basically between 60 and 160 mm). The molding mode of the transverse press is left and right pressing, upper and lower magnetization, and the molding pressure head does not need to be fixed, so there are fewer restrictions on the molding pressing size, so the maximum size of the material molded by the transverse press is 1.5 to 2.5 times larger than the maximum size of the conventional vertical press molding. At present, with the iteration and update of various technologies, large-scale oblique-oriented NdFeB materials will be used in many fields such as new energy vehicles, wind power generation, and medical equipment. In the past, the production samples were formed in sections, and finally the required large-scale oblique-oriented NdFeB materials were obtained by splicing. However, there will be magnetic line faults at the joints of the spliced ​​products, which will affect the comprehensive performance and cause a large loss of magnetic energy product. If a material with specified performance is required, the performance of the material used for splicing will be improved by 1 to 2 grades to meet the requirements of the spliced ​​products, which will increase the manufacturing cost of the material. The invention provides a method for preparing large-size oblique-oriented sintered NdFeB materials, which can directly form large-size oblique-oriented green billets without the need for subsequent splicing and other processes, and the performance of the finished product is not lost. Using this method to form oblique orientation is conducive to improving the utilization rate of materials, reducing the difficulty of machining processes, reducing process steps, and improving efficiency and benefits.

[0072] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A mold for preparing large-size obliquely oriented sintered NdFeB, characterized in that: It comprises an upper cover plate (1), an upper mold cavity plate (2), a side plate (3) disposed inside the oil cylinders (14) on both sides of a transverse press, a lower mold cavity plate (5), a positioning pin (6) and a lower cover plate (7); the upper cover plate (1) and the lower cover plate (7) are arranged opposite to each other up and down, the upper mold cavity plate (2) and the lower mold cavity plate (5) are respectively arranged on opposite sides of the upper cover plate (1) and the lower cover plate (7), the upper mold cavity plate (2) and the lower mold cavity plate (5) enclose an obliquely oriented mold cavity (4), and the side plate (3) is connected between the side portions of the upper cover plate (1) and the lower cover plate (7); The steps of designing the contour of the mold cavity (4) include: 1) The three sides of the material are A, B, and C, the angle between each side is 90°, M is the orientation direction of the magnetization axis, and the angle between the side length A and the orientation direction of the magnetization axis is α, and the length of C is 0 to 200 mm; 2) Rotate the material clockwise at an angle (90°-α) around its center point; 3) Determine the actual sintering shrinkage ratio in each direction, set the sintering shrinkage ratio in the direction of the magnetization axis as m, the sintering shrinkage ratio in the left and right direction perpendicular to the magnetization axis as n, and the sintering shrinkage ratio in the front and back direction perpendicular to the magnetization axis as v; then enlarge the material according to the corresponding sintering shrinkage ratios in the three directions to obtain the mold cavity profile.

2. A mold for preparing large-size obliquely oriented sintered NdFeB according to claim 1, characterized in that: It also includes a positioning pin (6), the sides of the upper cover plate (1) and the lower cover plate (7) extend towards each other, the side plate (3) is provided with a vertical through hole, the positioning pin (6) passes through the vertical through hole, and the ends are respectively inserted into the holes of the upper cover plate (1) and the lower cover plate (7).

3. A mold for preparing large-size obliquely oriented sintered NdFeB according to claim 1, characterized in that: The upper cover plate (1) is magnetic, the upper mold cavity plate (2) is non-magnetic, and the two are connected by non-magnetic screws; the lower mold cavity plate (5) is non-magnetic, the lower cover plate (7) is magnetic, and the two are connected by non-magnetic screws.

4. A mold for preparing large-size obliquely oriented sintered NdFeB according to claim 1, characterized in that: The upper cover plate (1) and the upper mold cavity plate (2) are an integral structure and are made of magnetic conductive material; the lower mold cavity plate (5) and the lower cover plate (7) are an integral structure and are made of magnetic conductive material.

5. The mold for preparing large-size obliquely oriented sintered NdFeB according to any one of claims 1 to 4, characterized in that: The distance T from the top of the mold cavity (4) to the upper cover plate (1) is 8 to 15 mm, the thickness of the top of the depression of the upper cover plate (1) is T1 = (1.5 to 2.5) × T, and the distance T2 extending from both sides of the upper cover plate (1) toward the lower cover plate (7) is (2 to 3.5) × T.

6. A device for preparing large-sized obliquely oriented sintered NdFeB, characterized in that: It comprises a transverse press, an electric cylinder (8), a shoulder block (11), a traction platform (13), and an oil cylinder (14), wherein the oil cylinders (14) for driving are arranged on both sides of the transverse press; The transverse press is provided with a press outer frame (10), and a traction platform (13) is located inside the press outer frame (10); an electric cylinder (8) is provided at one end of the transverse press, and the end of the electric cylinder (8) is connected to the traction platform (13), and the traction platform (13) can be dragged to the loading station (16) and the forming station (15) through the movement of the electric cylinder (8), and at the forming station (15), the center of the traction platform (13) coincides with the center of the pole head of the magnetizing coil distributed at the upper and lower positions of the press; The mold (12) is placed on a traction platform (13). The traction platform (13) is provided with an adjusting screw (9) for positioning. The adjusting screw (9) is threadedly connected to a crossbeam arranged on the traction platform (13). The end of the adjusting screw (9) abuts against a shoulder block (11). The shoulder block (11) abuts against one end of the mold (12).

7. A method for preparing large-sized obliquely oriented sintered NdFeB, characterized in that: The following steps are involved: 1) Mold assembly: two side plates (3), a lower mold cavity plate (5), a positioning pin (6), a lower cover plate (7) and two side pressure heads are assembled into a mold unit, and the mold unit is placed on the traction platform (13) of the loading workstation; ensure that the center of the mold (12) is aligned with the center of the platform, and the pressure heads on both sides are kept centered and symmetrical to achieve uniform filling of powder, and the target density is set to ρ; first add one-half of the total required amount of powder, then perform 3 to 15 uniform powder insertion operations to spread over the pressing area, then add the remaining powder, and use a long scraper to sort it out to form a pre-formed hill-like structure; 2) Preliminary mold closing: installing the upper cover plate (1) and the upper mold cavity plate (2), completing mold closing, and preparing to enter the molding stage; the traction platform (13) is driven by the rear servo of the transverse press to the molding station (15); 3) Molding and pressing stage.

8. The method for preparing large-sized obliquely oriented sintered NdFeB according to claim 7, characterized in that: The molding process is divided into three stages: The first stage: the two-side oil cylinders (14) simultaneously apply pressure to the center of the mold (12) until the powder density in the mold cavity (4) reaches ρ1, and satisfies 1.1ρ≤ρ1≤1.25ρ, and this state is maintained for 1 to 5 seconds, during which a preliminary charging and demagnetization process is carried out to ensure that the magnetic field strength is controlled within the range of 1.2 to 1.4 Tesla, and the charging and demagnetization is completed; The second stage: continue to apply pressure until the powder density in the mold cavity (4) reaches ρ2, satisfying 1.35ρ≤ρ2≤1.45ρ, and pause for 1 to 5 seconds again. At this time, the magnetic field is increased to 1.5-1.8 Tesla, and the second charging and demagnetization is performed; The third stage: Final pressure is applied until the powder density in the mold cavity reaches ρ3, satisfying 1.55ρ≤ρ3≤1.65ρ, with a short delay of 0.1 to 2 seconds. At the same time, high-intensity magnetization is performed to the molding size, and the magnetization magnetic field strength is ≥1.8 Tesla. After molding is completed, the final demagnetization step is performed.

9. The method for preparing large-sized obliquely oriented sintered NdFeB according to claim 7, characterized in that: The sintering basin method for large-sized obliquely oriented sintered NdFeB materials is as follows: a layer of gauze is laid flat on the bottom of the graphite basin, the mesh diameter D is between 0.25 and 1.5 mm, and the mesh spacing L meets the requirement of 1.5D≤L≤5D, and then the isostatically pressed green body is placed vertically on the flat mesh.

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