CN114373618A - Method for reducing surface magnetic difference of two surfaces of sintered neodymium-iron-boron magnet - Google Patents
Method for reducing surface magnetic difference of two surfaces of sintered neodymium-iron-boron magnet Download PDFInfo
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- CN114373618A CN114373618A CN202111571882.3A CN202111571882A CN114373618A CN 114373618 A CN114373618 A CN 114373618A CN 202111571882 A CN202111571882 A CN 202111571882A CN 114373618 A CN114373618 A CN 114373618A
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- 238000000034 method Methods 0.000 title claims abstract description 41
- 229910001172 neodymium magnet Inorganic materials 0.000 title claims abstract description 37
- 239000000843 powder Substances 0.000 claims abstract description 78
- 239000000314 lubricant Substances 0.000 claims abstract description 33
- 239000002245 particle Substances 0.000 claims abstract description 22
- 230000005389 magnetism Effects 0.000 claims abstract description 20
- 238000004519 manufacturing process Methods 0.000 claims abstract description 10
- 238000003825 pressing Methods 0.000 claims description 103
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 42
- 229910052739 hydrogen Inorganic materials 0.000 claims description 42
- 239000001257 hydrogen Substances 0.000 claims description 42
- 239000000047 product Substances 0.000 claims description 22
- 238000005245 sintering Methods 0.000 claims description 21
- 238000002156 mixing Methods 0.000 claims description 18
- 230000002146 bilateral effect Effects 0.000 claims description 14
- 238000005266 casting Methods 0.000 claims description 9
- 229910000831 Steel Inorganic materials 0.000 claims description 8
- 230000005347 demagnetization Effects 0.000 claims description 8
- 238000003754 machining Methods 0.000 claims description 8
- 239000010959 steel Substances 0.000 claims description 8
- 238000000227 grinding Methods 0.000 claims description 6
- 238000003723 Smelting Methods 0.000 claims description 5
- 229910001004 magnetic alloy Inorganic materials 0.000 claims description 5
- 238000007873 sieving Methods 0.000 claims description 5
- 239000002253 acid Substances 0.000 claims description 4
- 238000009713 electroplating Methods 0.000 claims description 4
- 239000007791 liquid phase Substances 0.000 claims description 4
- 238000005406 washing Methods 0.000 claims description 4
- 238000005520 cutting process Methods 0.000 claims description 3
- 230000005284 excitation Effects 0.000 claims description 3
- 239000012535 impurity Substances 0.000 claims description 3
- 239000011265 semifinished product Substances 0.000 claims description 3
- 239000004020 conductor Substances 0.000 claims description 2
- 238000002360 preparation method Methods 0.000 claims description 2
- 230000008569 process Effects 0.000 abstract description 8
- 238000000465 moulding Methods 0.000 description 8
- 239000000463 material Substances 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 6
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
- 239000000654 additive Substances 0.000 description 3
- 230000000996 additive effect Effects 0.000 description 3
- 239000011449 brick Substances 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 230000006872 improvement Effects 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 230000002457 bidirectional effect Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000006073 displacement reaction Methods 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 238000010902 jet-milling Methods 0.000 description 2
- 238000011068 loading method Methods 0.000 description 2
- 238000003801 milling Methods 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000035699 permeability Effects 0.000 description 2
- 229910052761 rare earth metal Inorganic materials 0.000 description 2
- 150000002910 rare earth metals Chemical class 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 238000005507 spraying Methods 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- PXAWCNYZAWMWIC-UHFFFAOYSA-N [Fe].[Nd] Chemical compound [Fe].[Nd] PXAWCNYZAWMWIC-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- 239000004615 ingredient Substances 0.000 description 1
- 238000009434 installation Methods 0.000 description 1
- 230000005381 magnetic domain Effects 0.000 description 1
- 239000006247 magnetic powder Substances 0.000 description 1
- 230000005415 magnetization Effects 0.000 description 1
- 238000004886 process control Methods 0.000 description 1
- 230000000750 progressive effect Effects 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/047—Alloys characterised by their composition
- H01F1/053—Alloys characterised by their composition containing rare earth metals
- H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
- H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/047—Alloys characterised by their composition
- H01F1/053—Alloys characterised by their composition containing rare earth metals
- H01F1/055—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5
- H01F1/057—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B
- H01F1/0571—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes
- H01F1/0575—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together
- H01F1/0576—Alloys characterised by their composition containing rare earth metals and magnetic transition metals, e.g. SmCo5 and IIIa elements, e.g. Nd2Fe14B in the form of particles, e.g. rapid quenched powders or ribbon flakes pressed, sintered or bonded together pressed, e.g. hot working
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F13/00—Apparatus or processes for magnetising or demagnetising
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/02—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets
- H01F41/0253—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties for manufacturing cores, coils, or magnets for manufacturing permanent magnets
- H01F41/0286—Trimming
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- Crystallography & Structural Chemistry (AREA)
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- Manufacturing Cores, Coils, And Magnets (AREA)
- Powder Metallurgy (AREA)
Abstract
The invention discloses a method for reducing the difference of the surface magnetism of the two sides of a sintered neodymium iron boron magnet, which is characterized in that a powder process is improved, so that a lubricant can uniformly wrap and soak powder particles, the internal stress of fine powder is fully removed, the fluidity is remarkably improved, and the subsequent feeding uniformity is fully guaranteed; the method has the advantages that the product percent of pass and the production efficiency can be improved while the difference of the surface magnetism of the two surfaces of the sintered neodymium iron boron magnet is obviously reduced.
Description
Technical Field
The invention relates to a technology for reducing the difference of the surface magnetism of two sides of a sintered neodymium iron boron magnet, in particular to a method for reducing the difference of the surface magnetism of two sides of the sintered neodymium iron boron magnet.
Background
With the rapid development of the application of products such as servo motors, sensors, mobile phone vibration motors, wireless chargers and the like, the reduction of cost, the reduction of volume and the improvement of efficiency become the current development trend of these industrial products, and at the same time, the requirement on the consistency of the double-surface magnetism of the sintered neodymium iron boron magnet applied to these products is also improved. Due to the limitation of production technology, the current common method for producing the sintered neodymium iron boron magnet with high requirement on the difference between the two surface magnetism (less than or equal to 5%) is mainly carried out by increasing the blank grinding allowance and fully detecting the finished product, but the method has low product yield and low material utilization rate, and causes the cost of the sintered neodymium iron boron magnet to be high.
The Chinese patent application with publication number CN111489889A discloses a method for preparing rare earth permanent magnet with high homogeneity and high performance, which comprises uniformly adding mixed liquid additive in a pulse spraying manner during jet milling to improve powder fluidity, and improving blank density and local magnetic domain orientation uniformity, arranging a magnetic-gathering plate in a female die, and making upper and lower pressure heads of a press from near magnetic-permeability material with relative magnetic permeability of 200-400, so as to optimize the magnetic circuit structure of the forming die and improve the orientation degree of the magnet, thereby improving the NS pole difference of the magnet, and simultaneously sieving fine powder into a female die cavity with near magnetic-permeability magnetic-gathering plate by a powder-loading boot, vibrating the lower pressure head by a vibrator to homogenize initial powder distribution, wherein the powder is in loose state, and the loose size of the powder is 1.5-2 times of the forming size, and then adopting a 3-time magnetization opposite progressive prepressing process, wherein the magnetic powder is automatically and uniformly arranged in the female die cavity under the action of a magnetic field by the magnetic vibration orientation of a pulse magnetic field, when the magnetic field orientation is finished once, an upper pressure head and a lower pressure head are automatically controlled by a PLC (programmable logic controller) of a press to respectively enter the female die cavity to preset four-five displacement points, the peak value of an instantaneous orientation magnetic field is 2-3.5T, the orientation is repeated for many times, the upper pressure head and the lower pressure head are repeatedly and oppositely prepressed for many times, the size is not less than 1.25 times of the final pressing and forming size after the repeated prepressing, after the last magnetic vibration orientation is finished, the upper pressure head and the lower pressure head are bidirectionally pressed until the set pressing and forming size value is reached, and a green body is prepared after demagnetization is finished.
However, in the method, the mixed liquid additive is uniformly added in a pulse spraying mode during jet milling, and the hydrogenated nanometer heavy rare earth metal is added in the mixed liquid additive, so that the core purpose is to improve the coercive force of the magnet, and the effect of improving the surface magnetic difference of two surfaces cannot be directly achieved, the magnetic gathering plate arranged in the female die, the upper pressure head and the lower pressure head are all made of near-permeability materials with the relative permeability of 200-400, although the surface magnetic difference of two surfaces can be improved to a certain extent, the magnetic gathering plate has residual magnetism after molding and pressing is finished, the friction force of a green body is increased in the demolding process, and the green body is easy to generate defects such as corner defect, crack defect and the like. After the demolding of unburned bricks is completed, because of the existence of residual magnetism of the upper pressing head and the lower pressing head, the unburned bricks are easy to fall off after the upper pressing head is lifted, so that the unfilled corners are caused, or the unburned bricks are adsorbed on the lower pressing head, so that the problem that the materials are difficult to take is solved, and the product yield is low. In addition, the automatic reciprocating feeding of the powder loading shoe is adopted, the pressure head can not make the initial powder distribution achieve the optimal homogenization effect after the feeding is finished, and the process method of multiple prepressing and multiple orientation is adopted, so that the time consumption of a molding single-mode production period is more than 30% compared with that of the conventional process, and the molding production efficiency is low and is not advisable.
Disclosure of Invention
The invention aims to solve the technical problem of providing a method for reducing the difference of the surface magnetism of the two surfaces of a sintered neodymium-iron-boron magnet, and the method can improve the product percent of pass and the production efficiency while obviously reducing the difference of the surface magnetism of the two surfaces of the sintered neodymium-iron-boron magnet.
The technical scheme adopted by the invention for solving the technical problems is as follows: a method for reducing the difference of the surface magnetism of the two sides of a sintered NdFeB magnet comprises the following steps:
(1) the preparation method comprises the steps of preparing a casting sheet by a smelting furnace, crushing the casting sheet, removing impurities, feeding the casting sheet into a hydrogen crushing furnace, crushing by hydrogen to obtain hydrogen crushed powder, sorting the hydrogen crushed powder, removing undersize with the particle size below 5 mu m and oversize with the particle size above 100 mu m to obtain hydrogen crushed powder with the particle size ranging from 5 mu m to 100 mu m, adding a lubricant into the hydrogen crushed powder, uniformly mixing, feeding the hydrogen crushed powder into an airflow mill, grinding into powder by the airflow mill to obtain fine powder with the particle size ranging from 2.5 to 5 mu m, wherein the mixing time of the hydrogen crushed powder and the lubricant is controlled to be more than 80 minutes, the adding amount of the lubricant is 0.5-1.5 per thousand of the weight of the hydrogen crushed powder, then adding the lubricant into the fine powder, uniformly mixing, standing for more than 8 hours at the temperature of 15-22 ℃, the mixing time of the fine powder and the lubricant is controlled to be more than 200 minutes, and the adding amount of the lubricant is 0.5-2.0 per thousand of the weight, finally, sieving by a sieve with 100-200 meshes and bottling to obtain premixed powder;
(2) preparing a forming die and a press, and installing the forming die on the press, specifically:
the forming die comprises an upper pressing head, a lower pressing head, a female die cavity and 4 inserts, wherein the female die is of a cuboid structure, the female die cavity is formed by arranging a cuboid-shaped inner cavity which is communicated up and down in the middle of the female die, the female die is made of non-magnetic alloy or non-magnetic conductive die steel, the 4 inserts are made of magnetic conductive materials, the upper pressing head and the lower pressing head are made of non-magnetic alloy or non-magnetic conductive die steel, the width of the female die cavity is obtained by subtracting the green body resilience from the black sheet width which is obtained by multiplying the sintering width shrinkage factor by 1-2 times, the orientation of the female die cavity is obtained by subtracting the green body resilience from the black sheet orientation which is multiplied by 1-15 times, and the orientation of the female die cavity is controlled between 20-45 mm so as to guarantee the uniformity and production efficiency of a magnetic field in the female die cavity, wherein a semi-finished product of the sintered neodymium iron boron magnet blank after cutting is called a black sheet and contains machining allowance, 4 inserts are embedded into the female die, the 4 inserts are respectively called a first insert, a second insert, a third insert and a fourth insert, the first insert and the second insert are arranged at the front side of the female die cavity in a bilateral symmetry mode and are in bilateral symmetry relative to the symmetry plane of the female die cavity in the front-back direction, the third insert and the fourth insert are arranged at the rear side of the female die cavity in a bilateral symmetry mode and are in bilateral symmetry relative to the symmetry plane of the female die cavity in the front-back direction, the first insert and the third insert are in front-back symmetry relative to the symmetry plane of the female die cavity in the left-right direction, and the second insert and the fourth insert are in front-back symmetry relative to the symmetry plane of the female die cavity in the left-right direction, the included angles between the first insert, the second insert, the third insert and the fourth insert and the symmetrical plane of the female die cavity along the front-back direction are all 45 degrees, the width of each insert is 4-10 mm, and the distance between each insert and the width working surface of the female die cavity is 3-5 mm;
the press comprises a PLC control system, a press workbench, a die carrier, an upper oil cylinder, a lower oil cylinder, an upper punch, a lower punch, a feeding system, a magnetizing system and a vibrator, wherein the die carrier is arranged on the press workbench, the upper punch is arranged on the upper oil cylinder, the lower punch is arranged on the lower oil cylinder, the vibrator is respectively connected with the die carrier and the lower punch, the magnetizing system comprises two coils, two polar columns and two magnetizing polar heads, the two coils are wound on the two polar columns in a one-to-one correspondence manner, the two polar columns are arranged at intervals left and right, the two magnetizing polar heads are fixed on the inner sides of the two polar columns in a one-to-one correspondence manner, the two magnetizing polar heads are convergent cones and are arranged in a bilateral symmetry manner, the two magnetizing polar heads are symmetrically grooved along the central line thereof, the groove depth is equal to the wall thickness of the orientation female die, the length of the groove is 0.02-0.05 mu m larger than the length of the female die;
the upper pressing head of the forming die is arranged on the upper die punch of the press, the lower pressing head of the forming die is arranged on the lower die punch of the press, the female die is arranged on the die carrier and clamped in the notches of the two magnetizing pole heads, the extension lines of the outer edges of the first insert and the third insert are intersected with the top point of the notch on the left magnetizing pole head, and the extension lines of the outer edges of the second insert and the fourth insert are intersected with the top point of the notch on the right magnetizing pole head;
(3) adjusting the press to enable the upper oil cylinder and the lower oil cylinder to be located at initial positions, enabling the upper pressing head and the lower pressing head to be located at preset initial positions, automatically reciprocating the feeding system to feed the premixed powder obtained in the step (1) into the cavity of the female die repeatedly, and vibrating the female die and the lower pressing head by using a vibrator, wherein the method specifically comprises the following steps: the vibrator vibrates once every time the feeding system feeds, the vibration excitation frequency is 50-100 Hz, and the vibration duration is more than 0.2 s; the PLC automatically controls the upper pressing head to move downwards and the lower pressing head to move upwards to a pre-pressing position preset by the PLC, and the pre-pressing density is 2.3-2.6 g/cm3When the distance is 5-10 mm from the pre-pressing position, the PLC automatically controls the micro-drop of the upper pressing head and the micro-lift of the lower pressing head to reach the set pre-pressing position to finish pre-pressing, wherein the micro-drop speed of the upper pressing head and the micro-lift speed of the lower pressing head are controlled to be 2-5 mm/s;
(4) the magnetizing system is adopted to generate a pulse magnetic field at the female die for magnetizing and orienting, meanwhile, the upper pressing head and the lower pressing head continue to be pressed in two directions until a set pressing and forming size value is reached, the forming position of the two-way pressing needs to be controlled within 0-20 mm downward from the central line of the magnetizing pole head, then demagnetization is carried out, and demolding is carried out after the demagnetization is finished to obtain the product with the density of 3.9-4.2 g/cm3The press-forming size value is the height size of the black piece multiplied by the sintering and pressing shrinkage rate by 1-3 times;
(5) and (3) sintering the green body obtained in the step (4) through a sintering furnace at a high temperature and a liquid phase to obtain a sintered neodymium iron boron magnet blank, obtaining a black sheet from the sintered neodymium iron boron magnet blank through a machining method, and obtaining a final sintered neodymium iron boron magnet finished product with low double-sided surface magnetic difference through acid washing and electroplating of the black sheet.
Compared with the prior art, the invention has the advantages that the batching operation of the sintered neodymium-iron-boron magnet is completed according to the formula, the cast sheet is prepared by adopting a smelting furnace, the cast sheet is crushed and purified and then sent into a hydrogen crushing furnace for hydrogen crushing to obtain hydrogen crushed powder, the hydrogen crushed powder is sorted, undersize and oversize products with the particle size of below 5 mu m and oversize products with the particle size of above 100 mu m are removed to obtain the hydrogen crushed powder with the particle size range of between 5 mu m and 100 mu m, the hydrogen crushed powder and the lubricant are added into the hydrogen crushed powder and mixed uniformly and then enter an airflow mill device for grinding and milling to obtain fine powder with the particle size range of between 2.5 and 5 mu m, wherein the mixing time of the hydrogen crushed powder and the lubricant is controlled to be above 80 minutes, the adding amount of the lubricant is 0.5-1.5 per thousand of the weight of the hydrogen crushed powder, the lubricant is added into the fine powder and mixed uniformly and then stands for more than 8 hours at the temperature of 15-22 ℃, and the mixing time of the fine powder and the lubricant is controlled to be above 200 minutes, the adding amount of the lubricant is 0.5-2.0 per mill of the weight of the fine powder, the fine powder is sieved by a sieve with 100-200 meshes and bottled, so that premixed powder with better granularity consistency is obtained, the lubricant is added twice in the process of preparing the powder, the lubricant can uniformly wrap and infiltrate the powder particles, and the internal stress of the fine powder is fully removed, so that the flowability of the fine powder is remarkably improved, the feeding uniformity of subsequent green body molding is fully guaranteed, in addition, the structure of a molding die and a magnetic pole charging head of a press is improved, the molding die is constructed by an upper pressing head, a lower pressing head, a female die cavity and 4 inserts, the female die is of a cuboid structure, the female die cavity is realized by arranging a cuboid-shaped inner cavity which is communicated up and down in the middle of the female die, the female die is made of non-magnetic alloy or non-magnetic-conductive die steel, and the 4 inserts are made of magnetic-conductive pure iron, the upper pressing head and the lower pressing head are made of non-magnetic conductive alloy or non-magnetic conductive die steel, the width of the female die cavity is obtained by subtracting the green body resilience amount from the black sheet width with the sintering width shrinkage rate multiplied by 1-2 times, the orientation of the female die cavity is obtained by subtracting the green body resilience amount from the black sheet orientation with the sintering orientation shrinkage rate multiplied by 1-15 times, the orientation of the female die cavity is controlled to be 20-45 mm, so that the uniformity of a magnetic field in the female die cavity is ensured, and the production efficiency is considered, wherein the neodymium iron is sinteredThe semi-finished product of the boron magnet blank after cutting is called a black piece and contains machining allowance, 4 inserts are embedded into a female die, the 4 inserts are respectively called a first insert, a second insert, a third insert and a fourth insert, the first insert and the second insert are arranged at the front side of the female die cavity in a bilateral symmetry mode and are bilaterally symmetric relative to the symmetry plane of the female die cavity in the front-back direction, the third insert and the fourth insert are arranged at the rear side of the female die cavity in a bilateral symmetry mode and are bilaterally symmetric relative to the symmetry plane of the female die cavity in the front-back direction, the first insert and the third insert are bilaterally symmetric relative to the symmetry plane of the female die cavity in the left-right direction, the second insert and the fourth insert are bilaterally symmetric relative to the symmetry plane of the female die cavity in the left-right direction, and included angles between the first insert, the second insert, the third insert and the fourth insert and the symmetry plane of the female die cavity in the front-back direction are both 45 degrees, the width dimension of each insert is 4-10 mm, and the distance between each insert and the working surface of the width of the female die cavity is 3-5 mm; the press comprises a PLC control system, a press workbench, a die carrier, an upper oil cylinder, a lower oil cylinder, an upper punch, a lower punch, a feeding system, a magnetizing system and a vibrator, wherein the die carrier is installed on the press workbench, the upper punch is installed on the upper oil cylinder, the lower punch is installed on the lower oil cylinder, the vibrator is respectively connected with the die carrier and the lower punch, the magnetizing system comprises two coils, two polar columns and two magnetizing polar heads, the two coils are wound on the two polar columns in a one-to-one correspondence manner, the two polar columns are arranged at intervals on the left and right, the two magnetizing polar heads are fixed on the inner sides of the two polar columns in a one-to-one correspondence manner, the two magnetizing polar heads are both convergent cones and are symmetrically arranged on the left and right, the two magnetizing polar heads are symmetrically grooved along the central line thereof, the grooving depth is equal to the wall thickness of the orientation direction of the female die, and the grooving length is 0.02-0.05 mu m larger than the length size of the female die; an upper pressure head of the forming die is arranged on an upper die punch of the press, a lower pressure head of the forming die is arranged on a lower die punch of the press, a female die is arranged on a die carrier and clamped in the slots of the two magnetizing pole heads, the extension lines of the outer edges of the first insert and the third insert are intersected with the top point of the slot on the left magnetizing pole head, and the extension lines of the outer edges of the second insert and the fourth insert are intersected with the top point of the slot on the right magnetizing pole head; during forming, the feeding system feeds every timeVibrating the material once by using a vibrator, wherein the vibration excitation frequency is 50-100 Hz, and the vibration duration is more than 0.2 s; the PLC automatically controls the upper pressing head to move downwards and the lower pressing head to move upwards to a pre-pressing position preset by the PLC, and the pre-pressing density is 2.3-2.6 g/cm3When the distance is 5-10 mm from the pre-pressing position, the PLC automatically controls the micro-drop of the upper pressing head and the micro-lift of the lower pressing head to reach the set pre-pressing position to finish pre-pressing, wherein the micro-drop speed of the upper pressing head and the micro-lift speed of the lower pressing head are controlled to be 2-5 mm/s; when a magnetizing system is adopted to generate a pulse magnetic field at a female die for magnetizing and orienting, the upper pressing head and the lower pressing head continue to be pressed in two directions until a set pressing and forming size value is reached, the forming position of the two-way pressing needs to be controlled within 0-20 mm downward of the central line of the magnetizing pole head, then demagnetization is carried out, and demoulding is carried out after the demagnetization is finished to obtain the product with the density of 3.9-4.2 g/cm3The pressing and forming size value of the green body is the height size of the black piece, which is obtained by multiplying the sintering and pressing shrinkage rate by 1-3 times; the special prepressing process control method comprises the steps that a vibrator works once every time a feeding system feeds, powder fed into a cavity of a female die is uniform in loose density, an upper pressing head drops and a lower pressing head drops slightly, the density of a green body is guaranteed to be uniform through subsequent magnetizing orientation, the female die is clamped in grooves of two magnetizing pole heads, and a forming die and a press are matched in a clamping mode, so that magnetic lines in the cavity of the female die are distributed in parallel during magnetizing orientation, the problem of divergence of magnetic lines at the edge of the cavity of the female die is solved, meanwhile, the specific size of the cavity of the female die is set, the magnetic field uniformity of the cavity of the female die can be improved, and the friction force between the periphery of the green body and the side wall of the cavity of the female die during forming and demoulding is reduced, so that the surface magnetism difference between a corner black piece and a middle black piece in a magnet blank is reduced; through the improvement of the forming die structure, the magnetizing pole head structure of the press, the feeding method and the forming method, after the fine powder of each particle of the obtained green body is magnetized, oriented and pressed, each particle does not have obvious displacement, the density of the green body is extremely uniform, and therefore the accumulated error caused by the subsequent black piece machining process is reduced, namely the difference of the two-sided surface magnetism of the magnet is reduced.
Drawings
FIG. 1 is a schematic diagram of the size of a sintered Nd-Fe-B magnet blank and the black piece production;
FIG. 2 is a schematic view of the installation structure of a forming die and a press in the method for reducing the difference of the surface magnetism of the two sides of the sintered NdFeB magnet;
fig. 3 is a schematic diagram of an insert in a forming mold in the method for reducing the difference in surface magnetism of two surfaces of a sintered neodymium-iron-boron magnet according to the present invention.
Detailed Description
The invention is described in further detail below with reference to the accompanying examples.
Example (b): as shown in fig. 1 to 3, a method for reducing the difference between the surface magnetism of two sides of a sintered ndfeb magnet includes the following steps:
(1) finishing the batching operation of the sintered neodymium-iron-boron magnet according to the formula, preparing a casting sheet by adopting a smelting furnace, crushing the casting sheet, removing impurities, sending the crushed casting sheet into a hydrogen crushing furnace, crushing by hydrogen to obtain hydrogen crushed powder, sorting the hydrogen crushed powder, removing undersize with the particle size below 5 mu m and oversize with the particle size above 100 mu m to obtain hydrogen crushed powder with the particle size ranging from 5 mu m to 100 mu m, adding a lubricant into the hydrogen crushed powder, uniformly mixing, sending the mixture into an airflow mill, grinding and milling to obtain fine powder with the particle size of 4 +/-0.1 mu m, wherein the mixing time of the hydrogen crushed powder and the lubricant is controlled to 90 minutes, the adding amount of the lubricant is 0.7 per thousand of the weight of the hydrogen crushed powder, then adding the lubricant into the fine powder, uniformly mixing, standing for 9 hours at the temperature of 20 ℃, wherein the mixing time of the fine powder and the lubricant is controlled to 240 minutes, the adding amount of the lubricant is 1.2 per thousand of the weight of the fine powder, finally adopting a 150-mesh screen and sieving, obtaining premixed powder;
(2) preparing a forming die and a press, and installing the forming die on the press, specifically:
the forming die comprises an upper pressing head, a lower pressing head, a female die 1, a female die cavity 2 and 4 inserts, wherein the female die 1 is of a cuboid structure, the female die cavity 2 is realized by arranging a cuboid-shaped inner cavity which is communicated up and down in the middle of the female die 1, the female die 1 is made of non-magnetic-conductive die steel, the 4 inserts are made of pure iron, the upper pressing head and the lower pressing head are made of non-magnetic-conductive die steel, the width dimension of the female die cavity 2 is the sintering width shrinkage factor multiplied by 1 time of the black piece width dimension W minus 0.2mm of green piece resilience, the orientation dimension of the female die cavity 2 is the sintering orientation shrinkage factor multiplied by 7 times of the black piece orientation dimension L minus 0.4mm of green piece resilience, the 4 inserts are embedded into the female die 1, the 4 inserts are respectively called as a first insert 3, a second insert 4, a third insert 5 and a fourth insert 6, the first insert 3 and the second insert 4 are arranged on the front side of the female die cavity 2 in a bilateral symmetry manner and are symmetrical to the left side and right side relative to the symmetrical plane of the female die cavity 2, the third mold insert 5 and the fourth mold insert 6 are arranged on the rear side of the female mold cavity 2 in a bilateral symmetry manner and are bilaterally symmetric relative to a symmetry plane of the female mold cavity 2 in the front-rear direction, the first mold insert 3 and the third mold insert 5 are bilaterally symmetric relative to the symmetry plane of the female mold cavity 2 in the left-right direction, the second mold insert 4 and the fourth mold insert 6 are bilaterally symmetric relative to the symmetry plane of the female mold cavity 2 in the left-right direction, included angles E between the first mold insert 3, the second mold insert 4, the third mold insert 5 and the fourth mold insert 6 and the symmetry plane of the female mold cavity 2 in the front-rear direction are both 45 degrees, the width dimension F of each mold insert is 6mm, and the distance G of each mold insert from a width working surface of the female mold cavity 2 is 4 mm;
the press comprises a PLC control system, a press workbench, a die carrier, an upper oil cylinder, a lower oil cylinder, an upper punch, a lower punch, a feeding system, a magnetizing system and a vibrator, wherein the die carrier is arranged on the press workbench, the upper punch is arranged on the upper oil cylinder, the lower punch is arranged on the lower oil cylinder, the vibrator is respectively connected with the die carrier and the lower punch, the magnetizing system comprises two coils, two polar columns 7 and two magnetizing polar heads 8, the two coils are wound on the two polar columns 7 in a one-to-one correspondence manner, the two polar columns 7 are arranged at intervals from left to right, the two magnetizing polar heads 8 are fixed on the inner sides of the two polar columns in a one-to-one correspondence manner, the two magnetizing polar heads 8 are convergent cones and are arranged in a left-to-right symmetry manner, the two magnetizing polar heads 8 are symmetrically grooved along the central line thereof, the grooving depth A is equal to the wall thickness B of the female die 1 in the orientation direction, and the grooving length C is 0.04 mu m larger than the length D of the female die 1;
an upper pressure head of a forming die is arranged on an upper die punch of a press, a lower pressure head of the forming die is arranged on a lower die punch of the press, a female die 1 is arranged on a die carrier, the female die 1 is clamped in the slots of two magnetizing pole heads 8, the extension lines a of the outer edges of a first insert 3 and a third insert 5 are intersected with the top point of the slot on the left magnetizing pole head, and the extension lines of the outer edges of a second insert 4 and a fourth insert 6 are intersected with the top point of the slot on the right magnetizing pole head;
(3) the adjusting press makes its upper oil cylinder and lower oil cylinder be located initial position, goes up the pressure head and is located predetermined initial position with lower pressure head this moment, adopts the automatic reciprocal powder feed of premixing that makes a round trip to obtain step (1) of feeding system to the bed die cavity 2 in, uses vibrator vibration bed die 1 and lower pressure head simultaneously, specifically does: the vibrator vibrates once every time the feeding system feeds, the vibration exciting frequency is 80Hz, and the vibration duration is 0.3 s; the PLC automatically controls the upper pressure head to move downwards and the lower pressure head to move upwards to a pre-pressing position preset by the PLC, and the pre-pressing density is 2.3g/cm3When the distance is 5mm from the pre-pressing position, the PLC automatically controls the micro-drop of the upper pressing head and the micro-lift of the lower pressing head to reach the set pre-pressing position to finish pre-pressing, wherein the micro-drop speed of the upper pressing head and the micro-lift speed of the lower pressing head are controlled at 3 mm/s;
(4) adopting a magnetizing system to generate a pulse magnetic field at the female die 1 for magnetizing and orienting, simultaneously continuing bidirectional pressing by the upper pressing head and the lower pressing head until a set pressing and forming size value is reached, controlling the forming position of the bidirectional pressing within 5mm downward from the central line of the magnetizing pole head, then demagnetizing, and demoulding after the demagnetization is finished to obtain the product with the density of 3.95g/cm3The press-molding size value of the green body of (1) is the height size H of the black piece, which is obtained by multiplying the sintering and pressing shrinkage rate by 2 times;
(5) and (3) sintering the green body obtained in the step (4) through a sintering furnace at a high temperature and a liquid phase to obtain a sintered neodymium iron boron magnet blank, obtaining a black sheet from the sintered neodymium iron boron magnet blank through a machining method, and obtaining a final sintered neodymium iron boron magnet finished product with low double-sided surface magnetic difference through acid washing and electroplating of the black sheet.
The sintered neodymium-iron-boron magnet of the grade 42M is prepared by the method of the embodiment, wherein the width dimension W of the black piece is 54.8mm, the height dimension H of the black piece is 9mm, the orientation dimension L of the black piece is 4mm, and the green body is designed in the following dimensions: 56.3mm (width, corresponding to width direction) × 20.2mm (height, corresponding to pressing direction) × 32.14mm (length, corresponding to orientation direction), sheet discharge manner: 1 (width direction) × 2 (height direction, corresponding to pressing direction) × 7 (length direction, corresponding to orientation direction) ═ 14. Wherein, the two-sided central table magnetism discrepancy data of sintered neodymium iron boron magnet finished product that obtain is shown in following table 1:
TABLE 1
Comparative example: in order to verify the performance of the method for reducing the difference of the surface magnetism of the two sides of the sintered NdFeB magnet, the sintered NdFeB magnet with the mark number of 42M is prepared by adopting a conventional process as a comparative example, and the method comprises the following steps:
(1) preparing a cast piece by adopting the same formula and ingredients as in the embodiment and a smelting furnace as in the embodiment, feeding the cast piece into a hydrogen crushing furnace as in the embodiment, crushing the cast piece by hydrogen to obtain hydrogen crushed powder with the particle size range of 1-300 microns, adding a lubricant into the hydrogen crushed powder, uniformly mixing, then grinding the hydrogen crushed powder into powder by an airflow mill device to obtain fine powder with the particle size of 4 +/-0.1 microns, wherein the mixing time of the hydrogen crushed powder and the lubricant is controlled to be 40 minutes, the adding amount of the lubricant is 0.7 per thousand of the weight of the hydrogen crushed powder, then adding the lubricant into the fine powder, uniformly mixing, the mixing time of the fine powder and the lubricant is controlled to be 80 minutes, the adding amount of the lubricant is 1.2 per thousand of the weight of the fine powder, finally sieving by adopting an 80-mesh sieve and bottling the mixture to obtain premixed powder;
(2) preparing a forming die and a press, and installing the forming die on the press, specifically: compared with the example mold, the comparative example forming mold has the same structure and mold material except that 4 inserts are omitted; the width dimension of the female die cavity is the green body resilience value obtained by subtracting 0.2mm from the black sheet width dimension W obtained by multiplying the sintering width shrinkage rate by 1 time, and the orientation dimension of the female die cavity is the green body resilience value obtained by subtracting 0.4mm from the black sheet orientation dimension L obtained by multiplying the sintering orientation shrinkage rate by 10 times; an upper pressure head of the forming die is arranged on an upper punch of the press, a lower pressure head of the forming die is arranged on a lower punch of the press, a female die is arranged on a die carrier of the press, and the female die is clamped between two magnetizing pole heads and is not embedded with the pole heads;
(3) The prepressing density of the material is 2.3g/cm by the conventional process method3And the molding density is 3.95g/cm3The green compact of (1) is pressed to form a black piece height dimension H, wherein the value of the pressed and formed dimension is the sintering and pressing shrinkage rate multiplied by 4 times;
(4) and (3) sintering the green body obtained in the step (3) through a high-temperature liquid phase of a sintering furnace to obtain a sintered neodymium-iron-boron magnet blank, obtaining a black sheet from the sintered neodymium-iron-boron magnet blank through a machining method, and obtaining a final sintered neodymium-iron-boron magnet finished product with low double-sided surface magnetic difference through acid washing and electroplating of the black sheet, wherein the step (4) is completely the same as the step (5) in the embodiment.
The comparative example used a black flake having exactly the same dimensions as the examples, i.e., a width dimension W of 54.8mm, a black flake height dimension H of 9mm, a black flake orientation dimension L of 4mm, and a green size designed: 56.3mm (width, corresponding to width direction) × 39mm (height, corresponding to pressing direction) × 45.2mm (length, corresponding to orientation direction), sheet discharge manner: 1 (width direction) × 4 (height direction) × 10 (length direction) ═ 40. Wherein, the two-sided central table magnetism discrepancy data of sintered neodymium iron boron magnet finished product that obtain is shown in table 2 below:
TABLE 2
The data in the table 1 are analyzed, so that the maximum value of the double-sided surface magnetic difference of the finished magnet product prepared by the method is 2.14%, and the detected black piece 100% meets the technical requirement that the double-sided surface magnetic difference is less than or equal to 5%; as can be seen from the analysis of the data in Table 2, the maximum value of the double-sided surface magnetic difference of the finished magnet product obtained by the prior method (comparative example) is 6.36%, wherein 15% of the 40 black pieces fail to meet the technical requirement of not more than 5% of the double-sided surface magnetic difference, and the method of the invention is reduced by 4.22% compared with the maximum value of the double-sided surface magnetic difference of the finished magnet product obtained by the prior method (comparative example), and the improvement is obvious.
Claims (1)
1. A method for reducing the difference of the surface magnetism of the two sides of a sintered NdFeB magnet comprises the following steps:
(1) the preparation method comprises the steps of preparing a casting sheet by a smelting furnace, crushing the casting sheet, removing impurities, feeding the casting sheet into a hydrogen crushing furnace, crushing by hydrogen to obtain hydrogen crushed powder, sorting the hydrogen crushed powder, removing undersize with the particle size below 5 mu m and oversize with the particle size above 100 mu m to obtain hydrogen crushed powder with the particle size ranging from 5 mu m to 100 mu m, adding a lubricant into the hydrogen crushed powder, uniformly mixing, feeding the hydrogen crushed powder into an airflow mill, grinding into powder by the airflow mill to obtain fine powder with the particle size ranging from 2.5 to 5 mu m, wherein the mixing time of the hydrogen crushed powder and the lubricant is controlled to be more than 80 minutes, the adding amount of the lubricant is 0.5-1.5 per thousand of the weight of the hydrogen crushed powder, then adding the lubricant into the fine powder, uniformly mixing, standing for more than 8 hours at the temperature of 15-22 ℃, the mixing time of the fine powder and the lubricant is controlled to be more than 200 minutes, and the adding amount of the lubricant is 0.5-2.0 per thousand of the weight, finally, sieving by a sieve with 100-200 meshes and bottling to obtain premixed powder;
(2) preparing a forming die and a press, and installing the forming die on the press, specifically:
the forming die comprises an upper pressing head, a lower pressing head, a female die cavity and 4 inserts, wherein the female die is of a cuboid structure, the female die cavity is formed by arranging a cuboid-shaped inner cavity which is communicated up and down in the middle of the female die, the female die is made of non-magnetic alloy or non-magnetic conductive die steel, the 4 inserts are made of magnetic conductive materials, the upper pressing head and the lower pressing head are made of non-magnetic alloy or non-magnetic conductive die steel, the width of the female die cavity is obtained by subtracting the green body resilience from the black sheet width which is obtained by multiplying the sintering width shrinkage factor by 1-2 times, the orientation of the female die cavity is obtained by subtracting the green body resilience from the black sheet orientation which is multiplied by 1-15 times, and the orientation of the female die cavity is controlled between 20-45 mm so as to guarantee the uniformity and production efficiency of a magnetic field in the female die cavity, wherein a semi-finished product of the sintered neodymium iron boron magnet blank after cutting is called a black sheet and contains machining allowance, 4 inserts are embedded into the female die, the 4 inserts are respectively called a first insert, a second insert, a third insert and a fourth insert, the first insert and the second insert are arranged at the front side of the female die cavity in a bilateral symmetry mode and are in bilateral symmetry relative to the symmetry plane of the female die cavity in the front-back direction, the third insert and the fourth insert are arranged at the rear side of the female die cavity in a bilateral symmetry mode and are in bilateral symmetry relative to the symmetry plane of the female die cavity in the front-back direction, the first insert and the third insert are in front-back symmetry relative to the symmetry plane of the female die cavity in the left-right direction, and the second insert and the fourth insert are in front-back symmetry relative to the symmetry plane of the female die cavity in the left-right direction, the included angles between the first insert, the second insert, the third insert and the fourth insert and the symmetrical plane of the female die cavity along the front-back direction are all 45 degrees, the width of each insert is 4-10 mm, and the distance between each insert and the width working surface of the female die cavity is 3-5 mm;
the press comprises a PLC control system, a press workbench, a die carrier, an upper oil cylinder, a lower oil cylinder, an upper punch, a lower punch, a feeding system, a magnetizing system and a vibrator, wherein the die carrier is arranged on the press workbench, the upper punch is arranged on the upper oil cylinder, the lower punch is arranged on the lower oil cylinder, the vibrator is respectively connected with the die carrier and the lower punch, the magnetizing system comprises two coils, two polar columns and two magnetizing polar heads, the two coils are wound on the two polar columns in a one-to-one correspondence manner, the two polar columns are arranged at intervals left and right, the two magnetizing polar heads are fixed on the inner sides of the two polar columns in a one-to-one correspondence manner, the two magnetizing polar heads are convergent cones and are arranged in a bilateral symmetry manner, the two magnetizing polar heads are symmetrically grooved along the central line thereof, the groove depth is equal to the wall thickness of the orientation female die, the length of the groove is 0.02-0.05 mu m larger than the length of the female die;
the upper pressing head of the forming die is arranged on the upper die punch of the press, the lower pressing head of the forming die is arranged on the lower die punch of the press, the female die is arranged on the die carrier and clamped in the notches of the two magnetizing pole heads, the extension lines of the outer edges of the first insert and the third insert are intersected with the top point of the notch on the left magnetizing pole head, and the extension lines of the outer edges of the second insert and the fourth insert are intersected with the top point of the notch on the right magnetizing pole head;
(3) adjusting the press to enable the upper oil cylinder and the lower oil cylinder to be located at initial positions, enabling the upper pressing head and the lower pressing head to be located at preset initial positions, automatically reciprocating the feeding system to feed the premixed powder obtained in the step (1) into the cavity of the female die repeatedly, and vibrating the female die and the lower pressing head by using a vibrator, wherein the method specifically comprises the following steps: the vibrator vibrates once every time the feeding system feeds, the vibration excitation frequency is 50-100 Hz, and the vibration duration is more than 0.2 s; the PLC automatically controls the upper pressing head to move downwards and the lower pressing head to move upwards to a pre-pressing position preset by the PLC, and the pre-pressing density is 2.3-2.6 g/cm3When the distance is 5-10 mm from the pre-pressing position, the PLC automatically controls the micro-drop of the upper pressing head and the micro-lift of the lower pressing head to reach the set pre-pressing position to finish pre-pressing, wherein the micro-drop speed of the upper pressing head and the micro-lift speed of the lower pressing head are controlled to be 2-5 mm/s;
(4) the magnetizing system is adopted to generate a pulse magnetic field at the female die for magnetizing and orienting, meanwhile, the upper pressing head and the lower pressing head continue to be pressed in two directions until a set pressing and forming size value is reached, the forming position of the two-way pressing needs to be controlled within 0-20 mm downward from the central line of the magnetizing pole head, then demagnetization is carried out, and demolding is carried out after the demagnetization is finished to obtain the product with the density of 3.9-4.2 g/cm3The press-forming size value is the height size of the black piece multiplied by the sintering and pressing shrinkage rate by 1-3 times;
(5) and (3) sintering the green body obtained in the step (4) through a sintering furnace at a high temperature and a liquid phase to obtain a sintered neodymium iron boron magnet blank, obtaining a black sheet from the sintered neodymium iron boron magnet blank through a machining method, and obtaining a final sintered neodymium iron boron magnet finished product with low double-sided surface magnetic difference through acid washing and electroplating of the black sheet.
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