CN110491615A - A kind of neodymium-iron-boron preparation for DC micro-motor - Google Patents

Abstract

The invention relates to the technical field of NdFeB magnets, and provides a method for preparing NdFeB magnets for small DC motors, comprising the following steps: 1) preparation of coated powder; 2) magnetic powder compounding; 3) pressing; 4) curing ; 5) hot rolling or hot stamping, and finally an anisotropic NdFeB magnet or an arc-shaped isotropic NdFeB magnet. The invention uses new magnetic powder materials, and the new neodymium-iron-boron magnets prepared by the new magnet preparation steps have excellent magnetic properties, good winding capacity, and small size. Applying the new magnets to small DC motors can further reduce the size of DC motors. The size of the DC motor reduces the current consumption of the DC motor and increases the mechanical output of the DC motor. Compared with traditional magnets, the application of anisotropic NdFeB magnets to small DC motors can reduce the current consumption to two-thirds; the application of arc-shaped isotropic NdFeB magnets to small DC motors can reduce the mechanical The output is increased by about 0.6 times.

Description

A preparation method of NdFeB magnets for small DC motors

technical field

The invention relates to the technical field of neodymium-iron-boron magnets, in particular to a method for preparing neodymium-iron-boron magnets used in small DC motors.

Background technique

Neodymium iron boron (Nd-Fe-B) magnets are the most commonly used rare earth permanent magnets and are widely used in electronic products. Nd-Fe-B (Nd-Fe-B) rare earth permanent magnets can be divided into bonded magnets and sintered magnets. Bonded magnets are made of Nd-Fe-B magnetic powder and binder through injection molding, compression molding or calendering. to prepare. Bonded magnets have the advantages of good shape freedom, high cost performance, small size, and excellent performance, so they are widely used in computer peripheral equipment, office automation, and DC motors. Compared with sintered magnets, bonded magnets can be formed at one time and can be made into magnets with various complex shapes. Applying them to motors can greatly reduce the weight and volume of the motor.

In order to further reduce the size of small DC motors, a new technique for preparing novel magnets with excellent magnetic properties needs to be developed. The relationship among technical components related to the preparation of bonded magnets, including new technologies, is shown in Figure 1. It is necessary to change the preparation method of magnets to improve the overall performance of bonded magnets. Anisotropic HDDR magnetic powder and isotropic spherical magnetic powder are not mainly used in the preparation of ring and arc magnets for small DC motors. In order to apply them to small DC motors, it is necessary to develop a new method that can prepare high-density bonded magnets.

Contents of the invention

Aiming at the problems in the prior art above, the present invention provides a method for preparing a NdFeB magnet for a small DC motor, using a new type of magnetic powder material, and preparing a bonded NdFeB magnet that can be applied to a small DC motor through a new magnet preparation method. Iron boron magnets. The new NdFeB magnets prepared have excellent magnetic properties and small size, and applying the new magnets to small DC motors can further reduce the size of DC motors.

The present invention adopts following technical scheme:

A method for preparing a neodymium-iron-boron magnet for a small DC motor, comprising the following steps:

(1) Coating powder preparation: take solid epoxy oligomer and magnetic powder, and use a fluidized bed reactor to prepare solid epoxy oligomer-coated magnetic powder. The magnetic powder is anisotropic HDDR magnetic powder or isotropic spherical magnetic powder;

(2) Magnetic powder compounding: dry-mix the magnetic powder coated with solid epoxy oligomer with powder curing agent and lubricant using a cold mixer to obtain composite magnetic powder;

(3) Compression: Pour the composite magnetic powder into the cavity of the powder compactor, under the pressure of 0.4-0.6GPa, in the axial magnetic field of 1.5-1.6MA/m, and press it into a similar mesh shape at a temperature of 80°C High-density green body;

(4) Curing: Curing the high-density green body at a temperature of 160°C to 200°C for 20 minutes to obtain a sheet-shaped rigid bonded magnet;

(5) When the magnetic powder in step (1) is anisotropic HDDR magnetic powder, carry out hot rolling:

The sheet-shaped rigid bonded magnet is rolled into a sheet-shaped magnet by a hot rolling mill at a temperature of 60°C-80°C at a rolling rate of 20%-80%, and an anisotropic NdFeB magnet is obtained;

When the magnetic powder in step (1) is isotropic spherical magnetic powder, carry out hot stamping:

The sheet-shaped rigid bonded magnets are subjected to hot stamping treatment, and the sheet-shaped rigid bonded magnets are stamped under the pressure of 1GPa and 110°C to 130°C to obtain arc-shaped isotropic NdFeB magnets.

Further, the thickness of the anisotropic NdFeB magnet is 2.0-2.5mm; the inner radius, outer radius, maximum thickness and maximum length of the arc-shaped isotropic NdFeB magnet are 3.55mm and 3.65mm respectively. mm, 1.9mm and 5mm.

Further, the NdFeB magnets were put into a rolling mill and rolled at a rolling temperature of 70°C.

In the above technical solution, the prepared magnet should be coiled into a ring shape and installed on a small DC motor, which requires a new type of NdFeB magnet to have a certain flexibility, and the prepared magnet has a certain winding ability through rolling.

In order to make the prepared magnets have certain flexibility, put the NdFeB magnets prepared through the above steps into the rolling mill, and roll them at a rolling temperature of 70°C to make them have better flexibility and good winding capacity.

Further, the thickness of the NdFeB magnet after rolling is about 1.15mm.

Further, the rolling mill is a two-roll thin plate rolling mill, and the diameters of the upper roll and the lower roll of the rolls are both 90 mm.

Further, the solid epoxy oligomer is selected from one of brominated bisphenol A epoxy resin, novolac epoxy resin, bisphenol A epoxy resin, and phenol formaldehyde epoxy resin.

Further, the powder curing agent is selected from one of amino resins, aromatic polyamines, hydrazides, resole phenolic resins, dicyandiamide, and acid anhydrides.

Further, the lubricant is zinc octadecanoate.

Further, when the magnetic powder described in step (1) is anisotropic HDDR magnetic powder, the mass percentages of anisotropic HDDR magnetic powder, solid epoxy oligomer, curing agent and lubricant are respectively 96.2-98.1wt%, 1.5- 3.0wt%, 0.1-0.3wt%, 0.3-0.5wt%.

Preferably, the anisotropic HDDR magnetic powder is composed of: Nd: 10% to 15%, Dy: 0.1% to 0.5%, Co: 5% to 20%, Zr: 0.05% to 0.2%, Ga: 0.2%～0.9%, B: 5%～10%, the balance is Fe.

Preferably, the anisotropic HDDR magnetic powder is an anisotropic bonded magnet magnetic powder prepared by HDDR (ie hydrogenation-disproportionation-desorption-recrystallization) method.

Further, when the magnetic powder described in step (1) is isotropic spherical magnetic powder, the mass percentages of isotropic spherical magnetic powder, solid epoxy oligomer, curing agent and lubricant are respectively 96.1 to 98.1 wt%, 1.5 to 3.0wt%, 0.1-0.2wt%, 0.3-0.7wt%.

Preferably, the isotropic spherical magnetic powder is composed of: Nd: 7.0% to 9.5%, B: 5% to 6%, Ti: 0.2% to 0.4%, Zr: 0.1% to 0.25%, and the balance For Fe.

The beneficial effects that the present invention has are:

In the present invention, the new-type NdFeB magnet preparation material powder is compounded, and a high-density green body is prepared by pressing, and then the sheet-shaped green body is solidified, and anisotropic and isotropic new-type magnets are respectively obtained by hot rolling and hot stamping. , and finally the magnet has a certain winding ability through rolling, which can be wound into a ring and applied to a small DC motor.

Compared with traditional magnets, the new-type NdFeB magnets prepared by the new magnet powder materials in the present invention have excellent magnetic properties and good winding ability, so the rolled magnets can be wound into a ring shape, Applied to small DC motors.

Applying the new type of magnet to a small DC motor can further reduce the size of the DC motor, reduce the current consumption of the DC motor, and increase the mechanical output of the DC motor.

The present invention uses isotropic spherical magnetic powder to prepare a bonded NdFeB magnet applied to small DC motors, which can reduce the current consumption of DC motors compared with traditional magnets. The magnet prepared by the present invention is applied to small DC motors The motor can reduce the current consumption to two-thirds.

The present invention uses anisotropic HDDR magnetic powder to prepare a bonded NdFeB magnet applied to small DC motors, which can increase the mechanical output of DC motors compared with traditional magnets, and apply the magnets prepared by the present invention to small DC motors It is possible to increase the mechanical output of a DC motor by a factor of about 0.6.

Description of drawings

Figure 1 is a relationship diagram between the technical components related to the preparation of bonded magnets;

Fig. 2 is a technical roadmap of the present invention.

Detailed ways

In order to enable those skilled in the art to further understand the present invention, the present invention will be described in detail below in conjunction with specific embodiments.

Referring to Fig. 2, a kind of NdFeB magnet preparation method for small DC motor comprises the following steps:

(1) Coating powder preparation: take solid epoxy oligomer and magnetic powder, and use a fluidized bed reactor to prepare solid epoxy oligomer-coated magnetic powder. The magnetic powder is anisotropic HDDR magnetic powder or isotropic spherical magnetic powder;

(2) Magnetic powder compounding: dry-mix the magnetic powder coated with solid epoxy oligomer with powder curing agent and lubricant using a cold mixer to obtain composite magnetic powder;

(3) Compression: Pour the composite magnetic powder into the cavity of the powder compactor, under the pressure of 0.4-0.6GPa, in the axial magnetic field of 1.5-1.6MA/m, and press it into a similar mesh shape at a temperature of 80°C High-density green body;

(4) Curing: Curing the high-density green body at a temperature of 160°C to 200°C for 20 minutes to obtain a sheet-shaped rigid bonded magnet;

(5) When the magnetic powder in step (1) is anisotropic HDDR magnetic powder, carry out hot rolling:

The sheet-shaped rigid bonded magnet is rolled into a sheet-shaped magnet by a hot rolling mill at a temperature of 60°C-80°C at a rolling rate of 20%-80%, and an anisotropic NdFeB magnet is obtained;

When the magnetic powder in step (1) is isotropic spherical magnetic powder, carry out hot stamping:

The sheet-shaped rigid bonded magnets are subjected to hot stamping treatment, and the sheet-shaped rigid bonded magnets are stamped under the pressure of 1GPa and 110°C to 130°C to obtain arc-shaped isotropic NdFeB magnets.

Example 1

Include the following steps:

(1) Ingredients: Take 2915g of anisotropic HDDR magnetic powder, 67g of bisphenol A epoxy resin, 6g of dicyandiamide, and 12g of zinc octadecanoic acid.

(2) Magnetic powder compounding: pre-mixing is performed first, coating powder is prepared through a fluidized bed reactor, and anisotropic HDDR magnetic powder is coated with bisphenol A epoxy resin. Then, the anisotropic HDDR magnetic powder coated with bisphenol A epoxy resin, dicyandiamide, and zinc octadecanoic acid are dry-mixed by cold mixing equipment.

(3) Compression: Pour the composite magnetic powder obtained in step (2) into the cavity of a powder compactor, and press it under a pressure of 0.55GPa, an axial magnetic field of 1.5MA/m, and a temperature of 80°C to form an approximate Mesh-like high-density green body.

(4) Curing: curing the high-density green body obtained in step (3) at a temperature of 180° C. for 20 minutes to obtain a sheet-shaped rigid bonded magnet.

(5) Hot rolling: the sheet-shaped rigid bonded magnet obtained in step (4) is rolled into a sheet-shaped magnet at a temperature of 70° C. at a rolling rate of about 50% by a hot rolling mill.

(6) Rolling: put the NdFeB magnet prepared by the above steps into a two-roll thin plate mill with a diameter of 90mm for the upper roll and the lower roll, and roll at a rolling temperature of 70°C to make it It has good flexibility and good winding ability.

Example 2

(1) Ingredients: 2900g of isotropic spherical magnetic powder, 75g of bisphenol A epoxy resin, 10g of dicyandiamide, and 15g of zinc octadecanoic acid.

(2) Magnetic powder compounding: pre-mixing is performed first, coating powder is prepared through a fluidized bed reactor, and isotropic spherical magnetic powder is coated with bisphenol A epoxy resin. Then dry-mix the isotropic spherical magnetic powder coated with bisphenol A type epoxy resin, dicyandiamide and zinc octadecanoic acid through cold mixing equipment.

(3) Compression: Pour the composite magnetic powder obtained in step (2) into the cavity of a powder compactor, and press it under a pressure of 0.5GPa, an axial magnetic field of 1.5MA/m, and a temperature of 80°C to form an approximate Mesh-like high-density green body.

(4) Curing: curing the high-density green body obtained in step (3) at a temperature of 180° C. for 20 minutes to obtain a sheet-shaped rigid bonded magnet.

(5) Hot stamping: Hot stamping is performed on the sheet-shaped rigid bonded magnet obtained in step (4), and the sheet-shaped rigid bonded magnet is stamped out at a pressure of 1GPa and 120°C to obtain an arc-shaped isotropic magnet. NdFeB magnets.

(6) Rolling: put the NdFeB magnet prepared by the above steps into a two-roll thin plate mill with a diameter of 90mm for the upper roll and the lower roll, and roll at a rolling temperature of 70°C to make it It has good flexibility and good winding ability.

Example 3

(1) Ingredients: Take 962g of anisotropic HDDR magnetic powder, 15g of brominated bisphenol A epoxy resin, 1g of amino resin, and 3g of zinc octadecanoic acid.

(2) Magnetic powder compounding: pre-mix first, prepare coated powder through a fluidized bed reactor, and use brominated bisphenol A type epoxy resin to coat anisotropic HDDR magnetic powder; then brominated bisphenol A type The epoxy resin-coated HDDR magnetic powder is dry-mixed with amino resin and octadecanoic acid zinc salt using a cold mixer to obtain composite magnetic powder.

(3) Compression: Pour the composite magnetic powder into the cavity of the powder compactor, under the pressure of 0.4GPa, in the axial magnetic field of 1.6MA/m, and at the temperature of 80°C, it is pressed into a high-density material in the shape of a mesh green body.

(4) Curing: The high-density green body was cured at a temperature of 160° C. for 20 minutes to obtain a sheet-shaped rigid bonded magnet.

(5) Hot rolling: the sheet-shaped rigid bonded magnet is rolled into a sheet-shaped magnet at a temperature of 60° C. at a rolling rate of about 20% by a hot rolling mill. The finally prepared anisotropic NdFeB magnet has a thickness of about 2.5mm.

(6) Rolling: put the NdFeB magnet prepared by the above steps into a two-roll thin plate mill with a diameter of 90mm for the upper roll and the lower roll, and roll at a rolling temperature of 70°C to make it It has good flexibility and good winding ability.

Example 4

(1) Ingredients: Take 981g of anisotropic HDDR magnetic powder, 30g of phenolic epoxy resin, 3g of aromatic polyamine, and 5g of zinc octadecanoic acid.

The anisotropic HDDR magnetic powder is composed of Nd: 10%, Dy: 0.1%, Co: 5%, Zr: 0.05%, Ga: 0.2%, B: 5%, and the balance is Fe.

(2) Magnetic powder compounding: pre-mix first, prepare coated powder through a fluidized bed reactor, and use phenolic epoxy resin to coat the anisotropic HDDR magnetic powder; then the phenolic epoxy resin coated HDDR magnetic powder It is dry mixed with aromatic polyamine and octadecanoic acid zinc salt using a cold mixer to obtain composite magnetic powder.

(3) Compression: Pour the composite magnetic powder into the cavity of the powder compactor, under the pressure of 0.6GPa, in the axial magnetic field of 1.6MA/m, and at the temperature of 80°C, it is pressed into a high-density, approximately mesh-like green body.

(4) Curing: The high-density green body was cured at a temperature of 200° C. for 20 minutes to obtain a sheet-shaped rigid bonded magnet.

(5) Hot rolling: the sheet-shaped rigid bonded magnet is rolled into a sheet-shaped magnet at a temperature of 80° C. at a rolling rate of about 80% by a hot rolling mill. The finally prepared anisotropic NdFeB magnet has a thickness of about 2.0 mm.

(6) Rolling: put the NdFeB magnet prepared by the above steps into a two-roll thin plate mill with a diameter of 90mm for the upper roll and the lower roll, and roll at a rolling temperature of 70°C to make it It has good flexibility and good winding ability.

Example 5

(1) Ingredients: Anisotropic HDDR magnetic powder 970, 20 g of phenol-formaldehyde epoxy resin, 2 g of resole phenolic resin, and 4 g of zinc octadecanoic acid.

The anisotropic HDDR magnetic powder is composed of Nd: 15%, Dy: 0.5%, Co: 20%, Zr: 0.2%, Ga: 0.9%, B: 10%, and the balance is Fe.

Anisotropic HDDR magnetic powder is an anisotropic bonded magnet magnetic powder prepared by HDDR (ie hydrogenation-disproportionation-desorption-recrystallization) method.

(2) Magnetic powder compounding: first pre-mix, prepare coated powder through a fluidized bed reactor, use phenol formaldehyde epoxy resin to coat anisotropic HDDR magnetic powder; then phenol formaldehyde epoxy resin coated HDDR magnetic powder is dry mixed with resole phenolic resin and zinc octadecanoic acid using a cold mixer to obtain composite magnetic powder.

(3) Compression: Pour the composite magnetic powder into the cavity of the powder compactor, press it into a mesh-like high-density powder under a pressure of 0.45GPa, an axial magnetic field of 1.6MA/m, and a temperature of 80°C. green body.

(4) Curing: The high-density green body was cured at a temperature of 180° C. for 20 minutes to obtain a sheet-shaped rigid bonded magnet.

(5) Hot rolling: the sheet-shaped rigid bonded magnet is rolled into a sheet-shaped magnet at a temperature of 65° C. at a rolling rate of about 60% by a hot rolling mill.

(6) Rolling: put the NdFeB magnet prepared by the above steps into a two-roll thin plate mill with a diameter of 90mm for the upper roll and the lower roll, and roll at a rolling temperature of 70°C to make it It has good flexibility and good winding ability.

Example 6

(1) Ingredients: 961g of isotropic spherical magnetic powder, 15g of phenolic epoxy resin, 1g of hydrazide, 3g of zinc octadecanoate. ,

(2) Magnetic powder compounding: first pre-mix, prepare coated powder through a fluidized bed reactor, use phenolic epoxy resin to coat the isotropic spherical magnetic powder; then coat the isotropic spherical magnetic powder coated with phenolic epoxy resin The homogeneous spherical magnetic powder is dry mixed with hydrazide and octadecanoic acid zinc salt using a cold mixer to obtain composite magnetic powder.

(3) Compression: Pour the composite magnetic powder into the cavity of the powder compactor, under the pressure of 0.4GPa, in the axial magnetic field of 1.6MA/m, and at the temperature of 80°C, it is pressed into a high-density material in the shape of a mesh green body.

(4) Curing: The high-density green body was cured at a temperature of 160° C. for 20 minutes to obtain a sheet-shaped rigid bonded magnet.

(5) Hot stamping: Perform hot stamping treatment on the sheet-shaped rigid bonded magnet, and stamp out the sheet-shaped rigid bonded magnet under the pressure of 1GPa and 110°C to obtain an arc-shaped isotropic NdFeB magnet.

(6) Rolling: put the NdFeB magnet prepared by the above steps into a two-roll thin plate mill with a diameter of 90mm for the upper roll and the lower roll, and roll at a rolling temperature of 70°C to make it It has good flexibility and good winding ability.

Example 7

(1) Ingredients: 981g of isotropic spherical magnetic powder, 30g of phenol-formaldehyde epoxy resin, 2g of acid anhydride, 7g of zinc octadecanoic acid.

The isotropic spherical magnetic powder is composed of Nd: 7.0%-9.5%, B: 5%-6%, Ti: 0.2%-0.4%, Zr: 0.1%-0.25%, and the balance is Fe.

(2) Magnetic powder compounding: first pre-mix, prepare coated powder through a fluidized bed reactor, use phenol formaldehyde epoxy resin to coat isotropic spherical magnetic powder; then phenol formaldehyde epoxy resin coated The isotropic spherical magnetic powder is dry mixed with acid anhydride and octadecanoic acid zinc salt using a cold mixer to obtain composite magnetic powder.

(3) Compression: Pour the composite magnetic powder into the cavity of the powder compactor, under the pressure of 0.6GPa, in the axial magnetic field of 1.6MA/m, and at the temperature of 80°C, it is pressed into a high-density, approximately mesh-like green body.

(4) Curing: The high-density green body was cured at a temperature of 200° C. for 20 minutes to obtain a sheet-shaped rigid bonded magnet.

(5) Hot stamping: Perform hot stamping treatment on the sheet-shaped rigid bonded magnet, and punch out the sheet-shaped rigid bonded magnet under the pressure of 1GPa and 130°C to obtain an arc-shaped isotropic NdFeB magnet.

(6) Rolling: put the NdFeB magnet prepared by the above steps into a two-roll thin plate mill with a diameter of 90mm for the upper roll and the lower roll, and roll at a rolling temperature of 70°C to make it It has good flexibility and good winding ability.

Example 8

(1) Ingredients: 970g of isotropic spherical magnetic powder, 20g of brominated bisphenol A epoxy resin, 1.5g of resole phenolic resin, 5g of zinc octadecanoic acid.

The isotropic spherical magnetic powder is composed of Nd: 7.0%-9.5%, B: 5%-6%, Ti: 0.2%-0.4%, Zr: 0.1%-0.25%, and the balance is Fe.

(2) Magnetic powder compounding: first pre-mix, prepare coated powder through a fluidized bed reactor, and use brominated bisphenol A type epoxy resin to coat isotropic spherical magnetic powder; then brominated bisphenol A type The isotropic spherical magnetic powder coated with epoxy resin is dry-mixed with resole phenolic resin and zinc octadecanoate using a cold mixer to obtain composite magnetic powder.

(3) Compression: Pour the composite magnetic powder into the cavity of the powder compactor, under the pressure of 0.5GPa, in the axial magnetic field of 1.6MA/m, and at the temperature of 80°C, it is pressed into a high-density material in the shape of a mesh green body.

(4) Curing: The high-density green body was cured at a temperature of 190° C. for 20 minutes to obtain a sheet-shaped rigid bonded magnet.

(5) Hot stamping: Perform hot stamping treatment on the sheet-shaped rigid bonded magnet, and punch out the sheet-shaped rigid bonded magnet under the pressure of 1GPa and 120°C to obtain an arc-shaped isotropic NdFeB magnet.

(6) Rolling: put the NdFeB magnet prepared by the above steps into a two-roll thin plate mill with a diameter of 90mm for the upper roll and the lower roll, and roll at a rolling temperature of 70°C to make it It has good flexibility and good winding ability.

Example 9

(1) Ingredients: 975g of isotropic spherical magnetic powder, 25g of bisphenol A epoxy resin, 1.8g of aromatic polyamine, 6g of zinc octadecanoate.

The isotropic spherical magnetic powder is composed of Nd: 7.0%-9.5%, B: 5%-6%, Ti: 0.2%-0.4%, Zr: 0.1%-0.25%, and the balance is Fe.

(2) Magnetic powder compounding: first pre-mix, prepare coated powder through a fluidized bed reactor, use bisphenol A epoxy resin to coat isotropic spherical magnetic powder; then bisphenol A epoxy resin coated The coated isotropic spherical magnetic powder is dry mixed with aromatic polyamine and octadecanoic acid zinc salt using a cold mixer to obtain composite magnetic powder.

(3) Compression: Pour the composite magnetic powder into the cavity of the powder compactor, under the pressure of 0.55GPa, in the axial magnetic field of 1.6MA/m, and at the temperature of 80°C, it is pressed into a high-density material with a similar mesh shape. green body.

(4) Curing: The high-density green body was cured at a temperature of 185° C. for 20 minutes to obtain a sheet-shaped rigid bonded magnet.

(5) Hot stamping: Perform hot stamping treatment on the sheet-shaped rigid bonded magnet, and punch out the sheet-shaped rigid bonded magnet under the pressure of 1GPa and 115°C to obtain an arc-shaped isotropic NdFeB magnet.

(6) Rolling: put the NdFeB magnet prepared by the above steps into a two-roll thin plate mill with a diameter of 90mm for the upper roll and the lower roll, and roll at a rolling temperature of 70°C to make it It has good flexibility and good winding ability.

Of course, the above descriptions are not intended to limit the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or replacements made by those skilled in the art within the scope of the present invention shall also belong to the present invention. protection scope of the invention.

Claims (10)

1. A method for preparing a neodymium-iron-boron magnet for a small DC motor, characterized in that it may further comprise the steps: (1) Coating powder preparation: take solid epoxy oligomer and magnetic powder, and use a fluidized bed reactor to prepare solid epoxy oligomer-coated magnetic powder. The magnetic powder is anisotropic HDDR magnetic powder or isotropic spherical magnetic powder; (2) Magnetic powder compounding: dry-mix the magnetic powder coated with solid epoxy oligomer with powder curing agent and lubricant using a cold mixer to obtain composite magnetic powder; (3) Compression: Pour the composite magnetic powder into the cavity of the powder compactor, under the pressure of 0.4-0.6GPa, in the axial magnetic field of 1.5-1.6MA/m, and press it into a similar mesh shape at a temperature of 80°C High-density green body; (4) Curing: Curing the high-density green body at a temperature of 160°C to 200°C for 20 minutes to obtain a sheet-shaped rigid bonded magnet; (5) When the magnetic powder in step (1) is anisotropic HDDR magnetic powder, carry out hot rolling: The sheet-shaped rigid bonded magnet is rolled into a sheet-shaped magnet by a hot rolling mill at a temperature of 60°C-80°C at a rolling rate of 20%-80%, and an anisotropic NdFeB magnet is obtained; When the magnetic powder in step (1) is isotropic spherical magnetic powder, carry out hot stamping: The sheet-shaped rigid bonded magnets are subjected to hot stamping treatment, and the sheet-shaped rigid bonded magnets are stamped under the pressure of 1GPa and 110°C to 130°C to obtain arc-shaped isotropic NdFeB magnets. 2. A kind of NdFeB magnet preparation method for small DC motor according to claim 1, characterized in that, the thickness of the anisotropic NdFeB magnet is 2.0-2.5mm; the arc-shaped The inner radius, outer radius, maximum thickness and maximum length of the isotropic NdFeB magnets are 3.55mm, 3.65mm, 1.9mm and 5mm respectively. 3. A method for preparing NdFeB magnets for small DC motors according to claim 1, wherein the NdFeB magnets are put into a rolling mill and rolled at a rolling temperature of 70°C . 4. A method for preparing an NdFeB magnet for a small DC motor according to claim 3, wherein the thickness of the NdFeB magnet after rolling is about 1.15mm. 5. a kind of NdFeB magnet preparation method that is used for small DC motor according to claim 3 is characterized in that, described rolling mill is a two-roll thin plate mill, and the diameter of described roll upper roll and lower roll is 90mm . 6. A kind of NdFeB magnet preparation method for small direct current motor according to claim 1, is characterized in that, described solid epoxy oligomer is selected from brominated bisphenol A type epoxy resin, phenolic type One of epoxy resin, bisphenol A epoxy resin, and phenol formaldehyde epoxy resin. 7. A kind of NdFeB magnet preparation method for small DC motor according to claim 1, is characterized in that, described powder curing agent is selected from amino resin, aromatic polyamine, hydrazide, resole phenolic resin , dicyandiamide, anhydride in one. 8. A method for preparing a NdFeB magnet for a small DC motor according to claim 1, wherein the lubricant is zinc octadecanoate. 9. A kind of NdFeB magnet preparation method for small DC motor according to claim 1, is characterized in that, When the magnetic powder described in step (1) is anisotropic HDDR magnetic powder, the mass percentages of anisotropic HDDR magnetic powder, solid epoxy oligomer, curing agent and lubricant are respectively 96.2-98.1wt%, 1.5-3.0wt% , 0.1～0.3wt%, 0.3～0.5wt%; When the magnetic powder described in step (1) is isotropic spherical magnetic powder, the mass percentages of isotropic spherical magnetic powder, solid epoxy oligomer, curing agent and lubricant are respectively 96.1-98.1wt%, 1.5-3.0wt% , 0.1-0.2wt%, 0.3-0.7wt%. 10. A kind of NdFeB magnet preparation method for small DC motor according to claim 9, is characterized in that, The anisotropic HDDR magnetic powder is composed of: Nd: 10% to 15%, Dy: 0.1% to 0.5%, Co: 5% to 20%, Zr: 0.05% to 0.2%, Ga: 0.2% to 0.9%, B: 5% ~ 10%, the balance is Fe; The isotropic spherical magnetic powder is composed of Nd: 7.0%-9.5%, B: 5%-6%, Ti: 0.2%-0.4%, Zr: 0.1%-0.25%, and the balance is Fe.