JP2870883B2 - Method for producing radially anisotropic NdFeB magnet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a radially anisotropic NdFeB-based magnet, and more particularly, to a radially anisotropic NdFeB having a high yield and an annular cross section. The present invention relates to a method for manufacturing a system magnet.

(Prior art) Recently, NdFe has been used as a magnet with low cost and excellent magnetic properties.
B magnets are attracting attention. When this NdFeB-based magnet is used for motors, etc., its shape should be a thin sleeve or ring, and its radial direction (radial direction)
It is preferable to perform magnetic anisotropy.

As a method of manufacturing an NdFeB-based ring magnet having such radial anisotropy, for example, the following method is available.

That is, first, the NdFe
After ultra-quenching the melt of the B-based alloy to prepare its ribbon or flake, it is roughly pulverized. Next, as shown in FIG. 16, after the lower punch 1 is filled with the above-mentioned alloy powder 3 in a die 2 arranged at one end, an upper punch 4 is set thereon, and for example, Under an inert atmosphere such as a vacuum or Ar gas atmosphere, the lower punch 1 and the upper punch 4 are relatively moved in the direction of the arrow at a temperature of 600 to 900 ° C., preferably about 700 to 800 ° C. 2ton / cm
^2. Hot-press at a pressure of preferably 1 to 1.5 ton / cm ^{2 to} preform a magnetically isotropic solid block. At this time, the solid block has a theoretical density ratio of 99% or more.
In addition, at the time of this preforming, if a lubricant such as sodium stearate is added, for example, about 2% by weight or less,
This is preferable because the lubricity between the solid block 3 and the die 2 is improved and molding is facilitated.

When forming an annular hollow block, as shown in FIG. 17, the alloy powder is placed in a forming die in which a center core 5 having a predetermined diameter penetrating the center of the lower punch 1 and the upper punch 4 is arranged. After filling the alloy powder 3, the alloy powder 3 may be hot pressed with the upper punch 4 and the lower punch 1.

Next, the NdFeB-based magnet molded body molded as described above is subjected to plastic deformation with a surface area reduction of 40% or more at a temperature of 900 ° C or less under a vacuum or an inert atmosphere, and then, in a radial direction. Magnetization causes magnetic anisotropy in the radial direction.

The manufacturing example in this case will be described with reference to a solid block. As shown in FIG. 18, a solid preformed as shown in FIG. 16 is formed on a lower punch 1 'arranged at the lower end of a die 2. After the block 3 'is arranged and the upper punch 4' having a diameter smaller than the inner diameter of the die 2 'is set at the center thereof, the upper punch 4' is lowered by a predetermined pressure as shown by an arrow in FIG. .

The solid block 3 'is pressed by the mold surface of the upper punch 4', and is restrained by the inner wall 2'a of the die 2 'and the mold surface 1'a of the lower punch 1'. It is plastically deformed by being extruded into an annular space formed by the upper punch 4 '. As a result, a bottomed cylindrical molded body is obtained.

Next, by cutting off the lower and lower parts of the molded body and subjecting the obtained ring molded body to magnetization treatment in the radial direction, it has a magnetic anisotropy in the radial direction, and is a radially anisotropic NdFeB-based ring with a circular shape. A magnet is obtained.

(Problems to be Solved by the Invention) However, in the forming block 3 'in FIG.
The surface portion 3'a which is not in contact with the upper punch 4 'is a free surface on which no deformation load is applied, and is hardly restrained by the upper punch 4' or the inner wall 2'a of the die 2 '. The amount of deformation is extremely small. Therefore, the magnetic anisotropy of the upper end portion 3'a after the processing shown in FIG. 19 does not sufficiently proceed, and its magnetic characteristics deteriorate. In addition, the inner wall of the obtained ring-shaped magnet (the portion that comes into contact with the upper punch 4 ') extends downward from the free surface portion of the upper surface.
Periodic cracks running diagonally occur. Therefore, it is necessary to cut off the upper end portion by a predetermined length and to remove cracks on the inner wall. As a result, the yield of the obtained product decreases.

The present invention solves the above-mentioned problems, and can give a large plastic deformation also in the vicinity of the above-mentioned free surface, enhances the magnetic anisotropy of the upper end portion of the magnet after molding, and thereby reduces the amount of cut off of the upper end portion. It is an object of the present invention to provide a method for manufacturing a radially anisotropic NdFeB-based magnet capable of realizing a high yield by reducing cracks and preventing cracks on an inner wall.

(Means for Solving the Problems) In order to achieve the above object, in the present invention,
In a forming die in which a first punch is arranged at one end, a magnetically isotropic NdFeB-based magnet formed body preformed in a solid or hollow shape is arranged, and the other of the forming die From the end of the cylindrical punch, a cylindrical punch having a predetermined thickness and a second punch are disposed in a hollow portion of the cylindrical punch, and while applying a predetermined pressure to the cylindrical punch, the first punch and the second punch are arranged. A method for producing a radially anisotropic NdFeB-based magnet is provided, wherein the NdFeB-based magnet compact is plastically deformed by relatively moving a punch and then magnetized in a radial direction.

Hereinafter, the method of the present invention will be described with reference to the accompanying drawings in the case where the NdFeB-based magnet molded body is a solid block.

First, as shown in FIG.
A first punch (a lower punch in the figure) 12 having a diameter substantially equal to the inner diameter of the die 11 is fitted into one end (the lower end in the figure) of the die 11, and the lower end of the die 11 is sealed.

In this die 11, NdFeB is placed on the mold surface 12a of the lower punch 12.
A solid block 13, which is a system magnet molded body, is set. The solid block 13 is formed, for example, by a hot press method using a mold as shown in FIG.

A cylindrical punch 14 having an outer diameter substantially equal to the inner diameter of the die 11 and having a predetermined thickness is fitted into the die 11, and a die surface 14 thereof is provided.
a is in annular contact with the upper surface of the solid block 13. An upper punch 15 having a diameter substantially equal to the diameter of the hollow portion is inserted into the hollow portion of the cylindrical punch 14, and the mold surface 15 is formed.
a is in contact with the upper surface of the solid block 13.

The atmosphere at this time is a vacuum of 1 Torr or less or an atmosphere of an inert gas such as Ar to prevent the solid block 13 from being oxidized.

When an antioxidant film that does not decompose even under the temperature at the time of plastic deformation described below is formed on the surface of the solid block 13 by plating or spraying Cu, Ni, or the like, an oxidizing atmosphere such as the atmosphere is not used. In the lower part, the plastic deformation described below can be performed, and the antioxidant coating exerts lubricity between the die 11 and the wall surface of the upper punch 15 to smoothly perform the composition deformation of the solid block 13. This is preferable because

When the solid block 13 is set in the mold, the solid block 13 is heated by high-frequency heating in advance, or the entire mold is preheated, and the temperature of the solid block 13 is set to 650 to 900 ° C., preferably 700 It is preferred to keep the temperature at 〜850 ° C.

Next, while applying a predetermined pressure to the cylindrical punch 14,
Lower upper punch 15. At this time, the pressure of the upper punch 15 is set to be higher than the applied pressure of the cylindrical punch 14.

The central part of the solid block 13 is pressed by the mold surface 15a of the upper punch 15, and as a result, as shown in FIG. A predetermined thickness formed by the inner wall and the peripheral surface of the upper punch 15 to be pressed down, that is, a gap having a thickness corresponding to the thickness of the cylindrical punch 14 is extruded upward and processed into a bottomed cylindrical molded body 13 ′. Is done. At this time, since the upper end portion 13'a of the peripheral wall of the cylindrical body 13 'which is in contact with the mold surface 14 of the cylindrical punch is processed while being restrained by the cylindrical punch, the inner wall of the die, and the upper punch, Unlike the case of the conventional free surface state as shown in FIGS. 18 and 19, the occurrence of cracks on the inner wall can be prevented.

In order to sufficiently secure the magnetic anisotropy of the obtained ring-shaped magnet, in the pressing process shown in FIGS. 1 and 2,
The area reduction rate of the solid block 13 is 40 to 80%, preferably 55 to 65
%, The area of the end face of each punch and the pressing force are set.

3 and 4 show another method of the present invention, in which the mold surface of the cylindrical punch 14 is an inclined surface 14b having an angle θ.

In this case, the surface pressure of the cylindrical punch 14 and the upper punch 15 is 1 to 4 ton.
/ cm ² , preferably 1.5-3 ton / cm ² . After the peripheral portion 13a of the solid block 13 is flow-deformed and filled in the gap 14c formed between the cylindrical punch 13 and the mold surface (inclined surface) 14b, only the upper punch 15 is pressed down, The actual block 13 is plastically deformed, and as shown in FIG. 4, the cylindrical molded body 1 in which the upper end portion 13'a of the peripheral wall is inclined at an angle θ.
Form 3 '.

Also in this case, in order to obtain a sufficient magnetic anisotropy, the area reduction rate must be reduced to 40 to 40 in the process of plastic deformation shown in FIGS.
It should be 80%, preferably 55-65%. Pushing force at this time, 2~5ton / cm ² in surface pressure of the upper punch 15, preferably 2.5~4ton / cm ^2. Further, for the cylindrical punch 14, a surface pressure corresponding to its own weight may be used,
Applying a surface pressure of about 1.0 ton / cm ² is effective in preventing the occurrence of internal cracks in the obtained ring-shaped magnet.

As described above, when the mold surface of the cylindrical punch 14 is formed into the inclined surface 14b, and the peripheral portion 13a of the solid block 13 is first subjected to flow deformation at this portion, the tip portion 13'a of the obtained ring-shaped magnet is formed. Since the magnetic anisotropy proceeds well, it is possible to reduce the number of the excision portions at the tip as in the related art, and it is possible to improve the yield. In this case, the larger the angle θ is, the more effective the flow deformation becomes. However, in practice, 30 ° or more is sufficient.

Although FIGS. 3 and 4 show the case where the inclined surface 14b of the mold surface of the cylindrical punch 14 is formed from the hollow portion to the outer peripheral surface, the inclined surface 14b is limited to this embodiment. Instead, a surface inclined from the lower end of the outer peripheral surface toward the hollow portion may be used. Also in this case, the peripheral portion 13a of the solid block flows and deforms into the gap formed by the inclined surface and the upper punch 15, so that the upper end portion is plastically deformed.

FIGS. 5 and 6 show still another method of the present invention. In this case, the mold surface of the cylindrical punch 14 has a stepped shape.

Also in this case, the peripheral portion 13a of the solid block 13 has an annular space 14d formed by the cylindrical punch 14 and the inner wall of the die 11.
And the upper end portion 13 'in FIG.
a is plastically deformed and magnetic anisotropy proceeds.

The state of the magnetic anisotropy at this time changes depending on the shape of the step portion of the cylindrical punch 14. For example, as shown in FIG. 5, the thickness of the cylindrical punch 14 and t _1, when the radial depth of the stepped portion was _{t 2, (1-t 2} / t 1) in × 100 When the indicated thickness reduction (%) increases, the magnetic properties of the peripheral portion 13'a of the obtained cylindrical molded body 13 'improve. Peripheral This, the wall thickness rolling reduction rate is increased, it t ₂ when t ₁ is constant is small, that is that the voids 14d is small, therefore, the flow deformation in the gap 14d This is because the number of the portions 13a increases and the degree of the plastic deformation increases. It is preferable that the thickness reduction is 20% or more.

Although FIGS. 5 and 6 show the case where the air gap 14d is formed outside the cylindrical punch 14, the method of the present invention is not limited to this mode, and the mold surface of the cylindrical punch 14 may be formed. By forming a step on the inside, a gap in which the peripheral portion 13a of the solid block can flow and deform may be formed on the inside, that is, on the upper punch 15 side.

The in FIGS. 7 and 8 show an alternative of the method of the present invention FIG, which is a mold surface of the cylindrical punch 14 flat, in the direction of the real block 13, depth width cylindrical in l ₀ This is a case where a step portion having a shape substantially equal to the thickness of the punch 14 is formed.

Also at this time, if the upper punch 15 is lowered, the cylindrical punch
The peripheral portion 13a of the solid block 13 which is in contact with the flat mold surface of 14 is deformed upward in the die 11 while being restrained, so that the upper end portion 13 of the obtained cylindrical molded body 13 'is formed. 'A undergoes plastic deformation, and the magnetic anisotropy of that portion is realized.

In this case, the magnetic the anisotropy of the state of the upper end portion 13'a is affected by the depth l ₀ of the stepped portion, as the l ₀ is increased,
An improvement in magnetic anisotropy is obtained. This is as l ₀ is large, because the degree of plastic deformation of the peripheral portion 13a of the hollow block 13 is increased.

FIGS. 9 and 10 show another method of the present invention, in which the lower punch 12 is driven in the method shown in FIGS. 3 and 4, so-called forward extrusion.

FIG. 11 and FIG. 12 are diagrams showing the method of the present invention when the NdFeB-based magnet molding is a hollow block 13 ″.

In the figure, a lower punch 12 having a center hole 12b having a predetermined diameter formed in the center is set at the lower end of a die 11, and a hollow block 13 ″ is disposed thereon.
A cylindrical punch having a predetermined thickness and an inclined mold surface
The upper punch has a stepped shape in the hollow part, and the tip 15b has the same diameter as the diameter of the hollow part of the hollow block 13 ″ and the diameter of the center hole 12b of the lower punch 12. 15 is inserted.

When the upper punch 15 is moved by a predetermined amount by lowering the cylindrical punch 14 and the upper punch 15, as shown in FIG. 12, the peripheral portion 13 "a of the hollow block 13" is pushed upward, and as a whole, A ring-shaped magnet is formed. Also in this case, since the peripheral portion 13 "a of the hollow block 13" is plastically deformed, its magnetic anisotropy is progressing.

(Examples of the Invention) Example 1 A melt of a magnetic alloy having a plasticity of Nd ₁₄ Fe ₇₈ B ₆ Co ₇ is super-quenched to form a 20 μm-thick ribbon, which is pulverized to a size of about 200 μm.
A μm flake powder was obtained.

This powder was filled in a preforming mold having the structure shown in FIG. 16 and was heated at 750 ° C. and 1 to 1 under Ar gas atmosphere.
Hot pressing was performed under the condition of n / cm ² to obtain a solid block having a diameter of 30 mm and a height of 79 mm. This solid block has a theoretical density ratio of 9
9.5%.

Next, the solid block 13 is set in a mold having the structure shown in FIG. 3, and the inclination angle θ of the mold surface of the cylindrical punch 14 is changed to make the inner diameter 22 mm, the outer diameter 30 mm, and the height 25 mm Was manufactured.

The manufacturing conditions were as follows: Ar gas atmosphere, temperature 750 ° C,
2.5 ton / cm ² applied pressure of both punches 14 and 15 until the material is filled in the gap 14b, then 0.5 ton / cm ² into a cylindrical shape punch 14, pressure was applied of 4 ton / cm ² to the upper punch 15 .

The bottom of the obtained molded product 13 'was cut off to form a sleeve, and the sleeve was magnetized in the radial direction to obtain a radially anisotropic ring magnet.

The maximum magnetic energy product of the ring magnet in the radial direction was measured, and the distribution of the magnet in the longitudinal direction was examined.

In this case, since the maximum magnetic energy product at a position 10 mm or more below the upper end of the ring magnet was 34 MGOe, the variation up to 5% reduction was allowed, and the maximum magnetic energy product was 32.3 MGOe or more. Indicates,
It was examined as the relationship between the distance l from the upper end of the magnet to the lower side and θ. The results are shown in FIG.

As is clear from FIG. 13, when the inclination angle θ of the mold surface of the cylindrical punch 14 is increased, l representing the length of the magnetically insufficient region rapidly decreases.

Example 2 The solid block used in Example 1 was set in a mold having the structure shown in FIG. At the mold surface step portion of the cylindrical punch 14, the values of t ₁ and t ₂ are changed to reduce the thickness reduction ratio: (1−t ₂ /
t ₁₎ was manufactured sleeve-shaped magnet 13 'in different states × 100 (%).

For these magnets, the distribution of the maximum magnetic energy product in the longitudinal direction was measured in the same manner as in Example 1. FIG. 14 shows the relationship between the l value and the thickness reduction at that time.

As is clear from FIG. 14, t ₂ is reduced, i.e., l value as the gap 14c to increase rapidly decreases.

Example 3 At the time of the preforming in Example 1, a solid block was formed by providing steps of various depths (l ₀ ) in the peripheral portion.

The solid block 13 was set in a mold having a structure as shown in FIG. 7 to produce a sleeve-like magnet. Per resulting magnet, in the same manner as in Example 1, to measure the maximum magnetic energy product in the longitudinal direction, it was examined a relationship between the depth l ₀ of the stepped portion of the l at that time. The results are shown in FIG.

As is clear from FIG. 15, when l ₀ increases, that is, when the step of the solid block 13 is deepened, the l value sharply decreases.

(Effect of the Invention) As is clear from the above description, according to the method of the present invention,
The peripheral part of the molded block, which was less likely to undergo plastic deformation as a free surface in the past, undergoes plastic deformation by flowing while being constrained by the cylindrical punch, so the upper end of the resulting magnet is magnetically deformed. Anisotropy is also appropriate,
As a result, the cut amount of the upper end portion is reduced, and the overall yield can be improved.

Therefore, the method of the present invention is inexpensive and has excellent magnetic properties.
Its industrial value is great as a method for producing NdFeB ring magnets.

[Brief description of the drawings]

1 and 2 are cross-sectional views for explaining one example of the method of the present invention, FIGS. 3 and 4 are cross-sectional views for explaining another example of the method, and FIGS. FIGS. 7 and 8 are cross-sectional views for explaining another method example, and FIGS. 9 and 10 are cross-sectional views for explaining another method example. Sectional views of FIGS. 11 and 12
FIG. 13 is a cross-sectional view for explaining an example of application of the method of the present invention to a hollow block. FIG. 13 is a graph showing the relationship between l and θ in Example 1. FIG. FIG. 15 is a graph showing the relationship with the ratio in the third embodiment.
graph showing the relationship between l _0, Fig. 16 is a sectional view for explaining a preform of solid blocks, FIG. 17 is a sectional view for explaining a preform of a hollow block, FIG. 18 and 19 FIG. 1 is a sectional view for explaining a conventional method. 11 ... die, 12 ... lower punch (first punch), 12a ...
… Mold surface, 12b …… center hole, 13 …… solid block, 13a ……
Peripheral part of solid block, 13 ': molded magnet (cylindrical molded body), 13'a: Upper end of molded magnet, 13 "... hollow block, 14: cylindrical punch, 14a: cylindrical Punch die surface, 14b ... inclined surface, 14c, 14d ... gap, 15 ... upper punch (second punch), 15a ... die surface, 15b ... tip.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Yoshida 18 Minamikamochi, Kagiyacho, Tokai City, Aichi Prefecture (72) Inventor Toshiya Kinan 18 Minamikamochi, Kagiyacho, Tokai City, Aichi Prefecture (56) References JP Hei 1-169910 (JP, A) JP-A-62-10259 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01F 1 / 08,41 / 02 B22F 3 / 00,3 / 20 C22C 33/02

Claims (4)

(57) [Claims] 1. A magnetically isotropic NdFeB-based magnet molded body preformed in a solid or hollow shape is arranged in a molding die in which a first punch is arranged at one end. From the other end of the forming die, a cylindrical punch having a predetermined thickness and a second punch inserted into the hollow portion of the cylindrical punch are arranged, and while applying a predetermined pressure to the cylindrical punch, The first punch and the second punch are relatively moved to form the NdFeB
A method for producing a radially anisotropic NdFeB-based magnet, which comprises subjecting a magnet-based molded body to plastic deformation and then magnetizing in a radial direction. 2. The method according to claim 1, wherein said plastic deformation is performed at a temperature of 650 to 900 ° C. in a vacuum of 1 Torr or less or in an inert gas atmosphere. 3. The method according to claim 1, wherein an antioxidant coating is applied to the surface of the NdFeB-based magnet molded body, and the plastic deformation is performed in an atmosphere at 650 to 900 ° C. 4. The manufacturing method according to claim 1, wherein the cylindrical punch has a mold surface which is an inclined surface or a step surface.