JP6618836B2 - Manufacturing method of rare earth sintered magnet - Google Patents

Description

  The present invention relates to a method for producing a rare earth sintered magnet.

  In applications such as communication devices and acceleration sensors, rare earth sintered magnets such as Sm-Co (samarium-cobalt) and Nd-Fe-B (neodymium-iron-boron) are widely used. Among these, small-sized rare earth sintered magnets whose both ends are smaller than 10 mm are required to have various shapes and dimensions in accordance with applications, such as a cylinder, a cylinder, and a rectangular parallelepiped. On the other hand, among these magnets, in a magnet that is manufactured only in a small amount due to the demand for on-board equipment, the cost may not be commensurate when a mold having a desired shape is manufactured and manufactured. In such a case, a block having a larger sintered magnet is cut out and processed without using a mold, so that it is usually formed into a desired shape and size.

  This sintered magnet block body is obtained by subjecting a rare earth sintered magnet raw material powder produced by finely pulverizing a melted alloy to orientation in a magnetic field, press molding, sintering and aging heat treatment, etc. be able to. At the time of this press molding, the orientation of the raw material powder is tilted by tilting the direction of the magnetic field at the end of the compact. In the block body formed in this way, the orientation of crystal grains deviates from an ideal direction at the end, and the magnetization direction after magnetization is bent.

  In particular, the non-magnetized region (neutral zone), which is the boundary between the magnetic fields of the N and S poles, is not accurately formed in the direction perpendicular to the magnetizing direction, but is inclined obliquely in the magnetizing direction. It becomes an unsuitable magnet. Thus, a small magnet cannot be cut out and processed from the end of the block body where only a magnet with a tilted neutral zone can be obtained. For this reason, since the magnets that can be taken out from one block body are limited, the manufacturing yield is reduced.

  In order to improve such bending of the magnetization direction, for example, it has been proposed to improve the bending of the magnetization direction during press molding by using a mold used for press molding as a magnetic material. (For example, refer to Patent Document 1.)

Japanese Patent Laid-Open No. 9-35977

However, when a magnetic material is used for the die and punch constituting the mold, since the raw material powder is in direct contact with the raw material powder, the raw material powder tends to adhere to the die and punch, and the yield of the block itself is not sufficient. It will occur.
In view of such a problem, an object of the present invention is to provide a small magnet having a stable magnetization direction and to provide a method for manufacturing such a small magnet with a high yield.

This invention has the following structures as a structure which solves the said subject.
The method for producing a rare earth sintered magnet according to the present invention is to produce a molded body by applying a transverse magnetic field to a raw material powder filled in a cavity of a die consisting of a die, an upper punch, and a lower punch, and press-molding it. Next, in the method of manufacturing a rare earth sintered magnet produced by subjecting the molded body to heat treatment, then cutting out a plurality of the molded bodies and further processing them into a predetermined shape, a magnetic body is provided inside the upper punch and the lower punch. In the press molding, the orientation of the transverse magnetic field at the end of the cavity is maintained parallel to the orientation of the transverse magnetic field at the center in the height direction of the cavity.
According to the present invention, the magnetic body is provided inside the upper punch and the lower punch so as to be disposed at the upper and lower positions of the cavity of the mold during press molding. With this magnetic body, the magnetic field direction at the position of the end of the block molded body can be kept parallel to the vertical center of the cavity during press molding. Thereby, the neutral zone after magnetization of the small magnet cut out from the position of the edge part of a block molded object can be formed horizontally, and a manufacturing yield can be improved.

In the method for producing a rare earth sintered magnet according to the present invention, the die, the upper punch, and the lower punch are made of a non-magnetic cemented carbide at least at a position in contact with the raw material powder.
According to the present invention, the die, the upper punch, and the lower punch constituting the mold are not made directly from a magnetic material, but are made from a material containing a nonmagnetic cemented carbide, and the magnetic material is housed therein. The configuration. Thereby, adhesion of the raw material powder to the mold can be suppressed during press molding.

In the method for manufacturing a rare earth sintered magnet according to the present invention, the magnetic body is disposed inside the upper punch and the lower punch so as to be aligned with a height of a pole piece for applying a magnetic field during press molding. It is characterized by that.
According to the present invention, the size of the magnetic body accommodated in the upper punch and the lower punch can be minimized. Thereby, the strength of the upper punch and the lower punch can be sufficiently maintained.

In the method for producing a rare earth sintered magnet according to the present invention, the magnetic body is a magnet including an alloy having a composition the same as or close to that of the raw material powder.
According to the present invention, by using a magnet having the same or similar composition as the rare-earth sintered magnet to be produced as a magnetic material housed in the upper punch and the lower punch, the orientation magnetic field at the time of press molding can be set appropriately. Can do.

  According to the method for producing a rare earth sintered magnet of the present invention, a block-shaped molded body having a desired size and a stable magnetization direction can be produced. This makes it possible to provide a small amount and a wide variety of ultra-small sintered magnets with a high yield.

It is sectional drawing which shows the principal part of the press molding apparatus in a magnetic field which shows embodiment of this invention. It is sectional drawing which shows the detail of the positional relationship of a metal mold | die and a magnetic body which shows embodiment of this invention. It is a figure which shows an example of the rare earth sintered magnet produced by the manufacturing method of this invention.

(Outline of the present invention)
Hereinafter, a method for producing a rare earth sintered magnet according to the present invention will be described in detail with reference to the drawings.
The method for producing a rare earth sintered magnet according to the present invention includes a raw material step for obtaining a magnet powder as a raw material, a filling step for filling the magnetic powder of the raw material in a die comprising a die, an upper punch, and a lower punch, A molding process in which magnet powder in a mold is press-molded in a magnetic field to obtain a block body that is a molded body, a heat treatment process for the block body, and a processing process in which the block body after heat treatment is cut into a required size and processed into a desired shape It is comprised from each process of these.

  Here, the main part of the press forming apparatus in a magnetic field used in the filling step and the forming step, which are the main steps among the above steps, will be described with reference to FIG. A press forming apparatus 1 in a magnetic field shown in FIG. 1 includes a die 2 that defines a size in a side surface direction of a magnet to be molded, an upper punch 3 and a lower punch 4 that define a vertical size, and a pole piece for applying a transverse magnetic field. 5 and a coil 6. Then, at the time of press molding in the molding process, a cavity 7 is formed which is a space formed by the die 2, the upper punch 3, and the lower punch 4 in order to accommodate the magnet powder. The size of the cavity 7 is defined in plan view by the die 2, and the height is defined by the upper punch 3 and the lower punch 4.

  At the time of press molding of the present invention, the cavity 7 is filled with magnet powder. Then, a magnetic field is applied in the lateral direction from N to S in FIG. 1 by the pole piece 5 and the coil 6. While the magnetic powder is oriented in this magnetic field, the upper punch 3 and the lower punch 4 are moved up and down to compress the magnetic powder. Thereby, the block body which has predetermined | prescribed thickness and planar view shape can be shape | molded.

  In the present invention, in particular, by arranging the magnetic body 8 inside the upper punch 3 and the lower punch 4, the magnetic field orientation in the cavity 7 is kept parallel even at the end of the cavity 7 during press molding in the molding step. It has the feature that it can be.

(Mold)
Next, the details of the mold used in the filling step and the molding step of the rare earth sintered magnet in the present invention will be described.
In the mold shown in FIG. 2, a space is formed inside the upper punch 3 and the lower punch 4. A magnetic body 8 is accommodated in this space, and a sealing material 9 for confining the magnetic body 8 in the mold is accommodated.

  In the present invention, the die 2, the upper punch 3, and the lower punch 4 are each formed of a general material of a mold used in press molding, such as cemented carbide or alloy tool steel. In particular, at least a portion exposed on the side of the cavity 7 in contact with the raw material powder can suppress adhesion of the magnetic powder after molding to the mold by using a non-magnetic cemented carbide and maintain the yield. It is more preferable because it is possible. Examples of the non-magnetic cemented carbide include, but are not limited to, a WC—Ni alloy, a WC—Ni—Cr alloy, a WC—Ni—Cr—Mo alloy, and a WC—TiC—TaC alloy.

  The sealing material 9 combined with the upper punch 3 and the lower punch 4 is made of an alloy used for the upper punch 3 and the lower punch 4. This sealing material 9 is embedded from the outside after embedding the magnetic body 8 in the mold, and integrated with each of the upper punch 3 and the lower punch 4 by welding, brazing or the like. Although not shown, instead of using the sealing material 9, the upper punch 3 and the lower punch 4 are constituted by a plurality of parts, and the magnetic body 8 is accommodated inside the plurality of parts, and these are accommodated. You may form integrally by welding, brazing, screwing, etc.

(Magnetic material)
Next, the magnetic body 8 used in the present invention will be described in detail.
The present invention is characterized in that a magnetic material is arranged inside the upper punch 3 and the lower punch 4. With such a configuration, the magnetic field orientation in the cavity 7 can be kept parallel not only at the center but also at the end of the cavity 7 during press molding.

  As described above, the magnetic body 8 is accommodated in the upper punch 3 and the lower punch 4 shown in FIG. In the present invention, since a magnetic material is not used for a punch or die, or a magnetic material is not disposed in contact with the raw material powder at the tip of the punch, the raw material powder does not remain in the punch or die. Can be prevented and the production yield can be improved.

  The magnetic body 8 should just be arrange | positioned inside the upper punch 3 and the lower punch 4, and what kind of thing may be sufficient as a size and the position arrange | positioned. However, in order to keep the magnetic field orientation parallel to the entire cavity 7 during press molding, it is necessary that the magnetic body 8 be formed at a location close to the cavity 7 in the upper punch 3 and the lower punch 4. In particular, it is preferable that the magnetic body 8 is formed inside the upper punch 3 and the lower punch 4 so as to fit in the height position of the pole piece 5 (position of the broken line A in FIG. 2) during press molding. Moreover, it is more preferable that the position of the end portion of the magnetic body 8 is aligned with the height of the pole piece 5 (the position of the broken line A in FIG. 2). With such an aspect, in addition to being able to keep the magnetic field orientation in parallel with the minimum necessary configuration, the cost can be minimized and the strength of the upper punch 3 and the lower punch 4 can be maintained.

As the magnetic body 8, various materials having magnetic characteristics capable of keeping the magnetic field orientation in the cavity 7 in parallel can be used. In particular, if the magnetic body 8 includes an alloy having the same or similar composition as the rare earth sintered magnet produced according to the embodiment of the present invention, the magnetic characteristics are also approximated. They can be formed in parallel. Here, the approximate composition is that the composition of the magnet composing the magnetic body 8 is Sm ₂ Co ₁₇ , while the rare earth sintered magnet to be manufactured further contains trace elements such as Fe and Zr of less than 1% by mass. When added, or when a rare earth sintered magnet having a composition in which a part of Sm ₂ Co ₁₇ is replaced with another rare earth element such as Y is produced. For example, when the magnetic body 8 is a sintered magnet manufactured using the same raw material powder as that of the rare earth sintered magnet 1 to be manufactured, the upper punch 3 and the lower punch 4 containing the magnetic body 8 are used to form the composition. Of these, other rare earth sintered magnets that differ only in the configuration of trace elements may be press-molded.

The magnetic body 8 is preferably an R—Co (rare earth-cobalt) based sintered magnet such as SmCo ₅ or Sm ₂ Co ₁₇ . Since sintered magnets made of these materials have better corrosion resistance than ferrite magnets and Nd—Fe—B magnets, the durability of the upper punch 3 and the lower punch 4 can be ensured.
The magnetic body 8 made of a sintered magnet may be chamfered or rounded in each of the punch and the magnetic body in order to facilitate embedding in the internal space of the upper punch 3 and the lower punch 4.

  In the said embodiment, although the magnetic body 8 showed about the aspect comprised with a rare earth sintered magnet, it is not restricted to this, It can be set as the magnetic body 8 which consists of a bond magnet containing the powder of rare earth magnets. In this case, it is preferable not to use a sintered magnet as the magnetic body 8 in that the magnet can be embedded easily without undergoing processing such as cutting the sintered magnet.

  Specifically, the magnetic body 8 made of a bond magnet can be disposed on the upper punch 3 and the lower punch 4 as follows. First, a bond magnet material consisting of a mixture of magnet powder and resin binder is embedded in a space 8 formed inside the upper punch 3 and the lower punch 4 and heated in accordance with the curing temperature of the resin to bond the magnet. To fix. Next, the sealing material 9 is further embedded in and integrated with the upper punch 3 and the lower punch 4. Furthermore, the magnetic body 8 made of a bonded magnet is magnetized by applying a magnetic field from above.

(Rare earth sintered magnet)
Next, the rare earth sintered magnet manufactured in the present invention is shown in FIG.
The rare earth sintered magnet 10 produced by the manufacturing method of the present invention has a non-magnetized region (neutral zone) 13 which is a boundary region generated between a portion that becomes the N pole 11 and a portion that becomes the S pole 12 after magnetization. have. Here, when the orientation of the rare earth sintered magnet 10 is defined so that the N pole 11 and the S pole 12 are arranged vertically, if the non-magnetized region 13 is formed horizontally without inclination, a sensor or the like It can correspond to the accuracy required by the equipment to be used.

The shape of the rare earth sintered magnet 10 can be various shapes such as a cylindrical shape and a rectangular parallelepiped in addition to the columnar shape shown in FIG.
In addition, the kind of the rare earth sintered magnet in the present invention is not particularly limited, and an Sm—Co based material or an Nd—Fe—B based material can be used. Among these, Sm-Co-based rare earth sintered magnets such as SmCo ₅ and Sm ₂ Co ₁₇ are particularly suitable for use in a high-temperature environment because of their high Curie temperature and excellent high-temperature characteristics. It can be said that it is an aspect.

(Production method of rare earth sintered magnet)
Here, each process of the manufacturing method of the rare earth sintered magnet in this invention is explained in full detail.
(Raw material process)
The raw material powder of the rare earth sintered magnet produced in the present invention is obtained as follows. First, raw materials composed of samarium and cobalt corresponding to the target composition and trace element metals added as necessary are blended and heated and melted using a vacuum melting furnace or the like to produce an alloy. Next, the obtained alloy is coarsely pulverized, and then finely pulverized using a jet mill or the like until the maximum length becomes a particle size of about several μm, thereby obtaining a target raw material powder.
If necessary, a release agent such as stearate may be added to and mixed with the raw material powder.

(Filling process)
The raw material powder produced by the above raw material process is filled in a die composed of a die 2, an upper punch 3, and a lower punch 4 constituting the magnetic field press molding apparatus shown in FIG. First, a concave space is formed by using the die 2 and the lower punch 4, and necessary raw material powder is filled by scraping. Thereafter, the position of the lower punch 4 is lowered, and the upper punch 3 is pushed into the concave space, whereby the raw material powder is filled in the cavity 7.
The cavity 7 is preferably a rectangular parallelepiped having one side of 100 mm or less, for example, a rectangular parallelepiped having one side of 20 to 40 mm.

(Molding process)
Next, this raw material powder is molded in a magnetic field.
From the side of the die 2, while applying a transverse magnetic field using the pole piece 5, the upper punch 3 and the lower punch 4 are brought close to each other to press-mold the raw material powder. At this time, the raw material powder is compressed in a state of being oriented in the horizontal direction.

The dimensions of the magnetic body 8 embedded in each of the upper punch 3 and the lower punch 4 are, for example, when the cavity 7 is a rectangular parallelepiped having a length × width × height of 40 × 30 × 40 mm, the upper punch 3 and the lower punch 4. The magnet embedded within can be 30 × 20 × 20 mm. The size of the magnet to be embedded can be appropriately determined depending on the size of the rare earth sintered magnet to be produced, the strength of the upper and lower punches, and the like. In particular, if the end of the pole piece 5 and the outermost end of the magnet to be embedded are substantially equal due to the size of the outer periphery of the pole piece 5 to which a magnetic field is applied from the side during press molding, the magnetization by the pole piece 5 The direction can be substantially parallel.
In this manner, a molded body obtained by press molding the raw material powder is produced.

(Heat treatment process)
Further, the compact is sintered by heating at a temperature higher than the melting point. For example, in the case of an Sm ₂ Co _17- based magnet compact, it is heated to about 1200 ° C. Then, a block body is produced by performing an aging heat treatment.

(Processing process)
Finally, the block body obtained by the heat treatment step is cut into a desired size and processed into a necessary shape by cutting or the like, whereby a magnet having a desired shape can be obtained. The shape of the magnet can be various shapes such as a rectangular parallelepiped, a column, and a cylinder. As a preferred dimension, for example, the outer dimension can be 10 mm or less.

DESCRIPTION OF SYMBOLS 1 ... Magnetic field press molding apparatus 2 ... Die 3 ... Upper punch 4 ... Lower punch 5 ... Pole piece 6 ... Coil 7 ... Cavity 8 ... Magnetic body 9 ... Sealing material 10 ... Rare earth sintered magnet 11 ... N pole 12 ... S Pole 13 ... non-magnetized region (neutral zone)

Claims (2)

And the die, to prepare an upper punch, a molded body by press-molding while applying a transverse magnetic field with a pole piece in the raw material powder filled in a cavity of a mold consisting of a lower punch, then the molded body after Netsusho management excised plurality, in the manufacturing method of the rare earth sintered magnet produced by further processing into a predetermined shape,
The die, the upper punch, and the lower punch are made of a non-magnetic cemented carbide at least at a location in contact with the raw material powder,
Inside the upper punch and the lower punch, a magnetic body made of a sintered magnet containing an alloy having the same or similar composition as the raw material powder is disposed,
In the press molding, by arranging the magnetic body so as to be close to the cavity and at the height position of the pole piece, the orientation of the transverse magnetic field at the end of the cavity can be adjusted in the height direction of the cavity. A method for producing a rare earth sintered magnet, characterized in that the rare earth sintered magnet is maintained parallel to the orientation of the transverse magnetic field at the center of the magnet. The magnetic material, so that the position of the end portion during press forming are aligned to the height position location of the pole pieces, according to claim 1, characterized in that arranged inside of the upper punch and the lower punch Manufacturing method of rare earth sintered magnet.

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