JPH06330103A - Die for compacting magnetic powder - Google Patents

Abstract

PURPOSE:To provide a die for compacting, a magnetic powder, with which the parallel orientation and the radial orientation can be appropriately mixed as the orientation in the easy axis of magnetization of the compact of the magnetic powder, by arranging plural ferromagnetic iron cores respectively on the inside and outside of the circular arc of each of the hollow parts having circular-arcuate cross sections, in which the magnetic powder is formed into compacts through filling the hollow parts with the magnetic powder. CONSTITUTION:In the die for compacting a magnetic powder, the hard metallic part 82 that is shrinkage-fitted with the metallic ring 80 made of non-magnetic stainless steel is provided with the hollow parts 84a and 84b having circular-arcuate cross sections which are filled with the magnetic powder. The magnetic powder is formed into compacts for the magnets having circular-arcuate cross section by the punching while applying magnetic fields to the magnetic powder from the right and left. The inside magnetic core for the radial orientation 86 and the inside magnetic cores for the parallel orientation 90a to 90d are arranged on the inside of the circular arc of each of the above hollow parts 84a and 84b. On the other hand, the outside magnetic cores for the radial orientation 88a and 88b and the outside magnetic cores for the parallel orientation 92a to 92d are arranged on the outside of the circular arc of each of the hollow parts 84a and 84b. Thus the magnetic field in the central part of the circular-arcuate cross section of each of the hollow parts 84a and 84b is oriented radially and the magnetic fields in both of the end parts of the above cross section are oriented parallel to the symmetry axis of the circular-arcuate cross section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold used in the molding step, which is the first step in the production of permanent magnets by powder metallurgy, and in particular, molding is performed while orienting the easy magnetization direction of magnetic powder in a magnetic field. Regarding the mold to do. The permanent magnet produced by sintering and heat-treating a molded body molded using the magnetic powder molding die of the present invention is used for a synchronous motor such as an industrial motor and a motor for electric equipment of an automobile.

[0002]

2. Description of the Related Art An anisotropic permanent magnet is generally produced by a powder sintering method by orientation in a magnetic field. For example, in the case of producing a rare earth permanent magnet, finely pulverized magnetic powder having a particle size of 3 to 4 μm is placed in a magnetic field of 10 to 15 kOe, and the magnetic powder is pressed with the easy magnetization direction oriented in the magnetic field direction. Molding is performed to form a molded body. This manufacturing method makes it possible to anisotropy the molded body (make the direction of easy magnetization of the molded body the direction of the applied magnetic field). The produced compact is subjected to a sintering heat treatment to become an anisotropic sintered magnet. During this sintering heat treatment, the easy magnetization direction of the compact is basically preserved. Therefore, of the factors that determine the easy magnetization direction of the magnet, the direction of the applied magnetic field during press molding is the most important factor.

An apparatus for pressing while applying a magnetic field is
Usually, it has a structure in which an electromagnet is attached to a hydraulic press or a mechanical press. FIG. 2 shows two examples of the press device in a partial sectional view.

Magnetic powder 6a is placed in the die 4a (4b).
(6b), and the magnetic field generating coils 10a and 10b (1
0c and 10d) indicate arrows 12a and 12b (12c and 1).
Magnetic powder 6a (6b) by generating a magnetic field in the direction of 2d)
The direction of easy magnetization is oriented as shown by an arrow 8a (8b). Further, the upper punch 14a (14b) and the lower punch 16
a (16b) and arrows 18a (18b) and 20 respectively
Press in the direction of a (20b). Reference numeral 2 in FIG.
2c and 22d are pole pieces.
In (a), the upper punch 14a and the lower punch 1 made of a magnetic material are used.
6a also serves as a pole piece.

An apparatus in which the magnetic field directions 12a and 12b are parallel to the press directions 18a and 20a as shown in FIG. 2A is a longitudinal magnetic field forming apparatus, and the magnetic field direction 12c is as shown in FIG. 2B.
And 12d and the device in which the press directions 18b and 20b are perpendicular to each other are called transverse magnetic field forming devices.

In FIG. 2, since the generated magnetic fields are parallel, the direction of easy magnetization of the molded body to be molded is also parallel. On the other hand, when it is desired to make the easy magnetization direction of the molded body a radial orientation (radial orientation), it is necessary to make it as shown in FIG. That is, the coils 32a and 32b are arranged so that the facing surfaces of the pole pieces 30a and 30b have the same poles.
It is necessary to pass a current through. By doing so, the magnetic force lines pseudo-flow in the radial direction as shown by the arrow 34. Therefore, if a die provided between the pole pieces 30a and 30b is filled with magnetic powder and press-molded, it is possible to mold a molded body in which the direction of easy magnetization is radial orientation.

However, the flow of magnetic field lines in the case of FIG. 3 and FIG.
In this case, the flow of magnetic force lines is significantly different, and therefore the shape of the yoke provided outside the die and the pole piece must be different in each case. Therefore, it is difficult to produce both a parallel-oriented molded body and a radial-oriented molded body with the same pressing device (a pressing device having a yoke of the same shape). That is, when press-molding a molded body having a different orientation in the easy magnetization direction, there has been a problem that the shape of the pressing device itself must be different.

Next, the shape of a magnet actually used in a motor and the like, and problems in the motor will be described.

The magnet used in the motor is a roof tile magnet having an arc-shaped cross section as shown in FIG. 4 (hereinafter referred to as an arc magnet).
In many cases, the magnetization is oriented in the thickness direction (radial direction) of the magnet as shown by the arrow 40. A plurality of such magnets are provided on the yoke, and a rotor (or a stator) of the motor is manufactured.

In the case of a slotted motor, a ripple of static torque called cogging torque becomes a problem. That is, the cogging torque hinders smooth rotation of the motor, and vibration and magnetic noise of the motor due to the cogging torque are also problems. Moreover, if the magnet is made to have high characteristics in order to increase the static torque, the cogging torque also increases, and there is a big problem that it is not possible to achieve both a large static torque and a small cogging torque.

Although the magnetic flux density of the gap between the rotor and the stator changes along the direction of rotation of the rotor (a plurality of arc-shaped magnets are connected so that the directions of magnetization are alternated, The outer portion of the motor (the portion that becomes the rotor or the stator) is formed, and the magnetic flux density changes significantly at the joint between the arc-shaped magnets. If the change is rapid, a large cogging torque is generated. Therefore, various methods have been tried for smoothing the change of the magnetic flux density like a sine waveform.

One is a method of twisting a motor slot or a magnet. However, when twisting the slot, there are many problems in terms of cost and manufacturing, such that it is troublesome to manufacture this twisted shape and winding to the twisted slot becomes difficult. On the other hand, when twisting the magnet,
There are many problems in terms of cost and manufacturing, such as chipping easily occurring during press molding of the magnet, shape deformation easily occurring during sintering, and further difficult processing.

The other method is to reduce the cogging torque by thinning the both ends of the magnet (the two ends of the arc of the magnet in FIG. 4) to smooth the change in the magnetic flux density at this part. .

The thin arc-shaped magnets at both ends are produced by forming a compact in that shape in advance, or by molding a non-thin arc-shaped compact and sintering it, followed by grinding.
Can be made. However, in the case where both ends are thinly formed in advance, there is a problem that they are easily deformed during sintering, and when grinding is performed after sintering, the material yield is reduced and the manufacturing cost is high. There's a problem.

The other one is a method in which the arcuate magnet is oriented in the easy magnetization direction so that the central portion is close to the radial orientation and the both ends are oriented in parallel. The reason why this method is effective is described below.

As shown in FIG. 5, when the orientation 52a of the arcuate magnet 50a in the easy magnetization direction is parallel (FIG. 5 (a)), the radial magnetic flux density B is sinusoidal (see FIG. 5 (b)). ))
And the orientation 52b of the arc magnet 50b in the easy magnetization direction.
Is radial orientation (FIG. 5C), the radial magnetic flux density B is trapezoidal (FIG. 5D). Here, FIG.
The horizontal axis θ of (b) and (d) indicates the arc-shaped magnet 50a (5
0b) from the center line 54 to a line 56 drawn in the radial direction from the center point when arc-shaped magnets are connected to form a circle, which is the angle θ in the direction of the arrow in the figure.

From the above, it is understood that when the magnets are oriented in the easy magnetization direction in parallel, the magnetic flux density in the radial direction has a sinusoidal shape, and the cogging torque can be reduced. However, it is preferable that the static torque itself is large, and in order to increase the static torque, it is preferable to adopt the radial orientation in which the total magnetic flux amount becomes large.

Therefore, considering both points, it is understood that the center part should be close to the radial alignment and both ends should be parallel alignment. An example of this case is shown in FIG.
The easy magnetizing direction 52c at the center of the arcuate magnet 50c is a radial orientation, and the easy magnetizing directions 52d and 5 at both ends are set.
2e has a parallel orientation.

A mold 58 as shown in FIG. 6 has been conventionally used for molding a molded body which is a base of such an arc-shaped magnet having an easy magnetization direction orientation. By using a die, it is not necessary to make the yoke shape special (the shape of the yoke required in the case of FIG. 3), and if the die is changed, the same press device can be used. There is an advantage that a molded body with easy magnetization direction can be press-molded.

The mold 58 shown in FIG. 6 has hollow portions 64a and 64 for filling magnetic powder into a hard metal portion 62 that is shrink-fitted in a shrink-fitting metal ring 60 made of a non-magnetic material.
b, and a magnetic core 66 is provided at the center.

This die 58 is the die 4a (4b) of FIG.
Instead of, it is installed in a press machine and used. Therefore, the coils 68a and 68b and the pole pieces 70a and 70b are present outside the die 58. This coil 6
A current is applied to 8a and 68b to generate pole piece 70a.
And 70b generate magnetic fields in the directions of arrows 72a and 72b. At this time, the hollow portion 6 is affected by the magnetic core 66.
The easy magnetization direction orientations of the magnetic powders filled in 4a and 64b can be an orientation which is an appropriate mixture of radial orientation and parallel orientation. By pressing this magnetic powder in a direction perpendicular to the plane of the paper, it is possible to produce a tile-shaped molded body having an orientation in which the easy magnetization direction is an appropriate mixture of radial orientation and parallel orientation.

However, the magnetic core 66 and the pole piece 70
Since the distance between a and 70b is very large, the easy magnetization direction cannot be sufficiently controlled. For example,
Since the distance between the magnetic core and the pole piece is very large, there is a problem that the gradient of the radial orientation cannot be increased so much only by changing the size of the magnetic core.

In order to solve this, not only the mold but also the shape of the pole piece may be changed. However, since the pole piece is fixed to the pressing device, it is difficult and impractical to replace the pole piece every time it is desired to change the orientation of the easy magnetization direction.

[0024]

SUMMARY OF THE INVENTION An object of the present invention is to provide a parallel orientation as an orientation of an easy magnetization direction when forming a molded body which is a base of an arc magnet (a roof tile magnet having an arc cross section). It is an object of the present invention to provide a magnetic powder molding die capable of appropriately mixing radial orientations.

[0025]

[Means for Solving the Problems] Magnetic powder is filled in a hollow portion having an arcuate cross section and placed in a horizontal magnetic field to orient the easy magnetization direction of the magnetic powder so that it is perpendicular to the magnetic field direction of the horizontal magnetic field. In a molding die for press molding in various directions, a plurality of ferromagnetic iron material cores are arranged inside and outside the hollow portion, and the magnetic field orientation of the central portion in the arc-shaped cross section of the hollow portion is set. Provided is a magnetic powder molding die characterized in that the magnetic field orientation of both ends in the arc-shaped cross section of the hollow portion is radial and is parallel to the axis of symmetry of the arc-shaped cross section.

[0026]

EXAMPLES An example of a magnetic field molding die according to the present invention is shown in FIG. Although omitted in FIG. 1 for simplification, pole pieces with coils are provided on the right and left sides of the mold, so that a magnetic field can be generated in a direction from right to left in the figure.

The shrink-fitted metal ring 80 made of non-magnetic stainless steel has shrink-fitted hard metal portions 82 having hollow portions 84a and 84b, which are filled with magnetic powder. As the hard metal, a super hard alloy (WC / Ni), high manganese steel, or nonmagnetic stainless steel whose surface on the hollow portion side is hardened is used. This is the hollow part 8
This is to prevent scratches due to the sliding of the inner walls of 4a and 84b and the upper (lower) punch.

An inner magnetic core 86 for radial orientation is provided at the center, and an outer magnetic core 88a for radial orientation 88a (88b) is provided facing the hollow portion 84a (84b). Further, along with them, the parallel orientation inner magnetic cores 90a and 90b (90c and 90d)
And outer magnetic cores for parallel orientation 92a and 92b (92
c and 92d) are provided. As the magnetic core, a magnetic material that is magnetically soft and has a high saturation magnetization, such as SS41 and SUY of low carbon steel, is suitable.

The magnetic force lines try to flow in a place having a higher magnetic permeability. In the mold according to the present invention shown in FIG. 1, the magnetic force lines flowing from the right outside the mold are the outer magnetic core 88a,
92a, 92b, passing through the magnetic powder in the hollow portion 84a, passing through the right end of the inner magnetic core 86, 90a, 90b, and passing through to the opposite side, this time, conversely, the left end of the inner magnetic core 86, 90c, 90d, through the magnetic powder in the hollow portion 84b, through the outer magnetic cores 88b, 92c, 92d, and exit outside the mold to the left.

Therefore, by changing the shapes and positions of the inner and outer magnetic cores, it is possible to change the degree of mixing of the parallel orientation and the radial orientation and the degree of the radial orientation (the degree of inclination of the orientation direction). That is, unlike the conventional mold, there is no trouble of replacing the pole piece fixed to the pressing device.

One of the easy magnetizing direction orientations of the arc-shaped magnet that can realize a motor having a large static torque and a small cogging torque is that the central portion has a radial orientation and both ends have a parallel orientation. Mentioned in the section of technology. In the mold as shown in FIG. 1, the gap L1 between the magnetic cores for radial alignment and the gap L between the magnetic cores for parallel alignment.
If 2 is made substantially equal, a magnet (FIG. 5 (e)) having a radial orientation at the center and parallel orientation at both ends can be produced.

As described above, the mold of the present invention is also provided with the magnetic core outside the hollow portion. This is the reason why the conventional mold in which the magnetic core is provided only inside the hollow portion (see FIG. 6).
58).

In the mold of the present invention, by providing the magnetic cores on both sides of the hollow portion, the degree of freedom of orientation of the magnetic powder in the direction of easy magnetization is significantly widened. That is, without replacing the pole piece fixed to the press machine, the central part of the arc-shaped magnet prepared by filling the magnetic powder is close to the radial orientation, and both ends can be oriented in parallel. Became. Therefore, in the motor using the magnet made by the molding die of the present invention, the cogging torque can be reduced while the static torque remains large.

Further, the magnetic core of the present invention is not cylindrical, and this point is also different from the conventional one. Since the magnetic core is not cylindrical (the cross section is not point-symmetrical), there is a problem with the matching between the core and the hole of the hard metal part that houses the core. However, in processing the hole part of the core and the hard metal part,
By using a machining center with a numerical control or an electric discharge machine, good consistency can be provided, so that this problem can be solved. Therefore, it is possible to use a core having a more complicated shape, and it is possible to further expand the degree of freedom of orientation of the magnetic powder in the easy magnetization direction.

[0035]

EFFECTS OF THE INVENTION It is possible to provide a mold capable of appropriately mixing parallel orientation and radial orientation as the orientation of the easy magnetization direction when molding a molded body which is a base of an arc-shaped magnet. Therefore, by using a permanent magnet produced by sintering and heat-treating a molded body molded by the magnetic powder molding die of the present invention, an ideal motor having a large static torque and a small cogging torque is realized. It has become possible.

[Brief description of drawings]

FIG. 1 shows an example of a magnetic powder molding die according to the present invention.

FIG. 2 is a diagram for explaining a magnetic field orientation press device.

FIG. 3 is a diagram for explaining a homopolar opposing pole piece capable of realizing radial orientation.

FIG. 4 is an arc magnet (a roof tile magnet having an arc cross section).

FIG. 5 is a diagram for explaining radial magnetic flux densities in a parallel orientation and a radial orientation.

FIG. 6 shows an example of a conventional magnetic powder molding die.

Claims (1)

[Claims] 1. A magnetic powder is filled in a hollow portion having an arcuate cross section and placed in a horizontal magnetic field to orient the easy magnetization direction of the magnetic powder and press in a direction perpendicular to the magnetic field direction of the horizontal magnetic field. In a molding die for molding, a plurality of ferromagnetic iron material cores are arranged on each of the inner side and the outer side of the hollow portion, and the magnetic field orientation of the central portion in the arcuate cross section of the hollow portion is radial, A magnetic powder molding die, characterized in that the magnetic field orientation of both ends in the arc-shaped cross section of the hollow portion is parallel to the axis of symmetry of the arc-shaped cross section.