JP2860858B2 - Mold for magnetic powder molding - Google Patents

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 a molding step, which is the first step in the production of a permanent magnet by powder metallurgy, and more particularly to a molding method in which the direction of easy magnetization of magnetic powder is oriented in a magnetic field. About the mold to do. A permanent magnet produced by sintering and heat-treating a compact 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 an automobile electric device.

[0002]

2. Description of the Related Art Anisotropic permanent magnets are generally manufactured by a powder sintering method using orientation in a magnetic field. For example, when manufacturing a rare earth permanent magnet, a finely ground 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 in a state where the easy magnetization direction of the magnetic powder is oriented in the magnetic field direction. The molded body is formed by molding. According to this manufacturing method, it is possible to make the molded body anisotropic (the easy magnetization direction of the molded body is set to the direction of the applied magnetic field). The formed compact becomes an anisotropic sintered magnet through a sintering heat treatment. During the sintering heat treatment, the easy magnetization direction of the formed body is basically preserved. Therefore, among 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.

[0003] An apparatus that performs pressing while applying a magnetic field includes:
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 partial cross-sectional views.

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

As shown in FIG. 2A, a device in which the magnetic field directions 12a and 12b and the pressing directions 18a and 20a are parallel to each other is a vertical magnetic field shaping device, and as shown in FIG.
And 12d, and a device in which the pressing directions 18b and 20b are perpendicular to each other, is called a transverse magnetic field forming device.

In FIG. 2, since the generated magnetic fields are parallel, the direction of easy magnetization of the molded article also becomes parallel orientation. On the other hand, when it is desired to set the easy magnetization direction of the molded body to the radial orientation (radial orientation), it is necessary to make it as shown in FIG. That is, the coils 32a and 32b are arranged such that the opposing surfaces of the pole pieces 30a and 30b have the same polarity.
It is necessary to supply current to By doing so, the lines of magnetic force flow in the radial direction in a simulated manner as indicated 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 form a compact whose radial direction of magnetization is radially oriented.

However, the flow of lines of magnetic force in the case of FIG.
In this case, since the flow of the magnetic field lines is greatly different, the shape of the yoke provided outside the die and the pole piece needs to be different in each case. Therefore, it is difficult to produce both a parallel-oriented compact and a radial-oriented compact with the same press device (press device having a yoke of the same shape). That is, when press-forming molded bodies having different orientations in the easy magnetization direction, there is a problem that the shape of the pressing device itself must be changed.

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

The magnet used in the motor is a tile-shaped magnet having an arc-shaped cross section as shown in FIG. 4 (hereinafter referred to as an arc-shaped 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 stator) of the motor is manufactured.

In the case of a slotted motor, there is a problem of static torque ripple called cogging torque. That is, the cogging torque hinders the smooth rotation of the motor, and the vibration and the magnetic noise of the motor due to the cogging torque also pose a problem. In addition, if the magnet is made to have high characteristics in order to increase the static torque, the cogging torque also increases. Therefore, there is a major problem that it is impossible to achieve both a large static torque and a small cogging torque.

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

One is a method of twisting a slot or a magnet of a motor. However, in the case of twisting the slot, there are many problems in terms of cost and manufacturing, such as manufacturing of the twisted shape is troublesome, and winding of the twisted slot becomes difficult. On the other hand, when twisting the magnet,
There are many problems in terms of cost and production, such as chipping easily at the time of press forming of the magnet, deformation of the shape at the time of sintering, and difficulty in processing.

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

The thin arc-shaped magnets at both ends are prepared by preparing a molded body of the same shape in advance, or by shaping and molding a non-thin arc-shaped molded body at both ends, followed by grinding.
Can be made. However, in the case where the both ends are thinned in advance, there is a problem that they are easily deformed during sintering, and in the case where grinding is performed after sintering, the material yield decreases and the manufacturing cost increases. There's a problem.

Still another method is to make the orientation of the easy magnetization direction of the arc-shaped magnet close to the radial orientation at the center and parallel at both ends. The reason why this method is effective is described below.

As shown in FIG. 5, when the orientation 52a in the easy magnetization direction of the arc-shaped magnet 50a is parallel orientation (FIG. 5A), the magnetic flux density B in the radial direction has a sine wave shape (FIG. 5B ))
And the orientation 52b of the easy magnetization direction of the arc-shaped magnet 50b.
Is radial orientation (FIG. 5C), the magnetic flux density B in the radial direction becomes trapezoidal (FIG. 5D). Here, FIG.
The horizontal axis θ in (b) and (d) is the arc-shaped magnet 50a (5
The angle θ from the center line 54 in 0b) to the line 56 drawn in the radial direction from the center point when the arc-shaped magnets are connected to form a circle is indicated by the arrow in the drawing.

From the above, it can be understood that when the orientation of the easy magnetization direction of the magnet is set to the parallel orientation, the magnetic flux density in the radial direction becomes a sine wave 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 better to adopt a radial orientation that increases the total magnetic flux amount.

Therefore, considering both points, it can be seen that the central portion should be close to the radial orientation and both ends should be in the parallel orientation. An example of this case is shown in FIG.
The easy magnetization direction 52c at the center of the arc-shaped magnet 50c has a radial orientation, and the easy magnetization directions 52d and
2e is in a parallel orientation.

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

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

The die 58 is a die 4a (4b) shown in FIG.
Instead, it is installed in a press and used. Therefore, the coils 68a and 68b and the pole pieces 70a and 70b exist outside the mold 58. This coil 6
8a and 68b, the pole piece 70a
And 70b generate magnetic fields in the directions of arrows 72a and 72b. At this time, the hollow 6
The orientation of the easy magnetization direction of the magnetic powder filled in 4a and 64b can be an appropriate mixture of radial orientation and parallel orientation. By pressing this magnetic powder in a direction perpendicular to the paper surface, a tile-shaped molded body having an easily magnetized direction with an appropriate mixture of the radial orientation and the parallel orientation can be produced.

However, the magnetic core 66 and the pole piece 70
Since the distance between a and 70b is very large, the direction of easy magnetization 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 degree of inclination 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 press 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 It is an object of the present invention to provide a magnet having a parallel orientation as an orientation of an easy magnetization direction when molding a molded article which is a base of an arc-shaped magnet (tile-shaped magnet having an arc-shaped cross section). An object of the present invention is to provide a magnetic powder molding die capable of appropriately mixing radial orientations.

[0025]

The magnetic powder is filled in a hollow portion having a circular arc cross section and placed in a horizontal magnetic field to orient the direction of easy magnetization of the magnetic powder so as to be perpendicular to the magnetic field direction of the horizontal magnetic field. In a molding die that performs press molding in various directions, a plurality of ferromagnetic iron cores are arranged on the inside and outside of the hollow portion, and the magnetic field orientation at the center in the arc-shaped cross section of the hollow portion is adjusted. A magnetic powder molding die having a radial shape, wherein magnetic field orientations at both ends in an arc-shaped cross section of the hollow portion are parallel to an axis of symmetry of the arc-shaped cross section.

[0026]

FIG. 1 shows an example of a molding die in a magnetic field according to the present invention. Although omitted in FIG. 1 for simplicity, there are pole pieces with coils on the right and left sides of the mold so that a magnetic field can be generated from right to left in the figure.

The hard metal portion 82 shrink-fitted in the shrink-fitting metal ring 80 made of non-magnetic stainless steel has hollow portions 84a and 84b, which are filled with magnetic powder. As the hard metal, a super hard alloy (WC / Ni), a high manganese steel, or a nonmagnetic stainless steel having a hardened surface on the hollow side is used. This is the hollow part 8
This is to prevent scratches due to sliding between 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 (88b) for radial orientation is provided across the hollow portion 84a (84b). Also, alongside them, the inner magnetic cores 90a and 90b for parallel orientation (90c and 90d)
And the outer magnetic cores 92a and 92b for parallel orientation (92
c and 92d) are provided. As the magnetic core, a magnetic material that is magnetically soft and has high saturation magnetization, such as low-carbon steel SS41 and SUY, is suitable.

The lines of magnetic force tend to flow where the magnetic permeability is higher. In the mold according to the present invention shown in FIG. 1, the lines of magnetic force flowing from the outside right side of the mold are outer magnetic cores 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 exiting to the opposite side, and 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 to the outside left of the mold.

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 in the orientation direction). That is, there is no trouble of replacing the pole piece fixed to the press device as in the conventional mold.

One of the easy magnetization direction orientations of an 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 on technology. In the mold as shown in FIG. 1, the distance L1 between the magnetic cores for radial alignment and the distance L1 between the magnetic cores for parallel alignment
By making the two approximately equal, a magnet (FIG. 5 (e)) having a radial orientation at the center and parallel orientations at both ends can be produced.

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

In the mold of the present invention, since the magnetic cores are provided on both sides of the hollow portion, the degree of freedom of the orientation of the magnetic powder in the easy magnetization direction is greatly increased. That is, without replacing the pole piece fixed to the press device, the center of the arc-shaped magnet produced by filling the magnetic powder is close to the radial orientation, and both ends can be parallel orientation. 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 is kept 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-symmetric), consistency between the core and the hole of the hard metal part that accommodates the core becomes a problem. However, when machining the hole of the core and the hard metal part,
By using a machining center or an electric discharge machine with numerical control, good consistency can be provided, so that this problem can be solved. Therefore, a core having a more complicated shape can be used, and the degree of freedom of the orientation of the magnetic powder in the easy magnetization direction can be further increased.

[0035]

According to the present 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 the molded body which is the base of the arc-shaped magnet. Therefore, by using a permanent magnet produced by sintering and heat-treating a compact formed 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 became possible.

[Brief description of the drawings]

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

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

FIG. 3 is a view for explaining a same-pole opposing pole piece capable of realizing radial orientation.

FIG. 4 is an arc-shaped magnet (tile-shaped magnet having a circular cross section).

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

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

Claims (1)

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