JP2024054785A - Molding Method - Google Patents

Abstract

To provide a molding method capable of easily and efficiently orientating powder containing magnetic powder.SOLUTION: A molding method of the present disclosure includes: preparing a dice 20 with a cavity 40, and a punch 10 sliding inside the cavity 40; charging raw material powder 50 containing magnetic powder inside the cavity 40; and subjecting the raw material powder 50 to compression molding using the punch 10 while applying a magnetic field to the raw material powder 50 from the outside of the dice 20. Parts of the dice 20 are made of a soft magnetic material while the remainder is made of a non-magnetic material, and the parts of the dice 20, the parts being made of the soft magnetic material, are made to face each other with the cavity 40 directly or indirectly sandwiched therebetween, at a part of the cavity 40 in a circumferential direction.SELECTED DRAWING: Figure 1

Description

This disclosure relates to a molding method. In particular, this disclosure relates to a molding method for raw material powders that contain magnetic powders.

There are two types of permanent magnets: isotropic magnets and anisotropic magnets. Anisotropic magnets have a higher residual magnetization than isotropic magnets. For this reason, anisotropic magnets are generally used in applications that require high residual magnetization, and various methods of imparting anisotropy are being investigated.

For example, Patent Document 1 discloses that in order to impart anisotropy to a samarium-iron-nitrogen rare earth magnet, a magnetic field is applied to the samarium-iron-nitrogen magnetic powder at room temperature prior to warm compression molding, and a magnetic field is applied during warm compression molding.

International Publication No. 2015/199096

To apply a magnetic field to raw material powder containing magnetic powder while compressing the raw material powder, it is common to use a press molding machine equipped with a magnetic field application coil. However, to sufficiently magnetically orient the magnetic powder in the raw material powder, it is necessary to use a large magnetic field application coil, which creates the problem of the overall size of the device.

This disclosure has been made to solve the above problems. In other words, the purpose of this disclosure is to provide a molding method that can easily and efficiently orient powder containing magnetic powder.

The inventors have conducted intensive research to achieve the above-mentioned objective, and have completed the magnetic field molding method disclosed herein. The molding method disclosed herein includes the following aspects.

That is, the molding method of the present disclosure is
Providing a die having a cavity and a punch sliding within the cavity;
Charging raw material powder containing magnetic powder into the cavity; and compressing and molding the raw material powder with the punch while applying a magnetic field to the raw material powder from the outside of the die.
Including,
A part of the die is made of a soft magnetic material and the remaining part is made of a non-magnetic material; and
This is a molding method in which a portion of the die made of the soft magnetic material is opposed to the cavity directly or indirectly in a circumferential portion of the cavity.

This disclosure provides a molding method that can concentrate magnetic poles within a cavity and orient powder containing magnetic powder simply and efficiently.

FIG. 1 is an explanatory diagram that shows a schematic overview of an example of a molding apparatus used in the molding method of the present disclosure. FIG. 2 is a cross-sectional view that illustrates an example of a die used in the molding method of the present disclosure. FIG. 3 is a cross-sectional view that illustrates another example of a die used in the molding method of the present disclosure.

Below, an embodiment of the molding method of the present disclosure will be described in detail. Note that the molding method of the present disclosure is not limited to the embodiment described below. First, the findings of the present inventors regarding the reason why the molding method of the present disclosure allows for easy and efficient orientation of powder containing magnetic powder will be explained using drawings.

Figure 1 is an explanatory diagram showing a schematic overview of an example of a molding device used in the molding method of the present disclosure. The molding device 100 includes a punch 10, a die 20, and a magnetic field application coil 30.

The molding method of the present disclosure includes preparing a die 20 having a cavity 40 and a punch 10 that slides within the cavity 40, loading raw material powder 50 containing magnetic powder into the cavity 40, and compression molding it with the punch 10. The compression molding of the raw material powder 50 is performed while applying a magnetic field to the raw material powder 50 from outside the die 20 using a magnetic field application coil 30. This magnetically aligns the magnetic powder in the raw material powder 50. However, in conventional molding methods, the orientation of the magnetic powder was sometimes insufficient. In this case, it is possible to increase the magnitude of the magnetic field applied, but this would increase the size of the magnetic field application coil and the power required to apply the magnetic field would also increase.

In order to increase the strength of the magnetic field applied to the raw material powder 50 in the cavity 40, it is possible to magnetize the die 20 itself while keeping the strength of the magnetic field applied to the die 20 the same. In this case, for example, if the entire circumferential direction of the cavity 40 is made of a soft magnetic material, the magnetic field in the cavity 40 will actually decrease. This is thought to be because the magnetic poles in the cavity 40 will decrease.

Therefore, if a part of the die is made of a soft magnetic material and the remaining part is made of a non-magnetic material, and the part of the die made of the soft magnetic material is placed opposite the cavity directly or indirectly in a part of the circumferential direction of the cavity, the magnetic poles in the cavity 40 are concentrated. As a result, the present inventors have discovered that the magnetic powder in the raw material powder 50 is sufficiently oriented in the cavity 40.

The following describes the constituent elements of the molding method disclosed herein, which was completed based on the findings and other information discussed so far.

Molding method
The molding method of the present disclosure includes a mold preparation step, a raw material powder charging step, and a compression molding step. Each step will be described below.

<Mold preparation process>
First, a mold for use in the molding method of the present disclosure is prepared. The mold for use in the molding method of the present disclosure typically includes a punch 10 and a die 20, as shown in FIG.

Figure 2 is a cross-sectional view showing a schematic example of a die used in the molding method of the present disclosure. In the example shown in Figure 2, the die 20 has an outer die 60 and an inner die 70, and the inner die 70 has a pair of first split dies 72 and a pair of second split dies 74. The inner die 70 forms the cavity 40. In addition, a punch 10 (see Figure 1) that slides in the front-to-back direction of Figure 2 is prepared.

In the example shown in FIG. 2, only the pair of first split dies 72 are made of a soft magnetic material, and the rest (the remainder) are made of a non-magnetic material. This allows a part of the die 20 (the pair of first split dies 72) to face the cavity 40 directly in between at a portion of the circumferential direction of the cavity 40. This allows the magnetic poles to be concentrated within the cavity 40 when a magnetic field is applied.

In the example shown in FIG. 2, the die 20 has an outer die 60 and an inner die 70, but is not limited to this. For example, the outer die 60 and a pair of second split dies 74 may be made of a single non-magnetic material.

There are no particular limitations on the non-magnetic material, but a non-magnetic superhard material is preferable. A non-magnetic superhard material can prevent the die 20 from wearing down due to contact between the dies that make up the die 20, or due to contact between the die 20 and the hard magnetic powder in the raw material powder 50 on the inner surface of the cavity 40.

There are no particular limitations on the soft magnetic material, but examples include permendur, pure iron, silicon steel, and permalloy. From the perspective of concentrating the magnetic poles within the cavity 40, permendur is preferred.

3 is a cross-sectional view showing a schematic diagram of another example of a die used in the molding method of the present disclosure. In the example shown in FIG. 3, as in the example shown in FIG. 2, only the pair of first split dies 72 are made of a soft magnetic material, and the rest (remaining part) is made of a non-magnetic material. The difference from the example shown in FIG. 2 is that a part of the die 20 (the pair of first split dies 72) faces each other indirectly sandwiching the cavity 40. As a result, the first split die 72 does not come into contact with the raw material powder 50 containing hard magnetic powder, so that the first split die 72 made of an expensive soft magnetic material is less likely to wear out. In the example shown in FIG. 3, the second split die 74 is integrally formed, but this is not limited thereto. For example, the second split die 74 may be further divided, or the outer die 60 and the second split die 74 may be integrally formed.

<Raw material powder charging process>
Raw material powder 50 containing magnetic powder is charged into cavity 40. There is no particular limitation on the magnetic powder. Examples of magnetic powder include ferrite magnetic powder, neodymium magnetic powder, samarium-cobalt magnetic powder, and samarium-iron-nitrogen magnetic powder. If the magnetic powder has a large anisotropic magnetic field, a large magnetic field must be applied to orient the magnetic powder. For this reason, the molding method of the present disclosure is particularly advantageous for molding samarium-iron-nitrogen magnetic powder. This is because samarium-iron-nitrogen magnetic powder has an extremely large anisotropic magnetic field among magnetic powders.

The raw material powder may contain substances other than magnetic powder. Such substances are typically bond materials and modifier materials. When obtaining a so-called bonded magnet, the raw material powder may contain a resin bond material.

When the magnetic material is a samarium-iron-nitrogen magnetic powder, the raw material powder may contain a modifier powder. The samarium-iron-nitrogen magnetic powder contains a magnetic phase having at least one of the crystal structures of Th ₂ Zn ₁₇ type, Th ₂ Ni ₁₇ type, and TbCu ₇ type. This magnetic phase exhibits magnetism by containing nitrogen in an interstitial or substitutional form inside. In addition, the samarium-iron-nitrogen magnetic powder contains an α-Fe phase that causes a decrease in coercive force. The modifier powder renders the α-Fe phase harmless without dissociating the nitrogen in the magnetic phase when the compact obtained by the molding method of the present disclosure is subjected to low-temperature pressure sintering. Examples of such modifier powder include zinc powder and zinc alloy powder.

Compression Molding Process
The raw material powder 50 is compression-molded by the punch 10 while a magnetic field is applied to the raw material powder 50 from the outside of the die 20. This causes the magnetic material in the raw material powder 50 to be magnetically oriented.

The magnitude of the magnetic field to be applied may be appropriately determined taking into consideration the size of the compact (size of the cavity 40) and the magnitude of the anisotropic magnetic field of the magnetic powder. The magnitude of the magnetic field to be applied may be, for example, 0.1 T or more, 0.3 T or more, or 0.5 T or more, and may be 2.0 T or less, 1.5 T or less, or 1.0 T or less.

There are no particular limitations on the method of applying the magnetic field, but typically, as shown in Figure 1, a magnetic field is applied by placing a magnetic field applying coil around the outer periphery of the die 20.

There are no particular limitations on the direction in which the magnetic field is applied, but from the viewpoint of efficiently concentrating the magnetic poles within the cavity 40, the direction in which the magnetic field is applied may be -15° or more, -10° or more, -5° or more, or 15° or less, 10° or less, or 5° or less with respect to the opposing direction of the pair of first split dies 72, and the ideal direction for applying the magnetic field is the opposing direction of the pair of first split dies 72.

The compression molding pressure may be, for example, 5 MPa or more, 10 MPa or more, 50 MPa or more, 100 MPa or more, or 150 MPa or more, and may be 1500 MPa or less, 1000 MPa or less, or 500 MPa or less.

The molding method of the present disclosure will be explained in more detail below with reference to examples and comparative examples. Note that the molding method of the present disclosure is not limited to the conditions used in the following examples.

<Sample preparation>
Each sample was prepared as follows.

Examples 1 and 2
Samarium-iron-nitrogen magnetic powder was mixed with zinc powder, the mixed powder was molded using the die shown in FIG. 2, and the molded body was subjected to low-temperature pressure sintering to obtain samples of Examples 1 and 2. The pair of first split dies 72 was made of permendur, and the rest was made of non-magnetic superhard material. The amount of zinc powder mixed with respect to the entire mixed powder was 10 mass %. The mixed powder was compression molded at 50 MPa. The magnetic field (external magnetic field) applied during compression molding was as shown in Table 1. The low-temperature pressure sintering was performed at 400° C. and 1 GPa.

Example 3
A sample of Example 3 was produced in the same manner as Example 2, except that the die shown in FIG. 3 was used and the pair of first split dies 72 was made of pure iron.

Comparative Examples 1 and 2
The samples of Comparative Examples 1 and 2 were obtained in the same manner as in Example 1, except that the pair of first split molds 72 were also made of a non-magnetic superhard material, i.e., the entire die 20 was made of a non-magnetic superhard material, and the magnetic field applied during compression molding was as shown in Table 1.

"evaluation"
The degree of orientation of each sample was measured using a pulse BH tracer manufactured by Toei Kogyo Co., Ltd. The results are shown in Table 1.

From Table 1, it can be seen that the samples of Examples 1 to 3, in which the soft magnetic material is placed at a specified position on the die, have a higher degree of orientation than the samples of Comparative Examples 1 and 2. In the sample of Example 3, pure iron was selected as the soft magnetic material, so the degree of orientation is lower compared to Examples 1 and 2, but it can be seen that the degree of orientation is higher than that of Comparative Examples 1 and 2.

For reference, in Example 3, the pair of first split dies 72 was changed from pure iron to permendur, and the central magnetic field of the cavity 40 was calculated using a simulation program to be 2.3 T. This value is lower than that of Example 2, in which a magnetic field of 1.5 T was applied from the outside of the die 20. This is thought to be because in Example 3, the pair of first split dies 72 are indirectly opposed to each other across the cavity 40, that is, the tips of the pair of first split dies 72 are separated from the cavity 40, and therefore the magnetic poles in the cavity 40 are reduced. However, even when the pair of first split dies 72 are made of pure iron and are indirectly opposed to each other across the cavity 40 as in Example 3, the degree of orientation is better than that of Comparative Examples 1 and 2. For these reasons, it is extremely advantageous in practical use that the pair of first split dies 72 are made of relatively inexpensive pure iron, and that the pair of first split dies 72 indirectly sandwich the cavity 40, so that the cavity surface can be made into a second split die 74 made of a highly wear-resistant non-magnetic superhard material.

Reference Signs List 10 punch 20 die 30 magnetic field applying coil 40 cavity 50 raw material powder 60 outer die 70 inner die 72 first split die 74 second split die 100 molding device

Claims (1)

Providing a die having a cavity and a punch sliding within the cavity;
Charging raw material powder containing magnetic powder into the cavity; and compressing and molding the raw material powder with the punch while applying a magnetic field to the raw material powder from the outside of the die.
Including,
A part of the die is made of a soft magnetic material and the remaining part is made of a non-magnetic material; and
The portion of the die made of the soft magnetic material is opposed to the cavity in a circumferential part of the cavity, directly or indirectly sandwiching the cavity therebetween.
Molding method.

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