JP2023125565A - Green compact, powder magnetic core, and manufacturing methods therefor - Google Patents

Abstract

To provide a green compact, a powder magnetic core, and a manufacturing method therefor that can suppress density differences even in complex shapes.SOLUTION: A green compact 1 includes a middle leg 21 and outer legs 22a, 22b arranged side-by-side so that their directions of extension are parallel to each other, a yoke portion 3 that connects the middle leg 21 and the outer legs 22a, 22b, and a recess 4 provided on an end surface perpendicular to the direction of extension of the middle leg 21 and the outer legs 22a, 22b and perpendicular to the direction of alignment of the middle leg 21 and the outer legs 22a, 22b. An extended end surface 23 of the middle leg 21 and the outer legs 22a, 22b, an inner circumferential surface 31 of the yoke portion 3, and a back surface 32 of the yoke portion 3 are press surfaces to be pressed by upper or lower punches. Variations in length of the middle leg 21 and the outer legs 22a, 22b, including the yoke portion 3 in the extending direction of the middle leg 21 and the outer legs 22a, 22b are 0.57% or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a powder compact, a powder magnetic core, and a method for producing the powder compact and the powder magnetic core.

Powder magnetic cores are used as cores of coil components such as reactors. For example, a reactor is an electromagnetic component that converts electrical energy into magnetic energy, stores and releases it, and is used in drive systems for hybrid cars, electric cars, and fuel cell cars, as well as office automation equipment, solar power generation systems, and uninterruptible power supplies. It is used in various fields such as

The powder magnetic core is obtained by press-molding soft magnetic powder or soft magnetic powder with an insulating layer attached to the surface to produce a powder compact, and then annealing the powder compact. Generally, a high pressure of 10 to 20 tons/cm ² is applied during press molding.

FIG. 7 is a diagram showing the pressing direction of a conventional powder compact. As shown in FIG. 7, the compacted powder compact 100 may have an E-shape consisting of three legs and a yoke connecting the three legs. That is, the three legs are arranged side by side so that their extending directions are parallel, the yoke connects to the end of each leg, and the compact is approximately E-shaped. In such a powder compact, the pressing surface is a direction perpendicular to the extending direction of the legs and perpendicular to the horizontal direction of the legs, that is, a surface that looks like an E shape (E-shaped surface), and this E-shaped surface are formed on the same plane. In other words, the three legs have the same height in a direction perpendicular to the extending direction of the legs and perpendicular to the horizontal direction of the legs (hereinafter also referred to as "height direction").

Japanese Patent Application Publication No. 2018-133499

A coil is wound around the leg of the powder compact. If the lengths of the three legs are the same in the height direction, the coil will protrude to the outside of the powder compact by the line width, leading to an increase in the size of the coil component. Therefore, a shape is required in which the length in the height direction of the leg portion around which the coil is wound is shortened so that the coil does not protrude outside the powder compact. For example, when the coil is wound around the middle leg located in the middle of the three legs, the length of the middle leg in the height direction is made shorter than the outer legs located at both ends of the middle leg.

If the length of the middle leg in the height direction is short, if you press in a direction perpendicular to the E-shaped plane as in the conventional method, the pressing surfaces of the middle leg and outer leg are not on the same plane, so the middle leg will be pressed by the press machine. Difficult to press. Therefore, the pressing forces applied to the middle leg, outer leg, and yoke portion are different. As a result, a density difference occurs between the soft magnetic powder contained in the middle leg, the outer leg, and the yoke portion, and there is a risk that the portion where the density difference is large may be damaged.

If the core is not a dust core but a ferrite core, the purpose of pressing in the pressing step is only to form the desired shape. Then, since the powders are firmly bonded by the sintering action by annealing, sufficient strength can be obtained as a core. Therefore, since the pressing force is as low as 1 to 3 ton/cm ² , there is little difference in density. Therefore, in the case of a ferrite core, it is easy to make it into a complicated shape in which the heights in the direction perpendicular to the extending direction of the leg parts and the direction perpendicular to the horizontal arrangement direction of the leg parts are different.

On the other hand, in the case of powder magnetic cores, the purpose of pressing in the pressing process is not only to form the desired shape, but also to bring the powders closer together and to hold the powder compact by intermolecular forces. The compact is compressed under a high pressure of 10 to 20 tons/cm ² . Therefore, in the case of powder magnetic cores, density differences appear significantly. Therefore, it has been difficult to produce a compacted powder body or powder magnetic core having a complicated shape in which the heights in the direction perpendicular to the extending direction of the legs and the direction perpendicular to the horizontal arrangement direction of the legs are different.

The present invention was proposed in order to solve the above problems, and its purpose is to provide a powder compact, a powder magnetic core, a powder compact, and a compact with suppressed density differences even in complex shapes. An object of the present invention is to provide a method for manufacturing a powder magnetic core.

In order to achieve the above object, the powder compact of the present invention includes a plurality of legs arranged side by side so that their extending directions are parallel to each other, a yoke section connecting the plurality of legs, and a yoke section for connecting the plurality of legs, and a yoke section for connecting the plurality of legs. a recess provided in an end surface of the leg that is perpendicular to an extending direction and perpendicular to a lateral arrangement direction of the leg, the yoke communicating with the extending end surface of the leg and the leg; The inner circumferential surface of the yoke section and the back surface of the yoke section, which is the end surface opposite to the inner circumferential surface, are press surfaces that are pressed by a punch, and the extension direction of each leg section including the thickness of the yoke section. The length variation is 0.57% or less.

A powder magnetic core formed by annealing the above powder compact is also an embodiment of the present invention.

Further, the method for producing a compacted compact of the present invention includes a pressing step of press-molding soft magnetic powder with an upper punch and a lower punch to produce a compact, wherein the extending direction of the compact is parallel. a plurality of legs arranged side by side, a yoke part connecting the plurality of legs, and a yoke part provided on an end surface perpendicular to the extending direction of the legs and perpendicular to the direction in which the legs are arranged side by side. a recessed portion, in the pressing step, the extending direction of the leg is the pressing direction, and the lower punch includes an extended end surface punch that presses the extended end surface of the leg; an inner circumferential surface punch that presses the inner circumferential surface of the connecting yoke portion, and the variation in length of each leg including the yoke portion in the extending direction of the leg portion is 0.57% or less. It is characterized by:

Another aspect of the present invention is a method for producing a powder magnetic core, which includes an annealing step of heat-treating the powder compact produced by the above production method.

According to the present invention, density differences can be suppressed even in the case of complex-shaped powder compacts or powder magnetic cores.

FIG. 1 is a perspective view of a compacted powder body according to an embodiment. It is a figure showing the main composition of a mold. It is a perspective view of an upper punch. It is a perspective view of a lower punch. FIG. 3 is an exploded perspective view of the lower punch. It is a graph showing the relationship between leg length variations and density differences. FIG. 2 is a diagram showing the shape and pressing direction of a conventional compacted powder body.

(Embodiment)
A powder compact or a powder magnetic core according to an embodiment will be described with reference to the drawings. In each drawing, thickness, dimensions, positional relationships, proportions, shapes, etc. may be emphasized for ease of understanding, but the present invention is not limited to such emphasis.

FIG. 1 is a perspective view of the powder compact 1. FIG. In addition, in FIG. 1, the X direction is the direction in which the legs 2 extend, the Y direction is the direction in which the legs 2 are arranged side by side, and the Z direction is a direction perpendicular to the X and Y directions. The X direction is sometimes referred to as the pressing direction when press-molding soft magnetic powder, and the Z direction is sometimes referred to as the height direction.

A powder magnetic core is a magnetic material used as the core of coil components such as reactors installed in office automation equipment, solar power generation systems, automobiles, and the like. The powder magnetic core is formed by annealing the powder compact 1. The compacted compact 1 contains soft magnetic powder. If necessary, an insulating layer is formed on the surface of the soft magnetic powder. The compacted powder body 1 is produced by filling a mold with soft magnetic powder and press-molding it. Through press molding, a powder compact 1 having a desired shape is obtained. Finally, a powder magnetic core is produced by annealing this powder compact 1.

Soft magnetic powder has iron as its main component. As the soft magnetic powder, pure iron powder, permalloy whose main component is iron (Fe-Ni alloy), Si-containing iron alloy (Fe-Si alloy), sendust alloy (Fe-Si-Al alloy), or two of these are used. A mixed powder of the above powders can be used. Further, as the soft magnetic powder, an amorphous alloy powder or a nanocrystalline alloy powder may be used.

The Fe--Si--Al alloy powder contains, for example, approximately 7 wt% to 11 wt% of Si and approximately 4 wt% to 8 wt% of Al relative to Fe. The Fe--Si--Al alloy powder may contain, for example, about 1 wt% to 3 wt% Ni with respect to Fe. Furthermore, the Fe--Si--Al alloy powder may contain Co, Cr, or Mn.

The Si-containing iron alloy may contain Co, Al, Cr, or Mn. When permalloy (Fe--Ni alloy) is used, the ratio of Ni to Fe is preferably 50:50 or 25:75, but other ratios may be used. For example, it may be Fe-80Ni, Fe-36Ni, Fe-78Ni, or Fe-47Ni. In addition to Fe and Ni, it may also contain Si, Cr, Mo, Cu, Nb, Ta, etc. Examples of Fe-Si alloy powder include Fe-3.5%Si alloy powder and Fe-6.5%Si alloy powder, but the ratio of Si to Fe is other than 3.5% or 6.5%. It may be. Pure iron powder contains 99% or more of Fe.

The powder compact 1 of this embodiment consists of three leg parts 2 and a yoke part 3 that connects the three leg parts 2, and has a roughly E-shape when viewed from the Z direction. The leg portion 2 extends from the yoke portion 3. The three legs 2 are arranged side by side so that their extending directions are parallel. The leg portion 2 has a middle leg 21 arranged in the middle and a pair of outer legs 22a and 22b arranged on both sides of the middle leg 21. The yoke portion 3 has an inner circumferential surface 31 that connects to the leg portion 2 at an end surface perpendicular to the press direction (X direction), and a back surface 32 that is an end surface opposite to the inner circumferential surface 31.

The leg portion 2 extends and has a distal end surface 23 . The extending end surface 23 is perpendicular to the extending direction of the leg portion 2 and is a surface opposite to the surface connected to the yoke portion 3. Two powder magnetic cores obtained by annealing the powder compact 1 are prepared, and are extended to each other and joined at the tip surfaces 23 to form a closed annular core.

The variation in the length of each leg portion 2 in the extending direction, including the thickness of the yoke portion 3, is 0.57% or less. By reducing the variation to 0.57% or less, the density difference between the leg portion 2 and the yoke portion 3 can be reduced. In order to further reduce the density difference, it is preferably 0.44% or less. Note that the variation in length in the extending direction of each leg 2 including the thickness of the yoke 3 refers to the variation in the length in the extending direction of the leg 2 from the inner circumferential surface 31 of the yoke 3 to the back surface 32. This refers to the length including the thickness of the yoke portion 3. This length variation is obtained from the following equation (1).

(Formula 1)
Length variation = (1 - (shortest leg length) / (longest leg length)) x 100... (1)

The end faces of the middle leg 21, the outer legs 22a, 22b, and the yoke part 3 in the height direction (direction perpendicular to the extending direction of the leg parts 2 and perpendicular to the horizontal direction of the leg parts 2) are not on the same plane, and none of them are on the same plane. A recessed portion 4 is formed on this member. In this embodiment, a recessed portion 4 is formed on the upper surface of the middle leg 21. This recessed portion 4 is formed over the entire upper surface of the middle leg 21. In other words, the shape is such that it does not undercut with respect to the extending direction of the middle leg 21 toward the distal end surface 23 . That is, the middle leg 21 has a shorter length in the height direction than the outer legs 22a and 22b. Specifically, the length in the height direction of the outer legs 22a and 22b is approximately the same as the length in the height direction of the yoke part 3, but the length in the height direction of the middle leg 21 is the same as the height of the yoke part 3. shorter than the length in the horizontal direction. The middle leg 21 is in contact with one end of the yoke portion 3 in the height direction, but not with the other end. Note that the length of the leg portions 2 in the arrangement direction (Y direction) is that the middle leg 21 is longer than the outer legs 22a and 22b.

The extending end surfaces 23 of the middle leg 21 and the outer legs 22a, 22b, and the inner circumferential surface 31 and back surface 32 of the yoke portion 3 are press surfaces. On the other hand, the side surfaces of the middle leg 21 and the outer legs 22a and 22b that are parallel to the pressing direction, and the side surface of the yoke portion 31 that is parallel to the pressing direction serve as sliding surfaces. The press surface is a surface pressed by an upper punch 7 or lower punch 8, which will be described later, and the sliding surface is a surface on which traces of sliding of the upper punch 7 or lower punch 8 remain during press molding.

(Production method)
Next, a method for manufacturing the powder compact 1 or the powder magnetic core according to the present embodiment will be described. The method for manufacturing the powder compact 1 includes a pressing step. The method for manufacturing a powder magnetic core includes an annealing step of heat-treating the powder compact 1 produced by the pressing step. The pressing process is a process of filling the mold 5 with soft magnetic powder and pressing the soft magnetic powder to produce the compacted compact 1.

Here, the structure of the mold 5 will be explained with reference to the drawings. FIG. 2 is a perspective view showing the main structure of the mold 5. As shown in FIG. Note that for convenience of explanation, the die 6 is made transparent. The mold 5 has a die 6, an upper punch 7, and a lower punch 8. The upper punch 7 and lower punch 8 inserted into the die 6 press the soft magnetic powder against each other to compact the soft magnetic powder, and the soft magnetic powder is molded into the powder compact 1. The upper punch 7 and the lower punch 8 are movable along the extending direction of the leg portion 2 (X direction).

The die 6 is a cylindrical member, and an opening having approximately the same shape and size as the back surface 32 of the yoke portion 3 is provided in the center of the circle. The opening extends from one end surface perpendicular to the pressing direction to the other end surface, and is a penetrating hole. The inside of the die 6 is filled with soft magnetic powder through this opening, and the soft magnetic powder is pressed by the upper punch 7 and the lower punch 8 to form the powder compact 1.

FIG. 3 is a perspective view of the upper punch 7. The upper punch 7 is a member that presses the back surface 32 of the yoke portion 3. That is, the upper punch 7 has a pressing surface 71 that presses the back surface 32. The press surface 71 is a flat surface. The press surface 71 has approximately the same shape and size as the back surface 32 of the yoke portion 3.

FIG. 4 is a perspective view of the lower punch 8. FIG. 5 is an exploded perspective view of the lower punch 8. The lower punch 8 is a member that presses the extending end surface 23 of the leg portion 2 and the inner circumferential surface 31 of the yoke portion 3. The lower punch 8 is divided into an extended end surface punch 81 that presses the extended end surface 23 and an inner peripheral surface punch 82 that presses the inner peripheral surface 31.

The extending end surface punch 81 includes a pressing member 811 that presses the extending end surface 23 of the middle leg 21, and a pair of pressing members 812 that press the extending end surface 23 of the outer legs 22a and 22b. The pressing member 811 has a long plate shape and has a pressing surface 811a that presses the extending end surface 23 of the middle leg 21. The press surface 811a has approximately the same shape and size as the extending end surface 23 of the middle leg 21, and is a flat surface.

The pair of pressing members 812 are arranged opposite to each other with the pressing member 811 in between. The pressing member 812 has a long plate shape and has a pressing surface 812a that presses the extending end surfaces 23 of the outer legs 22a and 22b. The press surface 812a has approximately the same shape and size as the extending end surfaces 23 of the outer legs 22a and 22b, and is a flat surface. The pressing surface 811a of the pressing member 811 and the pressing surface 812a of the pressing member 812 are arranged on the same plane. Note that the length of the pressing member 811 in the direction perpendicular to the press direction and perpendicular to the direction in which the pressing members are arranged is shorter than that of the pressing member 812.

The elongated tip face punch 81 further includes a root portion 813. The root portion 813 is a circular plate-shaped member. The root portion 813 is connected to the end portions of the pressing members 811, 812 on the opposite side to the pressing surfaces 811a, 812a. That is, the pressing members 811 and 812 are integrated by the root portion 813. In other words, the pressing members 811 and 812 do not move individually, but are movable together. The base portion 813 is provided with a generally U-shaped opening 814 into which the inner peripheral surface punch 82 is inserted.

The inner circumferential surface punch 82 is a generally U-shaped member when viewed from the pressing direction. That is, the inner circumferential surface punch 82 includes a pair of linear portions that are arranged opposite to each other and a connecting portion that connects the pair of linear portions. The inner peripheral surface punch 82 has a press surface 82a that presses the inner peripheral surface 31 of the yoke portion 3. The press surface 82a is a generally U-shaped flat surface.

The inner circumferential punch 82 extends from the opening 814 of the root portion 813 and is inserted into the tip punch 81 . The inner peripheral surface punch 82 is inserted so that the press surface 82a protrudes beyond the press surfaces 811a and 812a. This protruding length becomes the length of the leg portion 2 in the extending direction. Further, the connecting portion of the press surface punch 82 is arranged between the pair of pressing members 812. A recessed portion 4 is formed on the upper surface of the middle leg 21 by this connecting portion. The inner peripheral surface punch 82 extends and slides independently of the end surface punch 81.

A pressing process is performed in such a mold 5. First, insert the lower punch 8 (extended tip face punch 81 and inner peripheral face punch 82) through the opening on one end face of the die 6, fill the die 6 with soft magnetic powder from the opening on the other end face, and punch the upper punch from the opening. Insert 7. Then, pressure is applied by the upper punch 7 and the lower punch 8 (the extended end face punch 81 and the inner peripheral face punch 82). The molding pressure at this time is 10 to 20 tons/cm ² . In this way, the powder compact 1 is produced. The boundary portion between the inner circumferential surface 31 of the leg portion 2 and the yoke portion 3 becomes a dividing surface of the mold.

The annealing process is a process of heat-treating the powder compact 1 produced through the pressing process. In the annealing process, heat treatment is performed at a temperature of 600°C or more and 900°C or less in nitrogen gas, a mixed gas of nitrogen and hydrogen, a non-oxidizing atmosphere such as a low oxygen atmosphere with an oxygen concentration of 0.01%, or in the air. . A powder magnetic core is produced through this annealing process. Through the annealing process, distortion and residual stress contained in the powder compact 1 are removed. In addition, when an insulating layer made of insulating resin is formed on the surface of soft magnetic powder, or when a binder made of resin that binds the soft magnetic powder is added, the annealing process allows the insulating resin and binder to contain Organic components are thermally decomposed. That is, the organic solvent contained in the insulating resin or binder before the annealing process is no longer contained after the annealing process.

Note that, after the annealing process, a polishing process may be performed in which the extending end surface 23 of the leg portion 2 is polished. In the polishing step, the polishing may be performed manually by an operator using a file or the like, or by using a polishing machine. Through the polishing process, the lengths of the legs 2 in the extending direction are made the same. Note that the above-described variation in the length of each leg portion 2 in the extending direction is set to 0.57% or less at a stage before the polishing process is performed.

Further, before performing the pressing step, a powder heat treatment step of heat-treating the soft magnetic powder or an insulating layer forming step of forming an insulating layer on the surface of the soft magnetic powder may be performed.

In the powder heat treatment step, the powder is heated for 1 to 6 hours in a non-oxidizing atmosphere such as nitrogen gas, a mixed gas of nitrogen and hydrogen, or a low oxygen atmosphere with an oxygen concentration of 0.01%, or in the air. The heat treatment temperature is 450°C or higher and 900°C or lower.

In the insulating layer forming step, an insulating resin is added and mixed with the soft magnetic powder, and the mixture is dried to form an insulating layer on the surface of the soft magnetic powder. The insulating layer that covers each particle of the soft magnetic powder may be attached so as to cover the entire surface of the particle, or may be attached so as to cover a part of the surface of the particle, or it may be attached so as to cover the surface of a part of the particle, or it may be attached so as to cover the surface of a part of the particle. Aspects may be mixed. Further, this insulating layer may be attached to each particle of the soft magnetic powder, or may be attached to the surface of an aggregate of particles, or both of these embodiments may be mixed. When covering a part of the surface of particles or aggregates, the insulating layer may be dispersed and attached in dots, dispersed and attached in lumps, or a mixture of these modes. You can.

The insulating resin includes a silane coupling agent, a silicone oligomer, a silicone resin, or a mixture of two or more thereof. When using multiple types of insulating resins, the insulating layer made of the multiple types of insulating resins may be divided into layers for each type, or may be a single layer in which each type is mixed.

Furthermore, a lubricant may be added before the pressing process. The lubricant may be added to and mixed with the soft magnetic powder before being filled into the mold 5, or may be applied to the inner peripheral surface of the die 6 from the opening of the die 6. The lubricant coats the surface of the soft magnetic powder or the surface of the insulating layer coated with the soft magnetic powder. Examples of the lubricant include, but are not limited to, stearic acid and its metal salts, ethylene bis stearamide, ethylene bis stearamide, ethylene bis stearate amide, and the like. The amount of lubricant added is preferably about 0.2 wt% to 0.8 wt% based on the soft magnetic powder. By setting it within this range, the sliding between the soft magnetic powders can be improved.

(effect)
As described above, in the powder compact 1 of the present embodiment, the end surfaces of the members 21, 22a, 22b, and 23, which are perpendicular to the extending direction of the leg parts 2 and perpendicular to the horizontal arrangement direction of the leg parts, are on the same plane. Instead, a recessed portion 4 is formed on the middle leg 21. Therefore, if the direction in which the E-shape appears is set as the pressing direction, it will be difficult to press the middle leg 21, and there is a possibility that cracks may occur in the powder compact 1 due to the density difference.

Therefore, in this embodiment, the pressing direction is set in the extending direction of the leg part 2, the upper punch 7 presses the back surface 32 of the yoke part 3, and the extension end surface punch 81 is used to extend the middle leg 21 and the outer legs 22a, 22b. The tip end surface 23 was pressed, and the inner peripheral surface 31 of the yoke portion 3 was pressed using the inner peripheral surface punch 82. Further, the variation in length of the plurality of leg portions 21 was set to be 0.57% or less. Thereby, the density difference between each leg 2 and the yoke 3 can be suppressed, and even if the powder compact 1 has a complicated shape in which the concave portion 4 is formed, it is possible to prevent the occurrence of cracks. Further, since the density difference in the powder magnetic core formed by annealing this powder compact 1 can be suppressed, cracks can be prevented from occurring even in the powder magnetic core with a complicated shape, like the powder compact 1. Can be done.

Further, when the powder magnetic core is used as an annular core, the annular shape is formed by joining the extending end surfaces 23 of two powder magnetic cores. If the extended end surface 23 becomes a sliding surface, when the punch slides, the extended end surface 23 will be scraped, creating an unexpected gap, and there is a risk that the magnetic properties will deteriorate, such as damaging the insulating layer and causing dielectric breakdown. There is. However, in this embodiment, the elongated tip surface 23 serving as the bonding surface is a pressed surface, so that deterioration of the magnetic properties can be prevented.

The extending end surface punch 81 has a plurality of pressing members 811 and 812 that press the extending end surfaces 23 of the middle leg 21 and the outer legs 22a and 22b, and the pressing members 811 and 812 are connected to the root portion 813 and are integrally formed. It is composed of Therefore, the pressing force applied to the middle leg 21 and the outer legs 22a, 22b can be made uniform, and the variation in the length of the legs 2 can be reduced compared to when the pressing members 811, 812 move individually to press. Therefore, it is possible to produce a compacted powder body 1 or a compacted powder core with less density difference.

Further, after the annealing process, a polishing process of polishing the extended tip surface 23 may be included. As described above, an annular core is formed by extending two powder magnetic cores and joining the tip surfaces 23. If the lengths of the leg portions 2 are different, a slight gap will be created between the shorter leg portions 2, which may deteriorate the magnetic properties. Therefore, by polishing the extended end surfaces 23 to make the lengths of the legs 2 the same, it is possible to prevent the magnetic properties from deteriorating.

(Example)
Next, the present invention will be explained in more detail based on examples. Note that the present invention is not limited to the following examples. The powder compacts of Examples 1 to 5 and Comparative Examples 1 to 5 were produced as follows. Note that Examples 1 to 5 and Comparative Examples 1 to 5 differ only in the variation in the length of the leg portion 2 in the extending direction, and the manufacturing method is the same.

First, an Fe--Si alloy was prepared as a soft magnetic powder. To this soft magnetic powder, 2.2 wt % of silicone resin was added and mixed as an insulating resin, and the mixture was dried in an air atmosphere for 2 hours.

In order to eliminate agglomeration, the soft magnetic powder was passed through a 500 μm sieve, and 0.5 wt % of a lubricant (stearic acid type) was added. A mold 5 was filled with soft magnetic powder to which a lubricant had been added, and pressed at 10 ton/cm ² using an upper punch 7 and a lower punch 8 (extended tip punch 81 and inner peripheral surface punch 82), as shown in FIG. A powder compact having a roughly E-shape was produced. In this way, powder compacts having different length variations in the extending direction were produced as shown in Table 1 below.

The lengths in the extending direction of the middle legs and outer legs of the produced powder compact were measured, and the variation in length was calculated using the above formula (1). The first outer leg shown in Table 1 below refers to the outer leg 22a, and the second outer leg refers to the outer leg 22b (see FIG. 1). In addition, the density of the middle leg, outer leg, and yoke portion was measured. Density is apparent specific gravity/volume, and was measured by the Archimedes method on a sample cut out from the middle leg, outer leg, and yoke. Specifically, it was measured as follows.

(1) Dry the sample in a constant temperature bath at 110°C, and measure the mass (dry weight) when cooled to room temperature after drying.
(2) After measuring the dry weight, submerge the sample in water to saturate it, and measure the mass (weight in water) while suspended in water with a wire (excluding the mass of jigs such as wire).
(3) Calculate the apparent specific gravity calculated using the following formula (2).
(Formula 2)
Apparent specific gravity = dry weight / (dry weight - weight in water)... (2)
(4) Calculate the density from the apparent specific gravity and the volume of the sample.

Furthermore, the density difference was calculated using the following formula (3) based on the lowest density value and the highest density value among the measured densities of each part. Note that the density of the outer legs in Table 1 is the average value of two outer legs.

(Formula 3)
Density difference = (1 - (lowest density value) / (highest density value)) x 100... (3)

The measurement results and calculation results are shown in Table 1. Further, FIG. 6 is a graph showing the relationship between leg length variations and density differences.

As shown in Table 1 and FIG. 6, it was confirmed that the greater the length variation, the greater the density difference. Further, in Comparative Example 1 in which the length variation was 0.61%, the difference in density between the outer leg and the yoke portion was large, and the connecting portion between the outer leg and the yoke portion was cracked and eventually broke. On the other hand, in Example 1 in which the length variation was 0.57%, the density difference was 0.5% or more smaller than in Comparative Example 1, and no cracks were observed at the connection portion between the outer leg and the yoke portion. Therefore, it was confirmed that the upper limit of length variation is 0.57%.

Moreover, looking at Examples 1 to 3, the density of the outer legs is all over 6.2 (g/cm ³ ). Therefore, the density difference between Examples 1 to 3 was 0.5% or more smaller than the density difference in Example 4, and it was confirmed that the density difference could be further reduced by reducing the length variation to 0.44% or less. .

(Other embodiments)
Although embodiments according to the present invention have been described in this specification, these embodiments are presented as examples and are not intended to limit the scope of the invention. The embodiments described above can be implemented in various other forms, and various omissions, substitutions, and changes can be made without departing from the scope of the invention. The embodiments and their modifications are included within the scope and gist of the invention as well as within the scope of the invention described in the claims and its equivalents.

In the above embodiment, the recessed part 4 is provided at the upper part of the middle leg 21, but the recessed part 4 is not limited to this, and is perpendicular to the extending direction of the leg part 2 and parallel to the arrangement direction of the plurality of leg parts 2. It is sufficient if the recessed portion 4 is provided on the end face in the orthogonal direction. For example, the length in the height direction may be such that the middle leg 21 is longer and the outer legs 22a, 22b are shorter, and the recessed portion 4 is formed at the upper part of each of the outer legs 22a, 22b.

Furthermore, the recessed portions 4 may be provided in the upper portions of all of the plurality of leg portions 2. That is, the yoke portion 3 may have the highest length in the height direction, and any of the leg portions 2 may be shorter than the yoke portion.

In the above embodiment, the powder compact 1 and the powder magnetic core have an E-shape, but it is sufficient that they have a plurality of legs 2, and they may have a U-shape.

1 Powder compact 2 Leg portion 21 Middle legs 22a, 22b Outer leg 23 Extended tip surface 3 Yoke portion 31 Inner peripheral surface 32 Back surface 4 Recessed portion 5 Mold 6 Die 7 Upper punch 71 Press surface 8 Lower punch 81 Extended tip surface Punch 811 Press member 811a Press surface 812 Press member 812a Press surface 813 Root portion 814 Opening 82 Inner peripheral surface punch 82a Press surface 100 Green compact

Claims (7)

A plurality of legs arranged side by side so that their extension directions are parallel;
a yoke portion that connects the plurality of leg portions;
a recess provided in an end surface of the leg that is perpendicular to the extending direction of the leg and perpendicular to the horizontal direction of the leg;
Equipped with
A press surface that is pressed by a punch, such as an extending end surface of the leg, an inner circumferential surface of the yoke that connects to the leg, and a back surface of the yoke that is an end surface opposite to the inner circumferential surface. and
The variation in the length of each leg in the extending direction, including the thickness of the yoke, is 0.57% or less;
A compacted powder body characterized by: The variation in length is 0.44% or less;
The powder compact according to claim 1, characterized by: The powder compact according to claim 1 or 2 is annealed;
A powder magnetic core featuring: Includes a pressing process in which soft magnetic powder is pressure-molded using an upper punch and a lower punch to produce a compact,
The molded body is
A plurality of legs arranged side by side so that their extension directions are parallel;
a yoke portion that connects the plurality of leg portions;
a recess provided in an end surface that is perpendicular to the extending direction of the leg and perpendicular to the horizontal direction of the leg;
Equipped with
In the pressing step, the extending direction of the leg portion is the pressing direction,
The lower punch is
an extended end face punch for pressing the extended end face of the leg;
an inner circumferential surface punch that presses an inner circumferential surface of the yoke portion connected to the leg portion;
has
The variation in length of each leg including the yoke in the extending direction of the leg is 0.57% or less;
A method for producing a compacted powder body characterized by: The extending end face punch has a plurality of pressing members that press the extending end face of each leg,
the plurality of pressing members are integrated;
The method for producing a compacted powder body according to claim 4. Including an annealing step of heat-treating the powder compact produced by the manufacturing method of claim 4 or 5;
A method for producing a dust core characterized by: After the annealing step, further comprising a polishing step of polishing the extending end surface of the leg portion;
The method for manufacturing a powder magnetic core according to claim 6, characterized in that:

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