JPH108102A - Press compact method for magnetic alloy powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of crushing crack and peeling crack and to obtain a green compact excellent in compactibility by compacting a magnetic alloy powder by means of upper and lower punches and a die and then drawing the resultant green compact while controlling holding pressure according to the height of the green compact. SOLUTION: In a press compacting apparatus by a fixed-type upper-and-lower punch double-ended pressing method, in which a core 2 is disposed in a fixed die 1 and cylindrical upper and lower punches 3, 4 are provided, the part between the punches is filled with a magnetic alloy powder of R-Fe-B (where R means rare earth elements including Y), etc. Then, the lower punch 3 is moved upward and the upper punch 4 downward to compact the magnetic alloy powder. The resultant green compact 5 is drawn from the die 1 by moving the lower punch 3 upward. At this time, particularly in the case where the ratio between the height and outside diameter of the green compact is >=1, the holding pressure by the upper and lower punches 3, 4 are changed so that it becomes a pressure not higher than the crushing crack initiation limiting pressure and not lower than the peeling crack initiation limiting pressure, according to the height of the green compact 5 in the course of drawing from the die.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a method for press-forming rare earth permanent magnet alloy powder containing R-Fe-B as a main component and having excellent magnetic properties. Depending on the height of the green compact in the middle of die removal, the holding pressure of the green compact to be held between the upper and lower punches is determined according to the height of the green compact during die removal. The present invention relates to a method of press-forming a magnet alloy powder, which is prevented by changing the value so as to obtain a value, and which improves press-formability.

[0002]

2. Description of the Related Art In the production of permanent magnets, generally, a lubricant is added to an alloy powder in order to secure the fluidity of the alloy powder during molding in a magnetic field and to facilitate release from a mold. You. This is because if there is no fluidity of the alloy powder during press molding, eaves, peeling, cracks, etc. may occur on the die wall surface or the compact surface due to friction between the powder and the mold (die wall surface) during molding. Also, this is because magnetic anisotropy is developed in accordance with the direction of easy magnetization of each powder, that is, rotation of the alloy powder for orientation is hindered.

[0003]

On the other hand, in order to prevent the occurrence of peeling cracks in the green compact, a method called holddown, in which a pressure is applied to an upper punch to remove the green compact from the die while holding the green compact ("Powder"). From Forming and Processing of Powder to Near Net Shape "edited by the Japan Society for Technology of Plasticity, JP-A-6-81
No. 006) is known.

[0004] The conventional holddown is a method of extracting a green compact from a die with a constant holding pressure to prevent peeling cracks of the green compact. This method is used for press molding of high hardness powders such as ceramic powders, intermetallic compound powders, etc., in which the hardness of the powders is high, plastic deformation is difficult and ductility is difficult, and is an effective method for obtaining good compacts. is there.

However, even in this method, when the height of the green compact is increased, the crushing strength of the green compact is greatly reduced, so that crushing cracks are easily generated. For this reason, crush cracks are liable to occur even when the dies are extracted from the die by applying a small holding pressure that does not cause peeling cracks, and it has been difficult to produce a good green compact.

According to the present invention, in the production of permanent magnets such as R-Fe-B sintered permanent magnets, the method of extracting a green compact from a die at the time of press molding is improved to produce a green compact having good moldability. And the residual magnetic flux density (Br), the intrinsic coercive force (iHc) and the maximum magnetic energy product ((BH) ma
The purpose of the present invention is to improve a press molding method capable of producing a permanent magnet having good magnetic properties of x). In particular, the crushing strength of the green compact is reduced due to an increase in the height of the green compact. It is an object of the present invention to provide a method for press-forming a magnet alloy powder capable of obtaining a green compact having good formability by preventing crushing cracks and peeling cracks when extracting the green compact obtained from a die.

[0007]

Means for Solving the Problems The present inventors have proposed R-Fe-
At the time of press forming of permanent magnet alloy powder such as B-based rare earth alloy powder, Sm-Co-based alloy powder, ferrite alloy powder, etc., in the hold-down method which is effective as a method of extracting a compact from a die, in particular, crushing of the compact As a result of various investigations on the formability when the height of the green compact with a low strength is a high dimensional ratio, by controlling the holding pressure of the green compact according to the height of the green compact during die removal Cracking, peeling,
The present inventor has found that it is possible to produce a green compact having good moldability without generating crushing cracks, and completed the present invention.

That is, the present invention relates to a press forming method for extracting a green compact of a magnet alloy powder by applying a pressure to the green compact at the time of removing a die after compression-molding with a press forming apparatus comprising upper and lower punches and a die. This is a press forming method in which the holding pressure is changed so as to be equal to or lower than the critical pressure for crush cracking and equal to or higher than the critical pressure for peeling crack generation in accordance with the height of the green compact during the extraction.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for press-forming a magnetic alloy powder according to the present invention will be described in detail with reference to the drawings. FIG. 3 shows a press forming apparatus used for a fixed die upper / lower punch double pressing method, in which a core 2 is disposed in a fixed die 1 and a cylindrical lower punch 3 is obtained in order to obtain a cylindrical green compact. The molding space is filled with magnetic alloy powder while the core 2 is inserted into the die 1 with the core 2 as a guide, and as shown in FIG. The powder 5 is obtained. Thereafter, when the obtained green compact 5 is extracted from the die 1, the holding pressure of the green compact 5 is adjusted by the upper and lower punches 3 and 4 to the height of the exposed green compact during the die extraction. Accordingly, a green compact 5 having good formability can be obtained by controlling the pressure to a predetermined value, that is, by changing the speed of the upper punch 4 and the lower punch 3 to hold down.

FIG. 4 shows a press forming apparatus used in a lower punch fixed type withdrawal method, in which a lower punch 10 is fixed, and a die 11 and an upper punch 12 can be moved up and down by a hydraulic device. A molding space formed by the lower punch 10 and the die 11 is filled with the magnet alloy powder, and the green compact 13 is obtained by lowering the upper punch 12 as shown in FIG. Upper punch 12 when extracting from
The die 11 descends and presses out while pressing the green compact 13, but the pressure is controlled to a predetermined value according to the height of the green compact exposed in the middle, that is, the speed of the upper punch 12 is changed. Then, by holding down, a green compact 13 having good moldability can be obtained.

In the present invention, the holding pressure when the green compact is extracted from the die is shown in FIG. 1 showing the relationship between the height of the green compact and the holding pressure on the limit of the occurrence of crush cracking and peeling crack of the green compact. As described above, it is an essential condition that the pressure is not higher than the green compact crushing strength and not lower than the pressure at which the occurrence of peeling cracks can be suppressed. In particular, the critical height of a green compact that can obtain a good green compact is the size, shape, surface roughness,
Although it varies depending on the green compact density, in the case of R-Fe-B alloy powder, a green compact having a height of 50 to 60 mm or more, or a height / outside diameter (long side) ratio of 1 or more is diced. In the case of extracting from the powder, the control of the holding pressure of the green compact according to the present invention is effective.

As shown in FIG. 2, peeling cracks are likely to occur in the initial stage of extracting the green compact from the die, but in the latter half stage of extracting the green compact from the die, the pressure for suppressing the occurrence of peeling cracks becomes small. On the other hand, since the green compact crushing strength becomes extremely low as the height of the green compact extracted from the die becomes high, the pressure is not more than the green compact crushing strength, and is not less than the pressure at which peel cracking can be suppressed. By performing the holddown so as to have a holding pressure within the range, a green compact having a high ratio of height / outside diameter (long side) can be stably obtained with good moldability. In addition, the control of the holding pressure can be performed by means of changing the pressure continuously or in two or more steps.

In the present invention, a molding method which can be applied,
As the press forming equipment, it can be applied to any of the fixed die single punch press forming method, the fixed die double punch press forming method, the lower punch fixed floating die forming method, the lower punch fixed wide draw forming method, etc. is there. The type of the press device may be either a mechanical type or a hydraulic type, and is not limited.

As a method for increasing the holding pressure limit range in which a green compact having good moldability can be obtained, there is the following method. (1) To increase the compaction crushing strength by increasing the press molding pressure (forming pressure of 200 MPa or less) to such an extent that the magnetic field orientation is not impaired. (2) Prevention of seizure by increasing the hardness of the die. (3) Reduction of frictional resistance by mirror finishing of the inner surface of the die. (4) Reduction of frictional resistance by improving the lubrication characteristics of the lubricant applied to the inner surface of the die. (5) Relaxation of springback stress by tapering the upper part of the inner surface of the die. (6) Uniform density by press forming with both punches. It is desirable to further improve the press formability by the method described above.

In the present invention, known permanent magnet alloy powders such as Sm-Co alloy powders and ferrite alloy powders can be used as the magnet alloy powders used for the production of permanent magnets.
In particular, R as represented by JP-B-61-34242.
-Fe-B based rare earth magnet alloy powder is preferred.

[0016]

【Example】

Example 1 Raw materials were blended to have a composition of 15% Nd-8% B-77% Fe in atomic%, melted in a high-frequency furnace in an Ar atmosphere, and then cast into a water-cooled copper mold to obtain an ingot. Was. This mirror mass is mechanically pulverized and coarsely pulverized to 35 mesh or less, and then finely pulverized by a jet mill to have a particle size of 1 to 20 μm.
R-Fe-B permanent magnet alloy powder was obtained. Further, the alloy powder was homogenized and mixed by a rocking mixer. The mixed powder was put into a feeder box of a ball screw type mechanical press forming apparatus shown in FIG. 3 and filled into a cavity to form a green compact. The green compact was extracted from a die by a conventional hold-down method. At this time, the molding pressure and the green compact height were variously changed, and the relationship between the green compact height and the green compact holding pressure at which crushing cracks and peeling cracks occurred was examined, and the results shown in FIG. 1 were obtained.

Example 2 In Example 1, when the height of the green compact was 100, the height (h ₁ ) of the green compact extracted from the die, the green compact in which crushing cracks and peeling cracks occurred The relationship with the holding pressure was examined, and the results in FIG. 2 were obtained.

Example 3 Using the ball screw type mechanical press forming apparatus shown in FIG. 3, the mixed powder obtained in Example 1 was used to form Invention Examples 1 to 4 and Comparative Examples 1 to 4 in Table 1. A green compact was produced under the following pressing conditions, the green compact was extracted from the die, and after sintering, an aging treatment was performed to form a permanent magnet. As a result, as shown in Inventive Example 1 to Inventive Example 4 in Table 1, the upper punch and the lower punch were extracted in order to use the hold-down method in which the holding pressure was controlled in real time so as to be in the good formability region of FIG. By changing the speed and extracting the green compact from the die,
It was found that a good green compact without crushing cracks and peeling cracks could be obtained.

On the other hand, as shown in Comparative Example 1 and Comparative Example 2, when the compact was extracted from the die by the hold-down method in which the holding pressure was kept constant, as shown in FIG. It was found that good compacts could not be obtained. Further, as shown in Comparative Examples 3 and 4, at a holding pressure outside the good moldability region of FIG. 2, even if the green compact is extracted from the die by the hold-down method controlled in real time, crush cracking or It was found that peeling cracks occurred and a good green compact could not be obtained.

Example 4 Raw materials were blended so as to have a composition of 17% Nd-7% B-76% Fe in atomic%, melted in a high frequency furnace in an Ar atmosphere, and then cast into a water-cooled copper mold. A lump was obtained. This ingot is mechanically pulverized and coarsely pulverized to 35 mesh or less, and then finely pulverized by a jet mill to have a particle size of 1 to 20 μm.
R-Fe-B-based rare earth alloy powder was obtained. Further, the alloy powder was homogenized and mixed by a rocking mixer. This mixed powder was put into a feeder box of a hydraulic press shown in FIG. 4 and filled into a cavity, and a green compact was produced under the press conditions of Invention Examples 5 to 8 and Comparative Examples 5 and 6 in Table 1. Then, the compact was extracted from the die.

As a result, as shown in Inventive Example 5 to Inventive Example 8 in Table 1, the hydraulic pressure was adjusted so as to be in the good formability region of FIG. By extracting the green compact from the die by the hold-down method in which the holding pressure is controlled in real time while adjusting, a good green compact without crushing cracks and peeling cracks can be obtained, and it has good magnetic properties There was found. On the other hand, as shown in Comparative Example 5 and Comparative Example 6, when the green compact was extracted from the die by the hold-down method in which the holding pressure was kept constant, as shown in FIG. 2, crushing cracks or peeling cracks occurred. It was found that a good green compact could not be obtained.

[0022]

[Table 1]

[0023]

According to the method for press-molding a magnet alloy powder according to the present invention, when a compact having a reduced compaction crushing strength due to an increase in compact height is extracted from a die,
By controlling the holding pressure of the green compact according to the height of the green compact in the middle of the die withdrawal, crush cracking and peeling cracks can be prevented, and a green compact having good moldability can be obtained. The magnetic properties of the magnet can be improved.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the green compact height and the holding pressure on the limit of the occurrence of crush cracking and peel cracking of the green compact.

FIG. 2 is a graph showing the relationship between the height of the green compact extraction portion and the holding pressure, which affects the limit of the occurrence of crushing cracks and peeling cracks of the green compact.

FIGS. 3A, 3B, and 3C are explanatory views showing a step of extracting a green compact in a press forming apparatus of a die-fixing type, upper and lower punch double-pressing type.

FIGS. 4A, 4B, and 4C are explanatory views showing a step of extracting a green compact in a lower punch fixed type withdrawal type press molding apparatus.

[Explanation of symbols]

 1,11 dice 2 core 3,10 lower punch 4,12 upper punch 5,13 green compact

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shuhei Okumura 1062 Oyabu, Yabu-cho, Yabu-gun, Hyogo Kinki Sumitomo Electric Co., Ltd.

Claims (3)

[Claims] In a press forming method for compressing a compact of a magnet alloy powder by a press forming apparatus comprising upper and lower punches and a die and applying pressure to the green compact at the time of die removal, a pressure during die removal is provided. A press molding method in which the holding pressure is changed according to the height of the powder so that the pressure is equal to or less than the critical pressure for crush cracking and equal to or greater than the critical pressure for peel cracking. 2. The method according to claim 1, wherein the raw material powder is R (where R is at least one selected from rare earth elements including Y).
Type) A method for press-molding a magnetic alloy powder that is a Fe-B-based magnetic alloy. 3. The method according to claim 1, wherein the ratio of the height of the green compact to the outer diameter (long side) is 1 or more.