JPH10152702A - Press forming method and forming apparatus for magnet alloy powder - Google Patents

Abstract

(57) [Problem] In a method of extracting a green compact from a die at the time of press-molding a permanent magnet such as an R-FeB permanent magnet, a green compact having good moldability without defects such as cracking and peeling is provided. Provided is a press molding method and a molding apparatus which can be manufactured to produce a permanent magnet having good magnetic properties. SOLUTION: The hydraulic pressure of a compression cylinder of a hydraulic press device is measured by a pressure sensor for a piston head side hydraulic pressure and a piston rod side hydraulic pressure, and a green compact holding pressure or load converted from a differential pressure thereof is slightly larger than a peeling pressure. When adjusting the pressure adjustment scale on the piston rod side so that
A molded product under any molding conditions can be stably manufactured without defects, with almost no trial and error.

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 magnetic alloy powders such as alloy powders for R-Fe-B permanent magnets. Is measured with a pressure sensor, and holddown is performed while controlling the holding pressure or load converted from the differential pressure within a certain range to prevent cracks and peeling that occur when the green compact is released. The present invention relates to a method and an apparatus for press-forming a magnet alloy powder with improved press-formability.

[0002]

2. Description of the Related Art In the production of a permanent magnet, a lubricant is generally added to a mold alone or an alloy powder or both to facilitate release from the mold during molding in a magnetic field. At this time, the internal lubricant prevents eaves, peeling, cracks, and the like from occurring on the die wall surface and the surface of the green compact due to friction between the powder and the mold (die wall surface) during press molding.
In addition, the magnetic anisotropy is developed according to the direction of easy magnetization of each powder, that is, the rotation of the alloy powder for orientation is facilitated, and there is an effect of improving the magnet properties, but the strength of the compact is reduced. There is a problem that causes.

On the other hand, in order to prevent the occurrence of peeling cracks in the green compact, a method called holddown, in which pressure is applied to the upper punch to remove the green compact from the die while holding the green compact ("Powder molding and processed powder To Near Net Shave "edited by the Japan Society for Technology of Plasticity, JP-A-6-81006.

[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.

[0005]

However, even in the hold-down method, when conditions such as the material and particle size of the powder to be molded change, the press operator himself or herself adjusts the appropriate holding pressure by trial and error. I need to find it.

For example, in a commonly used hydraulic press apparatus, after pressure molding is completed, the pressure on the piston head side of the hydraulic cylinder is released and the pressure on the piston rod side is increased after increasing the pressure adjustment dial, and then held down. In order to obtain an appropriate value of the rod-side pressure at that time, the presence or absence of a defect such as cracking or peeling of the green compact extracted from the die is checked each time to change the piston rod-side pressure. The set dial was appropriately adjusted.

As a result of a detailed investigation of these pressing methods, the inventors have found that, for example, in the case of molding R-Fe-B-based alloy powder, the piston rod side pressure adjustment scale indicates the powder particle size, molding pressure, Green compact shape, presence or absence of lubricant,
It changes depending on the oil temperature, etc., especially when internal lubrication is performed, and its suitability range is narrow, and even a skilled worker must repeat many times of trial and error to produce a compact without defects. It was found that there was a problem that efficient production was difficult and there were many defective products.

[0008] In view of the above situation, the present invention provides an R-Fe
-In the production of permanent magnets such as B-based permanent magnets, the method of extracting the green compact from the die during press molding has been improved, and a green compact with good moldability without defects such as cracks or peeling has been manufactured. Magnetic flux density (Br), intrinsic holding force (iHc)
Another object of the present invention is to provide a press molding method and a molding apparatus capable of producing a permanent magnet having good magnetic properties with a maximum magnetic energy product ((BH) max).

[0009]

Means for Solving the Problems The present inventors have proposed R-Fe-
In press-forming permanent magnet alloy powders such as B-based rare earth alloy powder, Sm-Co-based alloy powder, and ferrite alloy powder, various studies were conducted on the effective hold-down method as a method for extracting the compact from the die. It has been found that the holding pressure actually applied has an appropriate range irrespective of the molding conditions and is a pressure slightly higher than the peeling crack generation limit pressure.

The inventors who have found such an appropriate holding pressure,
As a result of further study, the hydraulic pressure of the compression cylinder of the hydraulic hydraulic press was measured using a pressure sensor to measure the piston head side hydraulic pressure and the piston rod side hydraulic pressure, and the green compact holding pressure or load converted from the differential pressure was controlled within a certain range. It was found that by holding down while performing, it was possible to produce a green compact having good moldability without occurrence of peeling cracks and crushing cracks without performing a trial and error by a press operator, and completed the present invention. did.

That is, the present invention relates to a method of molding a magnet alloy powder using a hydraulic press device, wherein the hydraulic pressure of the compression cylinder of the hydraulic press device is measured by a pressure sensor to determine the piston head side hydraulic pressure and the piston rod side hydraulic pressure. A press-forming method for a magnet alloy powder, characterized in that a hold down is performed while controlling a green compact holding pressure or a load converted into a predetermined range.

Further, the present invention provides the above-mentioned molding method, wherein the green compact holding pressure or load is equal to or less than a crush cracking limit and equal to or greater than a peeling cracking limit, or the magnet alloy powder is an R-FeB-based magnet alloy. In the case of powder (where R is at least one selected from rare earth elements including Y),
It is further proposed that the effect of the present invention be increased.

Further, the present invention provides a hydraulic press apparatus for forming a magnet alloy powder together with the above-described forming method.
The pressure sensor measures the piston head side oil pressure and the piston rod side oil pressure of the compression cylinder of the hydraulic press device, calculates the differential pressure between the two, and converts it into the green compact holding pressure or load based on the differential pressure during holddown. The present invention also proposes a magnet alloy powder compacting device having a calculation display device for displaying.

Further, according to the present invention, in the molding apparatus having the above-described structure, there is provided an arithmetic unit for calculating a pressure difference between the two and converting the pressure difference into a green compact holding pressure or load at the time of holddown based on the pressure difference; The present invention also proposes a magnet alloy powder molding apparatus having a control means for setting and maintaining a holding pressure or a load by operating a valve for controlling the pressure.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method and apparatus for press-forming a magnet alloy powder according to the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory view showing a press molding apparatus and a method for controlling a green compact holding pressure (load) according to the present invention. First, as shown in FIG. 1, in order to measure a numerical value actually applied to the green compact as a holding pressure or a load, a piston head chamber bounded by a piston 2 in a compression cylinder 1 of a hydraulic press device is used. 4 of the head-side pressure P ₁ and the rod-side pressure P ₂ of the piston rod chamber 5 is measured by the pressure sensor 6 and 7 annexed respectively, was calculated powder compact holding pressure or load in accordance with the following equation (1). In the figure, reference numeral 3 denotes a piston rod, and when the die 8 descends, the green compact 10 sandwiched between the piston rod 3 and the lower piston 9 is exposed.

The green compact holding pressure is given by the following equation (1). Holding pressure P (kgf / cm ² ) = (H × P ₁ −R × P ₂ + U) / S (1) where H = head side area, R = rod side area, U = upper ram (Piston and rod) Own weight and frictional force, P ₁ = head side pressure, P ₂ = rod side pressure, S = molded product area. In addition, in the equation (1), the one in which S is omitted is expressed as (2)
The holding load W is shown as an equation. Holding load W (kg) = (H × P ₁ −R × P ₂ + U) Equation (2)

Investigations were made on the occurrence of defective moldings in terms of holding pressure P and molding conditions, ie, molding pressure, molding shape, the presence or absence of lubricant, etc. As an example, FIG. 3 shows the relationship between the green compact holding pressure and the defect occurrence limit of the molded product.

From the above, it can be seen that in the adjustment of the holding pressure by the pressure adjustment scale on the piston rod side, the appropriate scale value fluctuates depending on the molding conditions, and the number of try and errors becomes extremely large. On the other hand, in the holding pressure P obtained from the pressure sensor according to the equation (1) and the occurrence of cracks in the molded product, the holding pressure for peeling is almost constant regardless of the molding conditions, and only the holding pressure for crushing varies depending on the molding conditions. You can see that there is.

That is, if the pressure holding pressure at the time of holddown is accurately measured by using the pressure sensors 6 and 7, and the pressure on the piston rod side is adjusted to be a holding pressure slightly larger than the peeling pressure, It is clear that a molded product under any molding conditions can be stably produced without any defect, with almost no trial and error. The load display at this time in the hydraulic press device is to display the green compact holding pressure at the time of die lowering (at the time of hold down) by a display hold signal until the next cycle starts.

In the present invention, the green compact holding pressure or load is a pressure or load that is equal to or less than the green compact cracking limit, and is equal to or greater than the peel crack generating limit shown in FIGS. It is preferable that defects such as cracking and peeling of the green compact can be further suppressed. In particular, the present invention is effective, as shown in FIG. 3, in that the green compact holding pressure at which the green compact causes peeling cracks is almost constant irrespective of powder conditions and molding conditions. By setting the green compact holding pressure slightly higher than the peeling pressure, a good green compact free of defects can be easily and stably obtained irrespective of powder conditions and molding conditions.

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.

In particular, as a press forming apparatus, a hydraulic pressure of a compression cylinder of a hydraulic press is measured by a pressure sensor on a piston head side and a piston rod side, and a differential pressure between the two is calculated and a hold-down operation based on the differential pressure is performed. It is possible to obtain an extremely workable device only by providing an arithmetic display device which converts and displays the green compact holding pressure or load. For example, in a general device, the head side pressure P
Since pressure relief valve for setting _a value typically remain constant opening and enter the dimensions and its proper holding pressure of pre-shaped articles, in the arithmetic and control unit, which controls the rod-side pressure P ₂ value Automatic control can be easily achieved simply by operating the valve so as to set and maintain an appropriate holding pressure.

As a method for increasing the holding pressure limit range in which a green compact having good moldability can be obtained, the following method is available. (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) Reducing springback stress by forming a taper at the upper part of the inner surface of the die. (6) Uniform density by press forming with both punches.

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
-FeB-based rare earth magnet alloy powder is suitable.

For example, when press-forming R-Fe-B-based magnet alloy powder in a magnetic field, there is no particular problem with the forming itself, but defects are likely to occur when the green compact is extracted from the die. Since the strength of the R-Fe-B based green compact is low, and particularly the strength of the green compact to which the internal lubricant is added is further reduced, it is difficult to set the rod-side pressure adjustment scale during hold down, In order to set an appropriate scale, many trials and errors were necessary for quality check by visual inspection, but according to the present invention, even if it is not a skilled worker,
A good green compact without defects can be obtained easily and stably.

[0026]

【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 in a water-cooled gold mold. Obtained. This ingot is mechanically pulverized and coarsely pulverized to 35 mesh or less,
Next, finely pulverize with a jet mill, and the particle size is 1 to 20μ.
m-R-Fe-B permanent magnet alloy powder (powder 1) was obtained. Further, a powder (powder 2) was prepared by adding a small amount of a lubricant to the obtained powder.

The hydraulic press device is a hydraulic press device (press device 1) equipped with a holding load control device comprising pressure sensors 6 and 7, a load calculating device, and a load indicator shown in FIG.
And a normal hydraulic press device (press device 2) without a holding load control device. Note that the load calculation was based on the aforementioned equation (2).

Each pressing device has a diameter of 30 mm.
After attaching a mold capable of molding a compact with a height of 10 mm,
Insert the powder 1 and powder 2 into the feeder box,
Press molded. The molding conditions were a molded product diameter of 30 mm × a height of 10 mm, a molding pressure of 1.3 ton / cm ^2, and a lubricant was applied to a mold only for powder 1. Table 1 shows the number of presses and the setup time until a compact having no defect is obtained.

[0029]

[Table 1]

As shown in Table 1, when a pressing device provided with a holding pressure control device according to the present invention is used, a green compact holding pressure that does not cause molding failure is known. A green compact free from defects such as cracking and peeling can be obtained in a very short time. On the other hand, in the molding using the conventional press device according to the comparative example, the number of trials and errors increases, and in particular, in the press molding of a powder to which a lubricant is added, the number of trials and errors further increases, and a long time is required. In addition, since it also depends on the skill of the press operator, it takes a long time to set again if the operator changes.

[0031]

According to the method and apparatus of the present invention, R-
It is possible to extract a green compact obtained by press-molding a magnetic alloy powder such as an Fe-B-based magnetic alloy powder from a die without generating defects such as cracking or peeling, thereby reducing the defective rate and reducing the number of manufacturing steps. Can be reduced, and a permanent magnet having excellent magnetic properties can be provided at low cost.
Further, since it is not necessary for the press operator to perform trial and error, the skill of the press operation is not required, and the time required for the setup is shortened, and the productivity is improved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a press molding apparatus and a method for controlling a green compact holding pressure or load according to the present invention.

FIG. 2 is a graph showing a relationship between a rod-side pressure adjustment scale and a green compact forming limit.

FIG. 3 is a graph showing a relationship between a green compact holding pressure and a green compact forming limit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Compression cylinder 2 Piston 3 Piston rod 4 Piston head chamber 5 Piston rod chamber 6,7 Pressure sensor 8 Die 9 Lower piston 10 Compact

 ──────────────────────────────────────────────────続 き Continued on front page (72) Inventor Koichi Ohara 2-15-17 Egawa, Shimamoto-cho, Mishima-gun, Osaka Sumitomo Special Metals Co., Ltd. Yamazaki Works

Claims (5)

[Claims] In a method of molding a magnet alloy powder using a hydraulic press, a hydraulic pressure is measured by measuring a piston head side hydraulic pressure and a piston rod side hydraulic pressure of a compression cylinder of the hydraulic press apparatus, and the pressure converted from the differential pressure is measured. A press molding method for magnet alloy powder that holds down while controlling the powder holding pressure or load within a certain range. 2. The method of press-forming a magnetic alloy powder according to claim 1, wherein the green compact holding pressure or the load is equal to or less than a crushing crack generation limit and equal to or more than a peeling crack generation limit. 3. The method according to claim 1, wherein the magnetic alloy powder is R-
A press molding method for a magnet alloy powder that is an Fe-B based magnet alloy powder (where R is at least one selected from rare earth elements including Y). 4. A hydraulic press apparatus for molding magnetic alloy powder, wherein a hydraulic pressure on a piston head side and a hydraulic pressure on a piston rod of a compression cylinder of the hydraulic press apparatus are measured by a pressure sensor, and the differential pressure between the two is calculated. A magnetic alloy powder molding apparatus having an arithmetic display unit which converts and displays the green compact holding pressure or load at the time of holddown based on the calculation. 5. A hydraulic press apparatus for molding a magnet alloy powder, wherein a hydraulic pressure of a piston cylinder side and a hydraulic pressure of a piston rod of a compression cylinder of the hydraulic press apparatus are measured by a pressure sensor, and a differential pressure between the two is calculated. And a control device for operating a valve for controlling the rod side pressure to set and maintain the holding pressure or the load.