JP2005240060A - Compact, in-magnetic-field compacting apparatus, and method for manufacturing magnetostrictive element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an in-magnetic-field compacting apparatus for effectively inhibiting the formation of crack without degrading the magnetic properties, and a method for manufacturing a magnetostrictive element. <P>SOLUTION: This manufacturing method includes setting a dimension h of the flat surface 12 of a compact 10 so as to be h/ϕ>0.5 on the basis of the dimension ϕ of a curved surface 11, which inhibits a compression ratio (density) of an alloyed powder in a portion of the flat surface 12 of the formed article 10 from extremely increasing with respect to a portion of the curved surface 11, and consequently inhibits the crack from forming in the compact 10 due to internal stress generated when the compact 10 is heated during baking. The manufacturing method also includes setting the working end position of a die for compacting the compact 10, on the basis of the ratio of the compression ratio of the alloyed powder in the dimensionally maximum part of the compact 10 to the compression ratio in the dimensionally minimum part. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a forming apparatus in a magnetic field used when manufacturing a magnetostrictive element or the like, a method for manufacturing a magnetostrictive element, or the like.

Conventionally, magnetostrictive elements have been used for linear actuators, vibrators, pressure torque sensors, vibration sensors, gyro sensors, and the like.
When this magnetostrictive element is used for a linear actuator, a vibrator, or the like, a driving force is generated by changing the size of the magnetostrictive element by changing the magnetic field to be applied. When a magnetostrictive element is used for a pressure torque sensor, vibration sensor, gyro sensor, etc., the dimension of the magnetostrictive element changes due to externally applied pressure, and sensing is performed by detecting the magnetic permeability that changes accordingly. Is going.

Such a magnetostrictive element is manufactured by forming a molded body by molding an alloy powder having a predetermined composition in a magnetic field, and then sintering the molded body in an inert gas atmosphere (for example, patents). Reference 1).
In the forming process in the magnetic field, the alloy powder is oriented with the mold while applying the magnetic field, and the alloy powder is pressure-molded. As the forming method in the magnetic field, the pressurizing direction and the direction of the applied magnetic field are matched. There are so-called longitudinal magnetic field shaping and transverse magnetic field shaping in which a magnetic field is applied from a direction (lateral direction) orthogonal to the pressing direction.
When it is desired to finally obtain a cylindrical (so-called round bar) magnetostrictive element, transverse magnetic field molding is used. On the other hand, in general, when a round bar is formed in a magnetic field by powder metallurgy, vertical magnetic field forming is adopted with emphasis on formability. However, in the vertical magnetic field shaping, the crystal orientation of the particles in the magnetic field is disturbed, so that the degree of anisotropic orientation is lowered and the magnetic properties are lowered. For this reason, transverse magnetic field shaping is employed in magnetostrictive elements that place importance on magnetic characteristics.

JP 2003-3203 A (page 4)

  However, in the case of transverse magnetic field molding, as shown in FIGS. 5 (a) and 5 (b), when the alloy powder is pressed up and down by the upper and lower molds 1 and 2, the pressing direction is finally a round bar. It becomes the “cross-sectional direction” with respect to the molded body 3 that becomes. For this reason, the mating surfaces 4 of the upper and lower molds 1 and 2 are positioned on the side surface of the molded body 3. Then, it is very difficult to make the cross-sectional shape of the molded body 3 a perfect circle, and in order to increase the roundness, the precision of the molds 1 and 2 must be greatly increased, resulting in an increase in mold cost, and consequently This leads to an increase in the manufacturing cost of the magnetostrictive element. In addition, so-called burrs and parting lines remain in the molded body 3 at positions corresponding to the mating surfaces 4, and in any case, removal of these burrs and parting lines is required in terms of quality. The

  Therefore, conventionally, as shown in FIGS. 6 (a) and 6 (b), a relief 5 is formed in a portion corresponding to the mating surface 4 of the molds 1 and 2, and as shown in FIG. 7 (a), molding is performed. As shown in FIG. 7 (b), after forming a flat portion (straight portion in the cross section) 3 s on the side surface of the body 3, forming in the magnetic field is completed, and the molded body 3 is removed from the molds 1 and 2. The flat part 3s is removed and the cross section is processed into a perfect circle.

However, in the molded body 3 (or the magnetostrictive element formed from the molded body 3) having the cross-sectional shape as shown in FIG.
This is because, in the molded body 3 having the flat portion 3s, the distribution of the compression ratio when the upper and lower molds 1 and 2 are pressed is greatly different. Here, the compression ratio is the dimension H ′ from the upper surface level 9 of the alloy powder filled between the molds 1 and 2 to the upper surface of the mold 2 in the state before pressurization shown in FIG. The ratio H ′ / H with the dimension H of the gap between the surfaces of the upper and lower molds 1 and 2 at the time of completion of pressurization shown in FIG.
In particular, the compression ratio H ₁ ′ / H ₁ and the compression ratio H ₂ ′ / H ₂ of the maximum dimension portion L at the center of the molded body 3 and the flat portion 3 s which is the minimum dimension portion S of the molded body 3 are also shown. to differ greatly. Along with this, the filling degree and density of the alloy powder in the molded body 3 that has been molded are also greatly different between the maximum dimension portion L and the minimum dimension portion S.
Of course, also on the curved side surface (hereinafter referred to as a curved surface) 3w of the molded body 3, the compression ratio H ′ / H changes from the maximum dimension portion L toward the minimum dimension portions S on both sides. The change is continuous. However, in the portion where the flat portion 3s and the curved surface 3w are adjacent, the change in the compression ratio H ′ / H (that is, the density) becomes discontinuous. For this reason, in particular, when heat is applied during firing, a crack C tends to occur in the molded body 3 in this portion due to internal stress.

In order to solve such a problem, it is effective to add a wax component having a lubricating action such as paraffin in the case of a normal magnet or the like other than the magnetostrictive element using rare earth as a raw material.
However, in the case of a magnetostrictive element, since the rare earth element of the raw material easily reacts with an organic substance contained in the wax component, the generated reaction product generates an internal stress during sintering, which causes the sintered body to be distorted and magnetic properties ( Magnetic permeability) is greatly reduced (halved). For this reason, such a countermeasure cannot be used in manufacturing the magnetostrictive element.

  The present invention has been made based on such a technical problem, and provides a forming apparatus in a magnetic field, a method of manufacturing a magnetostrictive element, and the like that can effectively suppress generation of cracks without deteriorating magnetic characteristics. The purpose is to do.

For this purpose, the molded body of the present invention is a molded body that contains Tb, Dy, and Fe and becomes a magnetostrictive element by sintering, and this molded body has a molded body body that has a substantially circular cross section. And an overhanging portion formed so as to project outward from the outer peripheral surface of the molding body on both sides of the center of the molding body, and the overhanging portion includes one overhanging portion and The dimension h of the projecting portion in the direction orthogonal to the direction connecting the other projecting portion is characterized in that h / φ> 0.5 with respect to the outer diameter φ of the molded body.
In this way, by setting the dimension h of the overhanging portion to a predetermined size or more with respect to the outer diameter φ of the formed body, the distribution of the cross-sectional dimensions of the formed body, more specifically, the minimum cross-sectional dimension (the overhanging portion) The difference between the dimension h) and the maximum cross-sectional dimension (the outer diameter φ of the molded body) can be suppressed. Thereby, it can suppress that the distribution of the density of the raw material powder in a molded object changes greatly with parts.
The upper limit of h / φ is h / φ <1.0. When h / φ = 1.0, the compact has a rectangular cross section having a constant thickness. In such a case, the density of the raw material powder is constant, and the above-described problem does not occur.

Here, the overhanging portion is formed, for example, at a position corresponding to the mating surface of the mold used when the molded body is formed. By removing the overhanging portion itself, the burrs formed on the overhanging portion are formed. And the parting line can be removed to obtain a molded body having a circular cross section. And a magnetostrictive element can be obtained by sintering this molded object main body. Of course, the use of the overhang portion is not limited to this, and the present invention can be applied to other uses as long as a molded body having the same overhang portion is formed.
The shape of the overhanging portion may be any shape, for example, the overhanging portions formed on both sides of the center of the molded body have flat surfaces formed substantially parallel to each other. can do. Further, the flat surface can be formed so as to circumscribe the molded body.

The present invention can also be regarded as a molding apparatus in a magnetic field in which a magnetic field is applied to a magnetic powder and the powder is molded into a predetermined shape by an upper mold and a lower mold to form a compact. In this case, in the magnetic field molding apparatus, the upper mold and the lower mold each have a curved surface portion having a predetermined radius of curvature on the molding surface, and a flat surface portion formed from both sides of the curved surface portion toward the outer peripheral side. And when the molded body is formed, the pressing completion position of the upper die and the lower die is determined by the distance between the upper end portion of the upper die curved surface portion and the lower end portion of the lower die curved surface portion, and the upper die plane portion. And the distance between the plane portions of the lower mold.
The pressurization completion position is a position when the molding of the molded body is completed when the powder is pressed by operating at least one of the upper mold and the lower mold.
Thereby, the difference in thickness between the curved surface of the molded body molded by the molding apparatus in a magnetic field and the planes on both sides thereof is controlled. By suppressing this difference, it is possible to suppress a significant difference in the powder density distribution in the molded body to be molded.
More specifically, a pressure end position of the upper mold and the lower mold, the distance S ₁ of the lower end portion of the curved surface portion of the upper portion and the lower mold of the curved surface portion of the upper mold when forming the molded body, the upper die It is preferable that the distance S ₂ between the flat surface portion and the lower mold flat surface portion is set so that S ₂ / S ₁ > 0.5.

Such a forming apparatus in a magnetic field can be used for producing a normal magnet other than a magnetostrictive element using rare earth as a raw material, but in particular, the formula (1) RT _y (where, R is one or more rare earth metals, T is one or more transition metals, and y is 1 <y <4.) For forming a molded body for forming a magnetostrictive element having the composition It is effective to use.
Further, this in-magnetic field molding apparatus can perform so-called transverse magnetic field shaping, further including a magnetic field applying unit that applies a magnetic field in a direction orthogonal to the pressing direction by the upper mold and the lower mold.

The present invention is a molding apparatus in a magnetic field that forms a compact by forming a powder into a predetermined shape while applying a magnetic field to the magnetic powder, and has a predetermined radius of curvature for molding the powder. Upper and lower molds each having a curved surface portion and a flat portion formed from both sides of the curved surface portion toward the outer periphery, and at least one of the upper and lower molds correspond to the curved surface portion and the flat portion between the upper and lower molds. It can also be understood as a molding apparatus in a magnetic field characterized by comprising a mold drive unit that operates to a working end position set based on the amount of powder filled in the region.
Here, the operation end position set based on the filling amount of the powder into the region corresponding to the curved surface portion and the flat surface portion between the upper and lower molds is the region corresponding to the curved surface portion and the region corresponding to the flat surface portion. The operation end position is set based on the filling amount of the powder in each of the above. That is, the operation end position is set in consideration of the powder compression ratio in the region corresponding to the curved surface portion and the powder compression ratio in the region corresponding to the flat surface portion.
Specifically, the compression ratio of the powder in the region corresponding to the plane portion is such that at least one of the upper and lower molds is operated, and the upper mold plane portion and the lower mold portion in the state where this is in the operation end position. Ratio H ₁ of the level H ₁ ′ of the powder filled in the portion between the plane portion of the upper mold and the plane portion of the lower mold in the state before molding with respect to the interval H ₁ of the mold plane portion '/ H ₁
The compression ratio of the powder in the region corresponding to the curved surface portion is determined by the bending of the upper end portion of the curved surface portion of the upper mold and the lower mold when at least one of the operated upper and lower molds is at the operation end position. The level H ₂ ′ of the powder filled between the upper end portion of the curved surface portion of the upper mold and the lower end portion of the curved surface portion of the lower mold in the state before molding with respect to the interval H ₂ of the lower end portion of the surface portion. The ratio becomes H ₂ ′ / H ₂ .
Therefore, the operation end position is set based on the ratio H ₁ ′ / H ₁ and the ratio H ₂ ′ / H ₂ .

As described above, when the operation end position of the mold is set based on the filling amount of the powder, the compression ratio of the powder, that is, the density of the powder in the molded body becomes excessively high in a specific portion of the formed molded body. Can be prevented.
For this purpose, for example, the ratio H ₁ ′ / H ₁ is preferably set to be less than 1.5 times the ratio H ₂ ′ / H ₂ .

Such a forming apparatus in a magnetic field can also be used when producing a normal magnet or the like other than the magnetostrictive element using rare earth as a raw material, but in particular, the formula (1) RT _y (where, R is one or more rare earth metals, T is one or more transition metals, and y is 1 <y <4.) For forming a molded body for forming a magnetostrictive element having the composition It is effective to use.

The present invention can also be understood as a method for manufacturing a magnetostrictive element. In this method, a magnetostrictive material is filled between the upper mold and the lower mold, and at least one of the upper mold and the lower mold is operated with a preset operation stroke, and the magnetostrictive material is molded in a magnetic field. Forming a body, and the operation stroke at this time is a compression ratio in a portion where the compression ratio of the magnetostrictive material is maximum between the upper die and the lower die and a portion where the compression ratio of the magnetostrictive material is minimum It is set based on the ratio.
The operating stroke refers to the dimension from the operation start position to the operation end position when at least one of the upper mold and the lower mold operates, and the operation start position is determined by each molding device, Here, the operation end position is set in particular.
This method can further include a step of processing the molded body obtained by the molding in a magnetic field into a substantially circular cross section and a step of sintering the molded body.
The molded body formed here can contain Tb, Dy, and Fe.

  According to the present invention, generation of cracks can be prevented even in a magnetostrictive element to which a wax component cannot be added, by forming a compact by controlling the powder compression ratio according to the shape of the compact.

The present invention will be described in detail below based on the present embodiment.
First, a method for manufacturing a magnetostrictive element in the present embodiment will be described.
In this embodiment, it is represented by the formula (1) RT _y (where R is one or more rare earth metals, T is one or more transition metals, and y represents 1 <y <4). A magnetostrictive element is obtained by sintering the alloy powder having the composition.
Here, R represents one or more selected from lanthanoid series and actinoid series rare earth metals including Y. Among these, R is particularly preferably a rare earth metal such as Nd, Pr, Sm, Tb, Dy, and Ho, and more preferably Tb and Dy. T represents one or more transition metals. Among these, as T, transition metals such as Fe, Co, Ni, Mn, Cr, and Mo are particularly preferable, Fe, Co, and Ni are more preferable, and these can be mixed and used.

In the alloy represented by formula (1) RT _y , _y represents 1 <y <4. RT _y is y = 2, and the RT ₂ Laves type intermetallic compound formed by R and T is suitable for a magnetostrictive element because it has a high Curie temperature and a large magnetostriction value. Here, when y is 1 or less, the RT phase is precipitated by the heat treatment after sintering, and the magnetostriction value is lowered. When y is 4 or more, the RT ₃ phase or the RT ₅ phase increases, and the magnetostriction value decreases. Therefore, in order to RT ₂ is more rich phase, y is 1 <range of y <4 is preferable. R may be mixed with rare earth metals, and it is particularly preferable to mix Tb and Dy.
Furthermore, in the alloy represented by the formula (2) Tb _a Dy _(1-a) , it is more preferable that a is in the range of 0.27 <a ≦ 0.50. Thus, the alloy represented by the formula (3) (Tb _a Dy _(1-a) ) T _y has a large saturation magnetostriction constant and a large magnetostriction value. Here, when a is 0.27 or less, a sufficient magnetostriction value is not exhibited at room temperature or less, and when it exceeds 0.50, a sufficient magnetostriction value is not exhibited near room temperature. T is particularly preferably Fe. By forming Tb, Dy and (Tb, Dy) Fe ₂ intermetallic compound, a sintered body having a large magnetostriction value and high magnetostriction characteristics can be obtained. At this time, a part of Fe may be substituted with Co and Ni. However, Co increases magnetic anisotropy but decreases magnetic permeability, and Ni lowers the Curie temperature. In order to reduce the magnetostriction value at room temperature and high magnetic field, Fe is 70 wt% or more, more preferably 80 wt% or more.

Further, it is preferable that a part of the alloy powder contains a raw material to be subjected to hydrogen storage treatment. By storing hydrogen in the alloy powder, distortion occurs and cracks occur due to the internal stress. For this reason, the alloy powder to be mixed is subjected to pressure when forming a compact, and is pulverized inside the mixed state to become fine, and when it is sintered, a dense high-density sintered body can be obtained. . Furthermore, since rare earths of Tb and Dy are easily oxidized, an oxide film having a high melting point is formed on the surface even if there is a slight amount of oxygen, and the progress of sintering is suppressed, but it is oxidized by occlusion of hydrogen. It becomes difficult. Therefore, a part of the alloy powder can be subjected to a hydrogen storage treatment to produce a high-density sintered body.
Here, the raw material for storing hydrogen preferably has a composition represented by the formula (4) Dy _b T _(1-b) and b is 0.37 ≦ b ≦ 1.00. T may be Fe alone, or a part of Fe may be substituted with Co or Ni. Thereby, the sintered compact density of the alloy powder of a raw material can be made high.

In the present embodiment, for example, the raw material powder is heated in a temperature range of 650 ° C. or higher and / or in a stable temperature range of 1150 ° C. or higher and 1230 ° C. or lower in a hydrogen gas atmosphere or hydrogen gas: argon (Ar) gas = X: Sintering is performed in a mixed atmosphere of hydrogen gas and inert gas in which X in Formula (5) expressed as 100-X is 0 <X <50.
In the alloy represented by the formula (1) RT _y , at least the raw material powder is made a mixed atmosphere of hydrogen gas and inert gas in the temperature rising process of 650 ° C. or higher.
Sintering is performed by heating the formed raw material powder in a furnace. The heating rate is 3 to 20 ° C./min. When the rate of temperature rise is less than 3 ° C./min, the productivity is low, and when the rate of temperature rise exceeds 20 ° C./min, the temperature of the raw material powder formed in the furnace is not uniform and segregation or heterogeneous phase occurs. The reason why the temperature is raised to 650 ° C. or higher is to prevent oxidation due to a small amount of remaining oxygen.
Sintering is preferably performed at a stable temperature that keeps the temperature substantially constant. This stable temperature is preferably in the range of 1150-1230 ° C. If the stable temperature is less than 1150 ° C., it takes a long time to remove internal strain, which is not efficient, and if the stable temperature exceeds 1230 ° C., it will be close to the melting point of the alloy represented by RT _y. This is because the bonded body may melt and other phases such as other RT ₃ phases may precipitate.

Further, the sintering is performed in a hydrogen gas atmosphere or an inert gas in which hydrogen gas atmosphere or hydrogen gas: argon (Ar) gas = X: 1 in formula (5) represented by 1−X, where 0 <X <0.5. It is preferable to carry out in a mixed atmosphere.
R reacts very easily with oxygen to form a stable rare earth oxide. These oxides have low magnetic properties but do not exhibit magnetic properties that make them practical magnetic materials. In high-temperature sintering, even with a slight amount of oxygen, the magnetic properties of the sintered body are greatly reduced. Therefore, in heat treatment such as sintering, an atmosphere containing hydrogen gas is particularly preferable. In addition, as an atmosphere for preventing oxidation, there is an atmosphere of an inert gas. However, it is difficult to completely remove oxygen with an inert gas alone, and a rare earth metal having a high reactivity with oxygen forms an oxide. In order to prevent oxidation, an atmosphere of a mixed gas of hydrogen gas and inert gas is preferable.

  As a reducing atmosphere containing hydrogen gas, it is preferable that X (vol%) is 0 <X <50 in the formula (5) represented by hydrogen gas: argon (Ar) gas = X: 100-X. Since Ar gas is an inert gas and does not oxidize R, it can be mixed with hydrogen gas to obtain an atmosphere having a reducing action. For this reason, in order to have a reducing action, X (vol%) is preferably at least 0 <X. Further, X (vol%) is preferably X <50 since the reducing action is saturated when 50 ≦ X. Here, a mixed atmosphere of hydrogen gas and Ar gas is preferably set in the temperature range of 650 ° C. or higher in the temperature rising process, or a mixed atmosphere of hydrogen gas and Ar gas is more preferable in the stable temperature range.

The details of the flow of the magnetostrictive element manufacturing process are as follows.
First, as one of the raw materials, Tb, Dy, and Fe are weighed and melted in an inert atmosphere of Ar gas to produce an alloy (hereinafter referred to as “raw material A”). Here, the raw material A has a composition of, for example, Tb _0.4 Dy _0.6 Fe _1.94 . This raw material A is subjected to a heat treatment for annealing to make the concentration distribution of each metal element uniform during the manufacture of the alloy, and after annihilating the precipitated foreign phase, it is pulverized by, for example, an atomizer.
Further, as one of the raw materials, Dy and Fe are weighed and melted in an inert atmosphere of Ar gas to produce an alloy (hereinafter referred to as “raw material B”). Here, the raw material B has a composition of, for example, Dy _2.0 Fe. Similarly, the raw material B is pulverized by, for example, an atomizer.
Further, as one of the raw materials, Fe is subjected to a reduction treatment for removing oxygen in a hydrogen gas atmosphere, and then pulverized with, for example, an atomizer (hereinafter referred to as “raw material C”).

Next, the obtained raw materials A, B, and C are weighed and then pulverized and mixed to obtain an alloy powder (raw material powder) whose composition is, for example, Tb _0.3 Dy _0.7 Fe _1.88 .
Thereafter, the obtained alloy powder is put into a mold and molded in a magnetic field having a predetermined strength, for example, 8 kOe to obtain a molded body.
And the obtained molded object is heated up with a predetermined | prescribed temperature profile in a furnace, and a sintered compact is obtained. At this time, for example, firing is performed in a mixed atmosphere of 35 vol% hydrogen gas and 65 vol% Ar gas in a stable temperature interval of 1150 to 1230 ° C. to obtain a sintered body.
A magnetostrictive element can be obtained by performing an aging treatment on the sintered body and then dividing the sintered body into a predetermined size.

In the present embodiment, in order to form a round bar-shaped magnetostrictive element having a high cross-sectional roundness, first, as shown in FIG. 1, an alloy powder having a predetermined composition as described above is formed in a magnetic field. After forming the cross-sectional molded body 10 having the flat surface 12 on the side surface, the molded body 10 is sintered in an inert gas atmosphere. And the magnetostrictive element 20 of a circular cross section is obtained by performing the additional process which deletes the part of the flat surface 12 with respect to the molded object 10 which sintered.
As shown in FIG. 1, a molded body 10 obtained by molding an alloy powder in a magnetic field has an arcuate curved surface 11 for forming the outer peripheral surface of the magnetostrictive element 20 that finally has a circular cross section, A flat surface 12 parallel to the center of the molded body 10 and an orthogonal surface 13 orthogonal to the flat surface 12 and formed between both ends of the flat surface 12 and the curved surface 11 are provided. From another viewpoint, the molded body 10 was formed so as to project outward from both sides of the molded body main body 14 which finally becomes the magnetostrictive element 20 having a circular cross section. A portion including the projecting portion 15 where the molded body 14 is exposed (a portion other than the portion where the projecting portion 15 is formed) becomes the curved surface 11, and the projecting portion 15 is formed by the flat surface 12 and the orthogonal surface 13. Has been.

In order to form the molded body 10 having such a shape, a molding apparatus 30 in a magnetic field as shown in FIG. 2 is used.
As shown in FIG. 2, a molding apparatus 30 in a magnetic field includes a mold mortar 31 and a lower mold punch (lower mold, mold) disposed in an opening 32 formed in the mold mortar 31. 40 and a die upper punch (upper die, die) 50 provided above the die lower punch 40 so as to be opposed to the die lower punch 40 and capable of moving up and down in the vertical direction.

  The mold die 31 has an opening 32 having a predetermined shape penetrating in the vertical direction, and the opening 32 has a pair of vertical surfaces 32a and 32a.

  The lower die punch 40 is provided in such a manner that it is inserted into the opening 32 from the bottom side of the opening 32, and a concave-shaped curve that forms the curved surface 11 of the molded body 10 at the center of the upper surface thereof. A flat surface portion 42 that forms the orthogonal surface 13 of the molded body 10 is formed continuously between both sides of the surface portion 41 and the vertical surface 32 a of the opening 32.

On the other hand, the mold upper punch 50 has a shape that is obtained by inverting the mold lower punch 40 upside down, and includes a concave curved surface portion 51 that forms the curved surface 11 of the molded body 10. The flat portion 52 forming the orthogonal surface 13 of the molded body 10 is continuously formed. The mold upper punch 50 is driven in a vertical direction with a predetermined stroke by a mold driving unit (not shown). A lower end position (operation end position) 50 _L (indicated by a two-dot chain line in FIG. 2) of the drive stroke of the upper mold punch 50 is a position above the predetermined lower dimension than the lower mold punch 40. Accordingly, between the lower mold punch 40 and the upper mold punch 50, the vertical surfaces 32a and 32a of the opening 32 of the mold die 31 are exposed on both sides thereof. Surface 12 is formed.

  In such a molding apparatus 30 in a magnetic field, when molding the molded body 10, a predetermined level, for example, the same level as the upper surface level 31 a of the mold mortar 31, is predetermined within the opening 32 of the mold mortar 31. The alloy powder 100 of composition is put. Then, the mold upper punch 50 is lowered, and the alloy powder 100 is pressure-formed with the mold lower punch 40. At this time, the alloy powder 100 is formed in the magnetic field by applying a magnetic field in a direction orthogonal to the pressing direction, that is, a horizontal direction, by a magnetic field applying unit (not shown).

After the molding in the magnetic field is continued for a predetermined time, the die punch 50 is raised. At this point, the alloy powder 100 molded in a magnetic field forms a molded body 10 having a predetermined shape as shown in FIG. At this time, the curved surface 11 of the molded body 10 is formed by the curved surface portion 41 of the lower mold punch 40 and the curved surface portion 51 of the upper mold punch 50, and the flat surface 42 of the lower mold punch 40 and the upper punch 50 of the mold. The flat surface 52 forms the orthogonal surface 13 of the molded body 10, and the vertical surface of the opening 32 of the mold die 31 exposed on both sides between the lower mold punch 40 and the upper mold punch 50. The flat surface 12 of the molded body 10 is formed by 32a and 32a.
In the molded body 10 thus formed, the flat surfaces 12 are formed in parallel to each other so as to face both sides of the center of the molded body 10. The height h of the flat surface 12 is a dimension of the overhanging portion 15 in the direction along the pressing direction of the molded body 10, and this direction corresponds to the one overhanging portion 15 sandwiching the molded body main body 14 and the other. This is a direction orthogonal to the direction connecting the overhang portions 15.

In the present embodiment, the shape (dimensions) of the flat surface 12 of the molded body 10 formed in this way is set as follows. Here, as shown in FIG. 1, the height of the molded body 10 (the dimension of the maximum dimension portion of the upper and lower curved surfaces 11, that is, the final diameter of the magnetostrictive element 20) is the dimension φ, and the height of the flat surface 12. H, and the width of the orthogonal surface 13 (the distance between the end of the curved surface 11 and the end of the flat surface 12) is the dimension w. The flat surface 12 is formed so as to circumscribe the surface of the final magnetostrictive element 20 (two-dot chain line in FIG. 1). Therefore, the width of the entire molded body 10 is also the dimension φ.
The dimension h of the flat surface 12 of the molded body 10 is set to the dimension φ of the curved surface 11.
h / φ ≧ 0.5
It is preferable to set the height h so that
In order to form the molded body 10 having such dimensions, the dimensions of each part of the mold lower punch 40 and the mold upper punch 50, and the operation lower limit position (operation end position) of the mold upper punch 50 are set as described above. What is necessary is just to set so that it may respond | correspond to each part dimension of the body 10. FIG.

Here, the dimension w of the orthogonal surface 13 can be geometrically calculated from the dimension h of the flat surface 12 and the dimension φ of the molded body 10.
That is, in the molded body 10 in FIG. 1, the distance S ₁ between the two points P ₁ and P ₂ that are located in the diagonal direction where the curved surface 11 and the orthogonal surface 13 are in contact is φ, and the flat surface 12 A distance S ₂ between two points P ₁ and P _{3 at which the} curved surface 11 and the orthogonal surface 13 are in contact in a parallel direction is h.
Therefore, the distance _{S 3} between the points _P 2, _{P 3} is
S ₃ = (φ ² −h ² ) ^1/2
It becomes.
Further, although the distance _{S 4} between the parallel flat surfaces 12, 12 to each other is phi,
S ₄ = φ = S ₃ + 2w
It is.
Therefore, from these equations:
w = (φ−S ₃ ) / 2
= (Φ− (φ ² −h ² ) ^1/2 ) / 2
It becomes.

In addition, the molding condition of the compact 10 can be set from the distribution of the compression ratio of the alloy powder 100.
Here, as shown in FIG. 2, the central portion of the molded body 10 (the portion having the smallest compression ratio: hereinafter, the largest dimension portion L) where the distance between the lower die punch 40 and the upper die punch 50 is maximized. ), The alloy powder 100 is in a state before pressing from the lower top (lower end) 41a of the curved surface portion 41 of the lower die punch 40 to a predetermined level (for example, the upper surface level 31a of the die mortar 31). It has a height H ₁ ′, and in the pressurization completed state (the state of the two-dot chain line in FIG. 2), the curved surface portion of the mold upper punch 50 extends from the lower top 41a of the curved surface portion 41 of the mold lower punch 40. 51 is compressed to a height H ₁ (interval S ₁ ) up to an upper top portion (upper end portion) 51a. Therefore, the compression ratio _{X 1} alloy powder 100 in the maximum dimension of L _{becomes H 1} '/ H 1.
On the other hand, in the portion (the portion where the compression ratio is maximized: hereinafter, the smallest dimension portion S) in which the orthogonal surfaces 13 on both sides of the molded body 10 are formed so that the distance between the lower die punch 40 and the upper die punch 50 is minimized. The alloy powder 100 has a height H ₂ ′ from the flat portion 42 of the lower mold punch 40 to a predetermined level (for example, the upper surface level 31 a of the mold die 31) before being pressed. In the pressurization completed state (the state of the two-dot chain line in FIG. 2), the height H ₂ (interval S ₂ ) from the flat surface portion 42 of the lower mold punch 40 to the flat surface portion 52 of the upper mold punch 50 is determined. Compressed. Therefore, the compression ratio _{X 2} alloy powder 100 in the minimum dimension portion S _{becomes H 2} '/ H 2.

Here, the position of the punch 50 on the mold in the pressurized state, that is, the operation end position of the punch 50 on the mold is the compression ratio X ₁ (X ₁ = H ₁ ′ / H) of the alloy powder 100 of the maximum dimension portion L. ₁ ) and the ratio X ₂ / X ₁ of the compression ratio X ₂ (X ₂ = H ₂ ′ / H ₂ ) of the alloy powder 100 of the smallest dimension portion S,
X ₂ / X ₁ ≦ 1.5
It is preferable to set so as to satisfy the above.

As described above, the dimension h of the flat surface 12 of the molded body 10 is set based on the dimension φ of the curved surface 11, and the operation end position of the punch 50 on the mold is set to the compression ratio X ₁ of the maximum dimension portion L. by setting based on the ratio of the compression ratio X ₂ of the smallest dimension of S, the flat surface 12 portion of the molded body 10, i.e. the minimum dimension portion S of the mold body 10, the compression ratio of the alloy powder 100 (density) Further, it is possible to suppress an excessive increase with respect to other portions, that is, the curved surface 11 portion. Accordingly, it is possible to suppress the occurrence of cracks in the molded body 10 due to internal stress when heat is applied during firing of the molded body 10.

Here, when the ratio of the dimension h to the dimension φ of the molded body 10 was varied, the occurrence of cracks in the molded body 10 was examined, and the results are shown below.
First, as raw material A, Tb, Dy, and Fe were weighed and melted in an inert atmosphere of Ar gas to produce an alloy having a composition of Tb _0.4 Dy _0.6 Fe _1.94 . Then, this raw material A was subjected to a heat treatment for annealing, to make the concentration distribution of each metal element uniform during the manufacture of the alloy, and to dissipate the precipitated foreign phase, and then pulverized with, for example, an atomizer. As the raw material B, Dy and Fe were weighed and melted in an inert atmosphere of Ar gas to produce an alloy having a composition of Dy _2.0 Fe, and similarly pulverized by, for example, an atomizer. As a raw material C, Fe was subjected to a reduction treatment for removing oxygen in a hydrogen gas atmosphere, and then pulverized by, for example, an atomizer.
Subsequently, the obtained raw materials A, B, and C were weighed and then pulverized and mixed to obtain an alloy powder having a composition of Tb _0.3 Dy _0.7 Fe _1.9 .
The obtained alloy powder was put in a mold and molded in a magnetic field of 8 kOe to obtain a molded body 10. As shown in Table 1, the dimensions of the compact 10 were 3.5 to 16 mm, the dimension h was 1.85 to 5.65 mm, and a total of seven samples (molded bodies 10) were obtained.
The obtained molded body 10 is placed in a sintering vessel and heated in a furnace, fired in a mixed atmosphere of 35 vol% hydrogen gas and 65 vol% Ar gas in a stable temperature zone of 1150 to 1230 ° C., and sintered. Got the body.

  The presence or absence of occurrence of cracks in the sintered body obtained as described above, and the occurrence length of cracks were measured. The results are shown in Table 1 and FIG.

  As shown in Table 1 and FIG. 3, it was confirmed that when the ratio h / φ ≧ 0.5 of the dimension h and the dimension φ was set, the crack generation length was 0, that is, no crack was observed.

Then, the results are shown in the following were studied when varying the compression ratio X ₂ compression ratio X ₁ and the minimum dimension portion S of the largest dimension of L, and occurrence of cracks in the shaped body 10.
The production conditions and production information for each sample were the same as in Example 1.
Maximum compression ratio X ₁ of dimension of _L, the compression ratio X ₂ of the smallest dimension of S determined according to the operating end position of the die on the punch 50 for forming the molded body 10 was as shown in Table 2.

  The presence or absence of occurrence of cracks in the sintered body obtained as described above, and the occurrence length of cracks were measured. The results are shown in Table 2 and FIG.

As shown in Table 2 and FIG. 4, the compression ratio X ₁ of the alloy powder 100 of the maximum dimension portion L and the compression ratio X ₂ (X ₂ = H ₂ ′ / H ₂ ) of the alloy powder 100 of the minimum dimension portion S are By setting X ₂ / X ₁ ≦ 1.5, it was confirmed that the number of cracks generated per 10 samples was 0, that is, no cracks were observed.

It is a figure which shows the shape of the molded object in this Embodiment. It is sectional drawing which shows the structure of the shaping | molding apparatus in a magnetic field for forming a molded object. It is a figure which shows the result of Example 1, and is a figure which shows the relationship between the dimension h and (phi) of a molded object, and the crack generation condition. Example is a diagram showing a result of 2, a diagram showing the ratio of compression ratio X ₂ compression ratio X ₁ and the minimum dimension portion S of the largest dimension of L, and the relationship between the crack occurrence. It is a figure which shows the structure of the metal mold | die for obtaining the molded object of circular cross section in the past, (a) is the state which raised the punch on a metal mold | die, (b) is the figure which shows the state which the punch on metal mold | die descend | falls It is. It is a figure which shows the structure of the metal mold | die for obtaining the molded object which has a flat part conventionally, (a) is the state where the punch on a metal mold | die rose, (b) is the state which the punch on a metal mold | die lowered. FIG. (A) is a figure which shows the molded object which has a flat part, (b) is a figure which shows the molded object with a circular cross section obtained by removing a flat part.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Molded object, 11 ... Curved surface, 12 ... Flat surface, 13 ... Orthogonal surface, 14 ... Molded body main body, 15 ... Overhang | projection part, 20 ... Magnetostrictive element, 30 ... Molding apparatus in a magnetic field, 31 ... Mold die body, 31a ... Upper surface level, 32 ... Opening, 40 ... Lower die punch (lower die, die), 41 ... Curved surface portion, 42 ... Plane portion, 50 ... Upper die punch (upper die, die), 51 ... Curved surface part, 52 ... Flat part, 100 ... Alloy powder, L ... Maximum dimension part, S ... Minimum dimension part

Claims (14)

A molded body that contains Tb, Dy, Fe and becomes a magnetostrictive element by sintering,
The molded body is a molded body body having a substantially circular cross section;
A projecting portion formed so as to project outward from the outer peripheral surface of the molded product body on both sides of the center of the molded product body,
The overhanging portion is such that the dimension h of the overhanging portion in a direction orthogonal to the direction connecting the one overhanging portion and the other overhanging portion is h / φ> 0 with respect to the outer diameter φ of the formed body. A molded product characterized in that it is .5.   2. The molded body according to claim 1, wherein the projecting portions formed on both sides of the center of the molded body have flat surfaces formed substantially parallel to each other.   The molded body according to claim 2, wherein the flat surface is formed so as to circumscribe the body of the molded body.   The molded body according to any one of claims 1 to 3, wherein the projecting portion is formed at a position corresponding to a mating surface of a mold used when molding the molded body. A magnetic field molding apparatus for forming a molded body by applying a magnetic field to a magnetic powder while molding the powder into a predetermined shape with an upper mold and a lower mold,
The upper mold and the lower mold each have a curved surface portion having a predetermined radius of curvature on the molding surface, and a flat surface portion formed from both sides of the curved surface portion toward the outer peripheral side,
The pressurization completion positions of the upper mold and the lower mold when forming the molded body are the distance between the upper end portion of the curved surface portion of the upper mold and the lower end portion of the curved surface portion of the lower mold, and the upper mold. An apparatus for forming in a magnetic field, which is set based on an interval between the flat portion of the lower plate and the flat portion of the lower mold. The pressurization completion positions of the upper mold and the lower mold when forming the molded body are the distance S ₁ between the upper end portion of the curved surface portion of the upper mold and the lower end portion of the curved surface portion of the lower mold, and 6. The magnetic field according to claim 5, wherein an interval S ₂ between the planar portion of the upper mold and the planar portion of the lower mold is set to satisfy S ₂ / S ₁ > 0.5. Medium forming equipment. The forming apparatus in a magnetic field is represented by the formula (1) RT _y (where R is one or more rare earth metals, T is one or more transition metals, and y represents 1 <y <4). 7. A molding apparatus in a magnetic field according to claim 5, wherein the molding apparatus is for forming the molded body for forming a magnetostrictive element having a composition.   The magnetic field forming apparatus according to any one of claims 5 to 7, further comprising a magnetic field applying unit that applies a magnetic field in a direction orthogonal to a pressing direction by the upper mold and the lower mold. A magnetic field molding apparatus that forms a compact by forming the powder into a predetermined shape while applying a magnetic field to the magnetic powder.
In order to mold the powder, upper and lower molds each having a curved surface portion having a predetermined radius of curvature, and flat portions formed from both sides of the curved surface portion toward the outer peripheral side,
A mold drive that operates at least one of the upper and lower molds to an operation end position set based on the amount of the powder filled into the region corresponding to the curved surface part and the flat part between the upper and lower molds And
An apparatus for forming in a magnetic field, comprising: The operation end position of at least one of the upper and lower molds is:
The flat portion of the upper mold and the lower mold of the upper mold in the pre-molding state with respect to the distance H ₁ between the flat section of the upper mold and the lower flat section of the mold at the operation end position. The ratio H ₁ ′ / H ₁ of the level H ₁ ′ of the powder filled in the part between the flat parts of the mold;
With respect to the actuation end of the curved surface portion of the mold of the upper at the position upper and spacing of H ₂ the lower end of the curved surface portion of the mold of the lower, the curvature of the upper of the mold at the previous molding conditions A ratio H ₂ ′ / H ₂ of the level H ₂ ′ of the powder filled between the upper end portion of the surface portion and the lower end portion of the curved surface portion of the mold below;
The apparatus for forming a magnetic field according to claim 9, which is set based on The operation end position is:
The ratio _{H 1} '/ _H 1 is the ratio _H 2' / to _{H 2,} the magnetic field in a molding apparatus according to claim 10, characterized in that it is set to less than 1.5 times. Filling a powdered magnetostrictive material between the upper mold and the lower mold;
With the operation stroke set based on the ratio of the compression ratio of the portion where the compression ratio of the magnetostrictive material is maximum between the upper mold and the lower mold and the portion where the compression ratio of the magnetostrictive material is minimum, And a step of operating at least one of the upper mold and the lower mold to form the magnetostrictive material in a magnetic field. A step of processing the molded body obtained by the molding in the magnetic field into a substantially circular cross section;
The method for manufacturing a magnetostrictive element according to claim 12, further comprising a step of sintering the molded body.   The method of manufacturing a magnetostrictive element according to claim 12 or 13, wherein the molded body contains Tb, Dy, and Fe.

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