JP2020113578A - Mold and method for forming magnet material - Google Patents

Abstract

To provide a mold that is formed by orientating a magnet material powder in a non-linear direction, suppresses leakage of magnetic flux at an end of a magnetic material arranged in the mold, and makes the orientation of the magnet material powder highly uniform and efficient, and a method for forming a magnet material in which the magnet material power can be oriented highly uniformly and efficiently using such a mold.SOLUTION: A mold 1 that orients and forms magnet material powder in a magnetic field H has a pair of yoke members 20 and 30 made of a magnetic material. The pair of yoke members 20 and 30 are arranged so as to be separated from each other, and a filling space 11 provided between the pair of yoke members 20 and 30 can be filled with the magnetic material powder. At least one of the pair of yoke members 20 and 30 has a plurality of slits 22 and 32 that are opened in molding surfaces 21 and 31 facing the filling space 11 and are cut out in a direction inclined with respect to an application direction y of the magnetic field H.SELECTED DRAWING: Figure 2

Description

The present invention relates to a molding die and a method for molding a magnetic material, and more particularly to a molding die for orienting and molding a magnet material powder, and a method for molding a magnetic material using such a molding die. is there.

When manufacturing an anisotropic sintered magnet from a magnet material powder such as a rare earth magnet, the magnet material powder is oriented and molded in a magnetic field using a molding die. The shape of the sintered magnet to be manufactured is a simple shape such as a rod shape, a plate shape, or a column shape, and the magnet material powder is oriented in a linear direction along the sides, faces, axes, etc. that compose those shapes. In that case, an orientation magnetic field may be formed in one direction to orient and shape the magnet material powder. However, in applications such as a motor, a sintered magnet having a curved surface portion such as an arc shape (roof tile shape) is used. In these sintered magnets, the desired orientation direction of the magnet material powder is often not linear. Radial orientation is required for arc-shaped magnets.

In order to orient the magnet material powder in a non-linear direction such as a radial direction, it is necessary to bend an externally applied magnetic field so as to follow the orientation direction. Therefore, a molding die in which a magnetic material is arranged may be used. For example, in Patent Document 1, a die forming a cavity having a tile-shaped cross section composed of an outer arc facing outward, an inner arc facing inward, and two lines, and a die interlocked with a press to compress the inside of the cavity. A mold comprising a possible punch and at least two magnetic cores provided in the die along the outer and inner arcs of the cavity is disclosed.

JP, 2005-286081, A

As described in Patent Document 1, by arranging a magnetic material in a molding die for orienting and molding the magnet material powder, the magnet material powder is directed in a direction other than a linear direction such as radial orientation. It becomes possible to orient. However, as shown in the simulation of the distribution of the magnetic flux in FIG. 3B, the magnetic flux is likely to concentrate at the end portion surrounded by the circle in the magnetic body (upper and lower dark gray arc-shaped portions). As a result, the magnetic flux density becomes spatially non-uniform, and the magnetic flux leaks, making it difficult to orient the magnet material powder in a desired direction in each part of the obtained molded body with high uniformity. Then, in the manufactured sintered magnet, the desired magnetic properties may not be achieved, or the magnetic properties may have an uneven spatial distribution. If a high magnetic field is applied to compensate for the leakage of magnetic flux from the ends, the coil for generating the magnetic field becomes larger and the required power increases, resulting in poor efficiency in the orientation of the magnet material powder. Will end up.

In Patent Document 1, it is said that the magnetic core along the outer arc of the cavity has a shape that extends from both ends of the outer arc and overhangs, so that a radial orientation magnetic field can be realized at both ends of the cavity. By forming the magnetic core in such a shape, even if the orientation of the magnet material powder at the end can be improved, the magnetic core tends to be large. Further, since it is not possible to prevent the leakage of the magnetic flux itself at the end of the magnetic core, it is difficult to avoid increasing the size of the coil and increasing the required power.

The problem to be solved by the present invention is to suppress the leakage of magnetic flux at the end portion of the magnetic body disposed in the molding die in the molding die that forms the magnet material powder by orienting it in a non-linear direction. Of a magnet material that can be highly efficiently and uniformly oriented, and a magnet material that can be highly uniformly and efficiently oriented by using such a molding tool It is to provide a molding method.

In order to solve the above-mentioned problems, a molding die according to the present invention is a molding die in which magnet material powder is oriented and molded in a magnetic field, wherein the molding die has a pair of yoke members made of a magnetic material, The pair of yoke members are arranged apart from each other, and the magnet material powder can be filled in the filling space provided between the pair of yoke members. At least one has a plurality of slits which are opened in a molding surface facing the filling space and are cut out in a direction inclined with respect to the application direction of the magnetic field.

Here, the molding surfaces of the pair of yoke members are formed in an arc shape having different radii of curvature, which are convex in the same direction along the magnetic field applying direction, and the slits have the arc shapes. It may be formed along the radial direction connecting the shapes.

Further, both of the pair of yoke members may have the slit.

The molding die is for performing orientation and molding on the magnet material powder filled in the filling space without applying mechanical pressure, and is a non-magnetic material that holds the pair of yoke members. It is preferable to further have a holding mold made of a body.

In this case, each of the pair of yoke members is provided with a locking portion projecting in a direction intersecting the magnetic field at a position separated from the molding surface with the slit interposed therebetween and locked by the holding die. Good to have. Further, it is preferable that the molding die further has an isolation wall made of a non-magnetic material, which constitutes a wall surface of the filling space facing the molding surface, integrally with the holding die. The thickness of the isolation wall is preferably 0.5 mm or less.

A method of molding a magnet material according to the present invention is such that the filling space of a molding die as described above is filled with magnet material powder, and the magnetic material powder is oriented while applying a magnetic field from the outside of the molding die. It is what is molded.

In the molding die according to the above invention, the yoke member is divided into a plurality of regions by forming the slits in the yoke member, thereby forming a plurality of narrow magnetic paths inclined with respect to the magnetic field application direction. ing. Since the magnetic flux passes through each of the narrow magnetic paths, the magnetic flux is not concentrated on the end portion of the yoke member but is dispersed over the entire area of the yoke member. Therefore, it becomes difficult for the magnetic flux to leak from the end of the yoke member, and the orientation magnetic field in the direction inclined with respect to the direction of the external magnetic field is applied to each part of the filling space with high uniformity, and the part is filled. The magnet material powder can be oriented. Further, in order to compensate for the leakage of the magnetic flux, it is not necessary to excessively increase the size of the coil used to generate the magnetic field or to apply a large current to the coil, so that the orientation of the magnet material powder can be efficiently achieved. be able to. As a result, even if the compact does not have a simple shape and the desired orientation direction of the magnet material powder is not linear, the magnet material powder can be efficiently and highly oriented in each part of the compact. You can Then, through the sintering of the molded body, an anisotropic sintered magnet having excellent magnetic property uniformity can be efficiently manufactured.

Here, the molding surfaces of the pair of yoke members are formed in an arc shape having different radii of curvature, which are convex in the same direction along the magnetic field application direction, and the slits connect the arc shapes. When the magnetic material powder is formed along the radial direction, an orienting magnetic field in the radial direction (radial direction) is applied to each portion of the filling space formed in an arc shape, and the magnet material powder is radially orientated. Since the yoke member is provided with the slits, highly uniform radial orientation can be efficiently realized in each portion of the molded body.

Further, in the case where both of the pair of yoke members have slits, the magnetic flux can be dispersed to each part with high uniformity and the leakage of the magnetic flux from the ends can be suppressed in both the yoke members. Therefore, the uniformity of the orientation of the magnetic material powder and the orientation efficiency can be particularly enhanced.

Then, the forming die performs orientation and forming on the magnet material powder filled in the filling space without applying mechanical pressure, and is made of a non-magnetic material holding a pair of yoke members. When a mold is further provided, anisotropic sintering by a so-called pressless method (PLP method) that can complete orientation, molding, and sintering of magnet material powder while controlling the atmosphere without a pressing step A molding die can be suitably used for manufacturing the magnet. As described above, by applying the orientation of the magnet material powder using the slitted yoke member to the PLP method, the influence of impurities is small, the shape accuracy is high, and the orientation of the magnet material powder is high. It is possible to efficiently manufacture an anisotropic sintered magnet having excellent uniformity.

In this case, according to the configuration, each of the pair of yoke members has a locking portion that projects in the direction intersecting the magnetic field and is locked to the holding die at a position apart from the molding surface with the slit interposed therebetween. Since the yoke member can be firmly fixed to the holding die, it is possible to prevent the yoke member from being displaced due to impact even when a pulsed magnetic field is applied in the PLP method. ..

Further, according to the configuration in which the molding die further has an isolation wall made of a non-magnetic material, which constitutes the wall surface of the filling space facing the molding surface, integrally with the holding die, the magnet material powder filled in the filling space is It is possible to prevent the magnetized material from adhering to the yoke member or entering into the slit, and the orientation and molding of the magnet material powder using the molding die can be efficiently advanced.

Further, according to the configuration in which the thickness of the isolation wall is 0.5 mm or less, it is possible to prevent the magnetic material powder from adhering to the yoke member or entering the slit while avoiding the attenuation of the orientation magnetic field due to the isolation wall. You can

In the method of molding a magnetic material according to the above invention, the magnetic material powder is oriented and molded in a magnetic field using the above-described molding die. The yoke member of the mold is divided by slits to form a plurality of narrow magnetic paths that are inclined with respect to the magnetic field application direction, so that each part of the filling space is filled while suppressing leakage of magnetic flux. An oriented magnetic field in a direction inclined with respect to the direction of the external magnetic field can be applied to the magnet material powder with high uniformity. As a result, the magnet material powder can be efficiently oriented in each part of the formed body with high uniformity even when producing a formed body that does not have a simple shape and the orientation direction of the magnet material powder is not linear. ..

It is a schematic sectional drawing which shows the shaping|molding die concerning one Embodiment of this invention with the coil for magnetic field generation, etc. Note that the hatching showing the cross section is omitted (the same applies to FIG. 2). It is sectional drawing which expands and shows the yoke member contained in the said shaping|molding die. It is a simulation result which shows distribution of magnetic flux in a forming die, (a) shows the case where a slit is provided in a yoke member, and (b) shows the case where a slit is not provided. It is a figure explaining evaluation of orientation in each part of an arc type sintered magnet. (A) has shown the shape and measurement position of a sintered magnet. (B) shows the result when the slit is provided in the yoke member, and (c) shows the result when the slit is not provided in the yoke member.

Hereinafter, a molding die and a method for molding a magnet material according to the embodiment of the present invention will be described in detail. A molding die according to an embodiment of the present invention is one in which magnet material powder is oriented in a magnetic field and molded. Further, in the method of molding a magnetic material according to an embodiment of the present invention, the magnetic material powder is oriented and molded using such a molding die. A specific method of molding performed by using the molding die according to the embodiment of the present invention is not particularly limited as long as the magnet material powder is oriented and molded in a magnetic field. Then, a molding die suitable for a pressless method (PLP method) for orienting and molding a magnet material powder without applying a mechanical pressure, and molding a magnet material by the PLP method using such a molding die. I will explain mainly.

[Structure of mold]
FIG. 1 shows a molding die 1 according to an embodiment of the present invention together with a magnetic field generating coil 2 and external yokes 3, 3. In addition, FIG. 2 shows the yoke members 20 and 30 forming the molding die 1 in an enlarged manner. Here, the width direction (horizontal direction in the figure) of the molding die 1 is the x direction, the front-rear direction (vertical direction in the figure) is the y direction, and the thickness direction (depth direction in the figure) orthogonal thereto is the z direction. Regarding the front-back direction, the front side (upper side in the drawing) is +y direction and the rear side (lower side in the drawing) is −y direction. An external magnetic field H along the y direction is applied to the mold 1 filled with the magnetic material powder, and the mold 1 is used.

The molding die 1 can be filled with magnet material powder inside, and the magnet material powder that has been filled is oriented by an external magnetic field H applied in the y direction and shaped into a predetermined shape. The magnet material powder used has a shape anisotropy and is not particularly limited as long as it is a powder made of a ferromagnetic material that is oriented in a specific direction by applying a magnetic field H. A powder of an RTB based magnet material (R is a rare earth metal and T is an iron group transition metal) such as an Fe—B based magnet can be a suitable target.

The molding die 1 according to this embodiment includes a holding die 10 and a pair of yoke members 20 and 30. The yoke member is composed of a pair of a front yoke member 20 and a rear yoke member 30 which are independent of each other.

The holding die 10 constitutes an outer shell of the molding die 1, and is made of a non-magnetic material, preferably a carbon material. The molding die 1 has a filling space 11 as a cavity inside. The filling space 11 has a predetermined shape in which the magnet material powder is to be formed. The specific shape of the filling space 11 may be defined according to the desired shape of the molded body, and is not particularly limited, but the direction of the magnetic field H applied from the outside (y direction) and the magnetic field thereof. It is preferable that the outer edge of the filling space 11 has an inclined or curved shape with respect to a direction perpendicular to H (x direction). In particular, in order to obtain an arc-shaped (roof-shaped) molded body, it is preferable that the cross-sectional shape of the filling space 11 in the xy plane is an arc shape, as shown in the figure. In this case, the filling space 11 has a front end surface 11a having an arc shape whose cross section is convex rearward (−y side) as a front (+y side) end surface, and the cross section has a front end surface 11a as a rear end surface. It has a rear end surface 11b having a larger radius of curvature and a rearward convex arc shape, and further has a pair of side end surfaces connecting the front end surface 11a and the rear end surface 11b at both ends. Preferably, in the cross section, the front end surface 11a and the rear end surface 11b are formed of concentric arcs.

The holding mold 10 further has yoke installation portions 12 and 13 as cavities into which the front yoke member 20 and the rear yoke member 30 can be fitted, respectively, in the front and rear (±y directions) of the filling space 11. There is. The yoke mounting portions 12 and 13 are formed to be slightly larger than the outer shapes of the respective yoke members 20 and 30 so that the yoke members 20 and 30 can be fitted therein with almost no space. The two yoke installation portions 12 and 13 and the filling space 11 are partitioned by thin plate-shaped isolation walls 14 and 15, respectively. In other words, the isolation walls 14 and 15 form the wall surface of the filling space 11 that faces the two yoke installation portions 12 and 13. The isolation walls 14 and 15 are made of the same non-magnetic material that constitutes the other part of the holding mold 10, and are continuously formed integrally with the other part of the holding mold 10. The isolation walls 14 and 15 are formed in a thin plate shape having a substantially uniform thickness, and the thickness thereof is preferably 0.5 mm or less. Further, the thickness of the isolation walls 14 and 15 is preferably 10% or less with respect to the length (L) of the region where the slits 22 and 32 are formed in the yoke members 20 and 30, which will be described in detail later.

The front yoke member 20 and the rear yoke member 30 are each formed as a block-shaped member made of a magnetic material. The material forming the yoke members 20 and 30 is not particularly limited, but a soft magnetic material, in particular, a material that exhibits higher soft magnetic characteristics (low coercive force and high magnetic permeability) than the magnet material powder to be molded. Is preferred. Fe or a Fe-Co alloy such as permendur can be preferably used.

The front yoke member 20 and the rear yoke member 30 are fitted in the yoke installation portions 12 and 13 provided in front of and behind the filling space 11 of the holding mold 10, and are fixed to the holding mold 10 by the fastening member 40. The front yoke member 20 and the rear yoke member 30 are arranged in the holding mold 10 so as to be separated from each other with the filling space 11 and the two isolation walls 14 and 15 interposed therebetween.

The front yoke member 20 and the rear yoke member 30 each have molding surfaces 21 and 31 as end surfaces. The molding surfaces 21 and 31 face the filling space 11 via the isolation walls 14 and 15. The front molding surface 21 that is the molding surface of the front yoke member 20 has a shape along the front end surface 11a of the filling space 11, and the rear molding surface 31 that is the molding surface of the rear yoke member 30 is the rear surface of the filling space 11. It has a shape along the end face 11b. That is, when the filling space 11 has an arc-shaped cross section as described above, the front molding surface 21 and the rear molding surface 31 are convex in the same direction along the application direction of the magnetic field H, It has arc-shaped cross sections with different radii of curvature. The radius of curvature of the rear molding surface 31 is larger than the radius of curvature of the front molding surface 21. Preferably, the front molding surface 21 and the rear molding surface 31 have concentric arc-shaped cross sections.

The front yoke member 20 and the rear yoke member 30 each have a plurality of slits 22 and 32. The slits 22 and 32 are opened and cut out in the molding surfaces 21 and 31 of the yoke members 20 and 30, respectively. That is, in the front yoke member 20, the front slit 22 is formed as an elongated notch from the front molding surface 21 toward the front (+y side). On the other hand, in the rear yoke member 30, the rear slit 32 is formed as an elongated notch from the rear molding surface 31 toward the rear (−y side).

Among the plurality of front slits 22 and rear slits 32 provided, at least a part thereof is cut out in a direction inclined with respect to the application direction (y direction) of the magnetic field H. In the illustrated form, the front slit 22 and the rear slit 32 are inclined with respect to the application direction of the magnetic field H, except for the central slit in the width direction (x direction). The specific notch direction of the slits 22 and 32 may be set along the direction in which the magnetic field (orientation magnetic field) for orienting the magnet material powder filled in the filling space 11 is desired to be applied. When the filling space 11 is formed in an arc shape to produce an arc-shaped compact, it is usually desirable to orient the magnet material powder in a radial direction (radial direction) connecting the inner arc and the outer arc of the compact. Therefore, in the molding die 1, it is required to generate an orientation magnetic field in the radial direction connecting the front end face 11a and the rear end face 11b of the filling space 11 formed in a convex shape in the same direction. In this case, as shown in the drawing, the front slit 22 and the rear slit 32 may be cut out in the radial direction connecting the front molding surface 21 and the rear molding surface 31.

The lengths (depths) and the intervals of the slits 22 and 32 are not particularly limited, but as will be described later, the divisions formed by dividing the yoke members 20 and 30 by the slits 22 and 32. For each of the regions 23 and 33, the length of the slits 22 and 32 is set so that the ratio (L/D) of the length (L) to the width (D) of the molding surfaces 21 and 31 is 5 or more and 10 or less. It is sufficient to set the height and the interval (in the drawing, the symbols D and L are shown only for the rear yoke member 30, but the same applies to the front yoke member 20). In addition, an angular interval is provided between the front slit 22 and the rear slit 32 so that the divided regions 23 of the front yoke member 20 and the divided regions 33 of the rear yoke member 30 respectively extend so as to be continuous with the filling space 11 interposed therebetween. Are preferably provided. That is, when the front molding surface 21 and the rear molding surface 31 are concentric arcs, it is preferable that the straight line group connecting the front slit 22 and the rear slit 32 extends in the radial direction of the concentric arcs.

Although the specific dimensions of the yoke members 20 and 30 are not particularly limited, it is preferable that the yoke members 20 and 30 have a thick shape in the front-rear direction (y direction). For example, when the slits 22 and 32 are formed in the radial direction, the ratio of the diameters of the circular arcs corresponding to the front end and the rear end of the region where the slits 22 and 32 are formed (R1/R2; the rear yoke member 30 in the drawing). Although the reference numerals R1 and R2 are shown only for the above, the same applies to the front yoke member 20), but it is preferable that both the front yoke member 20 and the rear yoke member 30 have 1.2 or more.

The front yoke member 20 and the rear yoke member 30 each have a pair of locking portions 24 and 34 at positions apart from the molding surfaces 21 and 31 with the regions where the slits 22 and 32 are provided sandwiched therebetween. .. That is, the front yoke member 20 has a pair of locking portions 24, 24 in the front (+y side) of the region where the front slit 22 is provided, and the rear yoke member 30 is provided with the rear slit 32. The pair of locking portions 34, 34 is provided on the rear side (−y side) of the region. Each of the locking portions 24 and 34 projects outward from the region where the slits 22 and 32 are provided along a direction intersecting the application direction (y direction) of the magnetic field H. In the illustrated form, the locking portions 24 and 34 project outward in the width direction (±x direction) of the yoke members 20 and 30. The yoke members 20 and 30 are attached to the holding die 10 by the fastening members 40 while being locked to the holding die 10 by the engaging portions 24 and 34.

[Method of molding magnet material]
Next, a method of molding a magnet material using the above-mentioned molding die 1 will be described. Here, molding is performed by the PLP method.

Prior to molding, the front yoke member 20 and the rear yoke member 30 are fitted into the yoke installation portions 12 and 13 of the holding mold 10 and fixed by the fastening member 40. Then, the filling space 11 is filled with magnet material powder. The packing density is not particularly limited, but a relatively low density is often adopted in the molding of the RTB-based magnet material by the PLP method, for example, 3.3 to 3.6 g. /Cm ² can be used.

Then, as shown in FIG. 1, the outer yokes 3 made of a soft magnetic material are arranged on the outer periphery of the molding die 1 in order to reduce the disturbance of the magnetic flux, and are placed inside the cylindrical magnetic field generating coil 2. Deploy. At this time, the front-back direction (y direction) of the molding die 1 is aligned with the axis of the coil 2. Further, it is preferable to control the atmosphere in the holding mold 10 by filling with an inert gas or evacuation.

In this state, a pulse current is passed through the coil 2 to generate a pulsed magnetic field H. The direction of the magnetic field H is the axial direction of the coil 2, that is, the front-back direction (y direction) of the molding die 1.

When the magnetic field H is applied from the outside, the magnetic flux passes through the yoke members 20 and 30 of the molding die 1, and the orientation magnetic field is formed in the filling space 11. The anisotropic magnet material powder filled in the filling space 11 is oriented by the orientation magnetic field. The direction of the orientation magnetic field is the direction along the magnetic path formed in the yoke members 20 and 30, that is, the direction of the slits 22 and 32. Since the slits 22 and 32 are inclined with respect to the application direction (y direction) of the external magnetic field H, the magnetic flux passing through the magnetic paths formed in the divided regions 23 and 33 of the yoke members 20 and 30 is , Y direction, it will be bent. When the filling space 11 has an arc shape and the slits 22 and 32 are formed in the radial direction, an orientation magnetic field in the radial direction is formed and the magnet material powder is radially oriented.

After applying the pulse magnetic field H until the magnet material powder is sufficiently oriented, the molding die 1 is appropriately moved to the heating chamber to sinter the magnet material powder. It is preferable to continue controlling the atmosphere in the holding mold 10 even during sintering. When the sintering is completed, the obtained sintered body can be taken out from the filling space 11 to obtain an anisotropic sintered magnet. The sintered magnet has an outer shape defined by the filling space 11 such as an arc shape, and has a structure in which the magnet material is oriented in a direction defined by the slits 22, 32 of the yoke members 20, 30 such as a radial direction. Will have.

[Orientation of magnet material powder using a molding die]
In the molding die 1 according to this embodiment, a pair of yoke members 20 and 30 are provided with the filling space 11 interposed therebetween. The magnetic flux generated by the external magnetic field H is bent according to the overall shape of the yoke members 20 and 30 when passing through the yoke members 20 and 30. Therefore, by providing the yoke members 20 and 30 having the molding surfaces 21 and 31 having a shape having an angle with respect to the direction of the external magnetic field H, such as an arc shape, outside the filling space 11, The orientation magnetic field formed can be inclined with respect to the application direction (y direction) of the external magnetic field H. Further, if the yoke members 20 and 30 are provided with the slits 22 and 32 as in the present embodiment, a magnetic path through which the magnetic flux passes is formed in the direction along the slits 22 and 32. By defining the direction of 32, it becomes easy to form the orientation magnetic field inclined with respect to the direction of the external magnetic field H, such as the radial direction. As a result, it becomes easy to orient the magnet material powder in a desired direction even in a non-linear direction such as a radial direction.

By providing the slits 22 and 32 in the yoke members 20 and 30, in addition to the effect of defining the direction of the orientation magnetic field, the effect of enhancing the spatial uniformity of the orientation magnetic field and the efficiency of applying the orientation magnetic field are obtained. be able to. If the yoke members 20 and 30 are not provided with the slits 22 and 32, a demagnetizing field is generated inside the yoke members 20 and 30 to cause leakage of magnetic flux at the ends of the yoke members 20 and 30. Is more likely to occur.

FIG. 3B shows a result of simulating the distribution of the magnetic flux in the case where the block-shaped front yoke member 20 and the rear yoke member 30 having no slits 22 and 32 are used. In the figure, the arc-shaped portions shown in dark gray are the front yoke member 20 and the rear yoke member 30, and the portion shown in light gray between them is the filling space 11. The simulation is performed by electromagnetic field analysis using the finite element method (FEM) (analysis software: JMAG). The front yoke member 20 and the rear yoke member 30 have concentric arc shapes. Further, it is assumed that the filling space 11 is not filled with the magnet material powder and air is present.

In this case, due to the effect of the demagnetizing field, the magnetic flux is concentrated at the end portions of the yoke members 20 and 30, as shown by the circle in the figure, and the magnetic flux leaks from the end portions. As the magnetic flux leaks from the ends of the yoke members 20 and 30, spatial non-uniformity occurs in the orientation magnetic field formed in the filling space 11, and along the arc shape of the filling space 11, at the ends, the center is formed. The orientation magnetic field becomes weaker than that of the part. As a result, the orientation of the magnet material powder filled in the filling space 11 becomes lower at the end portions than at the central portion. Then, in the manufactured sintered magnet, desired magnetic characteristics cannot be uniformly obtained. Further, the leakage of the magnetic flux causes the need to apply a large external magnetic field H in order to form the required orientation magnetic field, and thus a large coil 2 is used or a large current is passed through the coil 2. Will be required. Then, the energy efficiency for forming the orientation magnetic field necessary for orienting the magnet material powder is deteriorated.

On the other hand, if the magnetic paths can be formed to be elongated in the yoke members 20 and 30, the diamagnetic field coefficient decreases, and the magnetic flux easily passes through the magnetic paths. Like the molding die 1 according to the present embodiment, a plurality of slits 22 and 32 are provided along the molding surfaces 21 and 31 of the yoke members 20 and 30, and the yoke members 20 and 30 are divided into elongated divided regions 23 and 33. Then, by forming a number of elongated magnetic paths through which the magnetic flux can easily pass, the magnetic flux is highly uniformly distributed to each portion along the molding surfaces 21 and 31, and the magnetic flux from the end portions of the yoke members 20 and 30 is generated. Can be suppressed.

FIG. 3A shows the result of a simulation of the distribution of magnetic fluxes performed in the same manner as in FIG. 3B when the slits 22 and 32 are provided in the pair of yoke members 20 and 30, respectively. From this, it can be seen that the magnetic flux is distributed more densely in each part along the arc direction of the yoke members 20 and 30 than in the case of FIG. 3B. It can be seen that there is almost no difference in magnetic flux density when comparing the end portion and the central portion, and high magnetic flux density is obtained in the entire filling space 11 with high uniformity. Leakage of magnetic flux from the ends of the yoke members 2 and 30 is also significantly reduced.

As described above, the magnetic flux is distributed to each part along the molding surfaces 21 and 31 of the yoke members 20 and 30 with high uniformity, thereby forming the orientation magnetic field with high uniformity in each part of the filling space 11. You can As a result, the magnet material powder with which each part of the filling space 11 is filled can be oriented in a desired direction such as radial orientation with high orientation and uniformity. Then, in the manufactured sintered magnet, desired magnetic characteristics can be obtained with high spatial uniformity. It is not necessary to form the yoke members 20 and 30 in a large size in order to make the orientation magnetic field uniform.

Further, since the leakage of the magnetic flux from the yoke members 20 and 30 is suppressed, the applied external magnetic field H can be effectively used for generating the orientation magnetic field, and therefore, in order to obtain a desired orientation magnetic field, It is possible to avoid using a large-sized coil 2 and to apply a large current to the coil 2. Therefore, the efficiency in applying the orientation magnetic field can be increased.

As described above, by forming the slits 22 and 32 in the yoke members 20 and 30, the orientation magnetic field in a desired direction including the direction inclined with respect to the application direction of the external magnetic field H can be formed in the yoke members 20 and 30. The magnet material powder can be oriented on each part along the surfaces 21 and 31 with high uniformity and high efficiency. These effects can be obtained by providing the slit 32 in at least one of the yoke members 20 and 30, particularly in the rear yoke member 30 having the large rear molding surface 31. If the slits 22 and 32 are provided in 30, the effect can be further enhanced.

As the slits 22 and 32 are formed as longer notches and at smaller intervals, a longer and narrower magnetic path is formed, and the effect of promoting uniform distribution of magnetic flux and suppressing leakage can be enhanced. As described above, if the ratio (L/D) of the length (L) to the width (D) of the divided regions 22 and 32 is set to 5 or more, those effects can be sufficiently enhanced. However, if too many slits 22 and 32 are formed, it may be difficult to process the yoke members 20 and 30, and the mechanical strength may be reduced. Therefore, keep the L/D ratio at 10 or less. It is preferable to set.

With respect to the overall shape of the yoke members 20 and 30, the larger the thickness, the longer the magnetic path, so that a high effect can be obtained in promoting uniform distribution of magnetic flux and suppressing leakage. As described above, in both yoke members 20 and 30, the ratio (R1/R2) of the diameters of the circular arcs corresponding to the front end and the rear end of the region where the slits 22 and 32 are formed in the radial direction is 1.2 or more. If set, it is easy to enhance their effects sufficiently.

In the molding die 1 according to the present embodiment, by defining the shape of the filling space 11, a molded body having an arbitrary outer shape is formed, and the directions of the slits 22, 32 formed in the yoke members 20, 30 are defined. By doing so, the orientation direction of the magnet material powder can be controlled, and the orientation of the magnet material powder can be achieved with high uniformity and high efficiency. In particular, an arc-shaped sintered magnet having a radial orientation is in great demand as a material for motors and the like, and can be suitably molded using the molding die 1 according to this embodiment.

The molding die 1 according to the present embodiment is preferably used for molding magnet material powder by the PLP method. In the PLP method, the magnet material powder filled in the filling space 11 can be oriented and molded without applying a mechanical pressure, and the sintering can be completed as it is. Each step of filling the molding die 1 and sintering can be performed under controlled atmosphere. Therefore, it is possible to manufacture an anisotropic sintered magnet with high magnetic characteristics, which is less affected by impurities and has excellent shape accuracy. However, by using the molding die 1 according to the present embodiment, it is possible to obtain a desired direction. By allowing the magnet material powder to be highly uniformly oriented, the magnetic properties of the obtained sintered magnet can be further enhanced and the spatial distribution of the magnetic properties can be reduced.

In the PLP method, a strong pulse magnetic field H is applied from the outside of the molding die 1. At this time, if the magnet material powder comes into direct contact with the molding surfaces 21 and 31 of the yoke members 20 and 30, the magnetized magnet material is used. The powder may adhere to the molding surfaces 21 and 31. In particular, if the magnet material powder enters the slits 22 and 32 opened in the molding surfaces 21 and 31, it becomes difficult to remove the powder and the workability in molding the magnet material is deteriorated. Therefore, by providing the isolation walls 14 and 15 made of a non-magnetic material between the yoke members 20 and 30 and the filling space 11, the magnet material powder directly contacts the molding surfaces 21 and 31 of the yoke members 20 and 30. It is possible to prevent the magnet material powder from adhering to the molding surfaces 21 and 31 and from entering the slits 22 and 32 because of no contact. However, if the isolation walls 14 and 15 are too thick, it becomes difficult to efficiently form the orientation magnetic field in the filling space 11, so the thickness is 0.5 mm or less, and the slits 22 and 32 are formed. It is preferable to keep the length to 10% or less with respect to the length (L) of the formed region. Thereby, the magnet material powder with which the filling space 11 is filled can be efficiently oriented.

Furthermore, when a strong pulse magnetic field H is applied to the molding die 1, the impact of the pulse application may cause the yoke members 20 and 30 to be displaced relative to the holding die 10. However, by providing the yoke members 20 and 30 with the locking portions 24 and 34 that project in the direction intersecting the direction of application of the magnetic field H and locking them to the holding mold 10, the yoke members 20 and 30 are The position shift can be suppressed. By providing the locking portions 24 and 34 at positions distant from the molding surfaces 21 and 31 with the regions where the slits 22 and 32 are formed sandwiched therebetween, the direction and distribution of the orientation magnetic field formed in the filling space 11 can be obtained. In addition, it is possible to obtain a high effect of suppressing the positional deviation while avoiding the influence of the existence of the locking portions 24 and 34.

[Other forms]
The case where the molding die 1 is used for molding the magnet material by the PLP method has been described above in detail. However, the molding die according to the embodiment of the present invention may be applied to any molding method as long as the magnet material powder is oriented and molded in a magnetic field.

For example, as described in Patent Document 1, a forming die according to the embodiment of the present invention can be configured as a forming die used for press working in a magnetic field. In this case, unlike the molding die 1 for the PLP method described above, the holding die 10 and the isolation walls 14 and 15 are not provided, and one is placed inside the cavity formed by the pair of dies of the press machine. The pair of yoke members 20 and 30 are installed. The space between the pair of yoke members 20 and 30 facing each other becomes the filling space 11 in which the magnet material powder is filled. Then, by applying a static magnetic field from the outside of the die, mechanical pressure is applied in a state in which the magnet material powder filled in the filling space 11 is oriented, and the magnet material powder is molded. An anisotropic sintered magnet is obtained by taking out the obtained molded body from the pressing device and sintering it.

As described above, also in the molding die used for the magnetic field press molding, by providing the slits 22 and 32 in the yoke members 20 and 30, the orientation magnetic field inclined with respect to the application direction of the magnetic field H can be formed with high uniformity. You can Further, by suppressing the leakage of the magnetic flux, the efficiency in forming the orientation magnetic field can be increased.

Examples of the present invention will be shown below. The present invention is not limited to these examples.

[Preparation of sample]
Arc-shaped sintered magnets were produced by the PLP method using Nd-Fe-B powder as the samples according to the examples and comparative examples. As the arc shape, as shown in FIG. 4A, the outer diameter was 37 mm, the inner diameter was 32 mm, and the opening angle was ±40°.

A mold having a yoke member as described above was used for the orientation of the powder magnet material. In the example, as shown in FIGS. 1 and 2, a pair of yoke members provided with slits was used. The slits were provided at an angular interval of 4.5°. In the comparative example, a yoke member having no slit was used. In addition, in the embodiment, the thickness of the yoke member is also optimized.

The packing density of the magnet material powder was 3.5 g/cm ^{3 in the} examples. In the comparative ^{example, 3.34g / cm 3, 3.39g /} cm 3, and the three different 3.41 g / cm ^3. Also, the magnitude of the applied external magnetic field is varied by the magnitude of the pulse voltage applied to the coil, in the embodiment, the reference voltage as _{V 0, 1.0V 0, 1.5V 0} , 2.0V 0 There are three types. Moreover, in the comparative example, it was set to 2.5V ₀ . The sintering temperature of the molded body was controlled in the range of 985 to 1000°C.

[Evaluation of orientation]
With respect to the sintered magnets according to the examples and the comparative examples, magnets in each region indicated by hatching in FIG. 4A were cut out, the magnetization curve was measured, and the orientation of the magnet material powder was evaluated. The magnetization curve was measured by applying a magnetic field in a direction perpendicular to the longitudinal direction of the cut magnet using a pulse excitation measuring device.

Then, based on the measurement results, the values of the residual magnetic flux density (Br) and the saturation magnetic flux density (4πIs) were recorded for each sample. The ratio Br/4πIs of the residual magnetic flux density to the saturation magnetic flux density serves as an index of the orientation of the magnet material powder, and the larger the value, the higher the orientation.

The measurement was performed at three points on the sample. Specifically, as shown in FIG. 3A, the "center" is measured at the center of the arc shape, and the "end 1" and "end 2" are measured from the center along the arc shape. The measurements were taken at -20° and +20°.

[Evaluation results]
4B and 4C show the evaluation results of the orientation of the samples according to the example and the comparative example, respectively.

First, looking at the results of the comparative example of FIG. 4(c), it can be seen that the orientation is high at the central part and low at both ends for any packing density. This is because the radial orientation magnetic field is not uniformly formed in the filling space during molding using a molding die, and the orientation magnetic field is weaker at the end than at the central part, and sufficient orientation is obtained at the end. Interpreted as something that could not be achieved.

Next, looking at the results of the example of FIG. 4B, there is almost no difference in the orientation between the central portion and the end portion in any of the coil applied voltage data. This is because by forming slits in the yoke member of the forming die, the radial orientation magnetic field is formed with high uniformity in the filling space, and the powder magnet material is oriented with high uniformity in each part along the arc shape. Be interpreted as The improvement in the uniformity of orientation reflects not only the effect of forming the slits but also the effect of optimizing the thickness of the yoke member. However, the optimization of the thickness of the yoke member alone is not enough. , Confirmed that the degree of improvement will be low.

Further, in the result of FIG. 4B, regarding the degree of orientation (the value of Br/4πIs) and the uniformity of orientation at each position, when the coil applied voltage is changed in three ways. , Almost unchanged. This indicates that the effect of improving the orientation and homogenizing the orientation in each part of the filling space has already reached saturation even when the voltage applied to the coil is 1.0 V ₀ . On the other hand, in the case of the comparative example of FIG. 4A, even if the voltage applied to the coil is 2.5 V ₀ , the orientation cannot be sufficiently made uniform. From this, by orienting the magnet material powder by using a yoke member having a slit as in the example, compared with the case of using a yoke member without a slit, a current to be applied to a coil for applying a magnetic field can be increased. Even if it is reduced to 40%, it can be said that a sufficiently high orientation can be uniformly achieved and the efficiency of forming the orientation magnetic field is enhanced. This is interpreted to be because the leakage of magnetic flux from the yoke member can be suppressed.

The embodiments of the present invention have been described above. The present invention is not particularly limited to these embodiments, and various modifications can be made.

1 Mold 2 Magnetic Field Generating Coil 3 External Yoke 10 Holding Mold 11 Filling Space 11a Front End Surface 11b Rear End Surfaces 14, 15 Separating Wall 20 Front Yoke Member 21 Front Molding Surface 22 Front Slit 23 Dividing Area 30 Rear Yoke Member 31 Rear Molding Surface 32 rear slit 33 division area 40 fastening member H (external) magnetic field

Claims (8)

In a mold for orienting and molding magnet material powder in a magnetic field,
The molding die has a pair of yoke members made of a magnetic material, the pair of yoke members are arranged apart from each other, and a filling space provided between the pair of yoke members. Can be filled with the magnetic material powder,
At least one of the pair of yoke members has a plurality of slits opened in a molding surface facing the filling space and cut out in a direction inclined with respect to the application direction of the magnetic field. Mold to do. The molding surfaces of the pair of yoke members are formed in an arc shape which is convex in the same direction and has different radii of curvature, and the slit is formed along the radial direction connecting the arc shapes. The molding die according to claim 1, wherein The mold according to claim 1 or 2, wherein both of the pair of yoke members have the slit. The molding die is for performing orientation and molding without applying a mechanical pressure to the magnet material powder filled in the filling space,
The molding die according to claim 1, further comprising a holding die made of a non-magnetic material that holds the pair of yoke members. Each of the pair of yoke members has a locking portion projecting in a direction intersecting with the magnetic field and being locked to the holding die, at a position apart from the molding surface across the slit. The mold according to claim 4. 6. The molding die further comprises, as an integral part of the holding die, an isolation wall made of a non-magnetic material and forming a wall surface of the filling space facing the molding surface. Mold. The mold according to claim 6, wherein the thickness of the isolation wall is 0.5 mm or less. Filling the filling space of the molding die according to any one of claims 1 to 7 with magnet material powder,
A method of molding a magnet material, which comprises orienting and molding the magnet material powder while applying a magnetic field from the outside of the mold.