WO2016183824A1

WO2016183824A1 - Die and method for forming a permanent magnet from a preform and hot deformation system

Info

Publication number: WO2016183824A1
Application number: PCT/CN2015/079386
Authority: WO
Inventors: Jiaqing Yu; Bicheng Chen
Original assignee: Robert Bosch Gmbh
Priority date: 2015-05-20
Filing date: 2015-05-20
Publication date: 2016-11-24
Also published as: CN107851506B; CN107851506A; JP6463852B2; JP2018522400A

Abstract

A die (1, 101, 201, 301, 401) for forming a permanent magnet from a preform comprises a die body (3, 103, 203, 303, 403) and at least one die cavity (5, 105, 205, 305, 405) formed in the die body and having an input port (7, 107, 207, 307, 407) and an output port (9, 109, 209, 309, 409). The at least one die cavity each comprises at least two portions which open into each other, two adjacent ones of the at least two portions are deflected with respect to each other at an angle (α). A hot deformation system comprising the die and a method for forming a permanent magnet from a preform using the hot deformation system are provided. It is possible to restrain the grains from growing, thereby allowing the finished permanent magnet having a high coercivity.

Description

Die and method for forming a permanent magnet from a preform and hot deformation system

FIELD OF THE INVENTION

The invention relates to manufacturing a permanent magnet, in particular to a die for forming a permanent magnet from a preform and a method for forming a permanent magnet from a preform as well as a hot deformation system comprising the die for forming the permanent magnet from the preform.

BACKGROUND OF THE INVENTION

Permanent magnets such as rare earth/iron/boron-based permanent magnets usually have high enough remanence, coercivity and corrosion resistance, and are able to provide high enough magnetic flux within a wide temperature range such as -40 to 180℃. Thus, permanent magnets such as rare earth/iron/boron-based permanent magnets are widely used in electric motors of electric vehicle (EV) , hybrid electric vehicle (HEV) , and home appliances etc. Electric motors with rare earth/iron/boron-based permanent magnets have superior performance over induction motors due to a reduced copper loss, high power density, high efficiency and low rotor inertia.

There are two well-known approaches to manufacture the rare earth/iron/boron-based permanent magnets. One is a metallurgical sintering process which generally comprises strip-casting, hydrogen decrepitation, jet-milling, moulding, sintering and annealing. The permanent magnet manufactured by the metallurgical sintering process is called a sintered magnet, which is almost full density and possesses a high energy product. The other one is a bonding process which generally comprises moulding magnetic powder and organic binder together (via compacting, injecting, extruding or calendaring) and then curing at around 150℃. The permanent magnet manufactured by the bonding process is called a bonded magnet, which is low density, normally contains over 4 vol. ％organic binder and possesses a low energy product. The bonded magnets provide less magnet flux than the sintered magnets, but they can be moulded into the intricately shaped parts.

An uniaxial hot-deformation process is an emerging approach to manufacture the rare earth/iron/boron-based permanent magnets. This approach firstly cold-presses thin quenched magnetic ribbons or powders into a green preform, then hot-presses the green preform into a magnetically isotropic magnet body, finally subjects the isotropic magnet body to an uniaxial hot-deformation treatment. Driven by an applied pressure, the grains in the isotropic magnet body align their easy magnetization axes to the pressing direction during the uniaxial hot deformation treatment. As a result, the formed permanent magnet is magnetically anisotropic. Similar to the bonding process, this uniaxial hot-deformation process is also a net-shaping process, can form directly the magnets into ring, disc, block or other net-shapes.

Compared with the sintered magnets and the bonded magnets, the hot deformed magnets manufactured by the uniaxial hot-deformation process are nano-structured in microstructure, magnetically anisotropic in magnetic performance, possess a high energy product, show a high thermal stability due to the small grain size, and need only a very few or even no heavy rare earth element such as dysprosium (Dy) and terbium (Tb) for high coercivity. These properties of the hot deformed magnets are very attractive for EV/HEV motor.

There are several approaches to perform hot deformation treatment, such as die-upsetting, backward extrusion, forward extrusion and rolling. These approaches are implemented in specifically designed dies at an elevated temperature (normally 650-850℃) under a suitable atmosphere (vacuum, inert gas etc. ) . A hydraulic system is used to generate a mechanical pressure to press the magnetic ribbons or powders into a designed cavity or through a designed trajectory, thereby densifying the magnetic ribbons or powders and finally transforming the magnetic ribbons or powders into a dense magnet of ring, disc, block or other shape. The used magnetic ribbons or powders can be a pure magnetic ribbon/powder, or can be a mixture of a pure magnetic ribbon/powder with other pure magnetic ribbons/powders or non-magnetic ribbon/powder.

EP0513891B1 described a process of hot-pressing and/or hot working of rare earth-containing powders using open-to-the-air presses. This process firstly presses the rare earth-containing powders into a compact body at ambient temperature using a solid lubricant only on the die wall, then hot-presses the compact body in an open-air press utilizing a heated die flooded with argon. US7730755 described a process of extruding a preform into a plate-shaped permanent magnet in such a way that a dimension of a cross section of the preform is reduced in an X-direction and enlarged in a Y-direction perpendicular to the X-direction.

However, in these existing hot-deformation processes, the grains in the compact body or the preform tend to grow when the compact body or the preform is pressed or extruded at a high temperature, which deteriorates the coercivity of the finished permanent magnets.

Thus, there is a need to make improvements on the existing hot deformation process.

SUMMARY OF THE INVENTION

The present invention provides a die and method for forming a permanent magnet from a preform which may restrain the grains from growing, thereby allowing the finished permanent magnet having a high coercivity.

According to an aspect of the present invention, it is to provide a die for forming a permanent magnet from a preform comprising:

a die body； and

at least one die cavity formed in the die body and having an input port and an output port；

wherein the at least one die cavity each comprises at least two portions which open into each other, two adjacent ones of the at least two portions are deflected with respect to each other at an angle.

Preferably, the two adjacent ones of the at least two portions are configured such that the cross sectional area of a subsequent portion is smaller than that of a preceding portion.

Preferably, the angle is between 0° and 180°, preferably between 45° and 135°, more preferably 90°.

Preferably, a curved transition is formed between the two adjacent ones of the at least two portions.

Preferably, the at least two portions have a tapered or constant cross section.

Preferably, a portion of the at least two portions defining the output port of the die cavity has a rectangular, circular, arc-shaped, or triangular cross section.

Preferably, the at least two portions are straight.

Preferably, a portion of the at least two portions defining the output port of the die cavity is curved.

Preferably, a portion of the at least two portions defining the input port of the die cavity extends through the die body so that the die comprises two opposite input ports.

Preferably, the die further comprises an additional port opening into the portion of the at least two portions defining the input port and aligning with a portion of the die cavity subsequent to the portion of the at least two portions defining the input port.

According to a further aspect of the present invention, it is to provide a hot deformation system comprising a die for forming a permanent magnet from a preform as stated above.

Preferably, the hot deformation system further comprises a pressing machine comprising a punch which moves out of the die cavity and into the die cavity.

Preferably, the hot deformation system further comprises a feeding mechanism for feeding the preform into a portion of the die cavity defining the input port of the die cavity.

Preferably, the hot deformation system further comprises a heating mechanism for heating the preform to a predefined temperature.

According to a further aspect of the present invention, it is to provide method for forming a permanent magnet from a preform using a hot deformation system as stated above, comprising the steps:

feeding at least a part of a preform into a first portion of the at least two portions of the die cavity via the input port；

pressing the preform into the first portion of the at least two portions of the die cavity at a predefined temperature；

withdrawing the punch out of the first portion of the die cavity； and

feeding and pressing a coming preform into the first portion to extrude the preform as a finished permanent magnet out of the output port of the die cavity.

Preferably, these steps are repeated so as to continuously perform a near net-shaping hot deformation on the preforms without intermittence.

Preferably, the method further comprises the step of cutting the finished permanent magnet into many permanent magnet components.

These and other objects, features and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view showing schematically a die for forming a permanent magnet from a preform according to a first embodiment of the present invention.

FIG. 1B is a longitudinally sectional view taken along a line 1B-1B of FIG. 1A.

FIGS. 2A and 2B show schematically in a longitudinally sectional view that a preform is extruded into a permanent magnet by using a hot deformation system comprising the die according to a first embodiment of the present invention.

FIG. 2C shows schematically a finished permanent magnet extruded by the hot deformation system of FIGS. 2A-2B.

FIG. 3A shows schematically in a longitudinally sectional view a hot deformation system comprising a die for forming a permanent magnet from a preform according to a second embodiment of the present invention.

FIG. 3B is a sectional view taken along a line 3B-3B of FIG. 3A.

FIG. 3C is a sectional view taken along a line 3C-3C of FIG. 3A.

FIG. 3D shows schematically a finished permanent magnet extruded by the hot deformation system of FIG. 3A-3C.

FIG. 4A shows schematically in a longitudinally sectional view a die for forming a permanent magnet from a preform according to a third embodiment of the present invention.

FIG. 4B is a sectional view taken along a line 4B-4B of FIG. 4A.

FIG. 4C is a sectional view taken along a line 4C-4C of FIG. 4A.

FIGS. 5A-5C show schematically in a longitudinally sectional view that a preform is extruded into a permanent magnet by using a hot deformation system comprising a die for forming a permanent magnet from a preform according to a fourth embodiment of the present invention.

FIG. 6A shows schematically in a longitudinally sectional view a die for forming a permanent magnet from a preform according to a fifth embodiment of the present invention.

FIG. 6B is a sectional view taken along a line 6B-6B of FIG. 6A.

FIG. 6C is a sectional view taken along a line 6C-6C of FIG. 6A.

FIG. 6D is a left side view of the die shown in FIG. 6A.

FIG. 6E shows schematically that a big sector-shaped permanent magnet is cut into a plurality of small sector-shaped permanent magnet components.

FIGS. 7A-7D show schematically in a longitudinally sectional view that preforms are extruded into a permanent magnet by using a hot deformation system comprising a die according to a sixth embodiment of the present invention.

FIG. 7E shows schematically a finished permanent magnet extruded by the hot deformation system of FIGS. 7A-7D.

FIGS. 8A, 8B and 8C show schematically in a longitudinally sectional view that a preform is extruded into a permanent magnet by using a hot deformation system comprising a die according to a seventh embodiment of the present invention.

FIG. 8D shows schematically a finished permanent magnet extruded by the hot deformation system of FIGS. 8A-8C.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

As well-known, a near net-shaping continuous process for manufacturing a hot-deformed rare earth/iron/boron-based permanent magnet usually comprises two steps: preparing a densified preform by cold-pressing or/and hot-pressing the magnetic ribbons or powders； and extruding the preform into a permanent magnet by hot-deformation treating the preform at a high temperature. The magnetic ribbons or powders are formed by a well-known process. The raw material from which the preform is formed and the process for preparing the preform from the magnetic ribbons or powders are also known in the art and the detailed explanation for them thus is omitted. The present invention mainly focuses on how to extrude the preform into the permanent magnet by using a hot deformation system comprising a die for forming a permanent magnet from a preform.

FIG. 1A is a perspective view showing schematically a die for forming a permanent magnet from a preform according to a first embodiment of the present invention, and FIG. 1B is a longitudinally sectional view taken along a line 1B-1B of FIG. 1A. As shown in FIGS. 1A and 1B, a die 1 for forming a permanent magnet from a preform according to a first embodiment of the present invention comprises a die body 3 and a hollow die cavity 5 formed in the die body 3. The die cavity 5 generally comprises a first portion 5a and a second portion 5b which opens into the first portion 5a and is deflected relative to the first portion 5a at an angle α. Thus, the die cavity 5 has an input port 7 at an end of the first portion 5a and output port 9 at an end of the second portion 5b. Although the second portion 5b is deflected relative to the first portion 5a at an angle α of 90° in the embodiment shown in FIGS. 1A and 1B, it should be understood that the second portion 5b may be deflected relative to the first portion 5a at an angle α of between 0° and 180°, preferably between 45° and 135°. Further, although both the first portion 5a and the second portion 5b have a rectangular cross section, it also should be understood that the first portion 5a and the second portion 5b may have a cross section of any suitable shape such as circular, semi-circular, elliptical or triangular shape. In the embodiment shown in FIGS. 1A and 1B, both the first portion 5a and the second portion 5b are shown to have a constant cross section. It is also feasible that the first portion 5a and the second portion 5b have a tapered cross section. However, it should be noted that, in any event, the second portion 5b has a cross sectional area which is smaller than that of the first portion 5a.

FIGS. 2A and 2B show schematically in a longitudinally sectional view that a preform is extruded into a permanent magnet by using a hot deformation system comprising the die according to a first embodiment of the present invention. As shown in FIGS. 2A and 2B, a hot deformation system 11 generally comprises the die 1 according to the first embodiment of the present invention and a pressing machine (not shown wholly) comprising a punch 13 which can move upward and downward. Of course, the hot deformation system 11 also comprises a feeding mechanism (not shown) for feeding a part of a preform into the first portion 5a of the die cavity 5 via the input port 7 of the die cavity 5.

As shown in FIG. 2A, the feeding mechanism feeds at least a part of a preform P1 manufactured by a known process into the first portion 5a of the die cavity 5 via the input port 7 of the die cavity 5. Then, the punch 13 of the pressing machine moves downward to press the preform P1 into the first portion 5a. With downward movement of the punch 13 of the pressing machine, the preform P1 is pressed further into the first portion 5a or extruded partially from the first portion 5a of the die cavity 5 into the second portion 5b of the die cavity 5. After the preform P1 is pressed into the first portion 5a, the punch 13 of the pressing machine may be released and moves upward to withdraw out of the first portion 5a of the die cavity 5 so that the feeding mechanism feeds a part of a coming preform P2 into the first portion 5a, as shown in FIG. 2B. The punch 13 of the pressing machine moves downward again to press the coming preform P2 downward so that the preform P1 is extruded wholly as the finished permanent magnet M out of the output port 9 of the die cavity 5 by means of the coming preform P2, as shown in FIG. 2C. This feeding-pressing-withdrawing-feeding process is automatically, continuously and repeatedly carried out so as to continuously perform the near net-shaping hot deformation on the preforms without intermittence. It should be noted that, as well-known, the process as shown in FIGS. 2A and 2B is implemented at an elevated temperature (normally 650-850℃) under a suitable atmosphere (vacuum, inert gas etc. ) . The hot deformation system 11 may further comprise a heating mechanism for heating the preform to a predefined temperature. Further, to smoothly extrude the preform from the first portion 5a into the second portion 5b of the die cavity 5, a curved transition 6 is formed between the first portion 5a and the second portion 5b.

According to the process as shown in FIGS. 2A and 2B, when the punch 13 of the pressing machine presses the preform P1 into the first portion 5a of the die cavity 5, the preform P1 is hot-pressed into full density and hot-deformed into a flat plate-shaped magnet, then in sequence is extruded into the second portion 5b of the die cavity 5 by the coming hot-pressed and deformed preform P2 to perform a second hot deformation. After the second hot-deformation, the finished permanent magnet M is extruded out of the die cavity 5 by the coming hot-pressed and deformed preform P2. During the second hot deformation, the preform P1 is kept the flat plate shape (and can be changed in dimension depending on the geometry of the second portion 5b of the die cavity 5) , the grains inside the preform can be refined through stress shearing effect, which consequently improves the corcivity of the finished permanent magnet M. After this process, the preform becomes a flat plate-shaped permanent magnet M which is grain-oriented for anisotropic magnetic properties (i.e. high remanence) and grain-refined for improved coercivity (i.e high thermal stability) .

FIG. 3A shows schematically in a longitudinally sectional view a hot deformation system comprising a die for forming a permanent magnet from a preform according to a second embodiment of the present invention, FIG. 3B is a sectional view taken along a line 3B-3B of FIG. 3A, FIG. 3C is a sectional view taken along a line 3C-3C of FIG. 3A. The hot deformation system comprising the die for forming a permanent magnet from a preform according to the second embodiment of the present invention is similar substantially to that shown in FIGS. 2A and 2B. In the hot deformation system comprising the die according to the second embodiment of the present invention, the identical or similar components to those of the hot deformation system shown in FIGS. 2A and 2B are represented by the same reference numeral plus “100” . For the sack of simplification and conciseness, the detailed explanation for the identical or similar components is omitted. The hot deformation system 111 comprising the die 101 according to the second embodiment of the present invention differs from the hot deformation system 11 shown in FIGS. 2A and 2B by the fact that the second portion 105b of the die cavity 105 has an arc-shaped cross section other than a rectangular cross section. Thus, the finished permanent magnet M extruded out of the output port 109 of the die cavity 105 is an arc-shaped plate as shown in FIG 3D.

Although the finished permanent magnet M according to the present invention is shown to be flat plate-shaped (as shown in FIG 2C) or arc-shaped (as shown in FIG 3D) , the finished permanent magnet M may be in any suitable shape by choosing a shape of the cross section of the portion of the die cavity defining the output port. For example, by designing the portion of the die cavity defining the output port to have a circular or triangular cross section, the finished permanent magnet M according to the present invention may be a rod having a circular or triangular cross section. The finished permanent magnet M can be further cut into many short or small magnet components of disc, block, segment or other shape, and can be directly used in an electric motor after grinding. By changing the cross section size of the portion of the die cavity defining the output port, the size of these small magnet components can be adjusted accordingly.

FIG. 4A shows schematically in a longitudinally sectional view a die for forming a permanent magnet from a preform according to a third embodiment of the present invention, FIG. 4B is a sectional view taken along a line 4B-4B of FIG. 4A, and FIG. 4C is a sectional view taken along a line 4C-4C of FIG. 4A. The die for forming a permanent magnet from a preform according to the third embodiment of the present invention is similar substantially to that shown in FIGS. 1A and 1B. In the die according to the third embodiment of the present invention, the identical or similar components to those of the die shown in FIGS. 1A and 1B are represented by the same reference numeral plus “200” . For the sack of simplification and conciseness, the detailed explanation for the identical or similar components is omitted. The die 201 according to the third embodiment of the present invention differs from the die 1 shown in FIGS. 2A and 2B by the fact that the die cavity 205 comprises four portions, i.e., the first portion 205a, the second portion 205b, a third portion 205c and a fourth portion 205d. Similarly, each of the four portions of the die cavity 205 is deflected relative to an adjacent portion at an angle α. Further, a subsequent one of the four portions of the die cavity 205 has a cross sectional area which is smaller than that of a preceding one. Although in the illustrated embodiments the die cavity is shown to have two or four portions, the die cavity may have three or more than four portions. The more the portions of the die cavity there are, the more times of the hot deformation the preform is subjected to. As a result, the finished permanent magnet M has a further refined grain size in a microstructure (such as a further refined nano-structured grain size) to achieve a high coercivity but still keep a high magnetocrystalline anisotropy.

FIGS. 5A-5C show schematically in a longitudinally sectional view that a preform is extruded into a permanent magnet by using a hot deformation system comprising a die for forming a permanent magnet from a preform according to a fourth embodiment of the present invention. The hot deformation system comprising the die for forming a permanent magnet from a preform according to the fourth embodiment of the present invention is similar substantially to that shown in FIGS. 2A and 2B. In the hot deformation system comprising the die according to the fourth embodiment of the present invention, the identical or similar components to those of the hot deformation system shown in FIGS. 5A-5C are represented by the same reference numeral plus “300” . For the sack of simplification and conciseness, the detailed explanation for the identical or similar components is omitted. The hot deformation system 311 comprising the die 301 according to the fourth embodiment of the present invention differs from the hot deformation system 11 shown in FIGS. 2A and 2B by the fact that the die 301 comprises two die cavities 305 formed in the die body 301. Each of two die cavities 305 comprises a first portion 305a and a second portion 305b which is deflected relative to the first portion 305a at an angle α. It should be understood that a die comprising more than two die cavities is also feasible. The die comprising more than one die cavities can manufacture more than one magnet at the same time by the hot deformation process, thereby enhancing the production efficiency.

FIG. 6A shows schematically in a longitudinally sectional view a die for forming a permanent magnet from a preform according to a fifth embodiment of the present invention, FIG. 6B is a sectional view taken along a line 6B-6B of FIG. 6A, FIG. 6C is a sectional view taken along a line 6C-6C of FIG. 6A, and FIG. 6D is a left side view of the die shown in FIG. 6A. The die for forming a permanent magnet from a preform according to the fifth embodiment of the present invention is similar substantially to that shown in FIGS. 1A and 1B. In the die according to the fifth embodiment of the present invention, the identical or similar components to those of the die shown in FIGS. 1A and 1B are represented by the same reference numeral plus “400” . For the sack of simplification and conciseness, the detailed explanation for the identical or similar components is omitted. The die 401 according to the fifth embodiment of the present invention differs from the die 1 shown in FIGS. 1A and 1B by the fact that the second potion 405b of the die cavity 405 is curved other than straight. The second potion 405b of the die cavity 405 may be designed to have a gradually tapered cross section, thereby forming a sector-shaped permanent magnet. The sector-shaped magnets can be cut into many small sector-shaped magnet components (as shown in FIG 6E) which can be used after grinding. During the hot deformation process, grains in the microstructure are oriented to a direction perpendicular to the thickness direction of the magnet.

In the preferred embodiments, although only an upper punch is used to press the preform into the die cavity, it is feasible that more than one punch is used at the same time. FIGS. 7A-7D show schematically in a longitudinally sectional view that a preform is extruded into a permanent magnet by using a hot deformation system comprising a die according to a sixth embodiment of the present invention. The hot deformation system comprising the die for forming a permanent magnet from a preform according to the sixth embodiment of the present invention is similar substantially to that shown in FIGS. 2A and 2B. In the hot deformation system comprising the die according to the sixth embodiment of the present invention, the identical or similar components to those of the hot deformation system shown in FIGS. 2A and 2B are represented by the same reference numeral plus “500” . For the sack of simplification and conciseness, the detailed explanation for the identical or similar components is omitted. The hot deformation system 511 comprising the die 501 according to the sixth embodiment of the present invention differs from the hot deformation system 11 shown in FIGS. 2A and 2B by the fact that the first portion 505a of the die cavity 505 extends through the die body 501 so that the first portion 505a defines an first input port 507a and a second input port 507b. As a result, the pressing machine comprises an upper punch 513a and a lower punch 513b. In use, two preforms P1 may be fed into the first portion 505a of the die cavity 505 via the first input port 507a and the second input port 507b of the die cavity 505. FIG. 7E shows schematically a finished permanent magnet M extruded by the hot deformation system of FIGS. 7A-7D. To smoothly extrude the preform from the first portion 505a into the second portion 505b of the die cavity 505, the ends of the upper punch 513a and the lower punch 513b define a respective

curved portion

514a, 514b which contacts the preform when pressing the preforms.

FIGS. 8A, 8B and 8C show schematically in a longitudinally sectional view that a preform is extruded into a permanent magnet by using a hot deformation system comprising a die according to a seventh embodiment of the present invention. The hot deformation system 611 comprising the die 601 according to the seventh embodiment of the present invention differs from the hot deformation system 501 shown in FIGS. 7A-7D by the fact that the die 601 further comprises an additional port 608 opening into the first portion 605a and aligning with the second portion 605b of the die cavity 605. As a result, except an upper punch 613a and a lower punch 613b, the pressing machine comprises an additional punch 513c. Thus, the additional punch 513c helps smoothly extrude the preform from the first portion 605a into the second portion 605b of the die cavity 605.

When the pressing machine at least comprises the upper punch and the lower punch as shown in 7A-7D and 8A-8C, the preform may be pressed simultaneously along two opposite directions. As a result, the microstructure of the finished permanent magnet is more homogenous, and the mechanical property and the magnetic property of the finished permanent magnet are also more uniform.

In the above-mentioned embodiments, by designing the die cavity of the die for forming the permanent magnet from the preform to have at least two portions deflected with respect to each other, the preform is subjected to at least twice hot-pressed deformations to further reduce the grain size when the preform is pressed through the die, thereby restraining the grains from growing. As a result, the finished permanent magnet has a high coercivity.

The die and the process according to the present invention may be used to manufacture a permanent magnet of both rare earth-rich and rare earth-lean in chemical composition. The finished permanent magnet may be a single phase nano-structured material or a nano-composite material accordingly.

It has to be noted that embodiments of the invention are described with reference to different subject matters. In particular, some embodiments are described with reference to method type claims whereas other embodiments are described with reference to the device type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise notified, in addition to any combination of features belonging to one type of subject matter also any combination between features relating to different subject matters is considered to be disclosed with this application. However, all features can be combined providing synergetic effects that are more than the simple summation of the features.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing a claimed invention, from a study of the drawings, the disclosure, and the dependent claims.

In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor or other unit may fulfil the functions of several items re-cited in the claims. The mere fact that certain measures are re-cited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

A die (1, 101, 201, 301, 401) for forming a permanent magnet (M) from a preform comprising:

a die body (3, 103, 203, 303, 403) ； and

at least one die cavity (5, 105, 205, 305, 405) formed in the die body (3, 103, 203, 303, 403) and having an input port (7, 107, 207, 307, 407) and an output port (9, 109, 209, 309, 409) ；

wherein the at least one die cavity each comprises at least two portions which open into each other, two adjacent ones of the at least two portions are deflected with respect to each other at an angle (α) .
The die (1, 101, 201, 301, 401) according to claim 1, wherein the two adjacent ones of the at least two portions are configured such that the cross sectional area of a subsequent portion is smaller than that of a preceding portion.
The die (1, 101, 201, 301, 401) according to claim 1, wherein the angle (α) is between 0° and 180°, preferably between 45° and 135°, more preferably 90°.
The die (1, 101, 201, 301, 401) according to claim 1, wherein a curved transition is formed between the two adjacent ones of the at least two portions.
The die (1, 101, 201, 301, 401) according to claim 1, wherein the at least two portions have a tapered or constant cross section.
The die (1, 101, 201, 301, 401) according to claim 1, wherein a portion of the at least two portions defining the output port of the die cavity has a rectangular, circular, arc-shaped, or triangular cross section.
The die (1, 101, 201, 301, 401) according to claim 1, wherein the at least two portions are straight.
The die (1, 101, 201, 301, 401) according to claim 1, wherein a portion of the at least two portions defining the output port of the die cavity is curved.
The die (1, 101, 201, 301, 401) according to claim 1, wherein a portion of the at least two portions defining the input port of the die cavity extends through the die body so that the die comprises two opposite input ports.
The die (1, 101, 201, 301, 401) according to claim 9, wherein the die further comprises an additional port opening into the portion of the at least two portions defining the input port and aligning with a portion of the die cavity subsequent to the portion of the at least two portions defining the input port.
A hot deformation system comprising a die (1, 101, 201, 301, 401) for forming a permanent magnet (M) from a preform according to any one of claims 1-10.
The hot deformation system according to claim 11, further comprising:

a pressing machine comprising a punch which moves out of the die cavity and into the die cavity.
The hot deformation system according to claim 12, further comprising:

a feeding mechanism for feeding the preform into a portion of the die cavity defining the input port of the die cavity.
The hot deformation system according to claim 12, further comprising:

a heating mechanism for heating the preform to a predefined temperature.
A method for forming a permanent magnet from a preform using a hot deformation system according to any one of claims 11-14, comprising the steps:

feeding at least a part of a preform into a first portion of the at least two portions of the die cavity via the input port；

pressing the preform into the first portion of the at least two portions of the die cavity at a predefined temperature；

withdrawing the punch out of the first portion of the die cavity； and

feeding and pressing a coming preform into the first portion to extrude the preform as a finished permanent magnet out of the output port of the die cavity.
The method according to claim 15, wherein these steps are repeated so as to continuously perform a near net-shaping hot deformation on the preforms without intermittence.
The method according to claim 15 or 16, further comprising the step:

cutting the finished permanent magnet into permanent magnet components.