Patent Application
20220172889
Embodiments hereof relate to permanent magnets and to methods of producing permanent magnets.
Magnetic materials are usually divided into permanent magnets (also referred to as hard magnets) and soft magnets. Hard magnets typically have coercivity values Hc>10 kA/m, whereas for soft magnets typically the coercivity is Hc<1 kA/m. Permanent magnets are commonly used in electrical machines (motors, generators). The most advanced permanent magnets today are based on rare earth (RE) metals, wherein rare earth metals are one of the elements of the Lanthanide series. Sintered, rare earth-based permanent magnets materials exhibit the highest magnetic performance, i.e. the highest coercivity Hc and the highest remanence Br.
State of the art anisotropic permanent magnets are commonly produced by the following sequence of steps:
The state of the art methods have two major disadvantages. First, during production, the green body/magnet needs to be magnetised twice in order to achieve a maximum magnetic performance, which is required for many applications, such as in electrical devices. By applying a high magnetic field in steps ii) and vi) the particles of the green body/magnet can be oriented, which usually increases the magnetic performance compared to non-oriented particles, in particular by (partial) alignment of the magnetic easy axes of the micro-crystallites in the direction of the applied field. Yet, around 10% of particles remain non-oriented. Secondly, the production of permanent magnets is limited to the manufacture of very simple geometries, because the shaping is based on simple uniaxial die-pressing, isostatic pressing, or hot deformation in a uniaxial die-pressing step. Already very simple geometrical features, such as a slightly curved surface instead of a flat surface, comes with a significantly higher price of the magnet, because expensive additional machining steps have to be carried out.
In each magnetisation step the following situations appear: In step ii) of the production method, the (magnetic) powder needs firstly to be oriented by magnetisation and pressed. Pressing can be done either at the same time, or after orientation. Independently of the type of process to realise this, up to 5% of the magnetic orientation is lost.
After step iv) (sintering) the macroscopically non-magnetised magnet needs to be magnetised by applying an external magnetic field. This additional process step gives rise to higher costs of the permanent magnet, as this requires a special treatment, for example with a capacitive discharge magnetiser and/or depending on the desired magnetisation pattern (axial, parallel, radial, multi-polar etc.), special fixtures may be required.
In addition, magnets cannot be transported in a magnetised state, because of the attraction of metal dust or other consequences due to the presence of a magnetic field.
Briefly, a method of producing a permanent magnet, a permanent magnet and an electrical machine are provided to overcome at least some of the abovementioned limitations. This may be accomplished by means of a method according to claim 1, a magnet according to claim 14 and an electrical machine according to claim 15.
According to an embodiment a method of producing a permanent magnet comprises: A) Forming a magnetisable workpiece by additive manufacturing. The additive manufacturing comprising the following sequence of steps: i) Forming a first powder layer by depositing a first powder. The first powder being ferromagnetic. ii) Forming a first workpiece layer of the magnetisable workpiece by irradiating a predetermined first area of the first powder layer by means of a focused energy beam to fuse the first powder in the first area. iii) Repeating the sequence of steps i) and ii) multiple times to form further workpiece layers of the magnetisable workpiece. Further, the method of producing a permanent magnet comprises B) Forming the permanent magnet by partitioning the magnetisable workpiece. An exposed surface of the permanent magnet is formed by the partitioning, which is non-parallel to the first workpiece layer. Further, the permanent magnet produces an external magnetic field having a magnetic field strength of at least 1 kA/m.
According to an embodiment a permanent magnet is provided. The permanent magnet is obtained by a method according to any of the embodiments of the present disclosure. The permanent magnet comprises at least two magnetic poles. Optionally the permanent magnet comprises at least four magnetic poles. In one or more embodiments the permanent magnet is a Halbach array permanent magnet.
According to an embodiment an electrical machine is provided. The electrical machine comprises at least one permanent magnet obtained by a method according to any of the embodiments of the present disclosure.
Those skilled in the art will recognise additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings.
The components in the Figures are not necessarily to scale, instead emphasis being placed upon illustrating the principles of the one or more embodiments of the present disclosure. Moreover, in the Figures, like reference signs designate corresponding parts. In the drawings:
In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration specific embodiments of the present disclosure.
As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features.
It is to be understood that other embodiments may be utilised and structural or logical changes may be made without departing from the scope of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims. The embodiments described herein use specific language, which should not be construed as limiting the scope of the appended claims.
According to an embodiment a method of producing a permanent magnet 200 is disclosed. The method comprises two steps: A) Forming a magnetisable workpiece 100 by additive manufacturing; B) Forming the permanent magnet 200 by partitioning the magnetisable workpiece 100.
Additive manufacturing of workpieces is known as such to the skilled person. For example, additive manufacturing is disclosed in US 2017/154713 A1, which is incorporated by reference herein in its entirety.
The magnetisable workpiece 100 may be formed of a plurality of workpiece layers. The first workpiece layer may be formed by carrying out at least two steps. First, in step i) a first powder layer may be formed by depositing a first powder. The first powder may be deposited by a powder delivery system, in particular including a powder delivery piston and a roller (e.g. based on selective laser melting). In another embodiment, the first powder may be deposited by means of a nozzle (e.g. based on laser metal deposition).
The first powder may be ferromagnetic. The first powder layer may have any free-form shape and/or size, for example, the first powder layer may be a closed area such as a circle, a square or a rectangle. The material of the first powder may comprise one of the following compositions a) to k), wherein composition
In step ii) a first workpiece layer of the magnetisable workpiece 100 may be formed by irradiating a predetermined first area 101 of the first powder layer by means of a focused energy beam to fuse the first powder in the first area 101. In other words, the first area 101 may be a portion of the first powder layer such that the first powder is only fused within a predetermined area, i.e. the first area 101, whereas in the remaining area, i.e. within the first powder layer but outside the first area 101, the first powder may not be fused. The location and/or size and/or shape of the first area 101 and thus of the first workpiece layer may be freely predeterminable, for example based on CAD design data and directing the focused energy beam to a predetermined location, and along a predetermined path.
According to an embodiment, the focused energy beam may be a laser beam or an electron beam. In case the focused energy beam is a laser beam, step Aii), and possibly also step Ai) or even the entire step A), may be conducted under a protective, inert gas atmosphere (such as for example Argon). For example, the laser beam may be generated by a pulsed Nd:YAG laser. In case the focused energy beam is an electron beam, the step Aii), and possibly also step Ai) or even the entire step A), may be conducted under vacuum.
In a step Aiii), the sequence of steps Ai) and Aii) may be repeated multiples times to form further (second, third, . . . , nth) workpiece layers of the magnetisable workpiece 100 on top of the first workpiece layer. Further powder layers (second, third, . . . , nth) may be formed by depositing further powders (second, third, . . . , nth). In one or more embodiments, further powder layers may be formed by depositing the first powder. In other words, the first powder and the powder used for further layers may be the same. As described above, the first powder layer and thus also any further powder layer may have any free-form shape and/or size. Typically, the first powder layer and all further powder layers have the same location, shape and size. The location and/or size and/or shape of the further areas (second, third, . . . , nth) and thus of the first workpiece layer may be freely predeterminable. In some embodiments, for example if the magnetisable workpiece 100 has the shape of cuboid, the location and/or size and/or shape of the further areas may be identical. In other embodiments, for example if the magnetisable workpiece 100 is of a curved or inclined shape, the location and/or size and/or shape of the further areas may not be identical. In any case, a workpiece layer may at least partially overlap in top view with the workpiece layer underneath, such that an upper workpiece layer may be bonded locally to an underlying and adjacent workpiece layer at least partially, by fusing the powder in the respective areas.
Parallel to the first workpiece layer the largest dimension of the magnetisable workpiece 100 may be at least 1 mm, possibly at least 1 cm. Perpendicular to the first workpiece layer, i.e. in the building direction of the magnetisable workpiece 100, the largest dimension of the magnetisable workpiece 100 may be at least 1 mm, possibly at least 1 cm. The magnetisable workpiece 100 may be formed of at least 100 workpiece layers, in some embodiments of at least 1000 workpiece layers.
Fusing of the first powder by means of a focused energy beam may correspond to sintering of the first powder, or even melting of the first powder. By fusing the first powder in the first or further areas, i.e. in steps Aii) and/or Aiii), magnetic grains may be formed in the magnetisable workpiece 100. By fusing the first powder in the first or further areas, i.e. in steps Aii) and/or Aiii), pole-avoiding magnetic domains, also referred to as magnetic closure domains, may be formed in the magnetisable workpiece 100. The first workpiece layer may be magnetised in-plane, in particular due to the first workpiece layer comprising large or macroscopic magnetic closure domains, which may lead to a marginal or vanishing external magnetic field (i.e. stray field). An internal magnetisation pattern may occur in combination with a corresponding anisotropy pattern. A vanishing or marginal external magnetic field (stray field) is advantageous, or possibly even necessary, as the presence of an out-of-plane magnetic field may hamper the formation of a second (further) powder layer. In particular, the magnetic lines may remain in the plane of the first workpiece layer (parallel to the first workpiece layer) and thus do not perturb the second powder that is formed by depositing the first or second powder. Although not wishing to be bound to a particular theory, it is believed that the large or macroscopic magnetic closure domains may be obtained by the rapid fusing and solidification, and/or an in-plane magnetisation of the first workpiece layer may be fixed during cooling down of the first workpiece layer.
Step Aiii) of the method of producing a permanent magnet 200 may lead to vanishing or marginal external magnetic fields for most or even all further workpiece layers. The resulting magnetisable workpiece 100 may be substantially nonmagnetic. According to an embodiment, the magnetisable workpiece 100 may produce an external magnetic field having a magnetic field strength of less than 0.1 kA/m. Experimental methods to measure the magnetic field strength are known to the skilled person. For example, a pulsed field magnetometer may be employed.
Further, the method of producing a permanent magnet 200 comprises step B):
According to an embodiment, the partitioning may be carried out by a method selected from the group consisting of cutting; breaking the magnetisable workpiece 100 parallel to a plurality of predetermined breaking points; sawing; grinding an external surface of the magnetisable workpiece 100, wherein the external surface 150 is parallel to the exposed surface; jet cladding. The external surface may be non-parallel to the first workpiece layer.
The magnetic grains may be elongated and/or tubular shaped and/or may resemble needles. The orientation of the magnetic grains may be such that the magnetic grains appear as elongated and/or tubular when viewed from the exposed surface 150 and may appear circular when viewed parallel to the first workpiece layer. In other words, an axial dimension of the magnetic grains may be parallel to the exposed surface 150, whereas a radial dimension may be parallel to the first workpiece dimension. The magnetic grains may have an average size in the plane defined by the exposed surface 150 of at least 0.5 μm, possibly of at least 1 μm.
Step B) is carried out after step A). Step B) may be carried out immediately after step A). Step B) may also be carried out substantially later. For example, step B) may also be carried out 1 hour or 1 day or even 1 month after step A). Advantageously, this allows for handling and transport of the magnetisable workpiece 100 to a desired location, and subsequently carrying out step B) at the desired location to form the permanent magnet 200. The resulting magnetisable workpiece 100 may be substantially nonmagnetic, therefore the attraction of metal dust or other consequences that may occur due to the presence of a magnetic field may be alleviated or even fully eliminated. Advantageously, the remaining workpieces other than the permanent magnet 200 that are formed due to partitioning of the magnetisable workpiece 100, may be handled and transported together with the permanent magnet 200, i.e. step B) may be carried out, but the remaining workpieces may not be removed from the permanent magnet 200. Therefore, during handling and transport of the permanent magnet 200, the attraction of metal dust or other consequences that may occur due to the presence of a magnetic field may be alleviated or even fully eliminated.
Surprisingly, the inventors have identified a range of experimental parameters that, in connection with the method of producing a permanent magnet 200 according to embodiments of the present disclosure, result in a permanent magnet 200 which produces an external magnetic field having a substantial magnetic field strength. In particular, the inventors have observed this advantageous effect in case one or more, possibly all, of the experimental parameters selected from the group consisting of: a thickness of the first (and further) workpiece layer; a beam diameter of the laser beam at a point of impact; an irradiation time; a point distance; and a hatching distance are implemented in a range disclosed in the following.
The thickness of the first workpiece layer and/or any further workpiece layer may be at least 10 μm, possibly at least 50 μm. The thickness of the first workpiece layer and/or any further workpiece layers may be no larger than 150 μm, possibly no larger than 100 μm.
The term “point of impact” refers to a portion of the first (or further) powder layer, which is irradiated by the focused energy beam. In particular, the location of the point of impact corresponds to a centroid of the focused energy beam.
The term “beam diameter” refers to the diameter of the laser beam at the point of impact, and therefore not necessarily in a focal point of the laser beam in case it is focused. The beam diameter of the laser beam may refer to the 1/e2 width assuming a Gaussian beam profile. At a point of impact of the laser beam with the first powder layer, the laser beam may have a beam diameter of less than 150 μm, possibly of less than 30 μm.
According to an embodiment, at the point of impact of the laser beam with the first powder layer, the first powder layer may be irradiated for at least 20 μs, possibly at least 100 μs, and/or no longer than 500 μs, possibly no longer than 300 μs. A power output of the laser may be at least 10 W, possibly at least 40 W, and/or no greater than 300 W, possibly no greater than 120 W.
The first workpiece layer may be formed by irradiating the first area 101 of the first powder at a plurality of points of impact. Irradiating the first area 101 may be carried out by directing the focused energy beam over a plurality of printing trajectories 111. Each printing trajectory 111 may comprise a plurality of points of impact. Stated differently, the first area 101 may be viewed as being subdivided into a plurality of printing trajectories 111, and the printing trajectories 111 may be viewed as being subdivided into a plurality of points of impact.
The term “point distance” 160 refers to the mean distance between adjacent points of impact of one printing trajectory.
The term “hatching distance” 170 refers to the mean distance between adjacent printing trajectories.
Surprisingly, the inventors have identified beneficial modes of operation of irradiating the first area and/or further areas (steps Aii) and Aiii)) that, in connection with the method of producing a permanent magnet 200 according to embodiments of the present disclosure, result in a permanent magnet 200 which produces an external magnetic field having a substantial magnetic field strength. These embodiments are based on configuring the printing trajectories as such and the sequence of printing trajectories in a certain way, as will be explained in the following.
According to an embodiment, step Aii) may comprise directing the focused energy beam along a plurality of printing trajectories 111. The focused energy beam may be a laser beam. In an embodiment, each printing trajectory 111 may be one of a closed trajectory and a spiral-shaped trajectory. An example of a closed trajectory 114 is illustrated in
Step Aiii) may comprise directing the focused energy beam along a plurality of printing trajectories. The focused energy beam may be a laser beam. According to one embodiment, at least one printing trajectory of a second workpiece layer may be substantially perpendicular to at least one of the printing trajectories of the first workpiece layer. A plurality or even all of the printing trajectories of the second workpiece layer may be substantially perpendicular to a plurality or even all of the printing trajectories of the first workpiece layer. The printing trajectories of the first workpiece layer and of the second workpiece layer may be a line. A plurality or even all of printing trajectories of the third workpiece layer may be perpendicular to a plurality or even all of the printing trajectories of the second workpiece layer and so forth, such that the printing trajectories of workpiece layers may be perpendicular to the printing trajectories of adjacent workpiece layers.
The first area 101 layer may comprise a first end 180 and a second end 190. For illustration purposes, the first end 180 and the second 190 are shown in
According to an embodiment, the first workpiece layer may comprise a first section 110, wherein the first section 110 comprises one or more printing trajectories 111. One or more printing trajectories 111 of the first section 110 may define a first printing direction that is one of clockwise and counter-clockwise. For example,
In an embodiment, step A) may be carried out without applying a magnetic field. Advantageously, substantial magnetic properties may be obtained for the permanent magnet 200 without the need for applying an external magnetic field while forming the magnetisable workpiece 100. According to another embodiment, no external magnetic field may be applied at least until completion of step B), possibly no magnetic external field may be applied in the entire method of producing a permanent magnet 200. Advantageously, substantial magnetic properties may be obtained for the permanent magnet 200 without the need for applying an external magnetic in the production process of the permanent magnet 200. In a further embodiment, the magnetic properties of the permanent magnet 200, in particular the external magnetic field produced by the permanent magnet 200, may be increased by carrying out a step C): Exposing the permanent magnet 200 to an external magnetic field. In particular, it may be advantageous to carry out step C) after step B).
Advantageously, methods according to embodiments of the present disclosure allow for manufacturing permanent magnets comprising two production steps, whereas prior art methods require six production steps. In particular, the two magnetisation steps necessary in prior art methods may be omitted. In addition, embodiments of the present disclosure allow for manufacturing complex geometrical shapes without additional labour or production steps. In particular, the productions methods disclosed herein enable printing of near net shape permanent magnets or even net shape permanent magnets, such that the need for surface finishing or the like may be reduced or even no longer exists. Embodiments of the present disclosure allow for the production of magnets with complex, and in particular predeterminable, magnetisation patters without the need for exposing the permanent magnet 200 to an external magnetic field. Complex magnetisation patterns are either not feasible or very expensive to produce with prior art methods.
According to an embodiment a permanent magnet is provided. The permanent magnet may be obtained by a method according to any of the embodiments of the present disclosure. The permanent magnet may comprise least two magnetic poles. Optionally the permanent magnet may comprise at least four magnetic poles. In one or more embodiments the permanent magnet is a Halbach array permanent magnet.
The permanent magnets 200 obtained by a method according to any of the embodiments of the present disclosure may be used for a sensor and/or an electrical machine, perhaps wherein the electrical machine comprises at least one of an electric motor, a generator, a power transformer, an instrument transformer, a linear motion device and a magnetically biased inductor, and a magnetic actuator.
According to an embodiment an electrical machine is provided. The electrical machine may comprise at least one permanent magnet obtained by a method according to any of the embodiments of the present disclosure. The electrical machine may be a stepper motor. The electrical machine may comprise at least one of an electric motor, a generator, a power transformer, an instrument transformer, a linear motion device and a magnetically biased inductor, and a magnetic actuator.
According to an embodiment a sensor is provided. The sensor may comprise at least one permanent magnet obtained by a method according to any of the embodiments of the present disclosure.
The following are non-limiting examples of permanent magnets produced according to methods of the present disclosure. The examples are given solely for the purpose of illustration and are not to be construed as limitations of the present disclosure, as many variations thereof are possible without departing from the scope of the present disclosure, which would be recognised by one of ordinary skill in the art.
Example 1: A magnetisable workpiece was produced, wherein the magnetisable workpiece resembles the form of a torus. The following experimental parameters were employed. The laser beam has a beam diameter (at a point of impact with the first powder layer) of approximately 40 μm. The first (and the further) powder layers were irradiated for approximately 120 μs. The thickness of the first (and of the further) workpiece layers was approximately 40 μm. The output power of the laser was about 115 W. The point distance was about 40 μm and the hatching distance was approximately 100 μm. The magnetisable workpiece was then cut perpendicular to the first workpiece layer to form the permanent magnet. The magnetic stray field distribution was measured in the air, 1 mm above and parallel to the exposed surface of the permanent magnet. The measurements were carried out by employing a pulsed field magnetometer. The magnetic stray field distribution of the exposed surface of the permanent magnet is shown in
Example 2: A magnetisable workpiece was produced, wherein the magnetisable workpiece resembles the form of a cube. The following experimental parameters were employed. The laser beam has a beam diameter (at a point of impact with the first powder layer) of approximately 40 μm. The first (and the further) powder layers were irradiated for approximately 120 μs. The thickness of the first (and of the further) workpiece layers was approximately 40 μm. The output power of the laser was around 115 W. The point distance was about 40 μm and the hatching distance was approximately 100 μm. The magnetisable workpiece was then cut perpendicular to the first workpiece layer to form the permanent magnet. The magnetic stray field distribution was measured in the air, 1 mm above and parallel to the exposed surface of the permanent magnet. The measurements were carried out by employing a pulsed field magnetometer. The magnetic stray field distribution of the exposed surface of the permanent magnet is shown in
The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “100 μm” is intended to mean “about 100 μm”.
| Number | Date | Country | Kind |
|---|---|---|---|
| 19160069.1 | Feb 2019 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/054673 | 2/21/2020 | WO | 00 |
