The invention relates to a method for the production of a soft magnetic formed part and a soft magnetic formed part.
Soft magnetic substances are ferromagnetic materials which can be easily magnetized in a magnetic field. If formed parts made of such a substance, e.g. in the form of stator parts, are exposed to an external magnetic alternating field, a recurring magnetic reversal occurs. This results in magnetic reversal losses. In the case of electrically conductive formed parts, some of these losses are due to the induced eddy currents. In order to reduce the magnetic reversal losses, it is known to produce the formed parts from iron particles, which are completely surrounded by an electrical insulating layer to prevent current flow. For the manufacture of the formed part, the insulated iron particles are brought into the desired form by pressing and sintering in the furnace. This production method has several disadvantages:
DE 10 2014 006 519 A1 describes a method for the production of complex, magnetic and/or magnetizable formed parts using additive fabricators. No measures are provided to keep the specific electrical resistance of the formed parts low.
One object of the present invention is to specify a method of soft magnetic formed parts with improved properties.
A method that solves this problem is specified in claim 1 or 2. The further claims specify preferred embodiments as well as a formed part, which can be produced in particular by the method according to the invention.
According to a first aspect, magnetically conductive particles, which are free of a sheathing of an electrical insulating layer, are fused together in such a way that electrical insulating locations are locally arranged in the interspaces.
According to a second aspect, magnetically conductive particles are at least surface-fused by an energy supply. The energy supply is temporally concentrated and typically occurs in less than 1 second. Electrical insulating locations are formed in the interspaces due to an additive. These reduce in particular the eddy currents during magnetic reversal. The magnetically conductive particles do not necessarily have to be covered with a complete coating of an insulating layer. As a result, a high density can be achieved.
The electrical insulating locations, which are created during the method according to the first or second aspect, are formed island-like on the inside of the magnetic flux conducting formed part. The respective insulating location of the formed part has a current-interrupting effect. If the formed part is exposed to a magnetic field that changes over time, eddy currents are avoided or at least reduced, since a current flow through the insulating locations is interrupted. Iron losses can thus be reduced.
In a first embodiment, the formed part is produced in layers. Preferably an application device is provided to apply additional additives to a layer in a targeted manner. This allows the production of a formed part, which has a targeted inhomogeneous distribution of electrical insulating locations, in order to be able to conduct the magnetic flux B in a desired direction when used as a stator part.
In a second embodiment, the production is carried out by adiabatic pressing. This method makes it possible to produce formed parts in a short production time.
The fusion of the material, e.g. powder, takes place by means of an energy strike or several successive energy strikes. The at least one energy strike is carried out by means of a ram, for example. A particular advantage of the short-term energy introduced into the material, e.g. powder, is that the working temperatures in the formed part are typically less than 100° C. This means that additives with a low melting point can also be used as insulators, e.g. organic additives, which normally diffuse in the sintering process.
Preferably a negative form is used, which is filled with the magnetic particles and the additive, wherein the void space between the particles is reduced prior to adiabatic pressing, for example by mechanical means and/or by suctioning of air. In a special embodiment, the step of void space reduction is carried out by means of the punch, which is subsequently used as a ram for adiabatic pressing.
The invention is explained in the following by means of exemplary embodiments with reference to figures.
The system comprises a reservoir 10 for the intake and supply of the base material 21, 22, a manufacturing bed 11 in which the formed part 20 is manufactured, a coater 12 for the formation of a layer of the base material 21, 22 in the manufacturing bed 11, a laser 13 and a scanning device 14.
The reservoir 10 has a bottom 10a which can be lifted in the Z-direction and which for example, is part of a sliding piston.
The manufacturing bed 11 has a working platform 11a which can be lowered in the Z-direction and which is part of a sliding piston, for example.
The coater 12 is movable along the manufacturing bed 11, i.e. in X-direction, and is formed, for example, as a rotating roll or wiper.
The laser 13 and the scanning device 14 are designed for generating a laser beam 15, which is used for a local and temporally concentrated heating of a layer of the base material in the manufacturing bed 11. The laser 13 generates a beam that is typically in the infrared range. A CO2 laser or an Nd:YAG laser, for example, are suitable as lasers.
The scanning device 14 comprises optical members, one or more lenses and one or more mirrors, for example, and serves to focus or expand the beam generated by the laser 13, if necessary, and to guide it along a predetermined path in the manufacturing bed 11, which defines the form of the formed part 20 at the level at which the layer is heated.
A further reservoir 16 serves as a silo, from which base material 21, 22 can be transferred to the reservoir 10 and/or unused base material 21, 22 can be taken up from the manufacturing bed 11.
The reservoir 10, the manufacturing bed 11 and the reservoir 16 are delimited by walls 10b, 10c, 11b, 11c, 16a, 16b. These are connected at front and back, i.e. seen in Y-direction by further walls (not to be seen in
One possible method of producing a soft magnetic formed part 20 is as follows:
Geometric data are provided, which define the desired geometry of the formed part to be manufactured. These geometric data are available as CAD data, for example, and define the path along which the laser beam 15 is to be guided in each layer.
The base material 21, 22 is provided in the reservoir 10. For example, a mixture of magnetically conductive particles 21 and an additive 22 is used as the base material to form electrical insulating locations 22. In the finished formed part 20, these serve to interrupt or at least reduce eddy currents that occur during the magnetic reversal. The mixture is available, for example, in a pourable form, wherein the additive 22 is preferably present as particles. It is also conceivable to provide the additive 22 in pasty, liquid or gaseous form, so that it is in contact at least with the layer which has been formed from the magnetically conductive particles 21 in the manufacturing bed 11 and which is heated with the laser beam 15.
The magnetically conductive particles 21 are available as powder and/or granules. The respective particle 21 is preferably present in pure form, wherein the particles 21 can consist of different materials and thus form a mixture.
Suitable as material for the magnetically conductive particles 21 is, for example the following (content data in the following in percent by weight):
Other mixtures can also be provided, which comprise at least two of the following substances:
Preferably, the magnetically conductive particles 21 are free from a complete coating by an electrically insulating layer.
The following substances are suitable as additive 22:
The additive 22 can be present as particles whose grain size is smaller than that of the magnetically conductive particles 21. The median value (d50) of the grain size distribution of the additive 22 is then smaller than the median value (d50) of the grain size distribution of the magnetically conductive particles 21. It is also conceivable that the additive 22 is present as particles with a grain size that is at least as large as that of the magnetically conductive particles 21.
The bottom 10a is raised and a layer is formed on the work platform 11a by means of the coater 12. The layer is continuous and extends in the XY-plane according to
The energy of laser 13 can be introduced very quickly, so that an inclusion of additive 22 in the interspaces takes place.
Depending on its choice, for example as a gas, the additive 22 can lead to a surface change of the magnetically conductive particles 21 during heating, so that an oxide layer is formed in the interspaces, which act as electrical insulating locations. Optionally, the manufacturing bed 11 is located in a closed chamber, to which the additive 22 is supplied as a gas. It is also conceivable that the additive 22 is first in solid form (for example as Acrawax) and melts when heated, so that a gas is produced, which causes the formation of an oxide layer in the respective interspace.
The working platform 11a is lowered by a layer thickness after the heating. The bottom 10a is raised and a next layer of base material 21, 22 is applied in the manufacturing bed 11 by means of the coater 12. The heating is then carried out again at the predetermined locations by means of the laser beam 15.
The finished formed part 20 is produced by successively applying a layer and heating.
During the manufacture, the formed part 20 is embedded in the manufacturing bed 11 in the rest of the base material 21, 22 which has not been heated by means of the laser beam 15. At the end of the manufacture, the formed part 20 is removed from the manufacturing bed 11 and any base material 21, 22 still adhering to it is knocked off, brushed off and/or removed in some other way.
In the method described so far, each layer has an essentially homogeneous concentration of base material 21, 22. The formed part 20 has accordingly an essentially homogeneous distribution of the electrical insulating locations. In one embodiment of the production method, a formed part 20 can be manufactured, which has a locally different distribution of insulating locations. For this purpose, the system according to
In addition to the method described so far, other methods are also suitable for producing soft magnetic formed parts. For example, from DE 10 2013 021 944 A1, additive manufacture is known, in which material is applied to predetermined locations by means of electrophotographic image drums. In addition to the manufacturing material, which in this case consists of magnetically conductive particles 21 and additive 22, a supporting material can also be applied in this method, which is removed after the manufacture of the formed part and is used, for example, to manufacture undercuts. At least three rollers are preferably provided here, by means of which magnetically conductive particles 21, additive 22 and support material can be applied. A manufacturing head for applying the magnetically conductive particles 21 has a fixing unit with a laser, by means of which energy can be transferred to the magnetically conductive particles 21 in a temporally concentrated manner, in order to generate a fusing. By arranging several manufacturing heads for the applying of production and support material one after the other, a production line can be provided, which enables an efficient manufacture of formed parts.
In addition to an additive manufacturing method, it is also conceivable to produce a formed part 20 in one piece by means of a so-called adiabatic forming/densification (“adiabatic pressing”). In a first process step, for example by pressing, a blank which corresponds to the desired form of the formed part 20 is manufactured from the mixture of magnetically conductive particles 21 and additive 22. The blank is not yet solidified, so that the particles may only bind minimally. An additional binder may be provided and/or the additive 22 itself acts as such a binder, for example in the case of silicone. In a second process step, the blank is then densified, so that it gets the desired hardness. In this case, energy of more than 5000 joules per mm3 and preferably more than 6000 joules per mm3 is introduced by means of at least one strike, which causes the particles 21 to fuse with one another. The impact is carried out, for example, by means of high-speed presses, as described, for example, in WO 2016/135187 A1, according to which a ram which is moved, for example, at more than 5 m/s acts on the blank. However, in this known method densification is followed by a sintering by heating in a furnace. Such a subsequent sintering is not provided here for fusing the powder grains.
The inventor has found that adiabatic pressing may cause the particles 21 to fuse together insufficiently and/or create unwanted air inclusions if there is too much void space between the material to be densified beforehand. A method step before adiabatic pressing is therefore preferably provided, in which the void space is reduced. The void space reduction is carried out without heat input and is achieved, for example, by the action of a punch, vibration, air extraction, application of a vacuum and/or other suitable measures.
Preferably, the void reduction step and the adiabatic pressing step are performed on the same machine. In one embodiment, the machine has a negative form, which defines the form of the formed part and is open at the top. The negative form is filled with the magnetically conductive particles and, if appropriate, also with the additive if the additive is present, for example, in solid or liquid form. The void space between the particles is reduced as mentioned above. In one embodiment, the punch is used for this purpose, which is later used as a ram for the adiabatic pressing, wherein it is moved much more slowly and with a smaller downstroke. This is followed by adiabatic pressing.
Depending on the form of the formed part to be produced, it is also conceivable to design the punch for the adiabatic pressing in several parts. This allows the parts of the punch to be moved with a different downstroke and thus to compensate for density differences in the formed part.
The production by means of adiabatic pressing makes it possible to produce formed parts with the desired geometrical dimensions. This means that post-processing is not necessary. Typically, the following geometrical accuracies can be achieved by means of adiabatic pressing, wherein the specifications specify the maximum deviation from the target value:
The advantage of adiabatic pressing as a production method as opposed to a production using an additive method is that a formed part can be produced in a shorter time and is therefore particularly suitable for economical production in large quantities.
The production method described here can be used to manufacture soft magnetic formed parts that typically have the following properties:
The production methods described here have the advantage, in particular towards the known methods by sintering in the furnace, that formed parts with complex geometries can also be produced. For example, stator parts can be manufactured that are designed for a magnetic flux that should not only occur in one plane during operation, but in all three directions.
The form of the teeth on the stator part can also be selected as desired.
Stator parts can also be manufactured, which are provided with an inner cavity and/or integrally manufactured additional members. An example of such a stator part is shown in
Formed parts can also be manufactured, which have a targeted distribution of insulating locations. This allows the magnetic flux to be guided in such a way that it is not only in one direction, as is the case with the known lamination packages, but in several directions.
Further advantages of the production methods described here are as follows:
From the preceding description, numerous modifications are accessible to the person skilled in the art without leaving the scope of protection of the invention, defined by the claims.
Number | Date | Country | Kind |
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17209979.8 | Dec 2017 | EP | regional |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2018/086520 | 12/21/2018 | WO | 00 |