WO2014125104A2

WO2014125104A2 - Method for the locally targeted influencing of the magnetic flux in components made of soft magnetic material and a component produced by means of the method

Info

Publication number: WO2014125104A2
Application number: PCT/EP2014/053008
Authority: WO
Inventors: René SIEBERT
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2013-02-18
Filing date: 2014-02-17
Publication date: 2014-08-21
Also published as: DE102013002976A1; DE102013002976B4; WO2014125104A3

Abstract

The invention relates to a method for the locally targeted influencing of the magnetic flux in components made of a soft magnetic material and a component produced by means of the method. In the method according to the invention, the focal spot of a laser beam is moved, at least along one axis over the surface of a component. A volume expansion, with elastic or plastic deformation of the grains of the material initiated thereby, and/or thermally induced internal stresses at grain boundaries and in grains of the material microstructure is achieved in the irradiated region and thereby a reduction in the relative magnetic permeability μ_r and magnetic flux density B is achieved by means of a defined power density in the focal spot of the laser beam.

Description

Method for locally controlled influence of the magnetic flux on components made of soft magnetic material and a component produced by the method

The invention relates to a method for locally targeted influencing of the magnetic flux on components made of a soft magnetic material and a component produced by the method.

Electric motors or electric generators are used in a variety of industrial applications. Since the operating costs of electric motors exceed their cost of acquisition many times over and generators aim at high efficiency, the demand for efficient operation is given.

Soft magnetic, laminated and hard magnetic materials are used for these applications. The latter are used as permanent magnets. Soft magnetic materials have the property amplify external magnetic fields in their interior. In electrical machines, in particular the rotor or stator is meant, prevail therefore magnetic fluxes, which are essential for the conversion of electrical to kinetic energy and vice versa. In the magnetic flux-carrying areas, which directly determine the torque of the respective machine, dynamic losses occur. In general, it is known that the lower the magnetic flux, the lower these described losses.

To reduce the dynamic (eddy current) losses, thin individual plates of a soft magnetic material are used. During the production of these rotor and stator individual sheets, which are subsequently joined into a composite, damage occurs in the edge region along the entire contour, which can extend far into the component and lead to an increase in losses. It is important to reduce these losses. This can be achieved for example via a coordinated manufacturing technology or with an additional long-term heat treatment, which leads to an increased production cost. Usually, individual sheets are provided with at least one insulation protective layer on the top or bottom or optionally also on both sides, in order to avoid electrical contacting of two individual sheets in the composite. The function of an insulation protective layer should be maintained during processing.

The requirements of the later application, ie the design of the electrical machine, are usually realized via the design and the soft magnetic material used. The contour of the stator and the

Therefore, rotors influence the main magnetic flux directions and regions of both components that are in magnetic interaction with each other. That In areas of such a component in which the soft magnetic material has been removed during the contouring process, no magnetic flux enhancement of the external magnetic field occurs. Thus, the magnetic flux can be influenced via the contour, with material recesses being able to direct it in a certain way. As a result, however, the mechanical stability of the respective component is reduced to the same extent. In rotary operation, therefore, centrifugal forces can lead to damage to the component and to the entire electrical machine.

This can be a limitation of the maximum mechanical strength of the respective component required.

Furthermore, various process steps and component handling operations during manufacturing make certain demands on the mechanical stability of the individual sheets. To grant this, can be extra thin

Webs are provided in the single sheet contour. However, these inadvertently direct the magnetic flux into unwanted areas, where losses again occur. The main problem, however, is that this process undesirably reduces the magnetic flux elsewhere and may result in a reduction in the achievable or allowable torque. So far, a targeted local control of the magnetic flux is not possible. However, so-called river barriers have been realized. These usually consist of one or more successive air gaps (US Pat. No. 7,432,624 B2). Air has no reinforcing effect for external magnetic fields inside. Therefore, the resulting magnetic resistance increases across these air gaps. The disadvantage is the introduction of an additional contour in the form of a gap or cut, which requires a minimum geometry due to production and requires an additional process step in the production. Especially in areas such as webs, where only a small amount of soft magnetic material is left, the additional release of soft magnetic material leads to contour damage and magnetic component failure. Respectively, minimum distances to the component edge must be adhered to. The remaining material in the range of this distance is in turn leading magnetic flux. Another proposed solution was presented by means of mechanical damage to the unwanted flux-conducting regions (EP 2 169 805 A1). Localized stresses in the material degrade the magnetic properties in this area and serve as barriers to magnetic flux. In the production of these damages arise depressions on the upper side of the sheet (due to the punching tool) and a bulge on the underside. If now a single sheet with the vertical Fung on the top joined with another single sheet with a complementary corresponding bulge on the underside, it comes to damage the insulation protective layer due to the mechanical shaping process and an electrical contact between both sheets. The result is an increase in dynamic eddy current losses. Furthermore, this mechanical damage method is not controllable to the extent of its damage, locally limited and not fully applicable to the individual sheet metal contour to be produced. It is therefore an object of the invention to achieve a locally targeted influencing of the magnetic flux in a component of a soft magnetic material, without any material removal takes place or a change in shape of the component is made. According to the invention, this object is achieved by a method having the features of claim 1. The claim 15 relates to a machined with the method component. Advantageous embodiments and further developments of the invention can be achieved with features described in the subordinate claims.

The described unwanted magnetic flux-carrying regions in the rotor-which would also be possible for applications in the stator-are irradiated by means of a laser with the selection of a suitable processing strategy and adequate process parameters. These are based on the material to be machined and the lateral extent of the beam to be irradiated

Area.

The process principle is based on the laser beam-induced volume expansion and thus elastic or plastic deformation of the grains according to their crystallographic orientation in the irradiated area. Near the surface of the soft magnetic material acted upon by a laser beam, large portions of the laser radiation are absorbed. The overlying insulation layer should mainly transmit the laser radiation. The energy input, which determines the extent of damage via the thermal volume expansion, should have a sufficient temporal gradient in order to avoid unnecessary heat conduction in the material avoid. The processing time of individual areas should be designed so that thermal relaxation processes of the grains are avoided. For thermally induced residual stresses at the grain boundaries and in the grains themselves reduce the magnetic activity of the material, that is, the conductivity of the magnetic flux. Thermally induced damage to the crystal lattice consequently reduces the relative permeability of the soft magnetic material and leads to a reduction in the amplification of external magnetic fields. Thus, the magnetic flux density in the irradiated and changed material area also decreases compared to the untreated material when exposed to external magnetic fields of the same frequency and amplitude.

In the method according to the invention, therefore, the procedure is such that in the case of a component made of a soft magnetic material, for example an electrical sheet, the focal spot of a laser beam is moved over at least one axis over the surface of a component. In this case, in the irradiated area, a volume expansion is achieved with thereby initiated elastic-plastic deformation of several grains of the material and / or thermally induced residual stress at grain boundaries and in grains of the material structure and thereby occurs in this area a reduction of the relative magnetic permeability μ _Γ and the magnetic flux density B by a defined power density P _d in the focal spot of the laser beam.

The residual stresses can be tensile or compressive stresses, depending on the type and direction of the irradiation on the component.

The power density in the focal spot by means of the laser power can be influenced by adjusting the size of the focal spot area, selecting a wavelength of the laser beam used, which is suitably absorbed by the material of the component, and / or the feed rate at which the Focal spot is moved along the surface is adjusted. Of course, the absorption capacity of the material of the component and its structure or its crystal lattice structure plays a role, which can be considered correspondingly when carrying out the method according to the invention. A laser beam should be aimed directly at a thin sheet metal, as a component. A thin sheet is to be understood as meaning those having a thickness in the range of 0.1 mm to 3 mm, preferably in the range of 0.2 mm to 1 mm. A sheet should be made of a steel with non-oriented

Microstructure be formed. For example, a rotor or stator may be made from a plurality of stacked sheets stacked one above the other.

In the invention, components made of a steel alloy in which silicon, cobalt, nickel and / or gadolinium is contained as an alloying element (s) can be used. Particularly preferred are cobalt alloys.

The influence of irradiation should be limited to the effects described above. In particular, as a result of the irradiation, no conversion of cubic body-centered ferrite and / or carbide formation or modification of carbide crystals in the component material should be achieved, since these lead to embrittlement of the material and thus reduce the favorable mechanical properties.

Frequently, component surfaces are provided with an insulation protective layer, which should be dielectric. In these cases, a laser beam with a wavelength can be used, which is absorbed only insignificantly by the insulation protective layer, so that if at all only a slight damage to the insulation protective layer can occur. Under insignificant can be understood a maximum of 10%, preferably a maximum of 5% absorption. Most of the laser radiation should be absorbed by the component material. In this case, for the most part more than 50%, preferably more than 75%, of the radiation energy is to be understood. The material of the insulation protective layer should be predominantly transparent to the wavelength of the laser beam, so that the aforementioned minimum proportions of the radiation can be absorbed by the actual component material.

The focal spot of the laser beam should be moved and operated along the surface of the device so as to avoid a reduction in relative magnetic permeability μ _Γ and magnetic flux density B due to thermal conduction in unirradiated areas that only there a targeted change is achieved and unirradiated areas retain their original magnetic properties. The range changed in its crystallographic properties should accordingly have a width with respect to the advancing movement axis direction that is slightly wider, at most 300%, preferably at most 100%, than the maximum lateral extent of the focal spot perpendicular to this axial direction. It can also be a deviating from a circular focal spot, can be used with rectangular or elliptical shape. The alignment should be selected so that the largest lateral extent of the focal spot is aligned in the feed axis direction of the focal spot movement. As a result, the width can be reduced and the radiant energy can be used more effectively.

The power density can be achieved very easily by a selected adjusted feed rate at which the focal spot is moved along the surface. A suitable speed range is 1 m / min to 200 m / min, preferably 5 m / min to 50 m / min.

The feed can be achieved by a corresponding movement of the laser beam, a deflection of the laser beam with one or more pivotable reflective element (s) and / or movement of the component.

In addition to the cw operation of the laser beam and a pulsed laser beam can be used. In addition, an influencing of the magnetic properties can also be achieved by the pulse frequency and the pulse length.

It may also be beneficial to repeatedly irradiate a region to be processed, in which the magnetic properties are repeatedly irradiated, and thereby to move the focal spot of the laser beam several times along this region. As a result, a sufficient change of the magnetic properties can be achieved in this area thus irradiated and other areas as well as the insulation protective layer are not or at least not so far changed in their properties due to heat conduction that they lose their original function. In the invention, it is also possible to irradiate juxtaposed areas with a laser beam and to change these areas in the sense of the invention. In this case, two or more than two tracks which are at least partially parallel and / or at the same distance from each other can be formed in order to improve the effect of influencing a magnetic or electromagnetic field acting in this area. A reduction of the magnetic relative permeability μ _Γ and magnetic flux density B in one area should advantageously be achieved by repeatedly irradiating the surface of a component with tracks. The individual tracks can each have a distance in the range 0.5 mm to 20 mm from each other.

In the irradiated area of the focal spot and an additional gas can be supplied, which should essentially fulfill a protective function for optical elements from contamination, damage or destruction. It can be used with low pressure and flow.

In laboratory experiments, a local degeneration of the relative permeability of up to 75% could be achieved. The irradiated areas have a higher magnetic resistance. Irradiated and untreated areas exist side by side, the magnetic flux deviates to the area with lower magnetic resistance. Due to the local applicability and the various possibilities for temporal and lateral design of the intensity of the laser irradiation, a versatile control of the magnetic flux is possible.

Depending on the application, the effect of the intended technology is to increase the maximum speed of the rotor due to improved mechanical stability with otherwise the same magnetic behavior. With an unchanged torque behavior, this leads to an improved power output of the machine. On the other hand, if the focus is not on improving the mechanical stability, higher power densities and consequently higher efficiencies can be achieved since better utilization of the magnetizable material is possible. In another application, an increase in efficiency of the machine due to an adapted magnetic Flow behavior in the rotor or stator and consequently reduced losses possible with the same mechanical stability.

Advantageously, a locally targeted influencing the magnetic flux can be achieved without cuts and recesses or deformations must be formed. These can lead to damage to other single sheets during joining to the composite or pose weaknesses for the dynamic load. On the component rotor of an electric machine, after the processing according to the invention, at significant positions, e.g. of each individual sheet (or at least a larger number) to recognize certain processing patterns. The laser irradiation of these significant areas has at least a discoloration of the insulation protective layer with subtle processing. Significant positions are close to permanent magnets, thin ones

Webs and along recessed pockets, which especially at

Synchronreluktanzmaschinen happen to find. Becomes a

Metallographic cross-section made in the area of laser irradiation, a certain area is identified by the base material is melted and solidified again, but without a significant change in the

Microstructure or to cause grain refining.

Soft magnetic component materials may be processed which are used as iron alloys with e.g. are alloyed with cobalt, copper, silicon or nickel. A particular example is an iron-silicon alloy designated as DIN 80404-1 and the following as declared grade M330-35A electrical steel.

Machining can also be carried out around a permanent magnet integrated into the component or arranged thereat. The processing does not have to be done around the entire circumference. It may suffice to change only certain directions magnetically by a machining according to the invention.

Following processing to reduce magnetic permeability and magnetic flux, annealing may be performed in conventional be performed wisely.

Particularly advantageously, the same laser can also be used for cutting at least one contour on the component. As a result, for example, a formation of openings in the component can be achieved.

The following table shows materials and suitable parameters for machining.

The invention will be explained in more detail by way of example in the following. Figure 4 is a graph of the relative change in magnetic relative permeability, μ _Γ , obtained by locally targeting an M330-35A iron-silicon alloy component at various laser powers and moving focal-speed feed rates; a part of a single plate for a synchronous reluctance rotor; a portion of a single sheet for a rotor of a permanent magnet synchronous motor; a diagram of the distribution of the magnetic flux density B in a 5 mm wide and 0.35 mm thick component, which was exposed to laser radiation at a feed rate of 50 m / min; a diagram of the distribution of the magnetic flux density B in a 5 mm wide and 0.35 mm thick component, which was exposed to laser radiation at a feed rate of 80 m / min; a diagram of the deflection of an irradiated component with a width of 5 mm, a length of 250 mm and a thickness of 0.35 mm depending on the changed state of inherent stress at a modified track pitch T with multiple over-travel of the laser beam over the component surface at a maintained feed rate of 100 m / min, a laser power of 400 W and

Figure 7 is a graph of the change in the relative magnetic permeability μ _{Γ of} an irradiated component having a width of 5 mm, a length of 250 mm and a thickness of 0.35 mm in Dependence of the altered residual stress state with a modified track pitch T with multiple over-travel of the laser beam over the component surface at a feed rate of 100 m / min, a laser power of 400 W, determined at a magnetic field frequency of 50 Hz.

For the evaluation, a standardized (inductive) measuring device was used to determine the B-H characteristics (flux density-magnetic field characteristic), the relative permeability and the re-magnetization losses of soft magnetic materials. Thus, the performance of the laser processing could be evaluated with respect to the said magnetic parameters.

Due to the meter requirement, single strip samples with a length of 250 mm had to be manufactured. The width was chosen to be 5 mm. These samples were magnetically measured, laser irradiated and re-measured. As a contour, a line of length 100 mm was chosen in the first step. Other processing strategies are also possible.

Two laser beam sources with different wavelengths were used. These were a C0 ₂ laser with a maximum power of 300 W and a solid-state laser with a maximum power of 500 W. It was worked with a round focal spot.

When using the C0 ₂ laser, the following parameters were selected:

Wavelength 10.6 μητι. It worked without additional gas and with varying feed rates between 5 m / min and 40 m / min. It turned out that the higher the feed rate, the greater the magnetic damage. Thus, depending on the application by a suitable feed rate, without changing the other parameters, a desired relative permeability μ _Γ can be set.

It turned out that a defocusing of the focal spot diameter of 0.62 mm to about 0.9 mm proved to be advantageous. When using the solid-state laser, the following parameters were taken into account. Wavelength 1.03 μηι.

It was worked with additional gas at a very low pressure of 1 bar (to avoid spattering or damage to optical components). The

Feed rate was again varied between 5 m / min and 40 m / min. About the feed rate, the magnetic properties could be influenced by changing the residual stress state targeted.

This situation is illustrated by the diagram shown in FIG.

FIG. 2 shows a part of a single sheet 1 as a component which can be used in a synchronous reluctance rotor. Here are marked with 2 areas of magnetic flux. In the single sheet 1 are breakthroughs 3, which are free of soft magnetic material is formed. With 4 are areas in which a magnetic flux is undesirable, characterized. In addition, curves 5 magnetic field lines are shown schematically. Reflows 6 magnetic field lines are in areas around openings

3 indicated. These unwanted returns 6 can be avoided with the invention by there is a locally targeted influence with a laser beam. The regions which are correspondingly influenced in their magnetic properties may there be formed linearly as one or more tracks arranged next to one another.

The example shown in FIG. 3 of a single plate 7 for a rotor of a permanently excited synchronous motor differs from the example according to FIG. 2 in that buried or positively secured permanent magnets 8 are present. Again, in areas where one should

Reflux of magnetic field lines 6 would occur without additional processing a locally targeted processing according to the invention would be carried out in order to avoid this reflux 6, at least significantly reduce.

Otherwise, the same elements in FIG. 3 are given the same reference numerals. Chen, as indicated in Figure 2. In both Figures 2 and 3, a quarter of a single sheet 1 or 7 is shown in each case.

Claims

Patent claims

Method for locally targeted influencing of the magnetic flux on components made of a soft magnetic material, in which the focal spot of a laser beam moves at least along one axis over the surface of a component and thereby causes a volume expansion in the irradiated area with thereby initiated elastic or plastic deformation of the grains of the material and / or thermally induced residual stresses at grain boundaries and in grains of the material structure and thereby a reduction in the magnetic relative permeability μ _Γ and magnetic flux density B in this area is achieved by a defined power density in the focal spot of the laser beam.

Method according to claim 1, characterized in that the power density in the focal spot is influenced by means of the laser power, the size of the area of the focal spot, the wavelength of the laser beam used and / or the feed speed at which the focal spot is moved along the surface.

Method according to claim 1 or 2, characterized in that a laser beam is directed directly onto a thin sheet as a component, the sheet being made of a steel with a non-oriented

Microstructure is formed.

Method according to one of the preceding claims, characterized in that the component made of a steel alloy in which silicon cobalt, nickel and / or gadolinium is/are contained as alloying element(s) is used. Method according to one of the preceding claims, characterized in that, as a result of the irradiation, no conversion of body-centered cubic ferrite and/or no carbide formation or no change in carbide crystals in the component material is achieved.

Method according to one of the preceding claims, characterized in that a laser beam is used with a wavelength which is only insignificantly absorbed by an insulation layer formed on a component and predominantly absorbed by the material of the component.

Method according to one of the preceding claims, characterized in that the focal spot of the laser beam is moved and operated along the surface of the component in such a way that a reduction in the magnetic permeability μ in non-irradiated areas that occurs as a result of thermal conduction is avoided.

Method according to one of the preceding claims, characterized in that the focal spot is moved at a feed speed in the range of 1 m/min to 200 m/min, preferably in the range of 5 m/min to 40 m/min.

Method according to one of the preceding claims, characterized in that an additional gas is supplied to the irradiated area.

Method according to one of the preceding claims, characterized in that a laser beam with a rectangular or elliptical focal spot is used.

Method according to one of the preceding claims, characterized in that processing is carried out around a permanent magnet integrated into the component or arranged thereon.

12. The method according to any one of the preceding claims, characterized in that the laser beam is operated in a pulsed manner and/or is guided several times along an area whose magnetic properties are to be changed and/or several tracks are formed next to one another with changed magnetic properties next to one another.

13. The method according to any one of the preceding claims, characterized in that a reduction of the magnetic relative permeability μ _Γ and magnetic flux density B in an area by multiple irradiation of the surface of a component with tracks, the individual tracks each having a distance in the range 0.5 mm to 20 mm from each other is achieved.

14. Method according to one of the preceding claims, characterized in that the same laser beam is also used to cut at least one contour on the component.

15. Component processed using a method according to one of the preceding claims, in which a reduced magnetic relative permeability μ _Γ and a reduced magnetic flux density B are present in at least one area in order to specifically influence a magnetic field in its formation and effect.