Electric motor and method for producing a squirrel-cage rotor for an electric motor

Abstract

Electric motor comprising a squirrel-cage rotor in the form of a cage, which electrically conductively carries a plurality of rotor end rings formed as cast parts made of a casting material, wherein at least one reinforcing element made of a different material is cast into each of the cast parts, and wherein the casting material substantially forms the outermost free surface of the rotor end ring.

Description

[0001] Page 1 of 29

[0002] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland

[0003] ELECTRIC MOTOR AND METHOD FOR MANUFACTURING A SHORT-CIRCUIT TURN ...

[0004] FOR AN ELECTRIC MOTOR

[0005] The invention relates to an electric motor according to the preamble of claim 1 and to a method for manufacturing a

[0006] Squirrel-cage rotor for an electric motor according to the preamble of claim 15.

[0007] TECHNICAL BACKGROUND

[0008] The rotational speed of electric machines significantly influences their power density. This is particularly advantageous in applications with limited installation space, as increasing the rotational speed reduces the space required for the electric machine while maintaining the same power output.

[0009] Asynchronous machines are frequently used, particularly in the field of high-speed electrical machinery. Their simple design, robustness, and ability to operate efficiently in the field weakening regime make them attractive for numerous applications. Due to their longer service life, squirrel-cage rotors are typically used in high-speed asynchronous machines. In these rotors, the cage bars are electrically connected by a short-circuiting end ring at each end of the cage. The cage of a squirrel-cage rotor is typically manufactured from pure aluminum or pure copper using a die-casting process. The use of pure copper, in particular, reduces rotor losses and further increases the machine's energy efficiency due to its excellent electrical conductivity.

[0010] At high speeds, however, considerable centrifugal forces act on the cage and especially on the short-circuit end rings, which in turn leads to high mechanical stresses. Due to the relatively low yield strength of aluminum and especially copper, see page 2 of 29

[0011] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland maximum speed thus a mechanical limit is set.

[0012] STATE OF THE ART

[0013] To enable the use of copper or aluminum cages for squirrel-cage rotors even at very high speeds, there are various approaches known from the prior art.

[0014] One option is to use alloys of copper or aluminum instead of pure copper or aluminum. Copper or aluminum alloys are characterized by higher strength. However, this increase in strength comes at the cost of lower electrical conductivity, which in turn leads to a reduction in the efficiency of the electric machine.

[0015] Another method for increasing the strength of short-circuit end rings is the use of reinforcing sleeves. These cap-shaped components are arranged around the short-circuit end rings to support them. They consist of non-ferromagnetic metallic materials such as nickel-based alloys, high-strength aluminum alloys, titanium, or stainless steel with high nickel and chromium content, and are characterized by low permeability, high yield strength, and corrosion and temperature resistance. However, equipping the short-circuit end rings with such sleeves increases their weight and, due to the additional assembly step, also increases manufacturing effort.

[0016] Alternatively, so-called bandages made of fiber-reinforced plastic, in particular glass fiber reinforced plastic (GFRP) or carbon fiber reinforced plastic (CFRP), with epoxy resin as the matrix, are wrapped circumferentially around the short-circuit end rings. This method also leads to increased strength of the short-circuit end rings, but is time-consuming and expensive due to the layer-by-layer application process.

[0017] A general problem with almost all externally mounted support elements, such as sleeves or bandages, is that an additional element is required between the stator and the outer circumference of the well (page 3 of 29).

[0018] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland causes an increase in the electrically effective air gap in the conductive copper or aluminum area of ​​the short-circuiting end ring. This increases the magnetic resistance and impairs the efficiency of the electric machine.

[0019] Another possibility, already investigated internally, involves casting the copper or aluminum of the short-circuit end rings directly into a sleeve using a die-casting process. This sleeve then serves as a supporting element. An additional support element can also be inserted inside the mold to further increase strength.

[0020] However, several disadvantages have emerged with this design and process. The sleeve, which serves as the mold, complicates the installation of the feed and vent channels required for the casting process. This is particularly problematic if an additional support element is present inside, as this makes the material flow more complex. Furthermore, the sleeve makes subsequent machining of the short-circuit end rings, such as the drilling of balancing holes, more difficult. Depending on the sleeve material, it may also be necessary to increase the electrically effective air gap, which can impair the efficiency of the electric machine.

[0021] THE PROBLEM UNDERLYING THE INVENTION

[0022] In view of this, the object of the invention is to provide an electric motor whose squirrel-cage rotor has good electrical conductivity, is suitable for high speeds and can be manufactured efficiently.

[0023] THE INVENTIONAL SOLUTION

[0024] According to the invention, this problem is solved by the features of the main claim directed to the electric motor.

[0025] Accordingly, an electric motor with a novel squirrel-cage rotor is proposed, page 4 of 29

[0026] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland, electrically conductive, carries several short-circuit end rings. The short-circuit end rings are formed as castings made of a casting material. At least one, and preferably only one, reinforcing element made of a different material is cast into each of the castings. The electric motor is characterized by the fact that the casting material essentially forms the outermost free surface of the short-circuit end ring. In other words, a short-circuit rotor is proposed that is reinforced exclusively within its short-circuit end rings and does not require an external sleeve or bandage around its short-circuit end rings for reinforcement purposes.

[0027] The casting material is a material with high electrical conductivity, such as pure copper or pure aluminum. This facilitates the current flow in the cage of the squirrel-cage rotor and increases the efficiency of the electric machine.

[0028] The reinforcing element, however, consists of a different material with a significantly higher strength than the casting material.

[0029] The reinforcement element serves to strengthen the low-strength conductive material in the operation of the squirrel-cage rotor. For this purpose, the conductive material of the squirrel-cage end ring encases the reinforcement element in such a way that it provides internal support for the conductive material in its solidified state. The centrifugal forces occurring during operation are then absorbed by the reinforcement element, essentially following the principle of a steel belt tire. This reduces the mechanical stresses occurring in the conductive material and its tendency to expand under centrifugal force, which must be considered when designing the air gap.

[0030] This means that a highly conductive material, such as pure copper, can be used for the short-circuit end ring, and the squirrel-cage rotor can still be used at very high speeds. Instead of a bandage or sleeve made of non-conductive or less conductive material, the highly conductive material of the short-circuit end ring can extend right up to the inner edge. (Page 5 of 29)

[0031] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland of the air gap, then represents the inner boundary surface of the air gap.

[0032] The reinforcing element is typically a non-fibrous reinforcement structure measuring at least several centimeters in size (macroscopically speaking). Ideally, the reinforcing element is a single rotationally symmetrical part. This counteracts the risk of imbalance in the short-circuit end ring.

[0033] In its solidified state, the casting material essentially forms the outermost free surface – at least in the radial direction of the short-circuiting ring – but advantageously also in the axial direction. This allows for optimal placement of venting and supply channels during the casting process. Furthermore, subsequent machining of the hardened casting, such as turning or drilling, can be easily performed directly on the electrically conductive material. The latter may be necessary, for example, for balancing the short-circuiting ring.

[0034] The casting material essentially forms the outermost free surface if the short-circuit end ring is not wholly or partially enclosed by another supporting element in its operational state. However, this does not preclude individual sections of the reinforcing element from projecting from the inside into the outermost free surface of the short-circuit end ring.

[0035] ANOTHER PROBLEM UNDERLYING THE INVENTION

[0036] Furthermore, the object of the invention is to provide a method by which an electric motor according to the invention can be manufactured efficiently.

[0037] THE FURTHER INVENTIONAL SOLUTION

[0038] The solution to the aforementioned problem is achieved using a method for manufacturing a squirrel-cage rotor for an electric motor, as shown on page 6 of 29.

[0039] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland is claimed here. The process is characterized by the fact that a reinforcing element is produced by an additive primary forming process and then placed in a casting cavity to form a short-circuit end ring. Subsequently, the reinforcing element is cast into the short-circuit rotor and then the mold is removed.

[0040] The cage of the squirrel-cage rotor is manufactured using a casting process. Before the conductive material of the cage is poured in, a reinforcing element is inserted into each area of ​​the cage mold where a short-circuit end ring is formed. The subsequent pouring of the conductive material into the lamination stack produces a squirrel-cage rotor cage with high strength and good electrical conductivity. The slots, i.e., the openings in the lamination stack, are filled with the casting material. The teeth and the back of the cast material define the boundaries of the slots.

[0041] Manufacturing the reinforcement element using an additive manufacturing process allows for a high degree of flexibility in the design of the support structure that forms the reinforcement element. This enables precise adaptation of the reinforcement element, minimizing material flow during casting while simultaneously ensuring maximum support function in the solidified state. Furthermore, additively manufactured components exhibit a rough surface – typically on a scale that can even be felt with a fingernail. This is advantageous because it increases the adhesion of the solidified casting material to the reinforcement element.

[0042] Another advantage of this method is that the mold is removed after the casting process and is therefore not part of the supporting elements for the short-circuit end ring. This makes the hardened casting material fully accessible and allows for easy subsequent machining. Furthermore, this offers advantages for the casting process, as venting and feed channels can be positioned more flexibly, improving the efficiency of the casting process. Page 7 of 29

[0043] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland

[0044] PREFERRED DESIGN OPTIONS

[0045] There are a number of possibilities to design the invention in such a way as to further improve its effectiveness or usability.

[0046] It is therefore particularly preferred that the reinforcing element is essentially completely embedded in the material of the casting.

[0047] The essentially complete embedding of the reinforcement element in the casting is advantageous both with regard to the electromagnetic properties of the short-circuit end ring and with regard to the strength of the short-circuit end ring.

[0048] An “essentially complete” embedding of the reinforcement element in the material of the casting is given if the reinforcement element is completely encased by the casting.

[0049] In another preferred embodiment, there are several places where the reinforcing element projects into the outer surface of the casting.

[0050] The protruding sections on the outer surface can be used as centering lugs, allowing the reinforcement element to be supported against the inside of the mold. This enables the reinforcement element to be positioned in a defined location within the casting and securely held there during the casting process. For this purpose, the protruding sections are preferably designed so that they can be pressed against the draft angles of the mold and thus held in the defined position.

[0051] The areas projecting into the outer surface of the casting are spatially separated from one another and typically represent less than 3% and preferably less than 0.5% of the circumferential surface of the short-circuit end ring.

[0052] Preferably, the areas project into the circumferential surface area of ​​the outer surface of the casting. Page 8 of 29

[0053] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland

[0054] This makes centering the reinforcement particularly easy.

[0055] The "circumferential surface" of the short-circuit end ring is understood to be the surface of the short-circuit end ring facing away from the axis of rotation.

[0056] In another preferred embodiment, the reinforcing element consists of a material whose properties are not, or not substantially, deteriorated by coming into contact with the casting material or by exposure to a temperature that is essentially the same as the casting temperature.

[0057] The reason for this is that many metallic materials acquire their properties, especially increased tensile strength, through thermal, mechanical, or thermo-mechanical treatments (introduction of stresses and / or precipitation hardening). However, these positive property changes can be reversed by heat treatments in the range of the material's own solution annealing temperature.

[0058] This ensures that the reinforcing element does not deform or lose its mechanical properties during the casting process. Furthermore, it prevents undesirable material reactions between the reinforcing element and the casting material.

[0059] Ideally, the casting material is copper or a copper alloy; otherwise, aluminum or aluminum alloys are also conceivable.

[0060] Copper has very high electrical conductivity and is characterized by good castability. The insufficient strength of a short-circuiting ring made of pure copper for high-speed electrical machines is compensated for by the reinforcing element. This allows for the manufacture of an efficient electrical machine.

[0061] Preferably, the reinforcing element consists of a material that is not or only minimally magnetizable and preferably has a tensile strength that is more than negligibly higher than that of the casting material. Ideally, the tensile strength of the [page 9 of 29]

[0062] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland

[0063] The strength of the reinforcing material must be at least twice that of the casting material. For some particularly advantageous applications, it is required that this difference be greater than 300 MPa.

[0064] The lack of magnetizability of the reinforcement element ensures that the reinforcement element does not influence the magnetic field generated by the current-carrying squirrel-cage rotor or the magnetic field generated by the stator.

[0065] In another preferred embodiment, the reinforcing element consists entirely or at least substantially of a nickel-based alloy, temperature-resistant steel, titanium, a titanium alloy or a high-entropy alloy.

[0066] These materials are characterized by their lack of magnetism and high strength. Furthermore, the use of these materials ensures that the reinforcing element does not exceed its solution annealing temperature during the casting process. In addition, due to their density, these materials are advantageous for reducing the weight of the short-circuit end ring, particularly when copper is used as the casting material.

[0067] A preferred option is to manufacture the reinforcing element as a component made of sintered metal. In other, also optional, cases, the reinforcing element has a surface roughness of Ra > 15 pm (µm).

[0068] This ensures a secure bond between the hardened casting material and the surface of the reinforcement element. The transfer of centrifugal forces occurring during operation into the reinforcement element is thus improved.

[0069] Preferably, the reinforcing element is at least one circumferentially closed, mostly rotationally symmetrical ring. Preferably, the reinforcing element consists of several (see page 10 of 29).

[0070] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland

[0071] Circumferential direction in closed rings, which are ideally connected to each other via connecting bridges.

[0072] This ensures a uniform force distribution into the reinforcement element during operation of the squirrel-cage rotor. Furthermore, the ring shape of the reinforcement element maximizes the cross-sectional area of ​​the cast material acting as a conductor within the overall cross-section of the squirrel-cage end ring. This increases the electrical conductivity of the squirrel-cage end ring. A ring-shaped reinforcement element thus provides good ring strength combined with high electrical conductivity.

[0073] In another preferred embodiment, the reinforcement element consists of several rings that are at least essentially parallel to the axis of rotation of the squirrel-cage rotor and are usually firmly connected to one another.

[0074] This design ensures the strength of the short-circuit end ring just as it would with the help of a reinforcement element consisting of a single, thicker ring.

[0075] At the same time, however, the material flow of the casting material during the filling of the mold is less affected. Furthermore, this design reduces the thermal stresses that arise due to the different coefficients of thermal expansion of the casting and reinforcing materials.

[0076] Ideally, the reinforcing element consists of at least one inner ring with a smaller ring diameter and at least one outer ring with a larger ring diameter. Preferably, the ring cross-sectional diameter of the at least one outer ring is smaller than the ring cross-sectional diameter of the at least one inner ring.

[0077] This ensures that the centrifugal forces and stresses occurring at the short-circuiting end ring during operation are optimally transferred into the reinforcement element. Consequently, the short-circuiting end ring can also be used preferably at particularly high circumferential speeds of >150 m / s. Page 11 of 29

[0078] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland

[0079] In many cases, the reinforcing element is dimensioned and cast in such a way that it occupies a greater radial distance to the inner circumferential surface of the short-circuit end ring than to its outer circumferential surface. In this way, the directly reinforced outer surface of the short-circuit end ring acts almost like a bandage for the unreinforced inner surface.

[0080] Preferably, the reinforcement element has several retaining ribs or fixing elements by means of which the reinforcement element is held in position in the cavity of the mold for casting the short-circuit end ring. The fixing elements can also be in the form of an electrical steel sheet, and / or the reinforcement element can be fixed to the end face of the electrical steel stack.

[0081] The webs are preferably designed to protrude radially from the reinforcing element. Since the retaining webs do not contribute to increasing strength during operation, they can be easily partially or completely removed during post-processing of the short-circuit end ring, if necessary.

[0082] The “mold for casting the short-circuit end ring” represents a section of the mold for the entire cage of the short-circuit rotor.

[0083] In another preferred embodiment, all connecting and retaining webs of at least one window are perforated. It is preferable if all connecting and retaining webs of several windows are perforated. Alternatively, if the connecting and retaining webs are directly adjacent, they form a window between them with a clear cross-sectional area of ​​at least 3 mm². 2 and preferably at least 4.5 mm 2 out of .

[0084] The windows ensure that local blockages and thus the formation of voids do not occur during watering.

[0085] Ideally, the volume fraction of the reinforcement element in relation to the entire short-circuit end ring is between 5% and 15%.

[0086] These volume ratios result in a sufficient increase in the strength of the short-circuit end ring, without [page 12 of 29]

[0087] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland to excessively restrict electrical conductivity. Also, the

[0088] The castability of the short-circuit end ring is not significantly impaired.

[0089] Preferably, the actual material of the short-circuit end ring is introduced into the mold cavity forming the short-circuit end ring using a casting process that ensures a porosity of less than 1% of the cast material. This is preferably a laminar squeeze casting process.

[0090] Squeeze casting, also known as compression casting, is a specialized casting process characterized by slow, continuous mold filling and the application of very high metal pressures. The laminar squeeze casting process, in particular, offers significant advantages. In this process, the molten casting material is poured into an open, temperature-controlled mold, with the material flow occurring in a laminar manner. This type of mold filling allows for complete venting of the mold, thereby significantly reducing the formation of porosity in the hardened casting.

[0091] Reducing porosity is crucial for several reasons. Pores in the material negatively impact the physical and electrical properties of the cast conductor cage, as they reduce the effective cross-section of the conductors. This leads to a decrease in the theoretically possible conductivity of copper or aluminum conductors. Conversely, a low porosity allows for higher electrical conductivity and simultaneously improves mechanical stability. This enables the squirrel-cage rotor to achieve a higher rotational speed, which in turn increases the efficiency of the electric machine.

[0092] Furthermore, low porosity also has a positive impact on the mechanical post-processing effort. Pores or cavities in the material can significantly increase the effort required to balance the squirrel-cage rotor or cage, necessitating additional work steps. Therefore, the application of the laminar squeeze casting process not only optimizes the quality of the casting but also makes the entire manufacturing process more efficient. Page 13 of 29

[0093] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland

[0094] In a further preferred embodiment, the reinforcing element is supported against the inner surface of the mold by retaining ribs. The retaining ribs are adapted to the draft angle of the mold cavity and can be pressed against it. Additionally or alternatively, the mold has projections for contact with the reinforcing element, which does not have its own protruding retaining elements.

[0095] This allows the reinforcing element to be centered in the casting mold and accordingly in the conductive material of the short-circuit end ring, and to be held in position during casting.

[0096] Ideally, the reinforcing element is cast so deeply into the actual material of the short-circuit end ring that the short-circuit end ring can be balanced by drilling without also drilling into the reinforcing element.

[0097] This reduces the risk of weakening the reinforcement element during post-processing, which could lead to mechanical failure. Turning operations and the removal of the sprue and venting system are also facilitated by this design.

[0098] Preferably, in particular the retaining webs and the connecting webs of the reinforcement element are designed to be perforated in such a way that the flow of pouring is not significantly impeded.

[0099] The purpose of this opening is to allow the melt to exit and enter the ring area from the groove as freely as possible, so that it can distribute itself well (axially and tangentially) within the short-circuit ring. The gate and vent must also be sufficiently unobstructed and must not be blocked by the insert.

[0100] This reduces the risk of air inclusions and void formation. A more stable bond between the reinforcement element and the casting material is also achieved when it is ensured that the casting material can flow through the mold even in the area of ​​the reinforcement element's webs. Page 14 of 29

[0101] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland

[0102] In another preferred embodiment, the reinforcing element is designed in such a way that it does not interrupt the one-piece nature of the short-circuit end ring.

[0103] The entire part of the cage formed from the cast material is thus conductively connected. Therefore, the current flow through the cage is not interrupted by the reinforcing elements.

[0104] The term "one-piece" refers to the property of a component being manufactured from a single, continuous piece of material or casting without separate connections or assemblies.

[0105] Ideally, the short-circuit end ring is turned down after the reinforcement element has been cast in. Preferably, this is done in such a way that at least part of the retaining webs are also turned down.

[0106] This represents a particularly simple way to eliminate any coarse imbalances, although it does not usually replace the subsequent fine balancing of the squirrel-cage rotor.

[0107] LIST OF FIGURES

[0108] Fig. 1 shows an embodiment of a short-circuit end ring according to the invention, wherein the solid material of the short-circuit end ring is partially cut.

[0109] Fig. 2 shows the reinforcement element of the short-circuit end ring shown in Fig. 1 in an isometric view.

[0110] Fig. 3 shows one half of a cross-section through the short-circuit end ring shown in Fig. 1.

[0111] Fig. 4 schematically shows the material flow during the process according to the invention.

[0112] Fig. 4a shows a single sheet of the sheet metal bundle from Fig. 4 in a top view. Page 15 of 29

[0113] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland

[0114] Fig. 4b shows the sheet metal stack from Fig. 4 in a three-dimensional view.

[0115] Fig. 5 shows several stacked reinforcement elements that have not yet been segmented.

[0116] Fig. 6 schematically shows the cross-sectional area of ​​the short-circuit end ring shown in Fig. 1, which can be used for post-processing.

[0117] Fig. 7 shows a further embodiment of a short-circuit end ring according to the invention, wherein the solid material of the short-circuit end ring is partially cut.

[0118] Fig. 8 shows the reinforcement element of the short-circuit end ring shown in Fig. 7 in an isometric view.

[0119] Fig. 9 shows one half of a cross-section through the short-circuit end ring shown in Fig. 7.

[0120] Fig. 10 shows several reinforcement elements stacked on top of each other on a base plate as well as a single reinforcement element.

[0121] Fig. 11a shows a reinforcement element with retaining webs and a cross-section thereof.

[0122] Fig. 11b shows a reinforcement element on a base plate and a cross-section thereof.

[0123] Fig. 12a shows a cross-section of part of the mold in which a reinforcement element is placed and fastened in the mold using its anchor elements or retaining webs.

[0124] Fig. 12b shows a cross-section of part of the mold in which a reinforcement element is placed and secured in the mold by means of its base plate.

[0125] Fig. 13 shows the placement and fastening of the reinforcement elements together with a sheet metal package in a casting mold in cross-section.

[0126] Fig. 14 shows a cross-section of a cast mold. Page 16 of 29

[0127] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland

[0128] EXAMPLE OF EXECUTION

[0129] The functioning of the invention is explained by way of example with reference to Figures 1-9. The windows 11 and the axial connecting webs 12 are only provided with reference numerals for illustrative purposes.

[0130] Figures 1-3 show a first embodiment of a short-circuit end ring according to the invention. The short-circuit end ring 3 consists of a reinforcing element 6, which is cast into a casting 4. The casting 4 is made of pure copper, so the short-circuit end ring 3 has very good electrical conductivity. The reinforcing element 6, on the other hand, ideally consists of the nickel-based and very heat-resistant alloy Inconel 718.

[0131] The reinforcing element 6 serves, during operation of the squirrel-cage rotor 1, to strengthen the copper section of the short-circuit end ring 3 forming the casting 4 and to absorb, at least predominantly, the mechanical stresses occurring during operation. This allows the short-circuit end ring 3 to be used at rotational speeds at which a short-circuit end ring 3 made of pure copper would reach its yield strength due to the centrifugal forces.

[0132] The reinforcement element 6 comprises two coaxially arranged inner rings.

[0133] 7 of the same diameter and three coaxially arranged outer rings

[0134] 8 with the same diameter. The inner rings 7 each have an oval cross-section and the outer rings 8 each have a round cross-section. The cross-sections of the inner rings 7, however, preferably have an area approximately three times larger than the cross-sections of the outer rings 8.

[0135] The two inner rings 7 are each connected to each other via a plurality of axial connecting webs 12. The three outer rings 8 are also connected to each other via a plurality of axial connecting webs 12. In addition, radially outwardly directed connecting webs 10 are provided at regular intervals on the reinforcement element 6, which connect the inner rings 7 to the outer rings 8. Page 17 of 29

[0136] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland

[0137] The radial connecting webs 10 taper with increasing distance from the outer rings 8, so that when viewed from the side they have the shape of a right-angled triangle. The apex of the triangle of the radial connecting web 10 merges seamlessly into the outer rings 8. The opposite side merges seamlessly into the inner rings 7.

[0138] Both the axial connecting webs 12 and the radial connecting webs 10 are provided with windows 11. The windows 11 preferably form elliptical openings. The windows 11 reduce the weight of the reinforcing element 6. At the same time, the windows 11 ensure that the copper of the short-circuit end ring 3, which forms the casting 4, is not obstructed by the reinforcing element 6 during casting in a manner that would lead to material defects, but can flow through the mold as freely as possible. The windows 11 thus ensure that local blockages and porosity do not occur during the casting process.

[0139] To prevent high mechanical stresses from occurring on the solidified casting 4 due to notch effects, all components of the reinforcement element 6 are rounded. The reinforcement element 6 therefore has no sharp edges.

[0140] To center the reinforcement element 6 in the mold and hold it in place during the pouring of the copper, retaining webs 9 are provided on the outer rings 8. For this purpose, the reinforcement element 6 is positioned in the mold before the molten copper is poured in such a way that it is securely fastened within the mold. Viewed from the side, each retaining web 9 preferably has the shape of an isosceles triangle, with the apex of the triangle pointing radially away from the reinforcement element 6. Each retaining web 9 also has a window 11 in the form of an elliptical opening.

[0141] The process for producing the [product] can be illustrated using Figures 4-6.

[0142] Explain the design of a squirrel-cage rotor 1 and the construction of a squirrel-cage rotor 1 according to the invention. Page 18 of 29

[0143] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland

[0144] A squirrel-cage rotor 1 comprises a cage 2, which consists of the conductor bars (not visible) and the short-circuiting rings 3, which are integrally joined. Furthermore, a laminated core 13 (see Fig. 4b), consisting of a plurality of individual laminations 14 (see Fig. 4a), is provided on the squirrel-cage rotor 1. The laminated core 13 is provided with grooves N through which the conductor bars of the cage 2 protrude. The short-circuiting end rings 3 are positioned at the end faces of the laminated core 13 and electrically connect the individual conductor bars to one another. Each short-circuiting ring 3 contains a reinforcement element 6.

[0145] The squirrel-cage rotor 1 is manufactured by first placing the two reinforcement elements 6 into the mold (not shown in Fig. 4). The mold for the conductor bars is formed externally by the teeth Z and the back R of the lamination stack 13, with grooves N forming the recesses that are filled with the casting material. The mold for the short-circuit end rings 3, however, is completely removed after casting. Subsequently, the mold is filled from below, against gravity, with laminar flowing liquid copper via the sprue 15. The air contained in the mold can escape freely upwards.

[0146] The reinforcement elements 6 are additively manufactured by stacking a large number of them in a tower-like fashion using powder bed fusion laser technology. This tower-like construction allows multiple reinforcement elements 6 to be manufactured as a single component without support structures. Following additive manufacturing, the individual reinforcement elements 6 are separated from each other by wire EDM or sawing.

[0147] Since the short-circuit end rings 3 of the squirrel-cage rotor 1 generally require further processing for use in high-speed electrical machines, the reinforcement element 6 of a short-circuit end ring 3 is arranged as far as possible in the area adjacent to the laminated core 13. This results in the cross-sectional area of ​​the short-circuit end ring shown schematically in Fig. 6 (page 19 of 29).

[0148] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland

[0149] 3, in which the casting can be post-processed without damaging the supporting sections of the reinforcement element 6. For example, after the copper has hardened, holes can be drilled for balancing the short-circuit end ring 3 without drilling into the reinforcement element 6.

[0150] Figures 7-9 show a further embodiment of a short-circuit end ring 3 according to the invention. The short-circuit end ring 3 shown here differs from the short-circuit end ring 3 shown in Figures 1-3 in several respects. For example, the reinforcement element 6 of the embodiment shown in Figures 7-9 comprises a total of six inner rings 7 and six outer rings 8. The first three inner rings 7 have the same diameter and are arranged one above the other. Following these, three further inner rings 7 are arranged one above the other, but these have a larger diameter than the first inner rings 7. Three outer rings 8 are also arranged one above the other. The first outer rings 8 have a larger diameter than the inner rings 7 and a smaller diameter than the second outer rings 8. The cross-sections of the inner rings 7 and the outer rings 8 are the same in this embodiment.

[0151] The reinforcement element shown here is also equipped with radial connecting webs 10, which connect the individual rings 7, 8 in a radial direction. The radial connecting webs 10 have a rod-shaped geometry.

[0152] Further examples, also in conjunction with features from the examples above, in particular the manufacture of a squirrel-cage rotor 1, are shown in Figures 10-14. In particular, the strength and thus the maximum speed of cast induction motors is also improved here by reinforcements produced using multi-material additive manufacturing (hereinafter also referred to as MMAM).

[0153] The reinforcing additive structures consist of, or rather, the

[0154] Reinforcing element 6 consists of two materials: a high-strength material A, whose mechanical properties are determined by the casting process (page 20 of 29).

[0155] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland are not affected (e.g. steel or Ni alloy), and a material with high conductivity B, from which the induction rotor is also advantageously cast (e.g. aluminum or copper).

[0156] The MMAM reinforcement components, or reinforcement element 6, are manufactured using a Multi Material Laser Power Bed Fusion (LMBF) machine (also known as an LPBF machine or MM-LPBF). The reinforcement structures, or reinforcement elements 6, are formed as rows or as a network of closed rings 7, 8 or annular structures, as shown, for example, in Figures 11a and 11b. The resulting network or lattice structure must be sufficiently open to allow casting and venting and to avoid casting defects. The rings 7, 8 are made of a material A whose mechanical properties are not affected by the casting process (e.g., steel or a nickel alloy, in particular Inconel 718). The struts, anchoring elements, and support structures (see Figures 11a, 11b) are made of a material B. Material B is a highly conductive material, from which the induction rotor is also advantageously cast.Material B is, for example, aluminum or copper.

[0157] To maximize productivity, the MMAM parts can be printed M times (M being a positive integer greater than zero) in stacked form, as shown on the left in Fig. 10. Fig. 10 shows, in particular, how the MMAM parts, or several reinforcement elements 6, are stacked on top of each other on a base plate or print plate. After the additive manufacturing process, the parts or reinforcement elements 6 can be separated from the base plate and from each other. This is advantageously done, for example, by wire EDM (wire electrical discharge machining) or by sawing. Depending on the material, additional heat treatment can be performed. In the case of Inconel 718 (or similar) and a delicate geometry, heat treatment is not necessary or even advisable.Tests have even shown that when using Inconel 718, it is better if no heat treatment is carried out, as shown on page 21 of 29.

[0158] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland

[0159] Tests have shown that the typical microstructure from the LPBF process, after casting with copper, exhibits better mechanical properties than if it had undergone heat treatment, as the casting temperatures reset the microstructure to a "soft-annealed" state. However, in the case of thicker cross-sections of reinforcements or the use of other materials (i.e., not Inconel 718), heat treatment can certainly be beneficial. The heat treatment performed in the tests was as follows: heating to 954 °C and holding for 1 hour, followed by air cooling; warm curing at 718 °C for 8 hours; furnace cooling to 621 °C for the total curing time of 18 hours, followed by air cooling.

[0160] In Fig. 10, a single reinforcement element 6 is shown on the right-hand side, which has already been separated from the base plate and from the other MMAM parts or reinforcement elements 6.

[0161] An advantageous combination of materials A and B is, for example, Inconel 718 for material A and pure copper for material B. Inconel 718 is a nickel-chromium-iron alloy with niobium and molybdenum, as well as small amounts of aluminum and titanium. An advantageous chemical composition of Inconel 718 is NiCrMofFe(NblTa)AlTi with a mass fraction of: Chromium (Cr) : W Cr =0.18 or 18 wt.%; Iron (Fe) : W Fe =0.18 or 18 wt%; and nickel (Ni) as a balance; and with a mass fraction of: niobium and tantalum (Nb+Ta) : W N b+Ta=0.05 or 5 wt.%; Molybdenum (Mo) : W Mo =0.03 or 3 wt.%; Aluminum (Al) : W Ä i=0.06 or 6% by weight; Titanium (Ti): W Ti = 0.01 or 1 wt%; and with other (x) (e.g. impurities): w x <0.005 or 0.5 wt.%, where the stated wt.% (also referred to herein as wt.%) are nominal. The solidus temperature of Inconel 718 is 1260°C ± 10°C and the liquidus temperature of Inconel 718 is 1340°C ± 10°C.

[0162] The MMAM parts or reinforcement elements 6 must be placed and secured in the induction rotor casting mold. Since the rotor consists of a laminated core 13, i.e., a stack 13 of sheets 14, which is placed in the center of the mold, there are two (page 22 of 29).

[0163] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland

[0164] Ways to place or attach the MMAM part or the reinforcement elements 6.

[0165] Firstly, the MMAM parts or reinforcement elements 6 have anchor elements or retaining webs 9 with which they can be attached directly to the mold. An MMAM part or reinforcement element 6 with anchor elements or retaining webs 9 is shown in Fig. 11a.

[0166] On the other hand, the MMAM parts or reinforcement elements 6 can be printed with a base plate (which can be made of material A or B) that is attached to the sheet metal stack 13, as shown in Fig. 11b. The base plate can also advantageously be one of the sheets 14. If the MMAM parts or reinforcement elements 6 are arranged, formed, or printed on a base plate, no anchor elements or retaining webs 9 are necessary, nor are any anchor elements or retaining webs 9 attached to the reinforcement element 6, as can be seen in Fig. 11b.

[0167] Once the MMAM structures or reinforcement elements 6 are placed or secured in the mold, as shown in Figures 12a, 12b, and 13, the rotor can be cast. Figure 12a, which shows only a portion of the mold, illustrates how a reinforcement element 6 (shown in Figure 11a) is placed and secured in the mold using its anchor elements or retaining webs 9. Figure 12b, also showing only a portion of the mold, illustrates how a reinforcement element 6 (shown in Figure 11b) is placed and secured in the mold using its base plate.

[0168] The placement and fastening are important because they ensure that the reinforcement elements 6 remain in the desired position during casting, advantageously even at high temperature and high pressure. Figure 13 shows the placement and fastening of the reinforcement elements 6 (see, for example, Figure 11a) together with a sheet metal stack 13 in a mold in cross-section. Advantageous vents or vent channels in the mold to prevent air inclusions during casting are not shown in Figures 12a, 12b, 13, and 14. Page 23 of 29

[0169] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland

[0170] When material B (which is designated as sprue 15 in Fig. 14) is poured into the mold, which is shown, for example, in Fig. 13, the structures or parts made of material B fuse with the poured material B and form a complete metallurgical bond, as can be seen in Fig. 14. Fig. 14 shows a cross-section of a poured mold.

[0171] The reinforcement or reinforcing elements 6 are attached to the sheet metal stack 13 (see Figs. 11b, 12b) or by means of the

[0172] Anchoring elements or retaining webs 9 (see Figs. 11a, 12a, 13) made of material B ensure that no foreign substances or structures are present on the outer surface of the rotor after casting. This allows for conventional machining and finishing of the rotor after casting.

[0173] An advantageous method for manufacturing a squirrel-cage rotor 1 thus comprises the following steps: a) manufacturing a reinforcement element 6 with retaining webs 9 using MMAM, or a reinforcement element 6 on a base plate using MMAM, wherein the reinforcement element 6 consists of two materials, b) arranging the lamination stack 13 in a mold, c) placing or securing the reinforcement elements 6 in the mold, d) casting the mold with one of the two materials from which the reinforcement element 6 also consists, e) demolding the squirrel-cage rotor 1. Page 24 of 29

[0174] MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland

[0175] REFERENCE MARK LIST

[0176] 1 Squirrel-cage rotor

[0177] 2 cages

[0178] 3 Short-circuit end ring

[0179] 4 Cast part

[0180] 5 Available for post-processing

[0181] Cross-sectional area of ​​the short-circuit end ring

[0182] 6 Reinforcing element

[0183] 7 inner ring

[0184] 8 Outer ring

[0185] 9 landing stage

[0186] 10 Connecting bridge

[0187] 11 windows

[0188] 12 Axial connecting web

[0189] 13 sheet metal package

[0190] 14 Individual sheets

[0191] 15 sprue

[0192] N Nut

[0193] R back

[0194] Z tooth

Claims

Page 25 of 29 MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland PATENT CLAIMS 1. Electric motor with a squirrel-cage rotor (1) in the form of a cage (2) which electrically carries several short-circuit end rings (3) which are formed as castings (4) made of a casting material, wherein at least one reinforcement element (6) made of another material is cast into each of the castings, characterized in that the casting material essentially forms the outermost free surface of the short-circuit end ring (3).

2. Electric motor according to claim 1, characterized in that the The reinforcing element (6) is essentially completely embedded in the material of the casting (4).

3. Electric motor according to one of the preceding claims, characterized in that there are several places where the reinforcement element (6) projects into the outer surface of the casting (4).

4. Electric motor according to one of the preceding claims, characterized in that the reinforcement element (6) consists of a material whose solution annealing temperature is higher or only insignificantly lower than the casting temperature range of the casting material.

5. Electric motor according to one of the preceding claims, characterized in that the casting material is copper, a copper alloy, aluminium or an aluminium alloy.

6. Electric motor according to one of the preceding claims, characterized in that the reinforcement element (6) consists of a material that is not magnetizable and preferably has a tensile strength that is at least twice as high as that of the casting material. Page 26 of 29 MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland 7. Electric motor according to the immediately preceding claim, characterized in that the reinforcing element (6) consists entirely or at least substantially of a nickel-based alloy, temperature-resistant steel, titanium, a titanium alloy or a high-entropy alloy, or of a, ideally high-strength, copper or aluminum alloy.

8. Electric motor according to the immediately preceding claim, characterized in that the reinforcement element (6) is a sintered metal material and / or has a surface roughness of Ra > 15pm (=micrometers ).

9. Electric motor according to one of the preceding claims, characterized in that the reinforcement element (6) is at least one circumferentially closed ring (7, 8), and preferably consists of several circumferentially closed rings (7, 8) which are ideally connected to each other via connecting webs (10, 12).

10. Electric motor according to the immediately preceding claim, characterized in that the reinforcement element (6) consists of several rings (7, 8) that are at least substantially parallel to the axis of rotation of the squirrel-cage rotor (1).

11. Electric motor according to one of the preceding claims, characterized in that the reinforcement element (6) consists of at least one inner ring (7) with a smaller ring diameter and at least one outer ring (8) with a larger ring diameter, preferably being such that the ring cross-sectional diameter of the at least one outer ring (8) is smaller than the ring cross-sectional diameter of the at least one inner ring (7). Page 27 of 29 MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland 12. Electric motor according to one of the preceding claims, characterized in that the reinforcement element (6) has several retaining webs or fixing elements (9) by means of which the reinforcement element (6) is held in position in the cavity of the mold for casting the short-circuit end ring (3).

13. Electric motor according to one of the preceding claims, characterized in that all connecting (10, 12) and retaining webs (9) are perforated by at least one, preferably several, windows (11) or, if immediately adjacent, form a window (11) between them with a clear cross-sectional area of ​​at least 3 mm² 2 and preferably at least 4.5 mm 2 .

14. Electric motor according to one of the preceding claims, characterized in that the volume fraction of the reinforcement element (6) in relation to the entire short-circuit end ring (3) is ideally between 5% and 15%.

15. Method for manufacturing a squirrel-cage rotor (1) for an electric motor according to one of the preceding claims, characterized in that a reinforcement element (6) is manufactured by an additive primary forming process and then inserted into a casting cavity to form a squirrel-cage end ring (3), whereupon the reinforcement element (6) is cast into the squirrel-cage rotor (1) and then removed from the casting mold.

16. Method for manufacturing a squirrel-cage rotor (1) for an electric motor according to the preceding claim, characterized in that the actual material of the short-circuit end ring (3) is introduced into the mold cavity forming the short-circuit end ring (3) by means of a casting process, which has a porosity of the cast material of less than Page 28 of 29 MISSELHORN | mw-patent.de 05199PWO for Oerlikon & Wieland 1% guaranteed, preferably a laminar Squeeze casting process.

17. Method for manufacturing a squirrel-cage rotor (1) for an electric motor according to one of the preceding claims 15 or 16, characterized in that the reinforcement element (6) is supported against the inner surface of the mold by retaining webs or fixing elements (9) which are adapted to the draft angle of the mold cavity and can be pressed against it, and / or that the mold has projections for contact with the reinforcement element (6) which does not have its own retaining elements projecting from it.

18. Method according to one of the preceding claims 15, 16 or 17, characterized in that the reinforcing element (6) is cast so deeply into the actual material of the short-circuit end ring (3) that the short-circuit end ring (3) can be balanced by drilling without also drilling into the reinforcing element (6).

19. Method according to one of the preceding claims 15, 16, 17 or 18, characterized in that in particular the retaining webs (9) and the connecting webs (10, 12) of the The reinforcement element (6) is designed to be perforated in such a way that the flow of pouring is not significantly impeded.

20. Method according to any one of the preceding claims 15 to 19, characterized in that the reinforcement element (6) is designed in such a way that it does not interrupt the one-piece nature of the short-circuit end ring (3).

21. Method according to one of the preceding claims 15 to 20, characterized in that the short-circuit end ring (3) is turned down after the casting of the reinforcement element (6), preferably in such a way that at least a part of the retaining webs or fixing elements (9) is also turned down.

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