Die-casting arrangement, method for manufacturing a rotor and rotor for an electric machine

Abstract

The invention relates to a die-casting arrangement (1) for manufacturing a rotor (2) comprising a divisible die-casting mold (4) with a first mold half (5) and a second mold half (6), which in the closed state has a cavity (9) that can be filled with a flowable metal (7) and receives a rotor lamination stack (8), which can be coupled to a pressurizable feed system (10) by means of which the flowable metal (7) can be pressed into the cavity (9) under pressure, wherein the cavity (9) has a first annular cavity (11) for forming a first short-circuit ring (12) of the rotor (2) and a second annular cavity (13) for forming a second short-circuit ring (14) of the rotor (2), wherein the first annular cavity (11) and the second annular cavity (13) are connected by axially extending channels (15), and wherein the feed system (10) has a first Casting chamber (16) has,which opens into the first annular cavity (11), so that the flowable metal (7) from the first casting chamber (16) can be pressurized into the first annular cavity (11) and into the axially extending channels (15) and from there further into the second annular cavity (13), the second annular cavity (13) being connected to a melt reservoir (17).

Description

[0001] The present invention relates to a die-casting arrangement for manufacturing a rotor of an electric machine, comprising a divisible die-casting mold with a first mold half and a second mold half, which in the closed state has a cavity that can be filled with a flowable metal and accommodates a rotor lamination stack, which can be coupled to a pressurizable feed system by means of which the flowable metal can be pressed into the cavity under pressure, wherein the cavity has a first annular cavity for forming a first short-circuit ring of the rotor and a second annular cavity for forming a second short-circuit ring of the rotor, wherein the first annular cavity and the second annular cavity are connected by axially extending channels, wherein the feed system has a first casting chamber which opens into the first annular cavity.so that the flowable metal from the first casting chamber can be pressurized into the first annular cavity and into the axially extending channels, and from there further into the second annular cavity. The invention further relates to a method for manufacturing a rotor and a rotor for an electric machine.

[0002] Electric motors are increasingly being used for propulsion in motor vehicles to create alternatives to combustion engines that require fossil fuels. Considerable efforts have already been made to improve the everyday usability of electric drives and to offer users the familiar driving comfort.

[0003] A detailed description of an electric drive can be found in an article in the journal ATZ, 113th year, 05 / 2011, pages 360-365, by Erik Schneider, Frank Fickl, Bernd Cebulski, and Jens Liebold, entitled: Highly Integrated and Flexible Electric Drive Unit for E-Vehicles. This article describes a drive unit for one axle of a vehicle, comprising an electric motor arranged concentrically and coaxially to a bevel gear differential.

[0004] Such drive units are also referred to as e-axles or electrically operated drive trains.

[0005] In addition to purely electric powertrains, hybrid powertrains are also known. Such powertrains in hybrid vehicles typically comprise a combination of an internal combustion engine and an electric motor, enabling – for example, in urban areas – purely electric operation while simultaneously providing sufficient range and availability, especially on long-distance journeys. Furthermore, it is possible to use both the internal combustion engine and the electric motor simultaneously in certain operating situations.

[0006] In many such automotive applications, permanent magnet synchronous machines (PMSMs) or asynchronous machines (AMSMs) are used. Asynchronous motors, or three-phase asynchronous machines, are three-phase machines in which the rotor leads the rotating magnetic field of the stator when the machine is operating as a generator and lags behind when the machine is operating as an electric motor.

[0007] The rotor is also referred to as a passive rotor and can be either permanently or intermittently short-circuited. In the case of permanent short-circuiting, the rotor is designed as a squirrel-cage rotor. Squirrel-cage rotors comprise a short-circuit cage made of electrically conductive rods and short-circuit rings, as well as several laminations or at least one laminated core. The laminations are generally produced by a stamping process, and at least one laminated core essentially forms the rotor body. The rods are arranged in openings in the laminations, with their longitudinal direction through the rotor body having at least an axial component. A short-circuit ring is arranged at each axial end face of the rotor and connected to a rod protruding from an opening in an axially end-facing lamination.

[0008] In one method of manufacturing such squirrel-cage rotors, the rods and shorting rings are produced as separate components, and the rods are inserted through openings in the laminations. The rods are then soldered or screwed to a shorting ring, which is axially positioned at the end face of the rotor body, to form the squirrel-cage cage and secure the position of the rods and shorting rings relative to the laminations. The rods and shorting rings are usually made of the same material.

[0009] Another manufacturing option involves assembling the sheets and inserting them as a stack into one half of a casting mold. In a subsequent casting process, usually a die casting process, the material of the rods and short-circuit rings is introduced as casting material to cast the short-circuit rings and the rods as a single unit.

[0010] In principle, such die-casting processes can be used to produce thin-walled components by filling the permanent metal mold with molten metal at high speed and pressure. However, due to the rotor design and the resulting filling of thick-walled areas over thin-walled areas, the B-ring, located furthest from the gate, can only be fed to a very limited extent. The molten metal, entering the A-ring from a casting chamber via a pouring channel and gate, fills the B-ring through recesses in the lamination stack inserted into the mold. These filled, thin-walled recesses, known as groove bars, can then cool so rapidly that no further feeding by pressure from a piston located in the casting chamber is possible. This results in increased porosity or cavities in the B-ring due to solidification shrinkage and air entanglement.

[0011] Such defects can occur in both the short-circuit ring and the connecting rods. The cavities and / or pores in the short-circuit rings represent material defects, so that when the asynchronous motor is operated, under the rotational influence of centrifugal forces on the short-circuit ring, there is a risk that the short-circuit ring will deform impermissibly or even crack. Furthermore, cavities and / or pores in the connecting rods may cause a high electrical resistance to build up in an affected rod when current flows through the squirrel-cage rotor. This leads not only to electrical inefficiency but also to a significant temperature increase in that rod, potentially even causing it to melt.

[0012] To avoid or at least reduce such defects in the molded rotor component, so-called squeeze pins (post-compressors) are used, among other things, to supply thick-walled component areas far from the gate during die casting. These are a type of "mini-piston" that compresses these areas downstream, independently of the main piston. These units require sufficient space in the mold, which may not be available due to cooling channels running through the mold. Furthermore, the technology is cost-intensive and can lead to a less robust casting process, as moving elements can cause problems at the process temperatures involved, and the correct timing of the piston movement is crucial. This must occur simultaneously with the formation of solidification porosity in order to counteract it.If the molten metal is injected too early, porosity still develops; if it is injected too late, the molten metal has already solidified to the point where refeeding is no longer possible. To make matters worse, pure aluminum with a very narrow solidification range is used instead of an aluminum alloy, which further restricts the process window.

[0013] The production of a squirrel-cage rotor therefore requires extensive and precise testing and inspection. Current manufacturing processes for squirrel-cage rotors are thus associated with considerable technical complexity.

[0014] Based on this, the present invention aims to provide a die-casting arrangement that reduces or even completely avoids the problems known from the prior art. Furthermore, the invention aims to implement an optimized method for manufacturing a rotor that is technically simple and efficient and ensures the production of a rotor with a long service life. Finally, the invention aims to provide an improved rotor.

[0015] This problem is solved by a die-casting arrangement for manufacturing a rotor of an electric machine, comprising a divisible die-casting mold with a first mold half and a second mold half, which in the closed state has a cavity that can be filled with a flowable metal and accommodates a rotor lamination stack, which can be coupled to a pressurizable feed system by means of which the flowable metal can be pressed into the cavity under pressure, wherein the cavity has a first annular cavity for forming a first short-circuit ring of the rotor and a second annular cavity for forming a second short-circuit ring of the rotor, wherein the first annular cavity and the second annular cavity are connected by axially extending channels, wherein the feed system has a first casting chamber which opens into the first annular cavity.so that the free-flowing metal from the first casting chamber can be pressurized into the first annular cavity and into the axially extending channels, and from there further into the second annular cavity, the second annular cavity being connected to a molten reservoir which opens into the second annular cavity in an upper section in the direction of gravity, so that free-flowing metal can flow from the molten reservoir into the second annular cavity by gravity.

[0016] This offers the advantage that the die-casting arrangement according to the invention does not require a complex, controllable mechanism, since the replenishment occurs virtually "automatically" via gravity. This also eliminates any restrictions on the design of the cooling channels in the die-casting mold, as no larger recesses are necessary, unlike with squeezer technology.

[0017] In the die-casting arrangement, a second, in particular cylindrical or conical, melt reservoir is arranged in the direction of gravity directly above the second annular cavity, from which liquid melt can flow by gravity during the solidification of the second short-circuit ring in the die-casting process via a corresponding connection to the ring geometry of the second cavity.

[0018] In the direction of gravity, above the second annular cavity, at approximately the 12 o'clock position, lies the molten metal reservoir, which can also be called the feeder. During the die-casting process of the rotor, this reservoir is filled with the flowable metal (molten metal) via a suitable connection. After filling is complete and while the molten metal solidifies in the temperature-controlled die-casting mold, the comparatively thick-walled second short-circuit ring is replenished by gravity from the molten metal reservoir. This reservoir is cut off from the rest of the rotor and from the casting channel, through which replenishment normally occurs, by the freezing of the comparatively thin-walled groove bars.

[0019] The melt reservoir is preferably dimensioned such that the free-flowing metal in it remains liquid for significantly longer than the melt in the second short-circuit ring. The connection between the melt reservoir and the second annular cavity should preferably be designed so that this connection also solidifies after the second short-circuit ring due to heat input into the temperature-controlled die-casting mold. It is therefore preferred to form a connection extending to the inner diameter of the second annular cavity, since this is where the melt in the second short-circuit ring solidifies last, thus enabling a feed path to reach the lower part of the second short-circuit ring.

[0020] The die-casting setup is specifically configured for horizontal die-casting. In principle, the die-casting setup can also be designed for vertical die-casting.

[0021] It is also preferred that one of the mold halves is fixed immovably in the die-casting arrangement, while the other mold half is movable so that the die-casting mold can be opened and closed accordingly.

[0022] It is also possible that the feed system is connected to a second casting chamber in such a way that the flowable metal can be introduced directly into the second casting chamber under pressure.

[0023] The rotor produced using the die-casting arrangement is preferably designed as a squirrel-cage rotor, and the rods formed by the axially extending channels in the die-casting mold are part of a squirrel-cage cage for the squirrel-cage rotor. The rotor body is essentially a laminated core or a module assembled from several laminated cores.

[0024] A sheet metal stack is produced in particular from several identical, stamped sheets, wherein each sheet is essentially ring-shaped and the sheets are arranged coaxially to each other, so that the sheet metal stack is essentially hollow cylindrical in shape.

[0025] The openings created in the laminations are aligned with respect to their respective angular positions when the laminations are positioned to form a lamination stack, such that in the axial direction at least a partial overlap of the openings of immediately adjacent laminations is achieved. This creates elongated openings, cavities, or channels in the rotor body.

[0026] According to an advantageous embodiment of the invention, the molten reservoir may have a connecting section adjacent to the end face of the second cavity, extending radially from an inner diameter of the second annular cavity to an outer diameter of the second annular cavity, so that a flow of free-flowing metal can occur from the molten reservoir via the connecting section into the second annular cavity across its entire annular width. The advantage of this embodiment is that it allows for particularly effective prevention of shrinkage cavities.

[0027] According to a further preferred embodiment of the invention, the melt reservoir and / or the connection section can also be designed to be heated, in particular by means of heating cartridges, which can also contribute to preventing or reducing the formation of cavities. Here, the heating of the melt reservoir and / or the connection section is preferably configured such that the flowable metal is even warmer than the metal already present in the second annular cavity and thus exhibits higher flowability.

[0028] Furthermore, according to another advantageous embodiment of the invention, the melt reservoir and / or the connection section may be provided, at least partially, with ceramic molded parts to improve the thermal insulation effect. This also allows for improved flowability of the metal from the melt reservoir into the second annular cavity.

[0029] For the same reasons, according to a further particularly preferred embodiment of the invention, it may also be provided that the melt reservoir and / or the connection section are / are provided with a thermally insulating coating, at least in sections, to improve the thermal insulation effect.

[0030] To further optimize the feeding of the second annular cavity, the use of a local tool insert in the area of ​​the melt reservoir and / or the connection section made of a steel with lower thermal conductivity, e.g. 1.2709, can also be implemented.

[0031] It could also be advantageous to create a temperature gradient in the area of ​​the second annular cavity by appropriately designing the cooling channels in the casting tool, so that a greater cooling effect can be generated in the lower area of ​​the second annular cavity than in the upper area of ​​the annular cavity.

[0032] Furthermore, the invention can also be further developed in such a way that the first annular cavity is connected to a second molten reservoir, which opens into the first annular cavity in an upper section in the direction of gravity, so that fluid metal can flow from the second molten reservoir into the first annular cavity by gravity. The advantage of this embodiment is that it also reduces the risk of porosity formation in the first annular cavity without requiring complex modifications to the die-casting arrangement.

[0033] The fluid metal can be, for example, aluminum, an aluminum alloy, copper, a copper alloy, a zinc alloy, a magnesium alloy, steel, or a steel alloy.

[0034] It is also conceivable that a majority of the axially extending channels, preferably all of them, are connected to a third melt reservoir positioned above the channels in the direction of gravity, with each reservoir opening into one of the channels. This allows free-flowing metal to flow from the third melt reservoir into the channels by gravity. The advantage of this design is that it also reduces the risk of porosity formation in the channels without requiring complex modifications to the die-casting assembly. Furthermore, the third melt reservoir and its connection to the channels can be used as a venting path.

[0035] The object of the invention is also achieved by a method for manufacturing a rotor of an electric machine comprising a die-casting arrangement according to one of the preceding claims with the following steps: • Closing the split die-casting mold • Pressurized introduction of flowable metal into the cavity of the die-casting mold via the first annular cavity • Gravity-induced flow of free-flowing metal into the second annular cavity

[0036] It may also be advantageous to further develop the invention in such a way that the pressurized introduction of flowable metal into the cavity of the die-casting mold via the first annular cavity takes place before the gravity-induced flow of flowable metal into the second annular cavity, which can help to further minimize the risk of void formation.

[0037] Preferably, the time between the pressurized introduction of the flowable metal and the gravity-induced flow of the flowable metal is between 0.2 and 2.0 seconds, preferably between 0.5 and 1.5 seconds.

[0038] It has also proven advantageous that the gravity-induced flow of flowable metal takes between 3-10 seconds, preferably between 4-6 seconds.

[0039] Furthermore, the object of the invention can be achieved by means of a rotor for an electric machine, in particular manufactured by a method according to claim 7, comprising a first short-circuit ring and a second short-circuit ring, wherein the first short-circuit ring and the second short-circuit ring are connected by axially extending slotted bars, and wherein the first short-circuit ring and the second short-circuit ring are substantially free of voids. Finally, the invention can also advantageously be implemented such that the rotor is designed as a squirrel-cage rotor for an asynchronous machine.

[0040] For the purposes of this application, "free of voids" means that the density of the second short-circuit ring corresponds to between 95-100%, preferably 98-100%, most preferably 99-100% of the density of a geometrically identical short-circuit ring formed without porosities.

[0041] The invention will be explained in more detail below with reference to figures without limiting the general inventive concept.

[0042] It shows: Fig. 1 a schematic axial section view of an electric machine, Fig. 2 a rotor arrangement in an exploded view, Fig. 3 a rotor arrangement in a perspective view, Fig. 4 a die-casting arrangement in a first schematic axial sectional view, Fig. 5 a die-casting arrangement in a schematic cross-sectional representation, Fig. 6 a die-casting arrangement in a second schematic axial section view, Fig. 7 a die-casting arrangement in a schematic axial section view.

[0043] The Fig. Figures 4-6 show a die-casting arrangement 1 for the production of a rotor 2 of an electric machine 3 in various sectional views.

[0044] A corresponding electric machine 3 is in the Fig. 1 to be seen and a corresponding rotor 2 in the Fig. 2-3. In the illustrated embodiment, the electric machine 3 is configured as a radial flux asynchronous machine. Accordingly, the rotor 2 is designed as a squirrel-cage rotor, which is rotatably mounted relative to the stator 30 via a rotor shaft 26 and the rolling bearings 25.

[0045] The rotor 2 has a first short-circuit ring 12 and a second short-circuit ring 14, the first short-circuit ring 12 and the second short-circuit ring 14 being connected by axially extending slotted bars 24, which are inserted into the rotor slots 27 of the rotor lamination stack 8 formed from rotor laminations 28. Although the slotted bars 24 are shown as separate components in the exploded view for the purpose of clarifying the rotor structure, it is understood that the slotted bars 24 and the short-circuit rings 12, 14 are monolithic. The first short-circuit ring 12 and the second short-circuit ring 14 are essentially free of voids, which is achieved by manufacturing the rotor 2 in a die-casting arrangement 1 described below.

[0046] The die-casting arrangement 1 comprises a divisible die-casting mold 4 with a first mold half 5 and a second mold half 6, which in the closed state has a cavity 9 that can be filled with a flowable metal 7 and accommodates a rotor lamination stack 8, which can be coupled to a pressurizable feed system 10 by means of which the flowable metal 7 can be pressed into the cavity 9 under pressure.

[0047] The cavity 9 has a first annular cavity 11 for forming a first short-circuit ring 12 of the rotor 2 and a second annular cavity 13 for forming a second short-circuit ring 14 of the rotor 2, wherein the first annular cavity 11 and the second annular cavity 13 are connected by axially extending channels 15.

[0048] The feed system 10 has a first casting chamber 16, which opens into the first annular cavity 11, so that the flowable metal 7 can be forced under pressure from the first casting chamber 16 into the first annular cavity 11 and into the axially extending channels 15, and from there further into the second annular cavity 13. The first casting chamber 16 is arranged below the first annular cavity 11 in the direction of gravity. In the illustrated embodiment, the die casting takes place horizontally. If short-circuit rings 12, 14 with larger inner diameters are used, it is also conceivable that the first casting chamber 16 lies within the corresponding short-circuit ring 12, 14. It is important that after the horizontal casting chamber 16, the molten metal is initially directed vertically upwards.

[0049] The second annular cavity 13 is further connected to a melt reservoir 17, which opens into the second annular cavity 13 in an upper section 18 in the direction of gravity, so that fluid metal 7 can flow from the melt reservoir 17 into the second annular cavity 13 by force of gravity.

[0050] The melt reservoir 17 has a connection section 29 adjacent to the end face of the second cavity 13, which extends radially from an inner diameter 19 of the second annular cavity 13 to an outer diameter 20 of the second annular cavity 13, so that an inflow of flowable metal 7 from the melt reservoir 17 via the connection section 29 into the second annular cavity 13 over its entire ring width 21 can take place.

[0051] The melt reservoir 17 and / or the connection section 29 can be heated by means of heating cartridges. It is also conceivable that the melt reservoir 17 and / or the connection section 29 are / are provided with ceramic molded parts, at least in sections, to improve the thermal insulation effect. Furthermore, it would also be possible – although not shown in the figures – that the melt reservoir 17 and / or the connection section 29 are / are provided with a thermally insulating coating, at least in sections, to improve the thermal insulation effect.

[0052] One can recognize from the Fig. 5. Furthermore, it is advantageous that the die-casting mold 4 has several vent channels 31 in the upper section 18, through which air still present in the cavity 9 can escape during the gravity-induced flow of metal 7. The vent channels 31 are connected circumferentially to the second annular cavity 13 between 10 and 14 o'clock. The melt reservoir 17 is positioned at 12 o'clock, but can also be arranged between 10 and 14 o'clock.

[0053] In the Fig. Figure 7 shows an embodiment of the die-casting arrangement 1, in which the first annular cavity 11 is connected to a second melt reservoir 22, which opens into the first annular cavity 11 in a section 23 that is upwards in the direction of gravity. This allows free-flowing metal 7 to flow from the second melt reservoir 22 into the first annular cavity 11 by gravity. Therefore, after the free-flowing metal 7 has been injected into the cavity 11, more free-flowing metal 7 can flow from the second melt reservoir 22 by gravity, thus reducing the risk of porosity formation in the first annular cavity 11. The connection is made from both radial and axial directions, allowing the metal to flow into the first cavity 11 in both directions.

[0054] The connection section 29 of the first melt reservoir 17 represents – unlike in the embodiment of the Fig.4, only a radial supply of flowable metal 7 via the outer surface of the second cavity 13 is provided, and no supply via the end face. This allows for a simpler design of the die-casting mold 4, but may negatively affect the effectiveness of preventing shrinkage cavities.

[0055] The rotor 2 can be manufactured using the die-casting arrangement 1 as follows: First, the split die-casting mold 4 is closed, followed by the pressurized introduction of flowable metal 7 into the cavity 9 of the die-casting mold 4 via the first annular cavity 13. Simultaneously or sequentially, a gravity-driven flow of flowable metal 7 from the molten reservoir 17 into the second annular cavity 11 is initiated. It has proven advantageous for the pressurized introduction of flowable metal 7 into the cavity 9 of the die-casting mold 4 via the first annular cavity 13 to occur prior to the gravity-driven flow of flowable metal 7 into the second annular cavity 11.

[0056] The invention is not limited to the embodiments illustrated in the figures. The above description is therefore not to be considered restrictive, but rather explanatory. The following claims are to be understood in such a way that a stated feature is present in at least one embodiment of the invention. This does not exclude the presence of further features. Where the claims and the above description define 'first' and 'second' features, this designation serves to distinguish between two similar features without establishing a priority. Reference symbol list 1 die-casting arrangement 2 rotors 3 electric machine 4 die-casting mold 5 mold half 6 mold halves 7 Metal 8 Rotor lamination package 9 Cavity 10 Feed system 11 Cavity 12 Short-circuit ring 13 Cavity 14 Short-circuit ring 15 channels 16 Casting chamber 17 Melt reservoir Section 18 19 diameter 20 diameter 21 ring width 22 Melt reservoir Section 23 24 slotted rods 25 warehouses 26 Rotor shaft 27 rotor slots 28 Rotor laminations 29 Connection section 30 Stator 31 ventilation ducts QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited non-patent literature

[0000] Journal ATZ 113th year, 05 / 2011, pages 360-365 by Erik Schneider, Frank Fickl, Bernd Cebulski and Jens Liebold with the title: Highly integrated and flexible electric drive unit for electric vehicles

[0003]

Claims

[1] Die-casting arrangement (1) for producing a rotor (2) of an electrical machine (3), comprising a divisible die-casting mold (4) with a first mold half (5) and a second mold half (6), which, in the closed state, has a cavity (9) which can be filled with a flowable metal (7) and which receives a rotor laminated core (8), which cavity can be coupled to a pressurizable supply system (10), by means of which the flowable metal (7) can be pressed into the cavity (9) under pressure, wherein the cavity (9) has a first annular cavity (11) for forming a first short-circuit ring (12) of the rotor (2) and a second annular cavity (13) for forming a second short-circuit ring (14) of the rotor (2), wherein the first annular cavity (11) and the second annular cavity (13) are connected by axially extending channels (15), wherein the feed system (10) has a first casting chamber (16) which opens into the first annular cavity (11), so that the flowable metal (7) can be pressed from the first casting chamber (16) under pressure into the first annular cavity (11) and into the axially extending channels (15) and from there further into the second annular cavity (13), characterized by , that the second annular cavity (13) is connected to a melt reservoir (17) which opens into the second annular cavity (13) in a section (18) which is upper in the direction of gravity, so that flowable metal (7) can flow from the melt reservoir (17) into the second annular cavity (13) under the effect of gravity. [2] Die-casting arrangement (1) according to claim 1 characterized bythat the melt reservoir (17) has a connecting section (29) which adjoins the second cavity (13) on the end face and which extends radially from an inner diameter (19) of the second annular cavity (13) to an outer diameter (20) of the second annular cavity (13), so that an inflow of flowable metal (7) from the melt reservoir (17) via the connecting section (29) into the second annular cavity (13) over its entire ring width (21). [3] Die-casting arrangement (1) according to claim 1 or 2, characterized by that the melt reservoir (17) and / or the connecting section (29) are / is designed to be heatable, in particular by means of heating cartridges. [4] Die-casting arrangement (1) according to one of the preceding claims, characterized bythat the melt reservoir (17) and / or the connecting section (29) are / is provided at least in sections with ceramic molded parts to improve the thermal insulation effect. [5] Die-casting arrangement (1) according to one of the preceding claims, characterized by that the melt reservoir (17) and / or the connecting section (29) are / is provided at least in sections with a thermally insulating coating to improve the thermal insulation effect. [6] Die-casting arrangement (1) according to one of the preceding claims, characterized by in that the first annular cavity (11) is connected to a second melt reservoir (22) which opens into the first annular cavity (11) in a section (23) which is upper in the direction of gravity, so that flowable metal (7) can flow from the second melt reservoir (22) into the first annular cavity (11) under the effect of gravity. [7] Method for producing a rotor (2) of an electrical machine (3) comprising a die-casting arrangement (1) according to one of the preceding claims, comprising the following steps: • Closing the divisible die-casting mold (4) • Pressurized introduction of flowable metal (7) into the cavity (9) of the die-casting mold (4) via the first annular cavity (13) • Gravity-induced flow of flowable metal (7) into the second annular cavity (11) [8] Method according to claim 7, characterized by that the pressurized introduction of flowable metal (7) into the cavity (9) of the die-casting mold (4) via the first annular cavity (13) takes place before the gravity-induced inflow of flowable metal (7) into the second annular cavity (11). [9] Rotor (2) for an electrical machine (3), in particular produced by a method according to claim 7, with a first short-circuit ring (12) and a second short-circuit ring (14), wherein the first short-circuit ring (12) and the second short-circuit ring (14) are connected by axially extending slot bars (24), wherein the first short-circuit ring (14) and the second short-circuit ring (14) are substantially free of cavities. [10] Rotor (2) according to claim 9, characterized by that the rotor (2) is designed as a squirrel-cage rotor for an asynchronous machine.

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