METHOD AND TOOL FOR MAKING A COIL

Description

[0001] Wound coils are used in electrical machines. These coils only partially fill the available installation space. This results in a lower power or torque density of the electrical machines relative to their weight or installation space.

[0002] Cast Al and Cu coils can compensate for this disadvantage, but to date no processes suitable for series production of cast Al and Cu coils or cast coils made of Al and Cu alloys in permanent molds with sufficient service life are known.

[0003] To increase the power density or torque density of electrical machines, complex, often manually manufactured coils are wound to slightly improve the fill ratio compared to series production processes. Wire of the same cross-section is used across the winding height. In conventional electrical machines, the coil turns, which are arranged one on top of the other from the inside out, impair heat dissipation and lead to greater heating of the coils, thus necessitating a limitation of the maximum current density relative to the winding cross-section.

[0004] Cast Al and Cu coils or cast coils made of Al and Cu alloys are known per se, but are not currently produced in permanent molds, but in lost form such as in investment casting or in a lost foam process or by using salt cores that define the contour and prevent direct contact of the melt with the tool.

[0005] For the production of a wide variety of geometries, a contour-defining mold is used according to the state of the art. For complex geometries, cores or slides are inserted in addition to the mold, which has one or more divisions for easy part removal.

[0006] In the production of copper components, the high casting temperature, above 1100°C, places increased demands on the tool and core. The thermal stress, and especially the temperature shock during mold filling, cause rapid aging and damage to conventional materials. This aging manifests itself as erosion and cracks in the tool or core. These cracks, in turn, are evident as raised burrs on the surface of the cast components. As a result, tool life is very short, component quality is severely compromised, and considerable rework is necessary. Overall, economical results are hardly achievable with conventional tool steels.

[0007] Previous tool concepts always resulted in geometrically complex permanent molds or the additional use of movable permanent or non-permanent (lost) slides or cores. These molds could only be used in laboratory operations because they required significant maintenance effort and also resulted in high scrap rates.

[0008] EP 2 819 276 A2 discloses a geometrically modified model geometry that enables a simply formed, two-part permanent mold, for example, for a die-casting process. This is achieved by rotating the windings by 180°, thus significantly reducing the geometric complexity of the coil. However, after the casting process, a highly complex forming process step is required to achieve the coil geometry in the installed state. The geometric simplification is thus expensively achieved through a further, complex downstream process step.

[0009] The document DE 10 2012 212 637 A1 shows a coil for an electrical device, in particular an electrical machine, for arranging around at least one first core conducting a magnetic field with a coil longitudinal axis running in the direction of the magnetic field, wherein the coil has a plurality of turns cast from an electrically conductive coil material and the turns and / or turn sections have cross-sectional areas of different sizes and / or different shapes depending on their position in the coil longitudinal direction.

[0010] The document "Casting production of coils for electrical machines", by M. Gröninger et al., ELECTRIC DRIVES PRODUCTION CONFERENCE (EDPC), 2011 1ST INTERNATIONAL, IEEE, September 28, 2011, refers to the casting production of coils.

[0011] The document DE 10 2010 020897 A1 relates to a method for producing an electrotechnical coil with one or more winding(s), wherein a negative mold containing a coil geometry, in particular a lost mold or a permanent mold, is provided or produced, wherein a coil material suitable for forming the winding(s), in particular an electrically conductive metal, is poured in liquid form into this negative mold, and wherein this coil material is solidified and / or this coil material is allowed to solidify under controlled conditions.

[0012] The invention is based on the object of overcoming the described difficulties and disadvantages and of proposing a process suitable for series production, with which coils of the desired geometry, which are intended to utilize the available space as effectively as possible, can be produced with the least possible effort. The invention is further based on the object of offering a coil that can be manufactured easily and with little effort, which requires a comparatively small amount of space, and of proposing a suitable tool for producing such a coil or for carrying out a corresponding manufacturing process.

[0013] This object is achieved by a method according to claim 1 or by a casting tool according to claim 13. Advantageous embodiments and further developments of the invention result from the features of the subclaims.

[0014] In the proposed method for producing a coil, a semi-finished product in the form of an elongated conductor is first formed by casting in a cavity of a casting tool, and the coil is then formed by deforming the semi-finished product after the semi-finished product has been removed from the mold. According to the invention, the cavity of the casting tool is shaped such that the shape of the semi-finished product can be derived from a shape of the finished coil by stretching along a longitudinal axis of the coil and / or by curving this longitudinal axis. During forming to form the coil, the semi-finished product is bent and compressed accordingly such that coil turns already present in the semi-finished product are brought closer to one another, at least in some regions, during forming and arranged along the longitudinal axis of the finished coil, wherein the conductor is not twisted or bent by more than a right angle along the course of each individual turn during forming.

[0015] The advantages of this process arise, on the one hand, from the preferably undercut-free shape of the cast semi-finished product, which enables a simple construction of the casting tool without lost tool parts and makes demoulding easy, and, on the other hand, from the relatively uncomplicated forming by which this semi-finished product is converted into the shape of the finished coil.

[0016] The semi-finished product is formed in the shape of a rosette, so that the windings are arranged in a fan-out arrangement around a center before forming. The cavity of the casting tool corresponding to the shape of the semi-finished product can be filled from the center during casting, so that one or more sprues are formed centrally in the rosette. This advantageously results in short flow paths for the material forming the semi-finished product or the conductor of the coil. In particular, the cavity of the casting tool can be filled centrally from below during formation of the semi-finished product.

[0017] In particularly simple designs, the cavity can be formed by just two halves of the casting tool. The semi-finished product can be demolded by separating the tool halves in a direction where the semi-finished product is free of undercuts, preferably in the direction of the rosette axis. This typically does not require additional mold cores, slides, or lost mold parts. In any case, the casting tool can be a reusable permanent mold, which makes the process economical and suitable for series production.

[0018] The material used to cast the semi-finished product and form the conductor will typically be a metal with good conductivity. In particular, the semi-finished product can be formed from aluminum or copper, or an alloy containing aluminum or copper.

[0019] To form the coil, the semi-finished product is typically plastically formed, preferably without melting the material forming the semi-finished product.

[0020] To form the semi-finished product, the coils can be pushed over a guide rod or mandrel, at the end of which a shoulder can be arranged to serve as a stop for the first coil. Behind the resulting coil, another tool part can be pushed onto the guide rod or mandrel, which can be used to compress the coils.

[0021] Typically, the conductor is formed with a flat cross-section, with a smaller diameter along the coil's longitudinal axis and a larger diameter in a direction perpendicular to the coil's longitudinal axis. This allows for a particularly space-saving coil design.

[0022] Accordingly, a coil manufactured by a method of the type described is advantageous. Such coils are suitable for use in electrical machines, especially electric motors. The advantages of the coil manufactured in this way are particularly evident in applications where space- and weight-saving design is important, for example, in electric motors in aircraft, where appropriately equipped electric motors can be used, for example, to drive rudders, flaps, or landing gear components.

[0023] A casting tool suitable for carrying out the described method and for producing a corresponding coil or a corresponding semi-finished product comprises two tool halves enclosing a cavity without undercuts in a demolding direction. The cavity forms a sequence of turns arranged in a rosette shape around a center, the demolding direction corresponding to the direction of an axis of the rosette. This casting tool is preferably configured to fill the cavity from the center.

[0024] Embodiments of the invention are explained below with reference to the figures.

[0025] It shows Fig. 1 A frontal view of two halves of a casting tool, Fig. 2 a perspective view of this casting tool with both tool halves in a closed state, Fig. 3in perspective view a semi-finished product produced by casting in this casting tool, Fig. 4 a view of this semi-finished product, Fig. 5 each in perspective view two parts of a forming tool and a coil produced from the semi-finished product in three successive stages of a forming process, namely on the left in an exploded view each individually and on the right in the picture with turns of the semi-finished product or the resulting coil pushed onto a guide rod or mandrel, and Fig. 6 Also in perspective view, a variant of the forming tool in which the guide rod or mandrel is curved.

[0026] In Fig. 1 A lower mold half 1 of a casting tool is shown. A rosette-shaped cavity 2 of this casting tool is visible, which can be closed by connecting the lower mold half 1 with an upper mold half 3.

[0027] The complete closed casting tool is in Fig. 2 This also shows an inlet opening 4 through which the cavity 2 can be filled, specifically from the center of a rosette formed by the cavity. This casting mold is a reusable permanent mold.

[0028] In the Figures 3 and 4 A semi-finished product 5 is shown, which is formed by casting in this casting tool and can be made of aluminum, copper, or an aluminum- or copper-containing alloy. The semi-finished product 5 is an elongated conductor, which already forms turns of a coil that will later be formed therefrom. The semi-finished product 5 is formed in the shape of a rosette according to the shape of the cavity 2, so that the turns are arranged fanned out around the center. The Figures 3 and 4The semi-finished product 5 shown is free of undercuts in the direction of an axis of the rosette and can therefore be demolded by separating the tool halves 1 and 3 in the direction of this axis after casting and curing of the semi-finished product 5. This direction is in Fig. 2 illustrated by two arrows. The mold requires neither a mold core nor any slides or lost mold parts.

[0029] The semi-finished product 5 is plastically formed – without melting the material forming the semi-finished product or the conductor – in order to form the aforementioned coil 6. For this purpose, the semi-finished product 5 is bent and compressed in such a way that the turns of the resulting coil 6 are moved towards one another during the forming process, i.e., are brought closer together, and are arranged along a longitudinal axis of the finished coil 6. In the process, the conductor is twisted and bent by no more than approximately 20° along the course of each individual turn. This is possible because the cavity 2 of the casting tool is shaped in such a way that the shape of the semi-finished product 5 formed therein can be derived from the later shape of the finished coil 6 by stretching along the longitudinal axis of the coil 6 and by curving this longitudinal axis.

[0030] As in Fig. 5As illustrated, the forming of the semi-finished product 5 to form the coil 6 can be carried out by means of a forming tool that has a guide rod or mandrel 7, at the end of which a shoulder 8 is arranged. The turns of the semi-finished product 5 can be pushed over this guide rod or mandrel 7 for forming, which is threaded into the turns for this purpose. The shoulder 8 serves for a first turn. Behind the semi-finished product 5, from which the coil 6 is thus formed, a further tool part 9 can be pushed onto the guide rod or mandrel 7 in order to press the turns together and give the coil 6 its final shape, in which it fills only a very small volume.

[0031] In Fig. 5The semi-finished product 5 is already shown in a straightened form, in which the rosette is bent open and the windings are arranged along the longitudinal axis of the coil 6 and are aligned with each other. A modification of the forming tool, with which the straightening of the semi-finished product 5 or the rosette can be simplified and completed when the windings are pressed together, is shown in Fig. 6 shown. The guide rod or mandrel 7 is curved in this modification.

[0032] The conductor initially forming the semi-finished product 5 and later the coil 6 has a flat cross-section which has a smaller diameter in the direction of the longitudinal axis of the coil 6 and a larger diameter in a direction perpendicular to the longitudinal axis.

[0033] The coil 6 can be used in an electrical machine, for example, an electric motor. Such an electric motor can be used in an aircraft, e.g., as a drive for a rudder, a flap, or a retractable landing gear.

[0034] Due to the typically symmetrical arrangement of the casting, in the case of the described embodiment, the semi-finished product 5, production can also be carried out by centrifugal casting. For multiple occupancy, several cavities can be arranged one behind the other.

[0035] In a conventional procedure with two mold halves, the cavity in low-pressure casting can be filled centrally from below, and the gate can be closed mechanically or rapidly solidified through a correspondingly thin-walled design and / or temperature control in the gate area to achieve closure in the gate area. A punch can then be inserted from above into the still-molten center, and the contour can be refilled under the pressure of the punch. The laminar mold filling of low-pressure casting is then combined with pressure-assisted refilling, i.e., pressure die casting.

[0036] The casting machine can be designed so that the center of the cavity consists of a crucible into which a metallic granulate is filled, which is then melted inductively. After the crucible has been melted, The mold and crucible are rotated, whereby centrifugal force and the appropriate crucible design force the melt over the crucible rim into the cavity. Or a punch with recesses for the gate areas is inserted into the mold from above, pressing the crucible wall downward. The bottom of the crucible remains in its position. By pressing the crucible wall downward, the gates of the contour to be cast are exposed, and the melt in the crucible is pressed into the cavity through the punch openings corresponding to the gates.

[0037] The invention described here using various exemplary embodiments proposes a method for reducing the complexity of coils during their manufacture, whereby they can be manufactured in geometrically simple, two-part permanent molds. This is achieved through a combination of a casting process and subsequent plastic pre-deformation of the coil, which considerably simplifies the manufacturing process. Thus, the geometry of the coil is virtually pulled apart for tool construction and arranged in a circle (rosette-like) in order to realize a geometry that is free of undercuts and can be inserted into a two-part tool, as shown in the Figures 1 to 4 is illustrated.

[0038] After the casting process, the coil is plastically deformed again to maintain the geometric assembly state. The sprue is positioned in the center of the geometry, resulting in symmetrical mold filling and the shortest possible flow paths. Just as in the case illustrated in the figures, where deformation occurs along the long side of the coil, deformation along the short side, the winding head, is also possible. The geometry can be used in various casting processes, in particular gravity sand casting, low-pressure sand casting, gravity die casting, low-pressure die casting, and also die casting when using a central sprue. Likewise, a model for investment casting can be injected from wax or plastic in the development and foamed for the lost foam process.Furthermore, the central location of the sprue allows for stacked casting, in which multiple coil tools can be stacked on top of each other in all of the aforementioned processes and cast in a single casting. The tool inserts can be made of conventional tool materials or made of ceramic materials specifically designed for the high temperature stresses encountered when processing copper and the severe tool attack associated with aluminum.

[0039] The production of a coil described here is characterized by the simple tool geometry, the resulting simple production of a semi-finished product for the coil and the simple subsequent reworking. The sprue area can be used for the handling processes. The sprue stiffens the coil geometry and can be removed after the main downstream processes. With optimal gate positions, e.g. in the middle of the turn or at the edge, the gate can be removed as a last step before forming and any remaining burrs can be tolerated. Likewise, the entire mold geometry can be designed so that possible burrs can be tolerated in order to simplify production. For this purpose, the casting tool can, for example, be designed so that the burrs created during demolding end up in provided cavities on the surface of an adjacent turn in the finished coil.

[0040] After the developed geometry has been produced, it is subjected to further process steps such as deburring, polishing, cleaning, grinding, and coating. The geometry proves to be advantageous here due to the improved accessibility provided by the pre-formed coil. For necessary handling of the semi-finished product, positioning, fixing, and handling aids, etc., can be incorporated into the tool contour during the manufacturing process. These aids can be removed as needed or used for further processing. The second key advantage of this geometry variant is the simple forming process after casting by inserting a guide rod into the core of the coil and directly forming the coils onto one another.

[0041] This is achieved by threading it onto a mandrel with a shoulder, as in the Figures 5 and 6shown. With the help of this construction, the coil is deformed or brought back into its installed state. The forming process and calibration can be combined. The guide rod can be thin at the beginning to simplify threading and then becomes thicker towards the pressure-applying contact surface – i.e., shoulder 8 – where it corresponds to the final contour of the interior of the winding. Ideally, the final contour of the interior has at least the same height as the overall coil to be achieved, see Figures 5 and 6 .

[0042] The use of the manufacturing process proposed here can also be verified in the finished product. Simple visual examinations of the castings and metallographic analysis provide information about the manufacturing history of the castings. In particular, the plastically formed areas in the winding and winding head can be metallographically verified.

Claims

1. A method for producing a coil (6), in which, by way of casting, a semi-finished product (5) in the form of an elongate conductor is formed in a cavity (2) of a casting mould and, following a demoulding of the semi-finished product (5), the coil (6) is formed by reshaping this semi-finished product (5), wherein the form of the semi-finished product (5) is derivable from a shape of the finished coil (6) by stretching along a longitudinal axis of the coil (6) and / or by bending this longitudinal axis, wherein the semi-finished product (5) is bent and compressed during the reshaping, such that turns of the coil (5) already present in the semi-finished product (5) are brought closer towards one another, at least in regions, during the reshaping and are brought into an arrangement along the longitudinal axis of the finished coil (6), wherein the conductor, during the reshaping, is twisted or bent by no more than a right angle in a course of each individual turn, wherein the semi-finished product (5) is formed as a rosette, so that the turns are arranged fanned out around a centre prior to the reshaping.

2. The method according to claim 1, characterised in that, during the casting of the semi-finished product (5), the cavity (2) corresponding to the shape of the semi-finished product (5) is filled out from the centre.

3. The method according to any one of claims 1 or 2, characterized in that the cavity (2) is formed by two mould halves (1, 3) of the casting mould and the semi-finished product (5) is demoulded by separating these mould halves (1, 3) in a direction in which the semi-finished product (5) is free from undercuts.

4. The method according to any one of claims 1 to 3, characterised in that the casting mould is a permanent mould.

5. The method according to any one of claims 1 to 4, characterised in that the semi-finished product (5) is formed from aluminium or copper or an alloy that contains aluminium or copper.

6. The method according to any of claims 1 to 5, characterised in that the semi-finished product (5) is plastically reshaped to form the coil (6).

7. The method according to any one of claims 1 to 6, characterised in that the turns are slid over a guide rod or mandrel (7) to reshape the semi-finished product (5).

8. The method according to any one of claims 1 to 7, characterised in that the conductor has a flat cross-section, which in the direction of the longitudinal axis of the coil (6) has a smaller diameter and in a direction perpendicular to the longitudinal axis of the coil (6) has a larger diameter.

9. The method according to any one of claims 1 to 8, characterised in that the semi-finished product (5) is cast in a low-pressure and / or highpressure casting method and / or in a centrifugal casting or gravity casting method.

10. The method according to any one of claims 1 to 9, characterised in that, when forming the semi-finished product (5), following a first filling of the cavity (2) at a lower first pressure, a gate of the casting mould is closed mechanically or by accelerated solidification in a gate region and / or a ram is introduced into a centre of the casting mould that is still filled with molten liquid and the cavity (2) is topped up under a higher second pressure generated by the ram.

11. The method according to any one of claims 1 to 10, characterised in that a crucible arranged centrally in the casting mould is filled with a metal granular material, which is melted there and is used to fill the cavity (2) connected to the crucible.

12. The method according to claim 11, characterised in that the granular material is inductively melted in the crucible and / or is pressed into the cavity (2) by rotation of the crucible or by a pressure of a ram.

13. A casting mould for carrying out a method according to any one of claims 1 to 12, comprising two mould halves (1, 3), which enclose a cavity (2) which is free from undercuts in a demoulding direction, wherein the cavity (2) forms a sequence of turns which are arranged fanned out in the form of a rosette around a centre, wherein the demoulding direction corresponds to a direction of an axis of the rosette.