EP3208013B1 - Method for casting a component, having a complex geometry having a mould with a segmented design - Google Patents

Description

Technical field of application

The present invention relates to a method for casting an electrical coil, in particular by means of die casting, in which a casting mold is used, of which at least one molded part is designed as a lost mold.

The production of complex geometries by casting is often limited or can only be implemented with considerable technical effort if the complex geometry places special demands on the casting tool. In many cases, components cannot be produced by casting due to their geometric requirements, since their geometry cannot be demolded, is prevented from demolding by undercuts or draft angles required for demolding or other casting requirements for the mold cannot be implemented. For example, electrical coils must be manufactured with a high surface quality and, if possible, without draft angles.

State of the art

A well-known method for casting electrical coils is the lost-mold investment casting method. Here, in the first process step, a positively formed model of the coil is made from wax or a polymer, for example, which is then coated with a non-solid investment material is poured around, which then sets and hardens. The model is melted out of the hardened investment material and, if necessary, the investment material is additionally fired in order to achieve maximum strength and stability. In this case, any remaining or unmelted residue from the model burns almost completely. The resulting cavity in the embedding compound is then filled with molten metal. After the molten metal has solidified, the investment compound is then destroyed in order to expose the cast part. With this technique, however, the casting of the positively formed model - usually in the injection molding process with wax in metallic permanent molds - already poses a technological challenge.

When using a permanent mold for the production of an electrical coil, either the use of a comb-shaped permanent mold or the use of slides that can be drawn is required to depict the individual conductors or windings of the coil. For this purpose, however, draft angles must be taken into account in order to demould the cast part from the casting mold in metal casting. If there are no draft angles and the cast part is actively formed or ejected from the casting tool, experience has shown that streaks, grooves and scratches form on the cast part, the so-called drawing marks or drawing marks. These adversely affect the surface of the casting.

The EP 2387135 A2 describes a method for manufacturing an electrical coil using casting technology, in which a negative mold containing the coil geometry is used as a lost mold or as a permanent mold. Sand or an embedding compound is proposed as the molding material for the lost form. The publication also mentions the use of multi-part segments that are joined before or during the forming process to produce the negative mold, but without going into more detail on this.

The DE 102012006572 A1 describes a process in which a lost casting mold is first produced as a block mold and then inserted as a mold insert into permanent metallic molds in order to produce the component by means of pressure die casting. A ceramic embedding compound is used as the mold material for the lost form.

From the DE 102012022331 A1 the use of a lost salt core is known in order to realize aluminum die-cast parts with undercuts. Salt cores of this type are produced in one piece from salts and salt mixtures and can be removed again after the casting has been cast.

The surface quality of the manufactured component is very important, especially in the manufacture of electrical coils. A smooth, defect-free or defect-free surface is required for the subsequent application of a homogeneous electrical insulation coating. In particular when applying paint to an insulating coating on the cast electrical coil, the so-called edge effect, which leads to non-homogeneous layer formation of the coating at the edges of the coil, must be avoided. In the As a rule, therefore, after the coil has been manufactured, an edge rounding must be carried out, which is carried out as post-processing of the cast part and thus causes additional work.

The object of the present invention is to specify a method for casting an electrical coil, in which the component is obtained with a high surface quality. The process should manage without draft angles in the casting mold used.

Presentation of the invention

The object is achieved with the method according to claim 1. Advantageous configurations of the method are the subject matter of the dependent patent claims or can be found in the following description and the exemplary embodiments.

In the proposed method, a mold is used, of which at least one molded part is designed as a lost mold. The at least one molded part designed as a lost mold is produced from a salt or a salt mixture. Furthermore, at least one outer part of the casting mold, which defines an external geometry of the component, or at least one inner part of the casting mold, which defines an internal geometry of the component, is composed of more than two mold segments.

Through this use of a mold composed of more than two mold segments, from which at least one molded part is produced as a lost mold from a salt or a salt mixture, complex components with undercuts and/or cavities with high surface quality can be produced, for example electrical coils. For example, the production of molded parts from salt by casting, in particular in the pressure die-casting process, enables the molded part to have very smooth surfaces. These smooth surfaces are also reflected in the component cast with them, which then has a correspondingly high surface quality. The one or more lost mold molded parts are preferably produced by casting, particularly preferably by means of die casting.

In a preferred embodiment, the entire casting mold is made entirely as a lost mold. The casting mold is preferably composed of more than two mold segments stacked on top of one another. Especially when manufacturing complex components with periodically repeating structures, several of the mold segments can be designed identically, i.e. as identical parts. This simplifies the production and also enables a corresponding scaling of the components to be produced, for example the number of coil turns using the example of an electrical coil, without having to produce different casting molds for this purpose. Of course, the form segments can also vary individually or be mixed and matched.

In a preferred embodiment, the mold segments in a modular manner up, in or plugged together and thus gradually build up a complete casting mold. The mold segments can be connected to one another, for example, via a groove-key connection or via a dowel pin connection.

In a further advantageous embodiment, the segment construction described above is not used as the entire casting mold, but as a mold insert for a permanent mold. In one configuration, the mold insert can specify the entire geometry of the component to be cast. In another embodiment, the outer part of the casting mold, which defines the outer geometry of the component to be cast, is designed as a permanent mold and the inner part through the mold insert as a lost mold in the segment construction described above.

The dismantling of the casting mold or the mold insert into individual mold segments enables flexible, cost-effective production of complex components, which also have a high surface quality through the use of salts or salt mixtures as molding material for the resulting lost mold. Each mold segment is preferably designed without undercuts and can accordingly be manufactured using simple manufacturing processes, preferably again using a casting process or also sintering or pressing processes. The mold segments have no draft angles in the area of the cavity, which is filled with molten metal to form the component. Thus, complex components with several plane-parallel, flat sub-areas or windings - in the geometry of electric coils - can be cast with high quality.

Filling of the composite mold can be accomplished via an exposed cavity structure, if present. However, the mold segments preferably have corresponding structures, so that after assembly, a sprue that can be used for casting is obtained. An overflow or a ventilation system can also be implemented in the same way. For the production of electrical coils, the sprue is preferably carried out on the (short) side of the end winding. This serves to reduce mechanical reworking. As already explained above, the assembled mold can either be used directly as a casting mold and filled with molten metal or used as a mold insert in a permanent mold and stabilized by the permanent mold.

The individual mold segments can be designed in such a way that the edges of the inner component edges are rounded. Corresponding post-processing of the component is then no longer necessary. When producing an electrical coil as a casting, for example, the mold segments can be dimensioned and manufactured in such a way that they each define one turn of the coil. Furthermore, when manufacturing an electric coil, the inner and outer parts of the mold can be made to interlock. This avoids burrs on the inside of the coil turns and moves them to the surface of these turns or to the area of the edge rounding.

Components with very complex geometries can be produced with the proposed method. The process for the production of an electrical coil enables the realization of edge roundings on the inside when using a permanent mold in connection with a mold insert as a lost molded part, the realization of edge roundings on the outside of the component in connection with the elimination of draft angles when using a permanent mold or of permanent mold elements as well as the omission of draft angles in combination with a targeted shifting of the burr formation. Due to the use of lost molded parts as lost cores or mold inserts, no draft angles are required. The method has cost advantages in complex systems, since complex slide technology is not required in many configurations.

Brief description of the drawings

Fig. 1

ein Beispiel für den Aufbau einer mit dem Verfahren gießtechnisch herzustellenden elektrischen Spule;

Fig. 2

ein Beispiel für vier verlorene Formsegmente zur Bildung der Gießform oder des Formeinsatzes;

Fig. 3

die zusammengesetzten Formsegmente der Figur 2;

Fig. 4

einen Schnitt durch die zusammengesetzten Formsegmente der Figur 3;

Fig. 5

ein weiteres Beispiel für ein einzelnes Formsegment;

Fig. 6

ein Beispiel für zusammengesetzte Formsegmente der Figur 5;

Fig. 7

ein Beispiel für eine Dauerform, in die die Formsegmente der vorangegangenen Figuren eingesetzt werden können;

Fig. 8

die Dauerform der Figur 7 mit einigen eingesetzten Formsegmenten;

Fig. 9

ein Beispiel für die geometrische Ausgestaltung der Formsegmente im Querschnitt;

Fig. 10

ein weiteres Beispiel für die geometrische Ausgestaltung der Formsegmente im Querschnitt;

Fig. 11

ein weiteres Beispiel für die geometrische Ausgestaltung der Formsegmente im Querschnitt;

Fig. 12

ein Beispiel für die Nutzung einer Dauerform zur Festlegung der äußeren Geometrie des Bauteils in Verbindung mit einem verlorenen Kern;

Fig. 13

ein Beispiel für eine Ausgestaltung des verlorenen Kerns als Weiterbildung der Ausgestaltung der Figur 12;

Fig. 14

ein Beispiel für eine Ausgestaltung der Dauerform als Weiterbildung der Ausgestaltung der Figur 12;

Fig. 15

ein weiteres Beispiel für eine Ausgestaltung der Dauerform als Weiterbildung der Ausgestaltung der Figur 12;

Fig. 16

ein Beispiel für eine Ausgestaltung der Dauerform und des verlorenen Kerns als Weiterbildung der Ausgestaltung der Figur 12;

Fig. 17

ein weiteres Beispiel für eine Ausgestaltung der Dauerform und des verlorenen Kerns als Weiterbildung der Ausgestaltung der Figur 16;

Fig. 18

ein weiteres Beispiel für eine Ausgestaltung der Dauerform und des verlorenen Kerns als Weiterbildung der Ausgestaltung der Figur 16;

Fig. 19

ein weiteres Beispiel für eine Ausgestaltung der Dauerform und des verlorenen Kerns als Weiterbildung der Ausgestaltung der Figur 16;

Fig. 20

ein weiteres Beispiel für eine Ausgestaltung der Dauerform und des verlorenen Kerns als Weiterbildung der Ausgestaltung der Figur 12;

Fig. 21

ein weiteres Beispiel für eine Ausgestaltung der Dauerform und des verlorenen Kerns als Weiterbildung der Ausgestaltung der Figur 20;

Fig. 22

ein weiteres Beispiel für eine Ausgestaltung der Dauerform und des verlorenen Kerns als Weiterbildung der Ausgestaltung der Figur 20;

Fig. 23

ein weiteres Beispiel für eine Ausgestaltung der Dauerform und des verlorenen Kerns als Weiterbildung der Ausgestaltung der Figur 20; und

Fig. 24

ein weiteres Beispiel für eine Ausgestaltung der Dauerform und des verlorenen Kerns als Weiterbildung der Ausgestaltung der Figur 12.

The proposed method is explained in more detail below using exemplary embodiments in conjunction with the drawings using the production of an electrical coil. Here show:

1

an example of the structure of an electrical coil to be produced by casting using the method;

2

an example of four lost mold segments to form the mold or mold insert;

3

the compound form segments of the figure 2 ;

4

a section through the assembled form segments of figure 3 ;

figure 5

another example of a single shape segment;

6

an example of compound shape segments of the figure 5 ;

7

an example of a permanent mold into which the mold segments of the previous figures can be inserted;

8

the permanent form of figure 7 with some inserted form segments;

9

an example of the geometric configuration of the mold segments in cross section;

10

another example of the geometric configuration of the mold segments in cross section;

11

another example of the geometric configuration of the mold segments in cross section;

12

an example of using a permanent mold to define the external geometry of the component in conjunction with a lost core;

13

an example of a design of the lost core as a further development of the design of figure 12 ;

14

an example of an embodiment of the permanent form as a further development of the embodiment of figure 12 ;

15

another example of an embodiment of the permanent form as a further development of the embodiment of figure 12 ;

16

an example of an embodiment of the permanent mold and the lost core as a further development of the embodiment of figure 12 ;

17

another example of an embodiment of the permanent form and the lost core as a further development of the embodiment of figure 16 ;

18

another example of an embodiment of the permanent form and the lost core as a further development of the embodiment of figure 16 ;

19

another example of an embodiment of the permanent form and the lost core as a further development of the embodiment of figure 16 ;

20

another example of an embodiment of the permanent form and the lost core as a further development of the embodiment of figure 12 ;

21

another example of an embodiment of the permanent form and the lost core as a further development of the embodiment of figure 20 ;

22

another example of an embodiment of the permanent form and the lost core as a further development of the embodiment of figure 20 ;

23

another example of an embodiment of the permanent form and the lost core as a further development of the embodiment of figure 20 ; and

24

another example of an embodiment of the permanent form and the lost core as a further development of the embodiment of figure 12 .

Ways to carry out the invention

figure 1 shows an example of an electrical coil 10 in the upper part of the figure, as it can be cast with the proposed method. The lower part of the figure figure 1 FIG. 12 shows the coil 10 again in an exploded form, just for illustration, around the individual turns 11 to be able to recognize better. For the casting production of such a coil with the proposed method, a mold insert for a metallic permanent mold is used in the present example, which is formed from lost mold segments stacked on top of one another. The individual mold segments 1 are made from a salt or a salt mixture, preferably in a casting process (particularly pressure-assisted casting) or in a pressing or sintering process. Suitable techniques are known to the person skilled in the art from the prior art, for example also from that already mentioned DE 102012022331 A1 , known. The production of these mold segments 1 by casting from a salt or a salt mixture results in a high surface quality of the segments, which is transferred to the windings of the electrical coil to be produced.

In the example of figure 2 four such mold segments 1 are shown, which are stacked on top of each other to form the mold insert. They can, for example, be connected to one another via a groove and feather key connection, not shown in the figure, in order to ensure correct and true-to-position assembly of the mold segments. figure 3 shows the mold segments 1 stacked on top of each other, figure 4 a cut through this stack of shape segments. figure 5 shows an example of a mold segment 1, which has holes 12 for a dowel pin connection and lateral openings 14 for filling and/or venting. figure 6 FIG. 12 again shows a plurality of mold segments 1 stacked one on top of the other with corresponding openings for filling and/or venting, wherein alignment pins 13 can be seen in this example.

The assembled mold segments 1 are then placed in a permanent mold 2 and filled with molten metal. An example of such a permanent form 2 is in figure 7 shown. The melt is guided into the cavity of the mold segments and vented via a gating and venting system 3a, 3b suitable for the casting process. In the example of figure 7 this gating and ventilation system 3a, 3b is implemented in the permanent mold and can optionally also be shown in the mold segments 1 (cf. figure 5 and 6 ). figure 8 shows an example of the permanent mold 2 with the mold segments 1 inserted therein.

In order to specifically shift the formation of burrs during casting to the outer edge of the cast part, the cavity for the individual winding to depict the cast part can only be introduced into the mold segment 1 on one side, as is the case in the example in FIG figure 9 is shown. This figure shows how the Figures 10 and 11 , Four stacked mold segments 1 in cross section, in which the cavity 4 for the formation of the coil windings 11 can be clearly seen.

If the burr formation is to be shifted to the middle of the cast part, the cavity 4 is introduced on one side in the upper and lower side of the mold segment 1 to depict the cast part, as shown in figure 10 is shown as an example.

For the production of electrical coils, the burr formation is preferably targeted at the level of Edge rounding of the casting relocated. For this purpose, the cavity 4 for imaging the cast part is made with a larger proportion in the upper side and with a smaller proportion in the lower side of the respective mold segment 1 with a corresponding mold offset. this is in figure 11 shown as an example.

The in the Figures 2 to 11 Mold segments 1 shown can also be used without an outer permanent mold, so that they form the complete casting mold. However, using an external permanent shape is advantageous for reasons of stability.

In the embodiments described below, the cavity for the production of the complex casting geometry by casting is formed by the combination of metallic permanent mold elements, which define an outer shape of the casting, with lost mold segments, which define the inner geometry of the casting.

In figure 12 a combination of an inner core 5 made of lost core material (salt core) with outer permanent mold elements 6, 7 is shown, which are preferably made of two mold halves of the permanent mold or as pullable slide elements. The exposed inner cavity 4 forms the casting. The one in the figure 12 The arrows shown indicate the structure of the permanent mold elements 6, 7 as a large number of slide elements that can be pulled.

In a preferred embodiment, the permanent mold elements 6, 7 and the inner core 5 are so designed so that an edge rounding of the casting - shown on the inside in the inner lost core 5 and on the outside shown by the permanent mold elements 6, 7 - is obtained. The formation of burrs on the inside is determined at the height of the edge rounding. This is achieved by the positioning of the parting plane between the inner core 1 and permanent mold elements 6, 7, as is also the case in FIG figure 13 is shown. A burr formation on the outside is also selected at the level of the edge rounding, produced by one-sided cavity formation in the permanent mold element, as is shown in FIG figure 14 is illustrated.

figure 15 shows an example where the burr formation on the outside is variably positioned along the edge rounding. For this purpose, a two-sided cavity formation in the permanent mold elements 6, 7 is selected.

At the in figure 16 In the exemplary embodiment shown, part of the cavity for the turns of the electric coil is formed by the inner core 5 . The cavity 4 is formed proportionately by the inner core 1 and by the permanent mold elements 6, 7, as in FIG figure 16 is shown. Here, too, the permanent mold is again designed with slide elements that can be pulled. However, two mold halves with a corresponding inner contour can also be used. figure 17 shows the design of the figure 16 again with a detail. The edge rounding of the cast part is achieved on the inside by the lost core 1 and imaged on the outside by the permanent mold elements 6,7. As a result, there is no burr formation on the inside, but on the top or bottom of the conductor or winding surface. This burr formation is caused by the positioning of the parting plane between the inner core 5 and the permanent mold element, as is shown in figure 17 is illustrated.

Due to the configuration of the permanent shaped elements 6, 7, the formation of burrs on the outside at the level of the edge rounding can be produced by one-sided cavity formation in the permanent shaped element. this is in figure 18 illustrated.

figure 19 shows an embodiment in which the formation of burrs on the outside is variably positioned along the edge rounding. This is achieved by two-sided cavity formation in the permanent mold elements 6, 7.

The design of figure 20 shows an inner core 1 made of lost core material with raised webs that engage in the cavities of the outer permanent mold elements 6, 7. The permanent mold elements can in turn consist of two mold halves or—as in the present example—be designed as slide elements that can be pulled. The exposed inner cavity 4 in turn forms the cast part. The design of figure 20 with the raised webs on the inner core 5 has the advantage that the permanent shaped elements 6, 7 engage in the lost core 5 (or vice versa) and thus both support each other.

figure 21 shows a further development of this embodiment, in which the edge rounding of the cast part is reproduced on the inside by the webs of the inner lost core 1 and on the outside by the permanent mold element 6, 7. A two-sided burr formation on the inside is produced by pushing the web 8 from the inner lost core 5 into the cavity of the permanent mold elements 6, 7. This burr formation can occur on the outside at the level of the edge rounding if a one-sided cavity formation in the permanent mold elements 6, 7 is chosen. this is in figure 22 illustrated. The formation of burrs can, as in figure 23 shown, can also be variably positioned along the edge rounding if a two-sided cavity formation is selected in the permanent mold elements 6, 7.

figure 24 Finally, FIG. 1 shows an embodiment in which the expendable core 5 has an integrated insert 9 which is integrated during the manufacture of this expendable core 5. After the lost core 5 has been cast, the integrated insert 9 can be pulled out and destroys or damages the lost core in order to demould it more easily. This insert 9 can be a mechanically stable element made of steel, iron, plastic, etc., or it can be a wire, a rope or a fabric. The insert 9 is designed in such a way that it leads to damage or destruction of the core 5 when it is pulled out of the lost core 5 .

The proposed method can be used with different casting techniques for metal casting, for example die casting, the semi-solid method/thixocasting, low-pressure casting, gravity die casting or metal injection molding. For the casting of the component, the casting mold is filled with a metallic melt, preferably with a melt of aluminum, copper, zinc, magnesium, steel, iron, cast iron and their alloys. For better infiltration and filling with molten metal, the casting mold can be thermally heated before casting. The molded parts designed as a lost mold can be designed in such a way that they are blown up or broken open by the solidifying molten metal after being filled with the molten metal due to thermal and/or mechanical stresses.

Reference List

1

shape segments

2

permanent form

3a

gating system

3b

ventilation system

4

cavity

5

internal lost core

6

permanent feature

7

permanent feature

8th

elevated jetty

9

integrated insert

10

electric coil

11

coil winding

12

Hole

13

dowel pin

14

side openings

Claims (16)

1. Method for casting an electric coil (10), in particular by means of die casting, in which a cast mould is used, of which at least one mould part (l, 5) is embodied as a lost mould, wherein

   - the at least one mould part (l, 5) embodied as lost mould is produced from a salt or a salt mixture, and

   - at least an outer part of the cast mould, by which an external geometry of the coil (10) is defined, or at least an inner part of the cast mould, by which an internal geometry of the coil (10) is defined, is composed from more than two mould segments (1) stacked one on top of the other, each of which defines one winding of the coil (10).
2. Method according to Claim 1, characterized in that the cast mould is produced entirely as a lost mould.
3. Method according to Claim 1, characterized in that the cast mould is formed from a permanent mould with a mould insert accommodated therein, wherein the mould insert is produced entirely as a lost mould.
4. Method according to Claim 2, characterized in that the cast mould is composed from the more than two mould segments (1) stacked one on top of the other.
5. Method according to Claim 3, characterized in that the mould insert is composed from the more than two mould segments (1) stacked one on top of the other.
6. Method according to any one of Claims 1 to 5, characterized in that the mould segments (1) are designed in such manner that they do not include any draft angles.
7. Method according to Claim 1, characterized in that the outer part of the cast mould is embodied as a permanent mould (2), and the at least one inner part is produced as a lost mould.
8. Method according to Claim 7, characterized in that the inner part is composed from the more than two sub-segments stacked one on top of the other.
9. Method according to Claim 7 or 8, characterized in that the inner part is designed in such manner that an edge rounding is achieved on inner coil edges.
10. Method according to any one of Claims 7 to 9, characterized in that the inner and the outer parts of the cast mould are designed in such manner that they interlock.
11. Method according to any one of Claims 1 to 10, characterized in that the at least one mould part (1, 5) embodied as lost form is produced from the salt or salt mixture in a casting operation, in particular by die casting.
12. Method according to any one of Claims 1 to 11, characterized in that the mould segments (1) are selected and dimensioned such that they do not include any undercuts.
13. Method according to any one of Claims 1 to 12, characterized in that several of the mould segments (l) are of identical design.
14. Method according to any one of Claims 1 to 13, characterized in that the mould segments (1) are connected to each other via a groove-feather key joint or a dowel pin joint.
15. Method according to any one of Claims 1 to 14, characterized in that the mould segments (1) are designed in such manner that an edge rounding is achieved on edges of the coil (10).
16. Method according to Claim 15, characterized in that the mould segments (1) are designed in such manner that burrs created on the coil (10) as a result of the segment construction method are located in the region of the edge rounding.

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