EP3600718B1 - Casting core and method for the production thereof - Google Patents

Description

The invention relates to a casting core which has the basic shape of a hollow body, the casting core being formed from a molding material which consists of a mixture formed from a molding sand and a binder and optionally from additives added to adjust its properties.

Casting cores of the type in question are used for the casting production of cast parts from a metal melt. The casting cores form cavities, such as channels or chambers, in the respective cast part. These cavities can be provided to save weight. As a rule, however, a fluid flows through them in practical use.

In order to be able to remove the casting cores from the cast part after the casting material has solidified, they are used as so-called "lost cores". To produce them, the molding material mixture mixed in the manner explained above is introduced ("shot") into the molding cavity of a core-shooting device at high pressure. The flowability of the molding material, the shooting pressure and the positions at which the molding material is introduced into the mold cavity of the machine provided for manufacturing the cores are coordinated so that complete mold filling is achieved even with particularly fine-grained cores. After the core shooting, the cores are solidified by applying heat or gassing with a reaction gas so that they are out removed from the core shooter and inserted into the respective casting mold, where they can withstand the stresses that occur when the molten metal is poured off.

Typical examples of cast parts in which such channels and cavities are molded using casting cores are housings for drive machines that have to be cooled during operation. In such machine housings, so-called "cooling jackets" are generally provided, i.e. a system of ducts that surround the area of the machine in which heat is generated during operation as a result of energy conversion. In order to ensure an optimal flow through the critical areas of the machine and in this way a maximum cooling effect with small dimensions, the highest demands are placed on the quality of the surfaces of the channels represented by the casting core.

The particular challenge in the production of casting cores of the type in question is that the casting cores usually do not form a solid body, but are often perforated, so that their walls form finely divided structures, the islands, in which larger amounts of the Core material are gathered, larger and thicker webs, finely branched webs, larger bridges and other filigree shaped elements. Due to the circumferentially closed basic shape of the casting cores, typically circular or ellipsoid in cross-section, with such finely divided casting cores demolding the cores from the core shooting machine is only possible with great effort. Complex slide designs and the like must be provided in order to be able to separate the shaping components of the core shooting machine from the finished core despite the large number of undercuts and openings. Apart from the high costs that such a complex machine entails, this effort complicates the large-scale, rapidly clocked series production of casting cores of the type in question.

From the US 2011/204205 A1 a casting core for the manufacture of a turbine blade is known. This casting core is formed from a molding material that is mixed, for example, from ceramic particles and a suitable binder. The casting core is composed of two subsegments, which have form elements that interact with each other in a form-fitting manner on those edge sides with which they abut, via which the adjacent part segments in two spatial directions, namely a direction normal to the outside of the segments and a transverse direction in the longitudinal direction of the segments aligned direction, are fixed immovably with respect to one another by positive locking.

Likewise from the EP 1 857 198 A1 a casting core is known which is composed of subsegments which are formed from a molding material and, when the casting core is assembled, are positively coupled to one another via interlocking projections and recesses formed on them.

Against the background of the prior art explained above, the task has arisen to design a casting core that corresponds in its basic shape to a hollow body and that enables simple manufacture.

The invention has achieved this object by a casting core which has at least the features specified in claim 1.

Advantageous embodiments of the invention are specified in the dependent claims and are explained in detail below, like the general inventive concept.

A casting core according to the invention, which has the basic shape of a hollow body, the casting core being formed from a molding material which is composed of a mixture, which is formed from a molding sand and a binder and optionally from additives added to adjust its properties, is thus characterized according to the invention in that the casting core is divided into at least two sub-segments and on the edge sides, with which sub-segments arranged adjacent to one another abut, or in the vicinity of these edge sides with each other positively cooperating form elements are provided, by means of which the mutually adjacent part segments are fixed immovably against each other at least in one direction by a form fit.

A casting core according to the invention is therefore not made in one piece, but rather is composed of two or more subsegments. Since these individual segments themselves no longer define a cavity, they can be produced in the conventional core shooting process with simply designed core tools. Complex slide arrangements, such as those required for mapping hollow bodies, are not required to produce the subsegments. At the same time, the sub-segments formed according to the invention are also comparatively insensitive due to their limited spatial extent if they are designed in a filigree manner with many openings and the like. This allows the subsegments to be stored in an uncomplicated manner and transported for assembling the casting core. The assembly of the casting core according to the invention can be carried out in the course of the assembly of the entire casting mold in which it is to be used or at a point separated therefrom.

The fact that the sub-segments of the casting mold according to the invention are fixed in their relative position by the form-fitting co-operating mold elements ensures, on the one hand, that the sub-segments find their correct position in a simple manner when assembling the casting core. On the other hand, the form-fitting coupling ensures that that the subsegments maintain their position during the casting process even under the load of the melt that is poured into the casting mold and penetrates the casting core.

In the case of a casting mold according to the invention, the secure hold of the subsegments can be supported by the fact that the subsegments are glued to one another in the area of the form elements that are positively coupled to one another. Alternatively or in addition, it is also possible to use the mold elements to couple the casting core according to the invention to the other casting cores or mold parts of the respective casting mold. For example, it can be expedient to form the shaped elements, via which the adjacent subsegments of a casting core according to the invention are fixed in relation to one another so as to be immovable in at least one direction, as projections protruding in the radial direction. Form elements designed as projections in this way and securing the sub-segments positively against one another allow, for example, a simple coupling of the sub-segments to the molded parts and cores surrounding the casting core in the casting mold, such as side cores, and thus a simple, automatable assembly of the casting mold according to the invention.

After removal from the mold, the projections, which are formed by the molded parts provided for the positive, mutual fixing of the partial segments, then form openings on the finished cast part, which lead to the cavities, channels, etc. depicted by the casting mold in the cast part. These openings can be closed by plugs that are subsequently inserted and connected to the surrounding material of the cast part, for example cohesively, for example by gluing or welding, or closed in some other way with additional material, for example in a welding process.

Before closing, the openings depicted by the projections can be used to overcast a possibly existing web, which can be formed by molten metal that has penetrated into the joint between two sub-segments that meet one another. For this purpose, a suitable cutting tool, such as a drill or milling cutter, can be passed through the respective opening.

According to the invention, the casting core has the basic shape of a hollow cylinder extending in a longitudinal direction with two end faces lying opposite one another in the longitudinal direction. By appropriately placed dividing joints between the subsegments, the individual subsegments can be shaped like a shell in the case of a casting core designed in the shape of a cylinder tube in this way. However, it can also be expedient to separate one or more subsegments from the other subsegments of the casting mold in such a way that the subsegments in question are annular. It goes without saying that such an annular design can also be advantageous for all sub-segments of the casting mold if the shape of the casting core produces a corresponding course of the dividing joints between the sub-segments.

A design of a casting core according to the invention, particularly typical for the production of a cooling jacket of an electrically operated drive machine, is achieved in that the casting core is designed according to the invention at least over a section as a band running around the space delimited by the casting core.

As already indicated above, in a casting core according to the invention, the course of the dividing joint between the sub-segments of a casting core according to the invention is selected in accordance with the course and the arrangement of the structures that are provided in the area of its wall to create cavities, channels and the like in the cast part map. The dividing joint can extend at least in sections in the longitudinal direction of the casting core or at least in sections in the circumferential direction of the casting core. Of course, a dividing joint can also change direction in its course, that is to say extend over a section in the longitudinal direction of the casting core and over another section in the circumferential direction and so on. In particular in the event that the casting core has the shape of a hollow cylinder body, it has proven to be expedient if the dividing plane extends between at least two mutually adjacent subsegments from one end to the other of the casting core.

For the positive definition of the abutting sub-segments of a casting mold according to the invention, it has been found to be particularly suitable if the form elements via which the adjacent sub-segments are fixed in at least one direction non-displaceably by positive locking, on the edge side of the first sub-segment and on the edge side of the second sub-segment a recess is formed which fills the projection of the first sub-segment. The recess can be designed, for example, as a wedge-shaped, conical-shaped or half-shell-shaped depression and the projection can be designed as a wedge-shaped or semicircular cross-section or shaped as a cone. In this way, the sub-segments to be coupled to one another find their intended relative position precisely via their form elements interacting in a form-fitting manner in the manner of self-centering when the casting core is assembled.

The core idea of the invention is therefore to split a complexly shaped casting core, which is a hollow body in its basic shape, into subsegments, which are easier to manufacture due to their spatially no longer closed shape, but at the same time in the casting core via suitably designed mold elements against each other are specified that a precise mapping of the cavities, channels and the like to be shaped by the casting core in the casting is guaranteed.

1. a) Herstellen der Teilsegmente des Gießkerns, wobei die Teilsegmente zueinander räumlich getrennt und körperlich unabhängig voneinander aus einem Formstoff geformt werden, der aus einem Formsand und einem Binder sowie optional zur Einstellung seiner Eigenschaften zugegebenen Additiven besteht;
2. b) Zusammenfügen der räumlich getrennt voneinander hergestellten Teilsegmente zu dem Gießkern.

Following this core idea, the method for producing a casting core according to the invention provides at least the following work steps:

1. a) producing the sub-segments of the casting core, the sub-segments being spatially separated from one another and physically formed independently of one another from a molding material consisting of a molding sand and a binder and additives optionally added to adjust its properties;
2. b) joining the subsegments produced spatially separately from one another to form the casting core.

"Spatially separated" and "physically independent" in this context means that a separate shaping cavity is provided in a core shooting machine for each of the subsegments. This of course includes the possibility, which is important in practice, of shaping the subsegments jointly and simultaneously in a core shooting box in which a mold cavity is provided for each of the subsegments. This variant of the method according to the invention enables a cost-effective and time-saving production of a respective set of subsegments which can be assembled together to form a casting core according to the invention.

• Fig. 1 einen Gießkern in einer perspektivischen Ansicht von oben;
• Fig. 2 einen Ausschnitt A des Gießkerns gemäß Fig. 1;
• Fig. 3 das Unterteil eines Kernschießkastens in Draufsicht.

The invention is explained in more detail below with reference to a drawing showing an exemplary embodiment. Their figures each show schematically:

• Fig. 1 a casting core in a perspective view from above;
• Fig. 2 a section A of the casting core according to Fig. 1 ;
• Fig. 3 the lower part of a core shooting box in plan view.

The casting core 1 has the basic shape of a cylindrical hollow body and accordingly delimits an interior IR, which extends in the longitudinal direction LR from the lower end face SU to the upper end face SO of the casting core 1.

The casting core 1 formed from a mold material, which has been tried and tested for this purpose and is mixed in a known manner from a molding sand and an organic or inorganic binder, is used to form a cooling water jacket in a housing for an electric motor serving as a vehicle drive, which is used in a not shown here, for example as Core package composed casting mold from a light metal melt, such as from a conventional aluminum casting material, is poured.

The peripheral wall 2 of the casting core 1 is formed by a ring segment-like ring section 3 that runs around the longitudinal axis LX of the casting core 1 and a meandering section 4.

Starting from a projection 5 protruding outward in the radial direction RR and constituting an inflow opening in the finished housing, the ring section 3, shaped like a band with a certain thickness, extends over approximately three quarters of the circumference of the casting core 1.

The beginning of the meander section 4 is connected to the end of the ring section 3. The turns 6 of the meander section 4 are each placed such that its longitudinal sections 7 are axially parallel to the longitudinal axis LX. The meander section 4 runs from the end of the ring section 3 in the opposite direction of the ring section 3 around the interior space IR delimited by the casting core 1 until it reaches the beginning of the meander section 4 with its end provided at the end of a longitudinal section 7 '. The projection 8 protruding radially outward there forms the outflow opening of the water jacket to be formed by the casting core 1 in the finished housing.

The casting core 1 is divided into nine subsegments 9-17. The first sub-segment 9 extends, starting from the projection 5, over half the length of the ring section 3. The second sub-segment 10 occupies the second half of the ring section 3. The third to ninth subsegments 11-17 each extend over approximately one seventh the length of the meander section 4, the ninth subsegment 17 being longer than the other subsegments 11-16 of the meander section 4 by the longitudinal section leading to the end of the meander section 4.

The dividing joints (of those in Fig. 1 the dividing joints 18-24 are visible), in which the subsegments 9,10; 10.11; 11.12; 12.13; 13; 14; 14; 15; 15.16; 16; 17 meet, each run in a first section 25 in the longitudinal direction LR and in an adjoining section 26 in the circumferential direction UR, the angle enclosed between the sections 25 and 26 being not equal to 90 °, i.e. the orientation of the section 25 not only one component in the longitudinal direction LR, but also in the circumferential direction UR and the alignment of the section 26 can have not only one component in the circumferential direction UR, but also in the longitudinal direction LR.

In this case, in the area of each dividing joint 18-24, a shaped element 27a, 27b, 28a, 28b, 29a, 29b, 30a, 30b in the form of a radially outward direction is adjacent to the edge sides of the subsegments 9-16 that meet in the dividing joint 18-24 protruding projection formed. Of the pairs 27a, 27b; 28a, 28b; 29a, 29b; 30a, 30b of shaped elements 27a-30b have one Shaped element 27a, 28a, 29a, 30a each have a recess 31 which extends over its projection length LV and which is shaped like a notch with a cross section corresponding to a third of a circle. The shaped elements 27b, 28b, 29b, 30b respectively assigned to the shaped elements 27a, 28a, 29a, 30a are accordingly wedge-shaped with a cross-section that is also third-circular. In this way, the shaped elements 27b, 28b, 29b, 30b each fill the recess 31 of the associated shaped elements 27a, 28a, 29a, 30a, so that pairs of shaped elements 27a, 27b; 28a, 28b; 29a, 29b; 30a, 30b formed, radially outwardly projecting projections have an overall circular cross section.

By means of the shaped elements 27a-30b provided on each of the subsegments 9-17 and their edge sides abutting one another in the area of the dividing joints 18-24, the subsegments 9-17 are positively fixed to one another in the circumferential direction UR and in the longitudinal direction LR so that a relative movement in the circumferential direction UR and is prevented in the longitudinal direction LR on the lower face SU.

To produce the toroidal core 1, a core shooting box is provided, of which in Fig. 3 the lower part 40 is shown. The core shooting box, which is not shown here for the sake of clarity, is set up in such a way that the subsegments 9-17 for two toroidal cores 1 of the same type can be shot in it. Correspondingly, two sets of spatially separated mold cavities 49-57 are formed in the lower part 40 of the core shooting box and in the associated upper part of the core shooting box (not shown here) in a corresponding manner. After the core box has been closed, two sets of subsegments 9-17 can be shot in a manner known per se in this way. These are then combined to form two toroidal cores 1. This assembly can take place before the casting cores 1 are placed in the respective casting mold, or the Subsegments 9-17 can be assembled in the respective casting mold to form the casting core 1 provided in it.

REFERENCE MARK

1

Casting core

2

Peripheral wall of the casting core 1

3

Ring section of the casting core 1

4th

Meander section of the casting core 1

5

head Start

6th

Turns

7, 7 '

Longitudinal sections

8th

head Start

9-17

Subsegments

18 - 24

Dividing joints

25th

Section of the dividing joints running in the longitudinal direction LR

26th

Section of the dividing joints running in the circumferential direction UR

27a-30b

Form elements

31

Recess

40

Core box lower part

49-57

Mold cavities

IR

Interior delimited by the casting core

LR

Longitudinal direction of the casting core 1

LV

Protrusion length

UR

Circumferential direction of the casting core 1

RR

radial direction

SU

lower face of the casting core 1

SO

upper face of the casting core 1

LX

Longitudinal axis of the casting core 1

Claims (7)

1. Foundry core, wherein the foundry core (1) is shaped from a moulding material consisting of a mixture which is formed from a moulding sand and a binder and optionally from additives added to set its properties wherein the foundry core (1) is divided into at least two sub-segments (9 - 17) and wherein forming elements (28a - 30b) interacting with one another in a positive-locking manner are provided on the edge sides, with which sub-segments (9 - 17) arranged adjacent to one another abut on one another, or in proximity to these edge sides, via which forming elements the sub-segments (9 - 17) arranged adjacent to one another are fixed by positive locking immovably against one another at least in one direction (LR, UR), characterised in that it has the base form of a hollow cylinder extending in a longitudinal direction (LR) with two end faces (SO, SU) opposed to one another in the longitudinal direction (LR) and that it is formed at least over one section (4) as a strip running in a meandering shape around the space (IR) delimited by the foundry core (1).
2. Foundry core according to claim 1, characterised in that the sub-segments (9 - 17) are adhered to one another at least in the region of their forming elements (28a - 30b) fixed against one another in a positive-locking manner.
3. Foundry core according to any one of the preceding claims, characterised in that the separating joint (18 - 24) extends between two adjacent sub-segments (9 - 17) at least in sections in the longitudinal direction (LR) of the foundry core (1).
4. Foundry core according to claim 2, characterised in that the separating joint (18 - 24) extends between at least two sub-segments (9 - 17) adjacent to one another from one end face of the foundry core (1) to the other.
5. Foundry core according to any one of the preceding claims, characterised in that the separating joint (18 - 24) runs between two sub-segments (9 - 17) adjacent to one another in the circumferential direction (UR) of the foundry core (1).
6. Foundry core according to any one of the preceding claims, characterised in that as forming elements (28a - 30b), via which adjacent sub-segments (9 - 17) are fixed by positive locking immovably against one another in at least one direction (LR, UR), on the edge side of the first sub-segment (9 - 17) a projection is formed and on the edge side of the second sub-segment (9 - 17) a recess (31) is formed, which fills the projection of the first sub-segment (9 - 17).
7. Foundry core according to any one of the preceding claims, characterised in that the forming elements (28a - 30b) are formed as projections protruding in the radial direction, via which adjacent sub-segments (9 - 17) are fixed by positive locking immovably against one another in at least one direction (LR, UR).

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