DE102021000614A1 - Mold for the crack-free production of a metal object with at least one undercut, in particular from intermetallic alloys such as TiAl, FeAl and other brittle or crack-prone materials, as well as a corresponding method. - Google Patents

Abstract

Mold and method for producing a metal object with at least one undercut.Crack-prone and brittle alloys, e.g. TiAl or FeAl, cannot currently be processed in molds into components with at least one undercut without cracks, since they shrink onto the mold during solid body contraction and as a result of the high Tensions form cracks.Casting mold for casting a contoured metal object, consisting of several connectable mold parts (2a, 2b, 3a, 3b, 4), characterized in that the mold part (4) (hereinafter referred to as insert) mold parts 2a and 2a and 2b, 3a and 3b with each other and enables the melt flow along the entire cavity during mold filling and is arranged in such a way that the insert gives way to the volume contraction when the cast metal object cools down in order to reduce the contraction-related stresses between the variie along the longitudinal axis At least one pair of mold parts 2a/2b or 3a/3b must be movably mounted so that they can be moved towards one another by the contracting cast metal object. Production of castings with an undercut in permanent mold casting from crack-prone and brittle alloys, e.g. intermetallic alloys such as TiAl or FeAl .

Description

The invention relates to a mold for casting a metal object with an undercut, consisting of several mold parts that can be connected to one another, with the mold parts complementing one another when the mold is closed to form a cavity with a volume that varies along the longitudinal axis with one or more undercuts and along a flat or free-form parting plane from one another are solvable.

Molds are usually used to cast a metal object from a melt. These define the contour of the finished, cast metal object via a cavity, which is defined by the mold cavities of the mold parts that can be detachably connected to one another. The melt is poured into the mold, after which it solidifies. Although a large number of different metals or metal alloys can be processed by chill casting, there are groups of materials that have poor casting properties and/or brittle failure behavior, problems arising in particular if the metal object has a volume distribution that varies along its longitudinal axis with one or more undercuts . One of many examples of such a group of materials that is difficult to process in terms of casting technology is that of titanium aluminides. Due to their low density of around 4 g/cm ³ and good high-temperature properties, the material group of titanium aluminides offers the potential to replace superalloys in their area of application as a material for highly stressed components in piston engines and gas turbines, in particular blades, and at the same time to achieve a weight advantage. Due to the poor processing properties of these materials, it is currently not possible to produce components with complex shapes using permanent mold casting. For this reason, such components are usually manufactured using a combined casting/forging route. This includes the casting of a semi-finished product with a rotationally symmetrical, mostly cylindrical or conical geometry in a permanent metallic mould, i.e. the production of a semi-finished product with a geometrically very simple design and no undercuts or the like (Güther et al., “Metallurgical processing of titanium aluminides on industrial scale” , Intermetallics 103, pages 12-22, 2018) ( EP 3 109 337 B1 ). The casting is followed by a multi-stage forming and a final heat treatment and finishing to produce the final component (Janschek, "Wrought TiAl blades", Materials Today: Proceedings 2S, pages S92-S97, 2015). Good properties of the components can be achieved by forging and subsequent heat treatment, but this involves relatively high material consumption and processing costs. Alternatively, the end component is produced directly from the cast block by mechanical processing after heat treatment has taken place, see patents EP 3 083 132 B1 , EP 3 083 133 B1 , EP 3 083 134 B1 or WO 2015/092239 A1 , WO 2016/189254 A1 , WO 2016/142611 A1 .

This high use of material could be reduced if there were a possibility of being able to produce semi-finished products, which already after casting have a volume distribution that varies along the longitudinal axis with one or more undercuts, by means of permanent mold casting. The use of such a blank in the forging or machining process would reduce the number of forming steps ( DE 10 2015 103 422 B3 ) with subsequent heat treatment and finishing, or offer the possibility of being able to produce the finished part directly through a combination of heat treatment and finishing with a cast that is as near-net-shape as possible (Schievenbusch J., joint project Skin, final report by Access eV, 2017 ) (Janschek P., Skin joint project, final report by Leistritz Turbinentechnik GmbH, 2017).

Due to the casting properties of titanium aluminide alloys (TiAI alloys) and their ductile-brittle transition on cooling and the extremely brittle behavior at room temperature, the casting of pre-contoured semi-finished profiles in permanent molds, especially profiles that have defined undercuts in the mold, is not possible possible. This results in particular from the solid body contraction of the cooling TiAl alloy, i.e. the volume shrinkage. This results in a high load on the cast material, particularly in the area of the undercuts, which can lead to damage to the cast part through to the formation of cracks or breakage. Similar challenges arise when casting iron aluminides and other materials that are brittle or prone to cracking.

In the patents EP 3 225 330 A1 and EP 3 225 331 A1 various possibilities are mentioned for producing a contoured cast part, in particular from brittle materials, in a metallic permanent mold. Here, the force of the contracting casting is used to open the mold halves via the drafts attached to the casting or the mold. A certain amount of force is required to open the partially heavy mold halves. This force must already be applied in the initial phase of solidification, ie in the partially solidified casting. At these high temperatures, most alloys have low yield points. With low construction partial cross-sections, such as those found in filigree turbine blades, it is not possible to apply sufficient force to open the halves of the mold, so that only components with greater wall thicknesses can be produced. A further disadvantage of the solution presented in this patent is the additional material required to attach the draft angles required on the casting at an angle of 30-60° to the parting plane. At larger angles, the friction component between the casting and the mold increases to such an extent that the functional principle shown can no longer be used. The patent also mentions a solution for cast parts without inclined surfaces. In this case, the inclined surfaces are provided between the mold parts and also cause the mold to open. But here, too, friction is a decisive factor. During contraction, the still hot or even partially liquid cast part must overcome the friction between the mold parts and the friction between the cast part and the mold. In practice, this can only be implemented with very large component diameters. Therefore, there is still a need for a solution for thin-walled and complex castings. Some of the challenges can be solved by the actuator-supported opening principles also mentioned, but this is associated with considerable costs and maintenance effort, so that a cheap and low-maintenance solution is still required.

Furthermore, it is not possible with this solution to use free-form surfaces, as these would also lead to further increased friction or even act as an insurmountable resistance. A solution is therefore still needed to be able to produce cast parts with free-form surfaces, low wall thicknesses, with surfaces that have a large angle to the longitudinal axis of the cast part, preferably greater than 60° and without error-prone/expensive actuators.

The invention is therefore based on the problem of specifying a mold and a corresponding method that also allows the casting of materials with brittle failure behavior and a tendency to crack formation, in particular intermetallic alloys such as titanium aluminide or iron aluminide alloys or other brittle and crack-prone materials for production of complex contoured metal objects.

To solve this problem, in the case of a mold of the type mentioned at the outset, the invention provides that an insert is used in the area of the smallest diameter along the longitudinal axis of the metal object (casting) to be cast, which connects the mold parts in front of and behind it and completes the cavity. to ensure complete filling of the mold and is able to yield to the forces that occur through deformation as soon as the volume contraction begins. This insert (shrink ring) can yield either through elastic or through plastic deformation of the volume contraction of the cast part. In the case of elastic deformation, it can be reused again, in the case of plastic deformation, a new or revised insert must be used for each cast part. Alternatively, the insert may fail by brittle fracture, thus allowing free contraction of the casting through the exposed portion after fracture. It is important here that the break, the elastic or plastic deformation of the insert takes place before the casting is stressed beyond its yield point in order to avoid deformation or cracking in the casting. A major difference to the in EP 3 225 330 A1 The solution mentioned is that there is no opening of the mold and thus a high level of heat dissipation from the cast part is made possible by the small formation of gaps. Depending on the material used and the wall thickness of the insert, reduced heat dissipation can only occur in the area of the insert. A heat center can form if the wall thickness of the insert is low or if it is made of a material with a low thermal capacity and thermal conductivity compared to the rest of the mold. This can possibly lead to the formation of cavities at the appropriate point in the cast part. In order to avoid this, it can be useful to position the depositor in the vicinity of a feeder and to feed it densely by controlled solidification. A further advantage of the solution mentioned here is that it is not necessary to shear off the cast part via the drafts to open the mold and the resulting friction between the surfaces of the cast part and mold is avoided. The friction can lead to an increased surface load, which increases wear on the mold and can lead to surface defects on the casting.

The mold according to the invention is characterized in that means are provided which make it possible to yield to the contraction of the casting in order to avoid additional stresses in the blank caused by cooling and shrinkage, so that these do not have a negative effect on the properties of the cast metal object. For this purpose, several inserts are provided, which on the one hand enable the flow of the metallic melt from one mold cavity to the other and thus ensure complete filling of the mold and on the other hand can yield to the volume contraction after complete filling of the mold.

Subsequently, the process of filling the melt into the mold and the subsequent Volume contraction of the cast metal object explained in more detail. The insert can be fixed in one position by means of a recess (23) in the respective surrounding mold parts. The length of the insert defines the distance between the surrounding mold parts and thus the initial length of the cast part. When the melt flows in, the insert acts as a kind of "pipe" and ensures that the cavity is completely filled. The cast part now completely fills the cavity and is in close contact with the mold wall in all areas. The solidification of the casting occurs from the edge towards the center, which initially forms an edge shell. This outer shell contracts with increasing cooling according to the thermal expansion coefficient of the alloy used and partially detaches from the mold wall. As it cools down further, the metal object changes its size (solid body shrinkage) in every spatial direction, provided it can shrink unhindered. This change in size depends on the coefficient of thermal expansion, the temperature difference and the initial length of the casting. The coefficient of expansion and the temperature difference are the same for the entire cast part, but the initial length in each of the three spatial directions is usually not the same, so that the cast part shrinks/contracts to different extents along its different length expansions. The cast part therefore contracts more strongly along the greatest linear extent, which results in higher stresses between the cast part and the mold in this spatial direction. These must be removed from the mold in order to reduce the load on the still hot/partially liquid cast part and to prevent the cast part from cracking. This task is performed by the depositor in the mold. It has a lower strength than the contracting cast body and is therefore compressed. The greater the volume shrinkage of the metal object due to shrinkage, and thus its change in size, the closer the mold parts are moved to one another. This opening of the mold parts no longer has any effect on the shaping of the contoured metal object, since the metal object has already solidified at least at the edges and also in volume with increasing cooling. As a result of the upsetting of the mold caused by the metal object itself, the stresses between the metal object and the mold caused by shrinkage are consequently reduced or eliminated, so that the metal object can solidify and cool largely stress-free.

The upsetting of the mold by the solidifying metal object itself is explained in more detail below. As described, this occurs in that the solidifying metal object shrinks onto some surfaces of the mold due to the volume differences along its longitudinal axis. Depending on the contour of the metal object or the cavity, these surfaces can be freely formed. This surface acts as a kind of anchor for the contracting casting and would prevent volume contraction in a rigid mould. Depending on the casting material, this can lead to constriction due to plastic deformation, cracks or complete failure of the casting. Brittle materials in particular fail catastrophically in such a case by fracture. Therefore, in this invention, the force absorbed across said surface or surfaces is transmitted to the insert lying between two or more mold parts. This is compressed by the forces that occur and thus compensates for the volume contraction of the cast part. The insert must be designed in such a way that the stresses induced by the contracting cast part are sufficient. The insert must be able to deform to such an extent that it completely compensates for the volume contraction of the cast part.

The depositor is described in more detail below. The insert can be designed in different geometries and thus represent a large number of different cast components. It is possible to design the insert as a hollow cylinder, rectangular tube or free form (e.g. blade profile) and it can be made of different materials. Depending on the forces that occur, a suitable material and wall thickness can be used. The forces that occur depend on the casting alloy, the cooling conditions and the cross-section of the casting. Preferred wall thicknesses of the insert are between 0.2 mm and 10 mm. Different wall thicknesses can also be used within an insert if, for example, there is a complex geometry with different contraction forces occurring or if a predetermined breaking point of the insert is to be produced in a targeted manner. If the insert is inserted in one piece, it must be mechanically removed after casting using a suitable method. It has proven to be very practical to design the insert in several parts. After the cast part has completely cooled down, it can be removed and the finished cast part is ready.

The insert itself is preferably made of a metal material corresponding to the mold and should be selected with regard to the resulting forces as a result of the volume contraction of the cast part. Depending on its temperature and geometry, the insert must be flexible enough to avoid cracking or stretching of the cast material. Furthermore, the depositor of the metallic melt must offer sufficient resistance, for example to total deformation during mold filling, melting of the insert and leakage of the melt, contamination of the melt through reaction/partial dissolution or other conceivable faults. The insert can consist of the same material as the mold or can be made of a different material or a different material. However, the insert does not have to be made of a metallic material. An insert made of graphite, special glass or ceramic can also be used, as this has high temperature resistance and enables complete mold filling. When the volume of the cast part begins to contract and a critical stress is exceeded, the graphite, glass or ceramic insert shatters and then allows the volume of the cast part to contract with almost no resistance. To improve heat dissipation from the cast part, the insert can be covered with heat-dissipating materials that have little or no effect on the compression of the ring. Thermal paste and thermal mats, for example, are suitable for this.

The mold itself is preferably a permanent metal form. It consists of a metal material such as cast iron, steel, copper, niobium or molybdenum and any alloys formed from them. However, the mold can also be made of graphite. In principle, all materials that can be used due to their physical properties and chemical resistance to the molten metal can be used.

Depending on the design, the mold can be used in centrifugal casting, gravity casting or tilt casting, as well as other casting processes.

As described, the mold parts are coupled to one another in such a way that they can be moved towards one another by sufficient pressure exerted by the metal object on one or both mold parts, ie they are not completely immovably clamped together.

It is expedient if the mold parts can be moved, guided against one another, via guide means. The mold parts are thus arranged relative to one another in a defined manner via the connecting sections or guides, resulting in a mold that is closed in a defined manner with a closed cavity. When the mold parts are pulled in during the casting contraction, friction occurs between the adjacent mold parts and/or the mounting plate. In order to reduce this friction, a coating can be applied or the corresponding mold parts can be mounted in bearings. Ball bearings, plain bearings or other types of bearings are suitable for this.

Another way to support the casting during contraction is to preload the mold with the help of springs. For this purpose, the spring force must be selected in such a way that the tension acting on the insert is below its yield point in order to prevent the mold from being compressed prematurely. Alternatively, the use of actuators to support the compression of the insert can be used. After the mold has been successfully filled, the compression of the insert can be initiated by one or more actuators. To do this, the movement of the actuator(s) must be adapted to the solid body contraction of the cast part.

Description of the procedure

In addition to the mold itself, the invention also relates to a method for casting a metal object using a mold consisting of several mold parts that can be connected, with the mold parts forming a cavity with a volume that varies along the longitudinal axis with one or more undercuts when the mold is closed and along a flat or free-form parting plane are detachable from each other, in particular a mold of the type described above. The method is characterized in that after the introduction of a melt into the cavity, the mold is compressed to reduce shrinkage-related forces arising in the interior. According to the invention, the metal object, which shrinks along its longitudinal axis as a result of cooling, presses directly or indirectly against a surface due to shrinkage or contraction, from which the acting force is transmitted to the insert and this yields to the contraction of the cast part when its maximum strength is exceeded. Depending on the design, the mold can be used in centrifugal casting, gravity casting or tilt casting, as well as other casting processes.

According to the invention, a metal object made of an intermetallic alloy such as titanium aluminide or iron aluminide or another material which tends to form cracks on cooling is processed. A permanent mold is used as the mold, which has the physical and chemical properties that allow the casting of the alloy used or are sufficiently resistant to this material.

Preferably, but not necessarily, a mold of the type described above is used.

All statements relating to the mold apply in the same way to the method according to the invention, and vice versa.

• 1 eine Prinzipdarstellung einer Kokille in einer Schnittansicht,
• 2 eine Prinzipdarstellung eines Metallgegenstands mit Hinterschnitt einer ersten Ausführungsform, beispielsweise für die Herstellung einer Niederdruckturbinenschaufel,
• 3 eine Prinzipdarstellung einer Kokille einer zweiten Ausführungsform in einer Schnittansicht a) und einer Ansicht auf die Teilungsebene b),
• 4 eine Prinzipdarstellung eines Metallgegenstands einer zweiten Ausführungsform, beispielsweise für die Herstellung einer Niederdruckturbinenschaufel, in einer Seitenansicht a) und einer Draufsicht b), der in der Kokille nach 3 gegossen werden kann,
• 5 eine erfindungsgemäße Kokille einer ersten Ausführungsform in drei Zuständen a) Kokille mit eingefüllter Schmelze, b) Beginn der Gussteilkontraktion und Stauchung des Einlegers und c) Kokille und Gussteil nach vollständiger Abkühlung und Kontraktion mit verformten Einleger, zur Erläuterung des Kontraktionsvorgangs des Gussteils und der daraus resultierenden Stauchung des Einlegers,
• 6 eine erfindungsgemäße Kokille einer dritten Ausführungsform mit einem geführten Kokilleneinsatz zur Vermeidung von Verzug in drei Zuständen a) Kokille mit eingefüllter Schmelze, b) Beginn der Gussteilkontraktion und Stauchung des Einlegers und c) Kokille und Gussteil nach vollständiger Abkühlung und Kontraktion mit verformten Einleger,
• 7 eine erfindungsgemäße Kokille einer vierten Ausführungsform mit Kugellagern zwischen den Kokillenteilen,
• 8 eine erfindungsgemäße Kokille einer fünften Ausführungsform für den Vertikalschleuderguss in drei Zuständen a) Kokille mit eingefüllter Schmelze, b) Beginn der Gussteilkontraktion und Stauchung des Einlegers und c) Kokille und Gussteil nach vollständiger Abkühlung und Kontraktion mit verformten Einleger,
• 9 Prinzipdarstellung verschiedener Varianten des Einlegers mit Sicht in Flucht der Längsachse a) einteiliger, geschlossener Ring, b) mehrteiliger, geteilter Ring, c) einteiliges, geschlossenes Rechteckrohr, d) mehrteiliges, geteiltes Rechteckrohr, e) einteiliger freigeformter Einleger, angepasst an Schaufelprofil einer Turbinenschaufel, f) mehrteiliger, freigeformter Einleger, angepasst an Schaufelprofil einer Turbinenschaufel
• 10 eine Prinzipdarstellung eines Metallgegenstands einer dritten Ausführungsform, beispielsweise für die Herstellung einer Niederdruckturbinenschaufel,
• 11 eine Prinzipdarstellung einer Kokille einer weiteren Ausführungsform für den in 10 gezeigten Metallgegenstand
• 12 eine erfindungsgemäße Kokille einer weiteren Ausführungsform für Gussteile mit mehr als einer Hinterschneidung
• 13 eine Detailansicht des Einlegerbereichs einer erfindungsgemäßen Kokille ohne eingesetzten Einleger a) und mit eingesetztem Einleger b)

Further advantages and details of the invention result from the exemplary embodiments described below and from the drawings. Individual advantages and details can also be combined with one another and not all possible combinations are shown. show:

• 1 a schematic representation of a mold in a sectional view,
• 2 a schematic representation of a metal object with an undercut of a first embodiment, for example for the production of a low-pressure turbine blade,
• 3 a schematic representation of a mold of a second embodiment in a sectional view a) and a view of the parting plane b),
• 4 a schematic representation of a metal object of a second embodiment, for example for the production of a low-pressure turbine blade, in a side view a) and a plan view b), in the mold according to 3 can be cast
• 5 a mold according to the invention of a first embodiment in three states a) mold with melt poured in, b) beginning of the casting contraction and upsetting of the insert and c) mold and casting after complete cooling and contraction with deformed insert, to explain the contraction process of the casting and the resulting compression of the insert,
• 6 a mold according to the invention in a third embodiment with a guided mold insert to avoid distortion in three states a) mold with melt poured in, b) start of casting contraction and upsetting of the insert and c) mold and casting after complete cooling and contraction with deformed insert,
• 7 a mold according to the invention in a fourth embodiment with ball bearings between the mold parts,
• 8th a mold according to the invention of a fifth embodiment for vertical centrifugal casting in three states a) mold with melt poured in, b) start of casting contraction and upsetting of the insert and c) mold and casting after complete cooling and contraction with deformed insert,
• 9 Schematic representation of different variants of the insert with a view aligned with the longitudinal axis a) one-piece, closed ring, b) multi-piece, split ring, c) one-piece, closed rectangular tube, d) multi-piece, split rectangular tube, e) one-piece, free-form insert, adapted to the blade profile of a turbine blade , f) multi-part, free-form insert, adapted to the blade profile of a turbine blade
• 10 a schematic representation of a metal object of a third embodiment, for example for the production of a low-pressure turbine blade,
• 11 a schematic diagram of a mold of a further embodiment for the in 10 shown metal object
• 12 an inventive mold of a further embodiment for castings with more than one undercut
• 13 a detailed view of the deposit area of a mold according to the invention without insert a) inserted and with insert b) inserted

1 1 shows a mold 1 consisting of five mold parts 2a, 2b, 3a, 3b, 4. In the assembled form these define a cavity 5 which is to be filled with melt for casting a contoured metal object.

The two mold parts 2a and 2b as well as 3a and 3b can be separated from one another along a plane parting plane 6 in the example shown, in order to be able to remove the solidified and cooled metal object from the cavity 5.

In the example shown, the cavity 5 is designed for casting a metal object for the production of a low-pressure turbine blade. The cavity 5 has a volume that varies along its longitudinal axis with two larger volume areas 5a, 5b at the edge and a central, narrower volume area 5c. As can be seen, the volume areas 5a, 5b each have undercuts resulting from the increase in diameter. The volume sections 5a, 5b, 5c can be rotationally symmetrical, ie round, but they can also be triangular, quadrangular or polygonal or freely shaped, depending on the desired shape.

2 shows an example of a metal object 7, with a mold 1 according to 1 can be cast. As described, this metal object 7 is used, for example, to produce a low-pressure turbine blade. It is characterized by a shroud 8, which is imaged in the volume area 5b by the mold parts 3a and 3b, a blade root 9, which is imaged in the volume area 5a by the mold parts 2a and 2b, and a blade 10, which is imaged in the volume area 5c of all mold parts. Its shape corresponds to that of the cavity 5, it is only slightly smaller in volume due to shrinkage compared to the volume of the cavity 5. This will be discussed further below.

4 shows a top view a) and a side view b) of a second embodiment of a metal object 7' which is equally suitable for the production of a low-pressure turbine blade and which is produced in a mold 11 according to FIG 3 can be cast. This metal object 7' also has a shroud 8', a blade root 9' and a blade leaf 10'. However, a feeder 12 is attached to it, projecting laterally, which allows material to flow into the actual space of the cavity 5 . This feeder 12 thus serves as a material reservoir to compensate for the solidification-related volumetric shrinkage of the cast part. The cavity 5 has this, see 3 , a corresponding, laterally expanded mold cavity section 5d. In 3 is shown in the upper part a) an example of a sectional view through the five mold parts 2a, 2b, 3a, 3b and 4, while 3 in part b) shows a top view of the mold parts 2a, 3a and one half of the insert 4.

When casting such metal objects 7, 7 ', as in the 2 and 4 shown, for example made of a titanium aluminide alloy, there is a considerable volume contraction of the casting during cooling, which would lead to high stresses in the metal object enclosed in the cavity 5, since the volume shrinkage via the undercuts in the area of the volume sections 5a, 5b and 5d would be disabled. In order to realize a reduction in stress, however, as in the following 5 - 8th is shown, a possibility is given as to how the mold 1 and other embodiments can be contracted in a defined manner in order to realize a stress reduction.

5 shows a first embodiment of a mold 1 according to the invention consisting of the five mold parts 2a, 2b, 3a, 3b and 4. The mold parts 2a and 2b and 3a and 3b are connected to one another. This can be solved using clamps, screws or other tools. These two partial molds 2a/2b and 3a/3b can be moved relative to one another and are positioned by the insert 4 at a distance from one another that is dependent on its length. In the example shown, the mold is used in gravity casting. The two lower mold parts 3a and 3b connected to one another stand on the ground. The two upper mold parts 2a and 2b connected to one another stand on the insert 4 and thus form the complete cavity.

Starting from image section a), the melt is first introduced into the cavity 5 of the mold 1, which then slowly solidifies in the mold 1, so that the metal object 7 (the metal object 7′ could also be formed in the same way) is formed.

With increasing solidification and cooling, the metal object 7 shrinks, as shown in part b) of the figure. The two arrows 13 indicate that the volume is reduced, in particular axially, that is to say that the metal object is effectively shortened. After the metal object has solidified at the edge, possibly already in its entire volume, the metal object 7 shrinks onto the mold through the undercut as a result of the volume varying along the longitudinal axis. So it builds up a pressure on the depositor. Due to the lower strength of the insert compared to the solidifying cast part, the insert is deformed by the force transmitted by the mold as a result of the volume contraction of the cast part.

If the cooling and thus the volume contraction continue to increase, as in c ) is shown by the arrows 13, the metal object 7 presses or works more and more or more strongly against the insert, so that the insert is compressed more and more. In this case, the force is transmitted from the cast metal object 7 via the mold parts to the insert. The degree of shrinkage and deformation is overcharacterized in the figures (this applies to all figures) in order to be able to clearly illustrate the functional principle. In addition, only the contraction in the longitudinal direction of the casting is shown. The contraction that occurs in the other spatial directions is not shown.

Due to the fact that the insert is successively compressed in this case by the successively shrinking metal object, the tension between the metal object and the mold part pairs 2a/2b and 3a/3b is inevitably reduced or kept low. If the insert is designed correctly, these low stresses can no longer have a damaging effect on the metal object. The mold is compressed here solely by the shrinking metal object itself.

It is also possible to support the mutual movement of the mold part pairs 2a/2b and 3a/3b by means of spring elements and/or actuators. As a result, the force to be applied by the cast part is reduced in accordance with the spring force and/or the forces of the actuator in order to deform the insert.

6 1 shows an exemplary embodiment of a second embodiment of a mold 1 according to the invention. In the example shown, it consists of five mold parts 2a, 2b, 3a, 3b and 4, which in turn form the cavity 5 in their entirety. The mold parts 2a and 2b as well as 3a and 3b can each be separated from one another via a vertical parting plane 6 . The mold parts 2a and 2b as well as 3a and 3b can be connected with the aid of screws, clamps or other aids which prevent the mold from opening due to the metallostatic pressure of the melt that is poured in.

In the example shown, the mold part pair 2a/2b is in turn guided via corresponding guides 14 with the other mold part pair 3a/3b in contact and the two cavities formed are completed by the insert 4. The shape of the cavity is assumed to correspond to the cavity as in 5 described, ie that of the metal object 7. Equally, the cavity 5 could also have the shape as shown by the metal object 7'.

According to 6 a) Here, too, melt is first introduced into the cavity 5 of the mold 1, which solidifies to form the metal object 7. With increasing solidification and cooling, there is again a volume contraction, as shown by the arrows 13 in part b), which is primarily given in the longitudinal direction of the metal object 7 . Here, too, the metal object 7 pulls the mold part pairs 2a/2b and 3a/3b towards one another by deformation of the insert 4. In this case, the force is also transmitted from the cast metal object 7 via the mold parts to the insert. This is the weakest link and allows the cast metal object 7 to contract with little stress.

If a metal object 7' were cast, the cavity would have the 3 shape shown and would function on the same principle. After complete cooling and concomitant contraction of the cast metal object, shown in 6c) , the dimensional accuracy is improved by the guide 14 of the movable pair of mold parts 2a/2b by preventing the cast part from buckling at the side.

7 shows an extension of the in 6 described mold. A bearing 15 was introduced in the area of the guide 14 to reduce the friction between the mold part pairs 2a/2b and 3a/3b. The bearing 15 can be designed as a sliding bearing, roller bearing or similar bearing and is used to reduce the frictional forces between the mold parts during the contraction of the casting.

8th shows a further embodiment of a mold 1 according to the invention, which is designed for use in vertical centrifugal casting. The variant shown is a structure similar to that previously shown in 6 mold shown, the movable mold parts 2a/2b being guided. The principle can also be used without the guide in centrifugal casting, according to the variants shown above. In the variant shown above, the fixed mold parts 3a/3b are positioned towards the melt distributor (injection side) and the movable mold parts 2a/2b are further away from the center of rotation 17 of the turntable 18. In this variant, the end position of the movable mold parts 2a/2b is End stop 19 set, due to centrifugal force, the mold parts are pressed against this end stop. The same principle can also be used in reverse, so that the movable mold parts are aligned towards the center of rotation (injection side) and the fixed mold parts are mounted on the turntable outside of this. In this case, the end stop 19 is not required. By rotating the mold on a turntable 18, the inflowing melt is pressed outwards into the cavity by the centrifugal force 16. After the mold has been completely filled, the contraction of the cooling metal object 7 begins, as in the previously described variants, with the movable mold parts 2a/2b being drawn towards the center of rotation in the version shown and the insert 4 being compressed, 8 b) and c ).

9 shows various embodiments of the insert 4 shown above in cross section. As in figure part a), this can be designed cylindrically with wall thicknesses >0.2 mm and <the surrounding mold parts, or as in figure part c) as a rectangle. However, more complex geometries can also be implemented, as indicated by way of example in part e) for a turbine bucket blade. These and other cross sections for the insert 4 can also be realized with a dividing plane. This has the great advantage that the divided insert can be removed after the cast metal object has been removed. In the case of closed inserts, this must be removed after casting. The cross sections of possible inserts shown here only serve to illustrate the variety of variants that can be realized and do not restrict the solution mentioned in this patent to the geometries shown as examples.

10 shows a third embodiment of a metal object 7", which is equally suitable for the production of a low-pressure turbine blade and in a mold 20 according to FIG 11 can be cast. This metal object 7" also has a shroud 8", a blade root 9" and a blade 10". Of the The difference to the metal object 7 is the step 21 in the blade, which is formed from the step 22 present in the mold 20 . In this variant, the insert is not clamped between the pairs of mold parts, but rests directly on the metal object 7" on one side. This reduces the residual stresses remaining after the metal object has completely cooled down, making it easier to remove the metal object from the mold. This variant is However, it can only be used meaningfully if the solidifying metal object forms an edge shell at the beginning of the solidification process, against which the insert can lay.An adapted metal object 7' could also be produced with this variant.

12 shows a mold for producing cast parts with several undercuts according to the principle already described in detail above. In this representation, it is in principle a corresponding casting mold 1 , in which the mold parts 3a/3b are not closed at the bottom, but rather the metallic melt is conducted via a further depositor 4 into the two mold parts 24a and 24b. Accordingly, a casting with two undercuts is created. At the additional undercut, the volume contraction is compensated in the same way by the further insert. Additional elements can be added to the mold in order to produce multiple undercut castings. This cast part can then be used, for example, to manufacture camshafts or several turbine blades.

13 shows the possibility of accommodating an insert in a possible mold. A recess 23 made in the mold, which should be designed according to the wall thickness of the insert, allows the insert to be placed in the mold in such a way that the target geometry of the metal object to be cast is not changed.

The mold according to the invention, regardless of the embodiment, is used in particular to produce a metal object or a semi-finished product with a volume distribution that varies along the longitudinal axis for further processing by forging and/or machining to form a finished part or directly a finished part with a volume distribution that varies along the longitudinal axis. The finished part can be provided in particular, but not exclusively, for use in a piston engine or a gas turbine, in particular in aircraft engines.

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• EP 3109337 B1 [0002]
• EP 3083132 B1 [0002]
• EP 3083133 B1 [0002]
• EP 3083134 B1 [0002]
• WO 2015/092239 A1 [0002]
• WO 2016/189254 A1 [0002]
• WO 2016/142611 A1 [0002]
• DE 102015103422 B3 [0003]
• EP 3225330 A1 [0005, 0008]
• EP 3225331 A1 [0005]

Claims (12)

Mold for casting a metal object with at least one undercut, consisting of several connectable mold parts (2a, 2b, 3a, 3b, 4, possibly 24a and 24b), the mold parts forming a cavity (5) when the mold (1) is closed a volume that varies along an axis with one or more undercuts and are detachable from one another along a flat or free-form parting plane (6), characterized in that the mold part (4) (hereinafter referred to as the insert) has the mold parts 2a and 2b connected to one another in pairs, 3a and 3b, as well as possibly other mold parts (24a and 24b) and allows the melt to flow along the entire cavity during mold filling and is arranged in such a way that the insert(s) give way to the volume contraction when the cast metal object cools, in order to avoid the contraction-related occurrences Reduce tensions between the volumes that vary along the longitudinal axis , wherein at least one pair of mold parts 2a/2b or 3a/3b or 24a/24b must be movably mounted so that they can be moved towards one another by the contracting cast metal object. mold after claim 1 , characterized in that the end faces of the insert (4) are introduced into the surrounding mold parts in such a way that the forces occurring due to contraction can be transferred from the mold to the insert. mold after claim 1 , characterized in that the insert (4) rests with one or both end faces directly on the cast metal object. Chill mold according to one of the preceding claims, characterized in that the inserted insert (4) can be freely adapted geometrically to the contour of the metal object to be cast. Mold according to one of the preceding claims, characterized in that the insert (4) has a wall thickness >0.2 mm and < the wall thickness of the mold and consists of a material which does not react with the cast melt. Chill mold according to one of the preceding claims, characterized in that the insert (4) is encased with heat-dissipating materials to increase heat dissipation. Mold according to one of the preceding claims, characterized in that the insert (4) consists of several parts. Mold according to one of the preceding claims , characterized in that the various mold parts are guided towards one another in order to avoid distortion along the longitudinal axis of the cast metal object. Mold according to one of the preceding claims , characterized in that the movable mold parts are coated or mounted so that they can be pulled together more easily by the cast metal object. Mold according to one of the preceding claims , characterized in that the movable mold parts are supported by the cast metal object with a prestressed spring and/or actuators to facilitate contraction. Method for casting a contoured metal object using a mold (1) according to one of the preceding claims, consisting of a plurality of connectable mold parts (2a, 2b, 3a, 3b, 4), the mold parts forming a cavity (5 ) with at least one undercut and are detachable from one another along a flat or free-form parting plane (6), characterized in that after a melt has been introduced into the cavity (5), the insert (4) is compressed in order to reduce the pressure that occurs inside due to shrinkage , wherein - either the mold parts are pulled together by the shrinking metal object against the resistance emanating from the insert, - or the contraction of the metal object is supported by springs and/or actuators attached to the mold. procedure after claim 11 , characterized in that a metal object (7, 7', 7") is cast from an intermetallic alloy such as titanium aluminide, iron aluminide or another brittle alloy which tends to crack when shrunk onto the mold as a result of solid body contraction.

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