METHOD FOR PRODUCING A CERAMIC CORE FOR THE PRODUCTION OF A CASTING HAVING HOLLOW STRUCTURES AND CERAMIC CORE

Abstract

The invention relates to a method for producing a ceramic core (4, 4)and to a core produced by this methodfor preparing the production of a casting having hollow structures which the ceramic core is configured to form, making use of a 3D model of digital geometric co-ordinates of the casting, wherein the method comprises the following steps: a) Producing by means of casting technology at least one first portion (4) of the ceramic core including at least one first joining structure (24) in a surface of the portion; b) Producing by means of casting technology or 3D printing technology at least one second portion (4) of the ceramic core including at least one second joining structure (26) matching the first joining structure, in a surface of the portion, wherein the production by means of casting technology comprises the following steps: i. Unpressurized or low-pressure casting of a ceramic core blank, and specifically with an oversize relative to the core (4, 4) according to the geometric co-ordinates; ii. CNC processing of the core (4, 4), according to the 3D model, in a first CNC processing method; c) joining the at least one first and at least one second portion of the core at the matching joining structures to form the core according to geometric co-ordinates of the casting.

Claims

1. A method for producing a ceramic core for preparing the production of a casting having hollow structures which the ceramic core is configured to form, using a 3D model of digital geometrical co-ordinates of the casting, the method comprising acts of: a) producing at least one first portion of the ceramic core using casting technology, the first portion including at least one first joining structure in a surface of the first portion; b) producing at least one second portion of the ceramic core using casting technology or 3D printing technology, the second portion including at least one second joining structure, which matches the first joining structure, in a surface of the second portion, wherein producing the at least one second portion using casting technology in act b) comprises acts of: i. unpressurized or low-pressure casting of a ceramic core blank with an oversize relative to the core according to the geometric co-ordinates; and ii. CNC processing of the core, according to the 3D model, in a first CNC processing method; and c) joining the at least one first portion and the at least one second portion of the core at the matching first and second joining structures to form the core according to geometric co-ordinates of the casting.

2. A ceramic core for producing a casting having hollow structures which the ceramic core is configured to form, using a 3D model of digital geometrical co-ordinates of the casting, using a ceramic mould, wherein the core is produced by acts of: a) producing at least one first portion of the ceramic core using casting technology, the first portion including at least one first joining structure in a surface of the first portion; b) producing at least one second portion of the ceramic core using casting technology or 3D printing, the second portion including at least one second joining structure, which matches the first joining structure, in a surface of the second portion, wherein producing the at least one second portion using casting technology in act b) comprises acts of: i. unpressurized or low-pressure casting of a ceramic core blank with an oversize relative to the core according to the geometric co-ordinates; and ii. CNC processing of the core, according to the 3D model, in a first CNC processing method; and c) joining the at least one first portion and the at least one second portion of the core at the matching first and second joining structures to form the core according to geometric co-ordinates of the casting.

3. The method according to claim 1, wherein act a) further comprises acts of: i. unpressurized or low-pressure casting of a ceramic core blank with an oversize relative to the core according to the geometric co-ordinates; and ii. CNC processing of the core, according to the 3D model, in a first CNC processing method.

4. The method according to claim 1, wherein act i) is performed using slip casting, pressure slip casting, cold isostatic pressing, hot isostatic pressing, uniaxial pressing, hot casting, low-pressure injection moulding, gel casting or extrusion.

5. The method according to claim 1, wherein act ii) includes CNC milling.

6. The method according to claim 1, further comprising acts of: d) positioning the core in a processing holding device; e) pouring model material around the core, into a volume greater than the cubic dimensions of the casting, which, according to the 3D model, is spatially determined by the position of the core in the processing holding device, and allowing the model material to solidify; f) CNC production of an outer contour of a lost model of the casting from the solidified model material around the core, in accordance with the 3D model in a second CNC production method; g) applying a ceramic mould onto the outer contour of the lost model and forming a positioning connection of the ceramic mould with the core; h) removing the lost model from the ceramic mould around the core; i) pouring metal into the ceramic mould around the core; j) solidifying of the molten metal to form the solid casting and cooling channels; and k) removing the ceramic mould and the core from the casting.

7. The ceramic core according to claim 2, wherein act a) further comprises acts of: i. unpressurized or low-pressure casting of a ceramic core blank with an oversize relative to the core according to the geometric co-ordinates; and ii. CNC processing of the core, according to the 3D model, in a first CNC processing method.

8. The ceramic core according to claim 2 wherein act i) is performed using slip casting, pressure slip casting, cold isostatic pressing, hot isostatic pressing, uniaxial pressing, hot casting, low-pressure injection moulding, gel casting or extrusion.

9. The ceramic core according to claim 2, wherein act ii) includes CNC milling.

Description

[0114] These and other advantages and features of the invention are further described on the basis of the following illustrations of an exemplary embodiment of the invention. In the figures:

[0115] FIGS. 1 to 7 are schematic views of successive steps of a method according to the invention for producing a casting that comprises hollow structures.

[0116] FIG. 8a to c are schematic views of cores according to the invention, from the side (FIG. 8a), and in two alternative cross-sections,

[0117] FIGS. 9a and b are schematic views of a core according to the invention, from the side (FIG. 9a), and in cross-section, and

[0118] FIG. 10a to e are schematic cross-sections of joining points of core component regions of cores according to the invention.

[0119] These (highly schematic) figures illustrate the production of a casting 2 (FIG. 7) comprising hollow structures 3, 3 (using a 3D model, specifically a three-dimensional CAD model of digital geometric co-ordinates, of the casting) based on the example of a gas turbine blade 2 (FIG. 7) comprising inner cooling channels 3, 3, and specifically including producing a ceramic core 4, 4 (FIG. 1; also using the 3D model of the casting). The ceramic core 4, 4 is configured to form the hollow structures 3, 3.

[0120] Using a 3D model of a casting 2 (FIG. 7), a core 4, 4, shown in FIG. 1, is produced according to the 3D model in an initial method stage (see FIG. 8 ff below). According to FIG. 2, in a next method step the core 4, 4 is positioned in a processing holding device 6. Arranged around the core is a vessel (volume) 8, likewise positioned and secured in the processing holding device 6.

[0121] According to FIG. 3, in a next method step model wax 10 is poured into the volume 8 around the core 4. The volume 8 is larger than the cubic dimensions 12 of the casting, and therefore the model wax 10 is poured into the volume 8 and around the core 4 on all sides until it extends beyond the cubic dimensions 12 of the casting. According to the 3D model of the casting 2 (FIG. 7), the spatial position of the cubic dimensions 12 of the casting in the volume 8 is determined by the position of the core 4 in the processing holding device 6. According to FIG. 4, in a next method step the model material 10 is now allowed to solidify around the core 4, and the volume 8 is removed.

[0122] According to FIG. 5, in a next method step the outer contour of a temporary (lost) model 14 of the casting 2 (FIG. 7) is produced around the core 4, and specifically from the solidified model material 10 in accordance with the 3D model by CNC milling (not shown).

[0123] After this step, the resulting wax model 14, with the core 4 inside it, is removed from the processing holding device 6 (for example by releasing an adhesive connection or by severing ceramic core material at the transition point to the holding device). The processing holding device 6 is no longer present in the further steps. Instead, the wax model 14 with the core 4 is mounted on what is referred to as a wax cluster (not shown), which forms the gating system, and fixes the model by mechanical means.

[0124] The connection of the core to the ceramic shell 16, now to be produced with reference to FIG. 6, is produced by means of what are referred to as core locks 18 or core marks 18. These are areas in which the core 4 emerges from the wax model and, during coating with ceramic 16 (now taking place), connects securely to the ceramic shell 16. The positioning between the wax model 14 and the core 4 therefore no longer needs to be provided by the processing holding device 6.

[0125] According to FIG. 6, in the next method step, a ceramic mould 16 is therefore applied onto the outer contour of the lost model 14, and in this situation a positioning connection 18 of the ceramic mould 16 is formed by way of a core mark 18 with the core 6, such that the ceramic mould 16 is positioned dimensionally accurately in relation to the core 4 in accordance with the 3D model (not shown) of the casting 2 (FIG. 7) by the core mark 18. The lost model 14 is then removed from the ceramic mould 16 around the core 4 (both of these continue to be held and positioned in relation to one another by the positioning connection 18). A hollow mould 20 is formed between the surface of the ceramic core 4 and the inner surface 14 of the ceramic mould 16. The actual casting mould (to be destroyed after casting, i.e. lost) is finished.

[0126] Molten metal (not shown) is then poured therein. This is subsequently left to cool. The molten metal (not shown) solidifies to form the solid casting 2, which according to FIG. 7 becomes visible in a next method step (by the removal of the lost ceramic mould 16 and of the ceramic core 4 from the casting 2), and is therefore available as a component with a hollow structure 22 (corresponding precisely to the core 4) with a high degree of dimensional precision.

[0127] The method for producing the ceramic core 4, 4 shown in FIG. 1 serves, so to speak, as a preparation of the actual productiondescribed so farby means of casting (according to FIGS. 6 and 7) of the casting 2 comprising hollow structures 3, 3, in that it is an initial method stage for producing the core 4, 4 as a component of the (lost) mould 16 of the casting 2, which is followed by the subsequent method stages (according to FIGS. 2 to 6) for producing the (lost) mould 16 of the casting 2and to which, as described, these are geometrically oriented in a highly precise manner.

[0128] This particular method for producing the ceramic core 4, 4 shown in FIG. 1, and also the cores 4, 4 according to FIG. 8-10, is directed at producing the ceramic core from (at least) two portions 4 and 4, and comprises the following steps: [0129] a) Producing the first portion 4 of the ceramic corespecifically by means of casting technologyincluding at least one first joining structure 24 in a surface of the portion; [0130] b) Producing at least one second portion 4 of the ceramic corespecifically by means of 3D printing technologyincluding at least one second joining structure 26, matching the first joining structure 24, in a surface of the second portion 4; [0131] c) Joining the at least one first portion 4 and the at least one second portion 4 of the core, at matching joining structures 24, 26, to the core, according to geometric co-ordinates of the casting.

[0132] In this case, the production by means of casting technology comprises the following steps: [0133] i. Unpressurised or at least low-pressure casting of a ceramic blank of the core portion 4 by means of slip casting, pressure slip casting, cold isostatic pressing, hot isostatic pressing, uniaxial pressing, hot casting, low-pressure injection moulding, gel casting or extrusion, and specifically with an oversize with respect to the geometric co-ordinates of the core; [0134] ii. CNC processing, in particular CNC milling of the core according to the 3D model in a first CNC processing method.

[0135] In detail, in this case at least one interface or joining location 28 is defined in the 3D model, up to which the core geometry details are to be produced by casting technology as a one-piece core component region 4 or core base body 4 (as stated in particular by means of a core blank and the subsequent CNC processing thereof). In this way, the overall core 4, 4 can be assembled at the joining points 28 from at least two core component regions 4, 4. The core component regions 4, 4 can all be produced by means of casting technology (for example in order to be able to exceed dimension limits, for instance of the producibility of an overall core formed as one piece). Alternatively at least one core component region 4 on the other side of the joining point 28 is (as in the examples shown) produced by means of 3D printing technology, in particular in order to be able to produce smaller and more complex details 29 there (the latter for example undercuts, or also more complex cavities of the core (29 in FIG. 8c; i.e. ribs or other solid portions of a more complex shape in the cavity (to be formed later by the core) of the component to be produced), than can be achieved by means of casting techniques. A joined core component region 4 can for example be placed on a surface of another core component region 4 (for example according to FIG. 8b) or inserted into a penetration (for example according to FIG. 8c), and thus appear on more than one surface of the other core component region 4.

[0136] Thus, a first joining structure 24 and a matching second joining structure 26 of the at least one interface or joining location 28 is formed in greater detail in the 3D model, for production, using connection technology, of a mechanically secure bridging of the two core component regions 4 and 4.

[0137] The selection of the core component regions 4 which are produced as 3D ceramic by means of 3D printing technology, follows the preferred rule of implementing particularly finely detailed features or particularly small and complex details in 3D printing technology, for example in order to achieve greater design freedom with respect to gap widths, undercuts and the like (which are problematic in particular in CNC milling).

[0138] Following preparation of the two joining surfaces 24, 26 or joining structures 24, 26, for example as a clearance fit, with or without a ceramic adhesive, the two core component regions are joined. In this case, preparation steps may be (alternatively or cumulatively): cleaning, drying, deburring, chemical surface treatment, applying adhesive 30.

[0139] FIG. 10 schematically shows differently designed joining points 28 of the core component regions 4 and 4 in a form-fitting connection having a clearance fit in a conical or wedge seat: without adhesive (FIG. 10a); with adhesive 30 (FIG. 10b et seq.), and specifically in a cavity 32 formed in the joining surface 28 (FIG. 10b); with adhesive in pin-shaped chambers 34 which cross the joining surface 28 (FIG. 10c); with spacers 36 which, located in a form-fitting manner in grooves 38, hold the joining contours 24, 26 at a distance for the adhesive 30, which is filled with the adhesive 30 (FIG. 10d). It is also possible for the core component regions 4 and 4 to be locked together in a form-fitting connection, for example by means of a dovetail contour 40 (FIG. 10e), and then possibly also additionally adhesively bonded.

LIST OF REFERENCE SIGNS

[0140] casting 2 [0141] gas turbine blade 2 [0142] hollow structures 3, 3 [0143] inner cooling channels 3, 3 [0144] ceramic core 4, 4 [0145] processing holding device 6 [0146] vessel (volume) 8 [0147] model wax 10 [0148] model material 10 [0149] cubic dimensions 12 of the casting [0150] lost model 14 [0151] wax model 14 [0152] inner surface 14 [0153] portion 4 [0154] ceramic shell 16 [0155] lost mould 16 [0156] core locks 18 [0157] core marks 18 [0158] connection 18 [0159] hollow mould 20 [0160] hollow structure 22 [0161] joining structure 24, 26 [0162] interface or joining location 28 [0163] adhesive 30 [0164] cavity 32 [0165] pin-shaped chambers 34 [0166] spacer 36 [0167] grooves 38 [0168] dovetail contour 40