INVESTMENT CASTING PROCESS FOR HOLLOW COMPONENTS

• US 20110132563A1
• Filed: 12/07/2010
• Published: 06/09/2011
• Est. Priority Date: 12/08/2009
• Status: Active Grant

• Current Assignee: Mikro Systems, Inc., Siemens Energy Incorporated (Siemens AG)
• Original Assignee: Mikro Systems, Inc.
• Inventors: Appleby, Michael P., Fraser, Iain A., Paulus, John R., Burns, Andrew J., Merrill, Gary B.
• Granted Patent: US 9,272,324 B2
• Time in Patent Office: Days
• US Class Current: 164/15
• CPC Class Codes: B22C 7/02 Lost patterns
• CPC Class Codes: B22C 7/06 Core boxes
• CPC Class Codes: B22C 9/04 Use of lost patterns
• CPC Class Codes: B22C 9/10 Cores; Manufacture or installation of cores breaker cores B22C9/084
• CPC Class Codes: B22C 9/101 Permanent cores
• CPC Class Codes: B22C 9/103 Multipart cores
• CPC Class Codes: B22C 9/24 for hollow articles

Abstract

An investment casting process for a hollow component such as a gas turbine blade utilizing a ceramic core (10) that is cast in a flexible mold (24) using a low pressure, vibration assisted casting process. The flexible mold is cast from a master tool (14) machined from soft metal using a relatively low precision machining process, with relatively higher precision surfaces being defined by a precision formed insert (22) incorporated into the master tool. A plurality of identical flexible molds may be formed from a single master tool in order to permit the production of ceramic cores at a desired rate with a desired degree of part-to-part precision.

Claims

1. In an investment casting process wherein a hollow metal component is cast in a ceramic casting vessel which includes a ceramic core, the improvement comprising forming the ceramic core by a process comprising:

forming a master tool using a machining process to define a relatively lower precision region of the ceramic core;

incorporating a precision formed insert into the master tool to define a relatively higher precision region of the ceramic core;

casting a flexible mold in the master tool;

casting ceramic core material into the flexible mold to form the ceramic core; and

removing the flexible mold from the ceramic core while the ceramic core is in a green body state.

2. The investment casting process of claim 1, wherein the step of casting ceramic core material further comprises injecting a ceramic core material comprising an epoxy binder composition in slurry form into the flexible mold in a low pressure injection process.

3. The investment casting process of claim 1, wherein the step of casting ceramic core material further comprises vibrating the flexible mold during low pressure injection of the ceramic mold material to assist distribution of the slurry within the flexible mold.

4. The investment casting process of claim 1, further comprising incorporating an active device into the flexible mold and operating the active device during the step of casting ceramic core material.

5. The investment casting process of claim 1, further comprising forming two master tools and casting two flexible molds to define two respective portions of the ceramic core, and incorporating a joint geometry into the ceramic core for joining the two portions together to form the ceramic core.

6. The investment casting process of claim 1, further comprising:

heating the green body state core to above a reversion temperature of the ceramic core material after the step of removing; and

reshaping the green body state core while it is above the reversion temperature.

7. The process of claim 6, further comprising:

forming the ceramic core to include a reshaping alignment feature; and

performing the reshaping step with a setting die comprising an alignment feature cooperating with the reshaping alignment feature of the ceramic core.

9. The process of claim 1, wherein the ceramic core contains geometric detail in a plurality of pull planes, and further comprising removing the ceramic core from the flexible mold by deforming the flexible mold without causing damage to the green body state ceramic core in order to retain the geometric detail in the ceramic core in each of the pull planes.

10. The process of claim 1, further comprising casting the flexible mold by low pressure injection of a curable molding material into the master tool.

11. The process of claim 1, further comprising forming the master tool to define the ceramic core to have an overall outer envelope dimension aspect ratio of at least 20:

1.

12. The process of claim 1, further comprising forming the master tool to define the ceramic core to have an overall length of at least 30 inches.

13. The process of claim 1, further comprising:

casting a plurality of identical flexible molds in the master tool;

casting ceramic core material into each of the identical flexible molds in a parallel process to form a plurality of identical ceramic cores;

wherein a number of flexible molds in the plurality is selected to achieve a predetermined production rate.

8. The investment casting process of 1, further comprising:

forming an engineered topography in the precision insert;

replicating the engineered topography through the flexible mold to the ceramic core.

14. In an investment casting process wherein a hollow metal component is cast in a ceramic casting vessel which includes a ceramic core, the improvement comprising forming the ceramic core by a process comprising:

defining a geometry of the ceramic core comprising at least one of the group of;

a length dimension greater than 30 inches, a geometric detail having an aspect ratio of at least 20;

1, and two geometric details defining non-parallel pull planes;

forming a flexible mold defining a negative of the ceramic core geometry;

casting a ceramic core having a green body state modulus of rupture of at least 4,000 psi within the flexible mold; and

removing the ceramic core from the flexible mold in a green body state by deforming the mold to allow removal without damaging the green body state ceramic core.

15. The process of claim 14, further comprising forming the flexible mold by casting the flexible mold in a master tool comprising a relatively lower precision portion defined by a machining process and a relatively higher precision portion defined by a precision formed insert incorporated into the master tool.

16. The process of claim 14, further comprising:

forming a plurality of identical flexible molds from a single master tool;

casting ceramic core material into each of the identical flexible molds in a parallel process to form a plurality of identical ceramic cores;

wherein a number of flexible molds in the plurality is selected to achieve a predetermined production rate.

17. In an investment casting process wherein a hollow metal component is cast in a ceramic casting vessel which includes a ceramic core, the improvement comprising forming the ceramic core by a process comprising:

forming a master tool to define a shape of the ceramic core;

casting a plurality of identical flexible molds in the master tool; and

casting a plurality of identical ceramic cores in the plurality of flexible molds using a low pressure injection process in a parallel production process wherein a number of flexible molds in the plurality is selected to achieve a predetermined production rate.