Method of forming a cast metal article

• US 8,393,381 B2
• Filed: 05/18/2011
• Issued: 03/12/2013
• Est. Priority Date: 05/18/2011
• Status: Active Grant

• Current Assignee: PCC Airfoils LLC (Berkshire Hathaway Incorporated)
• Original Assignee: PCC Airfoils LLC (Berkshire Hathaway Incorporated)
• Inventors: Graham, Lawrence D., Barrett, James, Deptowicz, Don
• Primary Examiner(s): Kerns, Kevin P
• Assistant Examiner(s): Yoon, Kevin E
• Application Number:
  US13/110,362
• Publication Number:
  US 20120291983A1
• Time in Patent Office: 664 Days
• Field of Search: 164/131, 164/132, 164/369, 164/516, 134/2, 134/3, 134 221- 2212
• US Class Current: 164/132
• 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: B22D 15/02 of cylinders, pistons, bearing shells or like thin-walled objects
• CPC Class Codes: B22D 29/002 by leaching, washing or dissolving
• CPC Class Codes: B33Y 80/00 Products made by additive manufacturing

Abstract

A cast metal article is formed with an internal cavity. The internal cavity is formed by a ceramic core which is removed from the cast metal article to leave the cavity. The ceramic core is formed with a cavity to facilitate removal of the core from the cast metal article. To remove the core from the cast metal article, the cavity in the core is filled with a leaching liquid.

Claims

1. A method of forming a metal cast article, said method comprising the steps of forming a ceramic core containing a cavity by interconnecting layers of ceramic material to form the cavity with dimensions which are greater than a thickness of a plurality of said layers, positioning the core in a mold, at least partially filling a cavity in the mold with molten metal while maintaining the cavity in the core at least substantially free of molten metal, solidifying the molten metal in the mold to form a cast metal article which at least partially contains the core, and removing the core from the cast metal article, said step of removing the core from the cast metal article includes at least partially filling the cavity in the core with a leaching liquid while the core is at least partially disposed in the cast metal article and engaging the layers of ceramic material with the leaching liquid filling the cavity in the core.

2. A method as set forth in claim 1 said step of forming a ceramic core includes providing a body of liquid which is capable of solidification when exposed to a beam of radiation, exposing an upper surface of the body of liquid to a beam of radiation, moving the beam of radiation relative to the upper surface of the body of liquid to effect formation of a first layer of the core, moving the first layer of the core downward in the body of liquid, covering an upper surface of the first layer of the core with liquid of the body of liquid, and moving the beam of radiation relative to the body of liquid to effect formation of a second layer of the core on the first layer of the core.

3. A method as set forth in claim 1 wherein said step of removing the core from the cast metal article includes applying a first fluid pressure against the leaching liquid to urge the leaching liquid into the cavity in the core and, thereafter, exposing the leaching liquid to a second fluid pressure which is below atmospheric pressure and is less than the first fluid pressure.

4. A method as set forth in claim 1 wherein said step of forming a ceramic core containing a cavity includes forming a partition which divides at least a portion of the cavity into first and second sections, said step of forming a partition includes interconnecting a plurality of layers of ceramic material, said step of filling the cavity in the core with a leaching liquid includes conducting leaching liquid into the first and second sections of the cavity and engaging the partition with the leaching liquid.

5. A method as set forth in claim 1 wherein said step of solidifying the molten metal in the mold to form a cast metal article includes solidifying the molten metal to form a cast metal airfoil having leading and trailing edge portions, said step of forming a ceramic core includes forming a ceramic core containing a cavity having a first portion which is formed by interconnected layers of ceramic material and is disposed in the leading edge portion of the cast metal airfoil prior to removal of the core from the cast metal article and a second portion which is formed by interconnected layers of ceramic material and is disposed in the trailing edge portion of the cast metal airfoil prior to removal of the core from the cast metal article, said step of forming a ceramic core containing a cavity includes forming a ceramic core having at least a portion of a cavity formed in the first portion of the core to facilitate movement of leaching liquid into the leading edge portion of the cast metal airfoil and at least a portion of a cavity formed the second portion of the core to facilitate movement of leaching liquid into the trailing edge portion of the cast metal airfoil.

6. A method as set forth in claim 1 wherein said step of solidifying the molten metal to form a cast metal article includes forming a cast metal airfoil having a tip end portion, said step of forming a ceramic core containing a cavity includes forming a ceramic core having an end portion which is formed by interconnected layers of ceramic material and is disposed in the tip end portion of the cast metal airfoil prior to removal of the core from the cast metal article, said step of forming a ceramic core containing a cavity includes forming a ceramic core having at least a portion of a cavity formed in the end portion of the core to facilitate movement of leaching liquid into the tip end portion of the cast metal airfoil, said step of filling the cavity in the core with leaching liquid includes engaging the layers of ceramic material in the end portion of the ceramic core with the leaching liquid.

7. A method as set forth in claim 6 wherein said step of forming a cast metal airfoil includes forming a cast metal airfoil having an edge portion which is connected with the tip end portion of the cast metal airfoil, said step of forming a ceramic core containing a cavity includes forming a ceramic core having a second portion which is formed by interconnected layers of ceramic material and is disposed in the edge portion of the cast metal airfoil prior to removal of the core from the cast metal airfoil, said step of forming a ceramic core containing a cavity includes forming a ceramic core having at least a portion of a cavity in the second portion of the core to facilitate movement of leaching liquid into the edge portion of the cast metal airfoil, said step of filling the cavity in the core with leaching liquid includes engaging the layers of ceramic material in the second portion of the ceramic core with the leaching liquid.

8. A method as set forth in claim 1 wherein said step of forming a ceramic core includes forming a ceramic core having a longitudinal central axis by moving a beam of radiation in a direction transverse to the longitudinal central axis of the core and sequentially forming layers of the core as the beam of radiation moves in a direction transverse to the longitudinal central axis of the core.

9. A method as set forth in claim 1 wherein said step of forming a ceramic core includes forming a ceramic core having a longitudinal central axis by moving a beam of radiation along the longitudinal central axis of the core and sequentially forming layers of the core as the beam of radiation moves in a direction along the longitudinal axis of the core.

10. A method as set forth in claim 1 wherein said step of forming a ceramic core containing a cavity includes sequentially forming cross sectional layers of the core with portions of the cavity in the core disposed in at least some of the layers of the core.

11. A method as set forth in claim 1 wherein said step of forming a ceramic core includes forming a ring shaped core which extends around an open central area and forming a ring shaped cavity in the core with the ring shaped cavity extending around the open central area by interconnecting ring shaped layers of ceramic material, said step of filling the cavity in the core with leaching liquid includes filling the ring shaped cavity with leaching liquid and engaging the ring shaped layers of ceramic material with the leaching liquid.

12. A method as set forth in claim 1 wherein said step of forming a ceramic core includes forming a ring shaped core having a toroidal configuration by interconnecting circular layers of ceramic material and forming a circular cavity within the core, said step of filling the cavity in the core with leaching liquid includes filling the circular cavity with leaching liquid and engaging the circular layers of ceramic material with the leaching liquid.

13. A method as set forth in claim 1 wherein said step of forming a ceramic core includes forming a core which has layers of ceramic material extending around an open central portion and forming a cavity which extends around the open central portion of the core.

14. A method as set forth in claim 1 wherein said step of forming a ceramic core includes forming a core having layers of ceramic material forming a plurality of straight portions interconnected by a plurality of curving portions and forming a cavity having straight portions disposed in the straight portions of the core and having curving portions disposed in the curving portions of the core.

15. A method as set forth in claim 1 wherein said step of forming a ceramic core containing a cavity includes forming a honey comb structure with layers of ceramic material disposed in the cavity in the core.

16. A method as set forth in claim 15 wherein said step of forming a honey comb structure includes forming an open cell structure to enable liquid to be conducted through the honey comb structure.

17. A method as set forth in claim 15 wherein said step of forming a honey comb structure includes forming a closed cell structure to block a flow of liquid through the honey comb structure.

18. A method as set forth in claim 1 wherein said step of forming a ceramic core containing a cavity includes forming a close ended cavity to block a flow of liquid through the cavity.

19. A method as set forth in claim 1 wherein said step of forming a ceramic core containing a cavity includes forming an open ended cavity to enable liquid to flow through the cavity.

20. A method of forming a cast metal article, said method comprising the steps of forming a ceramic core having a root end portion and a blade portion, the blade portion of the core having first and second edge portions which are connected with a second end portion of the core which is opposite from the root end portion of the core, said step of forming a ceramic core includes interconnecting layers of ceramic material with at least some of the layers of ceramic material at least partially disposed in the first edge portion of the blade portion of the core, with at least some of the layers of ceramic material at least partially disposed in the second edge portion of the blade portion of the core, and with at least some of the layers of ceramic material disposed in the second end portion of the core, said step of interconnecting the layers of ceramic material includes forming at least a portion of a cavity in the first edge portion of the blade portion of the core, forming at least a portion of a cavity in the second edge portion of the blade portion of the core, and forming at least a portion of a cavity in the second end portion of the core, positioning the core in a cavity in a mold, said step of positioning the core in a cavity in the mold includes positioning the core in a cavity having a configuration corresponding to the configuration of an airfoil, at least partially filling the cavity in the mold with molten metal while maintaining cavities in the core at least substantially free of molten metal, solidifying the molten metal in the cavity in the mold to form a cast metal airfoil which at least partially contains the core, and removing the core from the cast metal airfoil, said step of removing the core from the cast metal airfoil includes conducting a flow of a leaching liquid from the root end portion of the core to the portion of a cavity disposed in the first edge portion of the core and engaging at least some of the layers of ceramic material disposed in the first edge portion of the blade portion of the core with the leaching liquid, conducting a flow of the leaching liquid from the root end portion of the core to the portion of a cavity disposed in the second edge portion of the core, and engaging at least some of the layers of ceramic material disposed in the second edge portion of the blade portion of the core with the leaching liquid, and conducting a flow of leaching liquid from the root end portion of the core to the second end portion of the core and engaging at least some of the layers of ceramic material disposed in the second end portion of the core with the leaching liquid.

21. A method as set forth in claim 20 wherein said steps interconnecting layers of ceramic material in the second end portion of the core and forming at least a portion of a cavity in the second end portion of the core includes forming a partition which is formed by layers of ceramic material and is effective to isolate a portion of a cavity formed in the second end portion of the core from cavities in other portions of the core, said step of conducting a flow of leaching liquid from the root end portion of the core to the second end portion of the core includes engaging the partition with the leaching liquid to effect disintegration of the partition.