Investment casting using core with integral wall thickness control means

A method for improving wall thickness control of a hollow airfoil casting between an internal casting cooling passage and an outer casting surface, comprising the steps of:

• a) providing a fired ceramic core having an airfoil-shaped external surface configured to form said cooling passage in the casting and having a plurality of integrally formed protrusions extending from said external surface at relatively thin, trailing edge passageway-forming regions of said core deviating from a determined relationship of a master core configuration relative to a molding cavity,
• b) positioning the core in a molding cavity having a configuration corresponding to the airfoil solely by engagement of the protrusions with rigid walls defining the molding cavity such that the core is substantially conformed to the determined relationship between the master core configuration and the molding cavity by said engagement,
• c) molding a fugitive airfoil-shaped pattern corresponding to the casting to be formed about the external surface of said core while said core is positioned in said determined relationship to said molding cavity whereby the wall thickness of the pattern is controlled about the core,
• d) investing a ceramic shell mold about the pattern and core,
• e) removing the pattern from the invested shell mold, leaving the core positioned in an airfoil-shaped shell mold cavity
• f) heating the mold with the core therein prior to casting molten metal in the shell mold cavity, and
• g) casting molten metal in the shell mold cavity about the core,
• h) wherein in at least one of steps e), f) and g), said protrusions of said core engage said mold in response to core displacement or distortion to maintain said core substantially conformed to said determined relationship.

A method for improving wall thickness control of a hollow airfoil casting between an internal casting cooling passage and an outer casting surface comprising the steps of:

• a) providing a fired core having an airfoil-shaped external surface configured to form said cooling passage in the casting and having a plurality of integrally formed protrusions extending from said external surface at relatively thin regions of said core prone to be distorted from a determined relationship of a master core configuration relative to a molding cavity,
• b) positioning the core in a molding cavity having a configuration corresponding to the airfoil solely by engagement of the protrusions with rigid walls defining the molding cavity such that the core is conformed substantially to a determined relationship between the master core configuration and the molding cavity by said engagement,
• c) molding a fugitive airfoil-shaped pattern corresponding to the casting to be formed about the external surface of said core while said core is positioned in said determined relationship to said molding cavity whereby the wall thickness of the pattern is controlled about the core,
• d) investing a ceramic shell mold about the pattern and core,
• e) removing the pattern from the invested shell mold, leaving the core positioned in an airfoil-shaped shell mold cavity,
• f) heating the mold with the core therein prior to casting molten metal in the shell mold cavity;
• and
• g) casting molten metal in the shell mold cavity about the core, and
• h) wherein in at least one of steps e), f) and g), said protrusions of said core engage said mold in response to core displacement or distortion to maintain said core substantially conformed to said determined relationship.