Gas Turbine Shroud Cooling Passage Manufacturing via PIM Inserts
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Solution Overview
Problem
The manufacturing of gas turbine engine shroud segments with elongated cooling passages is costly and limited by the accessibility of electric discharge machining (EDM) processes, particularly when coating is applied before machining, which can interfere with the creation of these passages.
Innovation Solution
A method involving powder injection molding using a mold with inserts to create elongated pins that define cooling passages, followed by debinding and sintering, and applying a coating while using a shoulder to protect the open ends of these passages from coating material, with subsequent machining to remove the shoulder and open the passages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If electric discharge machining (EDM) is used to create elongated cooling passages after shroud segment formation, then the cooling passages can be precisely formed, but manufacturing costs increase and the process is limited by accessibility to the geometry of the shroud segment
Solution Approach 1:
The cooling passages are formed during the powder injection molding process itself, before the shroud segment is fully manufactured. Inserts with pin members are placed in the mold cavity during molding, and the cooling passages are created as the feedstock is injected around these inserts. This preliminary formation eliminates the need for subsequent EDM operations, reducing both cost and complexity while maintaining precision.
Solution Approach 2:
The formation of cooling passages is merged with the main molding process. The inserts with pin members are integrated into the mold cavity, and the cooling passages are formed simultaneously with the shroud segment body during powder injection molding. This combines what were previously separate operations (molding and passage creation) into a single integrated process.
2Manufacturing precision
If coating is applied to the shroud surface before EDM machining, then the machined features are free of coating, but the coating application process becomes more complex and time-consuming
Solution Approach 1:
The cooling passages are formed during the molding process itself, before any coating is applied. The inserts with pin members create the passages as voids in the green part, and these passages remain free of coating because the coating is applied afterward to the external surfaces only. This eliminates the need for complex masking or selective coating procedures.
Solution Approach 2:
Instead of applying coating first and then creating passages (which would require removing coating from passages), the passages are created first during molding, and then coating is applied to the external surfaces. This reverses the conventional sequence and simplifies the overall process.
3Productivity
If elongated pins are used to define cooling passages during powder injection molding, then cooling passages are integrated during molding reducing subsequent machining needs, but the pins must be precisely positioned and removed without deforming the green part
Solution Approach 1:
The feedstock viscosity is carefully controlled during powder injection molding to ensure it is low enough to flow around the pin inserts without deforming them, yet high enough to maintain green part integrity after removal. The pin dimensions are also optimized - with cross-sectional dimensions of 0.020 inches or less and length-to-cross-sectional dimension ratios of at least 25 - to allow easy removal while defining the desired cooling passage geometry.
4Length of moving object
If the cross-sectional dimension of elongated features is reduced to 0.020 inches or less with length-to-cross-sectional dimension ratio of at least 25, then thin and long openings can be created, but the features are more susceptible to deformation during injection molding
Solution Approach 1:
The feedstock viscosity is optimized to accommodate thin, long pin inserts during injection molding. The viscosity is kept low during injection to allow the feedstock to flow around the delicate pins without deforming them, yet maintains enough body to support green part integrity. The pins are also supported at both ends by the mold cavity structure during injection, providing mechanical support that prevents deformation despite their high aspect ratio.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method reduces manufacturing costs and enhances the accessibility of creating elongated cooling passages by integrating them during molding and ensures effective coating application without clogging, improving the efficiency and accuracy of shroud segment production.
Implementation Method 1
injecting a powder injection molding feedstock into the mold cavity to obtain a green part
Implementation Method 2
disengaging the green part from the mold, including sliding the elongated pins out of the platform portion of the green part to define a plurality of elongated cooling passages
Implementation Method 3
debinding and sintering the green part to define the shroud segment
Implementation Method 4
debinding and sintering the green part to define the shroud segment
Implementation Method 5
applying a coating material on the inner surface from a source, the coating material being applied while providing an obstruction between the source and the open end with the shoulder to prevent the coating material from reaching the open end of each of the cooling passages
Data Source
AI summary
A method of manufacturing a shroud segment for gas turbine engine includes providing an insert having a plurality of pins that extend into a platform cavity portion of a mold cavity. A powder injection molding feedstock is injected. When the green part is disengaged from the mold, each elongated feature is slid out of the green part to define a respective elongated cooling passage in the platform. The method may include, after debinding and sintering, projecting a coating material while defining an obstruction between source of coating material and the open end of each elongated feature with a shoulder of the element to prevent the coating material from reaching the open end, followed by machining to remove at least a part of the shoulder.