Braze Repair of EDM Backwall Strikes in Turbine Cooling Holes
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Solution Overview
Problem
Electrical discharge machining (EDM) in gas turbine engines often results in backwall strikes due to the formation of recast layers, leading to extended holes and stress concentrations in hot gas path components, which can compromise the structural integrity and efficiency of the engine.
Innovation Solution
A repair process involving the identification of backwall strikes using borescopes or CT scans, followed by the insertion of a custom-made repair rod with a crimped plug, and deposition of braze paste to fill and solidify the void, effectively addressing the structural issues caused by EDM.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If EDM is used to form cooling holes in hot gas path components, then cooling passages can be created, but backwall strike occurs causing extended holes and stress concentrations
Solution Approach 1:
The patent applies preliminary action by first identifying the backwall strike void using borescope or CT scan, then determining its physical configuration before inserting the repair rod. This preliminary assessment allows for proper sizing and shaping of the repair rod to match the void, ensuring precise filling without creating additional manufacturing errors.
Solution Approach 2:
The patent changes the physical state and properties of materials through the braze process. The braze paste is applied in a molten or plastic state to fill the void, then heated to facilitate bonding and solidification. This parameter change (temperature, state) allows the repair material to conform to the void geometry and bond with surrounding structures, resolving the depth control issue.
2Ease of manufacture
If EDM is used to form cooling holes, then cooling passages are created, but recast layer forms affecting hole configuration
Solution Approach 1:
The patent converts the harmful recast layer and backwall strike void into a beneficial repair opportunity. Instead of discarding the component due to the void, the repair process uses the void as a target for precise material addition. The braze paste fills the irregular void created by recasting, restoring the intended hole geometry and even improving the area by eliminating stress concentrations.
Solution Approach 2:
The patent applies local quality by creating a repair rod with specific properties tailored to match the void's local characteristics. The repair rod is customized based on the void's depth, diameter, and shape, ensuring that the filled area has appropriate material properties and geometry. This localized approach restores the hole's contour and depth configuration precisely where needed.
3Reliability
If backwall strike is repaired by filling voids, then structural integrity is restored, but repair process complexity increases
Solution Approach 1:
The patent replaces complex mechanical repair operations with a more streamlined process. Instead of mechanical machining or welding operations that would require precise positioning and control, the process uses borescope inspection to identify voids, then inserts pre-configured repair rods followed by braze application. This substitution simplifies the repair mechanics while maintaining structural integrity restoration.
4Manufacturing precision
If extended holes are created by EDM to compensate for recasting, then recast layer is accounted for, but stress concentrations occur in cooling passages
Solution Approach 1:
The patent converts the harmful stress concentration caused by extended holes into a beneficial situation by filling the void with repair material. The backwall strike void, which created stress concentrations, becomes a target for precise material addition. The braze paste fills the irregular void geometry, eliminating stress concentration points and restoring uniform stress distribution in the cooling passage walls.
Solution Approach 2:
The patent creates a composite structure by combining the original component material with the braze repair material. The repair rod and braze paste form a composite fill within the void, creating a heterogeneous material structure that restores structural integrity. This composite approach allows the repair area to withstand stress concentrations by distributing loads across different material phases and interfaces.
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
The repair process mitigates stress concentrations and maintains the structural integrity of hot gas path components, enhancing the operational efficiency and longevity of gas turbine engines by preventing further damage from EDM-induced backwall strikes.
Implementation Method 1
depositing braze paste over the repair plug in the void
Data Source
AI summary
A process of repairing a component includes identifying a void in a component; determining at least one approximate physical configuration of the void; inserting borescope into the component in order to view the void; providing a repair rod approximately equivalent to at least one of the least one approximate physical configuration of the void; inserting the repair rod into component; confirming insertion of the repair rod in the void; separating the repair rod to leave a repair plug in the void; and depositing braze paste over the repair plug in the void.