Backwall Strike Braze Repair for EDM Cooling Hole Voids
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Solution Overview
Problem
Electrical discharge machining (EDM) in gas turbine engine components often results in backwall strikes due to the formation of recast layers, leading to extended holes and stress concentrations, which compromise the structural integrity of hot gas path components.
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 the void, effectively addressing the structural issues caused by EDM.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
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 complete filling without over-penetration that would cause further structural damage.
Solution Approach 2:
The repair rod serves as an intermediary element between the external repair access and the internal backwall strike void. It is inserted through the extended hole, filled with braze paste, and then the rod is broken off, leaving the braze material to seal and reinforce the void. This intermediary approach allows repair without requiring direct access to the void location.
2Manufacturing precision
If EDM drilling is extended to compensate for recast layer formation, then accurate hole depth can be achieved, but backwall strike occurs creating voids and stress concentrations
Solution Approach 1:
The patent converts the harmful backwall strike void into a beneficial repair opportunity. The void created by excessive drilling is identified and then completely filled with braze paste using the repair rod method. This transforms the defect into a reinforced area, converting the harmful stress concentration zone into a strengthened region that improves overall component reliability.
Solution Approach 2:
The patent changes the physical state and material properties at the backwall strike location by introducing braze paste that melts and fills the void, then solidifies to create a homogeneous reinforced structure. This parameter change transforms the void space into a solid, stress-distributing material that eliminates the harmful concentration effect.
3Reliability
If repair rod is inserted to fill backwall strike void, then void can be sealed, but rod must be separated leaving plug in void
Solution Approach 1:
The patent applies segmentation by dividing the repair rod into two functional parts: a insertion/removal portion and a remaining plug portion. The rod is designed with a specific break point that allows it to be inserted through the extended hole, filled with braze paste, and then cleanly separated. The remaining plug stays in the void to maintain structural integrity while the removed portion allows access for braze paste deposition.
Solution Approach 2:
The repair rod is designed to be self-breaking at a predetermined location within the void. This self-service feature eliminates the need for complex removal mechanisms or tools. The rod automatically separates at the designed weak point, leaving the plug in place to seal the void while the external portion can be easily removed, simplifying the overall repair process.
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 ensures accurate hole configurations, enhancing the structural integrity and performance of hot gas path components by preventing excessive drilling and recasting.
Implementation Method 1
inserting borescope into the component in order to view the void
Implementation Method 2
depositing braze paste over the repair plug in the void
Data Source
Figure 1~2
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AI summary
A process of repairing a component (110) includes identifying a void (255) in a component (110); determining at least one approximate physical configuration of the void (255); inserting borescope into the component (110) in order to view the void (255); providing a repair rod (270) approximately equivalent to at least one of the least one approximate physical configuration of the void (255); inserting the repair rod (270) into component (110); confirming insertion of the repair rod (270) in the void (255); separating the repair rod (270) to leave a repair plug (253) in the void (255); and depositing braze (252) paste over the repair plug (253) in the void (255).