ECM Electrode Fixture for In-Situ Turbine Dovetail Edge Rounding
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Solution Overview
Problem
In gas turbine engines, the edge regions of dovetail slots in turbine wheels are prone to cracking due to high mechanical stresses, and existing ECM techniques struggle to effectively round these edges without complete disassembly, often requiring costly and incomplete mechanical grinding and polishing processes.
Innovation Solution
A portable ECM fixture and cathode system that allows for in-situ electro-chemical machining of dovetail slots, using a clamp and electrode mount to position the cathode close to the edges, enabling precise rounding of edges with minimal polishing and blending, and can be used without disassembling the turbine rotor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If mechanical grinding and BPP methods are used to round edges, then material can be removed and edges can be blended, but the desired radius is difficult to achieve and cracks may remain
Solution Approach 1:
The patent replaces mechanical grinding and BPP methods with electrochemical machining (ECM). The ECM process uses electrochemical reactions to remove material precisely without mechanical contact, eliminating the inability to achieve desired radius and leave cracks. The electrolyte chemically dissolves metal at the edge regions with controlled precision, producing smooth rounded edges with radii of 0.002-0.010 inches while completely removing crack defects.
2Ease of operation
If complete disassembly of turbine rotor is performed to access wheels for ECM, then full access to dovetail slots is achieved, but downtime and operational disruption increase
Solution Approach 1:
The patent segments the ECM system into portable, modular components including a handheld electrode, flexible hoses for electrolyte delivery, and a compact power supply. This segmentation allows the ECM equipment to be brought to the turbine wheel without requiring complete rotor disassembly. The electrode can be inserted through existing access points or narrow openings to reach dovetail slots while the turbine remains partially assembled, significantly reducing downtime.
Solution Approach 2:
The patent introduces flexible electrolyte delivery hoses and positioning fixtures as intermediaries that bridge the gap between the external ECM equipment and the internal dovetail slots. These intermediaries enable material removal at difficult-to-reach locations without requiring complete disassembly of the turbine rotor, allowing maintenance personnel to access and treat edge regions while the turbine structure remains largely intact.
3Loss of time
If ECM is performed with limited access, then downtime is reduced, but bringing the tool into stable proximity to edges becomes difficult
Solution Approach 1:
The patent employs a handheld, movable electrode design rather than a fixed tooling system. The electrode can be dynamically positioned and repositioned by the operator to reach different edge regions within the dovetail slot. This dynamic positioning capability, combined with flexible electrolyte delivery hoses, allows the ECM process to adapt to limited access conditions while maintaining operational effectiveness, enabling stable material removal without requiring complete disassembly for rigid tool installation.
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 system effectively rounds sharp edges to reduce stress concentrations and extend turbine wheel life, achieving a mirror finish surface roughness of 0.025-0.25 microns while minimizing downtime and costs by allowing on-site, in-situ machining of critical components.
Implementation Method 1
electro-chemical machining (ECM) of a portion of the selected dovetail slot
Data Source
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AI summary
A fixture (200) for an electro-chemical machining (ECM) electrode (202) is provided. The fixture (200) includes a clamp (204) having a shape and size configured to selectively engage in at least a portion of a selected dovetail slot of a plurality of dovetail slots in a turbine wheel. An electrode mount (206) positions an electrode head (208) relative to the clamp (204) such that the electrode head (208) operatively engages a portion of the selected dovetail slot for electro-chemical machining of the portion. The fixture (200)'s electrode (202) acts as a cathode (300, 302) for the ECM process. The fixture (200) allows for ECM on site without removing a turbine wheel from a turbomachine.