Elliptical Seed Mould for Single-Crystal Casting
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Solution Overview
Problem
Current metal casting processes for single-crystal components, particularly in aeronautical turbomachines, face issues with parasitic grain growth due to defects caused by indexing elements in traditional cylindrical seeds, leading to structural weaknesses under thermomechanical stresses.
Innovation Solution
A mould with an elliptical cross-section housing for the single-crystal seed, eliminating the need for indexing elements like pins, reduces parasitic grain propagation by precise orientation and geometry, allowing for controlled epitaxial growth with reduced defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a cylindrical single-crystal seed with indexing elements (pin or flat) is used, then the crystallographic orientation can be controlled, but parasitic grains grow from the indexing elements causing defects in the component
Solution Approach 1:
The patent applies asymmetry by changing the seed geometry from a symmetric cylindrical shape to an asymmetric elliptical cross-section. The elliptical seed has a major axis and a minor axis with different lengths, creating an inherently asymmetric shape that eliminates the need for additional indexing elements like pins or flats. This asymmetric geometry provides unique crystallographic orientation control while avoiding the parasitic grain growth issues associated with traditional indexing elements.
Solution Approach 2:
The patent extracts and removes the harmful indexing elements (pin or flat) from the seed structure. By using an elliptical cross-section, the patent eliminates the need for separate indexing features, thereby taking out the source of parasitic grain growth while retaining the essential function of crystallographic orientation control through the geometric shape itself.
2Ease of operation
If an oblong seed with a flat side surface is used, then indexing is simplified, but positioning in the housing becomes difficult due to small clearance requirements
Solution Approach 1:
The patent uses asymmetry in the form of an elliptical cross-section that provides both simplified indexing and improved positioning. The elliptical shape with its distinct major and minor axes offers inherent orientation reference without requiring flat surfaces, while the continuous curved surface of the ellipse facilitates easier positioning in the housing compared to the sharp edges and flat surfaces of oblong seeds.
3Device complexity
If traditional cylindrical seeds are used, then the manufacturing process is simple, but defects are introduced that reduce component reliability under thermomechanical stresses
Solution Approach 1:
The patent introduces a moderate increase in complexity by using an elliptical cross-section instead of a simple cylindrical shape. This asymmetric geometry provides significant reliability benefits by eliminating parasitic grain growth while maintaining a relatively simple seed structure that can be manufactured and positioned effectively in the casting 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 elliptical seed configuration minimizes defects and enhances the robustness of single-crystal components by preventing parasitic grain growth, ensuring better thermomechanical stability and reducing the occurrence of defects in components like turbomachine vanes.
Implementation Method 1
the epitaxial growth of the grains from the single-crystal seed ensures the crystallographic orientation in the cast component
Implementation Method 2
During cooling, the metal solidifies and the epitaxial growth of the grains from the single-crystal seed ensures the crystallographic orientation in the cast component
Data Source
AI summary
A mould for use in manufacturing a single-crystal component by metal casting and epitaxial growth, includes a cavity in which the component is to be formed and a housing having an elliptical cross-section in which a single-crystal seed is disposed, the seed having an elliptical cross-section defined by a minor axis and by a major axis, the housing being in fluid communication with the cavity via an opening of circular cross-section through which molten metal is to flow, the single-crystal seed and the opening being centred on the same vertical axis, in which the minor axis and the major axis of the cross-section of the seed are oriented as a function of the secondary crystallographic orientations of the single-crystal forming the single-crystal seed.