Single-Crystal Casting Mould Orientation for Stray Grain Control
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Solution Overview
Problem
Conventional methods for forming single crystal components in gas turbine engines face challenges in preventing stray grain nucleation, which leads to surface defects and non-conformance with specifications, necessitating a mechanism to ensure desired crystallography and minimize secondary grain formation.
Innovation Solution
A method involving the determination of an optimal angular orientation of an initial mould unit relative to a central sprue, using a thermal model to position a seed crystal such that its primary growth direction forms a converging disposition with the mould wall in one region and a diverging disposition in another, thereby reducing the formation of secondary grains through controlled dendritic growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional methods are used to form single crystal components, then the manufacturing process is simpler, but stray grain nucleation occurs leading to surface defects and non-conformance with specifications
Solution Approach 1:
The mould assembly is made rotatable about the central sprue axis, allowing dynamic adjustment of the initial mould unit's angular orientation. This dynamic capability enables optimization of the relationship between the seed crystal's primary growth direction and the mould wall, thereby controlling dendritic growth patterns and preventing stray grain nucleation while maintaining manufacturing feasibility
Solution Approach 2:
The method involves determining and optimizing specific angular orientation parameters of the initial mould unit relative to the central sprue. By controlling this geometric parameter, the primary growth direction of the seed crystal is positioned to form specific angles with the mould wall, which directly influences crystal growth behavior and prevents secondary grain formation
2Reliability
If the primary growth direction of the seed crystal is positioned at specific angles to the mould wall, then secondary grain formation is reduced, but the mould assembly becomes more complex with precise orientation requirements
Solution Approach 1:
The optimal angular orientation of the initial mould unit is determined in advance before the actual casting process. This preliminary determination allows the mould assembly to be pre-configured with the correct orientation, ensuring that when the seed crystal is inserted and molten material is poured, the primary growth direction naturally forms the desired angles with the mould wall, thereby ensuring single crystal structure integrity without requiring complex real-time control
3Manufacturing precision
If tight specifications are adhered to prevent stray grains, then component quality improves, but the manufacturing process becomes more stringent and complex
Solution Approach 1:
The method replaces complex mechanical control systems with a geometric relationship-based approach. By establishing the optimal angular orientation between the seed crystal's primary growth direction and the mould wall through geometric configuration rather than complex mechanical actuation, the process achieves precise control over crystal growth while simplifying the overall manufacturing 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 method minimizes the formation and stabilization of secondary grains, resulting in components with reduced surface defects and improved conformance to specifications, ensuring desired operational performance.
Implementation Method 1
receiving the seed crystal within the seed holder, such that the primary growth direction of the seed crystal forms the converging disposition with the mould wall in the first region of the mould wall and the diverging disposition with the mould wall in the second region of the mould wall. Filling, via the central sprue, the mould cavity with molten castable material to form the component as a single crystal structure.
Implementation Method 2
determining, using a thermal model, curvatures of a plurality of liquidus isotherms of the molten castable material as a function of time along the unit axis for a given angular orientation of the initial mould unit with respect to the central sprue
Data Source
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AI summary
A method (800) of manufacturing a component (100) includes forming a mould assembly (402) including an initial mould unit (408), providing a seed crystal (428) including a primary growth direction (D1), determining an optimal angular orientation (O1) of the initial mould unit (408), rotating the initial mould unit (408) to dispose the initial mould unit (408) in the optimal angular orientation (O1), encasing the initial mould unit (408) in a refractory material, and forming a refractory mould unit (418) having a component mould (420) including a mould wall (424) defining a mould cavity (426), and a seed holder (422). In the optimal angular orientation (O1), the primary growth direction (D1) of the seed crystal (428) is angled away from the mould wall (424), thereby forming a converging disposition with the mould wall (424) in a first region (425) of the mould wall (424) facing the central sprue (404) and a diverging disposition with the mould wall (424) in a second region (427) of the mould wall (424) facing a mould heater (430). The method (800) includes receiving the seed crystal (428) within the seed holder (422) and filling the mould cavity (426) with molten castable material to form the component (100).