Forced-Flow CVI Tooling Assembly for Faster CMC Densification
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Solution Overview
Problem
The challenge in chemical vapor infiltration (CVI) is the lengthy processing time required to form a ceramic matrix composite (CMC) matrix via diffusion.
Innovation Solution
A tooling assembly comprising a hollow base plate, solid cover plate, and seal plates with support bars is used to create a pressure gradient for forced-flow CVI, accelerating the infiltration process by directing reactive gas through the preform stack.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional diffusion-based CVI processing is used, then the ceramic matrix composite is formed with adequate density, but the processing time is excessively long
Solution Approach 1:
The patent applies pneumatic principles by using pressurized gas flow to force reactive precursor gases through the preform structure. The gas delivery system delivers reactive gas at controlled pressures (e.g., 1-100 psig) to drive forced-flow CVI, replacing slow diffusion-based transport with pressure-driven convective flow, thereby dramatically accelerating matrix deposition rates
Solution Approach 2:
The invention changes the transport parameter from passive diffusion to active forced convection by introducing pressure gradients. By controlling gas flow parameters (pressure, flow rate, composition), the system achieves faster reactive species transport into the preform, reducing processing time from days to hours while maintaining adequate matrix density
2Loss of time
If forced-flow CVI is implemented, then processing time is reduced, but the tooling complexity increases due to sealing and gas distribution requirements
Solution Approach 1:
The tooling is segmented into modular components: base plate with gas distribution manifold, cover plate, seal plates, and support structures. This segmentation allows independent optimization of each component's sealing and gas distribution functions, making the complex forced-flow system manageable and reproducible
Solution Approach 2:
Seal plates and sealing elements act as intermediaries between the gas delivery system and the preform. These components mediate the pressure gradient establishment by creating sealed chambers that direct forced gas flow through the preform while isolating different pressure zones, simplifying the overall control architecture
3Productivity
If reactive gas flow is directed through the preform stack, then deposition rate increases, but sealing challenges arise to maintain pressure gradients
Solution Approach 1:
The patent employs flexible or conformal sealing elements (gaskets, O-rings, or deformable seal plates) that adapt to the preform geometry and tooling interfaces. These flexible sealing components maintain pressure gradients and prevent gas leakage while accommodating manufacturing tolerances and thermal expansion during forced-flow CVI processing
Solution Approach 2:
The seal plates combine multiple functions: sealing between preforms, sealing between preform and tooling, and gas distribution. By merging these functions into integrated seal components, the system reduces the number of separate sealing elements needed, simplifying assembly while maintaining pressure gradients for high-rate deposition
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 tooling assembly significantly reduces the time required to densify preforms by enhancing the deposition of reactive species within the preforms, facilitating faster formation of CMC components.
Implementation Method 1
creating a pressure gradient for forced-flow CVI, accelerating the infiltration process by directing reactive gas through the preform stack
Implementation Method 2
directing the flow of reactive gas into a hollow interior of the stack
Implementation Method 3
The gaseous flow diffuses into the porous preforms to and the reactants deposit to form a matrix of, for example, silicon carbide
Implementation Method 4
a plurality of seal plates in physical contact with disposed between adjacent ones of the plurality of fibrous preforms
Data Source
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AI summary
A tooling assembly (10) for use in infiltrating a plurality of hollow fibrous preforms (14) includes a hollow base plate (16) disposed at a first end of the tooling assembly (10) relative to a direction of a flow of reactive gas, a solid cover plate (18) disposed at an opposing second end of the tooling assembly (10), a plurality of seal plates (20) in physical contact with disposed between adjacent ones of the plurality of fibrous preforms (14), and a plurality of support bars (22) extending between the base plate (16) and the cover plate (18) and disposed about a periphery of the tooling assembly (10).