CVI Densification of Composite Preforms via Hole Formation
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Solution Overview
Problem
CVI type processes for densifying fibrous substrates often result in densification gradients due to preferential matrix deposition at the surface, leading to inhomogeneous properties and the need for multiple cycles with intermediate peeling to facilitate gas diffusion.
Innovation Solution
Forming holes in the substrates by removing material, such as with a high-pressure water jet or localized thermal action, to create a short path for the reaction gas phase, allowing for almost uniform densification in a single cycle without the need for peeling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If CVI type processes are used for densifying fibrous substrates, then the substrates can be densified by matrix deposition, but densification gradients occur due to preferential surface deposition
Solution Approach 1:
The substrate is segmented into multiple zones based on their densification status. The gas phase is directed to flow through different paths: superficial parts are bypassed while core regions receive enhanced gas phase access through created channels. This segmentation allows simultaneous treatment of different substrate regions with appropriate gas flow distribution, resolving the contradiction between surface deposition efficiency and core densification uniformity.
Solution Approach 2:
An intermediary structure (channels or pores) is introduced into the substrate to mediate gas phase transport. These intermediaries provide dedicated pathways for the gas phase to reach core regions without being completely blocked by surface deposition, thus maintaining composition homogeneity while enabling effective densification throughout the substrate volume.
2Productivity
If multiple CVI cycles are performed with intermediate peeling, then densification can be continued after surface porosity reopening, but the process complexity and time increase
Solution Approach 1:
Channels are created in the substrate before the CVI densification process begins. This preliminary action establishes gas phase pathways in advance, allowing the gas phase to efficiently reach core regions during the densification process without requiring intermediate peeling operations. The result is a single-cycle process that achieves uniform densification, eliminating the time loss associated with multiple cycles and intermediate peeling.
3Manufacturing precision
If holes are formed by needle insertion to provide gas phase access, then diffusion paths are shortened, but fiber damage occurs and densification gradient is not sufficiently minimized
Solution Approach 1:
The mechanical needle insertion process is replaced with a non-contact or gentle material removal process such as water jet machining or localized thermal action. This substitution eliminates fiber damage while still creating the necessary channels for gas phase access. The resulting channels provide sufficient diffusion paths for uniform densification without compromising substrate integrity.
Solution Approach 2:
The method of hole formation is changed from mechanical insertion to material removal by water jet or thermal action. This parameter change in the manufacturing process allows channel creation without the damaging mechanical forces of needle insertion, thereby maintaining substrate integrity while achieving the same functional goal of shortened gas phase diffusion paths.
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
Achieves almost uniform densification of fibrous substrates, reducing the number of densification cycles and eliminating the necessity for intermediate peeling, thereby enhancing the uniformity of composite material properties.
Implementation Method 1
Forming holes in the substrates by removing material, such as with a high-pressure water jet
Implementation Method 2
Forming holes in the substrates by removing material, such as with a high-pressure water jet or localized thermal action
Implementation Method 3
A reaction gas phase is admitted into the oven to deposit the material constituting the matrix within the porosity of the substrates by decomposition of one or more constituents of the gas phase, or reaction between several constituents, under conditions of temperature and pressure determined
Implementation Method 4
The substrate is heated for example by passing an electric current or by electromagnetic coupling with an inductor, the substrate being made of electrically conductive fibers such as carbon fibers
Implementation Method 5
The substrate is heated for example by passing an electric current or by electromagnetic coupling with an inductor
Data Source
Figure 1~2
Figure 3~6
Figure 7~13
AI summary
The invention concerns a composite material part made by forming a fibrous preform (20), forming holes (22) extending in the preform from at least one side thereof, and densifying the preform with a matrix formed at least partly by a chemical vapour infiltration in gas phase (CVI). The holes (22) are formed by removing the material thereof by rupturing the fibers, for example by high-pressure jet machining, the fiber arrangement in the preform provided with holes being substantially unmodified relative to the original arrangement prior to the formation of the holes. The densification gradient is thus highly reduced, and a density may be obtained in a single densifying cycle which, in prior art, required several cycles separated by intermediate decrusting.