Out-of-Autoclave Composite Curing via Double Vacuum
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Solution Overview
Problem
The existing methods for manufacturing composite aircraft structures, particularly those using carbon fiber reinforced epoxy or other thermosetting/thermoplastic resins, face challenges in void reduction and material quality, especially with the high costs and complexities associated with autoclave processes, and the slow acceptance of out-of-autoclave resin systems for primary aircraft structures due to concerns over material properties and process variability.
Innovation Solution
The use of an out-of-autoclave resin system in conjunction with a double vacuum and oven process, where a first vacuum is applied on one side and a second vacuum on the other, allowing for the evacuation of resin volatiles and by-products during the ramp portion of the cure cycle, followed by ambient pressure compaction during the high temperature hold segment, to achieve void reduction and robust manufacturing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If autoclave process is used to reduce void content, then manufacturing precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the autoclave from the manufacturing process by developing out-of-autoclave (OOA) resin systems that achieve comparable void content (≤1%) using only vacuum bagging and oven curing. This removes the complex pressurized vessel equipment while maintaining manufacturing precision through modified resin chemistry and extended vacuum application protocols
Solution Approach 2:
The patent changes the chemical parameters of the resin system by developing OOA-specific formulations with modified cross-linking chemistry and volatility profiles. These parameter changes allow the resin to cure effectively under vacuum bagging alone, without requiring autoclave pressures, thereby reducing device complexity while maintaining void content control
2Manufacturing precision
If autoclave process is used to reduce void content, then manufacturing precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces the expensive, multi-million dollar autoclave with disposable vacuum bags and standard oven equipment. The vacuum bag serves as a temporary, single-use component that achieves the necessary compression and void removal without requiring investment in permanent, costly pressurized vessel infrastructure
Solution Approach 2:
By extracting the autoclave from the process and using only vacuum bagging with OOA resins, the patent eliminates the primary cost driver in composite manufacturing, reducing equipment investment and operational costs while maintaining acceptable void content levels through resin system optimization
3Device complexity
If vacuum bagging is used alone to cure laminate, then device complexity is reduced, but manufacturing precision deteriorates due to higher void content
Solution Approach 1:
The patent changes the chemical parameters of the resin system to OOA formulations that maintain lower viscosity and slower cross-linking rates during vacuum bagging. This allows volatiles to escape more easily and resin to flow better under vacuum alone, achieving void content ≤1% without autoclave pressurization
Solution Approach 2:
The patent applies vacuum bagging earlier and for extended periods during the curing process, before full cross-linking occurs. This preliminary vacuum application removes volatiles and entrapped air while the resin is still sufficiently fluid, achieving void reduction without requiring subsequent autoclave pressurization
4Manufacturing precision
If traditional resin systems are used in autoclave, then manufacturing precision is improved, but loss of time increases due to long cure cycles
Solution Approach 1:
The patent changes the chemical parameters of the resin system to OOA formulations with modified cure kinetics that allow effective curing at lower pressures. These resins are designed to achieve full cross-linking and void removal under vacuum bagging alone, reducing total process time by eliminating autoclave pressurization and ramp-up phases
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
This approach enables the production of composite parts with void content comparable to autoclave-cured systems, reducing manufacturing costs and time, while ensuring material quality and safety, potentially leading to certification for primary aircraft structures.
Implementation Method 1
a first vacuum bag is placed over the laminate and a first vacuum is drawn through the first vacuum bag
Implementation Method 2
the laminate is then placed in an oven and heated at a time and temperature cycle
Implementation Method 3
Most high quality resin systems require elevated temperatures to complete the polymerization or curing of the resin
Implementation Method 4
an autoclave (a pressurized oven) to decrease the size of trapped air voids in the laminate
Data Source
AI summary
An aircraft part is manufactured using a process that prepares a laminate portion of the part using an out-of-autoclave resin system and then heat cures the laminate while applying a first vacuum one a first side of the laminate and a second vacuum on a second side of the laminate. This results in a high-quality aircraft part that has low cost and avoids the need for an autoclave. In preferred embodiments, each of the vacuums applied to the laminate has a pressure of less than 30 Torr. The aircraft part resulting from this process can further be advantageously cured at a temperature of at least 180° F. for at least 60 min. Especially preferred methods use the MTM-44 or MTM-45 out-of-autoclave resin systems, which have characteristics that permit the resin to be approved in the primary structure of an aircraft.