Expendable Flexure Forming for Wrinkle-Free Composite Bends
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Traditional methods for forming thermoplastic composite parts with multiple bends or curves often result in defects such as wrinkling, bridging, and vacuum bag creep, leading to non-functional parts, especially when forming complex shapes like Z-stringers.
Innovation Solution
A composite part forming system using a yieldable flexure with a higher melt temperature than the matrix, supported by forming tools and an impermeable membrane, applies a pressure differential to shape the composite laminate material, allowing it to conform to complex geometries without defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the composite laminate is positioned into the approximate desired shape before bagging, then wrinkling and premature compaction are prevented, but the positioning process becomes more complex and time-consuming
Solution Approach 1:
The flexure is pre-formed with thinned regions at specific locations before the composite laminate is applied. These pre-positioned thinned regions will automatically bend at the correct locations during vacuum bagging, eliminating the need for complex manual positioning of the composite laminate into approximate shape beforehand.
Solution Approach 2:
The flexure acts as an intermediary element between the vacuum bag and the composite laminate. It mediates the forming process by providing controlled bending through its thinned regions, simplifying the overall process while maintaining shape accuracy.
2Adaptability or versatility
If the composite plies are allowed to slide freely during forming, then complex curvatures can be achieved, but bridging occurs when plies touch the forming tool on both sides of a female radius
Solution Approach 1:
The flexure serves as an intermediary that allows controlled sliding of composite plies. The thinned regions provide localized flexibility that enables plies to slide into complex curvatures while the thicker regions prevent uncontrolled bridging at female radii, maintaining shape accuracy.
Solution Approach 2:
The flexure has non-uniform thickness with thinned regions at specific locations. This local variation in properties allows different parts of the flexure to perform different functions: thinned regions enable sliding for complex curvatures while thicker regions provide structural support to prevent bridging.
3Stress or pressure
If the vacuum bag is applied directly to the composite plies, then consolidation pressure is achieved, but the vacuum bag can get between the forming tool and composite plies causing configuration control defects
Solution Approach 1:
The flexure acts as an intermediary layer between the vacuum bag and the composite laminate. It transmits the consolidation pressure from the vacuum bag to the composite plies while maintaining configuration control, preventing the vacuum bag from getting between the forming tool and composite plies.
4Stability of the object's composition
If a rigid support is used during forming, then shape stability is maintained, but the support cannot conform to complex curved geometries
Solution Approach 1:
The flexure has varying thickness with thinned regions at specific locations, creating local differences in rigidity. The thicker regions provide structural support for shape stability while the thinned regions provide flexibility to conform to complex curved geometries, resolving the contradiction between rigidity and adaptability.
Solution Approach 2:
The flexure transitions from a relatively rigid state before forming to a more flexible state during forming due to the bending of thinned regions. This dynamic behavior allows it to provide support when needed while adapting to complex shapes during the forming 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 system effectively prevents defects by using a flexure with thinned regions to form composite parts with multiple bends or curves, ensuring precise shaping and reducing the need for manual intervention during high-temperature processing.
Implementation Method 1
When placed under a pressure differential, the impermeable membrane presses at least one portion of the unformed composite material and at least one portion of the flexure against the first side surface and presses at least one region of the flexure against the first corner of the first forming tool
Implementation Method 2
The flexure is a sheet of yieldable or bendable material with opposing side edges and a higher melt temperature than the matrix
Implementation Method 3
heating the unformed composite laminate material, the flexure, the impermeable membrane, and the first forming tool to a melt point of the matrix
Data Source
AI summary
A system and method for forming a composite part with multiple bends or curves, including placing an unformed composite laminate material onto a flexure and placing the flexure onto an engagement surface of a first forming tool. The flexure is a sheet of bendable material. The first forming tool has a first side surface, the first engagement surface, and a first corner between these surfaces. The flexure may have at least one thinned region aligned with the first corner. The method further includes sealing an impermeable membrane around the unformed composite laminate material, the flexure, and at least a portion of the first forming tool and heating them in an oven or autoclave. The method also includes applying a pressure differential to the impermeable membrane, pressing the unformed composite material and/or the flexure against the first side surface and to press the thinned region against the first corner.