Composite Fuselage Barrel Curing with Collapsible Mandrel
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Solution Overview
Problem
Current methods for manufacturing fuselage barrels in composite materials with stringers face challenges such as complex mandrel disassembly, sealing issues, and potential damage to the vacuum bag and forming tools, particularly for large-sized barrels with complex shapes.
Innovation Solution
A method involving a collapsible inner mandrel with radially retractable sectors and a vacuum bag system that minimizes wrinkles and ensures accurate shaping, using inflatable elements and a breather fabric to maintain the shape of the mandrel and prevent damage during curing, allowing for the use of a separate outer mould line tool for curing, which reduces the risk of porosity and structural defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a mandrel with radially retractable sectors is used to form the inner surface, then the inner surface precision is improved, but the device complexity and maintenance requirements increase
Solution Approach 1:
The mandrel is divided into multiple radially retractable sectors that can be independently positioned and locked. Each sector can be adjusted radially to maintain precise contact with the composite material during curing, while the segmented structure allows for easier maintenance and reduced complexity compared to a fully rigid mandrel.
2Manufacturing precision
If the mandrel sectors are made rigid to maintain shape accuracy, then the manufacturing precision is improved, but the risk of damage to the vacuum bag and composite material increases
Solution Approach 1:
The mandrel sectors are designed with localized rigid zones for maintaining shape accuracy and flexible zones for absorbing thermal expansion and positioning tolerances. This local differentiation allows the mandrel to maintain precise geometry while accommodating thermal stresses without damaging the vacuum bag or composite material.
Solution Approach 2:
A breather fabric layer is positioned between the mandrel surface and the composite material to cushion against potential damage during curing. This protective layer absorbs thermal expansion forces and prevents direct contact between rigid mandrel sectors and the vulnerable uncured composite, eliminating the need for overly complex compensation mechanisms.
3Manufacturing precision
If a vacuum bag system is used to minimize wrinkles, then the surface quality is improved, but the complexity of the forming system increases
Solution Approach 1:
A flexible vacuum bag system with breather fabric is used to apply uniform vacuum pressure across the composite material surface during curing. This flexible film system minimizes wrinkles and surface defects by conforming to the mandrel geometry and providing even pressure distribution, while remaining simpler than rigid mechanical pressing systems.
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 method simplifies the manufacturing process by ensuring a precise outer surface, reducing the risk of damage to the composite material and forming tools, and enabling the production of large-sized fuselage barrels with accurate aerodynamic surfaces.
Implementation Method 1
The plant includes a set of inflatable elements, arranged so as to be accommodated in the slots formed in the outer surface of the mandrel, and consisting of a plurality of tubular bags arranged one above the other in each slot
Implementation Method 2
preparing pathways for extracting the air and the gases (breather fabric and vacuum valves)
Data Source
AI summary
A vacuum bag (18) is placed around the inner forming surface (IML) of an inner mandrel with radially retractable sectors (11a, 11b) having parallel longitudinal slots (17) with composite stringers (30) in the slots (17). An inner support (31) in each stringer is covered by an impermeable tubular bag (32). A composite skin (37) is laminated around the stringers (30), the coated supports (31, 32) and the inner forming surface (IML). An outer curing tool (50, 51) closes around the skin (37) defining an fuselage barrel outer forming surface (OML), leaving an annular gap (G) between the skin outer surface (37) and the outer forming surface (OML). Vacuum is applied between the vacuum bag (18) and the outer tool (50, 51), enlarges the uncured barrel diameter, releasing the barrel from the inner mandrel (10) and bringing the skin outer surface (37) into contact with the outer tool inner surface (IML).