Solid Bladder for Aircraft Stringer Curing
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Solution Overview
Problem
The existing methods for manufacturing aircraft stringers using vulcanized rubber hollow tubes face issues such as bursting and high replacement costs due to pressure loss during the composite cure cycle, necessitating a more reliable and cost-effective support system.
Innovation Solution
A solid bladder made of silicone or urethane, engineered using Finite Element Analysis to provide uniform pressure and support within the composite stringer during the manufacturing process, which is sized and shaped to match the stringer and tooling, ensuring even resin distribution and preventing bulges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If vulcanized rubber hollow tubes are used to provide support during composite cure cycle, then pressure support is provided to prevent stringer collapse, but the tubes burst and require frequent replacement due to pressure loss
Solution Approach 1:
The patent changes the physical state parameter of the support medium from hollow (gas-filled) to solid, eliminating the pressure containment issue that causes rubber tube failure. The solid foam material maintains structural support without the bursting problem inherent in pressurized hollow tubes.
Solution Approach 2:
The patent replaces expensive, short-lived vulcanized rubber hollow tubes with a more durable solid foam alternative. The solid foam insert does not require replacement after each cure cycle like the rubber tubes, reducing both cost and downtime.
2Manufacturing precision
If vulcanized rubber hollow tubes are pressurized to maintain stringer shape, then uniform pressure is achieved, but the tubes lose pressure integrity and shrink with each cure cycle
Solution Approach 1:
The patent changes the material state from elastic hollow rubber to solid foam, eliminating the pressure loss and shrinking problems. The solid foam maintains its shape and support characteristics throughout multiple cure cycles without degradation.
Solution Approach 2:
The solid foam insert automatically maintains its shape and support function without requiring external pressurization systems or monitoring. It self-regulates its support properties throughout the cure cycle and can be reused across multiple cycles without maintenance.
3Manufacturing precision
If rubber hollow tubes with stiffened inserts are used during AFP, then composite material is pressed against tooling, but the tubes burst ruining the composite part
Solution Approach 1:
The patent changes the support medium from pressurized hollow rubber to solid foam, eliminating the bursting hazard. The solid foam provides consistent mechanical support during AFP without the risk of catastrophic failure that can ruin composite parts.
Solution Approach 2:
The solid foam insert is pre-positioned to provide cushioning and support before the AFP process begins. It absorbs and distributes pressure evenly during composite layup, preventing the localized stress concentrations that lead to tube bursting.
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 solid bladder solution provides consistent pressure and prevents the stringer from collapsing, reducing the need for frequent replacements and ensuring a uniform, high-quality composite structure by maintaining pressure integrity throughout the curing cycle.
Implementation Method 1
The bladder be configured to provide an appropriate contact force for creating uniform pressure throughout the composite stringer during the curing cycle
Implementation Method 2
Autoclave pressure keeps the stringer section from collapsing during the automatic fiber placement (AFP) and composite cure cycle
Data Source
AI summary
An apparatus and method of forming a stringer or an integral stringer and fuselage skin. The apparatus may be a solid bladder made of silicone, urethane, or any similar material or combination thereof. The method may comprise placing composite material onto a surface of a tooling having a channel sized and shaped to correspond to a desired stringer size and shape. Then the solid bladder may be placed onto the composite material relative the channel. The shape of the solid bladder may correspond to the shape of the channel. Composite material may then be placed over the solid bladder, vacuum-sealed against the bladder and the tooling, and cured to harden the composite material, thereby forming a stringer or an integral stringer and fuselage skin.