Tygavac Advanced Materials
Vacuum Bagging for Composite & Bonding Industries
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Airtech's Dahltexx Benefits BAE Systems Infusions
Toolside and Bagside breathing are long established techniques of using a semi permeable membrane to remove air and volatiles from a composite laminate while curing under a vacuum bag. Both these techniques have been employed successfully by BAE Systems during their recent UAV technology demonstrator project in support of the UK ASTRAEA programme.
The project, supported by Airtech Advanced Material Group, developed the use of Liquid Resin Infusion for manufacture of UAV structures. The ASTRAEA programme, part funded by the NWDA, aims to open the airspace to Unmanned Aircraft Systems. The programme included research into the qualification of affordable aircraft structures and was based on the HERTI UAV wing design.
Construction of the wing skins features non-crimped bi-axially oriented carbon fabrics around a polymer foam core, infused with an epoxy resin system. A common infusion technique is to drill and groove the foam core to promote the flow of resin. In order to reduce resin weight and avoid restrictions on mechanical performance created by drilled and grooved core, this technique was not used on the project. The lack of resin flow promotion in the core material provided a challenge to ensure complete fibre wet-out over the entire part.
To ensure complete fibre wet-out and avoid any surface porosity the BAE Systems Engineers employed Toolside and Bagside breathing techniques with the Airtech Dahltexx semi-permeable membrane. Dahltexx is a semi-permeable fabric supported membrane which due to its micro-porous structure will allow the passage of air and restrict the flow of resin. The liquid resin infusion was completed at room temperature with standard workshop vacuum connected through an Airtech RB451 vacuum reservoir. After infusion curing was completed at elevated temperature in an oven.
Trial moulding made without Toolside or Bagside breathing resulted in surface porosity over the part surface. Subsequent mouldings with Dahltexx used for Toolside and Bagside breathing resulted in zero porosity over the tool side of the part and zero porosity around the complex features of the access panel and aileron features on the bag side of the part. These Wing skins then passed NDT examination to Eurofighter Typhoon standard with a Grade A acceptance criteria.
The project delivered a reduction in labour of around 25%, reduction in raw materials of 30%, weight reduction of 30% and achieved 1.3 x ultimate load in static test. The success of the project has been to demonstrate affordable manufacturing of composite airframe structures with the LRI process employing Dahltexx for
Toolside and Bagside breathing, with opportunities for its use in present and future projects.
Circulation, publication and modification of this article is only permitted with the express permission of Airtech Advanced Materials Group.
Photographs courtesy of BAE Systems.
