The article is based on EU projects reporting "Sonaca WING flap process Development" We express profound gratitude to the SWING project authors and contributors, especially Christophe Cornu from CETIM, for their invaluable work on the thermoplastic placement process in Kruger flap manufacturing.
TLDR
The surface treatment before bonding (degreasing with IPA / Atmospheric plasma) is validated on PEAK / PEEK / PEKK surfaces. It can reach a mechanical strength (shear strength) up to 18MPa on C/PEAK materials. The polymerization of the adhesive can be accelerated from 24h@RT to 1h@65°C by using a heating tool for bonding or heating cover, oven, etc.
The bonding process of the three cells is an industrial process. Some modifications can improve the flow (clamping system to align parts, heating the parts…) but the C/PEAK covering is validated for the further TP filament winding.
The riveting of CTP parts can be improved by using rivets with a counter metallic plate in order to avoid the pull through of the rivet to composite part.
The complexity of the parts and in particular the concavity of the Bullnose pushed the development of a programming method of the trajectories. Cetim developed a programming methodology which enables to generate taping trajectories which are at the border between fibre placement and filament winding.
The biggest problem, on the manufacturing side, was to succeed in placing the tape in the concave part of the bullnose. Cetim carried out many tests with various configurations of deposit to validate the trajectories and the grip of the tape.
For the middle cell and rear cell, the defect is accentuated because the tooling cross-sections are smaller. This also causes defects in the positioning of the tape for 0° application.
The improvements to increase accuracy would be on the chucks. The important bending of the mandrels shifts the tape during the removal. A support system that would allow limiting the deflection could be planned. This solution was envisaged but was too costly for the project.
Why Thermoplastic Kruger Flaps are Needed?
Thermoplastic Kruger flaps are needed for several reasons based on the information provided:
Weight Reduction: The use of thermoplastic materials in the construction of Kruger flaps can lead to a significant reduction in the weight of these components. This, in turn, reduces the overall weight of the aircraft, leading to lower fuel consumption and thus lower CO2 emissions.
Aerodynamics Optimization: The development of thermoplastic Kruger flaps is part of the broader Hybrid Laminar Flow Concept, which aims to improve the aerodynamics of aircraft wings. Better aerodynamics can lead to more efficient flight, further reducing fuel consumption and emissions.
Manufacturing Efficiency: The In Situ Consolidation thermoplastic process being developed in the SWING project aims to outperform existing processes in terms of structural and economic performance. This means that the flaps can be produced more efficiently, reducing costs.
Complex Geometry: The Hybrid Laminar Flow Concept leads to more complexity in the structure of the wings and their accessories. Thermoplastic materials and the associated manufacturing processes are well-suited to creating complex shapes, making them a good choice for this application.
Assembly Solution: The project aims to develop an assembly solution to create a closed-wing section that includes the ribs and possibly other reinforcements. This will help in the creation of more structurally sound and efficient wings.
Designing Tool for Thermoplastic Placement of Kruger Flap
The process of designing a tool for the thermoplastic placement of a Kruger flap involves several steps:
Risk Mitigation Plan: The project begins with a risk mitigation plan that assesses potential challenges by work package. This includes technical-economic scenarios for the in-situ consolidation process of thermoplastics, cost assessment, selection of raw materials suitable for the prototypes, and the development of fabrication tools.
Design Requirement and Process Productivity: The design requirement and process productivity often ask for opposite concepts. This means that the design must meet the requirements of the process while also being efficient in terms of productivity.
Partnership with Tape Supplier: A partnership with a tape supplier has been established for the project. A specific tape was selected and ordered to produce the prototype.
Development of Fabrication Tools: Fabrication tools were developed for the project. These tools include integrated heating and a vacuum system.
Use of a Specific Program: A specific program was used to set the process parameters. The digital tool must be able to handle any complex cross-sectional geometry (polygonal radii, up to a fineness factor of 10, with local concavities), with the variation of cross-sections along the axis of the mandrel, while maintaining a controlled spacing between the taps.
New Part Design: A new part design was studied to make its manufacture possible within the constraints of the specifications. The concept proposes a thermoplastic flap composed of cells joined together to create span reinforcement (spars). This configuration has the advantage of being achievable with the winding tape placement process.
Manufacturing of Complex Geometry: In order to manufacture the complex geometry of the Kruger Flap, CETIM identified the need for a digital tool to generate trajectories on more complex profiles.
Please note that this is a high-level overview of the process and the actual implementation may involve more detailed steps and considerations.
Selecting Tapes for the Thermoplastic Placement
The selection of tapes for the thermoplastic placement of a Kruger flap involves several considerations, as outlined in the document:
Fulfilling Design, Process, and Economic Requirements: The thermoplastic composite pre-impregnated tape must fulfill the design and sizing, the process, and the economic requirements of the project
Partnership with a Tape Supplier: A partnership with a tape supplier has been established for the project. A specific tape was selected and ordered to produce the prototype
Quality and Consolidation: The quality of the available tape and its consolidation are considered as potential risks. The consortium has excluded a tape provider to maximize its options in material selection, but deep collaboration with the selected supplier is planned
Risk Mitigation Measures: If the quality of the available thermoplastic tape is not compatible with in situ consolidation process requirements, or if tape deliveries are not made on schedule or present quality variation, a partnership with a tape provider can be set up in the framework of the project. Specific tape may be ordered for the prototype manufacturing
Process Parameters and Planning
The process parameters and planning used during the manufacturing of the Kruger flap, as well as the problems faced, are outlined in the document as follows:
Process Parameters and Planning:
A specific program was used to set the process parameters. The digital tool must be able to handle any complex cross-sectional geometry (polygonal radii, up to a fineness factor of 10, with local concavities), with variation of cross-sections along the axis of the mandrel, while maintaining a controlled spacing between the taps
The surface treatment before bonding (degreasing with IPA / Atmospheric plasma) is validated on PEAK / PEEK / PEKK surfaces. It can reach a mechanical strength (shear strength) up to 18MPa on C/PEAK materials. The polymerization of the adhesive can be accelerated from 24h@RT to 1h@65°C by using a heating tool for bonding or heating cover, oven, etc
The bonding process of the three cells is an industrial process. Some modifications can improve the flow (clamping system to align parts, heating the parts…) but the C/PEAK covering is validated for the further TP filament winding
Problems Faced:
The complexity of the parts and in particular the concavity of the Bullnose pushed the development of a programming method of the trajectories. The biggest problem, on the manufacturing side, was to succeed in placing the tape in the concave part of the bullnose. Many tests with various configurations of deposit were carried out to validate the trajectories and the grip of the tape
The defects (gap) in the middle cell and rear cell, in radius C, are partly due to the bending of the mandrel. This can be seen from the roller positioning curves. For the middle cell and rear cell, the defect is accentuated because the tooling cross-sections are smaller. This also causes defects in the positioning of the tape for 0° application
The improvements to increase accuracy would be on the chucks. The important bending of the mandrels shifts the tape during the removal. A support system that would allow limiting the deflection could be planned. This solution was envisaged but was too costly for the project
Key Learnings and Future Improvements
Key Learnings:
The surface treatment before bonding (degreasing with IPA / Atmospheric plasma) is validated on PEAK / PEEK / PEKK surfaces. It can reach a mechanical strength (shear strength) up to 18MPa on C/PEAK materials. The polymerization of the adhesive can be accelerated from 24h@RT to 1h@65°C by using a heating tool for bonding or a heating cover, oven, etc
The bonding process of the three cells is an industrial process. Some modifications can improve the flow (clamping system to align parts, heating the parts…) but the C/PEAK covering is validated for the further TP filament winding
The complexity of the parts and in particular the concavity of the Bullnose pushed the development of a programming method of the trajectories. Cetim developed a programming methodology that enables to generate taping trajectories which are at the border between fibre placement and filament winding
Future Improvements:
The riveting of CTP parts can be improved by using rivets with a counter metallic plate in order to avoid the pull-through of the rivet to composite part
At a 5–8-year medium term, a specific project can be investigated to screen the future/new TP welding process capable to weld “high-temperature TP resin” on a large surface superior to 2500mm of rigid geometry with gaps between parts. To the CETIM’s point of view, this specific point is a huge R&T project himself to be investigated
The improvements to increase accuracy would be on the chucks. The important bending of the mandrels shifts the tape during the removal. A support system that would allow limiting the deflection could be planned. This solution was envisaged but was too costly for the project
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