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Out of autoclave technologies for frame and shear tie of Regional Aircraft

Periodic Reporting for period 2 - COFRARE 2020 (Out of autoclave technologies for frame and shear tie of Regional Aircraft)

Reporting period: 2020-03-01 to 2021-12-31

Composite materials are widely used in the aircraft industry for their outstanding strength to weigh ratio allowing to reduce fuel consumption and CO2 emission. But the manufacturing process associated to these materials appears to be expensive, as one of the main current focuses of the industry is to reduce manufacturing cost. In this regard, the autoclave manufacturing processes is progressively replaced by other processes which consume less energy, produce less waste, use cheaper raw material with potentially shorter manufacturing cycle. From this tendency, the so called “out-of-autoclave” manufacturing processes are being developed to produce complex and structural part.
Conventional composite materials are made from reinforcement such as carbon fibre, and usually a thermoset matrix. The industry shows high interest to orientate the development of composite materials toward thermoplastic matrices that will help to introduce new outstanding features such as better recyclability, better reparability, easier part joining while continuing to keep the potential for weight saving. This will help for CO2 reduction and will also be very helpful in the age of more electric vehicles.
The main objective of COFRARE 2020 is to investigate the possibility to produce primary structure of aircraft through these innovative materials and processes, that are more sustainable and cost-efficient. The primary structure of an aircraft is the essential part of the body of the plane that provides the strength of the machine to resist the forces produced during a flight. The targeted components are C-frames that will be manufactured from thermoset composite materials using the so-called Resin Transfer Molding (RTM) process that allows mixing resin and carbon fiber reinforcement, out of the autoclave, and cure it to get the desired part quality. These structural component will give the circumferential strength to the fuselage barrel throughout mating parts which are the so-called Shear Ties. These components will be manufactured from thermoplastic composite materials using the so-called thermoforming process.
Therefore, the aim of COFRARE 2020 project is to develop a full-scale fuselage barrel out of composite thermoset C-frame manufactured by out of autoclave processes and composite thermoplastic shear ties, being materials and processes more affordable and sustainable than the previous ones.
The first activities of the project were dedicated to defining the raw material to be used, thus a screening was carried out also considering material availability and the project duration, overall, for the purchase of carbon fiber.
Due to the high number of parts required to assemble a full-scale fuselage, the carbon fibre was purchased to a manufacturer able to deliver a so-called “preform” which is delivered with the layers of carbon fibre stacked onto each other and with pre-shape of the final part. The material procurement phase was strictly linked to the design phase and involved material manufacturers all over the world.
The cooperation with this selected manufacturer highlights the possibility of breaking down the cost by use of automated process for preform manufacturing such as the so-called Automated Dry Fiber Placement.
The manufacturing process development have been performed upstream by performing trial characterization at smaller scale and numerical simulation. These tools help to evaluate some of the following concept prior to the experimental approach allowing to optimize the key process parameters to be used afterwards in the prototypes manufacturing:
- permeability of the carbon fiber with the resin,
- dilatation of the mold at curing temperature,
- curing cycle times,
- tools temperature homogeneity,
- unmolding forces.

The simulation studies also allow for a more cost-effective industrialization phase, as it guided the design and manufacturing of RTM and thermoforming tools and helped to find the best compromises for low-cost equipment development.
The first full-scale protypes have been manufactured and subjected to a complete inspection to detect all the defects embedded into the final part. The inspection process goes from visual inspection and geometrical measurement to more complex technics as with the ultrasonic C-scan which allows to detect defect into the thickness of the part such as porosity, or inclusions. Specific problem-solving technics were used in the subsequent parts manufacturing to optimize the part quality and finally end up on prototypes free of any severe defects. These C-frames will be trimmed with a 5 axis CNC machine, inspected with a C-scan robot, and finally assembled for the fuselage demonstrator.
COFRARE 2020 push forward the integration of composite structure in the aircraft industry, making them lighter and therefore reducing CO2 fuel emissions during flight. For that reason, this new aircraft generation will be more economic and more eco-friendly throughout the lifetime of the product. The estimated gain in terms of weight saving can be evaluated as –39% for shear ties and -48% for frames, thanks to high performance strength value and low density values for the new developed materials. Moreover, during the industrial manufacturing process, equipment and techniques that require less energy absorption respect to the autoclave are used, thus a reduced CO2 emission is obtained also during the manufacturing phase of the parts.
The materials and processes selected and developed for the composite part manufacturing ensure the economic viability for their implementation in a production environment, as an overall value stream mapping were performed to assess the potential production cost benefit.
At the end of the project, around 1.000 prototypes have been produced which give huge information through process datasets and manufacturing and inspection reports to implement the technology in a production environment. All these prototypes will be used for 2 ground barrel fuselage assembly which shall demonstrate the strength resistance of this innovative composite aerostructure.
During the period of the project, the manufacturing process has reached TRL6 as the developed technology has been validated and demonstrated in a relevant environment, demonstrating the benefits of out of autoclave processes and thermoplastic materials.
In conclusion, the materials and processes developed throughout the project will have a lower environmental impact, but also a low cost and higher industrial manufacturing efficiency leading to a benefit in the competitiveness of the European aerospace industry
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