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Hybrid Fixed Leading Edge

Periodic Reporting for period 2 - HFLE (Hybrid Fixed Leading Edge)

Reporting period: 2018-08-01 to 2019-12-31

The project Hybrid Fixed Leading Edge (HFLE) addressed the topic JTI-CS2-2016-CFP03-LPA01-14 “ Automated RTM process based on innovative sensor technologies in a low cost smart manufacturing tooling prototype and any tooling involved in the manufacture or the validation of the structure “.

The tendency of aeronautical industry speeds up toward laminar-flow technology or active Hybrid Laminar Flow Control (HFLC) where suction of small amount of air throughout aircraft extrados surfaces. The technique has the potential of considerable drag reduction and consequently saving fuel consumption. It was expected that HLFC technique could reduce the fuel consumed by 30% of the current consumption for transport aircraft. As an answer, HFLE major objective was to produce the needed tooling to manufacture the Horizontal Tail Plane (HTP) leading edge structure using RTM process to produce the mentioned part. Moreover, the project focused on the automation of the RTM process including preforming and mold handling steps. Five elementary technology blocs were defined as contributing sub-objectives:
• low cost/ natural materials employed in the tooling manufactured
• eco-design for the mold machined
• energy savings during the manufacturing process of the future composite parts
• manufacturing processes simplification to improve the repetitiveness of the process
• production time savings to reduce the cost and production lead times

In addition to Coexpair strong experience on RTM process, the consortium gathered a well-balanced expertize in complex mould machining (Pégard) but also in robotic development (ULg) and preforming automation (Tecnalia).

In general, results are promising and the mission of the project has been accomplished. The full-scale demonstrator has proven the technology at a high level of demand. The demonstrator manufactured will be used on a large ground based demonstrator and will be statically displayed for functional operations. TRL5+ has been achieved and will be finally used for overall TRL6 maturity level demonstration after the Titanium sheet is co-bonded.
For the development of the HFLC on aircraft, a composite HTP leading edge was designed by Aernnova. However to ensure a good quality of a new composite part, several risks linked to the development of the process needed to be mitigated using the the block-building approach:
1. Perform mechanical tests on coupons to get basic material mechanical properties
2. Manufacture sub-elements representative of the complexity of the part
3. Manufacture the final demonstrator to validate the full development

As preliminary elementary tests, Coexpair made a plate with corrugated CFRP / cocured titanium foil to verify bonding with resin. A panel with omega stiffeners and cocured titanium perforated skin was also injected to check the sealing of holes with elastomers. All tests were successful and the manufacturing of the sub-scale elements was launched to validate the mould concept. Several modifications were carried out to improve sealing and bonding of the highly curvated titanium skin. The quality of the composite area of sub-scale parts was good but the quality of bonding / sealing of the cocured titanium skin was not sufficient. On the basis of these results, the final demonstrator was manufactured.

Materials used in the mold developed by Coexpair were efficient both in raw material price and processing costs, including surface treatment of the mold. No chemicals were used in the tool and just a thin layer of release agent was required thanks to the remarkable smooth surface finish achieved. The mold was as small as it can be for a part of the size requested showing eco-design in energy absorbed and heat dissipation as well as minimum resin paths. The thermal mass was minimal compared with state-of-the art RTM tools. With the improved assembly of the full-scale demonstrator, manufacturing time has been reduced. The avoidance of inner mandrels has definitively helped to keep the preform in shape during the assembly. The new sequence was much leaner than the sub-scale demonstrator and the final result of the part tells about the overall good quality of the tools used.

Moreover Coexpair widely addressed the automation of the RTM process. Manufacturing process involved a lot of manual operations, potential sources of deviations but also leading to a long manufacturing time. Within HFLE project, Coexpair focused on the automation of the resin injection while ULg & Tecnalia were deeply implied in automating other manufacturing steps: preforming of fabrics applied to the ribs (Tecnalia) and demolding / mold cleaning operations (ULg). As outputs, significant progress has been recorded and promising solutions beyond the state of the art were developed by the partners. In terms of validation, elementary tests of key points of the RTM automated process have successfully been performed in representative industrial conditions.
The use of aluminium for the mold was successful, the energy consumption was lower than what it would have been with steel, given the thickness of the mold reducing the ecological impact in future production. Moreover the automation of equipment for RTM injection was tested with now a more repetitive and faster composite manufacturing. In addition, as the production cost is reduced, the serial production in low cost countries is less interesting and production in Europe stay very competitive. Now Coexpair is currently supplying all RTM production equipment to a major Tier-1 in Aerospace sector. With these equipment and technology from Coexpair, this Tier-1 is opening the most automated composite plant in Europe.

The direct resistance process developed and validated by Tecnalia as a proof of concept was an important progress beyond the state of the art that reduced very significantly the process cycle time and the energy consumption involved. Tecnalia is now proposing this new technology to several aeronautic companies, and even equipment manufacturers, to implement this process in the preforming of different parts like ribs, leading edges etc.

ULg compared different gripping and cleaning approaches and made a selection of the most appropriate solution. Then ULg developed a new proof-of concept tool successfully tested at Coexpair in industrial conditions. However more maturation should be carried out with further testing and/or solutions based both on an improved tool design and process.

Through its involvement in improving the manufacturing process, Pégard was able to increase its productivity up to about 20% while reducing the energy required to machine materials. This gain is still limited by the intrinsic features of the machines, which are of robust and heavy design resulting in slow travel speeds. To gain more competitivity, Pégard decided to invest in the procurement of a new high-speed 5-axis SMD machine with large dimensions for machining aluminium and composite parts (from March 2020).

On a general way the positive environmental impact was reached by taking into account low cost/natural materials and eco-design considerations in the development of mold towards energy savings needed to manufacture future composite parts in production.
The automation of several steps of the RTM process shown the opportunity for developping cost effective new technologies and manufacturing while significantly decreasing the scrap rate and material waste in serial production.
Aernnova full-scale HTP leading edge manufactured by RTM process