CoCoNut (Complex Cores for New Utilities) is a project that is part of the Clean Sky 2 program.
The challenge is to design and implement an innovative solution to make a complex, hollow composite part for a critical aircraft structure, via a method compatible with high production rates.
In existing processes for manufacture of composite landing gear parts with complex hollow internal geometries, there is significant time wastage and part complexity associated with use of metal cores, which need to be machined and sectioned, increasing production time and cost. Improving the manufacturing process allows for more simplified, cost-effective, and environmentally friendly serial production of these parts.
The proposed solution is to use an internal core based on a water-soluble material, which can be easily removed from the finished part by washing. The core material is environmentally friendly and recyclable.
The overall project objective is to demonstrate the efficacy of a water-soluble internal core material for fabrication of a structural composite part with internal cavity, meeting the design requirements, withstanding the required process conditions, and showing an advantage over the existing technology in terms of manufacturing time and cost.
RESULTS AND CONCLUSIONS:
• A stable, reliable, repeatable method of manufacturing water-soluble cores was developed. The result was the production of 3 water-soluble mandrels, each conforming to the complex geometry requirements, allowing for successful fabric lay-up and installation in the RTM tool.
• Techniques for sealing the water-soluble mandrels were developed, tested, and applied. The 1st mandrel sealing material, PET shrink tube, did not withstand RTM injection conditions, the main problem being the temperature resistance of the sealing. Therefore, multi-layer sealing candidates with more robust design, including both shrink tube and wrapped Teflon tape, were selected for sealing the 2nd and 3rd mandrels.
• Improvements in the sealing resulted in substantial improvements in the results of the fabrication of the 2nd and 3rd parts. In the case of 3rd part production, the mandrel sealing was much more effective, resulting in minimal resin infiltration, allowing for rapid and effective demolding and wash-out, resulting in a smooth internal part surface. Final part dimensions were mostly within dimensional tolerances, and no delamination was detected.
• Sealing quality is of paramount importance to the success of RTM injection. Failure of the sealing results in resin infiltration into the mandrel, impeding full and effective washout of the water-soluble mandrel.
• Localized internal heating was implemented at thick areas of the part(where heating rates are slowest), via steel end-rings, to ensure the entire part reaches the injection and curing temperatures.
• Production of the parts shows that RTM production of structural aircraft parts with complex, hollow internal geometry using water-soluble mandrels is feasible, thus validating the technological concept behind the CoCoNut project.
