Currently, high performance thermoplastic composite parts are mainly used in aeronautical structures. Compared to thermoset resin systems, they have many advantages: impact behaviour, fire resistance, low moisture absorption and welding capabilities. Despite this, thermoplastics are generally restricted to simple geometry parts and limited dimensions as the material and global production costs remain generally high.
The aim of the DINAMIT programme was to foster the widespread use of high-performance thermoplastic (TP) composites on aircraft or helicopter structures. In order to reach that aim, the project focused on the following objectives:
- reduction of prohibitive material costs;
- reduction of the associated forming-consolidation costs;
- development of rapid, flexible, low cost processes for structure assembly;
- reduction of scraps.
The expected main innovations related with the above-mentioned objectives are:
- The development of low cost high performance thermoplastic composite applicable to aeronautical structural components;
- The development of new forming-consolidation processes;
- The development of new welding processes;
- The development of a cost optimisation tool which will assess the developments of innovative TPs materials and processes.
To achieve the general objectives of the programme, the work was divided into six technical Work Packages.
After the elaboration of specifications for this new structural TP material, with a polyether ether ketone (PEEK) tape reference, the focus was on the development of a ternary TP blend and its associated prepregs (tape and fabrics). The forming capabilities and mechanical properties of new TP multi-axial fabrics were evaluated. Polyphenylene sulfide (PPS) behaviour in the melt state was analysed for optimising the injection process. Processing routes for PEKK tapes were compared.
Forming processes for Skin:
A new automated lay-up technique associated with vacuum consolidation was developed, and the in situ consolidation (ISC) process was enhanced for double curvature part applications. Benchmarking tests were supplied for comparison of different ISC processes. A specific diaphragm technique was associated with the development of an IR heating model.
Forming processes for Substructure:
A specific TP resin transfer moulding process was developed. A thermoset roll-forming machine was upgraded for TP applications and a continuous forming technique was employed for the manufacturing of contoured profiles.
Laser technologies were investigated, either for the TP composite assembly, or for surface preparation before welding. An in situ welding technique was developed, to be coupled to the ISC process.
A reduced fuselage panel was designed, and sized for validation of the automated lay up technology. Part of a TP fuselage frame was designed for validation of the RTM process. Composite TP wing ribs were manufactured with laser welded roll formed stiffeners. A TP landing gear door was manufactured using in situ consolidation and welding processes.
Cost effective analysis:
Finally, the real impact on cost reduction was evaluated with a specific analytical tool.
The main conclusions on the technological advancements brought by the DINAMIT programme are as follows:
- New TP Materials – the solutions proposed are:
- 2 New ternary blends resin and associated prepregs.
- PEKK based prepregs seem to be also an acceptable solution for TP substructures manufacture.
- The evaluation of new TP multiaxial fabrics gave promising results.
- A new 1-inch width PEEK/AS4 tape seems now available for automated TP tape deposition applications.
- New TP Processes for skins:
- proposed are 2 innovative solutions to answer to the previously existing problem of first ply sticking to a curved tooling.
- cost efficient parallel route, which is based on high speed TP tape deposition step coupled to consolidation into oven of the panel.
- An innovative diaphragm technique using a specific elastomer membrane allowed to manufacture deep curvature Thermoplastics parts.
- New TP Processes for substructures:
- An innovative low pressure TP direct injection technique has been developed. First promising results allow thinking that it could be an interesting route for manufacturing complex geometry substructures (such as fuselage frames or fittings), which would be directly suitable for cost effective assembly to Thermoplastics skins.
- A continuous-forming process is available now for contoured stiffeners manufacturing.
- New TP assembly processes:
- A complete Laser welding feasibility study permit to draw the conclusion that the Laser techniques are not really suitable for aeronautical applications, because they are restricted to very thin High Performance Thermoplastic composite part. Applications to automated tape placement may nevertheless be imagined.
- Laser technologies seem interesting as a technology for surface preparation before TPs parts welding, compared to the actual manual sanding.
- New silicon membrane and a specific carbon Foam have been validated for welding PEE/C stiffeners to a PEEK/C carbon skin with PEI film at the interface of the components.
- Cost effective analysis:
- A specific tool is now available and must allow to see rapidly the most influent parameters of the process on the cost of the under development techniques.