Within the scope of the aerospace research project SOPHIA, the transformation of thermoplastic foams into structural foams was investigated. With this process, mechanical properties can be improved without changing the lightweight nature of the part. A twostep isothermal and isochorous hot press process was developed to manufacture polymer skins on both surfaces of the foam sheet through the local compaction of foam cells. Thermoplastic foams on the one hand exhibit a compression behavior that is highly dependent on process temperature and on the other hand, they show excellent insulation properties. This behavior can be exploited to only compact foam cells locally and manufacture polymer skins on the part surfaces while the low-density foam core stays intact. The commercial FE-code LS-DYNA® has been used to identify several simulations methods, which can be used to reproduce the compaction behavior. Stress-strain-curves determined in quasi-static and isothermal compression tests at different temperatures have been reproduced as a basis for the simulation of the hot press process. Optimization of simulation parameters has been achieved using the optimization software LS-OPT®. Using these parameter sets as a basis for the simulation model, the compaction behavior of the thermoplastic foam during the isothermal hot press process was reproduced. The results from the static hot press process were successfully transferred onto a continuous compression-molding machine to efficiently manufacture structural foam parts. These flat semi-finished products can be transformed into final part geometries using thermoforming processes with IR-heating and stamp forming.
Within the SOPHIA project, a fundamentally new integral foam construction with thermoplastic skin layer for aircraft cabin components is being developed using the sidewall as an example.