The "Digital Friend": Towards a sensor-supported simulation and the establishment of a new thermoplastic C-RTM process with Caprolactam

Kurzfassung

Fiber reinforced thermoplastic materials are becoming increasingly interesting for structural components in aerospace and automotive industry due to their beneficial properties (e.g. weldability). In the high-volume production segment, however, this class of materials is in strong competition with established thermoset manufacturing processes such as the Compression Resin Transfer Molding (C-RTM). For this reason, a thermoplastic material system (Caprolactam) is investigated in the research project CosiMo (Composites for sustainable Mobility), which seems to be suitable for a C-RTM process. Thus the favorable properties from both worlds, short cycle time and weldability, could be combined. This opens a completely new solution space for (process) design and production technologies. The challenge is now to understand and control this novel approach. Therefore, both, the process parameters must be identified and the process itself must be defined. The use of glass fiber nonwoven fabrics as reinforcement material represents a further challenge in the project, since no literature values regarding permeability and compression behavior are yet available. Addressing these challenges, the CosiMo project is dedicated to the research question of developing a novel efficient process for thermoplastic C-RTM with regards to its industrialization. The present study focuses on the modelling procedure of the C-RTM process based on real process data generated on a hot press. These investigations are conducted with a RTM machine by KraussMaffei Technologies GmbH, Munich, Germany at the facilities of the Center for Lightweight Production Technology of the German Aerospace Center in Augsburg, Germany. In the C-RTM process, the Caprolactam polymerizes with an activator and a catalyst under pressure and increased temperature to Polyamide 6 (PA6). To investigate this process the RTM tool is equipped with a variety of sensors like thermocouples, resistive pressure sensors, ultrasonic and dielectric sensors. This approach was chosen to verify the potential of inline process control and quality assurance based on the physical processes inside the mold. The evaluation of the C-RTM process was realized using standard carbon fiber woven material and glass fiber nonwoven fabrics. Due to its comparably low compaction the use of nonwoven fabrics results in no physical gap between fabric and tool, when closing the mold. By comparing process data from both material types, woven and nonwoven fabric, new insights of this novel process will be gained. In addition to the physical experiments, a simulation of the C-RTM process was set up in ESI PAM-COMPOSITES (PAM-RTM module). The C-RTM process with glass fiber nonwoven fabric is a novelty, especially because of the mentioned low compaction of the fabric which results in the elimination of the gap. For the simulation modelling of this special C-RTM set-up with nonwoven fabrics, a process-specific extension of the software was developed and implemented in the graphical user interface release version Visual-RTM 15.5. The assessment of this new development is currently being carried out based on the comparison between simulation results and sensor data from the physical experiments. In case of successful comparison, C-RTM process simulation can be used in future for tooling design and for the predetermination of process parameters from complex parts. By using a virtual simulation, the number of tests required to determine the limits of the process window can be significantly reduced. Consequently, time, material and tool costs (due to rework) can be considerably saved during the initial operation phase of a new process.