Complex sandwich structures made of thermosetting fiber composite material
In the SHOREliner research project, the Institute of Production Engineering and Machine Tools (IFW) at Leibniz University Hannover has automated the production of a geometrically highly complex, topology-optimized sandwich structure made of carbon fiber-reinforced thermosets for the first time. The aim of the project was to demonstrate the ability of automated fiber placement (AFP) to manufacture geometrically complex fuselage structures and to digitize and automate the entire development and manufacturing process.
The structure created in the project served as a demonstrator for a highly stressed fuselage section of an electrically powered aircraft. It was based on a topology-optimized lattice structure derived from the real load conditions of an aircraft fuselage. The design was carried out in close cooperation with the Institute of Aircraft Design and Lightweight Structures (IFL) at the Technical University of Braunschweig and combined structural optimization, material modeling, and production planning in a consistent, simulation-supported process.
The structure was manufactured using AFP technology. Carbon fiber tapes were automatically laid onto a shaping tool, then foam cores for the stiffening elements were precisely positioned and the cover layers were also applied automatically. The final curing process took place in an autoclave under controlled temperature and pressure conditions.
By combining digital design, automated fiber laying, and reproducible process control, IFW was able to create a structure that not only had a significantly improved mass-stiffness ratio but also a high degree of manufacturing precision.
The SHOREliner project thus demonstrated the feasibility of a fully digitized process chain – from topology-optimized component design and automatic path planning to the production of a functional demonstrator.
Greater sustainability through thermoplastic sandwich structures
This is the basis for the TheSaLab project: Its long-term goal is to establish the manufacturing technology fundamentals for replacing thermoset sandwich structures and producing thermoplastic sandwich structures using laser-based AFP.
This should increase the sustainability and thus the industrial relevance of the technology, as thermoplastic fiber composite systems offer decisive advantages: They enable short cycle times, local formability, reversible joining, and significantly improved recyclability, thereby contributing to increased ecological and economic sustainability.
While thermoset systems require time- and energy-intensive curing, thermoplastic composites can be joined directly during the AFP process (in situ) through in situ consolidation. This significantly shortens the process time, reduces energy requirements, and eliminates the autoclave as a cost-intensive manufacturing step. With the TheSaLab project, IFW is pursuing the goal of making these advantages available for complex, curved sandwich structures as well.
The project focuses on several key technological aspects:
Controlled heat transfer and consolidation: The quality of consolidation depends directly on the thermal process control. Too low temperatures lead to incomplete fusion, while overheating can cause delamination, porosity, or degradation of the material. For this reason, optical-thermal process models for laser-heated laying are being developed, among other things, in order to be able to precisely adjust temperature fields during deposition.
Bonding the cover layers to the sandwich core: The bond between the carbon fiber-reinforced cover layers and the foam core poses a particular challenge in thermoplastic systems. One focus is on the selection and characterization of miscible combinations of the cover layer and core material. In addition, the IFW is researching the behavior of the foam core during in-situ consolidation. Among other things, the local collapse of the foam core and the formation of a melt layer at the interface between the core and cover layer as a function of the thermal-mechanical load in the process are being investigated.
Evaluation of structural mechanics and sustainability: Experimental investigations are used to analyze the mechanical properties of the manufactured sandwich structures. At the same time, an ecological and economic evaluation is carried out to quantify the contribution of thermoplastic systems to resource-efficient manufacturing.
The TheSaLab project thus not only addresses material-specific further development, but also pursues a holistic approach: From material selection and process control to structural evaluation, all fundamental aspects for the implementation of a robust and scalable manufacturing technology are investigated.
Lightweight, resilient, and sustainable: Structures for tomorrow’s mobility
The SHOREliner and TheSaLab projects mark two successive stages of development in the field of automated lightweight construction at IFW.
The SHOREliner project successfully demonstrated the automated production of complex, topology-optimized sandwich structures based on thermoset CFRP systems. A continuous digital process chain was established, ranging from simulation to the finished demonstrator.
The TheSaLab project, funded by the German Research Foundation (DFG), continues this approach by focusing on thermoplastic materials and enabling in-situ consolidation during the AFP process. This opens up new perspectives in terms of process speed, energy efficiency, and recyclability.
Together, both projects form the basis for the next generation of automated fiber composite manufacturing. The combination of topology optimization, process simulation, automated deposition, and thermoplastic material technology opens up new possibilities for realizing lightweight, resilient, and sustainable structures for the mobility of tomorrow.
