In aviation production, the development of more efficient lightweight structures to reduce fuel consumption and environmental impact is a key challenge. Despite the introduction of high-performance composite materials, such as carbon fiber reinforced plastics (CFRP), conservative designs still dominate in construction for aircraft fuselages. The reasons for this are rooted in the high system complexity of the structures and uncertainties regarding manufacturing process limits and economic risks. The OptiFee project addresses these challenges by reorienting the conventional product development process geared specifically towards composite materials.
In the early design phases, there is often a lack of information about how the choice of new designs or manufacturing technologies might affect the overall design. This often leads to a reliance on proven designs to avoid unforeseen problems in the later development process. The project is therefore developing an integrated method that allows the evaluation of designs for stiffened fuselage structures at an early stage of development, with a minimum of information and without a fixed structural design. The method takes into account manufacturability limitations and a design suitable for fiber composites, as well as economic and structural-mechanical requirements.
In the first step, individual layouts are derived from a basic framework, dictating the position of stiffening elements within the fuselage barrel. A reduced finite element modeling developed by project partner IFL, the Institute for Aircraft Technology and Lightweight Structures at TU Braunschweig, then allows stability and strength analyses to be performed for the individuals, even without them being detailed (Step 2). The results of the modeling are target specifications for the structural properties of the individual construction elements.
The challenge in the next step is to derive a suitable process chain for the layout of an individual. This requires a novel approach, as the design is not yet detailed at this point. In addition, a wide range of process chains and manufacturing methods should be included. To minimize computation time, not all possible combinations of processes and work steps can be considered for all present components. The OptiFee method relies on a solution that is based on the automatic determination of component geometry and the combination of predefined sub-process chains.
A generative algorithm developed for this purpose conducts a manufacturability analysis to determine the optimal geometry of components that a shaping manufacturing process can create (Step 3). The structural requirements of the component and the process limitations of the manufacturing technology serve as constraints. Subsequently, feasible component geometries are established for each shaping manufacturing technology under consideration.
Instead of considering all possible process step combinations for each manufacturing technology in the next step (Step 4), certain sub-process chain variants are defined in advance for each shaping technology. For example, there are two process routes for the "Automated Fiber Placement" production technology: one with and one without the use of an autoclave, differing only in the "Consolidation" and "Curing" steps. This approach prevents the detailed calculation of inefficient or unfeasible sub-process chains and process combinations, thus reducing the number of solutions to be calculated.
The geometries developed for various sub-process chains are therefore adapted to the specific manufacturing requirements in each case. The combinations of sub-process chains of individual components can, where possible, be combined with each other using different joining processes. It is crucial to consider the interfaces between the various components and the manufacturing technologies used. State parameters assigned to individual components and sub-process chains provide information on whether these are ready for the joining processes. To reduce complexity, the same sub-process chains are used for components with similar properties. This helps to reduce the total number of possible solutions.
The final evaluation of each complete process chain includes suitable geometries as well as data on structural mass, quality parameters, process times and costs. The data is determined using analytical process time and cost models. For example, the process time model for Automated Fiber Placement considers the influence of component complexity on the layup speed. Fixed and variable factors such as machinery, energy, and materials, depending on the size and structure of the component, are incorporated into the cost model.
In conclusion, the chosen approach enables an efficient comparison of different stiffening layouts without a prior detailed design of the concepts. The goal in the last project year is to gain a deeper understanding of the interrelationships between components, manufacturing technology, and process costs for the design and selection of composite structures. In the LuFo project SHOREliner, which started last year, the IFW will continue to adapt the method for the development of a sustainable manufacturing process for a climate-neutral composite aircraft. The approach will be examined in the context of SME production and expanded to include important aspects for calculating CO2 emissions and energy efficiency.
The project "Layout Topology Optimization of Unconventionally Stiffened CFRP-Structures Considering Manufacturing Constraints (OptiFee)" - project number 450687126 is funded by the German Research Foundation (DFG). The IFW would like to thank the DFG for the financial support for the realization of the project.
Contact:
For further information, please contact Tim Tiemann, Institute of Production Engineering and Machine Tools at Leibniz Universität Hannover, on +49 4141 77638 207 or by e-mail at tiemann@ifw.uni-hannover.de.
