Fibre Placement in the Automation Era for Composite Manufacturing
Have you ever wondered how such large components of passenger airplanes and jet fighters can be manufactured in accordance with the tight tolerances required by aviation standards? Throughout the long history of aviation, this has been a significantly labour-intensive process and has always been a primary area for technological change. In recent decades, we have witnessed another significant shift in toward automated manufacturing, which affects many factors. This has sparked an ongoing debate between those who fear that automation will lead to a reduction in jobs and those who promote automation as an opportunity to upskill the labour force in this new century. In this article, you are invited to read through the opportunities and challenges in the transformation from conventional to modern manufacturing.
Airplanes are assembled from large-scale parts such as air ducts, wings, nacelle, etc. (see Figure 1). For the last couple of decades, the amount of carbon fibre reinforced plastic (CFRP) composites used in the manufacturing of these critical parts has been increasing exponentially, as shown in Figure 2. The replacement of metals with composites pose several technological and practical challenges in manufacturing, while also bringing benefits in design and performance.
Considering that a layer of carbon prepreg is around 0.250 mm thick, the CFRP design of such parts involves a high number of composite layers, each of which needs to be placed accurately at varying angles with respect to the initial layer, …i.e. 0, 45, and 90 degrees (see Figure 1d). Conventionally, hand lay-up techniques have been used in the fabrication of large-scale components for the aviation industry, with all the layers being cut to shape and manually placed on the relevant part, as shown in Figure 3a and Figure 3b. Considering the increasing demand for civil and military aircraft, the hand layup technique limits productivity in several ways such as (i) repeatability, (ii) capacity, (iii) shape of the design and (iv) hand skills of workers. At this point, automated fibre placement (AFP) technology is gradually replacing the hand layup effort, especially in the manufacturing of curvilinear parts subject to curvature constraint as well.
Figure 3: Manual and automated manufacturing of composite parts. [3].
Automated Fiber Placement is currently the state-of-the-art method for the fabrication of composite structures. Here, continuous fibre reinforced tapes, in the form of tows, are laid on a mould surface. In a typical AFP process, the material band is composed of multiple tapes, with widths of either 1/8” or 1/4”. Depending on productivity expectations, the number of tows (tapes) to be placed may vary from 1 to 32 and each tow is individually controlled. Such individual control of tows is vital for a significant reduction in the amount of scrap material when the AFP layup is required to comply with the double curvatures of complex surfaces while the tape is being steered (see Figure 4). In general, an AFP system can lay up thermoset, thermoplastic or dry fibres, with infrared (IR) heat sources being used for thermosets and laser heat source for thermoplastic and dry fibres. The heat will either melt the thermoplastic or increase the tackiness of the thermoset tape, allowing the tape to be stuck onto the substrate when compacted by a compaction roller. As each band is placed, the individually controlled tows are cut in turn and the robot moves to the start of the next band. This process is repeated until a whole ply is complete and the final part geometry is achieved ply-by-ply.
In AFP technology, the AFP head is manipulated by either a robotic or a gantry carriage (see Figure 3d), in order to build the structure one ply at a time while controlling the tows to be placed. In other words, the system can control the number of tows (fibres) to be placed at any portion of the tool path. In addition, each ply can be positioned along the direction set by the designer. In this way, the fabrication becomes highly customized for parts with different configurations and shapes. The use of a robot or gantry-type carriage enables the operator to take active control of the whole process, bearing in mind the variables critical to achieving the objective of high control and repeatability in fabrication. AFP technology can be applied in the fabrication of several composite parts such as concave parts (winglets, fuselage), sandwich structures (engine nacelles and casings) and even closed sections such as pressure vessels.
Although entailing high investment costs (from €2M to €8M), AFP systems enable (i) modular head configurations for multi-material type fabrication, (ii) reliable and repeatable layup for large-scale and complex geometries, and (iii) highly customizable and adaptable layups for research, development and manufacturing of composite structures. However, life in AFP technology is no wonderland and there are still significant challenges and problems in the application of AFP technology to complex structures. Among these are tow buckling, gaps and overlaps. Current research directions for AFP can be named as (i) path generation, (ii) online monitoring of AFP processes and (iii) correction of AFP processes.
In 2019, KordSA and Sabanci University, under the roof of the Composite Technologies Centre of Excellence (CTCE), completed the commissioning of a state-of-the-art robotic AFP System from Coriolis Composites © (see Figure 5). The system is currently known to be the second AFP system in Turkey and the first AFP system in Turkey established as part of a university in Turkey. With regards to the capabilities, it is the only system in Turkey which can lay up thermoset, thermoplastic and dry fibre. The layup head is capable of laying 8 tows (1/4 inch width) at a time. Sabanci University and KordSA are carrying out collaborative research projects in various directions to adopt this promising technology and help Turkish companies win work in the international composite manufacturing industries such as aerospace. Sabanci University is currently running a TUBITAK funded project (under grant no 218M715) to develop process monitoring techniques and tool path generation approaches for variably steered composites fibres. CTCE welcomes all potential industrial partners who are eager to collaborate in this emerging automation technology journey in the name of composite manufacturing.
SOURCES:
[1] https://www.aero-mag.com/safran-nacelles-airbus-a320neo/
[2] Zhang, L., Wang, X., Pei, J., & Zhou, Y. (2020). Review of automated fibre placement and its prospects for advanced composites. Journal of Materials Science, 1–35.
[3] Shirinzadeh, B., Cassidy, G., Oetomo, D., Alici, G., & Ang Jr, M. H. (2007). Trajectory generation for open-contoured structures in robotic fibre placement. Robotics and Computer-Integrated Manufacturing, 23(4), 380–394.
[4] Denkena, B., Schmidt, C., Völtzer, K., & Hocke, T. (2016). Thermographic online monitoring system for Automated Fiber Placement processes. Composites Part B: Engineering, 97, 239–243.
Written by L. Taner Tunç, PhD,
Faculty of Engineering and Natural Sciences Manufacturing Engineering Graduate Programme. Composite Technologies Centre of Excellence, Sabanci University
