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CFRP parts: When will manual work be phased out?

The endeavor to make aircraft lighter and more fuel-efficient is resulting in an increasing share of components made of carbon fiber reinforced plastics (CFRPs). The limits imposed on automated manufacturing are the main drawback here. Consequently, manual work still dominates this sector, at the expense of efficiency and profitability. As a result, the wish for comprehensive automation of the individual manufacturing steps is widespread throughout the branch.

Roughly 80 to 90 percent of the CFRP structures are manufactured today by using conventional, expensive prepreg/autoclave technology. This system uses a prepreg, or semi-finished fiber product that has been pre-impregnated with duroplastic resin, that must be stored at low temperatures. After assembly, it must be cured in an autoclave with the application of pressure and temperature. The method is expensive, as it involves high investment costs for the autoclave and substantial costs for the semi-finished product and its chilled storage. Experts estimate: Even a small CFRP component for an airplane currently costs up to 100 euros per kilogram, and a structural element costs roughly 400 euros per kilogram.

Against this backdrop, technically streamlined methods have become significantly more important in recent years. Instead of pre-impregnated CF textiles, simple, dry, supple textiles are cut from the roll and processed into preforms. Subsequently, special methods are used to infiltrate the forms with resin. At present, however, manufacturing CFRP structures with these techniques is also largely characterized by manual production steps. Although it is still more economical than production in the expensive autoclave, the savings achieved by the less expensive semi-finished product and the more economical storage and process costs are offset by high labor costs. This, in turn, makes it worthwhile to take a look at robots, as industrial robots have made significant progress in recent years, and can now be considered for jobs that used to be the exclusive domain of manual work.

Today’s robot tools contain powerful microsensors and microactuators for intelligent detection, gripping, holding and positioning of the most diverse materials. And so why not use robots to manufacture CFRP parts?
aerotec put this question to Otto Kellenberger, Key Technology Management at Kuka Roboter GmbH in Augsburg, recognized as a competent automation specialist in the automotive industry. In recent years, the firm has been expanding its know-how to branches whose requirements are similarly complex. “Automaton on the basis of flexible and adaptive production systems is the key to our markets of tomorrow. The Kuka Robot Group is more successful here than many of its competitors, and concentrates on progressive solutions to automating the most diverse industrial production processes,” Otto Kellenberger says confidently. He can back up this statement with two projects in the aerospace industry by way of example.

Production with light-weight construction materials calls for the application of new manufacturing techniques. The number of produced units is constantly increasing and, in his opinion, such production levels can only be economically reached if innovative robotic solutions are harnessed in the process automation. One line of attack here is found in adaptive production systems, where a greater number of cooperating robots reaches a level of flexibility similar to that found with human workers in group work processes.

Robot with handling tool for removing the cut parts with any contours from the cutting table.

12 cooperating robots place stringers
Kuka robots offer these capabilities, as open control structures and impressive kinematics has enabled them to penetrate make increasing inroads into extremely sensitive handling areas. Together with Canadian research partners, Kuka has completed the predevelopment and developed an adaptive production system for Airbus as a demonstration project. In this project, 12 cooperating robots place CFRP stringers up to 32 meters long in wing preforms or body parts with the greatest precision and repeat accuracy. As Otto Kellenberger relates, “Human workers cannot handle such long and bendable CFRP parts because the slightest deflection or twisting of the parts can result in damage.

Positioning of workpiece components of this length with one-millimeter accuracy is inconceivable when human labor is used.” And Kuka robots are turning in an impressive performance in a second project, as well. The IWB Anwenderzentrum Augsburg at Technische Universität München and the group for software technology and programming languages at Augsburg University are involved in the “CFK-TEX” research project funded by the Free State of Bavaria and the European Union. VDI /VDE Innovation & Technik GmbH is the organization executing the project.

IMA Ingenieurbüro Anton Abele + Partner GmbH, an engineering office in Augsburg, has likewise taken on an important assignment for this joint project. Bruno Haas, IMA managing director, reports, “We are developing a flat handling tool for removing the cut parts with any contours from the cutting table, and a joining tool for the automated, positionally accurate insertion of the extensive, dry CF textiles of various shapes into three-dimensional molding tools.” This sounds complicated – and it is, too. This is due to the fact that the structure of the fabric is not allowed to be changed under any circumstances – the smallest deviations in the fabric direction or distension of the dry fibers after curing leads to intolerable weak points in the components.

This means that a system has to be initially developed for the robot that makes almost flat gripping possible with a multitude of microgrippers. A robot with this “gripping mat” lifts the two-dimensional cut parts with individually controlled suction cups and places them in a process-controlled storage system. A second robot, with the joining tool that likewise works with suction, picks up the cut parts and places them, one after another, according to the three-dimensional geometry of the preform, using an unrolling movement without displacement, compression or stretching of the individual fibers or the fiber composite.

Bruno Haas says, “We consequently needed two very light tools that integrate a multitude of individually activated microactuators and robots that can drive to any given point in any number of traversing steps according to a complex positioning plan.” The development of the control concept was just as demanding, as could be seen at the Composites Europe trade fair in Stuttgart at the end of last October. The branch unanimously acknowledged the functional model presented as an important element for implementing an intelligent process chain for the economical manufacture of light products made of carbon fiber plastics.

Otto Kellenberger underlined, “The objective here is to automate the jobs previously handled exclusively by manual production.” As seen in the ‘CFK-Tex’ project, there is a great potential for cost reductions if robot-controlled units are used to pick up the cut parts and build up the layers in the preforms. This process requires a pre-defined sequence with a high level of positioning accuracy. But Kellenberger is certain that “the results achieved to date in the automation of CFRP production are already allowing us to see dramatic reductions in the high manufacturing and quality related costs – in connection high manufacturing speed.”
- Robert Wouters -

German Summary
Um Flugzeuge leichter und sparsamer zu machen, werden immer mehr Bauteile aus kohlefaserverstärkten Kunststoffen (CFK) eingesetzt. Ihr Nachteil: Sie lassen sich bisher nur teilweise von Automaten fertigen. Es dominiert also immer noch die Handarbeit, was auf Kosten der Effektivität und Wirtschaftlichkeit geht. Deshalb eint der Wunsch nach einer umfassenden Automatisierung der einzelnen Fertigungsschritte weite Teile der Branche. Wie sehen die konkreten Fortschritte aus? Der deutschsprachige Beitrag ist nachzulesen auf www.aerotec-online.com

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