KUKA handles fiber composite components at DLR

CFK Nord in Stade was established as an independent, state-of-the-art research center for companies involved in the production of carbon-fiber reinforced plastic components. One user is the German Aerospace Center (DLR). Together with KUKA Industries, DLR developed an automated production facility for research purposes.

The initial situation

The German Aerospace Center (DLR) set itself the goal of developing efficient production technologies for CRP components. CRP parts – such as aircraft frames – are produced fully automatically on a new production line measuring 45 meters in length. Manufacturing aircraft components from CRP is still very expensive and requires a high degree of manual labor. As a dedicated research institution, the DLR wants to change this situation for future generations of aircraft. 

CRP is light and stable, but the high requirements of aircraft manufacturers are only met if the entire process sequence, and thus the quality, is reproducible. Unlike aluminum, CRP can be of highly variable quality, for example if the fibers are not optimally aligned or if moisture enters the composite material through cut edges. Furthermore, any mechanical damage to the material is not outwardly visible. Utmost accuracy is thus required during manufacture.

The task

On the test system, large-volume frame components are produced with contours closely resembling those of the finished product. These components are used to stabilize the aircraft fuselage from the inside. The task here is the automatic production and trimming of the textile preform and its subsequent impregnation with liquid epoxy resin. In an upstream process, the different fiber raw materials required are unrolled from spools and prefabricated using a cutter (with a driven circular blade). The preforms are then stored in appropriate drawers of a magazine system until used. The sensor system was a particular challenge throughout the entire project, as the desired product quality can only be assured if the orientation and angle of the fibers correspond exactly to the specifications. With an integrated eddy current sensor, the angles of the fibers are visualized and evaluated. Altogether, the finished components currently produced in this research system consist of up to 26 layers of carbon fibers.
Altogether, the finished components consist of up to 26 layers of carbon fibers.
The system must be flexible, as it is designed for research contracts and not real series production. It was of decisive importance for both the system concept and the programming to be as free as possible. Tool changing must be quick and easy and robot programming should be intuitive. The students should be able to implement new tasks/products on the system after a brief learning phase. That is just as relevant for practical operation because a mid-sized airliner has around 140 frame segments, with virtually no two parts being identical.

The solution

Automation is carried out using a drape robot from KUKA Industries that removes a 2D ply in order to form it into the desired 3D contour. For this purpose, it is equipped with a gripper that always picks up just one ply at a time. The orientation of the plies on the intermediate support is detected by means of an image processing system. After the forming operation, the drape robot sets the preform down on the mold of the consolidation station. The mold is made of contour-milled aluminum and fastened to a substructure with an interface to the sliding table of the consolidation station. The consolidation station consists of a membrane press with a moving press table. The preform is heated with infrared radiation, thereby melting the powder binder on the textile to stabilize the laminate. 
The laminate is stabilized by applying infrared radiation to melt the powder binder on the textile.
After this forming step, the consolidated preform can be transferred by the handling robot to the mold of the following fine trimming station. The handling robot moves along a linear axis that is installed high up in order to maximize freedom of movement in the production shop. The robot links the individual process stations. Path programming of the robot is carried out offline on the basis of the CAD data of the workpiece and the fastCURVE path programming software from Cenit. Via a corresponding interface, the Reis ROBOTstarV controller enables a very precise, flowing path, as it is not just taught as a polygon with point-to-point motions. This means that a programmed path can also be offset subsequently by a specified amount.
The path programming of the robot is carried out offline on the basis of the CAD data of the workpiece and a path programming software package. Via a corresponding interface, the KRC ROBOTstar controller enables a very precise, flowing path. This means that a programmed path can also be offset subsequently by a specified amount. By selecting the optimal cutting tool, an ultrasonic knife can cut very precisely without affecting the surrounding material.

It was apparent to us after just a few conversations that the Obernburg-based company was no newcomer to project engineering for the automation of such large-volume components. The project managers were able to take a highly modular approach to the individual aspects of the preforming process and to present a coherent concept based on standard components.

Sven Torstrick, Project Manager at the center for lightweight production technology at DLR
Gripper system for handling CRP components

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