CFRP structures

Welding of CFRP structures has the potential to reduce aircraft structural weight and significantly save assembly time. In the EU-funded research project MultiFAL, different welding technologies were developed at TRL6 level. FFT Produktionssysteme was responsible for the setup of the assembly station, inclusing the overall automation and safety system as well as the motion system for the welding end effectors.

Three different welding technologies were demonstrated on an 8 m long fuselage with PAX and cargo floor. Two longitudinal joints were closed using laser and ultrasonic welding. All frame couplings were integrated with resistance welding. The result is the world´s largest thermoplastic CFRP fuselage demonstrator. It is currently on display in ZAL´s A-building.

Serveral European companies contributed to the succes of the project:

• Fuselage shells wer built by PAG, DLR Augsburg and the R&D´s "Stunning" Consortium.
• Welding end effectors were supplied by Fraunhofer, AIMEN, CTI and AITIIP.
• Fraunhofer, IFAM was responsible for positioning and alignment of the fuselage shells.
• The assembly station was designed by CTI, FFT and AIMEN. It was manufactured, set up and commissioned by FFT Produktionssysteme at the Fraunhofer IFAM facility in Stade, Germany.

"Welding of CFRP structures has the potential to reduce aircraft structural weight and significantly save assembly time."

Some ambitious requirements demanded particular attention:

• Close accuracy and significant operational loads needed substantial stiffness of the support structure to limit the deflections.
• Movement of large structures in conflict spaces: pllacement of the shells into the station and finally moving the welding fuselage section out of the station.
• Ergonomics and occupational safety for human access to the welding areas.

A strong 9 m cantilever bridge became the main station element, which holds accurately movable counterforce blocks for longiitudinal welding. In addition, it accommodates two light linear axes to move the frame coupling end effector. The lower shell, resting on adjustable pads, was aligned accurately. The upper shell was attached to ten hexapods with vacuum suction cups, which were used for position and ahape adjustment. The counterforce blocks were shimmed to the nominal fuselage geometry. Laser tracker measurements were employed to align the assembly station elements with the required accuracy . All elastic deformations were small during welding, even at maximum welding pressure.

For shell placement and fuselage section removal, the bridge must have an open end. During welding operations, a removable support structure was placed at the far bridge end. The counterforce blocks were extended while the longtidunial joints were welded. Frame coupling integration, shell integration and section movements were performed with retracted blocks.

Accuracy and stiffness of the assembly station has fulfilled the requirements. Visual inspection and geometry checks of the welded fuselage showed very satisfactory results. Investigations on achieved welding quality are ongoing. First results are very promising.

The longitudinal welding occured using with a few mm per second, which would be substantially faster than any riverting process.

FFT Produktionssysteme is working on several R&D projects to improve aircraft manufacturing technologies. These include gluing (e.g. project ATON), friction steer welding (e.g. project kaMeL) or new ergonomic concepts (e.g. project SeMoSys). All projects aim at efficient, high-rate series production of large, lightweight CFRP and metal structures for future generation, innovative aircraft. This project received funding from the Clean Sky 2 Joint Undertaking under the European Union´s Horizon 2020 research and innovation program under grant agreement no. 821277 MultiFAL.

Quelle: FUTURED. ZAL Magazin 2024 (yumpu.com)