Production times for aircraft doors drastically reduced

The assembly of the door structures with their bolted and riveted joints is particularly time-consuming in the production of doors for passenger aircraft. Many intermediate steps are required to avoid direct contact between different materials, which leads to corrosion. If, instead of aluminum, titanium and thermosets, mainly thermoplastic carbon fiber composite materials (CFRP) are used, which can be automatically welded together without separating layers, the process is much faster. The research project by the Fraunhofer Institute for Machine Tools and Forming Technology IWU, the Fraunhofer Institute for Structural Durability and System Reliability LBF, Trelleborg and Airbus Helicopters shows that this can reduce the production time for the door structure to just four hours.

Another key to shorter assembly times lies in the modular design for different aircraft door variants. To this end, the project team went on a targeted search for components in different door models that could be standardized. They found what they were looking for in the cross member, for example. The researchers designed a fully automated assembly line for the most common models and developed fixtures and clamping elements that are suitable for resistance welding and ultrasonic welding joining technologies.

Dr. Rayk Fritzsche, project manager at Fraunhofer IWU: "Together with our colleagues from Airbus, we took a close look at all the door structures in order to adapt the geometries for automatic clamping and joining. As a result, we were able to reorganize the individual assembly steps and automate them throughout. This means that only a fraction of the previous throughput time is required." Only the installation of the locking mechanism still requires manual work.

Two largely identical assembly or joining lines are now planned so that replacement capacity is available if one line fails (redundancy). Ten doors can be combined into a batch as a result of various standardization measures, before the line is fully automatically converted for the next model series at the end of the shift. In relation to the capacity of 4000 doors per year, the new material and production concept results in a considerable economy of scale.

No automation for the sake of automation

The TAVieDA project team: Christian Wolf, project manager at Airbus, presents an edge beam made of thermoplastic composite material. 4th from right: Dirk Herborg (DLR Project Management Agency); in the grey jacket: Dr. Rayk Fritzsche. 5th from left: Maxi Grobis. © Fraunhofer IWU

Maxi Grobis from the IWU Factory Planning, Simulation and Evaluation team simulated all technical and economic aspects of the new assembly line - which are usually mutually dependent. The most important technical evaluation criteria include the complexity of the product and production process, automation opportunities and risks, also from the perspective of flexibility and adaptability or the overall system availability in a chain of different individual automations.

Automation for automation's sake was not an option. Grobis emphasizes: "In order to come up with a solution from a single source, we looked at the overall process of production and assembly of the door and transferred it to a dynamic cost calculation. After all, what works technically should also be coherent in terms of acquisition costs, machine hour rates, maintenance costs, energy costs, capital commitment and depreciation. Simply pointing out the potential savings in labor costs or through shorter throughput times would not be enough."
The newly developed automation solution was to be implemented taking into account all technical, logistical and economic criteria. Grobis is particularly proud of the fact that it was also able to reduce planning times by around a quarter with its integrated simulation approach.