The production of doors for passenger aircraft is predominantly manual labor. The assembly of door structures with their screw and rivet connections is particularly time-consuming. Many intermediate steps are necessary to avoid direct contact between different materials, which leads to corrosion. When thermoplastic carbon fiber reinforced materials (CFRP) are primarily used instead of aluminum, titanium, and thermosetting plastics, which can be automated and welded together without separating layers, the process is significantly faster – the manufacturing time for the door structure decreases from 110 to just 4 hours. This is demonstrated by a research project from Fraunhofer IWU, Fraunhofer LBF, Trelleborg, and Airbus Helicopters.

A key to shorter assembly times also lies in the modular design for different aircraft door variants. The project team specifically searched for components in various door models that could be standardized. They found, for example, in the cross member. The researchers designed a fully automated assembly line for the most common models and developed devices and clamping elements suitable for the joining technologies of resistance welding and ultrasonic welding.
From manufacturing to a tightly scheduled industrial production process

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Dr. Rayk Fritzsche, project manager at Fraunhofer IWU: 'Together with colleagues from Airbus, we closely examined all door structures to adapt the geometries for automated clamping and joining. As a result, we were able to reorganize and fully automate the individual assembly steps. This now requires only a fraction of the previous lead time.' Only the installation of the locking mechanism still requires manual labor.
Now, two largely identical assembly or joining lines are planned so that in the event of a line failure, backup capacity is available (redundancy). Each batch of 10 doors can be combined as a result of various standardization measures before the line is fully automatically reconfigured for the next model series at the end of the shift. With a capacity of 4,000 doors per year, the new material and production concept results in a significant economies of scale.
Is the investment in new production facilities worth it 'in the end'?
Maxi Grobis from the IWU team for factory planning, simulation, and evaluation simulated all technical and economic aspects of the new assembly line – which often depend on each other. The most important technical evaluation criteria include the complexity of the product and production process, automation opportunities and risks from the perspective of flexibility and adaptability, or the overall equipment availability in a chain of various individual automations.

Automation for the sake of automation was not an option. Grobis emphasizes: 'In order for a solution to come out as a whole, we looked at the entire process of production and assembly of the door and transferred it into a dynamic cost accounting. What works technically should ultimately also be consistent in terms of acquisition costs, machine hour rates, maintenance expenses, energy costs, capital lockup, and depreciation. Just showing the savings potential in labor costs or through shorter lead times would be too short-sighted.' The result is clear.
Considering all technical, logistical, and economic criteria, the newly developed automation solution should be implemented. Grobis is particularly proud that with her integrated simulation approach, she was also able to reduce planning times by about a quarter: Those who consider business management from the outset save unnecessary change loops already during planning.
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