Digital Twins The Digital Twin in aircraft construction

From Leo Bartevyan*

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The joint project Eitec was tasked with developing a concept for the large component assembly at Airbus that could increase the degree of automation and reduce lead time. Different digital twins were used for this purpose.

The real model of a system of positioning units is complemented by digital twins.
The real model of a system of positioning units is complemented by digital twins.
(Source: Fraunhofer LBF)

The “Eitec” research project involved several different types of digital twins. During the assembly of CFRP fuselage structures, it is necessary to ensure that they are precisely shaped during the assembly process, since CFRP components can only be manufactured economically with a certain tolerance and are never absolutely identical and true to shape. The required elastic deformation of the CFRP components in the assembly process leads to residual stress in the component which must not exceed a certain value. Therefore the Eitec project was tasked with reducing residual stresses by means of automated control of the assembly process. The actuators, which bring the shell into shape and position, are equipped with force sensors, because the residual stress resulting from the deformation is critical for the load-bearing capacity of the aircraft. The component was to assume control of the holding device and its automation technology independently and in real time.

For this purpose, a digital twin of the component was created, which in addition to CAD data also features its own behavior models including deformation and the action of forces. Furthermore, the assembly system has its own digital twin, which was used for the design of the system and provides the automated assembly process with a predictive simulation in each process step.


Reality communicates with Digital Twin

Nine independently acting positioning units (hexapods), each equipped with its own sensors, drives and controls, are mounted on the supporting structure. Taking into account the sensor data gathered from the process, each hexapod must independently and in coordination with the adjacent hexapods guide the component within the process limits regarding residual stress values. Each positioning unit is assigned a digital twin, which processes the sensor data and calculates the corresponding correction positions. At the same time, communication takes place with the digital twin of the component, which determines the actual positions via a connected measuring system and transmits the new target positions for shape and position to the positioning unit, thus coordinating the entire assembly process.

The digital model - the Digital Twin - the Hexapods.
The digital model - the Digital Twin - the Hexapods.
(Source: Cenit)

Using a real application case from the aviation industry, the project could demonstrate that the concept of the digital twin makes it possible to virtually execute control functions at a higher level of abstraction — regardless of the manufacturer of the actual control hardware. This in turn makes the production logic more flexible and adaptable, which becomes inevitable due to the increasing variance in the products. The digital twin therefore has even more potential than the frequently cited examples of a pure data collector and the simulation model. The transfer of the control functions to several communicating digital twins is a further step on the way to autonomous production.

The Digital Twin as a gamechanger

These approaches can easily be transferred from the aviation industry to SMEs. The modular structure makes it possible to start at a manageable level of abstraction and then increase the level of detail step-by-step and according to one’s requirements. Depending on the situation, digital twins can be copied, modified, complemented or recombined in various ways. Digital twins can be coupled with real assemblies (hardware in the loop). In this way, the function and operability of entire systems can be tested during the project planning and design stage.

These features make this approach very interesting for smaller plant and machine builders and allow for a fast implementation. It is possible to start small and successively build up an individual digital construction kit in order to commission and operate plants faster, more safely and, above all, more competitively.

Ultimately, the right mix of long-term, strategic elements and an agile project approach that incorporates failures and is seen as part of the learning curve is critical for success. “Think big” — “start small” — “start now” should be the guiding principles of a Digital Twin and Digital Continuity" Project. In order to set the transformation process in motion, small steps with a clear benefits are sufficient at the beginning. Courage and continuity are decisive.

* Leo Bartevyan is IT Systems Engineer, Digital Factory Solutions at Cenit.


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