Towards Reconfigurable and Automated Assembly Lines for Aircraft Engine Nacelles

The Venegono plant of the Leonardo Aircraft Division, in collaboration with Competence Industry Manufacturing 4.0 of Turin, is studying a new Engine Nacelles Assembly Line. The assembly line intends to exploit the synergy between reconfigurable tooling and collaborative robots (cobots) to position the components, and an automatic drilling and fastening system. A demonstration cell is currently being designed. The aeronautical components, known for their flexibility and complex geometries, require precise assembly processes to meet the tight tolerance requirements typical of aerospace applications. The inlet cowl, the nacelle assembly focus of this paper, well represents such characteristics of the aeronautical product. The assembly relies on jigs and fixtures, widely used tools in aircraft manufacturing. The fixtures correctly position the components, keeping them in the correct shape through the use of numerous locators, supports and clamping elements. Additionally, the jigs are provided with tool guiding elements, such as drilling bushings. The drilling and fastening are performed manually using hand tools. The current techniques allow to meet the assembly requirements. However, the specialized design of jigs and fixtures, tailored to component shapes, makes them highly dedicated, and not reconfigurable tooling. Due to the multitude of components in an aircraft and the differences between the models in production, their design, construction and calibration lead to a significant increase in costs and time before starting the production of a new model. Moreover, their volume and structural complexity may cause accessibility problems to an end effector for the automated drilling and fastening. Testing activities were carried out to provide useful indications for the design choices and to receive feedback on the effectiveness of the solutions identified for the cell development. The setting up of a test bench allowed the comparison of different types of positioning tooling and allowed for the evaluation of component positioning using cobots. The tests provided important indications about the gripper design and the positioning strategies. By moving collaborative robots in response to measurements obtained from instruments such as laser profilometers, laser scanners or laser trackers, the components can be positioned in tolerance near the gripped points. A metrological system that performs a 3D scan of the components placed on the positioning tooling could instead solve the main problems related to the use of a not-dedicated version of the jig. The use of a laser radar is an advisable solution. The scan data enables the determination of target positions for the cobots and the drilling and fastening robot, taking into account the actual components’ position. The robot, which would need many known reference points to align through its end effectors’ vision module, can initially drill reference holes on the components using the scan data and an external measurement instrument, such as a laser radar, that enhances its accuracy by acquiring the position of several tooling balls on the end effector's frame. This paper provides an overview of the engine nacelle and its as-is assembly. The features of the robotic drilling and fastening system, of the cobots, and some issues related to the automation of the process are presented, along with possible solutions. The test bench configuration, the activities carried out, the obtained results, and the consequent project developments are then described.