16-Joining and Assembly Processes-Getting a pulse on fuselage panel assembly and NC programming

Getting a pulse on fuselage panel assembly and NC programming 31-五月-2012 12:55 GMT

Figure 1. Conventional fuselage panel assembly. Pulsed assembly lines are providing enormous potential to the aviation industry, especially in terms of reduced lead times, optimizing asset utilization, and increasing the ratio of value-adding processes, according to researchers from Brötje-Automation and Airbus. (Purchase their SAE technical paper, 2011-01-2771, here.)

There are special challenges for automated drilling and fastening processes because of the unique part positions upon each pulse and because of the need for balancing work on several serialized fastening machines. The key to overcoming those challenges is versatile NC part programming that eliminates the need for any additionally written NC programs.

For the Airbus A350 project, a harmonized concept for the assembly of typical fuselage panels has been developed and realized plants in Stade, Augsburg, and Nordenham, Germany. The main idea focuses on the integration of a pulsed assembly line that saves space and supports efficient and transparent assembly of the panels. In a conventional approach, fuselage panel assembly lines are built up by several locally separated cells (Figure 1), each dedicated to a specific production step.

Some aircraft have panels of different length for different sections of the plane or for derivatives of the base model. Thus each cell must be designed for the largest panel, with an accompanying accommodation in terms of space in the plant. Additional space has to be reserved for the transport of panels between cells.

The largest panel defines the cycle time from one cell to the next. Work may be in progress in a large cell while it is complete in smaller ones. This idle time can be addressed in a number of ways (including duplication of the overloaded cell), but typically they take up more plant space.

The pulse The pulse motion line (PML) is based on the idea of arranging automatic and manual cells successively without space between them (Figure 2). The number of work areas for each specific task can be determined based on its expected workload (Figure 3). During production the fuselage panels are located one after another within the line, separated by a minimal safety gap. When the work orders of all areas are completed, a pulse is performed; the panels simultaneously are moved by 4.5 m into the next work area.

For the A350 panel structure, up to seven frames are operated in a given work area within every cycle. When the pulse is executed, the next seven frames are worked on within this work area, regardless of whether belonging to the same or to the following panel. Thus, manufacturing large panels does not delay the completion of subsequent shorter panels.

The size of work centers for a certain task can be defined independently of the lengths of the panels to be produced. Further minimization of the required space is enabled by the elimination of transport zones between the work centers. The modularity of the PML offers a high level of flexibility: If in the course of ramp-up a certain task is revealed as a permanent bottleneck, the change of a work area from one task to the other is possible without the claim for additional space.

And with its scalability, PML allows for precise tweaks or extensions needed for a rate increase. The NC program Automated tasks such as clip frame riveting present challenges with PML. With a conventional clip frame fastening machine, the part to be processed is fixed in the cell before every frame of the panel is fastened. A predefined NC part program exactly defines movements, parameters, and the sequence of how the positions are processed in order to complete the panel in one go. The NC programmer needs to know the position of the part within the cell when writing the part program weeks before first production. This program can be used for processing all upcoming fuselage panels of this type.

With PML, the panels are not to be processed completely in one go; only the frames that are within the work area are machined (Figure 4). The current configuration of the frames in the work area depends on