The final aircraft assembly involves joining of fuselage sections, wings, tail panels and other highly elaborated subassemblies. Therefore, it is impossible to predict the actual shape of the parts to be assembled with standard methods of tolerance analysis. Thus, the simulation of final aircraft assembly with regard to compliance and contact interaction as well as shape variations of the parts requires specialized approaches to setting the initial gap between joined subassemblies.The generative mathematical model of the initial gaps is required for carrying out the variation simulations.

In this paper two models for generation of the initial gap are analyzed: the random field model and the mode-based model.

The considered random filed model represents the initial gap as a sum of two components. The first component called the global gap is large-scale, and it may come from inaccurate positioning and fixating of the parts being joined, as well as from deformations caused by other reasons. The second component called the local gap is relatively small and corresponds to the micro deviations and roughness that may emergeduring machining and mechanical processing of the parts’ surfaces.These components can be modeled as Gaussian random fields that are defined by a mean value and covariance function.

The mode-based model decomposes the initial gap into a series of the natural modes of the subassemblies with the corresponding modal coefficients. The mode shapes for studied subassemblies can be computed by the finite element analysis and sorted by the value of the associated natural frequency. This sorting naturally gives the mode shapes in increasing complexity order. The modal coefficients represent the coordinates of the projection of the initial gap on the basis of the selected number of first modes. Thus the model is defined by the number of employed modes and the distribution of modal coefficients.

To determine the parameters of both considered models the set of measured initial gap is needed. For final assembly simulation, the set of available measurements regularly establishes several challenges. Firstly, the measurement techniques usually used on assembly lines provide the data of low accuracy, and the measurement points are located sparsely on the edges of the connection area. Secondly, it is common to have a small number of measurements obtained during aircraft manufacturing for real assembled parts.

The goal of this paper is to compare how considered initial gap models can be used to handle these difficulties while modeling the initial gap for wing to fuselage joint. The additional goal is to see how these models affect the result of variation analysis of contact quality for wing to fuselage assembly process.


Approaches to Initial Gap Modeling in Final Aircraft Assembly Simulation

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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