Riveting and bolting are common assembly methods in the aircraft production.&nbsp; Temporary fasteners are installed into the holes for permanent rivets to join the parts and prevent the gap opening while such technological operations as drilling and reaming. The fasteners are installed immediately after hole drilling and fix the relative tangential displacements of the parts that took place due to deformation. If the assembled parts are flexible and have large curvature, these tangential displacements can be significant and can cause the misalignment of the parts. In such a case the proper fastener installation sequence is very important. The wrong one can lead to a “bubble effect” when the residual gap after fastening becomes larger rather than being reduced. The circumstance affects the quality of the final assembly and can cause fatigue stresses. For that reason, an efficient method of optimization of the fastener installation sequence is needed.The problem is complicated by several aspects. First of all, it is a combinatorial NP-hard problem with uncertain input data that cannot be solved in polynomial time. On the other side, the assembly quality evaluation demands time-consuming computations of the fastened parts deformed stress-strain state. It means the need to simulate the installation of fasteners one by one and recalculation of a target function after every fastener pattern modification. The most commonly used strategies include different heuristic algorithms,&nbsp; Monte Carlo methods, local search, greedy algorithms etc. The main disadvantage of them is that they require a large number of computational iterations during their work. Moreover, for high dimensional problems, it is impossible to obtain the solution in a reasonable time even though task parallelization is implemented.The paper proposes an efficient non-iterative method of temporary fastener sequence optimization. The probabilistic problem of fastener sequence optimization is formulated. A variational formulation of the contact problem is used as the first step in the analysis of a fastener pattern to evaluate the effect of the installed fasteners on the deformed stress state of the assembly. The residual gap between the joined parts is regarded as the target function while optimization. The proposed method is based on the physical sense of the problem and implies minimizing the deformation energy of the mechanical system. The obtained results are verified by comparison to exhaustive search and commonly used installation strategies over different clouds of input data. Analysis of the results shows the time and quality excellence of the proposed method.

Optimization of the Installation Sequence for the Temporary Fasteners in the Aircraft Industry

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.