Research On Tolerance Distribution Of Aircraft Components

The process route from part machining to component assembly and general assembly is very complex in the aircraft body. Because amounts of different types of manufacturing equipment are required. It is impossible to deal with the interchange and coordination problem only by improving the accuracy of manufacturing components, due to different kinds of links that would affect assembly errors. As a result, reasonable assembly tolerance analysis to ensure the assembly interchanges and coordination is one of the key technologies in aircraft manufacturing. The key research works covered in this dissertation are listed as follows:Firstly, assembly process of the aircraft workpieces was analyzed. By simplifying the assembly processes in the process of positioning, clamping, jointing and spring-back, the concept of key features which controlling assembly quality is defined. Then, the assembly variation model of aircraft weakly rigid parts based on influence coefficient method was constructed based on the linear elastic hypothesis of small deformation. The model carried out the mechanical analysis of aircraft weakly rigid parts in the typical assembly processes. Influence coefficient matrix of the key features which was effected by parts manufacturing variation and fixture variation was calculated through the Finite Element Method and Monte Carlo simulation.Secondly, Monte Carlo simulation method used in the assembly process was discussed. Assembly variation model and tolerance analysis was given by the VSA and 3DCS software in the aircraft assembly process for complex parts, which was focusing on how to select the adjustment object of tolerance, how to determine the rationality of the revised tolerance allocation scheme and so on. By analyzing the above problems, the most sensitive priority modification principle was put forward. Then, the iterative method in the tolerance optimization was analyzed.Thirdly, the assembly process of the outer flap components in certain aircraft was discussed as an example. The assembly process of the outer flaps, and the model of its tolerance can be determine based on VSA. According to the analysis, the distribution of the errors and the geometric factor and its contribution which the measurement error results can be obtained. According to the principle "the largest contribution to modify preferentially", we can adjust the tolerance factor, then verify the effective of adjustment scheme according to iterative method until the results were accorded with tolerance requirements. Lastly, the final optimization scheme was get.