Research On Computer Aided Tolerance Optimization In Aircraft Manufacturing

Interchange coordination technique is the central issue in process planning of aircraft manufacturing. Meanwhile, reasonable tolerance design can assure interchange coordination requirements and directly affects the assembly yield, manufacturing quality and cost. The current tolerance design methods in aircraft manufacturing are mainly based on manual analysis, the low efficiency and reliability of which have been unable to meet the development requirement of modern aircraft manufacturing. All of these seriously restrict the promotion of aircraft quality. According to the above fact and requirements of modern aviation technology, as well as associating with"National Natural Science Foundation of China"and"Jiangsu Planned Projects for Postdoctoral Research Funds", computer aided tolerance optimization in aircraft manufacturing has been deeply studied in this paper. The main achievements are as follows:According to the particularity of aircraft manufacturing, a new tolerance representation model based on standard dimension coordination relation definition is introduced as the basis of computer aided tolerance optimization. In this model, dimension coordination and tolerance information of each manufacturing process are integrated together. Computer-representation model based on tree structure and adjacency matrix is built, and dimension coordination file is introduced as the external representation model of tolerance. In addition, the algorithm for proposed coordination route diagram automatically building has been given.Coordination accuracy analysis of typical aircraft parts is studied. In aircraft manufacturing, coordination cases can be classified into two styles, configuration coordination and intersection coordination. In this paper, based on the hypothesis of tolerance obeying normal distribution, manufacturing and coordination accuracy model of the two styles are built. Based on the model, calculation formula of accumulated error and coordination yield are derived.Dimension chain analysis based on Monte-Carlo method is researched. In actual situation, sizes of composing loops obey various distributions, which analytical method could not well solve, while Monte-Carlo method is a suitable approach. Firstly, mathematical model for dimension chain simulation and assembly accuracy is built; Secondly, several random number generating algorithms for common distributions are given, including bimodal distribution, triangular distribution and so on. The size distribution of closed loop is proposed to be determined by K-S test, and quantitative analysis of assembly quality indexs, such as assembly yield, contribution rate, is researched. A new tolerance optimal allocation technology based on mixed cost-tolerance model is proposed. The relation between composing loop's relative cost and tolerance value can be expressed by polynomials, and the total relative cost of one dimension chain can be gained. Suppose minimum cost as the analysis objective and assembly requirements as the restraint condition, then the tolerance of each composing link's can be obtained by genetic algorithm.Based on the above theoretical studies, an aircraft tolerance optimal allocation system has been developed. It has been successfully applied in a large-scale aviation enterprise.