Study On Key Techniques Of Variation Modeling And Coordination For Large Aircraft Digital Assembly Based On Key Characteristics

The digital assembly technology has be turned out to be an important development direction of aircraft manufacturing and assembly, and China has achieved some breakthroughs in terms of research and development of aircraft digital assembly technology and equipment. However, it will be difficult to play digital assembly system utility effectively with the lack of the research on the theories and method on modeling and controlling the variation and the manufacturing and coordination accuracy of assembled objects. Therefore, for exploring coupling and transmission mechanism of aircraft digital assembly, this dissertation researches the assembly variation modeling and coordination control method systematically. The main research contents of the dissertation are as follows:The domestic and foreign development of aircraft digital assembly technology is introduced, and the status and role of the assembly variation analysis, modeling and coordination method in the whole technology system of aircraft digital assembly are expounded.The definition of reference systems required in aircraft digital assembly process are provided, including assembly reference system, measuring reference system, part reference system and plane reference system, etc. The spatial geometric relationships of reference systems, the object’s posture and KCs are established using rigid body transformation. Then a set of mathematical methods that explain the digitization transference are formed.According to the principle of elastic composite structures, the mechanical model is established based on beam elements, and considering the manufacturing error, positioning error caused by the numerical control localizer (NCL) group, and deformation error caused by redundant support positioning and the action of gravity. The constraints of the four typical stages of digital assembly are analyzed, which are positioning, joining and coordination and releasing stages. The variation model of aircraft digital assembly in a single station is established, which is dominated by the deformation. The prediction of aircraft digital assembly variation can be achieved by this model.Taking the object’s position as the variable, and the tolerances of the KCs as the constraints, the optimization model of the assembly objects bias is establish, and its solution is got using SVD method and Lagrange multiplier method. On this basis, the temperature compensation mechanism of large parts is added to the object’s position evaluation, which can eliminate the negative impact of temperature change to some extent. A unified coordination model of single object and multiple objects is expressed, and then a complete variation coordinate method of aircraft digital assembly is proposed, which is suitable for engineering practice and implements the initiative redistribution of the assembly variation.The aircraft digital assembly multi-stage process is described with a tree structure. And according to the discreteness of the modern aircraft assembly, the influence of assembly relocation, changing of assembly references and variation coordination to the variation propagation between assembly levels is analyzed. The state transfer equations of the assembly variation are established, which can reveal the variation transmission regularity of the aircraft digital assembly.Finally, summary for the whole work in this dissertation is given, and some advanced topics to be researched further are also discussed.