Modeling And Application Of Tolerance Allocation Method For Flexible Assembly Of Large Scale Thin-walled Structure

Large scale thin-walled structure is widely used in the aerospace field,which have flexible deformation during assembly,which lead to the variation field and the difficulty to predict the variation accurately.The deformation compatibility of large scale thin-walled structure will lead to the redistribution of component's variation.The tolerance allocation model based on dimension chain and stream of variation doesn't consider the flexible deformation and deformation compatibility during the assembly process of large scale thin-walled structures,which leads to unreasonable tolerance allocation for the assembly process of large scale thin-walled structures.The existing scheme of tolerance allocation for large scale thin-walled structures is mainly dependent on the designer's experience and the tolerance allocation scheme of the stereotyped products.The assembly needs to be repeatedly repaired at the scene,which greatly affects the assembly efficiency and assembly quality.For the lack of the transfer rule of assembly variation,the ‘trial and error' method is always applied for the control of assembly variation in engineering field,which affects the assembly quality and efficiency in practical application.In order to solve the problem of flexible deformation and deformation compatibility in the assembly process of large scale thin-walled structures,a method of tolerance allocation for thin-walled structures is proposed,which considers the deformation compatibility.Based on the improved genetic algorithm,a algorithm for tolerance allocation is established,which improves the convergence speed.Tolerance allocation of the typical thin-walled structure assembly process is carried out.The assembly simulation of parts is carried out with the assigned tolerance results to verify the validity of the results.Finally,tolerance allocation is assigned in conjunction with the 3350 mm diameter tank assembly process.The prototype system for tolerance distribution of aerospace thin-walled products is designed.Main contents and innovations of this dissertation can be explained as follows:(1)Tolerance allocation model of the large scale thin-wall structure considering deformation compatibilityConsidering the deformation compatibility during the assembly process,a method of tolerance allocation for thin-walled structures is proposed,which considers the deformation compatibility.Component's essential deformation patterns,which are used to describe the component's variation,can be established by using the modal analysis method.The correlative relationship between the variation factors is deduced based on the force balance and the deformation coordination condition in the assembly area.Considering the process capability of manufacturing and assembling,the optimization model of tolerance allocation for flexible thin-walled structures is established.(2)Multi-level tolerance allocation model and algorithm for large scale thin-walled structure.According to the hierarchical assembly of large scale thin-walled structures,the multi-level tolerance allocation model of thin-walled structure is established,and the complexity of the problem is simplified.Based on the tolerance allocation structure framework,the assembly design indexes are successively solved downward,and the geometrical index calculation method of the thin-wall structure is established,which improved computational efficiency.(3)Tolerance allocation and assembly quality analysis of typical thin-walled structuresAccording to the assembly process of the typical thin-walled structures,a corresponding tolerance allocation model is established.According to the result of tolerance allocation,the simulation of the cylinder shell's assembly is carried out.The results show that the method proposed in this paper has high rationality when dealing with the tolerance allocation of large scale thin-walled structures.(4)Rocket storage tank's multi-level tolerance allocationConsidering the assembly procedure of rocket tank with 3350 mm diameter,the tolerance allocation optimization models of the tank and the component are established,and tolerance allocation of tank's multi-station assembly process is realized.The prototype system for tolerance distribution of aerospace thin-walled products is designed,which improve the efficiency and accuracy of tolerance allocation for large scale thin-walled structures.Overall,a tolerance allocation method for large scale thin-walled structures considering the deformation compatibility and an algorithm that can quickly and accurately solve the model is established in this paper.Multi-level tolerance allocation is established for the tank's assembly,and the tolerance of assembly and parts is determined.The prototype system for tolerance allocation of aerospace thin-walled products was designed.