Multi-station Assembly Variation Analysis And Control Of Aircraft Compliant Parts

As a kind of typically complicated mechanical product,the aerodynamic outline accuracy of aircraft is extremely strictly required.The structure of aircraft contains a large multitude of compliant parts which are weakly rigid and easy to deform in assembly process.Such compliant parts include sheet metal parts,metal integral panel parts,thin-wall composite parts,et al.In the assembly process of aircraft components such as fuselage panels,the over-constrained fixtures are often used,and the common joining method is riveting.The aircraft components are often assembled during multiple stations.The assembly variations are caused by the coupling effects of error sources including part manufacturing variations,fixture locating variations and riveting variations,as well as the introduction of relocating variations with the change of stations.In assembly process of aircraft compliant parts,the assembly variations are usually large and difficult to predict,due to the characteristics such as small rigidity,multiple joining surfaces,complicated forces,complex assembly hierarchy,and multiple stations.However,the assembly quality of aircraft compliant parts directly affects the aerodynamic outline accuracy of aircraft.Therefore,variation analysis and control of multi-station assembly of aircraft compliant parts are studied,and the key research works covered in this dissertation are as follows:(1)A multi-station assembly variation modeling method of aircraft compliant parts is proposed,and the propagation model between error sources and assembly variations is established.For the single-station assembly process,coupled with the process and fixture characteristics of aircraft compliant parts,the variation propagation models for serial assembly and parallel assembly are built,where the variations caused by the deformation and the rigid body motion of parts are both considered.For the sub-process of locating by DA hole(i.e.self-locating of parts),the variation modeling method incorporating part deformation is presented.For the multi-station assembly process,the state space model is built.Due to the uncertainty of values of error sources,the statistical variation analysis is performed based on Monte Carlo method.The proposed assembly variation modeling method is applied to the case study of a fuselage panel assembly,and the rationality and reliability of this method are verified.(2)A fixture layout optimization method of multi-station assembly of aircraft compliant parts is proposed,to reduce the assembly variations caused by riveting force perturbation.For the construction of the optimization model,according to multi-station assembly variation model of aircraft compliant parts,the relationship between riveting force perturbation and assembly variations is obtained.Considering the uncertainty of riveting force perturbation,the certain objective function is constructed by using the principle of statistics,which effectively improves the efficiency of iterative solution.For the solution of the optimal fixture layout scheme,electromagnetism-like mechanism coupled with genetic algorithm is used.From the perspective of improving the accuracy and efficiency of the solution,the grid of the finite element model is divided once,and the stiffness matrices and coefficient matrices corresponding to alternative nodes of all fixture positions are extracted and only once.A case study is given,and the effectiveness of the proposed fixture layout optimization method is verified.(3)A fixture active compensation method of multi-station assembly of aircraft compliant parts is proposed.For multi-station assembly process of compliant parts,the feedforward control strategy for active error compensation is presented,where the adjustable fixture locators are used.The error compensation system is established,which contains three modules,i.e.measurement,computation and execution.According to the measuring values of the deviations of part,sub-assembly and fixture,the compensations of adjustable fixture locators are determined.For the computation of the optimal compensations,the relationship between compensations and assembly variations is obtained based on multi-station assembly variation model of compliant parts,and then the constrained multi-objective second time programming model is constructed.Sequential optimization technique and effective set method coupled with local enumeration are used to solve the optimization problem.As to multiple measurements and determinations in the error compensation system,updating mechanism is introduced.The experiment of multi-station assembly of compliant parts is designed,and the effectiveness,applicability and superiority of the proposed fixture active compensation method are verified.(4)A fixture tolerance design method of multi-station assembly of aircraft compliant parts is proposed.In order to explore the formation mechanism of the variations of working surfaces of fixture boards,the tolerance analysis method of rigid parts locating(or assembly)with multiple hole-pin-hole joints is presented,where the influence of gravity is considered.For the assemblability judgment and assembly deviation calculation,the search and optimization models are constructed,and such problems are solved by multiple search and optimization algorithms,such as particle swarm optimization,linear programming and dichotomy.The accuracy and reliability of the proposed tolerance analysis method are verified by a case study.According to multi-station assembly variation model of aircraft compliant parts,the relationship between the variations of working surfaces of fixture boards and assembly variations is obtained.The evaluation method for fixture tolerance design is given based on the multi-level sensitivity.For the station with the largest sensitivity,the relationship between the fixture manufacturing tolerance and the evaluation indices for fixture tolerance design is obtained by using the discrete value method.Then the method of fixture tolerance design is discussed.