Prediction And Analysis Of Assembly Precision And Contact Performance For Mechanical Structure

As the final link of manufacturing chain,assembly manufacturing is directly related to the performance indexes of mechanical structure.The theoretical and technical focus of performance guarantee for major equipment is expanding from the design and processing to the assembly links at home and abroad.The mechanical structures such as aeroengine rotors are often assembled by multiple components.In the assembly process,errors accumulate and transfer to form the assembly precision,and also form a series of the connection surfaces/joints,which are the weak links restricting the system stiffness and significantly affect the dynamic characteristics and service reliability of components/whole machine.Accurate prediction of assembly performance before assembly is the premise of high performance assembly.The accurate prediction of mechanical structure performance mainly involves two aspects:one is to predict the assembly precision of parts,and the other is to predict the contact stiffness and other contact properties of mechanical structure.In order to predict the assembly accuracy of complex mechanical structures,not only the influence of the manufacturing error should be considered,but also the assembly deformation(the deformation of components under assembly load)should be fully considered.In addition,to accurately predict the contact performance of parts after assembly,it is necessary to focus on the influence of the morphology characteristics,and then establish an efficient and high-precision contact performance prediction model.Therefore,this paper focuses on the following research:(1)The error model and assembly accuracy prediction model considering the manufacturing error and assembly deformation of parts are constructed to realize the accurate prediction of assembly precision.The formation process of error which synthetically manufacturing error and deformation information under assembly load is studied,and then the modeling method of error models for the parts is proposed based on the Small Displacement Torsor(SDT)theory;Based on the idea of state space,the mechanism of error transfer and accumulation in mechanical assembly process is studied,and an assembly precision prediction model suitable for two actual surfaces mating is constructed;Taking the high-pressure rotor system as an example,the errors between the prediction results and the test results in different directions are 9.42%and 8.91%respectively,which proves the accuracy of the prediction model and further explains the influence law of the deformation of parts under the load on the assembly accuracy of the mechanical structure.(2)The numerical simulation method of surface morphology is studied,which lays a foundation for efficient and accurate prediction of contact performance.According to the amplitude distribution and spatial correlation of the measured surface morphology,the numerical simulation surfaces which conform to the real surface morphology characteristics are constructed by using the fractal theory,the Gauss theory and the non-Gauss theory respectively;On this basis,the contact model of the mating surface is obtained by reverse engineering technology,which realize the theorization and modeling of the surface model and the contact model.Finally,taking the high-pressure rotor system as an example,the three-dimensional(3D)surface model and the contact model of the mating surface are constructed effectively.(3)The calculation method of contact performance are studied to achieve the efficient and accurate prediction of contact stiffness,contact area and other characteristics.In view of the multiscale superposition characteristics of surface morphology,the surface morphology features are decomposed and characterized by the combination of wavelet analysis and power spectral density;Based on the traditional calculation model,a multi-scale hierarchical algorithm of contact performance is proposed,which obtains the contact pressure distribution at the shape error scale and the contact stiffness of the local position at the waviness and roughness scale,and then the contact stiffness is finally obtained by hierarchical operations at different scales;The contact stiffness of grinding and milling specimens is obtained by mechanical experiments,and the error between the calculation results of multi-scale hierarchical algorithm and the test results is 2.04%and 1.00%respectively,which proves the effectiveness of the multi-scale hierarchical algorithm;Finally,the multi-scale hierarchical algorithm of contact performance is successfully applied to the high-pressure rotor.(4)The optimum methods of manufacturing error and surface morphology parameters are studied.A error optimization model considering the manufacturing error and assembly deformation is established by mapping the Small Displacement Torsor to tolerance domain,taking economic requirement as optimization objective and constraints,and the machining accuracy and assembly function requirements as constraints;Taking the high-pressure rotor of aeroengine as an example,the matching surface error of each stage disk is optimized respectively,and the relative manufacturing cost after optimization is 6.79%lower than that before optimization,which reflects the economic requirements;The functional relationship between the surface morphology parameters and the contact performance of the mating surface is established,which realize the optimal design of the surface morphology parameters under the premise of guaranteeing the contact performance.