Research On The Top-Down Transfer Method Of Geometric Tolerance Based On The Correlation Analysis Of Function And Structure

The guarantee of assembly accuracy in mechanical system is largely from the tolerance design of parts.With the development of high-precision mechanical equipment,geometric tolerance design has become a key link that must be considered in product design stage.Geometric tolerance design has become a key link that must be considered in the product design process.In traditional tolerance design,the selection of geometric tolerance items and values often depends on the designer's own experience,which has great uncertainty.Thus affecting the quality characteristics such as fit,service life and so on.According to the design requirements,the functional characteristics and structural attributes of the product itself are analyzed.And a digital analysis method combining qualitative analysis and quantitative calculation is proposed to provide a direct basis for geometric tolerance design.These are all important issues that need to be resolved urgently.Through consulting related literature,the research status of geometric tolerance design methods at home and abroad has been studied and analyzed in depth.This paper conducted in-depth research from three aspects: geometric tolerance modeling,geometric tolerance item generation and transfer,and geometric tolerance numerical optimization allocation,so as to realized the top-down allocation process of geometric tolerance that is synchronized with the product design process.The main content of this paper is as follows:The geometric tolerance design process model which is developed synchronously with the product design process is established.Some related basic concepts in the design process of geometric tolerance from top to down are analyzed.On this basis,the geometric tolerance design process model that is synchronized with the product design process is constructed-starting from functional requirements,the initial design requirements are gradually decomposed into the assembly level,the part level and the geometric element level.Based on the above path,the geometric tolerance item transfer and the optimal distribution of geometric tolerance values are realized.The geometric tolerance representation model based on function and structure correlation is established.Firstly,the functional requirements and structural association analysis are carried out on the product level,part level,geometric feature level and tolerance level.And the product data association model between function,structure and geometric tolerance is constructed,and the constraints between the three are defined.Then,based on the association constraints between functions and structures,a structural transformation model of functional requirements is constructed,which converted functional requirements into structural constraints between functional elements,and realized the unified expression of geometric tolerance information.On this basis,the mapping relationship among the functional requirements,structure associations and geometric tolerance items is defined.The geometric tolerance item generation specification based on the functional requirements and structural constraints is proposed,which lays a foundation for the transmission of geometric tolerance items.Finally,according to the association constraints between fit tolerances,cross-reference tolerances and self-reference tolerances,a tolerance association model based on fit constraints is constructed,which provides a basic model for the numerical distribution of geometric tolerances.The transfer method of geometric tolerance items based on assembly joints is proposed.Firstly,the parts required by the initial design are used as the starting point,and the transfer path of part-level geometric tolerance items based on the functional requirements and structural associations between parts is constructed.On this basis,by adding the composition of the assembly joints between the parts,the constraint type and the constraint relationship of the general structural surfaces,the geometric feature surface-level tolerance transfer path is established.The structural transformation rules of the functional requirements are established,the geometric tolerance items generation specification based on the structure association and the transfer specification of the datum are established,and the mapping relationship between the functional requirements,the structural association and the geometric tolerance items is defined based on the above specifications.Based on the above method,the synchronous transmission and analysis of geometric tolerance items in the product design process are realized,and an effective analysis tool is provided for realizing the top-down design of geometric tolerance items.The numerical optimization distribution method for geometric tolerances based on fit constraints is proposed.Firstly,based on the tolerance association model of fit constraints,the initial fit requirements at the assembly level are decomposed into the geometric tolerance requirements of the part level and the surface level;The assembly joint is used as the basic carrier of the fit tolerance transfer.According to the order and the surface type of the assembly joint,the analysis method of the mating surface spin matrix is proposed.And the geometric tolerance constraints of the mating surface are generated based on the matrix;The numerical constraints of dimensional tolerances to geometric tolerances,spin matrix-based tolerance constraints,machining accuracy constraints,and cross-reference tolerances to self-reference tolerance constraints are regarded as constraints,and the minimum total tolerance cost is regarded as the objective function.The genetic algorithm is selected to optimize the solution,and the minimum total tolerance cost and the corresponding geometric tolerance value are obtained.The top-down transfer design system for geometric tolerances based on correlation analysis of function and structure is developed.The system used SOLIDWORKS as the operating platform,Visual Studio as the development tool,C# as the development language,Access as the back-end database,and Matlab as a tool for numerical analysis and calculation of geometric tolerances.The system mainly includes a geometric tolerance items generation module based on function and structure correlation,a geometric tolerance items transfer module based on function and structure correlation,a geometric tolerance numerical optimization distribution module based on fit constraints,etc.