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Study On Computer Aided Tolerancing For Composite Dimensional And Geometric Tolerances

Posted on:2008-03-13Degree:MasterType:Thesis
Country:ChinaCandidate:B KuangFull Text:PDF
GTID:2132360215989453Subject:Mechanical Manufacturing and Automation
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Toleranceing play an important role in product's designing and manufacturing because it directly affects the quality and manufacturing cost of products. Tolerances conclude dimensional tolerances and geometric tolerances. In the process of tolerance design, dimensional tolerances and geometric tolerances are used to meet the requirement of products. Because of the complexity of geometric tolerance, the amphasis of the research in computer aided tolerancing focus on dimensional tolerances. Seldom attension was paid on geometric tolerances. To meet the engineering requirement, this paper carries out the composite tolerancing, which includes dimensional and geometric tolerances.Based on the latest researches of tolerancing, this thesis researches into the problem of composite tolerance design including to build the composite tolerance model based on graph theory, to present the generating method of assembly dimension chain based on Expert System, to build composite tolerance allocation model in allocation of dimensional and geometric tolerances simultaneously, and to realize the prototype system for composite tolerance design.The main contents are as following:(1) Establishment of the composite tolerance model. A new method to build the composite tolerance model based on graph theory is presented and the data structure of model and search method based on broad first search is given. The composite tolerance model includes feature constraint relation graph and assembly constraint relation graph. The former is used to describe feature constraint relation of a component and the later is used to describe assembly constraint relations of an assembly. All the possible component links of assembly dimension chain are obtained by searching the composite tolerance model.(2) Implementent of the generation of the assembly dimension chain based on Expert System. In terms of the characteristic of assembly dimension chain, the"rule + fact"structure of knowledge base is used and the forward inference tactics is as inference engine. Requirements of assembly and component type are used to perform knowledge inference to obtain assembly dimension chains which include dimensional tolerances and geometric tolerances.(3) Establishment of the model for allocating dimensional and geometric tolerances simultaneously. The relation between dimensional tolerances, geometric tolerances, and manufacturing cost is obtained according to the actual process data of manufacture enterprise. The optimal model for allocating tolerance is built. And the process of tolerance allocation is carried out based on Immune Genetic algorithm.(4) Implementent of the prototype system for composite tolerance design. The prototype system for composite tolerance design is completed through using the method for generating assembly dimension chain and the tolerance allocation.This thesis is financially supported by National Science Foundation of China, named"Modeling and Methodology for Integration of Design and Manufacturing in Tolerance Design"(No. 50465001), and Innovation Project Guangxi Graduate Education of China, named"Research on tolerance modeling and design method for Composite Dimensional and Geometric Tolerances"(No. 2006105950802M06).
Keywords/Search Tags:Dimensional tolerance, geometric tolerance, composite tolerance model, Expert System, tolerance allocation
PDF Full Text Request
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