Research On Computer-Aided Dimensional Tolerancing Technique

Computer Aided Tolerance, which was first proposed by Hillyard of Cambridge University since 1978 and went through the phases of basis establishment and theory formation, now has been developed prosperously and many research results has been obtained. Based on the plenty of documents, this paper carried out some research, including the method of automatic generation and representation about dimension chain, tolerance analysis and the integration way of CAT and CAD.Automatic generation of dimension chain is the foundation of CAT and the design function described by the chain offers basis of tolerance analysis and tolerance synthesis. As the present situation of dimension chain generation, this paper has researched the method of automatic generation about part dimension chain according to the description technique of dimension information in 3D modeling software. And it was discussed how to integrate the CAT based on the current modeling system and its feasibility. Finally prototype system was achieved in the platform of PRO/E through plug-in form.For the traditional design, database was the main method to describe and store the dimension chains and tolerance information, and with this technology we can retrieve and modify the dimension information. In this paper, tolerance expression method based on XML (Extensible Markup Language) technology was proposed, which had more advantages, such as self-description, open standard, structured well, easily transport and so on. So XML was superior in data storage, representation and exchange. On that basis, dimension chain form based XML and how to use table and figure to display dimension chain intuitively were also discussed in this paper.Tolerance analysis, based on the mathematical model of dimension chain and its links, was carried out to analyze the affection of consisting links to closing; it is how to ascertain the tolerance and distribution situation of the closing link according to the parameter of consisting links. Apart from this, linear method and statistical experiment method were used respectively for tolerance analysis test. The test results showed that it is more suitable for reality to use the statistical experiment method with correction coefficient applied, in which tolerance value was between the results of linear method and statistical method.