The Research On Computer-aided Dimensional Tolerancing

In the recent years, there have been great breakthrough and compelling achievements in the fields of CIMS and CAD/CAM. The development of Computer-Aided Tolerancing(CAT), however, lags highly behind that of CAD/CAM as an important part of machinery design and manufacture process. In view of this case, many experts at home and abroad have done a great deal of research work.In this paper, the research had been carried out on the basis of plenty of documents, including automatic generation of dimension chain, distribution law of divided link and sum link, tolerance analysis and tolerance synthesis. Among them the automatic generation of dimension chain is the foundation of CAT and the described design function offers basis of tolerance analysis and tolerance synthesis. Based on the Assembly Database, a new method of Automatic Generation of Dimension Chain has been put forward. Distribution laws of divided link and sum link relate exceedingly to the distribution parameters in tolerance analysis and tolerance synthesis. And the numerical value of these parameters influences directly the assembly's reliability. This paper is to study how to count those parameters or how to decide on the numerical value of it in a definite circumstance.Tolerance analysis aims to explore the effection of divided link on sum link, namely how to ascertain the assembled sum link's tolerance if knowing all divided link's dimension, tolerance and distribution parameter. Monte Carlo Method, as an extensively-applied statistical experiment method, had been applied in the tolerance analysis. And since the divided link's actual dimension is a random data which obeys a certain distribution, it is feasible in tolerance analysis using computer's random data according to a certain rule to simulate the actual dimension of parts in production. The experiment proves this method can not only achieve what have been expected but also save the time and cost of the experience.The task of tolerance synthesis is to ascertain divided link's economical and rational tolerance on condition of guaranteeing assemble technology. In this article, traditional tolerance synthesis method is introduced briefly, and it's done emphatically to deduce the Economical Principle Method theoretical and verify it with instances. The instance proves it can cut down the cost of producing parts and got good economic benefits to maketolerance synthesis. Economical Principle Method is divided into Optional Assignment Method and Linear Layout Method. We choose a normally-used tolerance-cost model(Reciprocal Square) for the former, and for the later, a linear tolerance-cost model is adopted, whose effect is worse and whose process is more simple than the former.