Research Of Computer Aided Tolerance Allocation For Typical Components Of General Aircraft Products

Analyzing the accuracy of the product by using the computer in the entire production process of mechanical parts is the main research content of Computer Aided Tolerance Technology(CAT).The process of assembly is an important procedure in product manufacturing process,and the assembly quality has direct influence on the quality and usability of the product.Based on the fact that complex products have the characters of large quantity of parts,complicated structure of assembly dimension chains and assembly relation.The assembly tolerance analysis technology of complex products was researched with the object of typical components of general aircraft products.Based on the new geometrical product specification technology and MBD technology,the assembly tolerance model structure of CATIA was analyzed.The TTRS level structure of the assembly tolerance model was established by applying topologically and technologically related surfaces theory.By extracting the tolerance information and constraint information of the assembly tolerance model,the dimension-related feature element matrix and constraint-related feature element matrix were built,the dimensional tolerance-assembly constraints graph was created,the automatic generation method of dimension chain based on searching related feature element was built.The tolerance analysis method of extremum seeking method,probability method,Monte Carlo method were studied.As the method of Monte Carlo,each component ring size value of the dimension chain is sampled randomly,and the size value of closing ring is solved with the tolerance design function,the samples of closing ring are statistically analyzed to solve the closing ring.The technology of tolerance allocation was studied,each of composing ring has been allocated a tolerance according to the dimension tolerance of closing ring.Finally,the assembly tolerance analysis system was built in VS2008 by adopting the secondary development tool CAA under CATIA platform.The system is composed of four modules: assigning closing ring,extracting assembly tolerance information,extracting assembly constraint information and analysis by Monte Carlo.The feasibility of the research method and technology under the system have been validated by testing the case of a certain type of general aircraft engine nacelle part assembly.