Research On The Tolerance Analysis Based On Monte Carlo Method And Optimal Design Method

The traditional Monte Carlo method has lots of shortcomings, such as the largenumber of the needed in simulation, the quality loss assigned difficultly inoptimization design, slowly convergence rate and so on, which determine theassembly process deformation has biggish influence to the analysis of design phase.In order to get the composition ring tolerance, a concurrent tolerance model isestablished for assembly, the tolerance are analyzed based on low discrepancysequence of Monte Carlo and optimized under the constraint of fuzzy quality lossand cost. Organization of the content is as follows:First of all, the geometric features of part geometric entities are analyzed underthe guidelines of new generation product geometrical technical manual. Then thetolerance zone model is established based on three dimensional geometric modelingby taking the spatial motion theory and small displacement torsor theory as thefoundation, the straightness and the plane dimension in position tolerance anddimensional tolerance are described respectively. The small displacement torsor isadded into deviation transfer model of parts in the assembly sequence, and get thetransfer function of tiny deformation to the key dimension in a dimension chaincaused by assembly. In addition, the coherence of established position tolerance anddimension tolerance are also verified in the process of solving mathematicalmodels.Secondly, the main characteristics of Monte Carlo and its application areanalyzed in the process of tolerance analysis. By making the research on thedistribution characteristics of machining dimension used in tolerance analysis, thetransformation of non-standard normal size distribution is completed, and a lowdeviation sequence and replaces the random sequence in the traditional Monte Carlomethod are constructed accordingly. The full amount of type safety valve stem axialsection dimension chain is taken as an example and the size distributioncharacteristics are used to carry on tolerance analysis, in order to verify the effectiveness and superiority of Monte Carlo tolerance analysis based on lowdeviation sequence.Finally, the linear dimension tolerance, manufacturing cost function model andposition tolerance cost function is proposed based on small displacement torsor, andthe process capability by the process capability index are also described. In order tosolve the problem that the quality function is difficult to assign, the fuzzy qualityloss as a replacement is used as well as establishing the fuzzy quality loss costfunction together with the process capability index. Furthermore, the feasibility andeffectiveness of tolerance analysis method based on manufacturing cost and fuzzyquality loss function are verified by taking the full amount of type safety valve stemcircumferential and the top of valve flap section dimension chain as an example.