Multi-objective Tolerance Optimization In Design Of Geometric Precision For Mechanical Products

It is difficult and time-consuming to guarantee quality requirements of complexmechanical products, such as aeronautics and astronautics products with more complicatedstructures on parts.As a result, tolerance optimization is required before actual assemblyprocesses to improve the success probability of assembly.In this dissertation, theoretical andcritical technologies on multi-objective tolerance optimization are explored and researchedin depth in order to meet demands during assembly and adjustment processes. The mainefforts and contribution of this dissertation are as following:(1)The background of tolerance optimization technologyisintroduced. Combiningwiththe study on current situation, some problems are pointed out as the research basis.(2)A precision information model oriented to tolerance optimization is proposed.Based on the classification of feature type to symmetrical Lee subgroup,thealteration valueand direction of tolerance are expressed by small displacement torsor, the variation range ofthe vector is resolved by the3D tolerance zone.(3)The tolerance transfer method based on geometrical tolerance zone isresearched.According to different types of geometry and function, the degrees of freedomthe function--al geometric feature isanalysised. Then the tolerance type and value is confirmed by thetolerance accumulation equation.(4)The tolerance optimization method based on niche PSOalgorithm is proposed.Amulti-objective model of tolerance optimization is presented, manufacturing cost, qualityloss cost and tolerance sensibility are taken as design objectives; The traditionalparticleswarm optimization is improved, with the concept of nicheand Pareto. Then the Paretofront of uniform distribution is obtained using the niche PSO algorithm to solve themulti-objective model of tolerance optimization.(5)TheProduct ToleranceOptimization Systemis developedbased on the research resultof this paper and engineering needs. The related technologies and algorithmsare verifiedwith concrete examples.Finally, the summing-up of the whole dissertation is made, prediction of the futureresearch and direction of relative techniques are made.