Computer Aided Tolerance Analysis And Robust Optimization Of Automobile Chassis Parts

Tolerance design consists of tolerance analysis and tolerance allocation, thetolerance analysis can judge if the current tolerance allocation plan can ensure theassembly performance, and tolerance allocation is the reverse process of toleranceanalysis. Tolerance design is necessary to concurrent design during design phase andmanufacturing process, as the tolerance not only affect the assembly qualityperformance but also determine the machinability and manufacturing cost of theassembly.The worst case and Root-Sum Square are the traditional tolerance analysismethod based on dimension chain, and often applied on machined parts. The computeraided tolerance design technology based on Monte-Carlo method would be moresuitable for complex assembly, because the dimension chain of complex assemblywould be very hard to gain, and the precision of traditional analysis result is poor.The three dimensional assembly variation analysis model can be built based on3DCS, the statistical analysis result and failure rate of the measurement target can begained after running the Monte-Carlo simulation, then the optimize target would belocked easily; The sensitive contributor and geometric factor of the measurementtarget can be got after running the HLM and Geo-Factor contribution analysis, whichwould be help to design the reasonable optimization scheme. The optimizationscheme including: Tighten the tolerance of parts, improve the assembly process ofwelding parts, change the structure design of parts.The merit and demerit of worst case, root sum square and monte carlo methodand their respective applicable scope were compared. Robust design method andindex was expounded. The mathematical and calculation formula of HLM andgeometric factor, two linear contribution calculation method, was introduced, andtheir different applicable conditions were discoursed based on experience.A robust optimization method based on variation analysis result was proposed,geometric factor and quality loss function were the robust optimization target function,manufacturing capability and parts dimensional and geometric toleran ce was theboundary condition. The concurrent design of design phase and manufacture phasewas realized, the efficiency of robust optimization was improved.The robust optimization based on3-D assembly variation analysis result of accelerator pedal assembly quality was researched. The manipulation interferenceproblem between the accelerator pedal and the front floor was solved, after optimizingthe datum layout of the accelerate pedal and the mounting plate, without tightentolerance of parts. The actual engineering application verifies the feasibility of robustoptimization based on variation analysis result.