Computer-aided Tolerance Analysis And Optimal Design For Assembly

Computer-aided tolerance analysis means building tolerance analysis model based onthree-dimensional solid mode, finding key sizes according to sensitivity and contributiondata to do optimization design, so that to meet the assembly demands or economicrationaization. Computer Aided Tolerance Design (Computer Aided Tolerancing, CAT forshort) refers to in the process of mechanical product design, processing, assembly andtesting, use computers to do optimize and monitor on components or the dimensions andtolerances of the product, design and manufacture products that meet user accuracyrequirements with the lowest cost[1].Computer-aided tolerance analysis and optimizationdesign is of great importance in the mechanical field, indispensable in engineeringapplications and necessary in the modern factory production mode.This subject is based on a project agreement that signed by experts of Chinese ITER(International Thermonuclear Experimental Reactor) committee and the ITER InternationalGroup, select the neutron shielding structure of the tokamak vacuum chamber, usecomputer-aided tolerance analysis ways to do tolerance analysis and optimization designfrom poloidal and radial directions.Built the tolerance model and did tolerance analysis and optimization design in use ofsoftware CETOL of CATIA. The main research works are as follows:1Cut and simplified the model. Built three-dimensional solid model in CATIA, segmentedmodel according to actual needs to get the initial study object. Simplified model based onthe actual assembly, set up the tolerance analysis model that can in line with the actualsituation and also efficiency and facilitate2Created the assembled model. Re-assembled the simplified model according to theassembly requirement, defined with the fit requirements and adjusted the freedom degreewith no constraint and under constraints to establish the intact assembly.3Established the tolerance analysis model. Established tolerance model on the assemblymodel have established according to the requirements of the actual situation. Use the thebenchmark, original features in model or derived characteristics as benchmarks. And thenadd the accuracy of dimensional tolerances, geometric tolerances and other requirements,and finally determine the tolerance analysis goals.4Did tolerance analysis. Found the critical dimensions according to sensitivity and thecontribution data from poloidal and radial three directions, find out unreasonable dimensions and tolerances from the critical dimension.5Finished the optimal design. On premise of satisfying the assembly gap in poloidal is3mm and radial assembly gap is32.788mm±5mm, optimized the tolerance model forreducing the manufacture cost and rationalizing process.6Use the extreme value method to analyze and verify the size of the representative chainto ensure that in the worst case can be fitted，also confirmed the practicality of the analysissoftware.