Optimal allocation of tolerances and clearances in complex assemblies to minimize the cost of manufacturing

摘要

A procedure has been developed for the optimal allocation of tolerances and clearances in complex assemblies for minimum manufacturing cost and sensitivity to variation keeping the deviations of the output from the ideal within designer specified limits. The assemblies that have been considered are the single loop planar and spatial mechanisms including analytically defined surface contact joints. The procedure allows the incorporation of manufacturing tolerances and clearances based on actual manufacturing process and cost information. This allows the designer's intent and the manufacturing and process capabilities to be tied together in the development of the product or assembly. The incorporation of tolerances in the case of analytically defined surface contacts like sphere to sphere contact, or sphere to cylinder contact etc. have also been studied in this work.;For each individual design parameter, the sensitivity of the output function with respect to the variations of these parameters are established. The sensitivities and the cost of incorporating individual tolerances and clearances are then studied together to see the overall effect on the assembly and also the cost of manufacturing. Sensitivities of the output with respect to the design parameters and also the link length and joint clearance parameters is often a very good information for the designer to have in studying the problem of variation of the output. This can be obtained as a part of the output generated in this work. It has been found that this gives a lot of insight on the actual behavior of the mechanism or assembly.;The allocation of tolerances are done with the idea of minimizing the overall "life cycle cost" of the assembly.;Use of the minimal L$sb2$-norm along with the objective weighting method have been found to be quite effective in this work. The multicriteria optimization procedure has been incorporated in an interactive fashion where the designer is allowed to interpret the results and modify the weighting factors of the objectives based on the current results and the designer's overall intent of the design.;An equivalent "clearance link" model has been proposed for various joint types with clearance and they have been tested with example cases. Clearance analysis procedure has been developed for the revolute, cylindrical, prismatic, and spherical joint types.;The multicriteria optimization based procedure makes the design "robust" against manufacturing variations and subsequent operating variations. Different cost vs. tolerance charts or functions can be used for estimating the cost of manufacture and the procedure can be used to evaluate the viability of alternative process and machine combinations to obtain the least manufacturing cost for the individual components of the designed mechanism. (Abstract shortened by UMI.).