| Summary: | 碩士 === 國立中興大學 === 機械工程學系所 === 97 === In the past, designers rely on experience, computer aided design or design manual which is supplied by plastic supplier for designing snap-fit and its analysis. But the limitations and demands for each case are different, and different designers solve problems with different solutions. It leads to no standard design process for snap-fit, result in design experiences can’t be transmitted. Moreover, Most of datas in the manual are obsolete and the formulations of stress, deflection only reflect the final state of snap-fit assembly. Therefore, designers can’t understand the variations of snap-fit for the stress and deflection during assembly.
In this paper, we figure out the deflection and stress formulations of snap-fit by mechanic of material. According to this research, designer can substitute the key dimensions into the formulations in the beginning. Then designers can understand the variations of deflection and stress during assembly procedure, then find out initial shape and reduce time.
Finally, to minimize von Mise stress of fixed part as the objective function. The first constraints of fixed part and moving part are that the ratio of width and length should be less 1/2 and its length of second portion should be greater than first portion. The second constraint for summation of length of fixed part and moving part need to equal to 6.4. The final constraint for stress ratio is that von Mise stress of fixed part divides by its yield stress should equal to the ration of moving part. Rely on the critical parameters, we can minimize the stress of fixed part and moving part.
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