| Summary: | 博士 === 國立中央大學 === 機械工程學系 === 104 === It is a challenge of superplastic forming, SPF, techniques to form a strake with large depth-to-width ratio from an aluminum sheet. It is tougher if the strake is asked to be uniform in thickness. To address this problem, the authors employ two different SPF techniques, namely two-stage gas forming (TSFG) and hot-bend assisted gas forming (HBAGF) to produce airplane strakelets from AA5083 aluminum sheets. The thickness of such sheets range from 1.0 mm to 2.5 mm. To study the size effect on wrinkle formation and thickness distribution and thus link subscale data to a full scale manufacturing process, experiments on three scales (1:2:4) were performed on the specimens. Undesired wrinkles appear on all strakes formed by each SPF techniques with different sheet thickness. The sites of wrinkle and their formation causes are different but their occurrences are repeatable.
To gain the insight of wrinkle formation on different size strakes, a three-dimensional finite element analysis software LS-DYNA was implemented to predict wrinkles’ shape and occurrence. We found that LS-DYNA is effective software that helps an engineer to design the forming die and to predict the wrinkles location. It makes us to understand the formation of a strake from a metal sheet during the SPF process easily. In the present study, the maximum thickness difference of strakes and its LS-DYNA prediction is less than 5.0%. That is adequate for estimating the thickness profile of SPF parts. Thus, the technique developed in this study promises to save the time of try and errors. It also shows that the HBAGF die led to significant improvement of the thickness profile of superplastically formed parts.
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