以超塑成形使鋁鈑成形至大深寬比且複雜的幾何形狀，並能得到滿意的厚度分布，是非常具有挑戰性的。為解決此類問題，兩階段氣吹成形(two-stage gas forming, TSGF)被提出來應用在飛機的整流罩製作上，前期研究結果顯示傳統超塑性成形以及兩階段氣吹成形方法仍不滿足厚度的需求且有皺折產生，因而提出熱折彎輔助氣吹成形法(hot-bent assisted gas forming, HBAGF)的概念。此法雖然改善了厚度的分布，卻與兩階段氣吹成形法同樣出現皺褶現象。然而，兩種成形方法皺褶形成部位及原因是不相同的，本文將詳細的探討皺摺成因。並藉由三維有限元素分析軟體LS-DYNA輔助，預測熱折彎階段以及氣吹成形後鈑材的變形過程。實驗模具使用三種不同等比例尺寸大小四分之一、二分之一、以及全尺寸。鈑材選用超塑性鋁合金5083，具0.5~2.5mm等各種厚度。比對實驗與有限元素分析結果，可以準確的預判皺褶發生的位置、形狀，以及熱折彎的挫曲情形。並且比較量測點各位置其減薄率實驗與分析結果誤差皆小餘5%。研究結果顯示，皺摺的位置是可被預測且設計。下模經過精進設計後，成功製做出符合厚度規格之整流罩產品。;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.
