可調式阻料條改善側壁捲曲之研究

Abstract

隨著環保意識的覺醒及日趨嚴重的溫室效應，為了降低二氧化碳的排放量，車體輕量化成為全球汽車廠一致的目標。先進高強度鋼具備輕量化及高強度化之特點，因此已逐漸應用於汽車結構件中。但隨著鋼板強度之提升，側壁捲曲及側壁外開等回彈缺陷越趨嚴重。為了改善高強度鋼之沖壓成形缺陷，於模具上設置阻料條是一種常見的方式。透過適當的設置阻料條可以有效的降低回彈、皺褶及扭曲等成形缺陷。然而阻料條之設計及修改除了仰賴個人經驗之外，所需耗費的時間成本也相當可觀，且由於先進高強度鋼延伸率較低，沖壓過程中板材容易發生破裂，傳統的阻料條難以應用於先進高強度鋼。基於降低修改阻料條的時間與成本及運用於先進高強度鋼等目的，本研究擬探討可調式阻料條運用於汽車結構件板金成形的可行性。 本研究的重點在於可調式阻料條設計技術之建立，同時提出一種新型可調式阻料條機構之設計概念。由於先進高強度鋼與一般的低強度鋼相比之下包辛格效應較為明顯，因此首先使用真實阻料條及等效阻料條進行模擬，探討包辛格效應對於側壁捲曲之預測是否會有所影響。模具設定參考NUMISHEET 2011之U形引伸試驗。模擬結果顯示對於側壁捲曲之預測，使用真實阻料條能準確模擬沖壓過程中包辛格效應的影響。接著比較常見的阻料條種類及其造型參數對於側壁捲曲的影響，根據模擬結果，半圓形阻料條最適合應用於改善汽車結構件側壁捲曲。因此針對半圓形阻料條比較不同阻料條設計參數對於側壁捲曲、減薄率的影響，並且透過模擬分析模具接觸力隨沖壓過程之變化，提出可調式阻料條之設計原則。根據模擬結果顯示，透過此流程可以在確保板材不發生破裂的情形下有效的改善側壁捲曲現象，無論是780、980或1180級高強度鋼側壁捲曲半徑皆可達1000mm以上。最後根據上述歸納出之結論，提出一種可調式阻料條機構之設計概念。

As environmental consciousness rises and greenhouse effect becomes worse, design for lightweight automobiles becomes a major goal for vehicle manufacturers in order to reduce 퐶푂2 emissions. Because advanced high strength steels (AHSS) are lightweight and high strength, AHSS have been widely used in automobile structural parts. However, as the strength of steels increases, stamping defects such as sidewall curl and distortion become worse. In order to reduce stamping defects of AHSS, such as springback, wrinkling and distortion, drawbeads are often used in stamping process. In order to design drawbeads quickly and properly in stamping processes, this study investigates the feasibility of active drawbeads in sheet metal forming. This study focuses on the establishment of active drawbeads design process. Because Baushinger effect is much stronger in AHSS than in low strength steels, this study investigates the difference between physical drawbeads and equivalent drawbeads in CAE simulation. According to the simulation results, physical drawbeads can correctly take Baushinger effect into account in stamping. This study also investigates the effect of geometric parameters of drawbeads on sidewall curl. In addition, this study investigates the effect of parameters of round bead on sidewall curl and thinning. By studying the contact forces among punch, mold and drawbeads during stamping process, this study establishes a design process of active drawbeads. It shows that sidewall curl can be significantly diminished. Radiuses of sidewall curl of NUMISHEET 2011 benchmark 4 are higher than 1000mm in 780Y, 980Y, 1180Y by using active drawbeads without cracking.