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A Study on Warm Stamping Process of Aluminum for Shock Absorber Housing Panel
김민기,류재창,홍종빈,이정흠,고대철 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.11
Recently the application of aluminum has been studied as a means of lightening the weight for automotive components. Warm forming of aluminum is necessary due to low formability at room temperature. However, it is difficult to maintain the temperature during stamping process because transfer time of heated blank is long and shape of shock absorber housing panel(SAHP) has deep forming depth. So pre-forming through cold stamping was performed to minimize temperature reduction before warm forming. In this study, preform optimization was investigated in warm and cold stamping process for manufacturing SAHP. First, effect of temperature and strain rate on the flow behavior of the material was investigated by uniaxial tensile tests. Next, interfacial heat transfer coefficient according to pressure was determined through experiments and inverse analysis for considering heat transfer between blank and tool. Based on these properties, in finite element(FE) simulation material model that describe behavior of elastic viscoplastic material with thermal effects was applied. Finally, FE-simulations of preforming and warm stamping were conducted to predict optimal preform by estimating the defects such as wrinkle and fracture according to punch stroke.
CFRP와 Al7075T6 동시성형/접합의 접합력 향상을 위한 레이저 표면처리에 관한 연구
조경환,주진혁,류재창,김민규,이태현,이정흠,오제훈,감동혁 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5
기후변화와 환경오염에 관한 문제로 인해 자동차 산업에서는 연료 소비를 줄이기 위해 차체 경량화에 대한 연구가 진행하고 있다. 비철금속, CFRP와 같은 경량 다종소재의 적용이 증가함에 따라 이종소재 접합의 필요성이 증가하고 있지만, 기존 용융용접을 적용하지 못하는 경우가 많기 때문에 기계적 체결, 접착제 접합 등과 같은 비용융접합이 제안되고 있다. 본 연구에서는 CFPR와 Al7075T6를 동시성형/접합을 한 후에 CFRP와 Al7075T6의 접합성을 평가하였다. 두 소재 간 접합성을 높이기 위해 Al7075T6에 레이저 표면처리를 진행하였다. 동시성형/접합은 알루미늄 모재를 바닥에 배치한 후 CFRP prepreg를 그 위에 놓고 가열된 punch를 하강하면서 성형과 접합을 동시에 하는 방식이다. 이 때 표면처리가 없이 동시성형/접합을 진행할 경우 접합이 불가한 것을 확인하였다. 이 문제를 해결하기 위해 Al7075T6에 표면처리를 진행하였다. 표면처리를 하기위해서 nanosecond pulse laser를 사용하였고, pattern pitch, scan speed를 변화하면서 실험을 진행하였다. 그 결과 접합부 최대 인장하중은 8.77 kN이였다.
Prediction of interfacial behavior by mode of hybrid composite part using a cohesive zone model
J. S. Park(박준수),J. C. Ryu(류재창),J. S. Jang(장진석),J. H. Kim(김재홍),D. C. Ko(고대철) 한국소성가공학회 2021 한국소성가공학회 학술대회 논문집 Vol.2021 No.5
In recent years, the automotive industry has focused on reducing CO<sub>2</sub> emissions through the development of electric vehicles and the lightweight parts of vehicles according to the strict environmental regulations of each country. A direct method for lightweight vehicle parts is to use carbon fiber reinforced plastic(CFRP) to replace conventional metal parts or join Steel/CFRP as hybrid composite parts. Hybrid composite parts have superior specific strength, flexibility, and fatigue strength compared to the existing conventional parts. However, in the manufacturing process for these parts, interfacial failure may be occurred because of the difference in deformation characteristics, such as spring back and thermal contraction. Therefore, fractures at the interface between dissimilar materials should be predicted to manufacture the hybrid composite parts. The purpose of this study is to predict the interfacial behavior for hybrid composite parts manufactured by steel sheet and CFRP. In this study, steel sheet and CFRP were joined by epoxy resin impregnated in CFRP prepreg during the curing process. Double cantilever beam(DCB) test and end-notched flexure(ENF) test were performed to obtain various adhesion properties, such as critical energy release rate of Mode I, Mode II(G<sub>I</sub>, G<sub>II</sub>) and critical stress(σ<sub>max</sub>), respectively. Traction-separation law was used to describe the interfacial behavior between Steel/CFRP. Also, Finite element(FE) analysis with Cohesive zone model(CZM) was performed to predict adhesive failure and its results were compared with experimental ones. Finally, experimental drawing of steel/CFRP hybrid parts, such as DP980/CFRP and DP590/CFRP hybrid part is performed to investigate the interfacial behavior of steel and CFRP due to spring back. Adhesive failures at the interface of steel and CFRP observed in experimental drawing are quantitatively compared with those of FE simulation