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한성경(Seongkyung Han),김성주(Sungju Kim),서용기(Younggi Seo),유은지(Eunji Yu),김종렬(Jongryoul Kim) 한국자동차공학회 2011 한국자동차공학회 부문종합 학술대회 Vol.2011 No.5
Automobile industries have been requesting increase of the strength in steel to reduce car weight and to improve and car crash worthiness for vehicles. Especially, application of AHSS(Advanced High Strength Steel) and UHSS(Ultra High Strength Steel) have been increasing for car remarkably in recent years. Although, Cold rolled UHSS mainly used to car body, we tried to develop UHSS using hot rolled process to reduce the cost and the manufacturing process of hot rolled sheet for substitude cold rolled UHSS. In this study, mechanical properties and microstructure characteristics of the developed 1.2㎬ grade hot rolled UHSS was analyzed.
임성준(Sung Jun Lim),배기현(Gihyun Bae),김석봉(Seokbong Kim),허훈(Hoon Huh) 한국자동차공학회 2011 한국자동차공학회 부문종합 학술대회 Vol.2011 No.5
This paper constructs the database of the dynamic tensile material properties and the formability of the ultra-high strength steel(UHSS) sheets. It is well known that the dynamic behavior of automotive steel sheets is dependent on the material strain rates. Therefore, the dynamic material properties of UHSS sheets are indispensable for the accurate crashworthiness analysis of auto-bodies. The dynamic uni-axial tensile tests of DP980 and TWIP980 were carried out with the variation of the strain rate and the loading angle from the rolling direction. From the tensile tests, r-values were also investigated by analyzing the deformation history with the digital image processing technique with respect to the strain rate and the loading angle from the rolling direction. Punch-stretch forming tests were carried out in order to establish the forming limit diagram(FLD) of DP980 and TWIP980. The formability of UHSS sheets was investigated from FLDs established.
UHSS급 강재의 초기 변형률 및 변형률 속도[에 따른 인장/압축 물성 평가
최민국(Minkuk Choi),허지향(Jeehyang Huh),배기현(Gihyun Bae),허훈(Hoon Huh) 한국자동차공학회 2011 한국자동차공학회 학술대회 및 전시회 Vol.2011 No.11
This paper investigates the effect of the pre-strain and the strain rate on the tension/compression material properties of two UHSS sheets, DP980 and TWIP980. A spring-loaded clamping device proposed by Bae [1] was adopted to tension/compression tests of the UHSS sheets. Tension/compression material properties were obtained after correcting the friction and biaxiality due to the clamping force and by using digital image correlation(DIC). Material properties of the UHSS sheets were then compared at different various pre-strains and the strain rates. The Bauschinger ratio, the transient behavior and the Young’s modulus were quantitatively compared in the compressive state to verify the effect of the pre-strain and the strain rate.
초고장력강판 성형용 냉간 프레스 금형의 Ti/Cr계 PVD코팅에 대한 마모 특성 평가
허재영,윤국태,송재선,강익수,윤일채,박춘달 한국소성∙가공학회 2022 소성가공 : 한국소성가공학회지 Vol.31 No.4
The application of UHSS sheet is being expanded up to 50% to reduce the weight of automobiles and improve safety. However, due to the high strength and low elongation of the ultra-high tensile strength steel sheet, product defects such as spring back and mold defects such as cracks and chippings also occur. In this study, Pin/Ring on Disc and Spiral wear tests were conducted to evaluate the durability of Ti/Cr-coated molds for forming 1.2GPa grade UHSS sheets. Component analysis and thickness were measured for each coating layer, and hardness and adhesion were investigated to determine mechanical properties. Combining the results of various wear tests, it was found that the TiAlN coating had the best wear and sticking resistance.
냉연 초고강도강 적용 차량용 리어 크로스 멤버 형상 설계 변수 최적화
김준영,김상훈,최돈현,홍석무 한국소성∙가공학회 2024 소성가공 : 한국소성가공학회지 Vol.33 No.2
With the increasing global interest in carbon neutrality, the automotive industry is also transitioning to the production of eco-friendly cars, specifically electric vehicles. In order to achieve comparable driving distances to internal combustion engine vehicles, the application of high-capacity battery packs has led to an increase in vehicle weight. To achieve light-weighting and durability requirements of automotive components simultaneously, there is a demand for research on the application of Ultra-High Strength Steel (UHSS). However, when manufacturing chassis components using UHSS, there are challenges related to fracture defects due to lower elongation compared to regular steel sheets, as well as spring-back issues caused by high tensile strength. In this study, a simulated specimen that is not affected by the property changes of four materials was designed to improve formability of the rear cross member, which is the most challenging automotive chassis component. The influence and correlation of material-specific variables were analyzed through finite element analysis (FEA) for each material with tensile strength of 440, 590, 780, and 980 MPa grades, resulting in the development of a predictive equation. To validate the equation, the simulated specimens of 980 MPa grade were produced from the test molds. Then the reliability of the FEA and predictive equation was verified with measured specimen data using a 3D scanner. The results of this study can be proposed to improve the formability of UHSS chassis components in future researches.
A Study on the Sheet Forming of the Lower Seat Rail using 1180 TRIP Steel
Oh, Won-Jung,Lee, Choon-Man Korean Society for Precision Engineering 2018 International Journal of Precision Engineering and Vol.19 No.2
The automotive industry is investing great effort to reduce the weight of vehicles to improve fuel efficiency and performance. To develop a lighter vehicle, Ultra high strength steel (UHSS) is being increasingly used, and is the focus of efforts to develop innovative sheet steel with high strength, durability and formability, including projects such as Ultra-light steel auto body (ULSAB) and Ultra-Light steel auto closure (ULSAC). Because UHSS is very difficult to form at room temperature, roll forming and hot forming processes have been proposed. However, the productivity of these processes is significantly lower than cold forming. In this study, a seven step cold forming process is proposed for forming a lower seat rail using 1180 TRIP steel, and was found to be more conducive to productivity than other processes. The design of the proposed forming process was determined by forming analysis and experiment. The forming analysis was carried out using DEFORM software, and the experiments were carried out using a mechanical press machine. The weight of conventionally formed seat rails (DP 980) and the proposed seat rails (1180 TRIP steel) were compared to determine the weight reduction.
성형공법에 따른 초고강도 모자형 박판부품 형상정밀도 평가
최병현(Byeung Hyeun Choi),김세호(Se Ho Kim),김흥규(Heung Kyu Kim) Korean Society for Precision Engineering 2013 한국정밀공학회지 Vol.30 No.10
In this paper, the shape accuracy of the stamped hat-type product is quantified and analyzed with ultra high strength steel (UHSS) sheets. The shape of the hat-type product is designed in order to simplify the geometry of the side sill and the stamping methodology is proposed in order to verify the effect of the stamping procedure on the springback amount. Experiments and finite element analyses are conducted with four kinds of the forming sequences. The springback amounts are measured and compared according to the forming procedure with the embossing shape. Experimental result in company with analysis one illustrate that the springback amount is reduced with embossing in the padding operation. They also fully demonstrates the proposed forming procedure and the analysis method can be effectively applied to the process design for producing parts with ultra high strength steel.
UHSS 하이드로포밍 개발을 위한 박육관의 롤 포밍 기술 연구
박성필(Sungpill Park),권용재(Yongjai Kwon) 한국자동차공학회 2015 한국 자동차공학회논문집 Vol.23 No.1
In the automotive industry, it is required to reduce weight of the car and improve fuel efficiency. Competitive pricing is also a very important issue. That’s why application of welded steel tube is increasing in order to produce a vehicle with a competitive price. Also, hydroforming technology is asking more and more for thinner tubing to realize to a lighter vehicle design. Steel tube is produced through a multi-stage process called roll forming. In that case, bucking and work hardening should be considered key forming technology is to prevent buckling and minimize work hardening during steel tubing for hydroforming To prevent buckling, it is required to optimize forming process in order to minimize stretching in edge sections and hold tightly cross-section during welding. And to minimize work hardening, it is needed to know the proper process to avoid reforming.
초고강도강 차체부품 양산성능향상을 위한 생산 고도화 기술 개발
김근호,윤석주,서혜정,최영배 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.5
최근 전 세계적으로 환경 및 배기가스 규제가 지속적으로 강화됨에 따라 자동차 메이커사에서는 저공해, 고연비, 배출가스 저감과 관련된 기술 개발에 많은 연구가 진행되고 있다. 이에 따라, 차체의 경량화 기술에 관심이 집중되고 있으며, 차체 경량화와 충돌안전성능을 동시에 만족하기 위해서 초고강도강을 이용한 차체 부품 개발 연구가 집중되고 있다. 하지만 초고강도강의 높은 강도와 성형성 및 접합성으로 인하여 부품 양산 시 피어싱, 절단 공정에서의 금형 내구성과 품질 안정성, 양산성이 문제가 되고 있어 이를 향상시킬 수 있는 생산 고도화 기술 개발이 요구되고 있다. 본 발표에서는 초고강도강 차체부품의 생산 고도화 기술 개발 중 성형성 확보를 위한 롤 포밍 공법 기술과 접합 공정에서의 Cycle Time을 감소시켜 양산성을 향상시키는 기술의 개발 현황을 소개하고자 한다. 본 과제의 기술 개발 차체부품은 차체의 측면 충돌 안전 성능 확보를 위한 핵심 부품인 Sill Side이며, 경량화를 위해 초고강도강을 적용하였고, 양산성능을 확보하기 위해 냉간 롤포밍 공법을 적용하였다. 생산 고도화 기술 개발 중 초고강도강에 대한 피어싱, 절단 공정의 금형 내구성 확보를 위해 최적화 설계 및 금형 개발을 진행하였고, 절단부 및 Hole에 대한 품질 안정성을 확보하였다. 또한, 제품의 형상과 안정적인 용접성 확보를 위핸 롤포밍 공정 중 교정단과 Turk’ Head 설비를 개발하여 단품의 품질 안정화를 확보하였으며 접합 공정에서의 용접성 향상과 Cycle Time 감소를 위해 용접시스템을 설계하여 현재 양산 적용을 위한 설비 개발을 진행하고 있다.