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손현성(Hyunsung Son),김홍기(Honggee Kim),최병근(Byungkeun Choi) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11
Hot-Press-Forming (HPF), an advanced sheet forming method in which a high strength part can be produced by forming at high temperature and rapid cooling in dies, is one of the most successful forming process in producing components with complex geometric shape, high strength and a minimum of springback. The thermo-mechanical coupled analysis for a hot-press-formed lower arm is performed by using the commercial program, LS-Dyna. To optimize conditions of forming quality in HPF process and secure a safe product without any failures, such as fractures and wrinkling, the simulations are coupled with Taguchi’s orthogonal array experiment. Three design and process variables―the friction coefficient, blank shape, and hole location for burring―are selected to be optimized. The most effective condition of forming quality for a hot-press-formed lower arm is suggested. The simulation results are confirmed with experimental ones.
최병근(Byungkeun Choi),손현성(Hyunsung Son),김홍기(Honggee Kim) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11
Hot Press Forming (HPF) process with which automotive product is formed at elevated temperature and cooled down in the tool to get the ultra-high strength has been applied to improve weight reduction and crash performance. AlSi coated material for HPF process is widely used to prevent oxidation of substrate during heating in the furnace and transport to the press in the air. This study observed surface color of the AlSi coated sheet with heating condition and analyzed the characteristics of AlSi coated layer. As heating time gets longer, surface color after cooling was changed from gray to blue. The coated layer has a thickness over 35㎛ after heating and reaction between coated material and substrate results in a specific alloy composition along with coated layer. Finally, pick-up of AlSi coated layer on the tool was observed and elimination of pick-up is one of the factors that stop the process and increase maintenance costs for the serial process.
송정한(Junghan Song),허훈(Hoon Huh),김홍기(Honggee Kim),박성호(Sungho Park) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Simulation of vehicle crashes using the finite element method has made major advances in the last several years. Every major automotive company now uses CAE to perform virtual crash tests. Designers can mow quickly adjust the structural performance before performing a physical crash test. Compared to physical crash tests, the virtual simulation is less costly and faster which allows manufactures to reduce costs and vehicle development time. In order to produce more efficient and precise simulations, it is needed to adopt the dynamic property of materials and the failure modeling of resistance spot weld. The resistance spot weld in most current finite element crash models are characterized as a rigid beam at the location of the weld. The role of this rigid beam is simply to transfer the load across the welded component. The spot weld elements is design to be failed by some failure criteria which is function of axial and shear load at the rigid beam. For this reason, the calculation of the load at the rigid beam is important to predict the failure of the spot weld. In this paper, the numerical simulations are carried out to evaluate the calculation of the load at the rigid beam. The first study conducted is to examine the effect of mesh size on the load at the rigid beam. The effect of element shape on the welded components is, then, investigated. Finally, the location and the number of welded constrains is changed for the correct prediction of the load on the spot weld element. The analysis results demonstrate that the correct prediction of the load on the spot weld element is achieved by the change of the element shape on the welded component s and the location of welded constrains.
안강환(Kanghwan Ahn),유동훈(Donghoon Yoo),석동윤(Dong-Yoon Seok),김홍기(HongGee Kim),박성호(SungHo Park),정관수(Kwansoo Chung) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5
In order to overcome drawbacks of the advanced high strength steel such as inferior formability and large springback, the hot press forming process(HPF) has been being applied for forming of automotive sheet parts. Good formability and dimensional accuracy without springback as well as good crash performance of final products are the advantages of the HPF process. In this work, a method to characterize the mechanical properties of the HPF steel was developed based on the simple tension test at high temperatures and its finite element analysis, while it was applied to obtain strain rate and temperature dependent flow curves of the HPF steel. The final flow curves were represented by utilizing the Johnson-Cook type equation both in uniform and post-uniform deformation regions.