• Title/Summary/Keyword: 초고강도 강판

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The Effects of Process Parameters of Multi-Stage Forming on Springback for a U-Channel made of Ultra-High-Strength Steel (초고강도 소재가 적용된 U 형 채널 제품의 다단공정변수에 따른 스프링백 영향)

  • Suh, Chang-Hee;Jung, Yun-Chul;Lim, Yong-Hee;Yun, Hyo-Yun;Lee, Kyung-Hoon;Kim, Young-Suk
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.36 no.3
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    • pp.283-288
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    • 2012
  • Ultra-high-strength steels (UHSSs) are widely used for lightweight automobile parts, and the control of springback is very important in sheet-metal forming. The object of this study is to verify the effects of multi-stage forming process parameters for U-channel-type automobile parts made of UHSS. Finite element analysis is carried out to predict the formability and springback. The main parameters considered for the multi-stage forming process are the die angle, die radius, and punch-forming direction. It is shown that multi-stage forming is very effective for reducing springback, and that a small punch-forming angle and die radius reduce springback, whereas the die angle does not have a large effect.

The Study on Weldability of Boron Steel and Hot-Stamped Steel by Using Laser Heat Source (II) - Laser Weldability of Hot Stamping Steel with Ultra-High Strength - (레이저 열원을 이용한 보론강 및 핫스탬핑강의 용접특성에 관한 연구 (II) - 초고강도 핫스탬핑강의 레이저 용접특성 -)

  • Kim, Jong Do;Choi, So Young;Park, In Duck
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.38 no.12
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    • pp.1373-1377
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    • 2014
  • Hot-stamping is a method of obtaining ultrahigh-strength steel by simultaneously forming and cooling boron steel in a press die after it has been heated at $900^{\circ}C$ or above. After heat treatment, boron steel has a strength of 1500 MPa or more. This material ensures a high level of quality because it overcomes the spring-back phenomenon, which is a problem associated with high-strength steel materials, and the degree of dimensional precision is improved by 90 or more because of the good formability compared with existing types of steel. In this study, the welding characteristics were identified through the butt and lap welding of hot-stamped steel using a disk laser. Full penetration was obtained at a faster speed with butt welding compared to lap welding, and a white band was observed in every specimen.

Experimental Study for Structural Behavior of Embed Plate into Concrete Subjected to Welding Heat Input (매입강판 용접열에 의한 고강도 콘크리트 접합부 구조성능 영향평가에 관한 실험적 연구)

  • Chung, Kyung Soo;Kim, Ki Myon;Kim, Do Hwan;Kim, Jin Ho
    • Journal of Korean Society of Steel Construction
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    • v.25 no.5
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    • pp.569-578
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    • 2013
  • In a super-tall building construction, thick and large-sized embed plates are usually used to connect mega structural steel members to RC core wall or columns by welding a gusset plate on the face of the embed plate with T-shape. A large amount of heat input accumulated by weld passes causes the plates to expand or deform. In addition, the temperature of concrete around the plates also could be increased. Consequently, cracks and spalls occur on the concrete surface. In this study, the effect of weld heat on embed plates and 80MPa high strength concrete is investigated by considering weld position (2G and 3G position), edge distance, concrete curing time, etc. Measured temperature of the embed plates was compared with the transient thermal analysis results. Finally, push-out tests were performed to verify and compare the shear studs capacity of the embed plate with design requirement. Test result shows that the shear capacity of the plate is reduced by 14%-19% due to the weld heat effect and increased as the concrete curing time is longer.

Development of Austomtive Cold-roiled High Strength Steel Sheets (자동차용 고강도 냉연강판 개발)

  • 김성주;진광근
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2004.05a
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    • pp.349-356
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    • 2004
  • 자동차의 외관품질과 관련된 외판재용 고강도강으로는 내 dent성을 향상을 위해서 IF-HSS강과 BH강의 사용량이 크게 증가하였으며, 최근에는 490MPa급 DP강이 적용되기 시작하고 있다. 그리고 내판 판넬의 경우에는 고가공성 을 갖는 고강도강의 개발으로 고강도강의 사용량이 늘어나고 있다. 내판재 중 승객의 안전과 관련된 멤버, 필라와 같은 구조부재는 중간 정도의 강도를 갖는 고강도강을 주로 적용되어 왔으나, 최근 차체경량화 요구의 증가로 590MPa급 이상 고강도강이 적용되기 시작하였으며, 특히 고속변형에서 에너지 흡수능이 우수한 TRIP (Trans-formation Induced Plasticity)강 및 DP(Dual Phase)강에 대한 관심이 크게 증대되고 있다. 저속충돌에서 차체를 보호하는 범퍼보강재는 고강도화가 빠르게 진행되어, 현재는 석출경화강에 변태 조직 강화를 더한 780MPa급 이상의 초고강도강을 주로 사용하고 있으며, 1370MPa급 까지 적용하고 있다.

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Design of Drawbeads for Advanced High Strength Steel Sheet Forming (초고강도 강판 성형용 드로비드 설계)

  • Kim, B.G.;Jeong, J.Y.;Kim, D.J.;Kim, G.S.;Keum, Y.T.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2009.10a
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    • pp.420-423
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    • 2009
  • In this study, the guideline for designing the drawbeads used in the stamping dies for advanced high strength steel (AHSS) sheets is investigated. In the drawbead drawing test, the drawbead forces for verifying the equivalent drawbead model(EDM) and the sheet strains for finding marginal strains from $FLC_0$ are measured. In the finite element analysis (FEA), the bending allowance, R/t, is obtained. Based on the forming and bending allowances obtained, the design guideline of the drawbead for determining height and width, which depends on the restraining force and the forming allowance, is prepared by using EDM.

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Surface Quality Improvements on the Spherical Shaped Mold using Ball End Milling (볼 엔드밀을 이용한 금형 구면 가공의 표면품질 향상에 관한 연구)

  • Yun, Il-Woo;Hwang, Jong-Dae
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.19 no.3
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    • pp.71-76
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    • 2020
  • Various machining methods are being studied to improve the processing quality of the spherical R shape in press die. In this paper, we confirmed that changes in machining quality were associated with changes in cutting direction, path, and cutting angle, which are commonly used in the machining of molds. We obtained a surface roughness graph with each condition change in one specimen using an instrument that measured geometry and surface roughness simultaneously. The results of the study showed that the best surface roughness in the finish cut of the spherical surface was obtained using upward pick feed machining.

Study on the Springback Reduction of Automotive Advanced High Strength Steel Panel (자동차 초고강도 강판 패널의 스프링백 저감에 관한 연구)

  • Kim, B.G.;Lee, I.S.;Keum, Y.T.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2009.05a
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    • pp.191-194
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    • 2009
  • Very big springback in advanced high strength steel(AHSS) sheets invokes undesired shape defects, which can be eliminated by the tool surface correction method or the forming process control method. Since the springback reduction by controlling the forming process is limited, in this study, the die correction method which finds die correction from the relationship between die design variable and springback is introduced to achieve springback reduction and is applied to the automotive side rail to reduce the springback of 75.8% within the assembly limit of 1 mm.

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Study on the Springback Reduction of Automotive Advanced High Strength Steel Panel (자동차 초고강도 강판 패널의 스프링백 저감에 관한 연구)

  • Kim, B.G.;Lee, I.S.;Keum, Y.T.
    • Transactions of Materials Processing
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    • v.18 no.6
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    • pp.488-493
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    • 2009
  • The very big springback of advanced high strength steel(AHSS) sheets invokes undesired shape defects, which can be generally eliminated by die correction or process parameter control. The springback reduction by controlling the forming process parameters is easy for the application, but limited for the bulky achievement. In this study, the effective die correction method, which obtains the modification of tool shape from the relationship between die design variable and springback, is introduced and is applied to the TWB tool of automotive side rail to show the validity and usefulness. Among the die correction trials repeatedly performed, the first trial is carried out by correcting the tool shape to the opposite direction to the springbacks of several tool sections. Next trials are done by extrapolating the springbacks of among the original tool uncorrected and the tools corrected negative amounts of the springback and by finding tool shapes without springbacks. After the angle of side wall and radius of curvature of horizontal bottom floor are chosen as design variables in the tool design of side rail, the tool shape is corrected 3 times. The accuracy of final shape within the assembly limit of 1mm and the springback reduction of 75.8% compared to the uncorrected tool are achieved.

Cyclic Behavior of Wall-Slab Joints with Lap Splices of Coldly Straightened Re-bars and with Mechanical Splices (굽힌 후 편 철근의 겹침 이음 및 기계적 이음을 갖는 벽-슬래브 접합부의 반복하중에 대한 거동)

  • Chun, Sung-Chul;Lee, Jin-Gon;Ha, Tae-Hun
    • Journal of the Korea Concrete Institute
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    • v.24 no.3
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    • pp.275-283
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    • 2012
  • Steel Plate for Rebar Connection was recently developed to splice rebars in delayed slab-wall joints in high-rise building, slurry wall-slab joints, temporary openings, etc. It consists of several couplers and a thin steel plate with shear key. Cyclic loading tests on slab-wall joints were conducted to verify structural behavior of the joints having Steel Plate for Rebar Connection. For comparison, joints with Rebend Connection and without splices were also tested. The joints with Steel Plate for Rebar Connection showed typical flexural behavior in the sequence of tension re-bar yielding, sufficient flexural deformation, crushing of compression concrete, and compression rebar buckling. However, the joints with Rebend Connection had more bond cracks in slabs faces and spalling in side cover-concrete, even though elastic behavior of the joints was similar to that of the joints with Steel Plate for Re-bar Connection. Consequently, the joints with Rebend Connection had less strengths and deformation capacities than the joints with Steel Plate for Re-bar Connection. In addition, stiffness of the joints with Rebend Connection degraded more rapidly than the other joints as cyclic loads were applied. This may be caused by low elastic modulus of re-straightened rebars and restraightening of kinked bar. For two types of diameters (13mm and 16mm) and two types of grades (SD300 and SD400) of rebars, the joints with Steel Plate for Rebar Connection had higher strength than nominal strength calculated from actual material properties. On the contrary, strengths of the joints with Rebend Connection decreased as bar diameter increased and as grade becames higher. Therefore, Rebend Connection should be used with caution in design and construction.

Study on the Friction Characteristics of Advanced High Strength Steel Sheet (초고강도강판의 마찰특성에 관한 연구)

  • Kim, N.J.;Kim, S.H.;Jung, K.R.;Park, S.B.;Keum, Y.T.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2009.10a
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    • pp.250-253
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    • 2009
  • In this study, the friction test was performed to find friction characteristics of advanced high strength steel (AHSS) sheets and the multiple regression method was employed to obtain friction models. The friction coefficients associated with the lubricant viscosity, drawing speed, and blank holding pressure are measured. Differently from GA steel sheets, the effects of the lubricant viscosity and pulling speed are a little, which are explained by a theory of adhesion and wear as well as a deformation of friction surface. In addition, the effects of friction parameters are numerically represented by friction regression models.

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