• Title/Summary/Keyword: metal sheets

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New Stress-Strain Model for Identifying Plastic Deformation Behavior of Sheet Materials (판재의 소성변형 거동을 동정하기 위한 새로운 응력-변형률 모델)

  • Kim, Young Suk;Pham, Quoc Tuan;Kim, Chan Il
    • Journal of the Korean Society for Precision Engineering
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    • v.34 no.4
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    • pp.273-279
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    • 2017
  • In sheet metal forming numerical analysis, the strain hardening equation has a significant effect on calculation results, especially in the field of spring-back. This study introduces the Kim-Tuan strain hardening model. This model represents sheet material behavior over the entire strain hardening range. The proposed model is compared to other well known strain hardening models using a series of uniaxial tensile tests. These tests are performed to determine the stress-strain relationship for Al6016-T4, DP980, and CP Ti sheets. In addition, the Kim-Tuan model is used to integrate the CP Ti sheet strain hardening equation in ABAQUS analysis to predict spring-back amount in a bending test. These tests highlight the improved accuracy of the proposed equation in the numerical field. Bending tests to evaluate prediction accuracy are also performed and compared with numerical analysis results.

Investigation of Shape Accuracy in the Forming of a Thin-walled S-rail with Classification of Springback Modes (스프링백 모드분류를 통한 박판 S-rail 성형공정의 형상정밀도 고찰)

  • Jung, D.G.;Kim, S.H.;Kim, M.S.;Lee, T.G.;Kim, H.K.
    • Transactions of Materials Processing
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    • v.22 no.8
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    • pp.477-485
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    • 2013
  • This paper aims to evaluate quantitatively the springback characteristics that evolve in the sheet metal forming of an S-rail in order to understand the reasons of shape inaccuracy and to find a remedy. The geometrical springback is classified into six modes: angle change of punch and die shoulders, wall curl, ridge curl, section twist, and axial twist. The measuring method for each springback mode is suggested and quantitative measurements were made to determine the tendency towards shape accuracy. Forming experiments were conducted with four types of steel sheets that have different tensile strengths, which were 340MPa, 440MPa, 590MPa and 780MPa, in order to evaluate the effect of the tensile strength and the bead shape on the springback behavior. Springback tendencies show that they are greatly affected by the tensile strength of the sheet and the shape of the tools. Almost all springback modes except the section twist and the axial twist show a linearly increasing trend as the tensile strength of the sheet increases. The results can be used as basic data for design and for compensation of the press die geometry when forming high strength steels which exhibit large amounts of springback.

Analysis of the Numerical Simulation Accuracy in the CFRP-Al Alloy SPR Joint Process According to the CFRP Modeling Method (CFRP 모델링 기법에 따른 CFRP-Al합금 SPR 접합공정의 수치해석 정확도 분석)

  • Kim, S.H.;Park, N.;Song, J.H.;Noh, W.;Park, K.Y.;Bae, G.
    • Transactions of Materials Processing
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    • v.29 no.5
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    • pp.265-271
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    • 2020
  • The purpose of this paper is to analyze the numerical simulation accuracy according to the CFRP modeling method in the CFRP-Al alloy SPR (Self-Piercing Rivet) joint process. The mechanical properties of the CFRP, aluminum sheet are precisely obtained from the tensile test according to the loading direction. Additionally, the hardening curve of rivet was calculated from the inverse analysis of the machined rivet-ring compression test. For the CFRP-Al alloy SPR simulation, two kinds of the CFRP modeling methods were established based on the continuum and layer-by-layer approaches. The simulation results showed that the CFRP layer-by-layer modeling method can provide more reliable prediction shape of the fractured sheets and deformed rivet. This simulation technique can be used in evaluating the CFRP-Metal SPR performance and designing the SPR process conditions.

A CAE Approach for Net-Shape Automobile Stamping Components of Aluminum Alloy (자동차용 알루미늄 합금 정형의 스탬핑 부품 성형을 위한 CAE 기법 개발)

  • Choi, Han-Ho;Ku, Tae-Wan;Hwang, Sang-Moon;Kang, Beom-Soo
    • Journal of the Korean Society for Precision Engineering
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    • v.16 no.10
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    • pp.164-171
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    • 1999
  • An optimum blank design technology is required for near-net of net-shape cold forming using sheets. Originally, the backward tracing scheme has been developed for preform design in bulk forming, and applied to several forming processes successfully. Its key concept is to trace backward from the final desirable configuration to an intermediate preform of initial blocker. A program for initial blank design in sheet forming which contains the capabilities of forward loading simulation by the finite element method and backward tracing simulation, has been developed and proved the effectiveness by applying to a square cup stamping process. In the blank design of square cup stamping, the backward tracing program can produce an optimum blank configuration which forms a sound net-shape cup product without machining after forming. Another general application appears in the blank design of a cup stamping with protruding flanges, one of typical automobile components. The blank configurations derived by backward tracing simulation have been confirmed by a series of loading simulations. The approach or decision of an initial blank configuration presented in this study will be a milestone in fields of sheet forming process design.

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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.

Experimental Study on the Formability of Simultaneous Deep Drawing of Circular and Rectangular Cups with AZ31 Magnesium Alloy (AZ31 마그네슘 판재의 더블 싱크형 딥드로잉 공정의 성형성에 관한 실험적 연구)

  • Kwon, K.T.;Kang, S.B.;Kang, C.G.
    • Transactions of Materials Processing
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    • v.17 no.8
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    • pp.586-593
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    • 2008
  • In warm press forming of magnesium alloy sheet, it is important to control the sheet temperature by heating the sheet in closed die. When forming a commercial AZ31 magnesium alloy sheets which are 0.5mm and 1.0mm thick, respectively, time arriving at target temperature and temperature variation in magnesium alloy sheet have been investigated. The deep drawing process with rectangular shape alone at the first stage and with both circular and rectangular shapes at the second stage was employed. At the first stage, through deep drawing process with rectangular shape alone according to various forming temperature($150{\sim}350^{\circ}C$) and velocity($0.1{\sim}1.0mm/s$), optimum forming condition was obtained. At the second stage, deep drawing process with the circular and rectangular shapes were performed following deep drawn square cups with Limited Drawing Height(LDH) obtained at the first stage. Here, clearance which is defined a gap between the die and the punch including sheet was set to ratio of 20, 40 and 100% to thickness in sheet. Accordingly, temperature, velocities, and clearances suitable for forming were suggested through investigating the thickness variation of the product.

A study on the characteristics of vertical welding positions using GA steel sheet in the $CO_2$ welding (GA 강판에 대한 $CO_2$ 수직용접자세의 특성에 관한 연구)

  • Kim, Jae-Seong;Jo, Yong-Jun;Lee, Gyeong-Cheol;Lee, Bo-Yeong
    • Proceedings of the KWS Conference
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    • 2007.11a
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    • pp.36-38
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    • 2007
  • The instability of the arc in the $CO_2$ arc welding affects the quality of the weld in the automotive industry. This paper evaluates the effects of the arc stability in $CO_2$ arc welding with respect to vertical welding positions. In this experiment, galva-annealed steel sheets(CA) were used as specimens, and these materials were welded by adopting new Cold Metal Transfer (CMT) process. For each sample, fillet joint welding trials were carried out using the same conditions. Each part of welding joints was welded with vertical-up, vertical-down position at $45^{\circ},\;90^{\circ}\;and\;135^{\circ}$ degrees. A high speed camera and a welding signal monitoring system were used for monitoring fluid-flow phenomena in weld pools and frequency measurements, respectively. Through this study, the welding position were found to be key factors mainly to influence the arc stability in $CO_2$ welding moreover and that the arc stability in the vertical-up welding position was observed to be more stable than the vertical-down welding position below $90^{\circ}$.

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Effect of Heat Treatment on Joint Strength of 300Grade 18% Ni Maraging Steel Sheet Welded with Electron Beam (전자비임 용접된 300Grade 18% Ni 마르에이징강 박판의 이음강도에 미치는 열처리의 방향)

  • Jung, B.H.;Kim, H.G.;Kang, S.B.;Kim, W.Y.;Park, H.I.
    • Journal of the Korean Society for Heat Treatment
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    • v.6 no.4
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    • pp.185-193
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    • 1993
  • The effect and Condition of heat treatment on the tensile strength of welded joint was investigated in 300 grade 18% Ni-Co-Mo-Ti maraging steel sheets welded with electron beam. A good tensile strength of welded joint was obtained by following heat treatment cycle ; At $1100^{\circ}C$ the specimen was high temperature solution treated for 1 hour and then it was repeated solution treated at $900^{\circ}C$, $820^{\circ}C$ for 1 hour respectively to recrystallize the coarsened ${\gamma}$ grain. These heat treatment cycle was completed by an final aging heat treatment at $480^{\circ}C$ for 4 hour. Moreover, dissolution of dendrite, a significant decrease in seregation of Mo, Ti in weld metal were observed and also the coarsened ${\gamma}$ grain formed at $1100^{\circ}C$, $1200^{\circ}C$ changed to fine grain due to the effect of recrystallization.

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Fabrication and Properties of MFSFET′s Using $BaMgF_4$/Si Structures for Non-volatile Memory ($BaMgF_4$/Si 구조를 이용한 비휘발성 메모리용 MFSFET의 제작 및 특성)

  • 이상우;김광호
    • Electrical & Electronic Materials
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    • v.10 no.10
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    • pp.1029-1033
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    • 1997
  • A prototype MFSFET using ferroelectric fluoride BaMgF$_4$as a gate insulator has been successfully fabricated with the help of 2 sheets of metal mask. The fluoride film was deposited in an ultrai-high vacuum system at a substrate temperature of below 30$0^{\circ}C$ and an in-situ post-deposition annealing was conducted for 20 seconds at $650^{\circ}C$ in the same chamber. The interface state density of the BaMgF$_4$/Si(100) interface calculated by a MFS capacitor fabricated on the same wafer was about 8$\times$10$^{10}$ /cm$^2$.eV. The I$_{D}$-V$_{G}$ characteristics of the MFSFET show a hysteresis loop due to the ferroelectric nature of the BaMgF$_4$film. It is also demonstrated that the I$_{D}$ can be controlled by the “write” plus which was applied before the measurements even at the same “read”gate voltage.ltage.

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The Effect of Welding Condition on Tensile Properties of Friction Stir Welds of KS5J32 Al Alloy (KS5J32 Al합금 마찰교반접합부의 인장성질에 미치는 접합조건의 영향)

  • Yoon, Tae-Jin;Kim, Sang-Ju;Kim, Nam-Kyu;Song, Sang-Woo;Kang, Chung-Yun
    • Journal of Welding and Joining
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    • v.29 no.5
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    • pp.82-89
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    • 2011
  • The effect of welding condition on tensile properties of KS5J32 Al Alloy was investigated under various welding conditions. The 1.6 mm thick KS5J32 alloy sheets were joined by friction stir welding (FSW) technique with butt joint. The tool rotation speeds were 1000, 1250 and 1500 rpm, and the welding speeds were varied within the range from 100 to 600 mm/min. Voids mainly occurred at the advancing side of the tool probe, when the tool rotation speed was low, due to insufficient materials flow. When the weld pitch exceeded 0.4 mm/rev, voids were observed under all welding conditions and the area of voids increased with increasing weld pitch. For void-free specimens, fracture always occurred at base materials. However voids affected the location of fractures, base metal or welded zone, when the voids existed within the welds.