• Title/Summary/Keyword: SIMA Process

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The Influence of Effective Strain on the Globular Microstructure by SIMA Process for Semi-Solid Forging (반용융 단조를 위한 SIMA 공정에서 유효 변형률이 구상화 조직에 미치는 영향)

  • Park, H.J.;Lee, B.M.;Park, J.C.
    • Journal of the Korean Society for Precision Engineering
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    • v.14 no.9
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    • pp.45-51
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    • 1997
  • For semi-solid forging, it is necessarily required to prepare a workpiece with globular microstructure. Among several processes to obtain golbular microstructure, SIMA process is very simple and advantageous with respect to equipment. This paper presents the influence of effective strain on the globularization with aluminium 2024 alloy in cold working stage by SIMA process. Upsetting and forward extrusion are tested for cold working and induction heating is also carried out for reheating to obtain golbular microstructure. Microstructure is observed with an optical microscope. And finite element simulations to obtain effective strain in cold working stage are performed by using commercial finite element code, DEFORM.

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Life cycle analysis of concrete and asphalt used in road pavements

  • lvel, Jocelyn;Watson, Rachel;Abbassi, Bassim;Abu-Hamatteh, Ziad Salem
    • Environmental Engineering Research
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    • v.25 no.1
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    • pp.52-61
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    • 2020
  • The article examines the impact differences between producing concrete and asphalt. Both materials are widely used in the construction industry. Construction activities account for a large portion of greenhouse gases. Therefore, it is important to consider the Life Cycle Analysis (LCA) to reduce environmental impacts. In this study, the material processes were inputted into an LCA program called SimaPro. The database used for the study was Ecoinvent as it is one of the major databases within SimaPro. The materials were compared against impacts per kg of material produced as the functional unit. Each process was created using the materials, energy and transportation required to produce the materials. Waste streams were also included in the process to determine the impacts after the product was done with its useful life. Using the ReCiPe method, an LCA was conducted. Midpoint and endpoint categories were examined for both the productions. The processes had similar results for the human health and ecosystems categories; however asphalt was marginally higher for both. Asphalt had exceeded concrete in the resource impact category by 100 mPt. The results indicate that concrete is the more sustainable building material. Determination of various impacts of the materials is important for material selection.

A fundamental study on semi-solid forging with light and hardly formable materials (난가공성 경량소재의 반용융 단조에 관한 기초 연구)

  • Choi, J.C.;Cho, H.Y.;Min, G.S.;Park, H.J.;Choi, J.U.
    • Journal of the Korean Society for Precision Engineering
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    • v.13 no.7
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    • pp.29-35
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    • 1996
  • For semi-solid forging with aluminuim alloys, it is required to develope the globular grain structure. It was studide that cold upsetting ration in SIMA process has effect on the globularization of grain structure. Globular microstructure was generated without cold upsettings for commercial aluminium alloys. In the case of A12024, the range of grain size was 40 .approx. 50 .mu. m. The grain growth in growth in globular microstructure depend on heating time. Spur gear was forged in semi-solid state to investigate the forging condition for A12024 with hydraulic press.

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Comparison of Conventional Hot Forging and Thixoforging of Al 7075 Alloy According to Microstructures, Formability and Hardness (Al 7075합금의 열간단조와 반응고 단조에 있어서 조직, 성형성 및 경도 특성 비교)

  • Lee, Sang-Yong;Jeon, Jae-Il;Lee, Jeong-Hwan;Lee, Yeong-Seon;Sin, Pyeong-U
    • Transactions of Materials Processing
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    • v.7 no.6
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    • pp.620-630
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    • 1998
  • Conventional hot forging and thixoforging of Al 7075 alloy have been compared with respect to microstructures, formability and hardness. Two distinctive temperature-strain rate ranges for hot forging of Al 7075 alloy were observed from the results of simple compression tests with strain rates of 10-3∼101 sec-1 in the temperatures between $250^{\circ}C$ and $500^{\circ}C.$ In the dynamic recovery range (low temperature-high strain rate range) multi-stage forging was necessary to form a complex shape part due to the lack of formability. In the high temperature-low strain rate range, in which dynamic recrystallization takes place a complex shaped park could be formed by single-stage forging. About 50% cold working in the SIMA process was necessary to get a fine and homogeneous microstructures. Microstructural study suggest that thixoforged Al 7075 part has fine grains and homogeneous microstructures. Its hardness number is almost same to that of conventional hot forged part after aging treatment.

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Process Control and Thixoforming of Cu Rotor for High Efficiency Motors (고효율 전동기용 Cu Rotor의 반응고 성형과 공정변수 제어)

  • Jung, W. S.;Lee, S. Y.;Shin, P. W.
    • Transactions of Materials Processing
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    • v.14 no.7 s.79
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    • pp.642-648
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    • 2005
  • Rotor in small-medium induction motor has been usually manufactured by aluminum diecasting. In order to improve the efficiency of induction motors, newly developed Cu-Ca alloys have been investigated. The electrical conductivity in the Cu alloys containing Ca less than $1.0wt\%$ was higher than $80\%$ IACS. Cu-Ca alloy is desirable for the thixoforming process because it has wide semi-solid range over $150^{\circ}C$. In this study, Cu-rotor with thixoforming process was developed to replace the conventional aluminum diecasting rotor. Analysis was performed for the microstructure of thixoforming rotor. Effect of incomplete filling on the efficiency of induction motor was discussed.

Process Control and Thixoforming Cu Rotor for High Efficiency Motors (고효율 전동기용 Cu Rotor의 반응고 성형과 공정변수 제어)

  • Jung W. S.;Lee S. Y.;Shin P. W.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2005.05a
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    • pp.233-236
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    • 2005
  • Rotor in small-medium induction motor has been usually manufactured by aluminum diecasting. In order to improve efficiency of induction motors, newly developed Cu-Ca alloys have been investigated. The electrical conductivity in the Cu alloys containing Ca less than $1.0wt\%$ was higher than $80\%$ IACS. Cu-Ca alloy is desirable for the thixoforming process because it has wide semi-solid range over $150^{\circ}C$. In this study, Cu-rotor with thixoforming process was developed to replace the conventional aluminum diecasting rotor. Analysis microstructure of thixoforming rotor. effect of incomplete filling defect on the efficiency of induction motor was discussed.

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Sphering of Primary Dendrites in Al-Si alloys by Mushy Zone Heat Treatments (고액 공존영역 온도 열처리에 의한 Al-Si합금의 초정 구형화)

  • Ahn, Jung-Ho;Song, In-Hyuk;Hahn, Yoo-Dong
    • Journal of Korea Foundry Society
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    • v.16 no.6
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    • pp.513-522
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    • 1996
  • In the present work, we have investigated the strain-induced melt activation (SIMA) process in Al-8%Si and Al-25%Si alloys. Primary dendrites were transformed into spherical microstrctures by mushy zone heat treatments of the cold-worked alloys. Various processing parameters which govern the sphering of the dendrites have been examined. The result showed that semi-solid alloys having a typically nondendritic spherical microstructure can be easily produced by this method.

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Measurements of Micro-Defects in the Aluminum Thixoformed Part using Computed Tomography(CT) Technology (CT를 이용한 알루미늄 반응고 성형품의 미세 결함 측정)

  • Lee, S.Y.;Kim, C.H.
    • Transactions of Materials Processing
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    • v.18 no.5
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    • pp.422-427
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    • 2009
  • Computed tomography(CT) has been applied to measure micro-defects in the aluminum knuckle parts manufactured by the thixoforming process. 6061 aluminum alloys were used to form knuckle samples in the semi-solid temperature after the SIMA processing of billets. Tensile specimens were cut from the different locations in a thixoformed knuckle. The size and the distribution of forming defects in tensile specimens were analyzed using CT scanning and image analysis technology before tensile tests. It has been qualitatively shown that the stress-strain curves were significantly affected by the size and the distribution of forming defects although the defect sizes lie in the range of micro-meters.

Analysis of Flat-Band-Voltage Dependent Breakdown Voltage for 10 nm Double Gate MOSFET

  • Jung, Hakkee;Dimitrijev, Sima
    • Journal of information and communication convergence engineering
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    • v.16 no.1
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    • pp.43-47
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    • 2018
  • The existing modeling of avalanche dominated breakdown in double gate MOSFETs (DGMOSFETs) is not relevant for 10 nm gate lengths, because the avalanche mechanism does not occur when the channel length approaches the carrier scattering length. This paper focuses on the punch through mechanism to analyze the breakdown characteristics in 10 nm DGMOSFETs. The analysis is based on an analytical model for the thermionic-emission and tunneling currents, which is based on two-dimensional distributions of the electric potential, obtained from the Poisson equation, and the Wentzel-Kramers-Brillouin (WKB) approximation for the tunneling probability. The analysis shows that corresponding flat-band-voltage for fixed threshold voltage has a significant impact on the breakdown voltage. To investigate ambiguousness of number of dopants in channel, we compared breakdown voltages of high doping and undoped DGMOSFET and show undoped DGMOSFET is more realistic due to simple flat-band-voltage shift. Given that the flat-band-voltage is a process dependent parameter, the new model can be used to quantify the impact of process-parameter fluctuations on the breakdown voltage.