• Title/Summary/Keyword: 성형결함

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Dislocation structure in hot-pressed polycrystalline $TiB_{2}$ (고온가압성형된 다결정 $TiB_{2}$내에서 전위구조)

  • Kwang Bo Shim;Brian Ralph;Keun Ho Auh
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.6 no.2
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    • pp.194-202
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    • 1996
  • Transmission electron microscopy has been used to characterize the dislocation structure in hot-pressed titanium diboride. The thin foil samples were prepared by the conventional ion beam thinning technique and reveal the main features associated with the dislocations ; low-angle grain boundaries with dislocation arrays, high-angle grain boundaries with ledges/steps on the boundary planes. The ledges/steps on the grain boundaries were characterized as the origin of defect structures such as dislocation formation or crack propagation near grain boundaries. A fraction of the high angle grain boundaries contained periodic arrays of grain boundary dislocations. The Burger's vectors of the dislocations in the $TiB_{2}$specimens were determined.

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Characterization of Cast-Forging Process in Hypereutectic Al-15wt.%Si alloy

  • Kim, Eok-Soo;Lim, Kyung-Mook;Hong, Young-Myung;Han, Yoon-Sung;Lee, Kwang-Hak
    • Journal of Korea Foundry Society
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    • v.27 no.5
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    • pp.212-216
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    • 2007
  • 과공정 Al-15wt.%Si 합금의 주단조 공정의 적용을 위해 주조 예비성형체를 제작하는 과정에서 P와 Sr을 첨가하여 과공정 Al-Si 합금의 응고과정에서 발생하는 초정 Si과 공정 Si의 미세화 개량처리를 행하였다. 미세화 조직의 변화에 따른 기계적성질 및 단조성을 조사하였으며, 미세화제로 첨가된 0.075wt.% Sr과 0.1wt.% P의 첨가에서 가장 효과적인 미세한 조직을 얻을 수 있었고, 인장강도와 연신율은 이들 첨가원가의 증가에 따라 향상되는 결과를 보였으나 일정 이상의 첨가에서는 더 이상의 향상은 없었다. 단조성 평가를 위한 열간가공 재현실험에서는 $450^{\circ}C$에서 약60N/mm2의 하중이 필요함을 알 수 있었다. 열간단조 및 열처리 후의 인장강도와 연신율은 보다 많은 향상을 가져왔으며, 이는 압축가공에 의한 주조 예비성형체 내부에 잔존하던 주조결함의 제어와 열처리에 의한 조직의 개량 및 균질화 효과에 의한 것으로 판단된다.

A Study on the Flow Control Forming Process and Experiment Device of Drum Clutch for Automatic Transmission (자동변속기용 드럼클러치의 유동제어 성형공정 및 실험장치 개발 연구)

  • Park, Jong-Nam
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.12 no.6
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    • pp.69-76
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    • 2013
  • This paper presents the development of the FCF method for the manufacturing of final products using numbers related to the minimum amount of work. The utilized product is a drum clutch, which is part of the transmission of an automobile. A double acting press is secured first and a prediction of the forming load on the practical material is made through an experiment with a plasticine model. Also, a finite element simulation using product shape and properties is performed, as well as a press experiment. A double acting press is manufactured that is suitable for a double acting experiment with a conventional hydraulic press(200 tons). A peripheral device for the press is additionally designed for experimental purposes. And, the press has as its essential points the drive speed, stroke control, etc., all of which influence the forming and is modified. Especially, a laser system is used for velocity measurement of two punches. The forming load of a practical material is predicted in order to derive a forming load formula for cold conditions on the basis of approximate similarity theory. Finite element analysis of the relative velocity ratio(RVR), etc., for most suitable flow defect(unfilling, etc.) prevention is achieved as well. The results are verified through a press experiment.

A Numerical Analysis for Plastic Deformation of a Ti Alloy and a study for Shear Band Analysis (Ti 합금 형단조에서의 소성 해석 및 전단 밴드 분석)

  • 윤수진;손영일;은일상
    • Journal of the Korean Society of Propulsion Engineers
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    • v.4 no.1
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    • pp.1-12
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    • 2000
  • This study summarizes the numerical analyses of a Ti alloy deformation under a back extrusion process. Amongst metallic parts in a small propulsion motor case, a Ti-6Al-4V alloy is used extensively. However, the Ti alloy shows a great deal of shear band formation which often leads to a fracture due to a narrow working temperature window. Moreover, the shear band tends to develop over an area where a contact occurs between the hot work piece and the die wall, due to localized cooling. Thus, heating the dies is often required to overcome the deformation localization. Therefore, it becomes necessary to investigate the internal temperature and strain rate distribution during forging process of a Ti alloy. Furthermore, a shear band analysis is peformed using a finite difference scheme and a comparison is made between steel and Ti alloy.

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Rheological and Debinding Properties of Al2O3/Paraffin Wax/High Density Polyethylen System Mixture by Injection Molding (사출성형에 의한 Al2O3/Paraffin Wax/High Density Polyethylen계 혼합물의 유동성 및 탈지 특성)

  • 김승겸;신대용;한상목;강위수
    • Journal of the Korean Ceramic Society
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    • v.41 no.5
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    • pp.395-400
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    • 2004
  • The effects of compositions of binders on the rheological properties of mixtures and the preparation conditions on the formation of defects and the debinding characteristics of compacts for the injection molding of ceramic powders (65 wt% aluminaㆍ35 wt% feldspar) were studied. Ceramic powders were coated with 2 wt% of stearic acid and then mixed with 15, 20, and 25 wt% of Paraffin Wax (PW) and High Density Polyethylene (HDPE) as binders at $160^{\circ}C$ for 2 h. Rheological properties were investigated by using capillary rheometer. Apparent viscosities of mixtures were 80∼300 Paㆍs at 1,000$s^{-1}$ of a shear rate, it was good for the injection molding and depending on the compositions of binders. Short shot was formed at 15H5P5 (the ratio of HDPE : PW=5 : 5 in 15 wt% of binders) compacts without injection pressures and any noticeable defects were not formed at 45 kgf/$cm^{2}$ in 20H5P5 compacts. PW and HDPE were removed by the solvent extraction and thermal debinding method. Thermal debinding of HDPE at $450^{\circ}C$ for 5 h, which followed the extraction of PW was using n-heptane solvent at $70^{\circ}C$ for 5 h. Continuous pores in compacts, which facilitate the removal of HDPE by the thermal debinding, were found to form in the compacts when PW was removed by the solvent extraction. The optimum composition of binder at which binder was removed by thermal debinding without defects while maintaining the compact strength was 20H5P5. Bulk density, porosity and 3-point bending strength of 20H5P5 compact sintered at 1,30$0^{\circ}C$ for 5 h were 2.8, < 3%, and 2,400 kgf/$cm^{2}$, respectively, and can be used as a structural materials.

The Effect of Stacking Fault on Thermoelectric Property for n-type SiC Semiconductor (N형 SiC 반도체의 열전 물성에 미치는 적층 결함의 영향)

  • Pai, Chul-Hoon
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.22 no.3
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    • pp.13-19
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    • 2021
  • This study examined the effects of stacking faults on the thermoelectric properties for n-type SiC semiconductors. Porous SiC semiconductors with 30~42 % porosity were fabricated by the heat treatment of pressed ��-SiC powder compacts at 1600~2100 ℃ for 20~120 min in an N2 atmosphere. XRD was performed to examine the stacking faults, lattice strain, and precise lattice parameters of the specimens. The porosity and surface area were analyzed, and SEM, TEM, and HRTEM were carried out to examine the microstructure. The electrical conductivity and the Seebeck coefficient were measured at 550~900 ℃ in an Ar atmosphere. The electrical conductivity increased with increasing heat treatment temperature and time, which might be due to an increase in carrier concentration and improvement in grain-to-grain connectivity. The Seebeck coefficients were negative due to nitrogen behaving as a donor, and their absolute values also increased with increasing heat treatment temperature and time. This might be due to a decrease in stacking fault density, i.e., a decrease in stacking fault density accompanied by grain growth and crystallite growth must have increased the phonon mean free path, enhancing the phonon-drag effect, leading to a larger Seebeck coefficient.

A Study on the Plastic Forming by Rotary Swaging Process (Rotary Swaging 공법을 적용한 탄체 소성가공에 관한 연구)

  • Shon, Byoung-Chul;Lee, Ho-Jin
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.21 no.6
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    • pp.672-678
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    • 2020
  • Ogive parts of large-caliber ammunition in Korea are manufactured by the Press Nosing method, but this method has the disadvantage of requiring additional processes such as lubrication before and after the press process. This study proposes the possibility of applying the Swaging method to improve these shortcomings. A large-diameter shell body was manufactured in sub-scale and plastic working experiments using a swaging process were performed. We investigated whether plastic processing is possible up to 75 % of the diameter reduction rate that satisfies the final molding dimension, and whether the dimensions of the product produced by swaging molding are satisfactory as the hardness changes according to the diameter reduction rate and the increase in thickness. The test using the prototype confirmed that the hardness increased proportionally with the diameter reduction rate and by more than HV 335 at the reduction rate of 75 %. The material thickness variation tended to be similar to the theoretical calculated value, and the thickness increase rate was proportional to 65.4 % at the reduction rate of 75 %.

Analysis of Defect Characterization in a Rectangular Shape Flange Hydroforming Process (사각형상 플랜지 액압성형 공정 시 결함특성 분석)

  • Shin, S.G.R.;Joo, B.D.;Han, S.W.;Lee, C.H.;Moon, Y.H.
    • Transactions of Materials Processing
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    • v.22 no.5
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    • pp.275-279
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    • 2013
  • The tube hydroforming process has received much attention in the automotive industry because of its advantages compared to conventional manufacturing technologies. A wide range of products such as sub-frames, camshafts, radiator frames, axles and crankshafts are made by hydroforming process. The hydroformed parts often need to be structurally joined to other components during assembly. Therefore, these automotive parts need to be manufactured with a localized attachment flange. In this study, FE forming analyses of a part with a rectangular flanged shape was performed with Dynaform 5.5. Using the optimized conditions determined numerically, hydroforming experiments were performed. Then, the characterization of defects was analyzed. Finally, the accuracy of the optimized internal pressure condition as well as that of the initial ram position were evaluated. The results demonstrated that flanged parts can be successfully produced using the tube hydroforming process.

Defect Prediction in Part Fabrication Process of Metal Matrix Composites by Thixoforging Process (Thixoforging을 이용한 중공형 금속복합재료 부품의 성형공정에 있어서 결함예측)

  • 윤성원;김병민;강충길
    • Transactions of Materials Processing
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    • v.12 no.2
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    • pp.102-109
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    • 2003
  • In the manufacturing process of metal matrix composites parts, thixoforging is one of the most effective forming processes. The major purpose of the current study is to provide the proper conditions such as the die shape, the forging velocity, the forging time, the forging pressure and reinforcement injection velocity and pressure on various defects in thixoforged cylinder liner, filling tests were performed by MAGMA S/W. In order to evaluate the effectiveness of the calculated conditions which is given by computer aided engineering, A357, A380 and SiC$_{p}$/A380 cylind~5$mu extrm{m}$r liner were fabricated under the calculated conditions. SiC$_{p}$/A380 composite billets were fabricated by both the mechanical stirring and electrical magnetic stirring process. Incase fo SiC$_{p}$/A380 composite cylinder liner, reinforcement distribution and effect of reinforcement(SiC$_{p}$) content(10~20 vol. %)and size(5.5~14${\mu}{\textrm}{m}$) on the mechanical properties were investigatedstigated.

Analysis of Microstructures and Defects of the Thixoformed Cu rotor for High Efficiency Electrical Motors (반응고 성형법에 의해 제조된 고효율 전동기용 Cu-Rotor의 미세조직 및 결함 분석)

  • 강병무;서동우;손근용;이상용
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2003.10a
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    • pp.55-59
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    • 2003
  • Rotor in small-medium induction motor has been usually manufactured by aluminum diecasting. In order to improve efficiency of induction motors, however, it is desirable that pure aluminum is replaced by high electrical conductivity copper alloy. For this purpose, a rotor is thixoformed with Cu-Ca alloy. Thermomechanical processing(TMP) is carried out to modify the semi-solid microstructure of the alloy and final microstructures and filling defects of thixoformed Cu- rotors are investigated. The characteristics of thixoformed Cu-rotor such as motor efficiency and torque are compared with those of Al rotor.

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