• 소성∙가공
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• 제17권8호
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• pp.649-656
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• 2008

Springback is one of factors affecting precision in metal forming. Its effect is particularly prominent in bending process. In this study, bending and forging process are used in order to manufacture a micro spring with two bending region from $60{\mu}m$ diameter wire. Springback in the process lowers the precision of the micro spring. Overbending for springback compensation has wide usage in a general way. However, this method requires repeated modifications of press dies until the tolerance is allowable, which causes that production cost and time increase. In this paper, we analyzed the mechanism of springback in the forming process of the micro spring using finite element method. In addition, a simple method to control springback without modifying dies was proposed by performing numerical analysis with various parameters.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.365-367
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• 2009

The use of aluminum alloy has been interested in the automotive industry, because of its specific strength. And hollow extruded billet is more attractive than solid extruded billet but its forming application has to be precisely processed to satisfy the product quality. In this research, the process design of forming of control arm for the vehicle was studied by press bending process with hollow extruded billet. The middle protrusion portions and the middle cylindrical cup were processed separately according to the analysis. It was concluded that a useful sequence is to bend the side flange and the middle protrusion portions firstly, and then to form the middle cylindrical cup.

• 한국정밀공학회지
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• 제24권6호
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• pp.58-65
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• 2007

The arbitrarily-bended pipe is widely used in a heat exchanger system. Thus, the pipe bending process has important role in performance and productivity of heat exchanger system. The purpose of this study is to investigate the bending process for manufacturing of sound pipe. And, the spring-back effect and the variation of pipe thickness should be controlled effectively. The change of spring-back ratio and the thickness variation of pipe according to the change of bending radius, bending angle and pipe thickness are analyzed by FEM analysis. The analytic results are compared with the experimental data, accordingly the results show good agreement. The method of the analysis can be applied for manufacturing of precision bended pipe.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 춘계학술대회 논문집
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• pp.560-563
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• 2008

A condensed model is proposed for the simulation of forming of sandwich sheet with pyramid core. A corresponding finite element analysis for L-type bending is carried out to prove the accuracy and the effectiveness. Simulation results are compared with those of experiment. Deformation shape and post-buckling behavior by simulation are in good agreement with those of experiment for the considerable range of deformation. From the comparison of force-displacement curve, it is shown that the proposed model shows good prediction of the forming force compared to the experiment. Thus, the effectiveness of the proposed method is sufficiently demonstrated.

• 한국정밀공학회지
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• 제14권5호
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• pp.76-84
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• 1997

A process sequence in precision press forming of electrnic components is investigated by the finite element method. Aperture, a key component of electronic gun, is formed through a sequence of about 15 operation, among which the beading & bending, the first piercing, the first coining, and the second coining operations are expected to be most critical in view of industrial experts opinions. Thus, the analysis per- formed by a commercial code MARC focuses on the three operations, and comparisons are made between the results of the analysis and the measurements of experimental forming of the component.

• 소성∙가공
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• 제33권1호
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• pp.43-49
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• 2024

A high strength steel sheet (HSSS) has widely used to improve the specific rigidity of parts and the safety of the passenger in automotive industries. However, the HSSS is difficult to manufacture precise parts through a forming process due to the reduced elongation and the increased elastic recovery. The goal of the paper is to investigate the improved design of bending dies for DP590 HSSS. The over forming type bending dies with cam systems added to the side of the formed part is proposed to improve the quality of the part. The effects of the die design and the forming parameter on formability and elastic recovery characteristics is examined using finite element analyses (FEAs). From the results of FEAs, proper die design and forming parameters are predicted.

• 대한기계학회논문집A
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• 제22권1호
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• pp.238-246
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• 1998

Surface residual stresses as well as wall thickness and ovality changes after U-bending process on UNS N06690 row-1 heat exchanger tubes, were estimated. Surface residual stresses were measured by Hole Drilling Method(HDM), calculating the stresses from relieved strains of 3 rosette strain gages. After bending of the tubes, dimensional tolerances for wall thickness and ovality were satisfied with ASTM requirements. Residual stresses at the extrados were introduced with compressive stress(-) by bending operations, and its maximum value reached-319 MPa in axial direction at ${\phi}=0^{\circ}$ in position. Tensile residual stresses(+) of ${\sigma}_zz=45$ MPa,${\sigma}_zz=25$ MPa were introduced in the intrados surface at position of ${\phi}=0^{\circ}$ Maximum tensile residual stress of 170 MPa was detected on the flank side at position of ,${\phi}=95^{\circ}$i.e., at apex region. It appeared that higher stress gradients were generated at the irregular transition regions. In the trend of residual stress changes with U-bend position, the extrados is related with the changes of ovality and the intrados is related with the changes of wall thickness.

• 대한기계학회논문집
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• 제17권1호
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• pp.51-61
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• 1993

본 연구에서는 에너지법으로 축대칭 박판성형 공정을 해석할 때, Lee와 Yang 이 제안한 방법을 적용함에 있어 굽힘효과를 효과적으로 고려할 수 있는 방법을 제안 하고 축대칭 컵드로잉 공정을 해석하여 본 이론의 타당성을 입증하고자 한다. 굽힘 효과는 박판소재를 몇개의 층(layer)으로 나눈 뒤, 각 층에서 소비되는 변형에너지를 합하여 전체 에너지를 최소화시킴으로써 고려하였다. 해석시 펀치 목부분과 다이목 부분에서의 접촉압력은 각각 균일한 분포를 갖는 것으로 가정하였다. 본 이론의 타 당성을 입증하기 위하여 계산결과를 실험치 및 탄소성 유한요소해석 결과와 비교하였 다.

• Elastomers and Composites
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• 제46권3호
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• pp.204-210
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• 2011

본 연구에서는 황마/폴리프로필렌 강화 섬유 복합재료를 사출성형 방법으로 제조하였으며, 섬유와 열가소성 기지재의 친화력과 접착력을 향상시키기 위해 말레산 무수물(Maleic anhydride, MA)을 결합제로 사용하였다. 천연 섬유인 황마의 표면처리 관찰을 위해서 주사전자현미경(SEM)과 적외선분광기(FTIR)를 사용하였고, 인장 및 굽힘 특성을 확인하기 위하여 기계적 특성 시험을 수행하였으며, 수분흡수율도 측정하여 비교하였다. 인장 및 굽힘 시험 결과 황마 복합재료(JFRP)는 기지재로 사용된 폴리프로필렌(PP)보다 높은 강도와 탄성계수를 나타내었고, 황마 복합재료의 강도 및 탄성계수는 결합제의 비율을 1~3%까지 증가시킴에 따라 높은 결과를 보였다. 이는 결합제의 비율을 증가시킬수록 섬유와 기지재 사이의 계면접착력을 향상시킬 수 있음을 의미한다.

• Composites Research
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• 제31권6호
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• pp.293-298
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• 2018

본 논문에서는 항공기용 스트링거(Stringer)로 사용하기 위한 브레이드 복합재료(Braided composites)의 물성에 대해 연구하였다. 브레이드 프리폼(braid preform)을 $30^{\circ}$, $45^{\circ}$, $60^{\circ}$로 제작하기 위해 드럼 와인더 속도, 브레이드 속도, 멘드럴 직경과 같은 공정변수들을 정량화시켰고, 에폭시 수지 종류를 TGDDM, YD-128로 브레이드 프리폼에 다르게 적용하여 각도에 따른 브레이드 복합재료의 인장강도, 굽힘강도를 섬유부피분율에 따라 규명하였으며, TGA 분석으로 열적 특성과 에폭시 수지의 분해 온도를 조사하였다. 그 결과 브레이드 프리폼의 각도가 낮을수록 인장강도와 굽힘강도가 향상됨을 확인하였고, 분자량이 높은 에폭시 수지를 사용할 때 물리적 성질이 향상되었다.