• Composites Research
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• 제27권6호
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• pp.254-259
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• 2014

고품질의 복합재료를 생산할 수 있는 Autoclave 공정의 단점인 긴 성형공정과 높은 생산비용을 보완하여 본 연구에서는 Autoclave 공정을 대체할 수 있는 Pressure press 공정과 장치를 개발하였다. Autoclave 공정의 가장 큰 특징이라고 할 수 있는 진공, 가압 공정을 금형 내부에 공간 설계를 통해 가능하게 하였고, 금형 내부 공기압이 소실되지 않도록 유압 press를 이용하여 가압장치를 설계하고 금형을 밀폐하였다. 가압장치에서는 가열과 냉각이 가능하게 하여 금형에 직접 온도를 전달할 수 있게 하였다. Autoclave 공정에 비해 내부 공간이 축소되어 가열 시간과 공기압 충전시간이 단축되었고 설비규모가 축소되어 초기설치비가 절감되었다. 가열방식에 따른 공정의 분석을 위해 V 자 형태의 금형을 제작하여 spring-back 현상 발생여부와 정도를 측정하고 Autoclave 공정과 비교하였으며, 복합재료 성형 시 금형의 온도를 측정하여 소재에 전달되는 각 부분의 온도를 관찰하였다. 그리고 같은 조건에서 Autoclave 공정과 Pressure press 공정으로 성형된 복합재료의 섬유 체적율을 비교하여 기계적 특성을 예측하였다.

• Design & Manufacturing
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• 제12권2호
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• pp.34-39
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• 2018

The biggest topics in the automobile industry are light weightening and fuel efficiency improvement. There's a lot of research going on. It is focused on light weight materials. Light weight material is seen as the best way to reduce fuel consumption and to solve the problem of environmental pollution and resource depletion. For the light weight materials, new materials such as aluminum, magnesium, and carbon-hardening materials can be found. Research on the joining techniques of dual materials, improvement of material properties by improving the method of manufacture of existing materials, and studies on ultra-high strength steel sheets are expected to take up the most weight in lightweight materials. As the strength of the ultra-high strength steel sheets increases during forming, it is difficult to obtain dimensional precision due to the increase in elastic restoring force compared to mild or high strength steel sheets. Spring back is known to be affected by a number of factors due to poor plastic molding, and can be divided into the effects of the material spraying and the process. The study on the plasticitic variables were studied as plasticitic factors that can be controlled by a part company. Tensile testing of ultra-high strength materials was conducted to derive properties for plasticitic analysis and to analyze spring back with two factors controlling the height of the bead and blank holding force by adding tensile force and controlling the flow rate.

• 한국산학기술학회논문지
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• 제18권2호
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• pp.450-455
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• 2017

쉴드 커넥터는 자동차 전장부품으로 차량 내 전기 배선을 연결하는데 사용된다. 이 부품은 전기 전도도가 높은 인청동 재질을 사용하고 프로그레시브 프레스 성형으로 제작된다. 본 제품 형상의 기하학적인 측면을 고려했을 때 복잡하지 않지만, 드로잉, 밴딩 등의 소성가공과 피어싱, 노칭 등의 전단 가공을 실시하여 제품 성형을 완성해야 한다. 프로그레시브 금형을 설계하는 과정 중에 공정 및 스트립레이아웃 설계단계의 성형 해석 모듈을 활용하여 제품의 재질에 따른 두께 변화 및 성형 안전성, 스프링 백 (Spring Back) 검토를 수행하여, 균열 혹은 주름의 경향과 불완전 소성 변형에 대한 보정치를 예측 및 발생 가능한 문제들을 사전에 확인하고, 드로잉 공정 초기에 발생된 성형 불량에 대한 대책으로 드로잉 형상을 수정하여 공정 설계에 반영하였다. 공정설계에서 얻어진 제품의 블랭크 전개 형상은 효과적인 재료 이용을 위해 네스팅에 의한 최적화된 블랭크 배치로 재료의 손실을 최소화하여 3차원 스트립레이아웃 설계를 완성하였다. 본 연구를 통해 프로그레시브 성형을 통해 생산되는 쉴드커넥터 제품의 균열과 스프링백 현상을 사전에 개선하여 생산안정도를 향상시켰다.

• Geomechanics and Engineering
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• 제25권3호
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• pp.221-231
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• 2021

A two dimensional model of linearly elastic soil spring used for the settlement analysis of the flexible mat foundation is suggested in this study. The spring constants of the soils underneath the foundation were modeled assuming uniformly vertical load applied onto the foundation. The soil spring constants were back calculated using the three-dimensional finite element analysis with Midas GTS NX program. Variation of the soil spring constants was modeled as a two-dimensional polynomial function in terms of the normalized spatial distances between the center of foundation and the analytical points. The Lysmer's analog spring for soils underneath the rigid foundation was adopted and calibrated for the flexible foundation. For validations, the newly proposed soil spring model was incorporated into a two dimensional finite difference analysis for a square mat foundation at the surface of an elastic half-space consisting of soft clays. Comparative study was made for elastic soils where the shear wave velocity is 120~180 m/s and the Poisson's ratio varies at 0.3~0.5. The resulting foundation settlements from the two dimensional finite difference analysis with the proposed soil springs were found in good agreement with those obtained directly from three dimensional finite element analyses. Details of the applications and limitations of the modified Lysmer's analog springs were discussed in this study.

• Composites Research
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• 제19권1호
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• pp.29-35
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• 2006

첨단 전자무기체계의 지속적인 발전으로 인하여 현대전의 승패는 적 레이더 탐지의 회피에 크게 좌우된다고 할 수 있다. 반사되는 레이더의 탐지신호를 최소화시키기 위한 다양한 연구가 수행되어 왔는데, 본 연구에서는 뛰어난 기계적, 전자기적 물성으로 응용분야가 지속적으로 확대되고 있는 섬유강화 복합재료를 이용하여 레이더 전자파 흡수체(Radar absorbing structure, RAS)를 제작하고 레이더 단면적(Radar cross section, RCS)을 평가하였다 유리섬유 복합재에 뛰어난 유전적 특성을 지닌 나노 크기의 카본블랙(Carbon-black)을 첨가하여 흡수층을 구성하고, 반사특성이 탁월한 탄소섬유 복합재를 후면의 반사층으로 배치하여 "C" 및 "U" 형상의 하이브리드 복합재 RAS 겔을 제작하였다. RAS 쉘의 제작간 서로 다른 두 재료의 열적물성치 차이로 스프링 백이라 불리는 변형이 발생하였는데, 금형의 굽힘각도 제어를 통하여 효과적으로 보정할 수 있었다. 또한 상용 유한요소해석 프로그램인 ANSYS를 이용하여 스프링 백 보정 결과를 예측하고 실험결과와 비교하였다. 제작된 RAS쉘의 RCS는 근사적 계산기법인 물리광학법을 이용하여 예측하고 컴팩트 레인지(Compact range)를 이용하여 측정한 실힘결과와 비교하였다 두가지 형상의 RCS 모두 측정결과와 예측된 RCS 값이 일치하며 우수한 레이더 전자파 흡수 특성을 지닌 것을 확인하였다.

• 한국전산구조공학회논문집
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• 제26권6호
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• pp.475-481
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• 2013

복합재료 사이에 주파수 선택적 투과막(Frequency Selective Surface)을 삽입하여 동시경화 공정을 이용하여 주파수 선택적 투과 기능을 가지는 하이브리드 복합재료를 성형하면 재료들 간의 열팽창 계수와 강성의 차이로 인해 구조 내에 잔류 열응력이 발생하게 되고, 이로 인하여 스프링 백 현상이 발생한다. 따라서 복합재의 적층에 따른 영향을 알아보기 위해 복합재료의 적층각을 선택적 투과막(Frequency Selective Surface)을 중심으로 대칭과 비대칭 적층으로 적용하여 하이브리드 구조의 잔류 열응력을 예측하고, 이에 대한 스프링 백에 대해서 연구하였다.

• 한국생산제조학회지
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• 제9권6호
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• pp.140-151
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• 2000

Springs for vehicle suspension control the vibration of a car and influence on the ridability, safety, and life of a car. in the paper, the computer aided design program has been developed, which design the leaf spring shape from the given specifications using basic theory and the expert\`s knowledge, and the design results are checked by the analysis theory in order to increase the accuracy, and feed back to the design input. For the purpose of easy use, this program consists of pull-down menu and interactive input mode. To prove the effectiveness of this program, two springs, of which one is symmetric, other asymmetric, are designed and analyzed, and the outputs are compared to the experiments. Considering the tolerance of the given specifications, the results are good.

• Restorative Dentistry and Endodontics
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• 제42권4호
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• pp.273-281
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• 2017

Objectives: The aims of this study were to quantify tug-back by measuring the pulling force and investigate the correlation of clinical tug-back pulling force with in vitro gutta-percha (GP) cone adaptation score using micro-computed tomography (${\mu}CT$). Materials and Methods: Twenty-eight roots from human single-rooted teeth were divided into 2 groups. In the ProTaper Next (PTN) group, root canals were prepared with PTN, and in the ProFile (PF) group, root canals were prepared using PF (n = 14). The degree of tug-back was scored after selecting taper-matched GP cones. A novel method using a spring balance was designed to quantify the tug-back by measuring the pulling force. The correlation between tug-back scores, pulling force, and percentage of the gutta-percha occupied area (pGPOA) within apical 3 mm was investigated using ${\mu}CT$. The data were analyzed using Pearson's correlation analysis, one-way analysis of variance (ANOVA) and Tukey's test. Results: Specimens with a strong tug-back had a mean pulling force of 1.24 N (range, 0.15-1.70 N). This study showed a positive correlation between tug-back score, pulling force, and pGPOA. However, there was no significant difference in these factors between the PTN and PF groups. Regardless of the groups, pGPOA and pulling force were significantly higher in the specimens with a higher tug-back score (p < 0.05). Conclusions: The degree of subjective tug-back was a definitive determinant for master cone adaptation in the root canal. The use of the tug-back scoring system and pulling force allows the interpretation of subjective tug-back in a more objective and quantitative manner.

• 소성∙가공
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• 제16권7호
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• pp.555-560
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• 2007

This paper shows some achievements at bending of extruded aluminum profiles during the extrusion process. The conventional process for the production of bent profiles involves a successive extrusion, stretching, and bending of the profiles. Conventional bending methods can not meet demands far precision and cost-effective production in some cases, due to cross sectional deformation, irregular decrease of tube wall thickness and a complication of the process design. An estimation of spring-back required for precision of the bending radius can not always be achieved by the over bending of the profile. Since the profile is hot during the bending process, the spring-back phenomenon can be avoided. This means that an additional bending process is not necessary. Consequently, flexible bending can be achieved with cost reduction and quality improvement. Experimental tests were completed to study the relationship between curvature radius of profile and position of guide on the extrusion for vehicle bumper. A7108 is applied as a billet material in order to increase strength. The overall correlation between the experimental and numerical results is good. It is therefore concluded that the present method provides an efficient means for the constant curvature extrusion process.

• Design & Manufacturing
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• 제14권1호
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• pp.15-21
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• 2020

Smart systems in different application areas such as automotive, medical and consumer electronics require a novel manufacturing method of electronic, optical and mechanical functions into products. Traditional methods including mechanical assembly, bonding of plastic and electronic circuit cause the problems in large size of products and complicated manufacturing processes. In this study, thermoforming and film insert molding were applied to fabricate a dome shaped plastic part embedded with electronic circuits. The deformation of patterns printed on PET film was predicted by thermoforming simulation using T-SIM, and the results were compared with those by experiment. In order to decrease spring-back after thermoforming, the Taguchi method of design of experiment was used. Through ANOVA analysis, it was found that mold temperature was the most dominant parameter for spring-back. By using flow analysis, gate design was performed to decrease injection pressure. During film insert molding, the wash-out of ink printed on film occurred for Polycarbonate. When the resin was changed to PMMA, the wash-out disappeared due to low melt temperature.