• Design & Manufacturing
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• 제16권2호
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• pp.39-45
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• 2022

Sheet Metal Forming by Press Forming Process takes a lot of time and cost from mold design to manufacturing. Therefore, all of die-makers are continuously conducting research to reduce the number of mold processes or the size of blanks to reduce costs. In the case of Forming complex shapes such as automobile component, wrinkles and cracks occur, so draw beads are used. Draw beads play an important role in suppressing the inflow of materials and minimizing the size of blanks. Factors that affect material flow include draw bead, blank holding pressure, lubricant, and surface roughness of punch and die. Most of the factors affect friction. In this study, after classifying circular beads and rectangular beads in cylindrical drawing molds using the AutoForm analysis program, the factors affecting the material inflow were considered.

• 한국터널지하공간학회 논문집
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• 제16권2호
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• pp.237-248
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• 2014

TBM의 사양을 설계하고 굴진성능을 예측할 때 실대형 선형절삭시험을 통하여 설계변수를 획득하는 것이 매우 효과적인 방법인 것으로 알려져 있다. 하지만 선형절삭시험을 위해서는 대형 시편을 획득하고 큰 하중용량의 시험을 수행하는 과정에서 상당한 비용과 노력이 소모된다는 단점이 있다. 따라서 선형절삭시험을 대체하는 경험적 예측 모델, 즉 CSM모델과 NTNU모델을 사용하여 몇 가지 지수를 산정하고 이로부터 설계변수를 추정하는 경우가 많다. 본 연구에서는 압입시험 및 세르샤 마모시험을 이용하여 TBM의 사양(추력, 토크)과 굴착에 따라 소요되는 디스크 커터의 개수를 추정하는 방법에 대하여 고찰하였다. 압입시험과 세르샤 마모시험은 TBM의 설계 변수를 추정하기 위한 유용한 시험법이나 그 활용법이 연구 되고 있지 못한 실정이다. 이 연구에서는 압입시험과 세르샤 마모시험결과를 간단한 형태의 지수형태로 도출하고 이를 선형절삭시험 및 실제 굴진자료와 비교하여 상관관계를 도출하고 이로 부터 디스크 커터의 작용력 및 수명을 예측하였다. 또한 이 일련의 계산 과정을 프로그램화 하였으며, 터널의 연장 정보, TBM의 기계정보, 구간별 암석의 물성을 입력변수로 하여 구간별 굴진율과 TBM 사양 및 운영조건, 디스크 커터의 소모개수를 예측할 수 있었다.

• Imaging Science in Dentistry
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• 제33권2호
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• pp.113-119
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• 2003

Purpose : To evaluate the relationship between morphometric analysis of bone microstructure from digital radiographic image and trabecular bone strength. Materials and Methods : One hundred eleven bone specimens with 5 mm thickness were obtained from the mandibles of 5 pigs. Digital images of specimens were taken using a direct digital intraoral radiographic system. After selection of ROI (100 × 100 pixel) within the trabecular bone, mean gray level and standard deviation were obtained. Fractal dimension and the variants of morphometric analysis (trabecular area, periphery, length of skeletonized trabeculae, number of terminal point, number of branch point) were obtained from ROI. Punch sheer strength analysis was performed using Instron (model 4465, Instron Corp., USA). The loading force (loading speed 1 mm/min) was applied to ROI of bone specimen by a 2 mm diameter punch. Stress-deformation curve was obtained from the punch sheer strength analysis and maximum stress, yield stress, Young's modulus were measured. Results: Maximum stress had a negative linear correlation with mean gray level and fractal dimension significantly (p<0.05). Yield stress had a negative linear correlation with mean gray level, periphery, fractal dimension and the length of skeletonized trabeculae significantly (p < 0.05). Young's modulus had a negative linear correlation with mean gray level and fractal dimension significantly (p < 0.05). Conclusions : The strength of cancellous bone exhibited a significantly linear relationship between mean gray level, fractal dimension and morphometric analysis. The methods described above can be easily used to evaluate bone quality clinically.

• Composites Research
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• 제29권5호
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• pp.236-242
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• 2016

본 연구에서는 유리섬유/폴리프로필렌 기반의 열가소성 복합재의 열성형 시험 평가를 위해, 성형온도에서의 인장 및 면내 전단 물성 시험을 실시하였고, 이를 비직교 구성방정식을 이용하여 정량화 하였다. 이를 통해 실험값과 잘 일치하는 고온에서의 인장 및 전단 물성값을 수식화하여 얻을 수 있었다. 열성형 시험을 위해 반구돔 시험을 실시하였고, 이형제 사용 유무 및 홀더의 무게를 달리해가며 성형품의 최종형상을 비교하였다. 그 결과 이형제를 사용하면 성형품의 대칭성이 확보되고 주름 개선 효과에 유리하다는 것을 확인하였고, 적당한 힘의 홀딩력 제어가 필수적이라는 것을 알 수 있었다. 더 나아가 비직교 구성방정식이 고려된 열성형 수치해석을 실시하여 실험 결과와 유사한 양상을 확인할 수 있었고, 홀딩력이 낮을 수록 주름이 많아지고, 마찰력이 클수록 더 많은 펀치력을 필요로 함을 확인하였다.

• 한국식품영양과학회지
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• 제32권7호
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• pp.1026-1031
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• 2003

냉동 백조기로 제조한 알칼리 수리미의 가열 겔 강도 증강을 위한 최적 전분 및 비근육 단백질의 선정과 이들 성분의 최적 첨가량을 설정하기 위해 2수준 fractional factorial과 mixture design을 실시하였으며, 반응 값은 punch test에 의한 물성과 색차계로 색을 측정하였다. 전분은 종류에 관계없이 파괴강도와 변형 값을 감소시켰다. 파괴강도 값은 전분의 농도 증가와 더불어 감소하였고, 변형 값은 유의적인 차이를 보이지 않았다. 비근육 단백질 중 소혈청 단백질이 겔의 파괴강도와 변형 값을 가장 크게 증가시켰으며, 첨가 농도가 증가함에 따라 파괴 강도와 변형 값은 증가하였다. 백색도는 전분과 근육 단백질의 함량이 증가함에 따라 다소 상승하는 것으로 나타났다. 파괴강도 100g 이상, 변형 값 4.6mm이상, 백색도 25.5 이상을 보이는 수리미, 감자전분, 소혈청의 최적 혼합 비율은 각각 89.4∼90.0%, 4.5∼5.2%, 5.3∼5.8%의 범위였다. 전분과 비근육 단백질을 첨가하여 제조한 가열 겔이 단백질의 균일한 분포와 치밀한 망상 구조 형태를 보이고 있었으며 이 같은 구조가 높은 물성 값에 기여하는 것으로 판단하였다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 춘계학술대회 논문집
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• pp.282-284
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• 2007

The hardening and the constitutive equation based on the crystal plasticity are introduced for the numerical simulation of hemispherical sheet metal forming. For calculating the deformation and the stress of the crystal, Taylor's model of the crystalline aggregate is employed. The hardening is evaluated by using the Taylor factor, the critical resolved shear stress of the slip system, and the sum of the crystallographic shears. During the hemispherical forming process, the texture of the sheet metal is evolved by the plastic deformation of the crystal. By observing the texture evolution of the BCC sheet, the texture evolution of the sheet is traced during the forming process. Deformation texture of the BCC sheet is represented by using the pole figure. The comparison of the strain distribution and punch force in the hemispherical forming process between crystal plasticity and experiment shows the verification of the crystal-based formulation and the accuracy of the hardening and constitutive equation obtained from the crystal plasticity.

• Journal of Mechanical Science and Technology
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• 제16권12호
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• pp.1687-1692
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• 2002

The problem analyzed here is a sheet metal forming process which requires a drawbead. The drawbead provides the sheet metal enough tension to be deformed plastically along the punch face and consequently, ensures a proper shape of final products by fixing the sheet to the die. Therefore, the optimum design of drawbead is indispensable in obtaining the desired formability. A static-explicit finite element analysis is carried out to provide a perspective tool for designing the drawbead. The finite element formulation is constructed from static equilibrium equation and takes into account the boundary condition that involves a proper contact condition. The deformation behavior of sheet material is formulated by the elastic-plastic constitutive equation. The finite element formulation has been solved based on an existing method that is called the static-explicit method. The main features of the static-explicit method are first that there is no convergence problem. Second, the problem of contact and friction is easily solved by application of very small time interval. During the analysis of drawbead processes, the strain distribution and the drawing force on drawbead can be analyzed. And the effects of bead shape and number of beads on sheet forming processes were investigated. The results of the static explicit analysis of drawbead processes show no convergence problem and comparatively accurate results even though severe high geometric and contact-friction nonlinearity. Moreover, the computational results of a static-explicit finite element analysis can supply very valuable information for designing the drawbead process in which the defects of final sheet product can be removed.

• 소성∙가공
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• 제23권6호
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• pp.363-368
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• 2014

Electromagnetic forming(EMF) is one of the high-speed forming methods, and has been used to deform metal sheets. The advantages of electromagnetic forming are reduced wrinkling due to non-contact characteristic and fine formability because of the high speed impact. In the current study, we suggest the application of electromagnetic forming to emboss pattern shapes using electromagnetic forces with only one forming coil and one punch. The high impact of the sheet at speeds of 100~300m/s produces significant coining pressure. In the current paper, electromagnetic forming was applied to Al 1100-O sheets; with thickness of 1.27mm and an area of $40mm{\times}40mm$. Using a single spiral coil, totally different types of patterns were created. Four different patterns were successfully produced on the aluminum sheet. The length and depth of the patterns were measured by three-dimensional scanning. Comparisons to the die shape showed good agreement. The test results confirm that emboss pattern forming by EMF using a single die can be used to replace the costly conventional method.

• 한국공작기계학회논문집
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• 제12권1호
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• pp.58-64
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• 2003

A mechanical press joining was investigated in ender for joining A1-5052 sheets for automobile body weight reduction. Static tensile and fatigue tests were conducted using tensile-shear specimens for evaluation of fatigue strength of the joint. During Tox joining process for A1-5052 plates, using the current sheet thickness and punch diameter, the optimal applied punching force was found to be 32 kN under the current joining condition. For the static tensile-shear experiment results, the fracture mode is classified into interface fracture mode, in which the neck area fractured due to influence of neck thickness, and pull-out fracture mode due to influence of plastic deformation of the joining area. And, during fatigue tests for the A1-5052 tensile shear specimens, interface failure mode occurred in the region of low cycle. The fatigue endurance limit approached to 6 percents of the maximum applied load, considering fatigue lifetime of $2.5\times10^6$ cycles.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.71-76
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• 2001

This paper describes a research work of developing system for conceptual die design system for Fine blanking. The method of approaching to the system is based on the knowledge-based rules. Knowledge for the system is formulated from experimental results and the empirical knowledge of field experts. This system has been written in VisualLISP on the AutoCAD using a personal computer and in Microsoft Visual Basic ver.6.0. Transference of data is accomplished by DXF (Drawing Exchange Format) method. This system consists of six modules, which are cognition of a drawing, cognition of shear length, calculation of shear force, materials properties database, determination of degree of difficulty of the product, determination of approximate life of punch and die modules. Results carried out in each module will provide efficiency to the designer and the manufacturer of die for Fine blanking. But the main focus of this system is the design of die for Fine blanking in the level of general concept. In order to use powerful tool in this field, developed system will be studied continuously.