• 한국산학기술학회논문지
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• 제18권3호
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• pp.320-326
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• 2017

다단 딥드로잉 기술은 제품의 생산성 향상과 비용 절감을 위해 휴대폰 배터리 케이스 제품의 생산 공정으로 많이 사용하고 있다. 휴대폰 배터리 케이스는 용량과 강성을 목적으로 세장비가 큰 사각 컵 형상으로 제조된다. 사각 컵 형상의 다단 딥드로잉은 세장비가 크고, 복잡한 변형 형태 메커니즘으로 인한 제품의 좌우 높이 차이가 발생한다. 이로 인해 제품 조립과 표면 품질에 문제가 발생한다. 본 연구에서는 이러한 문제를 개선하기 위해 제품의 높이 차이가 최소가 되는 블랭크 형상에 대해 연구했다. 제품 좌우 높이 차이가 최소가 되는 블랭크 형상을 찾기 위해 최적 설계와 해석을 수행했다. 타원형 블랭크의 장변과 단변을 설계 변수로 설정하고, 목적 함수는 높이 차이가 최소가 되도록, 제품의 두께 감소율이 목표 범위에 도달하도록 설정했다. 또한 최종 제품 형상의 높이를 구속 조건으로 설정하였다. 그 결과 최적 설계를 통한 초기 블랭크 설계로 높이 차이가 최소가 되었으며, 원하는 공정을 지정하여 높이 차이가 최소화 되도록 수행 가능하다. 향후 개발된 자동화 프로세스로 인해 모든 각형 타입의 초기 소재 설계가 가능할 것으로 판단된다.

• 소성∙가공
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• 제23권6호
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• pp.351-356
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• 2014

The current study aims to predict the forming limits considering the deformation characteristics of tailor rolled blank(TRB) during hot stamping. The formability of TRB is affected by the TRB line orientation because elongations change due to the intrinsic geometry within the sheet. To evaluate the forming limits, Nakazima tests were conducted at elevated temperatures with different TRB line orientations. Forming limit diagrams(FLD) of TRB can be predicted by an interpolating equation based on the Nakazima test. Predicted FLDs were used in FE-simulations of a rectangular drawing. The predicted limit drawing height was compared with experimental results. The simulation results show good agreement with the experimental ones with an error range of 3%.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1998년도 춘계학술대회논문집
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• pp.151-154
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• 1998

Stainless steel sheets are widely used to produce electrical appliances. But there are various problems occured in forming stainless steel sheets such as scratch, local fracture, earing. So the productivity of electrical appliances made of stainless steel sheets is decreased. And it is very important to improve the formability of stainless steel sheets. In this study, rectangular cup drawing tests have been carried out to obtain optimum process parameters for improving the formablity of stainless steel sheets. In the tests, selected process parameters are materials of dies and punches, lubricating conditions, and blank holding force. From the test results, we suggest the appropriate conditions to be applicable to the actual manufacturing processes.

• 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.

• 한국정밀공학회지
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• 제9권2호
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• pp.44-51
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• 1992

This paper is concerned with the propram of the automatic mesh generation for 2-dimensional domain which contains the curved boundaries and holes. This program treats a new vertical-line drawing method. This method starts with 4-subdivisions of problem domain and the classification of the cross points of grid lines and boundaries. The new node is generated by the vertical line to the line connecting the two intersections of a boundary and two grid lines in gereral. And the node very close to the boundary is moved to the boundary. The automatic mesh generation composed of only rectangular elements is achieved by this procedure. The boundaries are piecewise-curves composed of lines, circles, arcs, and free curves. The free curves are generated by B-Spline form. Although there were some bad elements for the complex boundary, it was possible to obtain the acceptible rectangular elements for the given boundaries.

• Wind and Structures
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• 제16권6호
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• pp.617-627
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• 2013

In wind load calculations based on pressure measurements, the concept of 'tributary area' is usually used. The literature has less guidance for a systematic computational methodology for calculating tributary areas, in general, and for scattered pressure taps, in particular. To the best of the author's knowledge, there is no generic mathematical equation that helps calculate the tributary areas for irregular pressure taps. Traditionally, the drawing of tributary boundaries for scattered and intensively distributed taps may not be feasible (a time and resource consuming task). To alleviate this problem, this paper presents a proposed numerical approach for tributary area calculations on rectangular surfaces. The approach makes use of the available coordinates of the pressure taps and the dimensions of the surface. The proposed technique is illustrated by two application examples: first, quasi-regularly distributed pressure taps, and second, taps that have scattered distribution on a rectangular surface. The accuracy and the efficacy of the approach are assessed, and a comparison with a traditional method is presented.

• 한국전산유체공학회지
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• 제16권4호
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• pp.110-115
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• 2011

A modern optical fiber manufacturing process requires the sufficient cooling of glass fibers freshly drawn from the heated and softened silica preform in the furnace, since the inadequately cooled glass fibers are known to cause improper polymer resin coating on the fiber surface and to adversely affect the product quality of optical fibers. In order to greatly enhance the fiber cooling effectiveness at increasingly high fiber drawing speed, it is necessary to use a dedicated glass fiber cooling unit with helium gas injection between glass fiber drawing and coating processes. The present numerical study features a series of three-dimensional flow and heat transfer computations on the cooling gas and the fast moving glass fiber to analyze the cooling performance of glass fiber cooling unit, in which the helium is supplied through the discretely located rectangular injection holes. The air entrainment into the cooling unit at the fiber inlet is also included in the computational model and it is found to be critical in determining the helium purity in the cooling gas and the cooling effectiveness on glass fiber. The effects of fiber drawing speed and helium injection rate on the helium purity decrease by air entrainment and the glass fiber cooling are also investigated and discussed.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.92-95
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• 2011

In manufacturing optical fibers, the process starts with the glass fiber drawing from the heated and softened silica preform in the furnace, and the freshly drawn glass fiber is still at high temperature when it leaves the glass fiber drawing furnace. It is necessary to cool down the glass fiber to the ambient temperature before it then enters the fiber coating applicator, since the hot glass fiber is known to cause several technical difficulties in achieving high quality fiber coating. As the fiber drawing speed keeps increasing, a current manufacturing of optical fibers requires a dedicated cooling unit with helium gas injection. A series of three-dimensional flow and heat transfer computations are carried out to investigate the effectiveness of fiber cooling in the fiber cooling unit. The glass fiber cooling unit is simplified into the long cylindrical enclosure at which the hot glass fiber passes through at high speed, and the helium is being supplied through several injection slots of rectangular shape along the cooling unit. This study presents and discusses the effects of helium injection rates on the glass fiber cooling rates.

• Structural Engineering and Mechanics
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• 제37권3호
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• pp.331-349
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• 2011

This study investigates the use of a vibration correlation technique (VCT) to identify the buckling load of a rectangular thin plate. It is proposed that the buckling load can be determined experimentally using the natural frequencies of plates under tensile loading. A set of rectangular plates was tested for natural frequencies using an impact test method. Aluminum and stainless steel specimens with CCCC, CCCF and CFCF boundary conditions were included in the experiment. The measured buckling load was determined from the plot of the square of a measured natural frequency versus an in-plane load. The buckling loads from the measured vibration data match the numerical solutions very well. For specimens with well-defined boundary conditions, the average percentage difference between buckling loads from VCT and numerical solutions is -0.18% with a standard deviation of 5.05%. The proposed technique using vibration data in the tensile loading region has proven to be an accurate and reliable method which might be used to identify the buckling load of plates. Unlike other static methods, this correlation approach does not require drawing lines in the pre-buckling and post-buckling regions; thus, bias in data interpretation is avoided.

• Design & Manufacturing
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• 제14권1호
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• pp.22-29
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• 2020

The analysis was carried out using the press molding analysis program by applying six parameters such as material type change, material thickness, friction coefficient, r_p, r_d and blank holder pressure. As a result of CAE analysis of the soft material DC04 and the relatively hard material HX300LAD, the thickness of the punch R part of the soft material was significantly reduced. The flange portion is greatly increased in thickness in the hard material by the compression action. As a result of considering the deformation amount of 0.6mm, 1.0mm, 1.5mm according to the material thickness, the influence of the thickness is considered to be very small. In case of the material thickness of 0.6mm, the rate of change increases due to the deep drawing depth relative to the material thickness. The sizes of the punches R and die R have the greatest influence on the change in thickness of the material in drawing molding, the smaller the punch R, the thinner the edges of the product, The larger the R of the die, the greater the material thickness of the flange portion. As the coefficient of friction and the blank holder pressure increase, the frictional force of the flange portion increases, which increases the radial force in the drawing process and increases the thickness change of the flange portion.