• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2000년도 봄 학술발표회논문집
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• pp.187-194
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• 2000

Weight reduction for an automobile body is being sought for the fuel efficiency and the energy conservation. One way of the efforts is adopting Ultra Light Steel Auto Body (ULSAB) concept. The ULSAB concept can be used for the light weight of an automobile door with the tailor welded blank (TWB). A design process is defined for the TWB. The inner panel of door is designed by the TWB and optimization. The design starts from an existing component. At first, the hinge and inner reinforcements are removed. In the conceptual design stage, topology optimization is conducted to find the distribution of variable thicknesses. The number of parts and the welding lines are determined from the topology design. In the detailed design process, size optimization is carried out to find thickness while stiffness constraints are satisfied. The final parting lines are determined by shape optimization.

• 한국산학기술학회논문지
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• 제18권2호
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• pp.349-355
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• 2017

프레스금형(press dies)에 의한 굽힘가공(bending work) 이라는 것은 평평한 블랭크(blank)를 필요로 하는 각도(角度)로 굽히는 것이다. 굽힘가공을 하면 굽혀진부분(flange)과 굽혀지지 않은 부분(web)으로 구분되며, 굽힘라인(bending line) 부분에는 굽혀진 각도(bending angle)와 굽힘반지름(bending radius)이 내측과 외측으로 성형된다. 이때, 내측 굽힘반지름의 크기는 제품의 재질별로 최소치수가 제시 된다. 제시된 최소치수 보다 작게 굽히면 절단면 굽힘부위에 덧살이 발생 하거나 외측 굽힘반지름 부위에는 균열(crack)이 생긴다. 굽힘가공에서의 외측 굽힘반지름은 자연적으로 생긴다. 그래서 외측 굽힘반지름 치수를 굽힘펀치와 다이블록으로 조정하면서 필요한 치수로 굽힐수 없다. 굽힘가공에는 V-굽힘, U-굽힘, Z-굽힘, O-굽힘, P-굽힘, 에지굽힘(edge bending), 트위스트굽힘(twist bending), 크림핑(crimping) 등이 있다.이 중에서 Z-굽힘은 굽힘라인이 2개로써 블랭크의 상면(上面)과 하면(下面)에 설정하여 상향(上向)굽힘이나 하향(下向)굽힘으로 작동되는 금형을 사용한다. Z-굽힘을 크랭크굽힘(crank bending) 이라고도 한다. 이런 구조의 금형으로 Z-굽힘가공을 하면 내측반지름은 표준치수로 굽혀진다. 표준치수라는 것은 굽힘가공에서 굽힐 수 있는 최소 굽힘반지름 치수로서 굽힘펀치의 각(角)반지름(Rp)를 뜻한다. 그런데 산업현장에서는 외측 굽힘반지름 치수를 굽힘펀치와 다이블록으로 굽힐수 없는 미세한 샤프에지(sharp edge) 형상인 매우 작은 치수(R=0.2mm)를 필요로하고 있는 바, 본 논문에서는 외측 굽힘반지름 치수를 0.2mm 이하로 굽힐수 있는 Z-굽힘가공 공법을 개발 하고자 하였다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 춘계학술대회 논문집
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• pp.322-325
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• 2007

Dent resistance is an important characteristic to avoid damage on automotive outer panels. From a practical point of view, dents can be caused in a number of ways. Considering doors as an example, denting can occur from stone impacts or from the careless opening of an adjacently parked vehicle door. Denting can occur where the door surface is smooth and may not have sufficient curvature to resist dent. These exterior body parts are designed to improve dent resistance using a combination of work hardening and bake hardening. In brief, dent is affected by the shape of the parts and the material properties such as yield strength, strain and thickness. In this work, forming of door outer panel is investigated by Taguchi method. Main parameters are yield strength, thickness, blank size, blank holding force and so on. For the given value of design parameters, forming analysis of the thirty six cases are carried out according to L18 orthogonal array. After comparing the performance by simple conversion of simulation results into dent resistance, the final suggestion of the forming parameters is verified for the best improvement of dent resistance.

• 소성∙가공
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• 제16권4호
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• pp.254-259
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• 2007

Dent resistance is an important characteristic to avoid damage on automotive outer panels. From a practical point of view, dents can be caused in a number of ways. Considering doors as an example, denting can occur from stone impacts or from the careless opening of an adjacently parked vehicle door. Denting can occur where the door surface is smooth and may not have sufficient curvature to resist dent. These exterior body parts are designed to improve dent resistance using a combination of work hardening and bake hardening. In brief, dent is affected by the shape of the parts and the material properties such as yield strength, strain and thickness. In this work, forming of door outer panel is investigated by Taguchi method. Main parameters are yield strength, thickness, blank size, blank holding force and so on. For the given value of design parameters, forming analysis of the eighteen cases are carried out according to L18 orthogonal array. After comparing the performance by simple conversion of simulation results into dent resistance, the final suggestion of the forming parameters is verified for the optimal improvement of dent resistance.

• Journal of Korean Society for Atmospheric Environment
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• 제17권E1호
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• pp.17-24
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• 2001

For the purpose of collecting fog droplets as a function of size a new sampling method was developed in this study. Formation of 100$\pm$10㎛ thickness of polymeric water absorbent film (PWAF) on a nuclepore filter could be successfully realized. Also applicability of particle induced X-ray emission (PIXE) method to the chemical analysis of size-segregated fog droplets collected on PWAF was examined experimentally with synthetic fog droplets generated from a nebulizer. Absorption capacity of S-PAAS polymeric water absorbent shows marked decreases in the range less than 1 wt% and slight decrease between 1 and 3.5 wt% of every salt concentration. Dependency of absorption capacity on pH shows the maximum at pH 7. No apparent peak which can influence the quantitative analysis of elements dissolved and suspended in fog droplets was found at PIXE spectrum of PWAF blank. PWAF kept the original shape without rupture under the PIXE analytical conditions of beam intensity for 10 to 60 nA and irradiation time of 4∼5 min. It should be said that the proposed new technique in the work is helpful to get more detailed information of fog droplets, to clarify the fog formation processes, and to develop a model of acid deposition process.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1998년도 금형가공 심포지엄
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• pp.28-42
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• 1998

Spinning is one of the incremental forming process by the rotating mandrel and forming roller, and has been applied to manufacturing the wheel disc of automobile to simplify the manufacturing process and to improve the mechanical properties of product. In the proesent study the process variables have been extracted and considered to decide the specification of the spinning machine. The maximum values of working load and power have been evaluated and the blank size has been disigned. The shape and dimensionof forming roller have been designed and the process condition such a s rotational velocity of mandrel and the feedrate of roller have been decided.

• 한국안전학회지
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• 제14권4호
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• pp.53-59
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• 1999

Recently, Tailor Welded Blank (TWB) is widely used in automotive industry since the transformation characteristic of its material can be changed. However, clearance between welding surfaces becomes the important factor which affect the quality of the laser weld, causing difficulties in preparing the sheet. The objective of this paper is to systematically evaluate the effects of previously presented fracture criterion and shearing condition on precise mechanical shearing simulation result. For this purpose, a parametric study was peformed to investigate the effect of finite element size and fracture criterion on simulation result. Also, in order to predict the optimum shearing condition, effect of shearing conditions such as clearance and punch radius on the shear plane shape was evaluated.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.410.1-410.1
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• 2016

Vanadium dioxide ($VO_2$) is a well-known material that exhibits a metal-semiconductor transition at 340 K, with drastic change of transmittance at NIR region. However, $VO_2$ based thermochromics accompany with low visible transmittance value and unfavorable color (brownish yellow). Herein, we demonstrate the adjustment of visible transmittance of $VO_2$ thin film by nanosphere template assisted patterning process using sol-gel method. 2-Dimenstional honeycomb shape was varied as function of diameter of nanosphere and coating conditions. The morphological geometry of the films was investigated by FE-SEM and AFM. Result shows that inversed shape of nanosphere was formed clearly and pattern width was altered according to the bead size. This structure creates the geometrical blank area from the position of nanosphere which improves the optical transmittance at the visible region. Moreover, such patterned $VO_2$ thin film not only maintains the optical switching efficiency, but also generate the gorgeous scattering effect which presumably support the glazing application.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.373-376
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• 2006

The ring rolling design for a large-scale Ti-6Al-4V alloy ring was performed with a calculation method and FEM simulation. The ring rolling design includes geometry design and optimization of process variables. The calculation method was to determine geometry design such as initial billet and blank size, and final rolled ring shape. A commercial FEM code, SHAPE was used to simulate the effect of process variables in ring rolling on the distribution of the internal state variables such as strain, strain rate and temperature. In order to predict the forming defects during ring rolling, the process-map approach based on Ziegler's instability criterion was used with FEM simulation. Finally, an optimum process design to obtain sound Ti-6Al-4V rings without forming defects was suggested through combined approach of Ziegler's instability map and FEM simulation results.

• 한국레이저가공학회지
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• 제7권2호
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• pp.1-10
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• 2004

This work was attempted to join SCP sheet and STS304 sheet by using Nd:YAC laser beam. SCP sheet has good formability and low cost, while STS304 has excellent corrosion resistance and mechanical properties in high temp. In this experiment, butt joint type was used to develop the tailored blank welding for dissimilar steel. Sheets which have different thermal properties. Computer simulation was conducted to obtain the off-set position for efficient welding by considering laser power, scanning speed, focal length and basic properties. The result showed that the optimum thermal distribution was obtained when the laser beam was irradiated at $0.05{\sim}0.1$ mm off-set toward the SCP sheet side. The experiment was conducted based on the result of computer simulation to show the same optimum conditions. Optimum conditions were 3KW in laser beam power, 6m/min in scanning speed, -0.5mm in focal position, 0.1mm off-set toward SCP. Microhardness test, tensile test, bulge test, optical microscopy, EDS, and XRD were performed to observe the microstructure around fusion zone and to evaluate the mechanical properties of optimum conditions, The weld zone had high microhardness values by the formation of the martensitic structure. Tensile test measured the strength of welded region by vertical to strain direction and the elongation of welded region by parallel to strain direction. Bulge test showed $52\%$ formability of the original materials. Bead shape, grain size, and martensitic structure were observed by the optical microscopy in the weld zone. Detailed results of EDS, XRD confirmed that the welded region was connected of martensitic structure.