• Transactions of Materials Processing
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• v.18 no.6
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• pp.488-493
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• 2009

The very big springback of advanced high strength steel(AHSS) sheets invokes undesired shape defects, which can be generally eliminated by die correction or process parameter control. The springback reduction by controlling the forming process parameters is easy for the application, but limited for the bulky achievement. In this study, the effective die correction method, which obtains the modification of tool shape from the relationship between die design variable and springback, is introduced and is applied to the TWB tool of automotive side rail to show the validity and usefulness. Among the die correction trials repeatedly performed, the first trial is carried out by correcting the tool shape to the opposite direction to the springbacks of several tool sections. Next trials are done by extrapolating the springbacks of among the original tool uncorrected and the tools corrected negative amounts of the springback and by finding tool shapes without springbacks. After the angle of side wall and radius of curvature of horizontal bottom floor are chosen as design variables in the tool design of side rail, the tool shape is corrected 3 times. The accuracy of final shape within the assembly limit of 1mm and the springback reduction of 75.8% compared to the uncorrected tool are achieved.

• Transactions of Materials Processing
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• v.20 no.6
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• pp.450-455
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• 2011

This paper presents an inverse design methodology for the cross section geometry of mold spring with a rectangular cross section as the starting material for a coiling process. The cross-sections of mold springs are universally rectangular, as the parallel sides minimize the possibility of failure under high service loads. Pre-coiled wires are initially designed to have a trapezoidal cross section, which becomes a rectangle by the coiling process. This study demonstrates a numerical exercise to predict changes in the sectional geometry in spring manufacture and to obtain the initial cross section which becomes the exact rectangle desired from the manufacturing process. Finite element analysis was carried out to calculate the sectional changes for various mold springs. Geometrical parameters were the widths at inner and outer radii, the inner and the outer corner radii, and the height. A partial least square regression analysis was carried out to find the main contributing factors for deciding initial design values. The height and the width mainly affected various initial parameters. The initial width at the inner radius was mostly affected by various specification parameters.

• International Journal of Precision Engineering and Manufacturing
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• v.4 no.3
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• pp.48-54
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• 2003

This paper deals with mirror grinding of a small-sized aspherical lens by a resin bonded diamond spherical wheel. Up to now, a spherical lens has been used for the lens of the optical communication optical part. However, recently, aspherical optical parts are mainly used in order to attempt the improvement in image quality and miniaturization of the optical device. It is possible to manufacture the aspherical lens which is presently being used in optical instrument through ultra-precision machining technology. Also, to realize compactness, efforts are being made to produce a micro aspherical lens, fur which the development of a high-precision, micro molding die is inevitable. Therefore, extensive research is being done on methods of producing a micro aspherical surface by high-precision grinding. In this paper, the spherical wheel was trued by cup-shaped truer and tool path was calculated by the radius of curvature of the wheel after truing and dressing. Then in the aspherical grinding experiment, WC material which is used as a melding die for the small-sized aspherical lens was ground. The results showed that a form accuracy of 0.1918 $\mu\textrm{m}$ P-V and a surface roughness of 0.064 $\mu\textrm{m}$ Rmax could be achieved.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.432-432
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• 2011

Dry adhesion caused by Nanoscale contact comes up to important scientific issue. Herein, we introduce bendable nanohairy locking fastener system with high shear strength and mechanically flexible backing. The polymeric patches like velcro are composed of an array of straight nanohairs with 100 nm diameter and $1{\mu}m$ height. To fabricate high aspect vertical nanohairs, we used UV molding method with appropriately flexible and rigid polyurethane acrylate material on PET substrate. Two identical nanohairy patches are easily merged and locked each other induced by van der Waals force. Because nanohairs can be arrayed with high density ${\sim}4{\times}10^8/cm^2$, we can obtain high shear adhesion force on flat surface (~22 N/$cm^2$). Furthermore, we can obtian nanohairy locking system with maximum shear adhesion ~48 N/$cm^2$ of curved surface due to flexibility of PET substrate. We confirm the tendency that shear adhesion force increases, as radius of curvature increases.

• Journal of Biosystems Engineering
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• v.27 no.6
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• pp.557-564
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• 2002

Corrugated board is an efficient low-cost structure material fur the boxes that are widely used for transporting, storing and distributing goods. Corrugated board is also considered as an orthotropic because the principal material directions are the same as in paperboard. The purpose of this study was to elucidate the principal design parameters of ventilating box through the FEA on the various types of ventilating hole. From the viewpoint of the stress distribution and stress level, the optimum pattern and location of the ventilating hole were vertically oblong, and symmetry position with a short distance to the right and left from the center of front and rear panel. And, the optimum location and pattern of hand hole were a short distance to the top from the center of both side panels, and modified shape to increase the radius of curvature of both side in horizontal oblong. In general, the optimum pattern and location of both the ventilating hole and hand hole based on the FEM analysis were well verified by experimental investigation. It is suggested that decrease in compressive strength of the box could be minimized in the same ventilating hole area under the condition of the length of major axis of ventilating hole is less than 1/4 of box length, the ratio of minor axis/major axis is 113.5∼l/2.5, and number of the ventilating holes is even and symmetrical.

• Journal of Biosystems Engineering
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• v.18 no.1
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• pp.15-20
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• 1993

Wearness has been a major failure criterion in Korean-made rotary blade. However, few studies have been conducted to improve it. In this study, the fundamental data obtained from the measurement of wearness and failure of rotary blade were analyzed to provide a guideline for the design of rotary blades. For the straight part(about 20-23 em from bolt hole) from the bolt hole to bending point of rotary blade, modifications were proposed for improvements, however, for the portion from bending point to tip was made no design recommendations because the failure behavior of that portion was difficult to analyze with the experimental data. The results are summarized as follows. 1. The current V-shape section has to be moved about 5 em toward the bending point of rotary blade. 2. The section modulus at the portion about 5-7 em distant from bolt hole has to be increased about 15-20 %. 3. The V-shape section has to be changed into U-shape to reduce the on account of recieving initial stress in blades. 4. The radius of curvature of the neck(the portion about 5-7 cm apart from bolt hole) has to be made larger to decrease the stress concentration.

• Fibers and Polymers
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• v.6 no.1
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• pp.55-65
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• 2005

Extensible elastica solutions of two-dimensional deflection of crimped fiber cantilever of circular wavy crimp were obtained for one end clamped boundary under concentrated, inclined and dead tip load Fiber was also regarded as a linear elastic material. Crimp was described as a combination of semicircular arcs smoothly connected with each other having con­stant curvature of all the same magnitude and alternative sign. Also the inclined load direction was taken into account. The solutions were expressed as the recursive forms of integrals in two different cases, which can also be transformed to elliptic integrals respectively. Comparing the data with inextensible ones was carried out. Consequently in the solution, the normal strain of neutral axis is expressed in terms of cross-sectional area, second moment of area and normalized load parameter. Examples of the circular cross-sectioned fiber are presented. As a result, the differences of normalized load between inexten­sible and extensible elastica solutions when the radius ratio becomes 0.1 were maximum $\Lambda$ = 0.1.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11b
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• pp.213-220
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• 2000

Numerical modeling of cut slope has some limits in simulating the real slopes. In the case of 2D analysis of slope stability, it is assumed that slope is simply straight even when it is concave or convex in plan view. In this study, 3D analysis in curved shape slopes has been conducted for the comparison with 2D analysis in terms of failure mode and factor of safety. For this, 3D analysis by FLAC3D was compared with 2D analysis in plane strain condition and axi-symmetric model condition by FLAC. It was also observed how safety factors of slopes were affected by the variation of the tensile strength and cohesion, which are important variables to decide whether the slope fails or not. 2D analysis of concave slopes under plane strain condition showed much smaller safety factors by 16-40 % errors depending on the radius of curvature of slopes, compared to the more realistic values from 3D analysis. In case of convex slopes, the lower values by 7-10 % has been reported. 2D analysis of axi-symmetric model showed also smaller safety factors by 6-10 % and by 2-4 %, in case of concave and convex slopes, respectively. Such results are expected to contribute to the better understanding of failure process and could be applied for improved design of slopes.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.637-642
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• 2008

The concept of district heating involves centralised heat production where heat is distributed to consumer via a piping network. The objective of this work is to identify the Flexible Pipe from an economy, execution, maintenance point of view. Flexible Pipe has in some countries, especially in Europe, been used for many years in district heating. In spite of years of experience, there still exist doubts about the possibilities of using flexible pipes in district heating applications, mostly because of no experiences in domestic market. The advantage of flexible pipe systems is their flexibility. This holds not only for the inner pipe but also for the total pipe system including insulation and jacket. Even for the largest diameter the minimum radius of curvature is given to 1.5m. The most important difference between flexible pipe systems and preinsulated steel pipes is their simple and quick assembly. Such information could provide a basis for making reasonable hypotheses about consumer preferences, to foam a basis for making future marketing more effective.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.1039-1044
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• 2008

By the result of efforts for the technology development of G7 trainset, the technology of domestic high-speed train KTX-II has lately been put to practical use while a forward countries of railway, which have their own developing ability of high-speed train, are competing against each other for the development of faster high-speed train system. Japan has been commissioning of FASTECH 360 which was developed in June 2005. Also France and Germany have been commissioning of next generation high-speed train such as AGV and ICE-3, developed basing on technology of their existing high-speed train system(TGV and ICE), its maximum commercial running speed is 360kph, and adopted multiple unit system. For the development of technology of domestic high-speed train and enhancement of national technology competitive power, HEMU (High-speed Electrical Multiple Unit) development project has been carried out as a national R&D project from last August. For the executing of HEMU's maximum speed test, we have investigated the high speed line characteristics (i.e. radius of curvature, gradient, cant etc.) of Seoul-Pusan line and Honam line which is under construction. We'd like to examine a study of condition for the best HEMU T&C line considering HEMU's characteristics (i.e. acceleration, deceleration etc.) and its interface with infrastructure in this paper.