• Transactions of Materials Processing
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• v.7 no.1
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• pp.81-93
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• 1998

Identification of forming limits of sheet metals is an important task to be done before the sheet metal forming processes. The information of the forming limit is indispensable for design of deformed shapes and related forming processes. This procedure becomes more important than ever as the auto-body becomes complicated and the number of auto-body parts is reduced for lower production cost. To identify the forming limit of sheet metals stretching with a hemispherical punch has gained popularity because of the convenient experimental procedure. The stretching experiment however has localized deformation or the shear band is originated from the non-unifrom deformation in the critical circum-stance instead of the absolute criterion. More accurate information of the forming limit therefore could be obtained by a more appropriate experiment to the real process. In this papaer an experiment program is devised to practivally identify the forming limits of sheet metals for auto-body parts. The experiment program contains not only stretching but deep-drawing Both forming experiments use the same hemispherical punch while they use different specimens. Deep-drawing experiments use speci-mens cut out in circular arc on both sides of circular blank to make it torn during the deep-drawing They also use speciments cut out straight in one side of a circular blank to make it deformed unevenly which causes local deformation during the deep-drawing. The experimental result demonstrates that the forming limit diagrams in the two cases show difference in their effective magnitude. The forming limit curve from deep-drawing is located lower than that from stretching. It is noted from the result that the deep-drawing process causes acceleration of localized deformation in comparison with the stretching process. From the experimental result the maximum value of forming limit could be pre-dicted for safe design.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.2
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• pp.660-665
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• 2014

Optimization of process parameters in polymer extrusion is an important task to reduce manufacturing cost. To determine the optimum values of the process parameters, it is essential to find their influence on the elongation of polymer breathable thin film. The significance of six important process parameters namely, extruder cylinder temperature, extruder speed, extruder dies temperature, cooling roll temperature, stretching ratio, stretching roll temperature on breathable film elongation of polymer extrusion was determined. Moreover, this paper presents the application of Taguchi method and analysis of variance(ANOVA) for maximization of the breathable film elongation influenced by extrusion parameters. The optimum parameter combination of extrusion process was obtained by using the analysis of signal-to-noise ratio. The conclusion revealed that stretching ratio were the most influential factor on the film elongation. The best results of film elongation were obtained at lower stretching ratio.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.637-640
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• 2008

The properties of oriented poly(3-hexylthiophene-2,5-diyl) in field effect transistors (FETs) have been investigated through mechanical stretching process as the original. Silicon-based FETs shown high mobility of $0.02\;cm^2/V$ s after thermal treatment and $0.0092\;cm^2/V$ s at r.t. PET-based FETs were expected to show a similar performance in mobility to that of silicon-based FETs.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.242-245
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• 1998

Effects of the anisotrpy due to the initial textures in the plane sheet on plane strain punch stretching has been investigated. In this study, the anisotropy from textures in the sheet is incoporated into the finite element process model by combining the theory of crstal plasticity. Three different textures such as random texture, plane strain compression texture and cube texture are considered. Variations of puch loads as well as thickness distributions of the sheets with three different initial textures are investigated.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.62-65
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• 2001

The effects of the initial torture of workpiece as well as the process conditions such as punch speed and lubrication on the formablity of sheet stretching are investigated by experiments. Two types of the initial textures of aluminum sheet plane strain compression torture and recrystallization texture are chosen since those are the most common in practice. Punch loads vs depth and thickness strain distributions along radial directions having the slope of $0^{\circ},\;45^{\circ},\;90^{\circ}$ with rolling directions are reported for hemishperical punch stretchings under a variety of process conditions.

• Elastomers and Composites
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• v.42 no.2
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• pp.86-92
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• 2007

A few of polytetrafluoroethylene(PTFE) membranes and PTFE fine powders were analyzed to chooce an optimum resin. The bi-axial stretching process was developed to set up the foundation of the preparation process and control the pore size and porosity of PTFE membrane. The pretreatment of PTFE fine powder used in the preparation process for PTFE was needed. The mixing of additives, the ripening of mixture, paste extrusion process of ripening powder, calendering process and the bi-axial process were conducted for controlling pore size, porosity and thckness of membrane. The aftertreatment which strengthened the mechanical properties was necessary. The control of pore size and porosity of the membrane were determined. The ratio of PTFE fine powder and additives at the paste extrusion process, the ripening time, the ripening temperature and the parameters of temperature and pressure at the paste extrusion process were optimized.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.400-403
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• 2004

A non-heat기leafed steel does not need quenching and tempering processes that are called a heat treatment differently from conventional steel. Since the tensile strength of this steel is higher than 900MPa, a conventional forming process should be changed to incremental forming process such as a cross wedge rolling that requires lower load capacity than conventional ones. In this paper, the cold cross wedge rolling (CWR) die has been designed using CAD/CAE In order to produce near-net-shaped component of ball stud of non-heat-treated cold steel. Finite element analyses were applied in order to investigate process parameters of CWR. Results provide that the stretching angle and the forming angie at knifing zone in CWR process is important parameter to be the stable process under the low friction coefficient condition.

• Journal of Sericultural and Entomological Science
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• v.15 no.1
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• pp.31-35
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• 1973

Strength, elongation and elasticity are essential properties with regard to the tensile properties of raw silk thread. The reasonable harmony of the above three physical characters appears to be the specific nature of the raw silk thread and the dynamical functions are determined by the cocoon filament forming the raw silk. From such viewpoint, the author has studied the tensile property of the thread when the cocoon filament is stretched and transformed. The results obtained are as follows: 1) The stretching strength of the inner layer filament is stronger than that of the outer and medium layer ones. 2) The stretching strength of the filaments is influenced by the moisture-heat denaturalization of cocoon layer sericin in the drying process. 3) The more transformed functions by the stretching become, the lower the elasticity index of the cocoon filament was shown. 4) When cocoon layer sericin is denatured by moisture and heat, elasticity index of the filament is decreased.

• Polymer(Korea)
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• v.24 no.3
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• pp.342-349
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• 2000

Hollow fiber membranes were prepared via thermally-induced phase separation process followed by stretching process from isotactic polypropylene and soybean oil system. Various operating parameters were examined in terms of their effects on the structure variation and performances of the membrane, and were optimized. Melt viscosity of the melt sample had influence on the formation of the microfibrils, and addition of nucleating agent increased the nucleation density to enhance the interspherulitic pore formation by stretching. Annealing the membrane at its stretched state relaxed the stress induced by stretching and helped the membrane maintain the stretched structure without shrinking. Solid-liquid Phase separation is more prevalent when the nucleating agent was added, and coagulation bath temperature determined the nucleation density, which affected the pore formation by stretching. In the absence of nucleating agent, nucleation was not effective and liquid-liquid phase separation governed the structure formation, which showed the opposite trend to that of the case with nucleating agent.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.5 no.4
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• pp.79-85
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• 2006

Multi-filament hydrostatic extrusion was developed as a fine wire manufacturing process and wire forming experiments were conducted. Also, single wire stretch forming process was proposed in the possibility of obtaining long wire with constant cross-section. In the multi filament extrusion since the workpiece, die and forming facility are in the macro forming circumstance, fine wire and fine hole structure with less than a few micrometer can be easily obtained. Although stretch forming does not use a die in order to avoid the friction problem between the workpiece and the die, it is necessary to have high level of technology to maintain cross-sectional shape and measure in longitudinal direction.